Micro-Cap 7
STUDENT EDITION
Software by:
Spectrum Software
Manual written by:
Martin S. Roden
Discovery Press
4
8Discovery Press, 2002
This manual is being made available at no charge
to faculty who have adopted the text
Electronic Design, From Concept to Reality, Fourth Edition,
by Martin S. Roden, Gordon L. Carpenter, and William Wieserman
Discovery Press, 2002
It may be freely duplicated for distribution
to students in classes where the text is being used.
If duplicated for this purpose,
this must be done on a "not-for-profit" basis
(i.e., faculty or departments may charge students
only for the actual cost of reproduction).
Multiple copies can also be obtained
at nominal charge from Discovery Press.
See website (www.discovery-press.com)
for details and ordering information.
CONTENTS
Preface
2
To the Student
2
Objectives
3
Features
4
Organization of this Manual
4
Installing the Student Edition of Micro-Cap 7 4
Chapter 1 - Introduction to the Student Edition 5
What Next?
5
Some Easy Examples
5
Another Easy Example
9
Transient Analysis
10
AC Analysis
14
DC Analysis
17
Chapter 2 - Creating a Circuit
20
Editing Schematics
37
Chapter 3 - Transient Analysis
38
Introduction
38
Transient Analysis Limits
39
Transient Analysis Menu
43
Scope Menu
46
Probe
47
Monte Carlo Analysis
49
Digital Analysis
56
Chapter 4 - AC Analysis
60
Introduction
60
Analysis Limits
62
AC Menu
65
Scope Menu
67
Probe
68
Monte Carlo Analysis
70
Chapter 5 - DC Analysis
71
Introduction
71
Analysis Limits
72
Running the Analysis
75
DC Pull-Down Menu
75
Probe
75
Monte Carlo Analysis
76
INDEX
77
Micro-Cap 7 Student Edition: Page 1
Preface
This manual is copyrighted by Discovery Press. It is being made available at no charge to
faculty who have adopted the text Electronic Design, From Concept to Reality, Fourth Edition,
by Martin S. Roden, Gordon L. Carpenter, and William Wieserman, 8Discovery Press, 2002. It
may be freely duplicated for distribution to students in classes where the text is being used. If
duplicated for this purpose, this must be done on a "not-for-profit" basis (i.e., faculty or
departments may charge students only for the actual cost of reproduction). Multiple copies can
also be obtained at nominal charge from Discovery Press. See the publisher=s website
(www.discovery-press.com) for details and ordering information.
To the Student:
Welcome to the world of computer-based circuit analysis with Micro-Cap 7. The Student
Version of Micro-Cap 7 is an integrated schematic editor and mixed analog/digital simulator
that provides an interactive sketch and simulate environment for electronics engineers.
Micro-Cap 7 makes it exceptionally easy to enter your circuits into a personal computer
because the entry process is menu driven. The circuit schematic unfolds before your eyes as
you interact directly with the software. The program uses screens with pull-down menus, hot
keys, and mouse support. It is easy to interface with SPICE circuit text files. Waveforms are
displayed in real time, so you can terminate runs without waiting for completion. You can
probe the schematic for various waveforms or use a scope feature to examine details of a
simulation result.
Circuit simulation programs are useful in design. A real-life circuit does not behave
exactly as the ideal theory predicts. Simplified models of elements and devices exclude many
of the more complex dependencies that occur when the circuit is constructed. Computer
simulation programs allow you to check the performance of a circuit before building it. You
can easily make changes in the circuit at this stage since you need only change the input to the
computer program. You avoid a lot of time and expense, and you can fine tune your design for
optimum performance. You can perform multiple simulations to examine the worst possible
case, or find the probability that a component or system will fail.
You have in your hands the Student Version of a software package used by engineering
professionals. The graduating engineer or engineering technologist cannot survive in the
technological world without an understanding of, and familiarity with, the use of the computer
as a design tool. Computer-aided engineering (CAE) is an integral part of electrical
engineering. Designers use state-of-the-art computer systems to optimize component selection.
Even small personal computers can aid in checking designs and indicating which parameters
require modification.
Micro-Cap is becoming the industry standard for use in electronic circuit analysis
and design. Very minor differences exist between the Student Version and the
Professional Version of this software: The Student Version limits the number of
components to 50 and the number of equations (nodes + inductors + sources) to 100. The
Professional Version easily handles circuits of 10,000 nodes or more. Speed is
deliberately reduced. Analysis run times vary from the same for small circuits to four
2
times longer for the largest circuits, relative to the Standard Version. The use of some
features such as optimization, filter design, 3D plots, PCB functions, performance plots,
and multiple parameter stepping is limited. The Professional Version includes a MODEL
program which is an interactive program that takes numbers from data sheet graphs or
tables and produces an optimized set of device model parameters. This MODEL program
is not included in the Student Version.
The Student Version libraries of pre-entered devices (such as bipolar transistors)
are limited to the most common devices, although you can add any device to the library.
Micro-Cap 7's SPICE-based circuit analysis program contains models of many popular
electronic devices. This program forms an ideal base for a student-oriented electronic
circuit design programBnot only because students will use the Professional Version after
they graduate, but also because the program's general features are representative of a
broad class of analysis software.
A word of caution is appropriate if this is your first experience with simulation
tools. Just as the proliferation of calculators did not eliminate the need to understand the
theory of mathematics, electronic circuit simulation programs do not eliminate the need
to understand electronic theory. As in the case of calculators, MICRO-CAP V can free
the designer from tedious calculations, allowing more time for doing the kind of creative
work a computer cannot do. Before performing a computer analysis of a network, you
should have some idea of what to expect. We suggest you use this software to check your
designs. In the process you may uncover some unexpected results, because a paper design
rarely incorporates models as sophisticated as those used by this program. To keep down
the price and make this software available to more students, we have intentionally
eliminated some material from this manual. For example, although the Student Version
and Professional Version operate in essentially the same ways, the manual you are
holding is less than 100 pages long while the documentation accompanying the
Professional Version spans about 500 pages. Not every fine point of the simulation is
covered in this student manual. Experimentation and the help screens should fill in many
of the blanks.
Objectives:
The primary objectives of the Student Edition of Micro-Cap 7 are as follows:
!To provide a tool for handling the tedious calculations of circuit design, thus
affording you more time for creative design work.
!To help you design circuit boards for your course work and prepare you for
using Micro-Cap 7 in your profession.
!To provide a package that has been carefully designed to save you money while
not compromising features significant at this phase in your education.
Micro-Cap 7 Student Edition: Page 3
Features:
The Student Edition of Micro-Cap 7 the following features:
!A library of standard passive and active devices, including popular models of BJTs,
MOSFETs, JFETs, op-amps, digital logic gates, digital ICs and diodes.
!The capacity to custom-define devices and add them to the library for later use.
!Three types of analysis: transient analysis, ac analysis, and dc analysis. Within each of
these types of analysis, you can perform iterative analysis (temperature stepping and
parameter stepping), PROBE analysis where you can display multiple waveforms by
clicking the mouse at the appropriate points in the circuit, and Monte Carlo
probabilistic analysis to provide for random variation of device parameters.
Organization of this Manual:
The Student Version manual is organized into five chapters. The first is a general
introduction, and that chapter will lead you through some simple examples in order to give an
overview of the power of the program.
Chapter two teaches you how to draw circuits using Micro-Cap 7's schematic capture
features and drawing tools. Chapters three through five present the three types of analysis,
transient, ac and dc.
Installing the Student Edition of Micro-Cap 7
Installation of the software is straightforward. Insert the CD in your computer=s CD-ROM
drive. Follow the installation instructions that appear. If the Micro-Cap screen does not appear,
select Run from the Start menu and enter drive:\setup.exe where Adrive@ is your CD-ROM
drive letter.
Now you are ready to start the program. Simply click on the Mc5demo icon, or navigate
to it from "My Computer" or other techniques (e.g., Windows Explorer).
We want to give you at least one way to exit from the keyboard in case you cannot wait
for that section of the manual (for example, if you get an important phone call and must turn
off the computer now). You can clear any window by pressing the Esc key. Then press the Alt
F4 function key. The program asks you to confirm that you want to exit, and you simply type Y
for yes. You have now left Micro-Cap 7. Of course, in Windows you exit as you do with any
other program by clicking on the X in the upper right corner.
4
Chapter 1
Introduction to the Student Edition
Now that you have installed the software, you are ready to explore the power of this simulation
program. There are two radically different approaches toward learning to use a piece of
software. One is to read the entire manual and then approach the computer, hoping you
remember most of what you have read. The second is to sit down at the computer and learn as
you go along. Fortunately, Micro-Cap 7 is sufficiently user-friendly that you can take the
second approach. The only possible damage you can do is to erase a portion of the files. Since
you have not yet created your own files, such damage is easily correctable by reinstalling the
software. Therefore, we encourage you to experiment. Learn what each instruction does by
reading the manual and then trying it on the computer.
Another feature of Micro-Cap 7 is the context-sensitive help screens available in each
menu. Any time you need more information before completing a task, simply press the F1
function key (or pull down the Help menu). If you do this before running a simulation, you get
a help index that allows you to select the topic in which you are interested.
The Help pull-down menu also provides options for running a tutorial. Before
attempting to draw your own circuit, we recommend that you run the tutorial. Do this by
pulling down the Help menu, and selecting the demo. You will either have a choice of running
the full (i.e., General) demo, or if you have Version 2.0 or later of the software, you can run
selected portions. Just click on your choice and sit back and relax. You can exit the demo at
any time by pressing the ESC key. You can pause at any time by pressing "Pause" (Break on
some keyboards), and resume by pressing "Pause" again. If you are a speed reader and want to
shorten the pauses between screens, press any key to move forward. Don't try to use your
mouse during the demonstration. This will only frustrate you as the demonstration program
takes complete control of your computer.
What Next?
OK, you have run the tutorial, and are now very excited about the program. There are
two distinct parts to using the program. (1) Drawing (or retrieving) a schematic, and (2)
running the simulation. You should now be sitting at your computer. This manual is NOT
bedside reading (unless you have a laptop in bed).
Some Easy Examples
We'll begin by skipping the drawing part (we'll come back to that in a few minutes). It's
really pretty easy, but we want you to see a simulation within the first five minutes of running
the program.
So let's save the time of entering a circuit by retrieving one of the schematics that came
packaged with your program. Pull down the File menu, select Open, and you have a list of
circuits in the file that came with your program. Note that these circuits end with the extension
".cir". Select the circuit that we used to illustrate performance, that is, perf1.cir. Your screen
should now contain the circuit shown in Figure 1.
Micro-Cap 7, Student Edition: Page 5
Figure 1
This is an RLC circuit driven by a pulse source. We will run a transient analysis, and
leave the other forms of analysis up to you. This type of analysis plots the output (or any other
parameter) as a function of time. You should pull down the Analysis Menu and select
Transient Analysis (note the hot key you can use to save time in the future). This presents you
with an Analysis Limits window, as shown in Figure 2. Let's look at the way this window is
currently configured (this is stored in memory with the sample circuit).
Figure 2
Micro-Cap 7, Student Edition: Page 6
The first entry is the Time Range. Note that the entry is "1u". This means that the
simulation will run from time zero to 1 microsecond (we hope you are not bothered by the
modified Greek mu. You certainly would not want to go through the trouble of entering a
symbol. However, if you prefer you can enter 1E-6 instead of u, or you could even enter
0.000001 if you wish). If you wanted the simulation, instead, to run from 1 microsecond to 2
microseconds, you would enter 2u,1u. The first number is the ending time and the second is the
starting time. The default starting time is zero, so we didn't need a second entry in the example
circuit.
The second line shows Maximum Time Step. Micro-Cap simulates operation of a
circuit by stepping in time. At each step, the program calculates parameters and compares them
with the previous calculated values. If a circuit contains capacitance or inductance, the program
also monitors the time rate of change of the charge and flux. Internal algorithms control the
size of the derivative. If it is too large, the time step is decreased. If it is too small, the time step
is increased up to the specified maximum. If the maximum time increment is too large, the
resolution suffers, while if it is too small, the program takes a long time to run. You can often
smooth a resulting curve by reducing the maximum time step. Note that we have set this to 5
nanoseconds. This means that there will be at least 200 points within the 1 microsecond
analysis window.
The Number of Points is used for numeric output (that is, a table, as opposed to a
graph). It sets the number of points to be printed (number of rows in the printout table). The
default value is 51. If the specified points do not fall directly on values used in the iteration, the
printed value is interpolated from calculated values.
Temperature enters into the parameter equations for devices and components. One or
more temperature values (in degrees Celsius) can be specified for the analysis. The format is
High [,Low[,Step]] where we have used the convention that square brackets indicate
parameters you can omit. The default value of Low is High, while the default value for Step is
the difference between High and Low. Therefore, if only one value is specified, the simulation
runs at that temperature. If two values are specified, the simulation runs at those two values.
We now move down to the waveform options fields. The first box is labeled P. When
several variables are plotted, you have a choice of superimposing them on the same set of axes
or having them appear on separate, non-overlapping graphs. The numeric entry in the P column
is a number from 1 to 9 specifying which graph you want that curve to appear in.
The X Expression field specifies the expressions for the X-axis variable. In most
transient cases, this is a time variable. You could do fancier things like plotting a hysteresis
curve, where in that case, the X expression would be an input voltage.
The Y Expression field specifies the expressions for the Y-axis variables. These may
be simple voltages or currents, or more complex math expressions. Examples of variables
include V(A) [voltage at node A], V(A,B) [voltage at node A minus voltage at node B], V(D)
[voltage across the device called D], I(D) [current through the device called D].
The next two fields are the ranges. The format is High[,Low]. We see in the example
that the X range is simply 1e-06. We could have also entered 1u, or 0.000001. This sets the X
range to go from zero to 1 microsecond. The Y range is "9,-6" which means it ranges from -6
volts to +9 volts. It's easy to see how we chose the X range (it matches the analysis range, but
you could have chosen just a portion of the analysis to display). The Y is not so easy to predict
unless you know how the circuit behaves. You have the option of entering "auto" for one or
both ranges. In that case, Micro-Cap does all the work for you. The X range will match the
Micro-Cap 7, Student Edition: Page 7
analysis window, and the Y range will be adjusted to include the maximum and minimum
outputs.
Enough talk…..let's run the simulation. Simply click "Run". The result is shown as
Figure 3.
Figure 3
My gosh, we seem to have gotten a number of curves. Why did the program run more
than once? Is it paid on commission?
Let's examine the screen and see if there is any hint as to why multiple runs occurred. Our
first clue is given by the title bar on Figure 3. Note that it says, "C1 Value=1e-010...4.1e-009".
Go back to the analysis limits window by pulling down the Transient menu and clicking on
Limits. Something seems to be stepping, so how about clicking on the "Stepping" box on the
Transient Analysis Limits window? Now you will see why this happened. The capacitor is
stepping from 0.1 nF to 4.1 nF in steps of 0.5 nF. That's why we got 9 separate plots. As you
get familiar with the program, you will learn how to label these multiple curves.
Now that we have solved the mystery of the multiple curves, you probably want to return to
the limits window. If you lose the Limits window as you jump around, just pull down the
Transient menu and select "Limits" to get it back on the screen.
Now we would like you to play around with this. Start changing entries and see the result.
Go to the stepping window and either eliminate the steps or increase them.
Add another plot (click "Add") either on the same graph (P=1) or a separate graph (P=2).
Play around until you are comfortable knowing what every button does.
Micro-Cap 7, Student Edition: Page 8
It's best to learn by experimentation, but if you get too frustrated, just pull down the Help
menu. You can get a table of contents, or you can search for help on a specific topic. Most of
the details from the professional version are contained in this help file.
Another Easy Example
Let's take a moment to explore another simple example. We'll look at an RLC circuit driven by
a pulse of height 5 volts and duration 1.4 microseconds. Once again, we will avoid drawing the
circuit, and take advantage of the fact that the RLC circuit has been drawn for you and stored
on the disk. We need simply retrieve it. Pull down the File menu, and select Open. The
contents of the data directory are now displayed. Scroll down to RISE.CIR. This is the RLC
circuit and it is similar to that used in the previous example. When you double-click on this
entry, your window should look like Figure 4.
Micro-Cap 7, Student Edition: Page 9
Figure 4
For now, don't be concerned with all of the words on the screen. We will be using this same
circuit later to learn about Monte Carlo analysis. The first three MODEL statements below the
circuit set tolerances that will become important later. The bottom MODEL statement
describes the input pulse. In case you cannot wait until later to examine this, we'll say a bit
about it now. The first two entries in parentheses specify the two voltage levels (zero and five).
The five times, designated P1 to P5, describe the corners of the waveform. The rise time and
fall time of this pulse are 10 nanoseconds each.
Micro-Cap 7 identifies voltages according to numbered nodes. Note that Figure 4 has three
nodes, and they are numbered 1, 2, and the ground. If your screen is not showing the node
numbers, click on the Options pull-down menu, select View and then select Node Numbers.
Micro-Cap automatically numbers any non-ground nodes for you.
Transient Analysis
We'll begin by running a transient analysis. Pull down the Analysis menu and select
Transient Analysis. Many of the selections also have keystrokes listed, and you may find this
to be a faster way to execute the analyses in the future. Once you select Transient Analysis,
your screen will present the Transient Analysis Limits, as seen in Figure 5.
Micro-Cap 7, Student Edition: Page 10
Figure 5
We need to make some adjustments before running the program. The first is to disable the
Monte Carlo Analysis. You will learn about Monte Carlo analysis later. For now, pull down the
Monte Carlo menu, select Options, and select OFF to turn off Monte Carlo.
Now we need to get the Transient Analysis Limits window back on the screen, so pull
down the Transient menu and select Limits. As you examine the Transient Analysis Limits
window, you will see lots of items, some of which will seem confusing and some of which will
look familiar from the previous example. Starting at the top middle, you see Time range,
Maximum time step, Number of points, and Temperature. We will not make any changes to
the last three of these entries, but we will change the "250N" in the time range. The stored
circuit is meant to illustrate the rise time so the time axis goes from zero to 250 nanoseconds.
However, since our pulse repeats every 11000 nanoseconds, let's enlarge the analysis window
to include part of the second pulse. Use your mouse to get to the "250N" entry and change it to
"12000N". This will plot the first 12000 nanoseconds (note that you could have entered 12u for
12 microseconds).
The next area to look at in the window is the plot information at the bottom. This tells
Micro-Cap what waveform(s) to display. The entry currently shows that plot #1 (actually there
only is one plot in this example) is V(2) vs. time [i.e., X expression is T for time and Y
expression is V(2), or the voltage between node #2 and ground]. This is why it is important to
know how the nodes have been numbered.
You need to change to X Range to 12000N. It currently shows 250N,0,5e-8. This sets the
maximum to 250 nanoseconds, minimum to 0, and grid spacing to 0.5 nsec. If you leave it as
is, you will only be plotting the first 250 nanoseconds (don't take my word for it, try it!). By
just entering 12000N, we will be using default values for the other variables. The Y Range
does not have to be changed.
Now click Run. Your screen should now look like Figure 6. Notice that the part of the
curve below zero volts has been cut off. Let's correct this. Pull down the Transient menu and
select Limits. Now in the Transient Analysis Limits window, lets change the Y range from
"10" to read "10,-2". This means that instead of displayed Y range values from zero to 10 volts,
we will display -2 to 10 V. Run the analysis and see what changes.
We don't want to overwhelm you this early in the game, but just one more nice feature. Go
back to the Transient Analysis Limits window (see previous paragraph), use your mouse to
highlight the Y range, and hit the Delete key to erase the range. Then use your mouse to click
Micro-Cap 7, Student Edition: Page 11
Figure 6
the box labeled Auto Scale Ranges. Now run the analysis one more time, and note that the
Y axis automatically adjusts to include the entire waveform (Figure 7). The same would have
happened for the time axis had we omitted that entry.
Figure 7
Micro-Cap 7, Student Edition: Page 12
Before leaving the plot, you should play around with the buttons at the top of the screen.
You should have two tool bars showing. If you do not, pull down the Options menu, and click
on Main Tool Bar. The item will be checked, and the tool bars will appear. Now locate the
button on the tool bar that shows a picture of a curve with dots on the curve. When you point
the mouse at this button, the help bar should read, "Marks the actual analysis Data Points".
Click on this button and see what happens to the curve.
Other buttons are used to mark points on the curve and display the actual X and Y values.
You can also find distances between two cursors. You should take the time to try some of these
buttons. You can't hurt anything in the process.
Let's now illustrate stepping of components. Let's try to step the resistor, R2, from 10 ohms
to 50 ohms in steps from 10. From the Analysis Limits Window, click on Stepping. This
