Using Multisim

An Introductory Tutorial
Gary D. Snyder
Prentice Hall
Boston Columbus Indianapolis New York San Francisco Upper Saddle River
Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montreal Toronto
Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo
Copyright ©2012 Pearson Education, Inc., publishing as Prentice Hall. All rights reserved. Manufactured in
the United States of America. This publication is protected by Copyright, and permission should be
obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or
transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To
obtain permission(s) to use material from this work, please submit a written request to Pearson Education,
Inc., Permissions Department, 1 Lake Street, Upper Saddle River, New Jersey, 07458.
Many of the designations by manufacturers and seller to distinguish their products are claimed as
trademarks. Where those designations appear in this book, and the publisher was aware of a trademark
claim, the designations have been printed in initial caps or all caps.
10 9 8 7 6 5 4 3 2 1
Prentice Hall
is an imprint of
www.pearsonhighered.com
Contents
Contents
Preface......................................................................................................................iv
1.
Introduction to the Multisim Software ..........................................................1
2.
Creating Circuits with Multisim.....................................................................9
3.
Modifying Circuits with Multisim................................................................17
4.
Circuit Simulation..........................................................................................29
5.
Basic Circuit Measurements .........................................................................35
6.
Power and Signal Sources .............................................................................45
7.
The Oscilloscope .............................................................................................55
8.
The Logic Analyzer........................................................................................63
9.
The Bode Plotter.............................................................................................73
iii
Using Multisim®: An Introductory Tutorial
Preface
About This Tutorial
The intent of this tutorial is to help you develop a basic working knowledge of the National Instruments©
Multisim software for entering and analyzing circuit designs. For best results, you should use this tutorial to
supplement, rather than replace, a textbook that discusses the subject material in depth. The documentation
that accompanies the Multisim software is also an excellent reference for topics beyond the scope of this
tutorial.
Using This Tutorial
Screen Images
The images in this tutorial may differ somewhat from what you will see depending upon your version of
Windows and Multisim. Generally, however, the images will be very similar.
Using Windows
This workbook assumes that you are familiar with using Microsoft® Windows® (starting applications,
opening files, etc.) and with standard Windows operations and terminology (double-clicking icons,
minimizing windows, etc.). If you have any questions about Windows software, refer to the on-line help or
standard Windows documentation.
Multisim Software
This workbook also requires you to have a copy of the Multisim software. Although the chapters may
reference and discuss material specific to a particular version of Multisim the information is generally
applicable to all versions released after Multisim 10.
Note that you can use Multisim to open and work with circuits created with earlier versions of Multisim or
Electronics Workbench, but that the opposite is not true. In addition, Multisim cannot save files in an
earlier Multisim format, even if the circuit was originally created in an earlier version of Multisim.
iv
Section 1 - Introduction to the Multisim Software
1.
1.1
Introduction to the Multisim Software
Introduction
The world of electronics is continually changing. To remain competitive, electronics companies must
rapidly design, prototype, test, manufacture, and market their products. In the past two-sided boards and
leaded components were the standard and companies could use perfboard, protoboards, and wire-wrap
boards to evaluate new parts and to build and test circuit prototypes. In modern electronics multilayer
boards and surface-mount components are the standard, so creating physical prototypes from scratch is both
problematic and expensive. To help solve this problem, component manufacturers often provide evaluation
kits so that customers can determine whether a new part will meet their needs and better understand the
practical requirements for using the part in circuits. Another valuable resource is specialized software to
quickly design, evaluate, and modify circuit designs.
The Multisim software is a program that acts as a virtual electronics laboratory. You can use the Multisim
program not only to create electronic circuits on your computer, but also to simulate (“run”) the circuits and
use virtual laboratory instruments to make electronic measurements.
In this chapter, you will:
1.2

Learn how to start and close the Multisim application.

Familiarize yourself with the Multisim workspace.

Identify the various Multisim toolbars and their components.
Starting the Multisim Program
You can use standard Windows methods to start the Multisim program. You will learn one more way in the
next section.
1.2.1
Starting the Multisim Program from the Windows Desktop
If you added a Multisim shortcut to your desktop during installation, then you can use the desktop shortcut
to start the Multisim program. To do so:
1.
Navigate to the desktop.
2.
Double-click the Multisim icon. The icon for your version of Multisim may differ from that of
Figure 1-1.
Figure 1-1: Multisim Icon
1.2.2
Starting the Multisim Program from the Start Menu
Note that the following instructions assume that you accepted the default locations for your version of the
Multisim software.
1.
Click the Start button in the lower left corner of the Windows screen.
2.
Click Programs.
3.
Click the “National Instruments” folder.
4.
Click the “Circuit Design Suite X” folder (where “X” is your version of Multisim).
1
Using Multisim®: An Introductory Tutorial
5.
1.2.3
Click “Multisim”.
Starting the Multisim Program Using the Run… Command
Note that the following instructions assume that you accepted the default locations for your version of the
Multisim software.
1.
Click the Start button in the lower left corner of the Windows screen.
2.
Click Run….
3.
Click the Browse… button.
4.
Select the C: drive in the Look in: drop-down list.
5.
Double-click the “Program Files” folder.
6.
Double-click the “National Instruments” folder.
7.
Double-click the “Circuit Design Suite X” folder (where “X” is your version of Multisim).
8.
Double-click the “Multisim.exe” file.
Alternatively, you can enter “C:\Program Files\National Instruments\Circuit Design Suite
10.0\Multisim.exe” in the Open… text box and click “OK”.
You may wonder why you would ever use the Run… command to start Multisim or any other Windows
application. The answer is that once you have used this method the Windows operating system will
remember the path to the Multisim program. You can then select Multisim directly from the drop-down list
in the Run… window, unless your computer’s security settings delete your session history.
1.3
The Multisim Interface
Once the Multisim program starts you will see the screen (or one much like it) shown in Figure 1-2. The
exact screen will depend upon your versions of Windows and Multisim and how you have configured the
Multisim interface.
The smaller window on the left of Figure 1-2 is the navigation pane. When the hierarchy tab is selected (as
shown), you can use the icons at the top of the pane to open, save, close, and move back and forth between
circuit files. If you are unsure what any icon does, let the point hover (remain stationary) over an icon and a
tool tip will appear that will indicate its function.
The larger window on the left is the workspace. This is the space in which you will create and simulate
circuit designs.
2
Section 1 - Introduction to the Multisim Software
Figure 1-2: Multisim Interface
In addition to the standard Windows title bar, menu bar, toolbar, and screen controls, the Multisim interface
contains a number of special toolbars that allow you to create and simulate circuits. The number and type of
toolbars that you will see in the Multisim interface depends upon which toolbars you enable in the View 
Toolbars… menu. The following sections provide a brief description of some of the toolbars that you will
use in this workbook.
1.3.1
Positioning the Toolbars
The Multisim toolbars are dockable, which means that you can position (or “dock”) them on any side of the
workspace. You can also place them in the workspace area. You must first unlock the toolbars to move
them.
To unlock the toolbars:
1.
Click on Options in the standard toolbar. Alternatively, you can right-click on an empty region of
toolbars area to open the Toolbars menu.
2.
Click on the Lock toolbars item in the menu so that it is NOT checked.
One the toolbars are unlocked, you can move them to where you wish to place them.
To move a toolbar:
1.
Move the pointer over the double-line on the left side of a toolbar or into the title bar area of the
toolbar.
2.
Click and hold the right mouse button to grab the toolbar.
3
Using Multisim®: An Introductory Tutorial
3.
While holding own the right mouse button, move the mouse to drag the toolbar to where you wish
to place it. An outline of the toolbar will indicate its approximate position as you move the pointer.
4.
Release the right mouse button to drop the toolbar.
One you have positioned the toolbars to where you wish them to be, you can lock them in place.
To lock the toolbars:
1.3.2
1.
Click on Options in the standard toolbar. Alternatively, you can right-click on an empty region of
toolbars area to open the Toolbars menu.
2.
Click on the Lock toolbars item in the menu so that it is checked.
The Title Bar
The Title bar is the region at the very top of the screen and is common to all Windows applications. The
left side of the bar contains information about the application and file, while the right side of the bar
contains controls to minimize, maximize, and close the application.
1.3.3
The Menu Bar
The Menu bar, shown in Figure 1-3, contains standard Windows menus (such as File, Edit, View, and
Help) and menus that are specific to Multisim (such as Place, MCU, Simulate, and Reports). These
menus let you configure and operate the application.
Figure 1-3: The Multisim Menu Bar
1.3.4
The Standard Toolbar
The Standard toolbar, shown in Figure 1-4, contains tools for performing common operations from the
File and Edit menus, such as creating a new file, printing a file, and pasting information from the Clipboard
into the open file.
Figure 1-4: The Standard Toolbar
1.3.5
The View Toolbar
The View toolbar, shown in Figure 1-5, contains tools for performing common Windows operations from
the View menu, such as zooming in on or zooming out from the current view.
Figure 1-5: The View Toolbar
1.3.6
The Main Toolbar
The Main toolbar, shown in Figure 1-6, contains tools to access various Multisim features and information
about the current circuit.
4
Section 1 - Introduction to the Multisim Software
Figure 1-6: The Main Toolbar
1.3.7
The Simulation Run Toolbar
The Simulation Run toolbar, shown in Figure 1-7, contains tools that let you start, stop, pause, and resume
a simulation.
Figure 1-7: The Simulation Run Toolbar
1.3.8
The Component Toolbar
The Component toolbar, shown in Figure 1-8, contains tools that let you access various components with
which to create and analyze circuits.
Figure 1-8: The Component Toolbar
1.3.9
The Instruments Toolbar
The Instruments toolbar, shown in Figure 1-9, provides instruments with which you can measure and
evaluate the operation of circuits. Some instruments, like the multimeter, oscilloscope, and logic analyzer,
are real devices that technicians and engineers use to analyze real-world circuits. Other instruments, like the
Bode plotter and logic converter, exist only within the Multisim application and are convenient tools for
you to simulate, analyze, and debug your circuit designs.
Figure 1-9: The Instruments Toolbar
You may have noticed that the two tools on the far right of the instrument toolbar have small arrows
pointing down next to them. These are “flyouts” that open menus that provide further selections for the
tools.
1.3.10
Tool Tips
With so many toolbars and tools available the Multisim interface may seem rather confusing at first. To
help you, the Multisim software uses tool tips to help you identify each tool. A tool tip is a small text box
that tells you what the tool is. To activate a tool tip, simply let the pointer hover, or remain stationary, over
the tool you wish to identify. After a short time the tool tip for that tool will appear, as shown in Figure
1-10. The tool tip indicates that the highlighted instrument (the tool with the border around it) is the
function generator.
Figure 1-10: Function Generator Tool Tip
5
Using Multisim®: An Introductory Tutorial
Table 1-1 shows some examples of Multisim tools, the toolbar in which each appears, and the identity of
the tool.
Table 1-1: Multisim Tool Identification
Tool Graphic
6
Associated Toolbar
Tool Identity
Component
Place Transistor
Main
Postprocessor
Instruments
Bode Plotter
Standard
Design
View
Zoom area
Component
Place Indicator
Standard
Save
Instruments
Function generator
Components
Place Source
Main
Multisim help
Simulation switch
Pause the running active
simulation
Component
Place Basic
Standard
Open...
Instruments
Oscilloscope
Section 1 - Introduction to the Multisim Software
Tool Graphic
1.4
Associated Toolbar
Tool Identity
Standard
Undo
Instruments
Multimeter
Closing the Multisim Program
There are two standard ways to close the Multisim program. If you made any changes to the circuit file
(even if the net effect of those changes did not change the circuit file, such as adding a component and then
deleting it) the program will display a dialog box similar to that in Figure 1-11.
Figure 1-11: File Save Reminder Dialog Box
If you receive this notification, click the No button. You will learn about saving files in the next chapter
1.4.1
1.4.2
Closing the Multisim Application from the File Menu
1.
Click File in the Multisim menu bar.
2.
Click Close.
Closing the Multisim Program with the Application Close Button
To use the Application Close button to close the Multisim application, click the Close () button at the
far right of the blue title bar. If you click the Close button in the Multisim menu bar, then you will close the
circuit file but not the program.
1.5
Chapter Summary
The Multisim interface provides a variety of toolbars and tools for creating, modifying, and simulating
circuit designs. Knowing which tools the Multisim software provides and where you can find them will
greatly simplify working with circuit designs. In the following section you will learn how to use some of
these tools to create, modify, and save your circuit designs.
7
Section 2 - Creating Circuits with Multisim
2.
2.1
Creating Circuits with Multisim
Introduction
A schematic is a graphical representation of a circuit design. Each symbol represents a specific type of
component, and typically displays such electrical information as the component value, tolerance, and power
rating. A component symbol can also show user-oriented information such as a reference designator and
manufacturer part number, and manufacturing information that indicates the physical package or footprint.
One of the Multisim program’s primary functions is to allow you to create schematics on your computer.
This process is called schematic capture and closely resembles the process of building an actual circuit.
Schematic capture consists of

selecting the necessary components,

arranging the components in the workspace, and

connecting the components together to create the desired circuit.
Designs can range from simple circuits that consist of a few parts (such as a flashlight or transistor switch)
to complicated circuits (like a multi-stage amplifier or digital state machine). Regardless of the size or
complexity of the circuit, however, the basic schematic capture process is the same.
In this chapter you will:
2.2

Construct a new circuit.

