ECE 210
Cadence Circuit Simulation Tool Fundamentals
Cadence is a company that makes electronics design software. The particular program you will
be using in this class is a circuit editor and simulation tool known by several names around the
department, including Capture, PSpice, Schematics, and Cadence. You will be using this
program in other electrical engineering classes and you may even use it after you graduate.
Accessing Cadence

To access Cadence tools from the start menu, select Programs > (Engg Apps for
computers in Fiedler Library) > Cadence SPB 16.01 > Design Entry CIS

A ‘Cadence Product Choices’ dialog box will pop up. Select Allegro PCB Design CIS XL
and set it as the default if you wish.
Figure 1

Selecting ‘OK’ opens the main Cadence window.
Figure 2
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)

Open a new project by clicking File > New > Project. Choose Analog or Mixed A/D for
project type (“Schematic” won’t do simulations). Give the project a name and place the
project in a location that’s easy to find.
Figure 3

A ‘Create PSpice Project’ dialog will pop up. This part is self explanatory. Create a blank
project unless you want to use elements from an old project in a new project. For this
first tutorial, select “Create a blank project”.
Figure 4
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)
Figure 5

Creating a blank project opens the schematic editor. Before building your circuit, you can
add the parts libraries by selecting Place > Part and then Add Library. This can make
searching for components easier. Select all of the files in the PSpice folder and click
‘Open’. Alternatively, you can skip this and just use Place > Part, but this will require you
to look through the many separate libraries when trying to locate a part in the Place >
Part window.
Figure 6
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)
Placing Parts
After adding the libraries, you should have a long list of parts available to construct your circuit.
Place parts by typing the part name into the text box highlighted in Figure 5. The most basic
parts are shown in Figure 7 with their corresponding part names. For example, place a DC
voltage source by typing ‘vdc’ into the text box, hit enter, and place the part wherever you want it.
Figure 7
The parts in Figure 7 are shown in their default state. Change a component value by doubleclicking on the value. Part labels for nearly all parts can be changed by double-clicking on the
label (i.e. V1 can be changed to Vs).
Sources
Sources require certain values to be set before they will simulate. Here’s a rundown of how to set
up your sources.
DC Voltage (VDC) and Current (IDC) Sources: The DC voltage and current sources are the most
straightforward. However, remember that they have default values of zero. This becomes a
problem when the user tries to power an amplifier with 0 V. Make sure to change your sources to
the correct values or your simulations results will be incorrect. Changing the label of a source to
5 V doesn’t change the value of the source to 5 V (yes, this has happened).
AC Voltage Source (VSIN): Notice that there are two AC voltage sources. VSIN is used for time
domain (transient) simulations. You must give this source an amplitude (VAMPL), a frequency
(FREQ), and an offset voltage (VOFF). Unless you want an offset voltage, set this value to 0.
AC Voltage Source (VAC): The second AC voltage source is VAC. This source is used for
frequency domain (AC sweep) simulations. This source comes ready to simulate.
Pulse Voltage Source (VPULSE): This is another time-domain source that should only be used
for time domain analysis. This source can be used in three different ways: 1) supply a single
pulse to a circuit, 2) supply a delayed DC voltage, and 3) supply a square wave.
VPULSE has several parameters that you must set before simulating. VPULSE can take on two
voltage levels: V1 and V2. Delay the time that the supply is activated by setting a delay time
(TD). Set the rise time (TR) and fall time (TF). As their names imply, these are the times it takes
to jump from one voltage level to the other. Set the time the pulse is at V2 with pulse width (PW)
and, finally, set the period of the waveform (PER). Making the pulse width half of the period will
create a square wave with a 50% duty cycle. To create a 1 kHz square wave that varies between
0 and 5 V, set V1 = 0, V2 = 5, TD = 0, TR = 0, TF = 0, PW = 0.5m, PER = 1m.
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)
Ground
All circuits need a ground in order to simulate. For
whatever reason, there are several different grounds
available. The only one you should use is the ground
labeled with a zero. Its part name is ‘0’ and it is found in the
toolbar on the right-side of the Allegro Design Entry CIS
window.
You don’t have to run wires all over the screen to connect
to a single ground. You can place any number of grounds
in your schematic and they will all be connected to each
other (provided you’re using the ground from the right-hand
toolbar for each instance).
Connectors
Connectors offer a convenient way to connect two nodes
without using a wire as shown in Figure 8. This helps when
you want to avoid crossing wires and makes circuits look
much nicer. Connect connectors together by giving them
the same name.
Connectors come in a variety of shapes. Ultimately, the
Figure 8
shape doesn’t matter, if two connectors have the same
name, they are connected. Although any connector will work, it’s best if you follow some
convention. For this class, use VCC_BAR for power connections and VCC for signal connections
(inputs, outputs, etc.).
Other Construction Notes
Here are a few other tips that help during the circuit construction process.
 All prefixes (m, k, n, etc.) are the same except micro and mega. Type ‘u’ for micro and
‘mega’ for mega. Cadence is case insensitive and interprets ‘M’ as milli.

Rotate a part by selecting it and pressing ‘r’.

Mirror a part horizontally by selecting it and pressing ‘h’.