yields the stepping dialog box of Figure 8.
Figure 8
Enter the component, the initial value, final value and step value in the appropriate boxes.
Then check "Yes" under stepping. You probably want linear rather than logarithmic stepping.
With linear stepping, the increment stays constant. With logarithmic, the ratio stays constant.
Click OK, and then select Run from the Transient pull-down menu, or simply press F2. The
result is as shown in Figure 9. Note there are now 5 plots where we previously had only one.
Micro-Cap 7, Student Edition: Page 13
Figure 9
AC Analysis
Now let's perform a frequency (ac) analysis on this same RLC circuit. In ac analysis, you
plot output as a function of frequency. The straight-line approximation to this plot is the
familiar Bode plot. The ac analysis is run in a manner similar to that of the transient analysis. If
you have just finished experimenting with the transient analysis, you already have the RLC
circuit loaded into the computer. However, rather than simply proceeding with the ac analysis,
we are going to ask you to unload the circuit and then reload it. The reason we do this is to
clear all the operations you entered during the transient analysis. For example, the last thing
you did was to step the value of the resistor. If you were to proceed immediately to the ac
analysis, the program would continue in the stepping mode.
Press F3 to exit the simulation and return to the circuit. Pull down the File menu and select
Close. You will be asked if you want to save changes. We suggest you answer No. Now reload
the circuit by selecting Open, and then select the circuit, rise.cir. Pull down the Analysis
window and select ac. The ac analysis limits window is now displayed as in Figure 10. It is
somewhat similar to the transient analysis limits window. The first set of entries gives the
Frequency range, number of points, temperature, and three additional entries for advanced
analysis. Note that the frequency limit is 1E8,1E6. This means the analysis starts at 1 MHz and
finishes at 100 MHz. As was the case with the transient analysis, the stored circuit has
Micro-Cap 7, Student Edition: Page 14
temperature stepping. Since the temperature steps from 27 to 227 in steps of 200 degrees, we
would only see two plots. Replace the temperature values with a single temperature, "27".
Figure 10
Moving to the entries that create plots, you should see six entries. Since only the first one
has a number in the "Plot" column, that is the only thing that will plot. The other quantities
(phases, real and imaginary parts) will not plot. The X expression is frequency (F). The Y
expression is the voltage at node #2 in decibels. If you click in this Y expression box and then
click the right mouse button, you will see examples of the types of complex analysis variables
you can select to plot.
The next two entries are X Range and Y Range. If you wish, you can leave these blank and
select "Auto Scale Ranges" to let Micro-Cap adaptively select the axis ranges.
Click on Run and obtain the plot shown in Figure 11.
Suppose you also wanted to plot the voltage across the inductor (in dB). Modify the second
line in the Analysis Limits Window by first putting a "1" in the P column and then selecting the
Y expression to be db(v(L1)). You should probably also clear the four ranges you are plotting,
and select Auto Scale Ranges. Click Run and see the two plots. To distinguish them
Micro-Cap 7, Student Edition: Page 15
Figure 11
from each other, locate the "Applies Tokens to Waveforms" button on the tool bar (near the
center), click it and see what happens. You should get curves that look like Figure 12.
Micro-Cap 7, Student Edition: Page 16
Figure 12
Now play around. Try changing the second plot P entry to a "2", then try applying some
stepping. You can't hurt yourself by trying lots of things. When you are finished, press F3 to
exit the analysis. Then close the circuit if you wish.
DC Analysis
The third type of analysis plots output versus input under dc conditions. Ideal capacitors
become open circuits, and ideal inductors become short circuits. The dc analysis is run in the
same manner as the transient and ac analysis. We'll perform this on the RLC circuit we have
been using even though the result is not very exciting.
Press F3 to cancel the previous analysis. Then select dc from the Analysis pull down menu.
In the DC Analysis Limits window (see Figure 13), first select Variable 1 as "PULSE". Then
let's plot V(2) as a function of V(1). Simply enter V(1) as the X expression and V(2) as the Y
expression. Empty the range boxes and select Auto Scale Ranges. Don't forget to place a "1" in
the P column. Then hit Run. The result is as shown in Figure 14.
Micro-Cap 7, Student Edition: Page 17
Figure 13
Figure 14
Hmmm. A 45 degree straight line. Not too surprising since the inductor is a short and the
capacitor is open. The output voltage is the same as the input voltage. The dc analysis mode
becomes much more interesting when non-linear devices are present in the circuit.
Micro-Cap 7, Student Edition: Page 18
We have illustrated the three circuit analysis options for a simple example. Even though the
circuit you analyzed did not contain any non-linear passive devices or any active electronic
devices, we hope you can sense the excitement and tremendous power of this program.
The only things we have not covered in this simple example are digital analysis, how to
draw your own circuit and some of the more subtle features of the program, such as Scope,
Probe, and Monte Carlo analysis.
The next major section of this manual takes a more detailed approach toward gaining skill
with the program by first learning how to draw complex circuits. We then explore the three
analysis packages in detail.
Micro-Cap 7, Student Edition: Page 19
Chapter 2
CREATING A CIRCUIT
When you first execute the program, you automatically open a circuit window with the
name, "CIRCUIT1", as shown in Figure 15. If you have already been using Micro-Cap 7, you
should use the File pull-down menu to close existing files (not really necessary, but if you a
finished working with a circuit, it is a good idea to preserve working memory). Then use the
File menu to select NEW. Don't be concerned if the title bar at the top calls this "CIRCUIT2"
or any other number. The counter resets to zero when you exit and then re-enter the program.
Figure 15
You should have two menu bars at the top of the screen. If you do not have these two "tool"
bars, pull down the Options menu and select Tools. Although it is not necessary to know the
function of each button at this time, we'll quickly review the major ones. Depending on the
version of Micro-Cap 7 you have, you may not see all of these buttons.
Each row has up to 30 buttons in it. If you point the cursor at any button, the help bar at the
bottom of the screen describes the function of the button. If you do not see a help bar, pull
down the Options menu and click on Help Bar.
The top starts with the normal Windows buttons you should be used to. The next set of
buttons serves as a type of "hot key" to select common types of components. We will see
several ways to do this. For example, if you want to add a resistor to the circuit, you can click
that component, then place the resistor anywhere you wish in the circuit. As you move to the
Micro-Cap 7, Student Edition: Page 20
right, the next set of buttons are useful if you subdivide a large circuit into sub-circuits and
place each in a separate window. These buttons allow you to view the various windows in
different ways.
The first four buttons on the second menu bar select the mode. The first (arrow) button
clears the existing mode. The second button enables the component mode where you will be
adding components to the diagram. The third button enables the text mode for adding text, and
the fourth and fifth buttons enter the wire mode for adding wires–either aligned horizontally,
vertically, or on a diagonal. The next button places you into the graphics mode where, by
clicking anywhere on the screen, you get a choice of adding simple graphics shapes (e.g.,
rectangle). You click and drag to draw the shape.
The button with an "I" enters the information mode. Enabling this and clicking on any
component gives you the detailed description of that component. The next button, "?" enables
the help mode. In this mode, if you click on any component, you will be presented with the
format for entering parameters for that component.
The remainder of buttons on the first row should be self-explanatory when you read the
help text at the bottom of the screen. With the exception of the right-hand set of buttons, you
probably will not be using most of these remaining buttons.
You will probably not be using the remaining buttons. You can experiment with these, but
in all cases, you can accomplish the same function by selecting from the pull down menus. We
describe these pull-down menus next.
File:
The File menu provides commands for the management of schematic or SPICE text circuit
files, model library files, or text document files. Equivalent tool bar buttons exist for some of
these entries:
!New: (CTRL+N). This command creates a new file.
!Open: (CTRL+O). This command loads an existing file from the last used directory.
!Save: (CTRL+S). This command saves the active window file to disk using the name and
path shown in the title bar.
!Save As: This option lets you save the active window file to disk. It invokes the Save As
dialog box to let you enter a new file name and a new path.
!Paths: This lets you specify one or more default paths (folders) for data and libraries and
pictures. This is a nice feature if you keep data on separate disks.
!Translate: This command gives y9ou various options to convert SPICE, Micro-Cap, and
earlier Micro-Cap version files.
!Revert: This command restores the file in the active window to the one currently on disk.
Since the Undo command can only undo the last edit, this command provides a convenient way
of undoing many edits.
!Close: (CTRL+F4) This command closes the active file.
!Print Preview: This option previews what the printed schematic will look like at a user
selected scale.
!Print: (CTRL+P) This command prints a copy of the document shown in Print Preview in
accordance with the instructions in Print Setup.
!Print Setup: This option changes the printer setting and page layout.
!Prior Files: This is a list of the most recently used files. You can reload any of them by
clicking on the desired file name.
Micro-Cap 7, Student Edition: Page 21
!Exit: (ALT+F4) This exits Micro-Cap 7.
Edit:
This menu provides the following commands:
!Undo: (CTRL+Z) Most operations that change a circuit file or a text field can be reversed
with the Undo command.
!Cut: (CTRL+X) This command deletes the selected objects and copies them to the
clipboard.
!Copy: (CTRL+C) This command copies selected objects to the clipboard.
!Paste: (CTRL+V) This command copies the contents of the clipboard starting at the current
cursor position.
!Clear: (DELETE) this command deletes the selected items without copying them to the
clipboard.
!Select All: (CTRL+A) This command selects all objects in the current window.
!Add Page: This command adds a new page to the schematic.
!Delete Page: This command deletes one or more schematic pages.
!Refresh Model: This command places model statements in the text area.
!Box: These commands affect objects enclosed in the selected box region.
!Step Box: This steps objects enclosed in a selected region a specified number of times.
!Mirror Box: This command creates a horizontal or vertical mirror image of the objects
enclosed in a selected region.
!Rotate: (CTRL+R) this command performs a counterclockwise rotation of the objects in a
selected region.
!Flip X: (CTRL+F) This command flips the objects in a selected region about the X-axis.
!Flip Y: Same as Flip X but flips around Y-axis.
!Change Attribute Display: This lets you change the Attribute Display status of the five main
attributes of all components in the circuit.
!Color: This option lets you change color of selected text or graphics.
!Font: This option lets you change the font, style, size, effects, and color of any selected text.
!Bring to Front: A mouse click on a stack of overlapping objects selects the front object in
the stack. This command makes the selected object the front object.
!Send to Back: this command makes the selected object the back object.
!Find: This command invokes the Search menu for searching the front window. You can
search for text, node numbers, components, or a part model.
!Repeat Last Find: (F3) Repeats the search and finds the next object in the circuit.
!Replace: Conducts a search and replace operation.
Component
This menu allows you to select a component for placement in the schematic. The selections are
numerous and are discussed elsewhere in this chapter.
Windows
The following selections are offered:
!Cascade: (SHIFT+F5) This command cascades the open circuit windows in an overlapping
manner.
Micro-Cap 7, Student Edition: Page 22
!Tile Vertical: (SHIFT+F4) This vertically tiles the open circuit windows in a nonoverlapping manner.
!Tile Horizontal: This horizontally tiles the open circuit windows in a non-overlapping
manner.
!Overlap: This neatly arranges any minimized circuit window icons.
!Maximize: Maximizes the selected circuit window or window icon.
!Zoom In: (CTRL++) Magnifies the central portion of a schematic (or the text point size).
!Zoom Out: (CTRL+-) Shrinks the central portion of a schematic (or the text point size).
!Toggle Drawing/Text: (CTRL+G) This command toggles the window display between the
drawing and text areas.
!Split Text/Drawing Areas Horizontal: Horizontally splits the front schematic window into
its drawing and text areas for simultaneous viewing.
!Split Text/Drawing Areas Vertical: Vertically splits the front schematic window into its
drawing and text areas for simultaneous viewing.
!Remove Splits: Gives full circuit window to the drawing area of the schematic.
!Component Editor: This Editor is used to manage the Component Library. You will
probably not use this.
!Shape Editor: Manages library shapes. You will probably not use this.
!Model Program: Not available in Student edition of Micro-Cap V.
!Calculator: Accesses calculator.
!Open Files: You can select any of the open files to become the front window circuit.
Options
!Mail Tool Bar: (CTRL+O) This toggles the display of the Tool bar on and off.
!Status Bar: This toggles the display of the Status bar on and off.
!Mode: This accesses the Mode submenu containing the following items:
!Select: (CTRL+E) Selects objects for editing.
!Component: (CTRL+D) Lets you add a component to schematic.
!Text: (CTRL+T) Lets you add grid text to schematic.
!Wire: (CTRL+W) Adds orthogonal wires to schematic.
!WireD: Adds diagonal wires to schematic.
!Line, Rectangle, Diamond, Ellipse, Arc, Pie: used to draw graphics objects.
!Flag: Place flags on the schematic to mark locations for quick navigation.
!(The next 7 selections are not available in the Student Edition)
!Help: Invokes Component Help system. You click mouse on a component to see its
parameter and model syntax.
!Info: Click on component to display model parameters.
!Point to End Paths: Clicking on a digital component displays all paths from that
component to all possible end points.
!Point to Point Paths: Clicking on a digital component displays all paths from that
component to the next component.
!View: This accesses the View submenu containing the following items:
!Attribute Text: If checked, this shows component attribute text.
!Grid Text: Shows grid text.
!Command Text: (ALT+.) Shows command text.
Micro-Cap 7, Student Edition: Page 23
!Node Numbers: Shows node numbers assigned by program. Analog nodes have rounded
rectangles and digital nodes have normal angular rectangles.
!Node Voltages/States: After a transient analysis is run, this displays node voltages and
digital states from the last simulation run.
!Pin Connections: Displays a dot at the location of each component pin.
!Grid: Displays schematic grid.
!Cross-hair Cursor: Adds cross-hair cursor.
!Border: Adds border
!Title: Add a title block to schematic.
!Show all Digital Paths: Displays a list of all possible digital paths together with their delays.
!Preferences: (CTRL+SHIFT+P) Accesses Preferences dialog box.
!Global Settings: (CTRL+SHIFT+G) Accesses Global Settings dialog box.
!Component Palettes 1-9 (Note only 1 to 4 available in Student Edition): Component Palettes
provide a convenient way to select a component instead of accessing through the Component
pull-down menu.
Figure 16
Now let's draw a simple circuit. We'll draw the RLC circuit of the previous chapter. That
circuit is repeated as Figure 16.
You draw the circuit much as you would with pencil on paper–one component at a time.
You have at least three different ways to select a component. Suppose, for example, you wish
to draw a resistor. First make sure you are in the component mode (second button on top bar–
the one with the wiggly resistor-type symbol). Then select resistor using one of the following
techniques: (1) click on the resistor icon button on the top tool bar (near the middle); (2) Pull
down the Component menu, select Analog Primitives and then Passive Components and
Micro-Cap 7, Student Edition: Page 24
then Resistor; (3) select Resistor from one of the four component palettes. You display the
component palettes by pulling down the Options menu and selecting Component Palettes.
Take the time now to see what components are on each of the four palettes. The passive
components are all on palette #1, and you may want to keep that palette displayed in the corner
of your schematic screen.
OK, so you have now selected Resistor using any of the techniques described. Let's add a
50 ohm resistor to the right side of the circuit, as shown in Figure 16. Click and hold the left
mouse button and position the resistor where you want it. While holding the left button, click
the right button to rotate by 90 degrees. Then release the buttons. This presents an Attribute
Dialog box. You need to enter the value. Since you want this resistor to be 50 ohms, simply
enter "50". Then press Return or click OK. The resistor is added to the circuit. In designating
component values, you can use any of three separate formats:
!Real numbers: Enter the value of the component. For example, 1 megohm would be
1000000 and 1 microfarad would be .000001.
!Floating point: (Scientific notation): enter a number using powers of 10. For example, 1
megohm is entered as 1E6 and 1 microfarad by 1E-6.
!Engineering notation: Use the following abbreviations for powers of 10:
F Femto
1E-15
P Pico
1E-12
N Nano
1E-9
U Micro
1E-6
M Milli
1E-3
K Kilo
1E3
MEG Mega
1E6
G Giga
1E9
T Tera
1E12
Thus 1 megohm could be entered as 1MEG or 1000K. You may also add unit designations
after the abbreviation without affecting the value. Do not, however, enter F by itself; 1F is 10-15 (Femto) r
Resistors, capacitors, and inductors are handled in a similar manner. You make your
selection and then draw the element by clicking the left mouse button. If you hold this button
down, you can drag the component to any desired location on the screen. If you click the right
button while still holding the left, you reorient (rotate or reflect) the element. After placing the
item in the circuit, you must use the keyboard to enter the number of ohms, farads, or henries.
Now continue drawing the circuit. Add the 1 nanofarad capacitor and 1 microhenry
inductor. Try to position these as best you can. We will be adding the connecting wires later.
We now add the pulse source. First click on Pulse Source if you have palette #1 showing.
If not, you can pull down the Component menu, select Analog Primitives and then Waveform
Sources. When you add this source to the diagram, the attributes box is a bit different. It seems
to want you to enter a model statement The model is stored in the program and displayed in the
window on the right. For now, if you select the only pulse source stored in the program, you
will have the correct model. But suppose you wanted to enter your own parameters. Pull down
the Help menu and search for help on Pulse Source. As an alternative, you can click Help in
the Attribute dialog box, then Analog Devices, and then Pulse Source. You will see the
following:
Pulse Source Model Parameters Table
Micro-Cap 7, Student Edition: Page 25
Name
VZERO
VONE
P1
P2
P3
P4
P5
Parameter
Zero level
One level
Time delay to leading edge
Time delay to one level
Time delay to trailing edge
Time delay to zero level
Repetition period
Units
Volts
Volts
s
s
s
s
s
Default
0
5
1e-7
1.1e-7
5e-7
5.1e-7
1e-6
The waveform value is generated as follows:
From
0
p1
p2
p3
p4
To
p1
p2
p3
p4
p5
Value
vzero
vzero+((vone-vzero)/(p2-p1))*(T-p1)
vone
vone+((vzero-vone)/(p4-p3))*(T-p3)
vzero
where From and To are time values, and T=TIME mod p5. The waveform repeats every
p5 seconds.
.MODEL PULSE PUL (VZERO=0 VONE=5 P1=100N P2=100N P3=500N P4=500N
P5=1U)
The pulse source is a repeating pulse train with parameters as indicated in Figure 17.
The pulse goes between voltages of VZERO and VONE, and P1 through P5 specify key times.
Try typing the model statement shown above instead of selecting from the model stored in the
program. That is, simply change the parameters in the Pulse Source box to PULSE PUL
(VZERO=0 VONE=5 P1=100N P2=100N P3=500N P4=500N P5=1U)
You should only have had to change two values since most of these agree with the default
values.
After adding the components, your screen should resemble Figure 18.
Micro-Cap 7, Student Edition: Page 26
Figure 18
Now let’s connect the components with wires. Click on the icon for orthogonal (horizontal and
vertical) wires and click and drag the mouse. Note that right angle corners are added as needed.
When you are finished, the circuit should look like Figure 19.
Figure 19
Micro-Cap 7, Student Edition: Page 27
Now try running a transient analysis. Recall that we need node numbers, so pull down the
Options menu, select View, and then Node numbers. Then try running the transient analysis
by pulling down the analysis menu and selecting Transient.
Whoops - you should get an error message. EVERY circuit MUST have a ground. You
better add one so the circuit looks like Figure 16. The ground is found in Palette #1, or on the
top toolbar, or from Components pull down menu, then select Analog Primitives and then,
Connectors. Note that the number of nodes changes from 1, 2, 3 to just 1 and 2. That is
because the ground is always node #0.
Take note of which node is the output. In our case, it is node #1. Now enter the transient
analysis mode. You will probably have correct values in the analysis limits to plot both V(1)
and V(2) on the same plot. If you only get one plot, don’t worry at this time. We will discuss
the settings in detail in the next chapter. For now, we simply run the analysis to get the output
of Figure 20. Now Press F3 to exit the analysis and return to the circuit.
Figure 20
Drawing Other Components
The Transformer is a passive component. When you select this, you insert a four-terminal
transformer model consisting of two inductors with a mutual inductance between them. You
are prompted to enter a "define" statement. If you click on "syntax", you will find that there are
three parameters. For example, if you enter
.01,.0001, .98
you are specifying a transformer with primary inductance of 10 millihenries, secondary
inductance of 0.1 millihenry, and a coefficient of coupling of 98%
Things start really getting interesting when we work with diodes and active devices. For
Micro-Cap 7, Student Edition: Page 28
example, the diode model contains 31 parameters. Try adding a diode and choosing any of the
models in the library. Then click on "Edit", and you will see a table of all of the parameters.
Many of these parameters can be deduced from data sheets. However, we recommend that you
select the part number of the diode closest to the one you plan to use and not worry about
creating your own model.
The active devices consist of the following 12 possibilities:
NPN, PNP, NMOS, PMOS, DNMOS, DPMOS, NJFET, PJFET, Opamp, GaAsFET,
NPN4 and PNP4.
You add these components to the circuit in the same way as you add passive components (left
mouse button and drag, right mouse button to rotate). We now briefly describe each of these.
NPN and PNP: Once you add either of these bipolar junction transistors to your circuit, you
can select from the list of models stored in the program. If necessary, you can modify the
parameters once you make a selection. For example, if you add an npn transistor, the
2N2222A, you can click on Edit and see a display of 54 parameters. As one example, BF is
301.483. This is the forward beta. If you want to change that, simply edit that entry.
The following table defines the major parameters for the BJT model. We don't expect you
to be familiar with all of these parameters. You would have to read about the computer models
used for SPICE to understand all of the details. You should, however, be familiar with some of
the major parameters from reading transistor data sheets.
NAME Parameter
Units
Default
Value
IS
Saturation Current
A
5E-12
BF
Ideal maximum forward beta