Learn how to save a circuit file.

Learn how to open an existing circuit file.

Learn how to modify an existing circuit.
Constructing a New Multisim Circuit
In this section you will build a flashlight, or at least a schematic representation of one.
2.2.1
Placing Components
1.
Use one of the methods from Section 1.2 to start the Multisim program.
2.
Click the Place Source tool in the Component toolbar to open the component browser in Figure
2-1.
Figure 2-1: Sources Component Browser
9
Using Multisim®: An Introductory Tutorial
3.
Select POWER_SOURCES in the Family window and DC_POWER from the Component list.
Note that the symbol in the window changes to that of a battery (i.e., a dc source).
4.
Click the OK button. You will return to the circuit window in the Multisim interface. Note that as
you move the pointer, the component symbol moves with it. Move the battery symbol to a position
near the left center of the circuit window (refer to Figure 2-2) and click to place it.
Figure 2-2: Circuit Window with Battery Placed
At this point, depending on your global preferences, the program may automatically return you to
the component browser. If it does not, click the Place Source tool again.
To configure how Multisim should behave after placing a component:
10
1.
Click Options in the Menu bar.
2.
Select Global preferences in the Options menu to open the “Global Preferences”
window.
3.
Select the Components tab to open the component global preferences window in Figure
2-3.
Section 2 - Creating Circuits with Multisim
Figure 2-3: Component Placement Global Preferences
4.
5.
In the “Place component mode” section, select the options you wish.

If the “Return to Component Browser after placement” box is check, Multisim
will return you to the component browser after you have place the current
component in the workspace. If the box is not checked, you must manually open
the component browser to place another component. This check box can be
checked or unchecked independent of the radio button selections below.

If the “Place single component” radio button is selected you can place only one
component at a time and must return to the component browser if you wish to
place another, even if you wish to place the same component. If the “Continuous
placement for multi-section component only (ESC to quit)” radio button is
selected you can place multiple copies of a component if it is one of several in a
single part (such as a NAND gate in a 7400 package) until you press the ESC
key. If the “Continuous placement (ESC to quit)” radio button is selected you
can place multiple copies of any component until you press the ESC key. Only
one radio button can be selected at a time.
When you are finished, clock the OK button to close the window or the Cancel button to
discard any changes you have made.
5.
In the component browser, select GROUND from the Component list.
6.
Click the OK button and place the ground symbol beneath the battery symbol, as shown in Figure
2-4.
11
Using Multisim®: An Introductory Tutorial
Figure 2-4: Circuit with Ground Placed
7.
Place a second ground symbol to the right of the other symbols on the board, as shown in Figure
2-5. This completes the power source symbols you will need to construct the circuit.
Figure 2-5: Circuit with Second Ground Placed
8.
Click the Place Basic tool in the Component toolbar. The component browser appears with the
basic components, as shown in Figure 2-6.
Figure 2-6: Basic Component Browser
9.
12
Select SWITCH in the Family window and SPST from the Component list. If you do not see
SPST in the component list, use the vertical scroll bar on the right side of the component list to
scroll down until you see it.
Section 2 - Creating Circuits with Multisim
10. Click the OK button and place the switch symbol above and to the right of the battery, as shown
in Figure 2-7.
Figure 2-7: Circuit with SPST Switch Placed
11. Click the Place Indicator tool. The component browser appears with the indicators, as shown in
Figure 2-8.
Figure 2-8: Indicators Component Browser
12. Select LAMP in the Family window and 12V_10W from the Component list.
13. Click the OK button and place the lamp to the right of the SPST switch, as shown in Figure 2-9.
This completes the component placement segment of your schematic capture project.
Figure 2-9: Circuit Window with Lamp Placed
13
Using Multisim®: An Introductory Tutorial
2.2.2
Connecting Components
The Multisim program has no Wire tool to connect components. You create a wire by clicking on the start
and end points for the wire.
Note that the program will not let you create a wire that does not begin on a component terminal or end on
a wire segment or component terminal. If you wish to begin a wire segment on a wire segment or leave one
end of a wire segment unconnected you must connect the wire to a special terminal called a junction. To
place a junction, select Junction from the Place menu or double-click in an empty part of the workspace.
When you end a wire on a wire segment the Multisim program automatically creates a junction for you.
1.
Move the tip of the pointer near the cathode (negative terminal) at the bottom of the battery. The
pointer will change from an arrow to a small crosshair, indicating that it is ready to make a
connection to the battery terminal.
2.
Click the left mouse button and drag the crosshair towards the left ground symbol. As you do so,
you will see a wire being drawn. If you do not, position the pointer near the battery and left-click
again when the crosshair is visible.
3.
When you reach the terminal at the top of the ground symbol, left-click the mouse. This will
connect the wire from the battery to the ground symbol, as shown in Figure 2-10. Depending on
your program settings, you may or may not see the net name (in this case “0”) for the wire. To
show or hide the net name select Sheet Properties... from the Options menu in the menu bar. In
the Net Names field of the Circuit tab, choose “Show All” to show the names of all nets and
“Hide All” to hide the names of all nets. “Use Net-specific Setting” will show only the nets that
you individually configure to show the net name. This example used the “Show All” setting.
Figure 2-10: Circuit with Battery Connected to Ground
4.
Finish connecting the remaining components, as shown in Figure 2-11.
Figure 2-11: Circuit with Completed Connections
Congratulations! You’ve just completed your first Multisim circuit!
14
Section 2 - Creating Circuits with Multisim
2.3
Saving a Multisim Circuit File
A good idea is always to save your work, especially after working for more than a few minutes. There are
two methods for saving a Multisim circuit file. Use one of the standard methods below to save your circuit
to your computer. You will be using this circuit in the next chapter.
2.3.1
Using the Save File Tool to Save a Circuit File
1.
Click the Save File tool on the standard toolbar.
2.
If you have saved the file before, the Multisim program will use the same name and location as
before to save the file. If you are saving the circuit for the first time the Save As window will
appear, as shown in Figure 2-12.
Figure 2-12: Multisim Save As Window
2.3.2
3.
Use the Save in: drop-down list to navigate to the folder in which you wish to save the file, and
enter the file name you wish to use in the File name: box.
4.
Once you have finalized the file name and location for your circuit file, click the Save button.
Using the File Menu to Save a Circuit File
1.
Click File on the standard menu bar.
2.
If you have previously save the file and wish to save the file under the same name, click Save on
the File menu. Otherwise, click Save As… on the File menu. The Save As window will appear, as
shown in Figure 2-12.
3.
Use the Save in: drop-down list to navigate to the folder in which you wish to save the file, and
enter the name of the file you wish to use in the File name: box.
4.
Once you have finalized the file name and location for your circuit file, click the Save button.
15
Section 3 - Modifying Circuits with Multisim
3.
3.1
Modifying Circuits with Multisim
Introduction
Electronic designs often require changes. Sometimes changes are necessary because the design does not
function as intended or testing shows potential problems. Other times the design is fine, but manufacturing,
marketing, or purchasing issues require design changes. A major advantage of drafting circuits with
software rather than by hand is that modifying circuits is much faster and easier. Specific modifications will
vary with each circuit and the reason for changes, but all circuit modifications in Multisim consist of one or
more of the following tasks:
1.
Adding, deleting, replacing, re-orienting, or moving components.
2.
Adding, deleting, or moving connections.
In this chapter you will:
3.2

Learn how to open an existing circuit file.

Learn how to modify an existing circuit.
Opening an Existing Multisim Circuit
You can use one of the standard methods below to open a Multisim circuit that you or someone else created
and saved. Multisim can open files created by earlier versions of Multisim or Electronics Workbench. For
example, Multisim version 10 can open circuit files created by Electronics Workbench 5 and Multisim
versions 6 though 10.
3.2.1
Using the Open File Tool to Open a Circuit File
1.
Click the Open File tool on the standard toolbar. The Open File window will appear, as shown in
Figure 3-1.
Figure 3-1: Multisim Open File Window
2.
To specify the file you wish to open, you can

use the Look in: and Files of type: drop-down lists to locate the file,
17
Using Multisim®: An Introductory Tutorial
3.
3.2.2
use the File name: drop-down list to select the file from files you have previously
opened, or

enter the path and name of the file in the File name: box.
Once you have selected a file, click the Open button.
Using the File Menu to Open a Circuit File
1.
Click File on the standard menu bar.
2.
Click Open… on the File menu. The Open File window will appear, as shown in Figure 3-1.
3.
To specify the file you wish to open, you can
4.
3.2.3


use the Look in: and Files of type: drop-down lists to locate the file,

use the File name: drop-down list to select the file from files you have previously
opened, or