Mirror a part vertically by selecting it and pressing ‘v’.

Connect parts using wires. Access wire mode either by pressing ‘w’ or by clicking on the
wire button in the side menu.

You should be able to make connections by dragging one component to another. If this
isn’t working, go to Options > Preferences > Miscellaneous. Check the box labeled
‘Allow component move with connectivity changes’.

In the same menu, you can uncheck the ‘Clear UNDO/REDO Data on Save’ if you want
Cadence to remember your past moves (and avoid the annoying warning).

To remove the dotted grid, go to Options > Preferences > Grid Display and uncheck
‘Displayed’ under the ‘Schematic Page Grid’ section. Do this before placing schematics
into a text document.
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)

The ‘V’ and ‘I’ buttons to the right of the marker buttons display DC voltages and currents
at various points throughout the circuit.
Simulation

To simulate, create a new simulation profile by clicking on the first of the simulation
buttons shown in Figure 5. A ‘New Simulation’ window will pop up.
Figure 9

Give the simulation a name and click create to access the ‘Simulation Settings’ menu.
Once here, choose the analysis type from the drop-down menu. Choose from Time
Domain (Transient), DC sweep, AC sweep/Noise, and Bias Point simulations.
Time Domain (Transient) Simulations: Use this simulation type to see how the circuit behaves
over time (voltage vs. time, etc.). Of the five sources above, use VSIN and VPULSE when
performing time domain analysis (DC voltage and current doesn’t change much over time).
Figure 10: Time Domain Simulation Settings
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)
‘Run to time’ specifies the range of time Cadence simulates your circuit. The frequency of VSIN
is the best indicator of how long to simulate the circuit. If the frequency of VSIN is 1 kHz, set
TSTOP between 2 and 4 ms.
If you want to look only at the steady state data and don’t care about the circuit’s transient
response, use the ‘Start saving data after’ feature. This is useful when working with a circuit with
a large time constant. Otherwise, the default of 0 is sufficient.
It’s optional to specify a maximum step size. However, failing to specify one may result in
waveforms that appear boxy because Cadence is plotting too few points. In general, make this
number 100 to 1000 times less than your range, depending on the resolution you want. The
smaller the number, the more precise your waveforms will be, but at a cost of longer simulation
times.
AC Sweep Simulations: Use this simulation type to perform frequency domain (transfer function)
analysis (gain and phase vs. frequency). The VAC source must be used to perform this
simulation.
Figure 11: AC Sweep Simulation Settings
Only concern yourself with what is inside the ‘AC Sweep Type’ box. Unless otherwise specified,
use a logarithmic scale using decades. Specify a starting frequency, an ending frequency, and
the number of points per decade. One hundred points per decade should be enough. A starting
frequency of zero will not work for a logarithmic scale.

Click OK when you’re satisfied with the simulation settings. You can edit your simulation
settings by clicking on the second of the simulation buttons shown in Figure 5.
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)

At this point, you’re almost ready to simulate. Before you do, add markers, which tell
Cadence which simulation results to display. A few marker buttons are shown in
Figure 5.

For time domain simulations, place a Voltage/Level Marker (V marker) at the output and,
if you wish, at the input. Unlike the Voltage Differential Marker(s), the Voltage/Level
Marker measures voltage with respect to ground. The simulation will then plot the output
and input voltages with respect to time.

For AC sweep simulations, use dB Magnitude of Voltage (VDB) and Phase of Voltage
(VP) markers from the advanced markers menu and place them on the circuit’s output.
The simulation will then plot the gain in decibels and the phase in degrees with respect to
frequency. Access advanced markers by selecting PSpice > Markers > Advanced.

After placing markers, simulate your circuit by pressing the ‘Run PSpice’ button located
third in the line of simulation buttons. The simulation window will open, showing the
simulation results.
Figure 12: Simulation Window (black backdrop removed through the magic of Paint)
There are a wide variety of modifications you can perform once you’re in the simulation window.
Double click on either axis to access the ‘Axis Settings’ window. Right click on the traces to
modify their properties. Figure 12 shows the traces with different colors and thicknesses than
they first appear in the simulation window.
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)
Use the ‘Toggle cursor’ button to take more accurate measurements on the graph. Left click
controls one cursor while right click controls another. Use this feature to find the difference
between two points on the graph.
Edit traces by double clicking on the trace names in the lower left corner of the simulation
window. You can also add traces from the Trace menu. The first brings up a ‘Modify Trace’
window and the second brings up an ‘Add Traces’ window. Both look the same.
Figure 13: Add Traces Window
From here, you can create (or modify) a trace to your liking. This menu is useful for quickly
changing the traces to the measurements you need without going back to the schematic, placing
a marker, and re-simulating. For example, a voltage trace can be changed to a decibel voltage
trace by simply replacing V with VDB. You can then change the decibel voltage trace to a phase
trace by changing VDB to VP. You can even add traces together, a feature that becomes useful
when plotting the overall response of a crossover network.
Created by Ryan Eatinger for Kansas State University; Special thanks to Dr. Ruth Miller and Tim Sobering; Updated on
3/30/09 (Version 2.1 – minor edits by WBK)