200.0
NF
Forward current emission coefficient

1.20
VAF
Forward Early voltage
V
100
IKF
BF high-current roll-off corner
A
0.1
ISE
BE leakage saturation current
A
2E-12
NE
BE leakage emission coefficient

1.50
BR
Ideal maximum reverse beta

2.00
NR
Reverse current emission coefficient

1.00
VAR
Reverse Early voltage
V
0
IKR
BR high-current roll-off corner
A
35
ISC
BC leakage saturation current
A
1E-14
NC
BC leakage emission coefficient

2.00
NK
High Current Roll-Off Coefficient

0.5
ISS
Substrate p-n Saturation Current
A
0.0
NS
Substrate p-n Emission Coefficient

1
RE
Emitter resistance

0.5
Micro-Cap 7, Student Edition: Page 29
RB
Zero-bias base resistance

0
RBM
Minimum RB at high currents

RB
IRB
Current where RB falls by half
A
0
RC
Collector resistance

1E-3
CJE
BE zero-bias depletion capacitance
F
4E-11
VJE
BE junction built-in potential
V
0.7
MJE
BE junction grading coefficient

0.5
CJC
BC zero-bias depletion capacitance
F
3E-10
VJC
BC built-in potential
V
0.7
MJC
BC junction grading coefficient

0.5
XCJC
Fraction of BC dep. Cap. To internal base

1
CJS
CS junction zero-bias capacitance
F
0.00
VJS
CS junction built-in potential
V
0.75
MJS
CS junction grading coefficient