enter the path and name of the file in the File name: box.
Once you have selected a file, click the Open button.
Using Windows Explorer to Open a Circuit File
If the Multisim program is not running, you can use Windows Explorer to both start the Multisim program
and open the circuit file.
3.3
1.
Open Windows Explorer.
2.
Navigate the folder that contains the circuit file you wish to open.
3.
Double-click the circuit file. Windows will start the Multisim program, and the Multisim program
will load the circuit file.
Modifying an Existing Circuit
Design is an ongoing process. At some point you will probably wish to change a circuit, whether to correct
an error, move to the next phase of an incremental design process, improve a design, or just to tinker and
see what the change will do. Changes to paper designs in the past were laborious and time-consuming. The
Multisim program offers a number of features and tools with which you can quickly and easily change
existing circuit designs. In this section you will learn some common ways to modify an existing circuit in
the Multisim environment. In this section you will modify the flashlight circuit you created in Chapter 2.
3.3.1
Open the Circuit to Modify
Open the flashlight circuit you just created and saved. You should see the circuit shown in Figure 3-2.
Figure 3-2: Practice Multisim Circuit
18
Section 3 - Modifying Circuits with Multisim
Next, compare the circuit you created with the circuit shown in Figure 3-3.
Figure 3-3: Reference Circuit
A comparison will reveal the following differences between the circuit file you created and the reference
circuit:
1.
Addition of two 10 Ω resistors R1 and R2.
2.
Addition of lamp X2.
3.
Addition of a second ground.
4.
Replacement of the SPST switch J1 with a SPDT switch.
You will modify the circuit in Figure 3-2 to match that of the reference circuit in Figure 3-3
If at any time you make a mistake while modifying the circuit, you can always use Undo in the Edit menu
or use the Undo tool in the Standard toolbar to correct it.
3.3.2
Adding Components Using the Component Browser
Adding components is very similar to placing components. For this exercise you will add resistor R1 from
the Virtual toolbar. Unlike the other Multisim tools, the virtual tools are in blue-shaded boxes. If you
cannot see the virtual tools in your Multisim interface, activate the Virtual toolbar as follows:
1.
Click View on the standard menu bar.
2.
Position your cursor over the Toolbars flyout.
3.
When the toolbar menu opens, select Virtual. If Virtual is already checked, the Virtual toolbar
should already be active and visible somewhere in the Multisim interface.
You should now see the Virtual toolbar, similar to that shown in Figure 3-4, in your Multisim interface.
Figure 3-4: Virtual Toolbar
As with the other toolbars, you can hover your cursor over the tools to activate the tooltips and identify
each of the tools. You will obtain R1 from the Show Basic Family flyout (the tool with the box containing
the resistor symbol).
19
Using Multisim®: An Introductory Tutorial
1.
Click the Show Basic Family button. A Basic window with the symbols for the basic family will
appear. Alternatively, you can click on the flyout symbol () to the right of the button to open a
list of virtual components.
2.
Click the Place Virtual Resistor tool in the Basic window.
3.
Position the resistor in the workspace under lamp X1. The circuit should now look like that in
Figure 3-5.
Figure 3-5: Circuit with Resistor R1 Placed
Do not worry that the value of the resistor is 1 kΩ. You will change it to the correct value later.
3.3.3
Adding Components by Copying
The second modification you make will be to add a second lamp identical to X1 to the circuit. One
difference between adding components to an existing design is that an existing design sometimes allows
you to copy an existing component. Because the second lamp is identical to the first lamp copying is an
option for adding the second lamp. To copy a component:
1.
Left-click on the component you wish to copy to select it (in this case lamp X1). A dashed box
will appear around the selected component, as shown in Figure 3-6.
Figure 3-6: Selecting Lamp X1
20
2.
Click on the Copy tool in the Standard toolbar. Alternatively, you can press CTRL + C (that is,
press the CTRL and C keys simultaneously). The Paste tool in the Standard toolbar will now
become active.
3.
Click on the Paste tool in the Standard toolbar. Alternatively, you can press CTRL + V (that is,
press the CTRL and V keys simultaneously). An outline of the new lamp will appear at the in the
workspace.
4.
Use the mouse to move the new lamp above lamp X1.
Section 3 - Modifying Circuits with Multisim
5.
Left-click the mouse to place the new lamp in the workplace, as shown in Figure 3-7. Note that
Multisim has automatically numbered the new lamp as X2.
Figure 3-7: Lamp X2 Added to Circuit
3.3.4
Changing Component Values
R1 has a default value of 1 kΩ, but the resistor in our new circuit must be 10 Ω. To edit R1:
1.
Double-click R1 to open the Resistor properties window. Alternatively, right-click R1 to select it
and open the right-click menu, and select Properties....
2.
Change the value in the Resistance (R) box from “1k” to “10”.
3.
Click the OK button. The circuit should now look like that in Figure 3-8.
Figure 3-8: Value of Resistor R1 changed to 10 Ω
3.3.5
Re-Orienting Components
Next, you will re-orient R1 so that it is vertical rather than horizontal.
1.
Right-click R1. A dashed box will appear around R1 to show that it is selected, and the right-click
menu shown in Figure 3-9 will appear.
21
Using Multisim®: An Introductory Tutorial
Figure 3-9: Right-Click Menu
2.
Click 90 Clockwise in the right-click menu. The right-click menu will close and the R1 will be
oriented vertically, as shown in Figure 3-10. Alternatively, you could press CTRL + R to rotate a
selected component 90° clockwise.
Figure 3-10: Resistor R1 Rotated
3.
Left-click in an empty space in the workspace or press ESC to de-select R1.
After rotating R1, save your work before continuing.
3.3.6
More on Selecting Components
Next, you will move R1 so that it is between X1 and ground. Moving existing components is similar to
placing components. The only difference is that you must first select the existing components, just as you
selected X1 to copy it.
To select a single component, left-click on that component. If you wish to select more than one component
you can either enter SHIFT + left-click (left-click while holding down the SHIFT key) on each component
or click and drag to window around the components you wish to select. If you accidentally select a
component you SHIFT + left-click on it to deselect it, because SHIFT + left-click actually switches
22
Section 3 - Modifying Circuits with Multisim
between, or toggles, the selection of a component. It will select a component that is not selected or deselect
a component that is selected. If you wish to deselect all the selecting items in a circuit, you can use the ESC
key.
Because you will be selecting only R1, left-click on R1 to select it as shown in Figure 3-11.
Figure 3-11: Selecting R1 for Movement
3.3.7
Merging Components into Existing Nets
You will next move R1 between X1 and ground. One way is to delete the wire between X1 and ground,
move R1 between X1 and ground, and then add wires between R1 and X1 and between R1 and ground.
Another method is to move R1 and merge it into the existing net between X1 and ground.
1.
Click and hold down the left mouse button on R1. If you are moving only one component (as in
this case) the component need not be selected already because this will automatically select the
component. If you are moving more than one component at the same time you must have already
selected the components you wish to move and click and hold down the left mouse button on one
of the selected components to move them.
2.
Hold down the left mouse button and drag R1 so that its leads line up with the vertical wire
between X1 and ground.
3.
Release the left mouse button to merge R1 into the nets as Figure 3-12 shows. Note that Multisim
has renumbered the net between X1 and R1 because it is no longer the same as the ground net.
23
Using Multisim®: An Introductory Tutorial
Figure 3-12: R1 Merged into Circuit
3.3.8
Replacing Components
Next, you will replace the switch J1. One way replace a component is to delete the component and add the
new component from the component browser. However, you also can use the component browser to
replace a component with another component. Use the component browser to replace J1.
1.
Double-click on J1 to open the Switch properties window, shown in Figure 3-13.
Figure 3-13: The Switch Properties Window
24
2.
Click the Replace button to open the component browser. The component browser will
automatically open to SPST in the component list for the Basic group and Switch family.
3.
Select SPDT from the component list and click the OK button. This will replace the SPST switch
with the SPDT switch, as shown in Figure 3-14. Note that Multisim retained the old J1 reference
designator when you replaced the switch.
Section 3 - Modifying Circuits with Multisim
Figure 3-14: SPST Switch Replaced by SPDT Switch
3.3.9
Deleting Wires and Components
The circuit in Figure 3-14 connects the top, rather than bottom, contact of the SPDT switch to X1. To
correct this, you will first delete that wire and connect the bottom contact of J1 to X1.
1.
Left-click the wire you wish to delete to highlight it as shown in Figure 3-15.
Figure 3-15: Wire Selected for Deletion
2.
Press the DELETE key to delete the selected wire. Alternatively, you can click Edit on the
Standard toolbar and select Delete from the menu list. The circuit should now look like that in
Figure 3-16.
25
Using Multisim®: An Introductory Tutorial
Figure 3-16: Circuit with Net 2 Wire Deleted
Using the DELETE key or the menu Delete command will delete any wire, component, or instrument that
is currently selected.
3.3.10
Completing the Circuit
You can now complete the remainder of the circuit using Multisim operations already covered in this
chapter.
1.
Connect the top contact of J1 to X2.
2.
Connect the bottom contact of J1 to X1. The circuit should now look like that in Figure 3-17.
Figure 3-17: Circuit with J1 Connected to X1 and X2
26
3.
Window around R1 and the ground to which it connects to select them.
4.
Copy and paste the selected resistor and ground to the right of R1. The circuit should now look
like that in Figure 3-18. Note that when you use a window to select two components Multisim will
also copy any wires between them that are contained within the window.
Section 3 - Modifying Circuits with Multisim
Figure 3-18: Circuit with Copied Resistor and Ground
5.
Connect X2 to R2 . Your circuit should now look like that in Figure 3-19.
Figure 3-19: Completed Circuit Modifications
3.3.11
Editing Text
Finally you will add text to the bottom of the circuit. Text is not part of the working circuit, but is often
used to provide descriptive information or instructions for the circuit. To add the circuit description at the
bottom of the schematic:
1.
Left-click Place on the Standard toolbar and select the Text item from the menu list.
Alternatively, click the Place Text tool in the Graphic Annotation toolbar. A vertical insertion bar
will appear.
2.
Move the insertion bar below the circuit and left-click to anchor the insertion point. A blinking
vertical bar will appear, indicating that the text editing mode is active.
3.
Type “MODIFIED FLASHLIGHT CIRCUIT” to enter text at the insertion bar.
4.
Left-click away from the text to finish. The circuit should now look like that in Figure 3-20.
27
Using Multisim®: An Introductory Tutorial
Figure 3-20: Circuit with Added Text
Editing text in Multisim is similar to editing text in other Windows applications. To edit existing text:
1.
Double-click anywhere inside the text. The blinking vertical bar will appear at the start of the text.
2.
Left click within the text to place the cursor anywhere within the text. Alternatively, use the rightand left-arrow keys ( and ) to move the cursor to the point at which you wish to edit the
existing text, the HOME key to move to the beginning of the text, and the END key to move to the
end of the text.
3.
Click and drag the mouse to select a block of text. Alternatively, use the SHIFT and right- and
left-arrow keys to select text one character at a time.
4.
Use the BACKSPACE key to delete the character to the left of the cursor and the DELETE key
to delete the character to the right of the cursor.
This completes the circuit modification exercise. Save your circuit file. You will use it in the next chapter.
28
Section 4 - Circuit Simulation
4.
4.1
Circuit Simulation
Introduction
Schematic capture is only the first step in designing a practical circuit. Correcting problems with actual
circuits is much slower and more expensive than correcting problems in a schematic. Before using Ulticap
or another schematic package and layout tool to build a real circuit, designers will use special software to
simulate the operation of the design to identify and correct any problems in the design. One of the first
circuit simulation programs was SPICE (for Simulation Program with Integrated Circuit Emphasis). SPICE
originally was a text-based program that process text-based circuit description files, or netlists, that
identified the circuit components and node numbers (like the numbers shown next to each wire in Figure
3-20) that described how components were connected together. Modern versions add a graphical user
interface to simplify building circuits but typically allow users to output text netlist files like those
originally used with SPICE. Multisim contains a SPICE simulation engine that allows the user to simulate
how a circuit created in Multisim will operate.
In this chapter you will:
4.2

Learn about basic Multisim simulation controls and operation.

Simulate the modified flashlight circuit from Chapter 3.
The Simulation Controls
Figure 4-1 shows the Multisim simulation controls. These controls allow you to start, pause, and stop the
simulation.
Figure 4-1: Multisim Simulation Controls
4.2.1
The Simulation Switch
The simulation switch, shown in Figure 4-2, starts and stops in the simulation. When you first start
Multisim the switch is in the OFF position of Figure 4-2.
Figure 4-2: Simulation Switch
To simulate a circuit, click on the simulation switch. The switch will change to the ON position shown in
Figure 4-3 and Multisim will begin running the circuit simulation.
Figure 4-3: Simulation Switch in ON Position
Clicking on the simulation switch will toggle the position of the simulation switch. To stop a simulation
that is running, click the simulation switch to change its position from ON to OFF.
29
Using Multisim®: An Introductory Tutorial
4.2.2
The Pause Control
The pause control temporarily halts a running simulation. The main difference between pausing and
stopping a running simulation is that stopping a simulation will cause Multisim to reset any circuit values
(such as voltage and current) that the simulation generates. Pausing the simulation preserves those values
so that the simulation can resume from the point at which the simulation was paused.
Figure 4-4 shows the pause control. The pause control is active only when a simulation is running, so that
when you first start Multisim the control is grayed out and non-functional.
Figure 4-4: The Pause Control
When a simulation is running Multisim activates the pause control, as shown in Figure 4-5. Clicking on the
pause control will toggle the running state of a simulation so that the control will pause a running
simulation and resume a paused simulation.
Figure 4-5: The Active Pause Control
4.3
Running a Simulation
Simulating a circuit involves two types of information. One is the information you provide to control the
operation of the circuit. The other is the information Multisim provides you to indicate what the circuit is
doing. For this example you will simulate the flashlight circuit that you modified and saved in Chapter 3.
This example will demonstrate some of the fundamentals of simulating a Multisim circuit.
4.3.1
Simulating the Circuit
Open the modified circuit, shown in Figure 4-6, that you saved at the end of Chapter 3.
Figure 4-6: Modified Flashlight Circuit
Click on the simulation switch to run the simulation. The circuit should now appear as in Figure 4-7.
30
Section 4 - Circuit Simulation
Figure 4-7: Circuit with Simulation Running
As you can see the top lamp X2 is shaded, showing that it is lit. Next, press the space bar. The circuit
should now appear as in Figure 4-8.
Figure 4-8: Circuit with Switch Position Changed
As the text “Key = Space” under J1 indicates pressing the space bar changes the position of the switch
from the top contact to the bottom contact so that current now flows through X1. If you wish you can
always edit the component properties to choose another key to actuate the switch. One caveat is that if you
specify the same key for more than one switch then pressing that key will affect every switch. This can be
convenient when you want to change more than one switch at the same time, but could be awkward if you
want to change just one. Fortunately, there is a way to actuate specific switches.
Click on J1. The circuit should now appear as in Figure 4-9.
31
Using Multisim®: An Introductory Tutorial
Figure 4-9: Circuit with Switch Position Change Back
This shows that clicking on a switch will actuate it. Even if other switches in the circuit use the same key
clicking on a switch will actuate that switch and no others.
As a final demonstration, stop the simulation and modify the circuit as indicated:
1.
Delete R1.
2.
Connect the right side of X1 to ground.
3.
Change the value of V1 from 12 V to 24 V.
Your circuit should now appear as in Figure 4-10.
Figure 4-10: Modified Flashlight Circuit
Start the simulation. Watch X1 carefully and press the space bar to toggle the position of the switch. If you
were observing carefully, you may have seen the lamp flash briefly and go out. The circuit appears as
shown in Figure 4-11.
32
Section 4 - Circuit Simulation
Figure 4-11: Circuit with Failed Lamp
Because the supply voltage exceeded the 12V rating of the lamp the filament burned out, as shown by the
graphic of X1. Multisim includes a number of animations that show what will happen if the current or
voltage rating of certain components is exceeded. These components include lamps, switches, and fuses.
4.3.2
Status Information
Although you may not have noticed it Multisim provides simulation status information when a simulation
is running. This information, shown in Figure 4-12, is located at the bottom of the Multisim window.
Although you will generally not need this information there are times when it can be useful.
Figure 4-12: Multisim Simulation Status Information
The first piece of information is the message stating that Multisim is simulating a circuit. In this case, the
message “Flashlight_Mod9: Simulating...” indicates that the simulation of the circuit “Flashlight_Mod9”
is running.
The second piece of information indicates how much simulation time has elapsed. “Tran: 0.187 s”
indicates that Multisim has simulated the transient (changing) response of the circuit for 0.187 seconds.
This means that the circuit information provided by Multisim corresponds to that of a real circuit being on
for 0.187 seconds (CPU time), not that the simulation has been running for 0.187 seconds (real time). In
some simulations you may wish to know how the circuit is changing over time. The elapsed time allows
you to pause the simulation at specific times to collect information, even though the time typically changes
too rapidly to pause the circuit at exact points in time.
The final piece of information is a bar indicator that oscillates as the simulation runs. Sometimes a
simulation will run very slowly so that the elapsed time does not appear to change. The visual indicator
allows you to tell whether the simulation has locked up or is just running slowly.
33
Section 5 - Basic Circuit Measurements
5.
5.1
Basic Circuit Measurements
Introduction
The last chapter demonstrated how Multisim could simulate the operation of a circuit by demonstrating the
behavior of the components. Simulating the flashlight circuit showed how the switch could change
position, the lamps could light, and even how the lamp would burn out if the applied voltage was too high.
This sort of analysis is called qualitative analysis because it provides information about some characteristic,
or quality, of the circuit. Qualitative analysis tells what is happening, but not to what extent. For example,
the analysis can indicate that the lamp is on, but not how bright it is, or that current flowing through the
lamp does not burn out the filament, but not how much current actually is flowing.
Simulations that work with actual values in the circuit are another type of analysis, called quantitative
analysis. Qualitative analysis provides information about the amount, or quantity, of some circuit value,
which requires measuring circuit values. Practically all circuit measurements are or are based on voltage,
current, or resistance measurements. Multisim provides two types of devices, based on real-world devices,
for measuring basic circuit values: the circuit meter and the digital multimeter.
In this chapter you will
5.2