0.00
FC
Forward-bias depletion coefficient

0.5
TF
Ideal forward transit time
S
4E-10
XTF
Transit time bias coefficient

0.5
VTF
VBC dependence on TF
V
10
ITF
Transit time dependence on IC
A
0.01
PTF
Excess phase

0
TR
Ideal reverse transit time
S
2E-7
EG
Energy gap
eV
1.11
XTB
Temperature coefficient for betas

0.00
XTI
Saturation current temperature exponent

3.00
KF
Flicker-noise coefficient

0.00
AF
Flicker-noise exponent

1.00
NMOS, DNMOS, PMOS, and DPMOS: The letter "D" stands for "discrete" while the
absence of a "D" indicates an integrated circuit MOS transistor. The appropriate symbols
appear on the screen when you add any of these active devices to your circuit. The library for
MOSFETs contains standard entries. The models have 56 parameters. Of these, 42 are from the
original SPICE 2G.6 model. We refer you to references for the details.
NJFET and PJFET: Adding either type of JFET is done in the same manner as other active
Micro-Cap 7, Student Edition: Page 30
devices. The library of JFETs contains 5 standard entries, each of which has a model with 20
parameters.
OP-AMPS: The op-amp model library contains 26 standard entries, each of which has 20
parameters. Note that the first parameter is the model level, which can take on one of three
values. Level 1 is the simplest model, and it is only uses three parameters. The reason you
might want to use one of the lower level models is that the simulation will run faster. Level 2
adds another four parameters to this list and is a three-stage, two-pole model with slew rate
limiting, finite gain, and output resistance. Level 3 is an enhanced Boyle model similar to those
implemented in other SPICE programs as subcircuits. It uses all 18 operational parameters.
The second parameter describes the op-amp type: NPN, PNP or JFET.
GaAsFETs: Gallium Arsenide n-channel FET devices are capable of much higher speeds than
devices fabricated using silicon. The MESFET is an example of this type of device. The
GaAsFET model used by Micro-Cap (SPICE 2G.6 has no model for the GaAsFET) contains 22
parameters.
The first parameter specifies one of three possible model levels. There are no models
stored in your program, so you will have to create a model if you wish to use Gallium Arsenide
devices. Refer to the Help screen for the syntax for the model statement.
NPN4 and PNP4 are four-terminal versions of the basic junction transistors. The additional
terminal is the substrate.
Waveform Sources
When you select Waveform sources from the Analog Primitives selection in the Components
menu, you are presented with another menu containing eight entries: Battery, Pulse Source,
Isource, User Source, Sine Source, V, I, and Fixed Analog.
Battery: If you select Battery and then enter the component on the schematic, you are
prompted for the battery voltage. Simply enter the battery voltage.
Pulse Source: We used this source earlier. The waveform is specified by seven parameters
(See Figure 15 presented earlier) as defined below:
!VZERO is the zero level, or the initial value of the waveform. The default value is zero.
!VONE is the one level, or the pulse height in volts. The default value is 5 volts.
!P1 is the delay time in seconds. This parameter models the time delay from time equals
zero to the leading edge of the waveform. It can be any non-negative value, including
zero. The default is 1.0E-7, or 0.1 µs.
!P2 is the time delay to the one level. The rise time is the difference between P2 and P1.
Default value for P2 is 1.1E-7, yielding a rise time of 10 ns. You can create an
infinite slope by setting P2 equal to P1.
!P3 is the time delay to the start of the trailing edge. Default is 5.0E-7 or 0.5 µs.
!P4 is the time at which the low value is reached. Fall time is P4 minus P3. Default value
is 5.1E-7 yielding a decay time of 10 ns.
!P5 is the period of the waveform. Default is 1.0E-6, or 1 µs.
Isource: This is a dc current source. You specify the value after drawing the source on the
screen.
User Source: This is a voltage source that gets its values from a user-defined file in an ASCII
Micro-Cap 7, Student Edition: Page 31
text file. This file contains N sequential values representing the waveform at N successive
time points.
Sine Source: This is an independent voltage source defined by seven parameters. Once you
add this, you can choose one of six in the library. You enter the model the same way you did
for the pulse source. If you simply enter "General", all seven default parameters will be used as
indicated in the following table.
Name
Parameter
Units
Default
F
Frequency
Hz
1E7
A
Amplitude
Volts
1
DC
DC level
Volts
0
PH
Phase
Radians
0
RS
Source Resistance
Ohms
0.001
Seconds
1E-6
Seconds
2.5E-7
RP
TAU

Repetition period of
exponential
Exponential time
constant
V and I: These are independent sources. You can specify pulse, sinusoid, exponential, tabular,
or frequency modulated waveform. In addition, you can specify an ac source with a given
magnitude and phase for use in ac analysis. We will see an example of this later.
The Analog Primitives selection on the Components pull down menu contains four other
types of sources, these being Function, Laplace, Z Transform, and Dependent. We briefly
describe these next.
Function Sources: When you select function sources, you are presented with another menu
containing six entries. These are NFV, NFI, NTVofI, NTIofI, NTIofV and NTVofV. The
function source can be specified either by an algebraic formula (NF) or by a table of values
(NT). The formula type function source uses an algebraic formula to compute the value of the
output variable as a function of any set of time-domain variables. The source can be either
current or voltage, designated as NFI or NFV respectively. The available functions are
summarized below:
P(X,Y,Z) 
E(X,Y,Z)
Power flowing into a circuit section. X, Y, and Z are nodes. There must
be a resistor or inductor between nodes X and Y. This is needed to
measure the current. The current is multiplied by the voltage drop
between nodes Y and Z.
Energy flowing into a circuit section.

T

Transient analysis simulation time.
F

Real ac analysis frequency value (in Hz.)
S

Complex radian frequency = 2jF
+

Addition
-

Subtraction
Micro-Cap 7, Student Edition: Page 32


*

/
MOD

Division

Modulus 


SIN(x)
Multiplication
COS(x) 
Sine function (x in radians)

Cosine function (x in radians)


TAN(x)

Tangent function (x in radians)
ATN(x)

Arc tangent function
SINH(x)

Hyperbolic sine


COSH(x)

Hyperbolic cosine

TANH(x)

Hyperbolic tangent

Hyperbolic cotangent

COTH(x) 
LN(x)

Natural log
LOG(x)
Base 10 log
EXP(x)
ex
ABS(x)
Absolute value
DB(x)
Decibels
D(x)
Delta, or change. A derivative can be formed as a ratio of two deltas.
SQRT(x)
Square root
SGN(x)
+1 if x>0, -1 if x<1 or x=0
^
Exponentiation operator
AND
AND operator
XOR
Exclusive OR operator
NOT
Negation operator
OR
OR operator
Laplace Sources: When you select this item, you are presented with another menu containing
eight entries, each beginning with "L" for Laplace. These are LFIofV, LFIofI, LFVofV,
LFVofI, LTIofV, LTIofI, LTVofV and LTVofI. These represent controlled sources where the
source and the controlling variable can be either voltage or current. This yields four possible
combinations (for example, voltage-controlled voltage source, current-controlled voltage
source). Each of the four possibilities has two types of sources: those specified by a formula
and those specified by a table. The formula sources contain an "F" in the specification, while
tabular sources contain a "T".
The formula sources can be used to simulate a transfer function. For example, if you
Micro-Cap 7, Student Edition: Page 33
specify the formula (after adding LFVofV source to the diagram. The formula is entered in the
"Value" box) as 1/(1+.001*s), your controlled source acts as a first-order lowpass filter with 3dB cutoff frequency at 1000 radians/sec (159 Hz). Figure 21 shows the circuit for this function.
Figure 22 shows the frequency response plot that results. Note that we have a generic
sinusoidal source, where we have specified default parameters. The plot was produced using
the ac analysis program, which we describe in Chapter 4.
Figure 21
Micro-Cap 7, Student Edition: Page 34
Figure 22
Z Transform Sources: These sources are mapped into their equivalent Laplace sources with
the transform of exp(S/FC) where FC is the clock frequency. The Z transform sources are used
to handle Z transform expressions. <fexpr> defines the Z transform expression, and it must
contain at least one instance of the variable Z. <freq> is the frequency at which the Z
expression is sampled. 1/<freq> is equivalent to the sampling period. This device lets you
model anything from a simple delay device to a complex digital filter. These sources come in
four configurations as follows:
ZIofI
Current dependent current source
ZIofV
Voltage dependent current source
ZVofI
Current dependent voltage source
ZVofV
Voltage dependent voltage source
You need simply enter the z transform expression [e.g., z/(z-1)]
Dependent Sources: When you make this selection, you are presented with eight choices:
IovV, IofI, VofI, VofV, HVOFI, GIOFV, FIOFI, EVOFV. The first four are conventional
dependent sources. If you add one of these to the diagram, you are prompted to enter the
proportionality constant for that source. For example, if you select VofV and enter 5, the
controlled source voltage is five times the voltage at the input nodes.
The last four entries (preceded by E, F, G, and H) are SPICE polynomial-dependent
sources. If you are familiar with the SPICE device statements, the conversion to MICRO-CAP
is simple. The syntax is identical. If you are not familiar, you probably will not need the
sources for the course you are taking.
Micro-Cap 7, Student Edition: Page 35
Connectors: If you select Connectors from the analog primitives, you are presented with 5
entries: Ground, Tie, Jumper, Jumper 2, and jumdiag1.
Ground: This entry is used to draw a ground. If you hold down the left mouse button, you can
drag the ground around the screen to any desired position. While holding down the
left button, you can reorient the ground by clicking the right button. Every circuit
must have a ground before you run a simulation.
Tie and Jumper: When two lines cross in Micro-Cap a drawing, it is assumed that a
connection exists between the two lines. It would therefore seem necessary to make a
two-dimensional drawing of the circuit without any intersecting lines (unless they are
to be connected). As circuits become more complex, it is not possible to make such a
planar drawing. We need ways to cross lines without making an electrical connection.
Jumper is used whenever lines that are not electrically connected intersect. You add
this component and position the loop to lie over the second line. Two different length
jumpers for horizontal or vertical placement in the circuit, and one for diagonal
placement are available.
Sometimes points that are widely separated must be electrically connected. We could
do this by drawing lines connecting the point, using jumpers when necessary.
However, this may clutter the diagram unnecessarily. The Tie selection provides a
simple alternative. You use it to mark the two points with any identical label. They
are then electrically tied together. You position the arrow over one of the points and
click the mouse. Then you type the label. You repeat the operations for the second
point. You can do this for any number of points.
SMPS: This entry produces various subcircuits.
Miscellaneous: The next entry in the Analog Primitives submenu is labeled Miscellaneous. It
contains a submenu with seven entries: Sample and Hold,
S(V-Switch), Switch,
W(I-Switch), Arrow, Bubble1 and Bubble2. The Arrow and Bubble entries are
included to illustrate that you can define a variety of shapes to suit your particular
applications. These particular shapes are included as drawing tools to make your
circuit diagram more complete.
We describe only the basic Switch and refer you to help screens for the other entries.
Three types of switches can be used in circuits: current-controlled, voltagecontrolled, and time-controlled. If you use a current-controlled switch, you must
insert an inductor across the input nodes of the switch. Voltage-controlled switches
are controlled by the voltage across the two input nodes, while time-dependent
switches use the time variable, In all cases, the open switch is represented by a high
resistance, ROFF, while the closed switch is represented by a low resistance, RON.
Switches are used only in transient analysis. After you draw a switch, you are prompted
to type in the value. This is done in the following format:
S,N2,N2
S is the controlling parameters (I for current-controlled and V for voltage-controlled and T for
time-controlled). N1 and N2 are threshold values of the controlled parameters
between which the switch changes state. You can simulate either a normally open or
normally closed switch, depending on whether N1>N2 or N2>N1. If N2>N1, the
switch is normally open, and it closes when the parameter is between N1 and N2. If
N1>N2, the switch is normally closed, and it opens when the parameter is between
N1 and N2.
Micro-Cap 7, Student Edition: Page 36
S Two Port gives a way of modeling devices using s-parameters.
Editing Schematics
Now that you know how to draw a schematic using the various tools and components
available to Micro-Cap 7, we are ready to see how to modify the diagram. This is done by
using the Edit pull-down menu accessed from the Schematic Editor window.
When you pull down the Edit menu, you are presented with the following choices,
some of which should already be familiar to your from other software:
!Undo: Undo reverses the last change.
!Cut: Deletes the selected objects and copies them to the clipboard.
!Copy: Copies selected objects to the clipboard.
!Paste: Copies contents of clipboard starting at current cursor position.
!Clear: Deletes the selected items without copying to clipboard.
!Select All: Selects all objects in current window.
!Add Page: Adds new page to schematic
!Delete Page: Deletes one of more schematic pages
!Add Model Statements: Places model statements in the text area for any parts that
don't have one. It searches through all model libraries including the default. If it
fails to find the part model, it places a default model statement in the schematic
text area.
!Box: These commands affect objects enclosed in a box you select. You can step
contents vertically or horizontally, you can create a mirror image of the contents,
you can rotate, or flip the entries.
!Change: Allows you to change attribute display, including color and font
!Bring to Front: A mouse click on a stack of overlapping objects selects the front
object in the stack. If the front object isn't the one you want, a method is needed to
select another object from the stack. This command makes the selected object the
front object and thus accessible to clicking.
!Send to Back: Selected object moves to back.
!Find: Invokes Search menu which is used to search the front window for a variety of
objects (text, parameters text, grid text, node numbers, components)
!Replace: Conducts a search and replace for text in a text window or the schematic
text area.
Micro-Cap 7, Student Edition: Page 37
Chapter 3
TRANSIENT ANALYSIS
INTRODUCTION
If you have gone through Chapter 2, you are now an expert at drawing any circuit on the
monitor. The next three chapters explore the various forms of analysis you can perform using
Micro-Cap 7.
Transient analysis is used to plot time waveforms at various points in the circuit. It
involves generating a new set of equations dynamically for each time point, solving these
equations, printing and graphing the solutions, and setting up a new set of equations whose
content depends on the prior solution. Transient analysis evolves from the state space
approach, which you may have been exposed to in your systems courses.
You begin by drawing a circuit, either by entering each component as described in Chapter
2, or by retrieving a network from the data file. We illustrate transient analysis using the
Differential Amplifier circuit that is one of the files already stored in the program. If you
currently have any circuit in the Schematic Editor window, close it using the File pull-down
menu. Then recall the differential amplifier file from memory by using the File pull-down
menu from the main (top) menu bar, selecting Open, and then loading "DIFFAMP.cir" (you
can scroll down to diffamp using the mouse or arrow keys, or type "d" to jump down to the
first entry starting with the letter d). The screen should look like Figure 23.
Figure 23
Once you have the network on the screen, initiate the analysis by pulling down the Analysis
menu, and selecting Transient analysis. Alternatively, you can use the keyboard by typing the
Micro-Cap 7, Student Edition: Page 38
hot key (identified on the pull-down menu) by simply pressing "ALT+1"
After you initiate the transient analysis, you are presented with the Transient Analysis
Limits window. This is shown in Figure 24. We begin this tutorial with a discussion of this
analysis limits window. We then discuss each of the menu selections in the transient analysis.
Figure 24
TRANSIENT ANALYSIS LIMITS
After activating the transient analysis, you are presented with a window showing limits used in
the analysis. When you store a circuit, the selected limits are stored with it. If you create a new
circuit, default limits are used until you choose different values. The limits stored in the
differential amplifier circuit are shown in Figure 24. If you wish to change any of the analysis
limits, click the mouse on that limit, and then type in the new value.
We now describe each field in this window. However, if you are impatient to see an
analysis run, you can simply click on Run (or press the F2 function key).
Numeric limits fields:
The upper portion of the window contains a field with four entries.
Time range: This is used to specify the time over which the simulation is performed. You can
specify two parameters: The starting time (tmin) and the ending time (tmax). The format for
simulation time is "tmax[,tmin]".
When we specify input parameters, the terms in square brackets are optional. If they are
omitted, the default values are used. The default value for tmin is zero. You are not permitted
to specify negative values for either of these times. The example of Figure 24 shows a time
range of 10us. This means the simulation runs from time 0 to 10 microseconds. We could have
specified the same range by entering "10us,0".
Maximum time step: Micro-Cap 7 simulates operation of a circuit by stepping in time. Each
time the program calculates parameters, these are compared with the previous calculation. If a
circuit contains capacitance or inductance, the program monitors the time rate of change of the
charge and flux. Internal algorithms control the size of this derivative. If it is too large, the time
step is decreased. If it is too small, the time step is increased up to the specified maximum. The
internal algorithm controls accuracy of the results. If the maximum time increment is too large,
Micro-Cap 7, Student Edition: Page 39
the resolution suffers, while if it is too small, the program takes a long time to run. You can
often smooth a resulting curve by reducing the maximum time step.
The default value for the time step is (tmax-tmin)/50. This means that 50 iterations are
performed over the length of the simulation. The program uses the default value if you either
leave the field blank on the Analysis Limits window, or if you enter zero for the maximum
time step as we have done in this example (clearly if the program ran with a zero time step, you
would have to wait forever for a single plot to develop).
Number of points: This specification is used for numeric output (i.e., a table, as opposed to a
graph). It sets the number of points to be printed (number of rows in the printout table). The
default value is 51 that corresponds to the default value for the time step. If the specified points
do not fall directly on values used in the iteration, the printed value is interpolated from
calculated values.
Temperature: Temperature enters into the parameter equations for devices and components.
One or more temperature values (in degrees Celsius) can be specified for the analysis. The
format is: High [,Low[,Step]]. The square brackets indicate you can omit Step, or you can
omit both Low and Step. The default value for Low is High while the default value for Step is
the difference between High and Low. Therefore, if only one value is specified, the simulation
runs at that temperature. If two values are specified, the simulation runs at those two values,
the Low and High temperatures. For example, "27,25" runs the simulation twice, once at 25
and once at 27 degrees centigrade (27o is room temperature). An entry of "35,20,5" runs the
simulation at 20, 25, 30 and 35 degrees. The "Linear" to the left of the parameter means that
the temperature is stepped in equal increments.
Waveform options fields:
We now turn our attention to the wide table occupying the lower half of the Analysis limits
window of Figure 24. The table contains four waveform option buttons in addition to five
columns. Each row in this table represents a plot on the resulting graph.
Linear/Log: The first two buttons toggle the x axis and y axis between linear and log scale.
Try clicking on these and see what happens. Notice that the markings on the button change
from linear to log and back again. Of course, if you choose a log scale, the scale ranges must be
positive numbers.
Color Menu: The third button, the solid color button, takes you to the color menu.
Numeric Values: The fourth button controls the table option. When pressed, a table of
numeric values is printed.
The remaining five columns specify details of the waveform. These are described below:
P: When several variables are plotted, we have a choice of superimposing the plots on the
same set of axes, or having them appear on separate non-overlapping graphs. The numeric
entry in the P column is a number from 1 to 9. This indicates to which group the particular
waveform is assigned. If you use the same number for several rows, these waveforms are
plotted on the same set of axes. If the ranges are not the same, the plot uses the union of the
individual ranges. Micro-Cap 7 analyzes equations independent of units. For example, a plot
Micro-Cap 7, Student Edition: Page 40
with a range from 0 to 1 could be used for a voltage curve ranging from 0 to 1 volts, and
simultaneously for a current curve ranging from 0 to 1 amps.
The example of Figure 24 creates two curves plotted on two separate sets of axes. If we
wanted the two curves superimposed, we would assign the same P number to both.
Expression fields:
The remaining four columns relate to the expressions to be plotted. You can see choices by
first clicking the item with the left mouse button, and then clicking the right mouse button.
X Expression: This field specifies the expressions for the X-axis variable. In most cases, this
is a time variable, but it could be another parameter. For example, you may wish to plot a
hysteresis curve, in which case the X expressions may be an input voltage.
Y Expression: This field specifies the expressions for the Y-axis variables. These may be
simple voltages or currents, or they could be more complex math expressions such as power.
For example, we might have an electronic circuit where we plot V(VCC)*I(VCC). If VCC is
the label assigned to the DC source, this plot represents the power flow from the source.
Alternatively, you could plot the output/input voltage ratio in decibels by specifying
DB(VOUT/VIN), where we assume you have labeled the input voltage as VIN and the output
as VOUT.
The section on Function Sources in Chapter 2 summarizes the various functions and
equations available in Micro-Cap 7. We will not repeat that list here, but we do take a moment
to list the variety of variables you can specify (we are restricting our attention to analog
variables for now).
V(A)
The voltage at node A. If the node is not labeled, you can use its
number.
V(A,B)
Voltage at node A minus voltage at node B.
V(D)
Voltage across the device called D.
I(D)
Current through the device called D.
T
Time
F
Frequency (in Hz.)
S
Complex frequency = 2*B*F*j
V(A)*I(A)
Power
Note that in the example of Figure 24, we plot two expressions, V(a,b) and V(Outa,Outb).
These represent differential voltages between pairs of nodes. The nodes are labeled on the
schematic of Figure 23.
Signal Processing Functions:
Micro-Cap 7 can perform a variety of signal processing functions. In specifying the Y
expression for plotting, you can choose any of 12 different processing functions. These are
listed below.
FFT(X) Forward Fourier transform of waveform X
IFT(X) Inverse Fourier transform of spectrum X
CONJ(X) Conjugate of spectrum X
CS(X,Y) Cross spectrum of X and Y = CONJ(FFT(x)*FFT(y))
AS(X)
Auto spectrum of spectrum X = CS(x,x)
CC(X,Y) Cross correlation of waveforms x and y = IFT(CS(x,y))
Micro-Cap 7, Student Edition: Page 41
AC(X)
Auto correlation of waveform x = IFT(CS(x,y))
COH(X,Y)Coherence of waveforms x and y = CC(x,y)/sqr(AC(x(0)*AC(y(0)))
REAL(X) Real part of spectrum X produced by FFT
IMAG(X) Imaginary part of spectrum X produced by FFT
MAG(X) Magnitude of spectrum X produced by FFT
PHASE(X)Phase of spectrum X produced by FFT
You can gain familiarity with some of these functions by experimenting with the circuits stored
in your program. In particular, FFT1.CIR demonstrates the use of some functions in transient
analysis. You should experiment with that circuit and plot the various FFT parameters as you
vary the length of the time interval. See if this agrees with what you learned about FFT in your
Digital Signal Processing course.
X range: This sets the scale ranges for the X waveforms. The format is "High[,Low]". In our
example, we have a single entry, 1E-5. This means that X runs from 0 to 10 microseconds.
Note that this matches the time range of the simulation. You can enter "auto" for this field and
Micro-Cap 7 automatically sets the range. Enter "auto" by placing the cursor on the appropriate
field and typing auto. We give a faster way to enter auto in the next section (if you can't wait,
just look directly above the "Y Expression" column heading). The range must be a subset of the
simulation time. That is, you cannot plot a response for a range of values if the simulation was
not performed for that range. If you use the "auto" entry, the program must run the entire
simulation prior to setting the plotting range. You will not see the result plotted in real time.
Y range: Same as X range, except for the Y variable. You can enter "auto" for this field, and
Micro-Cap 7 automatically scales the range so the plots fill the graph.
The upper right portion of the Transient Analysis Limits window contains some
additional choices. You have three choices for "Run Options". These are Normal (runs
simulation without saving to disk), "Save" (runs simulation and saves to disk) and "Retrieve"
(loads previously saved simulation and plots and prints as if it were a new run). You also have
three choices for state variables, depending on whether you want to set initial values to zero,