Learn how to configure, connect, and read circuit meters.

Examine and apply the features of the Multisim digital multimeter.
Circuit Meters
The Multisim circuit meters are based upon real-world meters, which indicate the amount of voltage or
current in a circuit. Circuit meters measure current and voltage. A meter that measures current is called an
ammeter, whereas a meter that measures voltage is called a voltmeter. You add ammeters and voltmeters
into circuits (as well as move, rotate, and otherwise manipulate them) in the same manner as for other
circuit components, such as resistors. To access ammeters and voltmeters use the Place Indicator tool
shown in Figure 5-1, which is located on the Component toolbar.
Figure 5-1: The Place Indicator Tool
5.2.1
The Ammeter
To select the ammeter, click AMMETER in the Family list, as shown in Figure 5-2.
35
Using Multisim®: An Introductory Tutorial
Figure 5-2: Selecting an Ammeter with the Component Browser
The AMMETER family provides four meter variations, shown in Figure 5-3, that differ in orientation and
polarity. These four variations exist only as a convenience because you can change the orientation and
polarity of any meter by right-clicking on a meter and flipping the meter horizontally, vertically, or both.
Figure 5-3: Multisim Ammeter Variations
The ammeter indicates the amount of current in amperes (often shortened to “amps”) flowing through a
specific part of the circuit. This means that the ammeter must be connected into the circuit so that all the
current flowing through that part of the circuit must also flow through the meter. Figure 5-4 shows the
correct and incorrect way to connect the ammeter to measure current flowing through a resistor.
Figure 5-4: Correct and Incorrect Ammeter Connections
36
Section 5 - Basic Circuit Measurements
The left ammeter connection is correct because all the current flowing from V1 through R1 must flow
through the ammeter to return through ground to V1. The right ammeter connection is incorrect because the
current flowing from V2 through R2 and the current flowing from V2 through the ammeter are not the
same. Because current must flow through the ammeter its resistance should be as small as possible so that it
doesn’t affect the total circuit resistance (and hence the measured current). This small resistance is why you
should NEVER connect an ammeter across a component. This would cause very high current to flow
through the meter, possibly damaging it.
The sign of the current indicates the lead into which conventional dc current is flowing. If the ammeter
reading is positive, the conventional dc current is flowing into the positive (+) ammeter lead. If the
ammeter reading is negative, the conventional dc current is flowing into the negative (–) ammeter lead.
As Figure 5-4 shows, the default values for the ammeter is 1 nΩ (which is extremely small) and dc current
measurement. You can change these values by double-clicking on the ammeter and using the Ammeter
properties window, shown in Figure 5-5.
Figure 5-5: Ammeter Properties Window
5.2.2
The Voltmeter
To select the voltmeter, click VOLTMETER in the Family list, as shown in Figure 5-2.
Figure 5-6: Selecting a Voltmeter with the Component Browser
37
Using Multisim®: An Introductory Tutorial
The VOLTMETER family also provides four meter variations, shown in Figure 5-8, that differ in
orientation and polarity. If you accidentally select the wrong meter, you can re-orient the meter by rightclicking on the meter and flipping the meter horizontally, vertically, or both.
Figure 5-7: Multisim Voltmeter Variations
The voltmeter indicates the amount of voltage in volts across a specific part of the circuit. This means that
the voltmeter must be connected into the circuit so that all the voltage across that part of the circuit must
also be applied across the meter. Figure 5-8 shows the correct and incorrect way to connect the ammeter to
measure voltage across a resistor.
Figure 5-8: Correct and Incorrect Voltmeter Connections
The left voltmeter connection is correct because voltage across R1 must also appear across the voltmeter.
The right voltmeter connection is incorrect because the voltage across R3 and the voltage across the
voltmeter are not the same. Because voltage is applied across the voltmeter its resistance should be as large
as possible so that it doesn’t affect the total circuit resistance (and hence the measured voltage).
The sign of the voltage indicates which voltmeter lead is connected to the higher (more positive) potential.
If the voltmeter reading is positive, the positive (+) voltmeter lead is connected to the point of higher
potential. If the voltmeter reading is negative, the negative (–) voltmeter lead is connected tot he point of
higher potential.
As Figure 5-8 shows, the default resistance is 10 MΩ, which is very large compared to most circuit values.
The default mode for the voltmeter is also for dc measurement. You can change these values by doubleclicking on the voltmeter and using the Voltmeter properties window, shown in Figure 5-9.
38
Section 5 - Basic Circuit Measurements
Figure 5-9: Voltmeter Properties Window
5.3
The Digital Multimeter
Ammeters and voltmeters are useful if only current or voltage will be measured (such as on the front panel
of a power supply), but the most common circuit measurement tool is the multimeter. Basic multimeters
combine the functions of a voltmeter, ammeter, and ohmmeter to measure voltage, current, and resistance,
respectively. More expensive multimeters can measure capacitance, test diodes, and perform other useful
functions. The Multisim program provides a Multimeter tool on the Instrument toolbar, shown in both
minimized and expanded form in Figure 5-10. The minimized form is the form you use to connect the
multimeter to the circuit, and the expanded form is the form with which you view the measured reading. To
open the expanded form, double click on the minimized form. To remove the expanded form, click the
Close button at the upper right of the expanded multimeter.
Figure 5-10: Multisim Multimeter Views
Table 5-1 summarizes the multimeter functions.
Table 5-1: Multimeter Functions
Button
Function
Selects ammeter mode.
Selects voltmeter mode.
Selects ohmmeter mode.
39
Using Multisim®: An Introductory Tutorial
Selects decibel mode.
Selects ac measurement mode.
Selects dc measurement mode.
Opens multimeter settings dialog box.
Decibel mode is a special measurement mode used in communications and other signal applications and is
beyond the scope of this tutorial.
5.3.1
Measuring Circuit Voltages
You always make voltage measurements with respect to some reference point. Usually this reference point
is circuit ground, but need not be. A common convention is to specify a voltage at point X with respect to
ground as VX, and the voltage at point X with respect to point Y as VXY. Voltage across a component is
often represented as VREFDES, where REFDES is the reference designator for the component. In Figure 5-11
XMM1 is measuring VA, the voltage at point A with respect to ground, XMM3 is measuring VB, which is
the voltage at point B with respect to ground, and XMM2 is measuring VAB, which is the voltage at point A
with respect to the voltage at point B, or VA – VB. This voltage is also referred to as VR1, as this is the
voltage across R1.
Figure 5-11: Voltage Measurement Conventions
The circuit must be powered when you make voltage measurements. Also, when making voltage
measurements, you place the meter across components, and not between them. This means that voltage
measurements are very convenient, as you do not have to disassemble a circuit to make them.
5.3.2
Measuring Circuit Current
The circuit must also be powered when you make current measurements. Unlike voltage measurements,
current measurements require you to insert the multimeter into the circuit. This is because current must pass
through the meter for the meter to measure it. NEVER connect an ammeter across a component to measure
current, as very high current could flow through and damage the meter. Refer to Figure 5-12 for the correct
and incorrect ways to connect an ammeter to a circuit.
40
Section 5 - Basic Circuit Measurements
Figure 5-12: Correct and Incorrect Meter Connections for Current Measurements
A common convention is to identify the current through a component as IREFDES, where REFDES is the
reference designator for the component. In Figure 5-12 the current through R1 would be IR1.
5.3.3
Measuring Circuit Resistance
You must remove power from the circuit when making resistance measurements, and will typically
disconnect the power supply from the circuit as well. You connect the meter across the points whose
resistance you wish to measure. As with voltage measurements, a common convention is to identify the
measured resistance as RXY, where X and Y are the points to which you connect the meter. The multimeter
in Figure 5-13 is measuring RDE. Note that this resistance this is not the same as R5, because resistors R2,
R3, and R4 affect the meter reading.
Figure 5-13: Measuring Resistance RDE
5.4
The Wattmeter
One way to determine power in a circuit is to use a multimeter to measure circuit values and calculate
power from one of the power formulas. Another way is to use the wattmeter, which is a real-world
instrument that measures the power in a circuit. Since power is the product of voltage and current, the
wattmeter has two sets of inputs to measure both voltage and current simultaneously. The wattmeter uses
these measurements to calculate the power. Figure 5-14 shows the minimized and expanded views of the
41
Using Multisim®: An Introductory Tutorial
Multisim wattmeter.
Figure 5-14: Multisim Wattmeter Views
To connect the wattmeter, you connect the voltage inputs (marked with a “V”) to the circuit as you would
connect a voltmeter and the current inputs (marked with an “I”) to the circuit as you would connect an
ammeter. The following example will illustrate this.
1.
Construct the circuit shown in Figure 5-15.
Figure 5-15: Wattmeter Demonstration Circuit
2.
Select the Wattmeter tool, shown in Figure 5-16, from the Instruments toolbar.
Figure 5-16: The Wattmeter Tool
3.
Place the wattmeter so that the voltage inputs are above R1, as shown in Figure 5-17.
Figure 5-17: Placing the Wattmeter
42
Section 5 - Basic Circuit Measurements
4.
Connect the wattmeter voltage inputs across R1 as shown in Figure 5-18.
Figure 5-18: Connecting the Wattmeter Voltage Inputs
5.
Next, you must connect the current inputs into the circuit so that they measure the current through
R1. You can connect the ammeter in series with either the left or right side of R1. Since the
current inputs are to the right of the voltage inputs it is easier to connect them into the circuit to
the right side of R1. Select the wire segment between the junction to the right of R1 and the top
terminal of R2. Press the DELETE key to delete the selected segment. Your circuit should now
look like that in Figure 5-19.
Figure 5-19: Opening the Circuit for the Current Input Connections
6.
Connect the current inputs in series with the circuit between R1 and R2, as shown in Figure 5-20.
Figure 5-20: Connecting the Wattmeter Current Inputs
43
Using Multisim®: An Introductory Tutorial
7.
Double-click the wattmeter to open the expanded view.
8.
Click the Run switch to run the simulation. After a few seconds the wattmeter should show the
readings in Figure 5-21.
Figure 5-21: Wattmeter Power Measurement for R1
The wattmeter shows the values. The first value, in the large window indicates that R1 is
dissipating 9.868 mW of power. The smaller window indicates that the power factor is 1.000. The
power factor of purely resistive circuits is always 1, but this is not always the case in ac circuits
that contain inductors or capacitors.
9.
Click the Run switch to stop the simulation.
10. Connect the wattmeter as shown in Figure 5-22.
Figure 5-22: Wattmeter Connection
11. Verify that the power dissipation of R2 is 5.033 mW and that the power factor is 1.000.
44
Section 6 - Power and Signal Sources
6.
6.1
Power and Signal Sources
Introduction
All circuits, from the simple flashlight you created in Chapter 2 to the most complex computers, require
power to operate. Many circuits also require some signal to function (such as a series of digital pulses that
clocks a microprocessor circuit) or that the circuit can process (such as a sine wave for a transistor to
amplify). The entities that provide power or signals to a circuit are called sources. Power sources can be dc
(the polarity of the source never changes) or ac (the polarity of the source periodically reverses). Signal
sources can be analog (the signal amplitude varies continuously over a range, like a sine wave) or digital
(the signal can assume only one of two specific levels, called LOW or HIGH).
Multisim sources can be one of two general types. The first type consists of circuit components that you
connect directly into the circuit just as you would any other component. The dc power source, or battery,
that you used in the flashlight circuit is an example of this type of source. The second type is instruments
that you connect to the circuit, similar to the way that you connect a digital multimeter to a circuit.
In this section you will:
6.2