read values from a file, or use the values at the end of the last run.
This leaves three more boxes on the window:
Operating Point: This calculates a dc operating point.
Operating Point Only: This calculates a dc operating point only, and does not run the
analysis.
Auto Scale Ranges: This does the same thing as entering "Auto" for the ranges. It sets the
X and Y range to whatever is necessary to display the entire waveform.
Once you are satisfied with the analysis limits, you are ready to run the analysis. Run the
analysis by clicking the Run button in the upper left corner of the screen. The transient analysis
is produced, as shown in Figure 25. You can stop the simulation at any time by pressing the
ESC key.
Micro-Cap 7, Student Edition: Page 42
Figure 25
Note that we have plotted two waveforms on the two graphs of Figure 25. You can play
around with the table in the transient analysis limits screen to plot in various formats. To get
back to this screen following the run, either pull down the Transient menu and select Limits,
or press F9. Then try changing the second table line by changing P=2 to P=1. Run the
simulation and see what happens. You can add a third plot either by typing the new line, or
copying and modifying an existing line. For example, if you click next to the P=2 entry on the
second line and then click Add at the upper left, a third line is added which is a duplicate of the
second line. If you click Delete, that line is removed.
Now let's look at the screen of Figure 25. Below the title bar for the Transient Analysis
window are three pull-down menus: Transient, Scope, and Monte Carlo. We now discuss
each of these.
TRANSIENT ANALYSIS MENU
Once you select transient analysis from the Run menu, you can pull down the Transient
menu either with the mouse, or by pressing "Alt+T". The menu contains 11 selections.
Run
Limits
Stepping
Optimize
Analysis Window
Watch
Breakpoints
Numeric output
State Variables Editor
Micro-Cap 7, Student Edition: Page 43
DSP Parameters
Reduce Data Points
Run: You select this menu entry to run the simulation without changing the analysis limits.
Limits: This opens the Analysis Limits window so you can change limits. The Analysis
Limits window is automatically opened when you select Transient analysis from the Run
menu, so you access this from the Transient Analysis menu only if you wish to make changes
following a simulation run.
Stepping: Component parameters may be stepped from one value to another, producing
multiple runs with multiple output waveforms. You activate this feature by selecting Stepping
from the Transient menu and then entering instructions in the dialog box. The dialog box for
the differential amplifier example is shown in Figure 26.
Figure 26
Step What: This is where you specify which parameter you wish to step. For example, if you
named one or more resistors "R1", you would enter R1 to step their values. In the case of
stepping device parameters, you enter the device name on the first line, and the parameter you
wish to vary on the second. The arrows to the right permit you to select from choices. In the
differential amplifier example, we are stepping the forward beta of the transistor labelled N1
(see model statement on the original circuit, Figure 23), so we enter NPN N1 for the
component (or select it from the list that results when the arrow is selected), and BF for the
entry on the next line. (Case makes no difference to Micro-Cap 7 so don't be concerned if your
screen shows npn n1 instead of NPN N1)
Limits: From specifies the starting value of the parameter. To specifies the ending value of the
parameter. Step Value specifies the amount by which to step the parameter. In our example
circuit, we are varying the beta of transistor 1 from 100 to 350 in steps of 50.
Before continuing with our analysis of the Transient pull-down menu entries, let's run this
stepping example. Move to the "Step it" radio buttons below the step value, and select "Yes"
(Figure 26 shows "No"). Note that the steps are linear and we are changing a parameter in the
transistor model. Also note that you can do a nested stepping of a second parameter, but we
Micro-Cap 7, Student Edition: Page 44
will not select "Yes" for this stepping operation. Click "OK". Then either pull down the
transient menu and select "Run", or simply press F2.
The simulation now produces a family of 6 curves. These are for beta values of 100, 150,
200, 250, 300 and 350.
We now return to entries in the Transient pull-down menu.
Optimize: The optimizer systematically changes user-specified parameters to maximize,
minimize, or equate a chosen performance function, while keeping the parameters within
prescribed limits and conforming to any specified constraints.
Analysis Window: This selection gives you the opportunity to change plot characteristics such
as the line width.
Watch: This displays the Watch window where you define expressions or variables to watch
during a breakpoint invocation.
Breakpoints: This accesses the Breakpoints dialog box. Breakpoints are Boolean expressions
that define when the program will enter single-step mode so that you can watch specific
variables or expressions. Typical breakpoints are T>=100ns AND T<=10ns, or V(OUT)>5.5.
Numeric output: If you have enabled the fourth waveform option button (associated with a
particular plot in the Transient Analysis Limits menu), the numeric output is available as soon
as you run the simulation. You access this numeric output table from the Transient pull-down
menu.
State Variables Editor:
This command activates the State Variables Editor. You use this after you run the simulation.
The editor is used to view and edit node voltages and inductor currents. The editor for the
differential amplifier example is shown in Figure 27. We are showing this for the case where
we DO NOT step transistor beta. The figure shows eight node voltages. Our differential
amplifier circuit does not contain any inductors, so the right portion of this editor window is
blank.
Micro-Cap 7, Student Edition: Page 45
Figure 27
You normally do not change these values unless you want to explore the effects of an initial
condition variation.
There are two other selections in the pull down menu, DSP Parameters, and Reduce Data
Points. We will not be using these in this basic introduction to Micro-Cap 7. However, you can
get details on any function by simply clicking on "Help". This generally gives you the text from
the professional version manual.
SCOPE MENU
The Scope pull-down menu, which can be accessed after a simulation is run, is used to select
various scope commands. The menu provides you with a number of options regarding the
display. Our suggestion is that you experiment with this and use the Help screens if you run
into difficulty. Of particular interest is the cursor mode that allows you to place cursors on the
plots. Once you place a cursor, you can drag it with the mouse. The text below the plot shows
the numerical values at the cursor points.
The cursor function selection allows you to set cursors at key points on the curve, such as
Peak, Valley, High, Low, and Inflection. Peak and valley are Local maxima and minima,
while high and low are the global maximum and minimum. The Inflection mode locates points
where the second derivative of the waveform goes through zero (changes sign).
[NOTE: We hope you are trying these operations for the differential amplifier example. If you
are doing so and thinking about what you are seeing on the screen, you are probably thinking
that the High and Low are yielding the opposite of what you expect. However, keep in mind
that V(a,b) is negative, so the high values are at the bottom of the graph and the low values are
at the top. Additionally, since the output curve for this example asymptotically approaches the
steady state values, it is not a good example to illustrate the use of Peak and Valley. You may
Micro-Cap 7, Student Edition: Page 46
get some incorrect answers due to roundoff error in the process of comparing adjacent slopes.]
PROBE
PROBE is a powerful tool that allows you to view waveforms at various points in the
schematic, just as you would use a probe from a laboratory oscilloscope. PROBE performs the
transient analysis, saves the entire analysis in a disk file, and then allows you to probe points in
the circuit. PROBE functions like a normal simulation, but you need not specify in advance
which outputs you wish to plot.
Let's continue working with the differential amplifier schematic. Exit any run that you are
currently in (press F3), and you should have the schematic on the screen. If you are just
starting, load the differential amplifier schematic. Before running the simulation, pull down the
Analysis menu and select Probe Transient Analysis. This places you in the probe mode. The
program runs the simulation, which may take a while since your computer is doing more work
than it does to plot one or two variables. After the run, click on any component with the mouse.
We have selected resistor R4. Your display should look like Figure 28.
Figure 28
The circuit (or part of it) is on the right, and a transient analysis plot is on the left. We now
describe four of the pull-down menus, Probe, Vertical, Horizontal, and Scope.
The Probe pull-down menu contains eight entries:
New run: Probe stores results in data files on the disk. These files are named
CIRCUITNAME.TSA. If you have not changed the circuit since the last PROBE run, the
program does not rerun the simulation when you go to the probe mode. If you have changed the
circuit, the program detects this and performs a new run. If you have not changed the circuit,
but still wish to have a new simulation (e.g., suppose you changed a component model), you
Micro-Cap 7, Student Edition: Page 47
select New run from the Probe menu.
Limits: Gives the transient analysis limits.
Add Curve: This allows you to add the plot of another parameter to the already existing graph.
You are prompted to type the name. For example, if you type V(R1), you will plot the voltage
across resistor R1.
Delete Curves: This option lets the user remove a single waveform from the plot by selecting
it from a scrollable list.
Delete All Curves: This option removes all waveforms from the plot.
One Curve: This command selects the single trace mode. When a new waveform is selected, it
replaces the previous one.
Many Curves: This command is used to select multiple traces for the Probe waveform display.
Up to six waveforms can be displayed. As you probe various points, the new waveforms are
added to the diagram. If you have multiple waveforms with widely varying ranges, this option
may make it difficult to read the smaller waveforms since the vertical axis will scale for the
largest waveform. In such cases, you may wish to select the One Trace option.
Save All: This command causes all Probe variables to be saved.
Save V&I Only: This causes only voltages and currents to be saved during the save run. If
these are the only variables you will wish to probe, this option will speed things up and save
disk space.
The Vertical and Horizontal pull-down menus contain identical entries. These are used to
determine the variables, operators, and scale types (log or linear) used for the horizontal and
vertical axes. If you have selected Save V&I Only in the Probe menu, many of the selections
will not be available to you (i.e., only the voltage or current can be selected for display). If you
have saved all variables, you can choose to display:
Voltage
Current
Energy (displays energy curves)
Power (displays power curves)
Resistance (displays the resistance when mouse is clicked on a resistor)
Charge (displays charge when the mouse is clicked on a capacitor)
Capacitance (displays capacitance associated with the charge)
Flux (displays flux when the mouse is clicked on an inductor)
Inductance (displays inductance associated with the charge)
B field (displays B field when the mouse is clicked on a core)
H field (displays H field when the mouse is clicked on a core)
Time (usually selected for horizontal display)
If you have selected Many traces from the Probe menu, you can click additional nodes and
superimpose up to 6 waveforms.
Micro-Cap 7, Student Edition: Page 48
In addition to node voltages, you can also select lead-to-lead voltages. First remove all
waveforms using the Probe pull-down menu and selecting Delete All Plots, or by pressing the
Cntrl+F9 function key. Then position the cursor midway between the base and collector of the
left Q1 and click the left mouse button. You will then plot either VCB or VBC, depending on
whether the cursor was closer to the base or closer to the collector. The result is shown in
Figure 29.
Figure 29
If a portion of the circuit extends beyond the visible region, you can scroll the circuit using
the right mouse button.
PROBE is a very powerful tool in debugging circuits. If the output is not what you expect it
to be, you can often determine the cause of the discrepancy by probing intermediate points in
the circuit.
MONTE CARLO ANALYSIS
In the real world, circuits do not behave in the simple manner one assumes in an
elementary circuits or electronics course. For example, a 100 ohm resistor is never exactly 100
ohms, but may have a value that varies over a range from about 90 to 110 ohms. The same is
true of the parameter values for electronic devices. For example, the beta of a transistor has a
certain tolerance associated with it.
In a paper design, one often uses "worst case" analysis where parameter values are set at the
appropriate extreme of the tolerance ranges (i.e., the end of the range which yields the "worst"
results). Comprehensive probability analysis of circuits is complicated by non-linear
operations. As an example, suppose you know that the beta of a transistor has a certain mean
value, and is Gaussian (normal) distributed around the mean. To see the effects of this random
distribution on an output parameter, you have to track probability distributions through each
Micro-Cap 7, Student Edition: Page 49
portion of the circuit. As soon as you come to a non-linear operation, your theoretical analysis
comes to an abrupt halt.
The computer opens up an exciting possibility in this area. It can randomly set parameters
within the tolerance limits, and run the simulation many times compiling a family of output
curves. The family of curves can then be examined to generate statistics of any output
parameter. If enough simulation runs are performed, the "law of large numbers" indicates that
we generate an approximation to the probability distribution of the output variables. This is the
essence of Monte Carlo analysis, the name deriving from the probabilities that apply to
gambling. During Monte Carlo analysis, multiple runs are performed. For each run, a new
circuit is generated from components whose numerical parameter values are randomly selected.
The selection process is based upon user-specified parameter tolerances and specified
distributions within these tolerances. The display of the outputs is both in the form of multiple
superimposed curves and histograms displaying statistical data.
We begin by running a simple example, and then follow up with detailed descriptions of
the various functions. We will abandon our differential amplifier example used so far in this
tutorial since the circuit specification does not contain any component tolerances. Instead, press
the F3 function key to exit the simulation, then close the differential amplifier and open the
schematic called CARLO.CIR from the file. The circuit is shown in Figure 30.
Figure 30
Before we printed this circuit, we displayed node numbers on the figure. We did this by
either pulling down the Options menu, selecting Viewing and then Node Numbers, or by
simply clicking on the icon in the second row with the picture of a component and a node
number. These node numbers are needed to identify the plotted parameters since we have not
labeled the nodes with names.
If you now run the transient analysis you are presented with the Transient Analysis Limits
Micro-Cap 7, Student Edition: Page 50
window as shown in Figure 31.
Figure 31
Note that two variables are to be plotted, V(1) and V(2). Since the P entry on the
Transient Analysis Limits window is 1 for both variables, they will be superimposed on the
same set of axes with a Y variable range of -3 to +7 volts. The stored circuit has enabled
Monte Carlo analysis. That is done from the Monte Carlo pull-down menu, selecting Options,
and clicking the On radio button. Figure 32 shows the Monte Carlo Options menu.
Figure 32
We will be discussing this in detail in a few moments. For now, note that 100 runs will be
performed.
Activate the simulation either by selecting Run from the Transient menu or by pressing
the F2 function key. The simulation runs 100 times. The result is shown in Figure 33. 100
curves for V(2) are drawn superimposed on each other.
Micro-Cap 7, Student Edition: Page 51
Figure 33
Now pull down the Monte Carlo menu and select Histograms; then Add Histograms. This
produces Figure 34. You should see an entry of the form, Risetime[V(1),1,1,1,2]. Then click
OK, and you will see a screen similar to Figure 35.
Figure 34
Micro-Cap 7, Student Edition: Page 52
Figure 35
Our selection of Rise_Time in the Add Histogram mode (Figure 34) means we are
plotting the distribution of the amount of time it took the waveform to rise from the low value
of 1 to the high value of 2 (note that this represents only the beginning portion of the rise). The
histogram shows that for 19 of the trials, the rise time as between 10.94 ns and 11.08 ns.
Similarly, 20 of the trials had rise times between 11.08 ns and 11.22 ns. You may have learned
in your probability course that the outline of this histogram should theoretically follow a
Gaussian density function. The numbers at the top of each bar represent the percentage of
results falling in the corresponding range (with 100 runs, it is also the number of outcomes).
100 runs is not sufficient to develop the true probability distribution of the output. We reran
this for 1000 runs, with the result displayed in Figure 36 (see next page).
The result approximates a Gaussian curve with mean value of 11.05 nsec and standard
deviation of 0.32 nsec (we are reading these from the bottom of the figure). The bar to the right
of the histogram lists every one of the outcomes.
This concludes the simple example of Monte Carlo analysis. Now that you have
experienced the excitement of this powerful tool, we take an organized look at the various
functions and features.
Tolerances
Before you can run a Monte Carlo analysis, you need to specify tolerances for the devices
and components in your circuit. In the case of components, the tolerance is applied to the
numeric parameter (e.g., ohms, farads). You can specify tolerance as an actual value or as a
percentage of the nominal value.
Absolute tolerances are specified using a LOT statement. The form of specification is
LOT=X[%]. As an example, suppose a resistor is labeled as R1 and it is nominally a 10 kohm
Micro-Cap 7, Student Edition: Page 53
Figure 36
resistor. The tolerance is 5%. Since 5% represents an actual tolerance of 500 ohms, you have a
choice of either of the following specifications for the resistor. We are using a .DEFINE
statement which you place anywhere on the screen.
".DEFINE R1 10K LOT=500 5 " or
".DEFINE R1 10K LOT=5% 5 "
In the case of components, you can also specify tolerances directly on the schematic as you
label the parameter values. Thus, for example, when drawing the resistor on the circuit, you
could enter its value as "10K LOT=5%".
The same approach is used to apply tolerances to device parameters. For example, suppose
transistor Q1 is an NPN transistor with a nominal beta of 100 and tolerance of 20%. The
.MODEL statement you type would read,
".MODEL Q1 NPN (BF=100 LOT=20%)"
The forward beta then ranges from 80 to 120. If there are several transistors labeled Q1, the
program selects a beta for each run and applies it to all Q1 transistors.
Absolute (LOT) tolerance applies to all components or devices given the particular name.
You can also specify a relative tolerance, where the lot tolerance, if any, is applied to all of
the similarly named devices, and then the relative tolerance is applied to each individual
device. To do so, you use DEV in the same way you used LOT. If there is only one device
with the particular label, it does not matter which designation you use. Suppose, for example,
that the absolute tolerance of the beta of our transistor is 10% (i.e., an entire lot can be
expected to have a beta between 90 and 110) and the relative tolerance is 1% (within the lot,
the variation is "1% of the lot value). The .MODEL statement then reads,
".MODEL Q1 NPN (BF=100 LOT=10% DEV=1%) 5 "
Micro-Cap 7, Student Edition: Page 54
Probability Distributions