Examine, compare, and contrast different types of commonly used power sources and how they
are configured.

Examine different types of commonly used signal sources and how they are configured.
Power Sources
A voltage source is an electrical entity that maintains a specified voltage across its terminals regardless of
the amount of current drawn from it. Voltage sources for which the voltage polarity does not change are dc
sources. Voltage sources for which the polarity periodically reverses, or alternates, are ac sources. To
access the Multisim voltage sources, first click the Place Source tool in the Component toolbar to open
the Sources group in the Component browser. Then Select the Power_Sources family to access the power
sources, as shown in Figure 6-1.
Figure 6-1: Accessing Voltage Sources in the Component Browser
As Figure 6-1 shows, there are a number of voltage sources from which to select.
45
Using Multisim®: An Introductory Tutorial
6.2.1
AC Voltage Source
The AC_POWER source, shown in Figure 6-2, selects a sinusoidal ac voltage source.
Figure 6-2: AC Voltage Source
This source has a number of properties that you can edit by double-clicking on the source to open the
AC_POWER properties window. The four most important are the voltage, offset, frequency, and
phase properties.
Voltage (RMS)
This property specifies the rms voltage in volts generated by the source. The default value is
120 Vrms.
Voltage Offset
The voltage offset is the dc value of the signal and effectively shifts the ac waveform “up”
(more positive) or “down” (more negative) relative to 0 V. An offset of 0 V means that there
is no dc component and that the positive and negative peak values of the ac voltage are equal
in magnitude. The voltage offset of a sine wave is the average of the positive and negative
peak values. The default value is 0 V.
Frequency (Hz)
This property specifies the frequency in Hertz of the ac waveform, or how many times per
second the sine wave repeats. The default value is 60 Hz.
Phase
The phase of a sine wave specifies the time relationship in degrees between a point on that
sine wave and the corresponding point on a reference sine wave. Each cycle consists of 360°,
so a phase of +90° means that the positive peak of the since wave occurs one quarter of a
cycle before the positive peak of the reference sine wave. Similarly, a phase of –45° means
that the positive peak of the sine wave occurs one eighth of a cycle after the positive peak of
the reference sine wave. The default value is 0° (i.e., the sine wave and the reference sine
wave are in phase).
6.2.2
DC Voltage Source
The DC_POWER source, shown in Figure 6-3, selects a dc voltage source (or battery).
Figure 6-3: DC Voltage Source
As with ac source, you can edit the properties of the source by double-clicking on it to open the
DC_POWER properties window. The most important is the voltage property.
46
Section 6 - Power and Signal Sources
Voltage (V)
This property specifies the dc voltage in volts generated by the source. The default value is
12 V.
6.2.3
Non-Ideal Battery
The non-ideal battery source, shown in Error! Reference source not found., selects a dc voltage
source that includes properties that exist in real-world batteries.
Figure 6-4: Non-Ideal Battery
You can edit the properties of the non-ideal battery by double-clicking on the source to open the
NON_IDEAL_BATTERY properties window. The most important is the voltage property.
Voltage (V)
This property specifies the dc voltage in volts generated by the source. The default value is
12 V.
Internal Resistance
The internal resistance of an ideal battery is 0 Ω so that the voltage of the battery is the same
whether or not any current is being drawn. Practical batteries have some internal resistance so
that the battery voltage drops it supplies more current to a circuit. The default value is 0.1 Ω.
Capacity (in Ampere-Hours)
All practical batteries can provide current only for a limited amount of time. The capacity of
the battery indicates how long in hours the battery will last if it continuously provides a
specific amount of current in amps. A battery with a capacity of 100 ampere-hours (or
100 Ah) can provide 100 amps for 1 hour, 25 amps for 4 hours, 10 amps for 10 hours, and
equivalent products of currents and times. The default value is 300 Ah.
6.2.4
Digital Power
The digital power sources, shown in Figure 6-5, are specifically intended to provide bussed power to
the devices in a digital system that use a common supply.
Figure 6-5: Digital Power Sources
You can edit the digital power components by double-clicking on the source to open the DC_POWER
properties window.
Voltage (V)
This property specifies the dc bus voltage in volts supplied by the source. The default values
are +5 V for VCC and VDD, -5 V for VEE, and 0 V for VSS.
47
Using Multisim®: An Introductory Tutorial
6.3
Signal Sources
Signal sources that you will use in Multisim will typically be signal voltage sources, because most circuits
are designed to process or operate using voltages. To access the Multisim voltage sources, first click the
Place Source tool in the Component toolbar to open the Sources group in the Component browser. Then
select the SIGNAL_VOLTAGE_SOURCES family to access the signal voltage sources, as shown in
Figure 6-6.
Figure 6-6: Accessing Signal Voltage Sources in the Component Browser
As Figure 6-6 shows, there are a number of signal voltage sources from which to select.
6.3.1
AC Signal Voltage Source
The AC_VOLTAGE source, shown in Figure 6-2, selects a sinusoidal ac signal voltage source.
Figure 6-7: AC Voltage Source
The ac signal voltage source is very similar to the ac voltage source, but a fundamental difference is
that the voltage of the ac signal voltage source is a peak rather than rms value. The voltmeters in
Figure 6-8, which measure rms voltage, illustrates the difference between the ac signal source and ac
voltage source.
48
Section 6 - Power and Signal Sources
Figure 6-8: Comparison of AC Power and Signal Source Voltages
The ac signal source has a number of properties that you can edit by double-clicking on the source to
open the AC_VOLTAGE properties window. The four most important are the voltage, offset,
frequency, and phase properties.
Voltage (Pk)
This property specifies the peak voltage in volts generated by the source. The default value is
1 Vpk. Because the amplitude of this source is specified as a peak voltage it is easier to
measure circuit voltages with an instrument (like an oscilloscope) that can measure peak
voltage directly, rather than one (like a multimeter) that measures rms voltage.
Voltage Offset
The voltage offset for the AC_VOLTAGE source is similar to the voltage offset for the
AC_POWER source. The default value is 0 V.
Frequency (Hz)
The frequency property of the AC_VOLTAGE sources is similar to the frequency property
AC_POWER source. The default value is 1 kHz.
Phase
The phase property of the AC_VOLTAGE sources is similar to the phase property
AC_POWER source. The default value is 0° (i.e., the sine wave and the reference sine wave
are in phase).
6.3.2
Clock Voltage Source
The CLOCK_VOLTAGE source, shown in Figure 6-9, selects a digital clock source. The clock
voltage source is typically used to provide a clock signal for synchronous digital circuits.
Figure 6-9: Clock Voltage Source
You can edit the properties of the clock voltage source by double-clicking on it to open the
CLOCK_VOLTAGE properties window.
49
Using Multisim®: An Introductory Tutorial
Frequency (F)
This property specifies the frequency in Hertz of the clock source. The default value is
1 kHz.
Duty Cycle
This property determines the percentage of time that the clock signal is HIGH compared to
the total period of the clock signal. A 20% duty cycle means that 20% of the time the clock
signal is HIGH, and that 80% of the time the clock signal is LOW. The default value is 50%.
Voltage (V)
This property determines the amplitude (peak value) in volts of the clock signal. The default
value is 5 V.
6.3.3
Pulse Voltage Source
The pulse voltage source, shown in Figure 6-10, is similar to the clock voltage source but provides
greater flexibility in specifying the properties of the pulses.
Figure 6-10: Pulse Voltage Source
You can edit the properties of the pulse voltage source by double-clicking on the source to open the
PULSE_VOLTAGE properties window.
Initial Value
This property specifies the baseline, or minimum, voltage for the pulse voltage. The default
value is –1 V.
Pulsed Value
This property specifies the voltage of the pulse. The default value is +1 V. The amplitude of
the pulse is the pulsed value minus the initial value.
Rise Time
The rise time is the time required for the pulse to increase from the initial value to the pulsed
value. The default value is 1 ns.
Fall Time
The fall time is the time required for the pulse to decrease from the pulsed value to the initial
value. The default value is 1 ns.
Pulse Width
The pulse width is the time for which the pulse remains at the pulsed value. The default value
is 0.5 ms.
Period
The period is the time between the start of consecutive pulses. The duty cycle is the pulse
width divided by the period. The default value is 1 ms.
50
Section 6 - Power and Signal Sources
6.3.4
Triangular Wave Voltage Source
The triangular wave voltage source, shown in Figure 6-11, provides a periodic voltage that changes
linearly from one voltage to another.
Figure 6-11: Triangular Wave Voltage Source
You can edit the triangular wave voltage source by double-clicking on the source to open the
TRIANGULAR_VOLTAGE properties window.
Voltage Amplitude
This property specifies the difference between the minimum and maximum values of the
triangular waveform. The default value is 5 V.
Period
The period is the time between the start of consecutive triangular pulses. The default value is
1 ms.
Fall Time
The fall time is the time required for the waveform to decrease from its maximum value to its
minimum value. The default value is 1 ns. The rise, or ramp, time is equal to the period minus
the fall time.
Voltage Offset
The voltage offset is the voltage difference between the minimum waveform voltage and 0 V
and allows you to adjust the minimum and maximum waveform voltages. The default value is
0 V.
6.4
Signal Generators
Signal generators are instruments that provide analog or digital signals that you can use as inputs to observe
the behavior of circuits. The analog signal generator in Multisim is the function generator, which can
output sine, rectangular, and triangular outputs. The digital signal generator in Multisim is the word
generator, which can output sequences of up to 32-bit binary patterns.
6.4.1
Function Generator
The function generator combines the functions of an ac signal voltage source, pulse voltage source, and
triangular wave voltage source. The function generator tool, shown in Figure 6-12, is located on the
Instrument toolbar. Figure 6-13 shows the minimized and expanded views of the function generator.
Figure 6-12: Function Generator Tool
51
Using Multisim®: An Introductory Tutorial
Figure 6-13: Minimized and Expanded Views of Function Generator
One thing that you may have noticed is that the function generator has three connections, as opposed to two
for the other signal sources that you have seen. The middle terminal, marked “Common”, is the reference
for the terminals marked “+” and “–”. A 5 Vpk amplitude means that the signal at the “+” output will be 5
Vpk relative to the output marked “Common”. The signal at the “–” output will also be 5 Vpk relative to the
output marked “Common” but have the opposite polarity of the signal at the “+” output. Typically (but not
always) the “Common” terminal is connected to circuit ground and the signal taken from either the “+” or
“–” output. If the signal is measured across the “+” and “–” terminals the amplitude of the measured signal
will be double the value specified in the function generator settings.
The settings for the function generator are explained further below.
Waveforms
The waveform buttons select the output of the function generator. The left button selects a sine
wave output, the middle button a triangular wave output, and the right button a rectangular wave
output. The type of output waveform can be changed at any time, even when a simulation is
running, but only one button can be selected at any time.
Frequency
This sets the frequency of the function generator output. When you click in the left window you
can type in (or us the arrows to step up or down to) a numeric value for the frequency. When you
click in the right window Multisim will display a drop-down list of frequency units for you to
select, ranging from fHz (femtohertz, or 1 × 10–15 Hz) to THz (terahertz, or 1 × 1012 Hz). The
default frequency is 1 Hz.
Amplitude
This sets the peak amplitude of the function generator output relative to the “Common” output
terminal. When you click in the left window you can type in (or us the arrows to step up or down
to) a numeric value for the peak amplitude. When you click in the right window Multisim will
display a drop-down list of voltage units for you to select, ranging from fV (femtovolts, or
1 × 10–15 V) to TV (teravolts, or 1 × 1012 V). The default amplitude is 5 Vpk.
Offset
The offset control is similar to the offset property of other signal sources and determines the
voltage value that is midway between the positive peak value and negative peak value. When you
click in the left window you can type in (or us the arrows to step up or down to) a numeric value
52
Section 6 - Power and Signal Sources
for the peak amplitude. When you click in the right window Multisim will display a drop-down
list of voltage units for you to select, ranging from fV to TV. The default value is 0 V for which
the positive and negative peaks have equal values but opposite signs.
6.4.2
Word Generator
The Multisim word generator does not exist as a real device, although its function can be duplicated with
computers, software, and interface circuits. The function of the word generator is to produce a specified
sequence of digital signals on one or more channels as input to digital logic circuits. A simple model of the
word generator is as a bank of multiple switches that you program to connect LOW and HIGH voltage
levels in a specific order.
Figure 6-14 shows the word generator tool, which is located in the Instruments toolbar. Figure 6-15 shows
the minimized and expanded views of the word generator.
Figure 6-14: The Word Generator Tool
Figure 6-15: Word Generator Minimized and Expanded Views
To use the word generator, you specify a sequence of HIGH (1) and LOW (0) logic levels for up to 32
channels, numbered from 0 to 31. To do so, click in the list of values in the pattern buffer window on the
right side of the word generator and enter the patterns you wish the generator to output. You can enter and
display these values in hexadecimal, decimal, binary, or ASCII, depending upon the radio button you select
in the Display section to the left of the window.
To the left of each value in the list is a box. If you right-click in the box next to a value, a menu will open.
The menu allows you to specify the start (Set Initial Position) and end (Set Final Position) of the pattern
you want the word generator to use, and the value at which you want execution to begin (Set Cursor). You
can also set a breakpoint (Set Break-Point) that will pause the generator at that value so that you can
examine the state of the circuit, or clear a previously set breakpoint (Delete Break-Point).
The Controls section allows you to specify how you want the word generator to operate. Cycle will
repeatedly execute the pattern between the specified start and end values of the list until you stop the
simulation or select Burst or Step. Burst will execute the values between the position of the cursor and the
end value in the list and then pause execution. Step will execute one value at a time and then pause
execution. Clicking on any of these buttons will automatically begin execution.
The Set... button permits you to clear the buffer, save the pattern that the buffer contains, load a saved
pattern into the buffer, or load one of several pre-defined patterns into the buffer, as shown in Figure 6-16.
It also allows you to specify the size of the buffer (up to 8192 values) and display the buffer size in decimal
or hexadecimal.
53
Using Multisim®: An Introductory Tutorial
Figure 6-16: Word Generator Setting Options
The Trigger controls allow you to specify whether the rising or falling edge of an internal or external
trigger is used to initiate execution.
The Frequency controls specify how rapidly the word generator outputs the values in the buffer. For
example, a “1 kHz” setting will output one value in the buffer every millisecond.
The connections to the word generator consists of 32 data lines (lines 0 through 15 are on one side of the
minimized instrument and lines 16 through 31 on the other side), a “Ready” output that indicates when the
word generator is ready to begin execution, and a “Trigger” input that will initiate the execution if an
external trigger is specified and connected.
54
Section 7 - The Oscilloscope
7.
7.1
The Oscilloscope
Introduction
The multimeter is ideal for making many types of precise circuit measurements, but its intent is to measure
values that are static (i.e., values that do not significantly change over time). The instrument for measuring
dynamic, or time-varying, values is the oscilloscope. An oscilloscope is generally less accurate than a
digital multimeter and limited to voltage measurements but can display rapidly changing signals. Most
oscilloscopes have multiple channels so that you can compare or combine signals, measure delays between
events, and use an event on one channel to initiate the capture of information on another. Other common
features of modern oscilloscopes include measurement cursors, digital time and amplitude displays,
automatic detection of maximum and minimum voltages, provisions to upload waveforms to removable
media or computers, and on-line help screens.
The Multisim software offers several varieties of oscilloscopes. The generic two- and four-channel
oscilloscopes provide basic features that are common to most oscilloscopes. The other oscilloscopes
emulate the form, features, and functions of actual oscilloscope models. Although the latter are excellent
tools for learning to use the actual oscilloscopes, this section will use the two-channel generic oscilloscope
to present the basic concepts and features that are common to all oscilloscopes.
In this section you will
7.2
7.2.1

Learn how to access the Multisim oscilloscope.

Learn the typical features of an oscilloscope.

Learn how to read an oscilloscope display.

Learn how to use the amplitude and time base controls.
The Oscilloscope Tool
Accessing the Oscilloscope
To access the two-channel oscilloscope, click the “Oscilloscope” tool (refer to Figure 7-1) in the
Instruments toolbar.
Figure 7-1: Oscilloscope Tool
Figure 7-2 shows the minimized view of the two-channel oscilloscope for the Multisim 10 software,
although the Multisim 9 oscilloscope is similar. The oscilloscope has three circuit connections. The two
connections on the bottom of the oscilloscope are for the A channel (left) and B channel (right) signal and
ground. The connections on the right of the oscilloscope are for the external trigger signal and ground.
Figure 7-2: Minimized 2-Channel Oscilloscope View
55
Using Multisim®: An Introductory Tutorial
Figure 7-3 shows the enlarged view of the two-channel oscilloscope with a sample display. The display is
that for the Multisim 10 oscilloscope, although the Multisim 9 oscilloscope is similar.
Figure 7-3: Enlarged Two-Channel Oscilloscope View
The oscilloscope controls consist of the following six sections:
1) Graphical display
2) Display controls
3) Time base controls
4) Channel A controls
5) Channel B controls
6) Trigger controls
The following sections discuss each of the oscilloscope control sections.
7.2.2
Graphical Display
The display occupies most of the upper portion of the enlarged oscilloscope view. This is the area in which
you view the channel signals and position the reference cursors. Practical oscilloscope displays are 10
divisions wide by 8 divisions high, but the Multisim generic oscilloscope displays are 10 divisions wide by
6 divisions high. The display in Error! Reference source not found. shows two signals, one from Channel
A and one from Channel B, and reference cursors (Multisim refers to these as “crosshairs”) 1 and 2. The
small triangle at the top of each cursor identifies the number of the cursor.
The reference cursors provide amplitude and time information for a specific point on the channel signals.
The cursors are normally located at the far right and left sides of the display. To directly position a cursor,
56
Section 7 - The Oscilloscope
click and drag the cursor to the desired position in the display and release the left mouse button. You can
also right-click the cursor and select a specific time or amplitude value for the cursor.
Directly beneath the graphical display is a scroll bar. If the collected data extends beyond one screen, you
can use the scroll bar to examine parts of the signal that are not on the screen.
7.2.3
Display Controls
The display controls are just below the oscilloscope display area. This section allows you to position the
cursors, view the amplitude and time information for the channel signals at the cursor positions, and select
the color of the display background. Refer to Figure 7-4.
Figure 7-4: Oscilloscope Display Controls
The  and  buttons to the right of the T1 and T2 labels adjust the position of reference cursors 1 and 2,
respectively. The information associated with reference cursors 1 and 2 is in the window to the right of the
T1 and T2 buttons, respectively. The amplitude and time information associated with each cursor will
update as you adjust the position of the cursors.
The information in the window to the right of the T2-T1 label is the difference in amplitude and time
between reference cursor 2 and reference cursor 1. This feature allows you to easily calculate time delays,
signal periods, peak-to-peak amplitudes, and other differential data.
The Reverse button allows you to change the background of the graphical display to black or white to
improve the visibility of the signals.
The Save button allows you to save the graphical display as a list of time and amplitude data points in a
scope display (.SCP), LabVIEW measurement (.LVM), or TDM file format so that you can import the data
into other applications. The .SCP and .LVM files are in text format that you can open with a number of text
editors, word processors, and spreadsheets. In addition, the Multisim program’s Grapher utility (under the
View menu) can open the .SCP file and display it as a graphic that you can view, save, and print. The
.TDM file format is in a binary file format that is compatible with National Instruments’ DIAdem data
management and analysis software.
7.2.4
Time base Controls
The controls in the Time base section allow you to adjust the horizontal position and scale of the display
and select the format of the display. Refer to Figure 7-5.
Figure 7-5: Oscilloscope Time base Controls
The Scale value specifies how much time each horizontal division represents. The time settings use a 1-2-5
progression so that each setting is about twice that of the previous setting. For example, the setting before
the 200 μs/Div setting is 100 μs/Div and the setting after it is 500 μs/Div. You can use the up and down
scroll buttons to set this value from 1 ps (10−12 seconds) per division to 1000 Ts (1012 seconds) per division.
Unless you have nothing else to do for a while should avoid using the 1000 Ts/div setting, as each
horizontal division at this setting equals approximately 31.7 million years.
57
Using Multisim®: An Introductory Tutorial
The X position value allows you to manual shift the display in 0.1-division increments or use the scroll
arrows to shift the display in 0.2-division increments to the left or right. This allows you to better align the
display with a specific point on the horizontal axis.
The four buttons at the bottom of the Time base section allow you to choose the format of the graphical
display.

The Y/T button configures the oscilloscope to display the Channel A and Channel B signals
separately with the vertical axis configured for volts and the horizontal axis configured for time.
This is the typical operating mode of oscilloscopes.

The Add button configures the oscilloscope to add the Channel A and Channel B signals and
display the result as a single signal with the vertical axis configured for volts and the horizontal
axis configured for time. The mode is useful for finding the voltage across a component that has
no direct connection to circuit ground.

The B/A button configures the oscilloscope to plot the Channel A signal against the horizontal
axis and the Channel B signal against the vertical axis to create a two-dimensional plot called a
Lissajous figure. This is a convenient display mode for determining the relative amplitude,
frequency, and phase of two signals. Both the vertical and horizontal axes are configured for
amplitude although the oscilloscope shows no units.

The function of the A/B button is similar to the B/A button, except that the oscilloscope plots the
Channel B signal against the horizontal axis and the Channel A signal against the vertical axis.
Note that the Scale and X position controls will work only with the Y/T and Add modes.
7.2.5
Channel A Controls
The controls in the Channel A section allow you to adjust the vertical position and scale of the Channel A
signal. Refer to Figure 7-6.
Figure 7-6: Oscilloscope Channel A Controls
The Scale value specifies how many volts each vertical division represents. The voltage settings use a 1-2-5
progression so that each setting is about twice the value of the previous setting. For example, the setting
before the 1 V/Div setting is 500 mV/Div, and the setting after it is 2 V/Div. You can use the up and down
scroll buttons to set this value from 1 pV per division to 1000 TV per division. Just for reference, 1000 TV
is enough electrical potential to generate a lightning bolt 189,000 miles long. If you plan to regularly
measure voltages on this order of magnitude be sure to observe adequate safety precautions.
The Y position value allows you to manual shift the display in 0.1-division increments or use the scroll
arrows to shift the display in 0.2-division increments up or down. This allows you to separate the Channel
A and B signals for better viewing or to compensate for some unwanted dc offset in the signal.
The AC, 0, and DC buttons determine the signal coupling for the channel.
58

The AC button removes any dc offset from the signal, so that Channel A couples (allows in) only
the ac portion of the signal into the oscilloscope.