During the simulation runs, the program randomly adds or subtracts a delta value to the
nominal value. The probability of adding a particular delta value depends upon the specified
probability distribution. Three distributions are available: Worst case, Linear, and Gaussian.
In the Worst case distribution, the delta value is the full tolerance value. Thus, for example,
if the only circuit device with an associated tolerance were transistor Q1 with a nominal beta
of 100 and tolerance of 10%, beta would only take on two values during the various
simulations, either 90 or 110. There would be a 50% probability of the value being either of
these two numbers. If more than one component or device has an associated tolerance, various
combinations of the extreme values would occur during subsequent simulation runs.
In a Linear distribution, the value of delta is uniformly distributed within the tolerance
range. All values within the range are equally likely.
In a Gaussian (or Normal) distribution, the value of delta is Gaussian distributed within
the tolerance range. Since the Gaussian probability density does not go identically to zero, and
values of delta outside the tolerance range are not permitted, we use a truncated distribution.
The default value for standard deviation is the tolerance/2.58. Therefore, the extreme values
represent 2.58 standard deviations away from the mean. Using this value, the delta is within the
tolerance range 99% of the time. You can specify a standard deviation different from this
default value by using the Global Settings menu. You may wish to do this if you have detailed
manufacturer specifications. Suppose, for example, the supplier of the device guarantees that
95% of all resistors fall within a specified tolerance. Reference to tables of Gaussian densities
(error function tables) indicate that you should set the standard deviation so that the tolerance
represents 1.96 standard deviations.
Before going further, let's change the distribution from Gauss to Worst case. Run the
simulation, and you will get the result of Figure 37.
Micro-Cap 7, Student Edition: Page 55
Figure 37
Although the simulation runs 100 times, only four distinct curves result. Think about this!
If you examine the circuit, you find that only two components have tolerances associated with
them. The inductor has a nominal value of 1 microhenry. Applying the tolerance, it has an
inductance of either 0.9 uh or 1.1 uh. The capacitor has a nominal value of 1 nf, and worst case
tolerance values of 0.9 or 1.1 nF. All simulations run using inductor values of either 0.9uh or
1.1uh, and capacitor values to 0.9nF or 1.1nF. Thus there are only four combinations of
parameter values. This leads to a total of four curves.
DIGITAL ANALYSIS
Micro-Cap 7 handles mixed analog and digital analysis. Producing a timing diagram for a
digital circuit is identical to producing a transient analysis run for an analog circuit. Digital
components are entered from the components menu, and Micro-Cap 7 contains a library of
many digital circuits. We illustrate transient analysis using the decoder circuit. Simply open
decoder.cir . Your circuit will look like Figure 38.
We are simply feeding a four bit counter into a 74145 decoder chip. If you study the data
sheets for this chip, you find that only one output is high depending on the input. If, for
example, the input is a binary 3 (0011), output number 3 is high and the others are low.
Let's run a transient analysis. Selecting Transient from the Analysis pull-down menu
presents the Transient Analysis Limits window, as shown in Figure 39. Notice we are
plotting all 14 pin waveforms, and instead of plotting voltage, we are using d( ) [recall that the
program is not case sensitive so d( ) is the same as D( )]which plots the digital state waveform.
Since this circuit is entirely digital, we could not use V( ) expressions (try it). We then run the
analysis to obtain the result shown in Figure 40.
Micro-Cap 7, Student Edition: Page 56
Figure 38
Micro-Cap 7, Student Edition: Page 57
Figure 39
Micro-Cap 7, Student Edition: Page 58
Figure 40
This is a classic timing diagram of the type that might be found in a data sheet. Note that
the model in Micro-Cap 7 is not ideal. The output waveforms are delayed about 25 nsec (you
can use the cursor to measure this delay). If you want another good example from the circuits
on your disk, we suggest you try the circuit called Counter2.
Micro-Cap 7, Student Edition: Page 59
Chapter 4
AC ANALYSIS
INTRODUCTION
AC analysis provides a means of evaluating the small-signal transfer characteristics of a
circuit. If the circuit contains any nonlinear elements, the program calculates the DC
operating point to determine the small-signal characteristics of each nonlinear element. The
element is then replaced with a linear element representing these small-signal
characteristics.
The circuit must contain one of more independent (waveform) sources. The simulation
replaces Pulse, Sine, and User sources with fixed 1-volt amplitude AC signals. In the case
of circuits containing SPICE independent sources (V and I), these already have userspecified AC signal amplitudes. The analysis is performed using complex phasor quantities.
Since the phasors are complex, the program performs specified operations on the output in
order to present plots. These operators include real, imaginary, dB, magnitude, phase, and
group delay. In addition to plotting voltages and currents as a function of frequency, the
program can also produce Nyquist diagrams. A Nyquist diagram is a plot of the imaginary
part of the output vs. the real part of the output.
Begin by drawing a circuit, either by entering each component as described in Chapter
2 or by retrieving a network from the data file. If you already have a circuit in the
Schematic editor window, close it using the File menu. Although you may use any circuit
you have created, we illustrate AC analysis for the perf1.cir circuit. Retrieve this by pulling
down the File menu, selecting Open, and then scrolling to perf1.cir (recall that you can
skip to the first "P" entry by typing "P"). The screen should look like Figure 41.
Micro-Cap 7, Student Edition: Page 60
Figure 41
This is and RLC circuit. Once the network is on the screen, the analysis is initiated by
pulling down the Analysis menu and selecting AC analysis. Alternatively, you can use the
keyboard by entering the hot key (identified on the pull-down menu) by simply pressing
ALT+2.
After you initiate the AC analysis, you are presented with the AC analysis limits
window. We begin this tutorial with a discussion of this analysis limits window. We then
discuss each of the menu selections in the AC analysis.
Micro-Cap 7, Student Edition: Page 61
Figure 42
ANALYSIS LIMITS
After activating the AC analysis, you are presented with a window showing the limits used
in the analysis. When you store a circuit, the limits are stored with it. If you create a new
circuit, default limits are used. The limits stored in the perf1 circuit are shown in Figure 42.
We now describe each of these analysis limits. However, if you are impatient to see an
analysis run, you can simply pull down the AC menu (using the mouse, or by pressing
"ALT+A") and select Run (or press the F2 function key).
Numeric limits fields:
The upper portion of the window contains a field with six entries.
Frequency range: The format for this is Fmax[,Fmin]. The analysis starts at Fmin and
ends at Fmax. If you omit Fmin, it defaults to Fmax so the analysis is performed at a
single point. Negative frequency values are not allowed.
If you perform an analysis at a single frequency, the output plot contains only one point.
In fact, when you look at the graph you may think it is blank. You can read the value at this
single frequency point in two convenient ways. You could specify numeric output in the
Limits menu, or you can use the cursor mode after the simulation is run. If you select the
Cursor mode from the Scope pull-down menu, the cursor will immediately position itself
at the single frequency point, and you can read out the values.
Number of points: There is no interpolation in AC analysis (as there is in transient
analysis), so the points calculated are the same as the points printed. The frequency values
at which the calculation is performed depends on a selection you make in the Options
window (we discuss this window in a few minutes). You select either Auto frequency,
Fixed linear step, or Fixed log step.
If you have selected Auto frequency, the number of points is controlled by the
Maximum change value. We discuss this shortly when we examine the Maximum change
selection.
If you have selected either fixed linear or fixed log step, the Number of points entry in
the Analysis limits window determines the selected frequencies. For fixed linear steps, the
frequency step size is
Micro-Cap 7, Student Edition: Page 62
(fmax-fmin)/(Number of points-1)
For fixed log steps, the frequency step is
(fmax/fmin)1/(Number of points-1)
The default value for Number of points is 51.
Temperature: Temperature enters into the parameter equations for devices and
components. One or more temperature values (in degrees Celsius) can be specified for the
analysis. The format is High [,Low[,Step]]. The square brackets indicate you can omit
Step, or you can omit both Low and Step. The default value for Low is High while the
default value for Step is the difference between High and Low. Therefore, if only one value
is specified, the simulation runs at that temperature. If two values are specified, the
simulation runs at those two values, the Low and High temperatures. For example, 27, 25
runs the simulation twice at 25 and 27 degrees centigrade (27o is room temperature). An
entry of 35,20,5 runs the simulation at 20, 25, 30 and 35 degrees.
Maximum change %: If the Auto step option is selected, the program automatically
adjusts the frequency step up and down during the analysis. The maximum change you
enter is a percentage. If the plot values change by more than this percent of full scale, the
system reduces the step size. Typical Maximum change values needed to produce smooth
curves range from 1 to 5 percent.
Noise input: This field is used to specify the name of the source where input noise is
calculated. The field applies only to the calculation of Inoise and Onoise.
Noise output: This field is used to specify the node at which output noise is calculated.
The format is node1[,node2]. Two nodes separated by a comma specify a differential
output noise voltage. This field applies only if Inoise or Onoise variables are calculated.
Waveform options fields:
We now turn our attention to the wide table occupying the lower half of the Analysis limits
window of Figure 42. The table contains 10 columns. Each of these is described below:
The first four entries consist of buttons. These perform the same function as in the transient
analysis case, as follows.
Linear/Log: The first two buttons toggle the x axis and y axis between linear and log scale.
Try clicking on these and see what happens. Notice that the markings on the button change
from linear to log and back again. Of course, if you choose a log scale, the scale ranges
must be positive numbers.
Color Menu: The third button, the solid color button, takes you to the color menu. There
are 16 possible color choices for each individual waveform.
Numeric Values: The fourth button controls the table option. When pressed, a table of
numeric values is printed.
Type of Chart: The final button chooses the type of chart: rectangular, polar or Smith
chart.
P: When several variables are plotted, we have a choice of superimposing them on the
same set of axes, or having them appear on separate non-overlapping graphs. The numeric
entry in the P column is a number from 1 to 9. This indicates to which group the particular
waveform is assigned. If you use the same number for several rows, these waveforms are
plotted on the same set of axes. If the ranges are not the same, the plot uses the union of the
individual ranges. You should exercise caution in plotting dissimilar variables on the same
set of axes. Micro-Cap 7 does not track the units in its calculations. If, for example, you
plot a gain that runs from 0 to 10 dB on the same set of axes as a phase that ranges from 0
to 360 degrees, the gain curve would only occupy a small portion of the range.
Micro-Cap 7, Student Edition: Page 63
The example of Figure 42 will generate three curves plotted on one set of axes. If we
wanted the curves on separate plots, we would assign different P numbers to them. Note
that we are not currently plotting either noise parameter. We examine noise later in this
tutorial.
Expression fields:
The remaining 5 columns relate to the expressions to be plotted.
X expression: This field specifies the expressions for the X-axis variable. In most cases,
this is a frequency variable. One notable exception is a Nyquist plot, where the X
expression is the real part of the output.
Y expression: This field specifies the expressions for the Y-axis variables. Since the
program operates with complex phasors, complex operators are used. You can choose from
among the following operators, where X is a labeled voltage or a variable such as V(A,B).
RE(X)
Real part of X
IM(X)
Imaginary part of X
MAG(X)
Magnitude of X
PH(X)
Phase of X in degrees
GD(X)
Group delay = rate of change of phase with (radian) frequency
You can also plot mathematical functions of these operators, such as dB(MAG(X)) for a
decibel plot of the magnitude. You can see all of the possibilities by clicking on the
particular entry and then using the right mouse button.
If you plot the phase of a variable, the plot begins at the second analysis point. This
delay occurs because of an algorithm written into the program that removes phase
ambiguity. It must compare the second point to the first before establishing a phase
reference. If you need the exact phase at a particular frequency, start the analysis below that
frequency.
X range: This sets the scale ranges for the X waveforms. The format is High[,Low]. (You
can also add two more numbers to specify grid spacing, which sets the spacing between
grid, and bold grid spacing, which sets the spacing between bold grids. You can only set
these grid spacings in the linear mode. Logarithmic scales use a natural grid spacing of 1/10
the major grid values and bold is not used.)
In our example, we run the simulation from 100 kHz to 100 MHz, so the entry reads,
1E8, 1E5 for the X range. The default for Low is zero [Caution: Do not use the default
value for Low if you a plotting X on a log scale. If you do so, an error message will be
produced.]. You can enter "auto" for this field and Micro-Cap 7 automatically sets the
range using the designated frequency range. You can enter "auto" by placing the cursor on
the appropriate field and typing "auto". A faster way is to use the Limits menu as discussed
in the next section.
Y range: Same as X range, except for the Y variable. You can use "auto" for this entry,
and Micro-Cap 7 automatically sets the range to fill the screen after running the simulation.
Once you are satisfied with the analysis limits, you are ready to run the analysis. Run
the analysis by clicking the Run box in the upper left corner of the screen. Alternatively,
you can simply pressing the F2 function key. The AC analysis is produced, as shown in
Figure 43.
Micro-Cap 7, Student Edition: Page 64
Figure 43
As in the case of other types of analysis, you can exert two types of immediate control
on the simulation as it is running. You can terminate the simulation by pressing the ESC
key. If you press "P" during the run, you toggle a numeric display. This display shows the X
and Y expression values during the simulation run.
We seem to have gotten three families of curves. Each family contains nine separate
curves. If you paid attention during the previous chapter, you should already realize that
something must be stepped. In fact, in the title bar just above the curves, we clearly see that
C1 is stepping from 0.1 nF to 4.1 nF. If we go back to the AC Analysis Limits window
(pull down the AC menu and select Limits, or press F9), we can click on the Stepping
button in the top row. We clearly see that C1 is being stepped. You can disable this by
selecting No in the stepping box.
Now looking back at Figure 43, we briefly describe the pull-down menus. These are
essentially the same as those for the transient analysis.
AC MENU
Once you select AC analysis from the Run menu, you can pull down the AC menu either
with the mouse, or by pressing "Alt+T". The menu contains 13 selections.
Run
Limits
Stepping
Optimize
Analysis Window
Micro-Cap 7, Student Edition: Page 65
Watch
Breakpoints
3D windows
Performance windows
Numeric output
State Variables Editor
DSP Parameters
Reduce Data Points
Run: You select this menu entry to run the simulation without changing the analysis limits.
Limits: This opens the Analysis Limits window so you can change limits. The Analysis
Limits window is automatically opened when you select AC analysis from the Run menu, so
you access this from the AC Analysis menu only if you wish to make changes following a
simulation run.
Stepping: Component parameters may be stepped from one value to another, producing
multiple runs with multiple output waveforms. You activate this feature by selecting Stepping
from the Transient menu and then entering instructions in the dialog box. The dialog box for
the perf1 example is shown in Figure 44.
Figure 44
Step What: This is where you specify which parameter you wish to step. For example, if you
named one or more resistors "R1", you would enter R1 to step their values. In the case of
stepping device parameters, you enter the device name on the first line, and the parameter you
wish to vary on the second. The arrows to the right permit you to select from choices. In the
perf1 example, we are stepping the capacitor, C1, so we enter C1 for the component and Value
(or select by clicking the arrow) for the entry on the next line. (Case makes no difference to
Micro-Cap 7, so don't be concerned if your screen shows VALUEn1 instead of Value)
Limits: From specifies the starting value of the parameter. To specifies the ending value of the
parameter. Step Value specifies the amount by which to step the parameter. In our example
Micro-Cap 7, Student Edition: Page 66
circuit, we are varying C1 from 0.1 nF to 4.1 nF in steps of 0.5 nF.
We now return to entries in the AC pull-down menu.
Optimize: The optimizer systematically changes user-specified parameters to maximize,
minimize, or equate a chosen performance function, while keeping the parameters within
prescribed limits and conforming to any specified constraints. The optimizer function is limited
in the Student Edition of the software.
Analysis Window: This selection gives you the opportunity to change plot characteristics such
as the line width.
Watch: This displays the Watch window where you define expressions or variables to watch
during a breakpoint invocation.
Breakpoints: This accesses the Breakpoints dialog box. Breakpoints are Boolean expressions
that define when the program will enter single-step mode so that you can watch specific
variables or expressions.
3D windows: This feature is not available on the Student Version of the software.
Performance windows: This feature allows you to sort and search individual results. Its
function is beyond the scope of this manual.
Numeric output: If you have enabled the fourth waveform option button (associated with a
particular plot in the Transient Analysis Limits menu), the numeric output is available as soon
as you run the simulation. You access this numeric output table from the AC pull-down menu.
State Variables Editor:
This command activates the State Variables Editor. However, in AC analysis, you are looking
for steady state values, so you will most likely not use this editor. In fact, if you select it, notice
that the state variables are all zero.
There are two other selections in the pull down menu, DSP Parameters, and Reduce Data
Points. We will not be using these in this basic introduction to Micro-Cap 7. However, you can
get details on any function by simply clicking on "Help". This generally gives you the text from
the professional version manual.
SCOPE MENU
The Scope pull-down menu, which can be accessed after a simulation is run, is used to
select various scope commands. The menu provides you with a number of options
regarding the display. Our suggestion is that you experiment with this and use the Help
screens if you run into difficulty. Of particular interest is the cursor mode that allows you to
place cursors on the diagram. Once you place a cursor, you can drag it with the mouse. The
text below the plot shows the numerical values at the cursor points.