The 0 button connects Channel A directly to ground. This is useful if you want to determine a 0 V
reference for a signal on Channel A or if you wish to view only the B channel when the
oscilloscope is in the Add mode.
Section 7 - The Oscilloscope

7.2.6
The DC button couples both the ac and dc components of the signal on Channel A into the
oscilloscope. You will often require this coupling when you are viewing low-frequency signals so
that the oscilloscope does not attenuate the signal.
Channel B Controls
The controls in the Channel B section are identical to those in the Channel A section, with the addition of
one more button. Refer to Figure 7-7.
Figure 7-7: Oscilloscope Channel B Controls
The extra button, marked with a “–”, inverts the signal on Channel B. You typically use this button when
you wish to find the difference between the Channel A and B signals. To do this, select the Add mode and
activate the Channel B “–” button. Because this will invert the Channel B signal, the oscilloscope will
display Channel A – Channel B, rather than Channel A + Channel B.
7.2.7
Trigger Controls
The controls in the Trigger section determine the conditions that will trigger the oscilloscope (that is, cause
the oscilloscope to display waveforms). Refer to Figure 7-8.
Figure 7-8: Oscilloscope Trigger Control
The Edge controls specify whether the trigger voltage must be increasing (rising edge) or decreasing
(falling edge) for the oscilloscope to display the Channel A and Channel B signals. Refer to Figure 7-9,
which specifies a rising edge trigger, also called a leading edge or positive edge trigger. This means that the
trigger voltage must exceed the Level value to trigger the oscilloscope. A falling edge trigger, also called a
trailing edge or negative edge trigger, means that the trigger voltage must fall below the Level value to
trigger the oscilloscope.
Figure 7-9: Rising Edge Trigger
The A, B, and Ext buttons specify whether oscilloscope uses the signal on Channel A, Channel B, or
External Trigger for the trigger voltage.
The Level value sets the voltage level for the trigger signal. You can use the scroll buttons to specify the
value of the trigger signal or manually enter the value in the text box. Click in the units box and select the
unit you wish to use for the trigger level from the list.
The Type buttons determine the type of triggering.

The Sing. (single-sweep) button configures the oscilloscope to make a single sweep when the
oscilloscope receives a valid trigger. After the oscilloscope completes a sweep across the screen, it
should halt until you use one of the Type buttons to initiate a new sweep. In actuality the scope
59
Using Multisim®: An Introductory Tutorial
will continue to capture waveforms, although the display will continue to show the date from the
first screen.

The Nor. (normal) button is similar to the single-sweep button, but after the oscilloscope
completes a sweep across the screen it will clear the screen and initiate a new sweep if it receives a
valid trigger.

The Auto (auto-trigger) button initiates a sweep whenever either of the following events occurs:

-
The oscilloscope receives a valid trigger.
-
A pre-defined amount of time has passed and the oscilloscope has not received a valid
trigger.
The None button specifies that there are no specific trigger conditions.
Most applications will use the auto-trigger mode, although nonperiodic signals or special conditions can
require other trigger modes for best results.
7.2.8
Oscilloscope Measurement Terminology
A static value possesses only a single characteristic, namely magnitude or amplitude, that describes it.
Time-varying signals have both time and amplitude characteristics to describe them. When you use an
oscilloscope to observe a time-varying signal you will measure specific amplitude and time characteristics
for the signal.
The most common signal you will observe in ac electronics is the sine wave. Refer to Figure 7-10.
VP
VPP
T
Figure 7-10: Example of Sine Wave Display
VPP is the peak-to-peak voltage. The peak-to-peak voltage for a sine wave is the difference between the
minimum and maximum amplitudes. VPP for the sine wave in Figure 7-10 is four divisions.
VP is the peak voltage, which is half the peak-to-peak value for a sine wave. VP for the sine wave in Figure
7-10 is two divisions.
T is the period of the sine wave, which is the time required for one cycle of the sine wave to repeat. You
will usually measure the period between consecutive positive zero-crossing points for the sine wave as
shown in Figure 7-10, but you can measure the period between any two corresponding points on
consecutive cycles. T for the sine wave in Figure 7-10 is five divisions.
Another characteristic of sine waves is f, the frequency. The frequency is the number of times per second
that a sine wave repeats and is equal to the reciprocal of the period, 1/T. The unit of frequency is Hertz
(Hz).
60
Section 7 - The Oscilloscope
7.2.9
Reading Oscilloscope Displays
To understand oscilloscope measurements you must learn to read the display. Refer to Figure 7-11.
Figure 7-11: Example Oscilloscope Display
The oscilloscope display does not show numerical markings for the divisions. To determine the amplitude
and period of the signal you must either
1) use the time base and channel scale settings to convert the number of vertical and horizontal
divisions into volts and seconds, or
2) use the cursors so that the Multisim program displays the measurement of interest in the display
controls window.
Table 7-1 shows the values of VPP, VP, T, and f for several different time base and channel settings for the
waveform of Figure 7-11.
Table 7-1: Calculated Waveform Values for Figure 7-11
Waveform Value
Time base = 5 μs/Div
Channel = 200 µV/Div
Time base = 200 µs/Div
Channel = 50 mV/Div
Time base = 1 ms/Div
Channel = 10 V/Div
VPP
1.0 mV
250 mV
50 V
VP = VPP / 2
500 µV
125 mV
25 V
T
40 µs
1.6 ms
8 ms
f = 1/T
25 kHz
667 Hz
125 Hz
7.2.10
Determining the Oscilloscope Time base and Voltage Scale Settings
If you know the approximate frequency and amplitude of a signal that you wish to measure, it is a good
idea for you to know the oscilloscope time base and channel scale settings that you will use to measure the
signal. This provides a check on the signal values that you expect to measure. Ideally you would like one
cycle to occupy the entire oscilloscope display so that the peak-to-peak signal amplitude is six divisions
high, and the period is ten divisions wide. Practically, however, you must round up to the nearest 1-2-5
scale settings that will show the full signal amplitude and period.
Table 7-2 shows the calculated ideal and practical (1-2-5 progression) oscilloscope time base and channel
scale settings for several values of voltage and frequency.
61
Using Multisim®: An Introductory Tutorial
Table 7-2: Calculated Oscilloscope Scale Settings
62
Waveform Value
Vp = 200 mV
f = 250 kHz
Vp = 10 V
f = 400 Hz
Vp = 189 V
f = 60 kHz
VPP = 2 × VP
400 mV
20 V
378 V
Ideal Channel Scale = VPP / 6
66 mV / div
3.3 V / div
63 V / div
Practical Channel Scale
100 mV / div
5 V / div
100 V / div
T = 1/f
4.0 µs
2.5 ms
16.7 µs / div
Ideal Time base Scale = T / 10
400 ns / div
250 µs / div
1.67 µs / div
Practical Channel Scale
500 ns / div
500 µs / div
2 µs / div
Section 8 - The Logic Analyzer
8.
8.1
The Logic Analyzer
Introduction
Just as the oscilloscope allows you to observe how analog voltages change over time, the logic analyzer
allows you to observe how digital signals change over time. While it is tempting to thing of the logic
analyzer as some sort of oscilloscope for digital signals, oscilloscope and logic analyzers have two
fundamental differences.
1) Oscilloscopes allow you to measure actual signal amplitudes. Logic analyzers provide no
information about the amplitude, other than that the measured signals are above or below some
logic threshold.
2) Oscilloscopes allow you to measure signal timing and the time between specific events. Logic
analyzers provide no information about the timing of signals, other than which signals were HIGH
(above a logic threshold) or LOW (below a logic threshold) at the time the logic analyzer sampled
the signals.
In this section you will:
8.2
8.2.1

Learn how to access the Multisim logic analyzer.

Learn the settings and purposes of the logic analyzer controls.