The cursor function selection allows you to set cursors at key points on the curve, such
as Peak, Valley, High, Low, and Inflection. Peak and valley are Local maxima and
minima, while high and low are global maximums and minimums. The Inflection mode
locates points where the second derivative of the waveform goes through zero (changes
Micro-Cap 7, Student Edition: Page 67
sign).
[NOTE: We hope you are trying these operations for the differential amplifier example. If
you are doing so and thinking about what you are seeing on the screen, you are probably
thinking that the High and Low are yielding the opposite of what you expect. However,
keep in mind that V(a,b) is negative, so the high values are at the bottom of the graph and
the low values are at the top. Additionally, since the output curve for this example
asymptotically approaches the steady state values, it is not a good example to illustrate the
use of Peak and Valley. You may get some incorrect answers due to roundoff error in the
processing of comparing adjacent slopes.]
PROBE
PROBE is a powerful tool that allows you to view waveforms at various points in the
schematic, just as you would use a probe from a laboratory oscilloscope. PROBE performs
the AC analysis, saves the entire analysis in a disk file, and then allows you to probe points
in the circuit. PROBE functions like a normal simulation, but you need not specify in
advance which outputs you wish to plot.
Let's continue working with the differential amplifier schematic we used in the previous
chapter. Exit any run that you are currently in (press F3), and then load the DIFFAMP
schematic on the screen. Before running the simulation, pull down the Analysis menu and
select Probe AC Analysis. This places you in the probe mode. The program runs the
simulation, which may take a while since your computer is doing more work than it does to
plot one or two variables. After the run, click on any component with the mouse. We have
selected resistor R4. Your display should look like Figure 45.
Micro-Cap 7, Student Edition: Page 68
Figure 45
The circuit (or part of it) is on the right and an ac analysis plot is on the left. We
describe four of the pull-down menus, Probe, Vertical, Horizontal, and Scope.
The Probe pull-down menu contains eight entries:
New run: Probe stores results in data files on the disk. These files are named
CIRCUITNAME.TSA. If you have not changed the circuit since the last PROBE run, the
program does not rerun the simulation when you go to the probe mode. If you have changed
the circuit, the program detects this and performs a new run. If you have not changed the
circuit, but still wish to have a new simulation (e.g., suppose you changed a component
model), you select New run from the Probe menu.
Add Curve: This allows you to add the plot of another parameter to the already existing
graph. You are prompted to type the name. For example, if you type V(R1), you will plot
the voltage across resistor R1.
Delete Curves: This option lets the user remove a single waveform from the plot by
selecting it from a scrollable list.
Delete All Curves: This option removes all waveforms from the plot.
One Curve: This command selects the single trace mode. When a new waveform is
selected, it replaces the previous one.
Many Curves: This command is used to select multiple traces for the Probe waveform
display. Up to six waveforms can be displayed. As you probe various points, the new
waveforms are added to the diagram. If you have multiple waveforms with widely varying
ranges, this option may make it difficult to read the smaller waveforms since the vertical
axis will scale for the largest waveform. In such cases, you may wish to select the One
Micro-Cap 7, Student Edition: Page 69
Trace option.
Save All: This command causes all Probe variables to be saved.
Save V&I Only: This causes only voltages and currents to be saved during the save run. If
these are the only variables you will wish to probe, this option will speed things up and
save disk space.
The Vertical and Horizontal pull-down menus contain identical entries. These are used to
determine the variables, operators, and scale types (log or linear) used for the horizontal
and vertical axes. If you have selected Save V&I Only in the Probe menu, many of the
selections will not be available to you (i.e., only the voltage or current can be selected for
display). If you have saved all variables, you can choose to display:
Voltage
Current
Inoise (displays the resistance when mouse is clicked on a resistor)
Onoise (displays charge when the mouse is clicked on a capacitor)
Frequency (displays capacitance associated with the charge)
The lower portion of the pull-down menu lets you select the type of plot (e.g., dB,
magnitude). If you have selected Many traces from the Probe menu, you can click
additional nodes and superimpose up to 6 waveforms.
In addition to node voltages, you can also select voltages across a component. First
remove all waveforms using the Probe pull-down menu and selecting Delete All Plots, or
by pressing the F9 function key. Then position the cursor over the component you are
interested in. You will then plot the voltage across this component.
If a portion of the circuit extends beyond the visible region, you can scroll the circuit
using the right mouse button.
PROBE is a very powerful tool in debugging circuits. If the output is not what you
expect it to be, by probing intermediate points in the circuit, you can often determine the
cause of the discrepancy.
MONTE CARLO ANALYSIS
Performing Monte Carlo AC analysis is virtually the same as with transient analysis.
We will not repeat the discussion of the previous chapter. Instead we urge you to
experiment and use the Help pull down menus when needed.
Micro-Cap 7, Student Edition: Page 70
Chapter 5
DC ANALYSIS
INTRODUCTION
DC analysis evaluates input/output characteristics in the DC condition. The input can be a
voltage appearing on a user-specified node (relative to ground) or a differential voltage
between two nodes. Alternatively, the input can be a current source. The program evaluates the
DC output, which can be either a voltage (for a node relative to ground, or differential between
two nodes) or a current flowing through a resistor specified by the two resistor nodes. The
system replaces all inductors with short circuits and all capacitors with open circuits. It then
applies a stepped DC source to the input and calculates the resulting DC output.
Begin by drawing a circuit on the screen, either by entering each component as described in
Chapter 2 or by retrieving a network from the data file. Although you may use any circuit you
have created, we illustrate DC analysis for the Differential Amplifier circuit. If you already
have a circuit in the Schematic editor window, begin by closing this circuit using the File
menu. Retrieve the differential amplifier circuit by pulling down the File menu, selecting
Open, and then scrolling to DIFFAMP.cir (recall that you can skip to the first "D" entry by
typing "D"). The screen should look like Figure 46.
Figure 46
Once the network is on the screen, the analysis is initiated by pulling down the Analysis
menu and selecting DC analysis. Alternatively, you can use the hot key (identified on the pulldown menu) by simply pressing ALT+3.
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After you initiate the DC analysis, you are presented with the DC Analysis limits window.
We begin this tutorial with a discussion of this analysis limits window. We then discuss each
of the menu selections in the DC analysis.
ANALYSIS LIMITS
After activating the DC analysis, you are presented with a window showing limits used in
the analysis. When you store a circuit, the limits are stored with it. If you create a new circuit,
default limits are used. The limits stored in the DIFFAMP circuit are shown in Figure 47.
Figure 47
We now describe each of these analysis limits. However, if you are impatient to see an
analysis run, you can simply select Run (or press the F2 function key).
Numeric limits fields:
The upper portion of the window contains a field with 7 entries.
Input 2 range: The program has the capability of stepping two independent inputs. Input 2 is
the secondary independent voltage/current sweep. The format is Final[,Initial[,Step]]. The
analysis starts at Initial and ends at Final. The system calculates N solutions spaced equally
over the range, Final-Initial with spacing of Step. If you omit Step, this parameter defaults to
(Final-Initial), so the simulation runs twice, once at the initial and once at the final value. If
you omit Initial, this parameter defaults to zero.
If the secondary independent source is not used, enter NONE, as we have done in this
example.
Input 2: This determines where this input will be placed. The format is Plus[,Minus][,I or V].
Plus is the node name or number of the node where the positive lead of the input source is to
be connected. For current sources, it can be thought of as the node toward which the directional
arrow is pointing. Minus is the node name or number of the node where the negative lead of
Micro-Cap 7, Student Edition: Page 72
the input source is to be connected. The third field designates whether the input is a current
source or a voltage source. The default for the third field is V (voltage source), and the default
for Minus is ground.
Instead of specifying nodes, you could give the label of the source. For example, you might
have a voltage sources labeled vin, in which case you simply enter this name.
Input 1 range: This is the main input source. The format is the same as that for Input 2 range
except that the specified step size is the maximum step size. Thus the format is
Final[,Initial[,MaxStep]]. MaxStep is the maximum step possible during a sweep. The actual
step size might be smaller since it is a function of the Maximum change (the last entry in this
field). The default value of Initial is zero. If you omit MaxStep, the program sets step values
based on the Maximum change. Note that Input 1 uses a variable step size while Input 2 uses
a fixed step size.
Input 1: This determines where this main input will be placed. The format is the same as that
for Input 2.
Number of Points: This entry specifies the number of points calculated for numeric output.
The default is 51 and the minimum is 5. Numeric output is calculated using linear interpolation
of the simulated results. Hence the number of points requested for numeric output need not
match the number of data points.
Temperature: One or more temperature values can be specified for the analysis. The format is
High[,Low[,Step]]. The simulation is performed at temperatures between the Low and High,
spaced by Step. Thus, for example, an input of 35,20,5 would produce separate runs at 20, 25,
30, and 35 degrees Centigrade. If Step is omitted, two runs are performed, one at the Low and
one at the High temperature. Thus the default value of Step is High-Low. If both the Step and
Low are omitted, one run is performed at the High temperature. Thus, the default value of Low
is High.
Maximum change %: This field affects the size of the step taken by "Input 1" during the
simulation. A setting of 5% usually gives acceptable results. You might need a smaller step if
device transitions (discontinuities in the input/output relationship) are involved. Of course, a
smaller specification forces the simulator to take smaller steps and increases the time required
for the simulation.
We see from Figure 47 that the selected limits for this example are as follows:
MThere is no secondary input.
MThe main input is the voltage source, V1.
MThe voltage source, V1, is stepped from -0.005 to +0.005 volts. Since no MaxStep is
specified, the step size is set so that the maximum change is 5%.
MThe simulation runs at one temperature, 27 degrees.
If you wish to change any of the analysis limits, click the mouse on that limit and then type
in the new limit.
Waveform options fields:
We now turn our attention to the wide table occupying the lower half of the DC Analysis
Limits window of Figure 47. The table contains ten columns. The first four of these are the
Micro-Cap 7, Student Edition: Page 73
same buttons we saw in transient and ac analysis.
Linear/Log: The first two buttons toggle the X axis and Y axis between linear and log scale.
Try clicking on these and see what happens. Notice that the markings on the button change
from linear to log and back again. Of course, if you choose a log scale, the scale ranges must be
positive numbers.
Color Menu: The third button, the solid color button, takes you to the color menu. There are
16 possible color choices for each individual waveform.
Numeric Values: The fourth button controls the table option. When pressed, a table of
numeric values is printed. These are each described below.
Now looking at the remaining columns, we see that you must enter information as follows:
P: When several variables are plotted, we have a choice of superimposing them on the same set
of axes, or having them appear on separate non-overlapping graphs. The numeric entry in the P
column is a number from 1 to 9. This indicates to which group the particular waveform is
assigned. If you use the same number for several rows, these waveforms are plotted on the
same set of axes. If the ranges are not the same, the plot uses the union of the individual ranges.
The example of Figure 48 shows two curves plotted on two different sets of axes.
Figure 48
Expression fields:
The remaining 5 columns relate to the expressions to be plotted.
X expression: This field specifies the expressions for the X-axis variable. Typical expressions
Micro-Cap 7, Student Edition: Page 74
are a voltage, say V(V1) or a current, I(V1), where we assume V1 is the specified Input 1
source. You can see a list of the various possible choices by selecting a table cell, then right
clicking the mouse.
Y expression: This field specifies the expressions for the Y-axis variables. This is typically a
voltage or a current. Note that for the second curve, we specify a Y expression as a derivative
showing the rate of change of the voltage at Outb with respect to the voltage at in. This
derivative is the slope of the first curve, and represents the gain of the circuit.
X range: This sets the scale ranges for the X waveforms. The format is High[,Low]. In our
example, we run the simulation from -0.005 to +0.005 volts for input V(In), so the entry reads,
0.005, -0.005 for the X range. The default for Low is zero. You can type "auto" for this field
and Micro-Cap 7 automatically sets the range. In such cases, Micro-Cap 7 must run a complete
simulation before it can determine a suitable scale range. You can enter "auto" by placing the
cursor on the appropriate field and typing "auto". A faster way is to click the “Auto Scale
Ranges” box on the DC Analysis Limits menu.
Y range: Same as X range, except for the Y variable. You can use "auto" for this entry, and
Micro-Cap 7 adjusts the range to fill the screen after running the simulation.
RUNNING THE ANALYSIS
Once you are satisfied with the analysis limits, you are ready to run the analysis. Run the
analysis by clicking Run. Alternatively, you can press the F2 function key. The DC analysis is
produced, as shown in Figure 48. To produce this plot, we have turned off the stepping feature
by pulling down the DC menu, selecting Stepping, and clicking on (Step it) NO.
DC Pull-Down MENU
Stepping: Component parameters may be stepped from one value to another, producing
multiple runs with multiple output waveforms. You activate this feature in the same way we
did in transient and ac analysis.
PROBE
The Probe mode is similar to that used in Transient or AC analysis. The major difference is a
greatly simplified list of choices for the variables. As an example, we will show the use of the
Probe mode for the DIFFAMP.CIR example. If you don't already have that circuit loaded, do
so at this time. Then pull down the Analysis menu and click Probe DC Analysis. Then click
on OUTA and on OUTB. Your screen should look like Figure 49.
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Figure 49
If you pull down the Vertical menu in the AC Analysis window, you will find only two
choices, Voltage or Current. You can also choose whether you wish the plot to be linear or
log. The same choices exist for the Horizontal axis. If we select Voltage for both of these, we
will be plotting the voltage at the selected points as a function of the input voltage. Then click
the cursor on the point(s) you desire to plot. As an example, we clicked on OutA and OutB to
produce the curves of Figure 50. We also used the Scope pull-down menu to select Tokens for
V(OUTB) so that the two curves could be distinguished from each other when a print copy is
made (they are in different colors on the monitor).
MONTE CARLO ANALYSIS
The operation of Monte Carlo Analysis is identical whether you are performing a transient,
AC, or DC analysis. We therefore do not repeat the detailed discussion of Chapter 3.
Micro-Cap 7, Student Edition: Page 76
INDEX
AC Analysis Limits, 14,62
AC Analysis, 14,62
AC Menu, 65
Add Histogram, 52
Add Page, 22,37
Add Curve, 48
Analog Primitives, 24,32
Analysis Menu, 6
Analysis Window, 45,67
Attribute Text, 23
Auto Frequency, 62
Auto Scale Ranges, 12,42
Battery, 31
Border, 24
Box, 22,37
Bring to Front, 22,37
Calculator, 23
carlo.cir, 50
Cascade, 22
Change Attribute Display, 22,37
Clear, 22,37
Close, 21
Color Menu, 40,63
Color, 22
Command Text, 23
Component Editor, 23
Component Mode, 22
Component Palettes 1-9, 24
Component, 22
Connector, 36
Copy, 22,37
Cross-hair Cursor, 24
Cut, 22,37
DC Analysis Limits, 72
DC Analysis, 17,71
DC Pull-Down Menu, 75
decoder.cir, 56
Delete All Curves, 48,64
Delete Page, 22,37
Delete Curves, 48,69
Dependent Source, 35
DEV Statement, 54
Differential Amplifier, 38
Digital Analysis, 56
DNMOS, 30
DPMOS, 30
DSP Parameters, 46
Edit Menu, 22,37
Engineering Notation, 25
Exit, 22
Features, 4
File menu, 5,20
Find, 22,37
Fixed Linear Step, 62
Fixed Log Step, 62
Flag, 23
Flip X, 22
Flip Y, 22
Floating point, 25
Font, 22
Frequency Range, 62
Function Source, 32
GaAsFET, 31
Gaussian Distribution, 55
Global Settings, 24
Grid Text, 23
Grid, 24
Ground, 36
Ground, Need for, 36
Help, 9
High, 46
Histograms, 52
Horizontal Pull-Down Menu, 48
Inflection, 46
Info, 23
Input 1 Range, 73
Input 1, 73
Input 2 Range, 72
Input 2, 72
Installation, 4
Isource, 31
Jumper, 36
Laplace Source, 33
Limits, 44,66
Line, Rectangle, Diamond,
Ellipse, Arc, Pie, 23
Linear distribution, 55
Linear/Log, 40,63,74
LOT statement, 53
Low, 46
Many Curves, 48,69
Maximize, 23
Maximum Change %, 63,73
Maximum Time Step, 7,39
Mirror Box, 22
Miscellaneous, 36
Mode, 23
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Model Program, 23
Monte Carlo Analysis, 49,70
New Run, 47
New, 21
NJFET, 30
NMOS, 30
Node Numbers, 10,23
Node Voltages/States, 24
Noise Input, 63
Noise Output, 63
Normal Distribution, 55
NPN, 29
NPN4, 31
Number Formats, 25
Number of Points, 7,40,62,73
Numeric Limit Fields, 39
Numeric Output, 45
Numeric Values, 40,63,74
Objectives, 4
One Curve, 48,69
Op-Amps, 31
Open Files, 23
Open, 5,21
Operating Point Only, 42
Operating Point, 42
Options Menu, 23
Options Pull-down menu, 10
Overlap, 23
P, 40,63,74
Paste, 22,37
Peak, 46
Pin Connections, 24
PJFET, 30
PMOS, 30
PNP, 29
PNP4, 31
Point to End Paths, 23
Point to Point Paths, 23
Preferences, 24
Print Preview, 21
Print Setup, 21
Print, 21
Prior Files, 21
Probability Distributions, 55
Probe DC Analysis, 75
Probe Pull-Down Menu, 47
Probe Transient analysis, 47
Probe, 68
Pulse Source, 26,31
Real numbers, 25
Reduce Data Points, 46
Refresh Models, 22
Remove Splits, 23
Repeat Last find, 22
Replace, 22,37
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Resistor, 24
Revert, 21
Rotate, 22
Run, 44
Save All, 48,70
Save As, 21
Save V&I Only, 48,70
Save, 21
Schematics, editing, 37
Scope Menu, 46,67
Select All, 22,37
Select, 23
Send to Back, 22,37
Shape Editor, 23
Show All paths, 24
Signal Processing Functions, 41
Sine Source, 32
Split Text/Drawing Areas, 23
State Variables Editor, 67
Step Box, 22
Stepping Dialog Box, 13
Stepping, 8,13,44,66
Switches, 36
Temperature, 7,40,63,73
Text, 23
Tie, 36
Tile Horizontal, 23
Tile Vertical, 23
Time Range, 6,39
Title, 24
Tokens, 16
Tolerances, 53
Translate, 21
Transformer, 28
Transient Analysis Limits, 39
Transient Analysis Menu, 43
Transient Analysis, 6,38
Undo, 22,37
User Source, 31
V and I Source, 32
Valley, 46
Vertical Pull-Down Menu, 48
View Menu, 23
Toggle Text/Drawing, 36
View, 10
Waveform Options Fields, 40
Waveform Source, 31
Windows Menu, 22
Wire Mode, 21
Wire, 23
WireD, 23
Worst Case Distribution, 55
X Expression, 7,41,64,75
X Range, 15,42,75
Y Expression, 7,41,64,75
Y Range, 15,42,64,75
Z Transform Source, 35
Zoom Out, 23
Zoom In, 23
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