Investigate an example logic analyzer application with a 3-bit ripple counter.
The Logic Analyzer Tool
A Note on How the Logic Analyzer Operates
The logic analyzer does not continuously collect and display digital data, as does an analog oscilloscope
with analog data. Instead, the logic analyzer samples the data in its inputs (called terminals) and stores the
data in a data buffer. The size of this buffer limits how much data the logic analyzer can store so that the
logic analyzer must overwrite older data in the buffer with new samples once the buffer is full. When a
specific condition called a trigger occurs the logic analyzer will display the data that the buffer contains.
The logic analyzer’s controls provided great flexibility in collecting and displaying the data. Specifically
the controls allow you to specify when and how often the logic analyzer samples the terminals, when the
logic analyzer should look for a trigger, the data patterns that constitute a trigger, and how many samples
preceding and following the trigger the logic analyzer should retain and display.
8.2.2
Accessing the Logic Analyzer
To access the logic analyzer, click the “Logic Analyzer” tool (refer to Figure 8-1) in the Instruments
toolbar.
Figure 8-1: Logic Analyzer Tool
Figure 8-2 shows the minimized view of the Multisim logic analyzer. The oscilloscope has sixteen inputs,
or terminals to connect up to sixteen digital signals. The three connections on the bottom of the logic
analyzer are for an external clock (“C”), external clock qualifier (“Q”), and trigger qualifier (“T”).
63
Using Multisim®: An Introductory Tutorial
Figure 8-2: Minimized Logic Analyzer View
Figure 8-3 shows the enlarged view of the logic analyzer with a sample display.
Figure 8-3: Enlarged Logic Analyzer View
The oscilloscope controls consist of the following five sections:
1) Graphical display
2) Operating controls
3) Cursor controls
4) Clock controls
5) Trigger controls
The following sections discuss each of the oscilloscope control sections.
8.2.3
Graphical Display
The display occupies most of the upper portion of the enlarged oscilloscope view. This is the area in which
you view the channel signals and position the reference cursors. The display consists of ten equal divisions,
each of which represents an amount of time that depends upon the frequency of the logic analyzer clock
and the number of clocks per division, and up to sixteen digital signals. The display in Figure 8-3 shows
three signals and reference cursors (Multisim refers to these as “crosshairs”) 1 and 2. The small triangle at
the top of each cursor identifies the number of the cursor.
64
Section 8 - The Logic Analyzer
The reference cursors provide logic level and time information for a specific point on the channel signals.
The cursors are normally located at the sides of the display. To directly position a cursor, click and drag the
cursor to the desired position in the display and release the left mouse button. You can also right-click the
cursor and select a specific logic level or time value for the cursor.
Directly beneath the graphical display is a scroll bar. If the collected data extends beyond one screen, you
can use the scroll bar to examine parts of the signal that are not on the screen.
8.2.4
Operating Controls
The operating controls, shown in Figure 8-4, are on the left side of the logic analyzer below the graphical
display.
Figure 8-4: Logic Analyzer Operating Controls
The logic analyzer will begin operating when a circuit simulation begins. The Stop button will stop the
logic analyzer, although it will not stop the circuit simulation. Halting the circuit simulation will
automatically stop the logic analyzer.
The Reset button will clear the logic analyzer display. If the simulation is still running this button will also
restart the logic analyzer.
The Reverse button toggles between a black and white background for the graphical display. Note that the
display will toggle only after a simulation has run.
8.2.5
Cursor Controls
The cursor controls, shown in Figure 8-5, are immediately to the right of the operating controls.
Figure 8-5: Logic Analyzer Cursor Controls
T1 shows the time for the logic signals indicated cursor 1, whereas T2 shows the time indicated cursor 2.
T2 – T1 shows the time difference between cursor 2 and cursor 1.
The  and  buttons allow you to move each cursor to the left or right. This allows you to position the
cursors more precisely than you generally can by directly clicking and dragging the cursors.
The numbers to the left to the time values for T1 and T2 show the values (in hexadecimal) represented by
the digital signals at the cursor position, with the top (Term 1) signal representing the least significant bit
and unconnected terminals assumed to be 0. In Figure 8-3 the signals at the position for cursor 1 are (0000
0000 0000 0)0112 = 316. Similarly, the signals for the position at cursor 2 are (0000 0000 0000 0)1002 = 416.
8.2.6
Clock Controls
The clock controls, shown in Figure 8-6, are immediately to the right of the cursor controls.
65
Using Multisim®: An Introductory Tutorial
Figure 8-6: Logic Analyzer Clock Controls
The “Clocks/Div” value specifies how many clock pulses each division should represent. In Figure 8-3
each division represents four pulses. This  and  buttons allow you to set the “Clocks/Div” value.
The Set... button opens the Clock Setup window, shown in Figure 8-7, that allows you to specify and
configure the clock that the logic analyzer will use to sample the data inputs.
Figure 8-7: Logic Analyzer Clock Setup
The Clock Source radio buttons determine the source of the sampling clock. Only one option may be
selected at a time. The clock frequency should be higher than that of the highest data input frequency to
help ensure that the logic analyzer does not miss any changes on a data input.
If the “External” button is selected the logic analyzer uses an external clock signal connected to the
“C” terminal (shown in Figure 8-2) to sample the data terminals.
If the “Internal” button is selected the logic analyzer uses an internal clock to sample the data
terminals.
The Clock rate controls specify the frequency of the internal clock. If an external clock is specified as the
clock source this value is ignored.
The Clock Qualifier value indicates whether a sample is taken if the “Q” input (shown in Figure 8-2) is
LOW (0), HIGH (1), or either (x). This allows you to determine when the logic analyzer begins to sample
data. If an internal clock is specified as the clock source Multisim will gray out this value so that it cannot
be configured.
The Sampling setting values specify how the logic analyzer will sample the input data.
The “Pre-trigger samples” setting specifies the number of samples preceding a valid trigger that the
logic analyzer will retain and display. This is useful if you wish to know what sequence of digital
signals led to a valid trigger.
The “Post-trigger samples” specify the number of samples following a valid trigger that the logic
analyzer will retain and display. This allows you to see what sequence of digital sequences occurred
after a valid trigger occurred.
The “Threshold volt. (V)” value indicates the voltage above which the logic analyzer will display data
samples as a 1 and below which it will display data samples as a 0.
66
Section 8 - The Logic Analyzer
8.2.7
Trigger Controls
The trigger controls, shown in Figure 8-8, are on the right side of the logic analyzer below the graphical
display.
Figure 8-8: Logic Analyzer Trigger Controls
The Set... button opens the Trigger Settings window, shown in Figure 8-9, that allow you to specify when
the logic analyzer checks for a valid trigger and the data patterns that constitute a valid trigger.
Figure 8-9: Logic Analyzer Trigger Settings
The Trigger clock edge radio buttons determine whether the logic analyzer should check for a trigger.
Only one option may be selected at a time.
If the “Positive” button is selected the logic analyzer will check for a valid trigger on the rising edge of
the sampling clock (i.e., when the sampling clock transitions from a LOW to HIGH level).
If the “Negative” button is selected the logic analyzer will check for a valid trigger on the falling edge
of the sampling clock (i.e., when the sampling clock transitions from a HIGH to LOW level).
If the “Both” button is selected the logic analyzer will check for a valid trigger both edges of the
sampling clock (i.e., whenever the sampling clock changes).
The Trigger qualifier setting specifies the level of the signal on the “T” input (shown in Figure 8-2)
required for the logic analyzer to search for a valid trigger. This setting is chosen from a drop-down list.
If “0” is selected the “T” input must be LOW for logic analyzer to check for a valid trigger.
If “1” is selected the “T” input must be HIGH for logic analyzer to check for a valid trigger.
If “x” is selected the logic analyzer will check for a valid trigger regardless of the level on the “T”
input.
The Trigger patterns settings specify the data patterns that constitute a valid trigger.
“Pattern A:”, “Pattern B:”, and “Pattern C:” specify the signal levels on each of the sixteen data
terminals that make up a valid trigger pattern. A “0” indicates the signal level on the specified data
terminal must be LOW, a “1” indicates that the signal level must be HIGH, and an “x” indicates that
the signal level can be either LOW or HIGH (i.e., a “don’t care”). If all three patterns have “x” values
for all sixteen data terminals, as shown in Figure 8-9, the logic analyzer will trigger on any pattern.
The “Trigger combination” setting determines which data patterns or combination of data patterns the
logic analyzer will use to determine a valid trigger. The drop-down list, accessed by clicking the 
button, contains 21 different pattern options, providing great flexibility in selecting a trigger.
67
Using Multisim®: An Introductory Tutorial
Once you have completing configuring the trigger settings in this window, click Accept to apply the
settings or Cancel to discard them.
8.3
An Example Application
This example will illustrate some of the basic features of the Multisim logic analyzer. To begin, use
Multisim to construct the circuit shown in Figure 8-10.
Figure 8-10: Example Application Circuit
To place the JK_FF_NEGSR flip-flops:
1) Click on the Place Misc Digital tool, shown in Figure 8-11, in the Component toolbar to open the
component browser.
Figure 8-11: The Place Misc Digital Tool
2) Select TTL in the Family window.
3) Scroll down the Component list to select the JK_FF_NEGSR flip-flop, as shown in Figure 8-12.
68
Section 8 - The Logic Analyzer
Figure 8-12: Selecting the J-K Flip-Flop with Negative Set and Reset
4) Click the OK button and place the flip-flop.
5) Repeat to place the other two flip-flops.
6) Place the other components and connect them together.
The wires to the logic analyzer can be any color, but it is helpful to color code them so that you can keep
track of which signal on the logic analyzer corresponds to which circuit wire. To change the color of a wire
or wire segment:
1) Right-click on the wire.
2) Select “Segment color” from the right-click menu.
3) Choose a color from the palette in the Colors window.
4) Click the OK button to accept the color change or the Cancel button to discard it.
Once you have completed the circuit, double-click the logic analyzer to access the expanded view. First,
configure the clock by setting the “Clocks/Div” value to 8 as shown in Figure 8-13.
Figure 8-13: Setting the Clocks/Div Value
Next, open the Trigger Settings window by clicking the Set... button in the Trigger section. Configure the
settings as shown in Figure 8-14, and click the Accept button to accept them.
69
Using Multisim®: An Introductory Tutorial
Figure 8-14: Configuring the Trigger Settings
The settings shown in Figure 8-14 specify three things:
1) The logic analyzer will sample the data terminals on the rising edge of the internal clock.
2) The T input must be LOW for the logic analyzer to search for a valid trigger.
3) The logic analyzer will trigger when it detects a 1002 on data terminals 4 through 2 and any value
on data terminal 1.
Clock the Run button to start the simulation. The logic analyzer should look similar to that in Figure 8-15.
Figure 8-15: Logic Analyzer Display with No Valid Trigger
Although the simulation time at the top of the scale continues to change the logic analyzer does not save or
allow you to view any of the data that has passed by. This is because switch S1 is holding the trigger
qualifier input “T” HIGH, as indicated by the “Trigg_Qua” signal, and the logic analyzer requires a LOW
to find a valid trigger. Note that the “Clock_Int” activity shows that the internal clock is running and that
the logic analyzer is sampling data to find a trigger although it cannot find one.
Click the Run button to stop the simulation and click the Reset button on the logic analyzer to clear the
display. Click the Run button again to restart the simulation and then press the SPACE bar to close S1.
After the logic analyzer’s data buffer fills and the simulation stops (after approximately 104 ms of
simulation time) click the Run button to stop the simulation and drag the scroll bar below the logical
analyzer’s graphical display area all the way to the right. The logic analyzer should look similar to that in
Figure 8-16.
70
Section 8 - The Logic Analyzer
Figure 8-16: Logic Analyzer Display with Valid Trigger
As Figure 8-16 shows, the logic analyzer detected a valid trigger that is indicated by the vertical line in
graphical display area. At this point the signal levels on data terminals 4 through 2 are 1002 and the level on
“Trigg_Qua” is LOW, qualifying the trigger so that the logic analyzer can accept the trigger and collect
data.
Click the Reset button to clear the display again and press the SPACE bar to open S1 again. The click the
Run button to start the simulation. After allowing the simulation to run for a few seconds, press the SPACE
bar to close the switch. The logic analyzer again will begin collecting data and stop once its buffer is full.
Click the Run switch to stop the simulation and drag the scroll bar beneath the logic analyzer’s graphical
area to the left until you locate the vertical trigger indicator. The logic analyzer should look similar to that
in Figure 8-17.
Figure 8-17: Trigger Qualified Just Before Valid Trigger Pattern Occurs
In Figure 8-17 the valid trigger pattern occurred almost immediately after the switch was closed, pulling the
“Trigg_Qua” signal LOW. This is not always the case however. The logic analyzer will trigger on the first
valid pattern that occurs after the trigger qualification is valid, but there is no way to determine when the
switch will close as the counter is running. As an example, consider the display in Figure 8-18.
71
Using Multisim®: An Introductory Tutorial
Figure 8-18: Trigger Qualified Well Before Valid Trigger Pattern Occurs
As Figure 8-18 shows, the switch happened to close several counts before the valid trigger pattern
occurred. In either case, the logic analyzer triggered on the first valid trigger pattern that followed the
trigger qualifier going LOW.
For further investigation, experiment by changing the trigger pattern and trigger qualification settings and
determining whether the results are as you would expect.
72
Section 9 - The Bode Plotter
9.
9.1
The Bode Plotter
Introduction
The Bode plotter, which resembles an oscilloscope, is not a real instrument. Its name comes from “Bode
plot,” which is a graphical representation of the magnitude and phase circuit as function of frequency. The
Bode plotter is useful for analyzing the frequency response of filters, amplifiers, and other circuits whose
behavior is frequency-dependent.
In this section you will:
9.2
9.2.1

Learn how to access the Multisim Bode plotter.

Learn the settings and purposes of the Bode plotter controls.

Investigate an example Bode plotter application with a passive low-pass filter.
The Multisim Bode Plotter
Accessing the Bode Plotter
To access the logic analyzer, click the Bode Analyzer tool (refer to Figure 9-1) in the Instruments toolbar.
Figure 9-1: Bode Plotter Tool
Figure 9-2 shows the minimized view of the Bode plotter. The two terminals on the left are for the input
(reference) signal and the two terminals on the right are for the measured signal.
Figure 9-2: Bode Plotter Minimized Views
Figure 8-3 shows the enlarged view of the Bode analyzer.
Figure 9-3: Bode Plotter Expanded View
The Bode plotter settings consist of five sections:
1) Graphical display
73
Using Multisim®: An Introductory Tutorial
2) Mode settings
3) Horizontal settings
4) Vertical settings
5) Plot controls
9.2.2
Bode plotter graphical display
The Bode plotter graphical display is the large area on the left side of the instrument. The display, shown in
Figure 9-4, is similar to an oscilloscope display.
Figure 9-4: Bode Plotter Graphical Display
The Bode plotter magnitude and phase displays each possess one cursor so that you can select specific
points on the Bode plot. The status bar below the display provides the magnitude (or phase) of the selected
point. Note that the left and right arrows move the cursor and do not scroll the graphical display, as the
Bode plotter always uses the horizontal and vertical settings that you specify to fit the data into a single
screen. You can also use the mouse to drag the cursor or right-click the cursor to open a right-click menu
similar to that for the oscilloscope cursor.
9.2.3
Mode Settings
The mode settings, shown in Figure 9-5, determine the Bode plotter mode of operation. Only one option
may be selected at one time.
Figure 9-5: Bode Plotter Mode Settings
If the “Magnitude” mode is selected, the Bode plotter will display the magnitude (gain) of the circuit
frequency response.
If the “Phase” mode is selected, the Bode plotter will display the phase of the circuit frequency
response.
9.2.4
Horizontal settings
The horizontal settings, shown in Figure 9-6, configure the horizontal axis for the Bode plotter display.
74
Section 9 - The Bode Plotter
Figure 9-6: Bode Plotter Horizontal Settings
“Log” specifies a logarithmic frequency scale and “Lin” specifies a linear frequency scale. Only one of
these options may be selected at one time.
“F” sets the final frequency and “I” sets the initial frequency for the measured frequency range.
9.2.5
Vertical Settings
The vertical settings, shown in Figure 9-7, configure the vertical axis for the Bode plotter display.
Figure 9-7: Bode Plotter Vertical Settings
“Log” specifies a logarithmic scale and “Lin” specifies a linear scale.
“F” sets the final vertical axis value and “I” sets the initial vertical axis value.
Note that if you select “Magnitude” as the Bode plotter mode then the vertical axis will represent gain (that
is, the ratio of Vout to Vin). A linear scale will represent the magnitude as the ratio of Vout / Vin. A
logarithmic scale will represent the gain in decibels.
If you select “Phase” as the Bode plotter mode then the vertical axis always will be linear and have units of
degrees.
9.2.6
Plot Controls
The plotter control settings, shown in Figure 9-8, allow you to work with the plotter data.
Figure 9-8: Bode Plotter Plot Controls
The “Reverse” button allows you to select between a white or black background for the Bode plotter
display, just as for the two-channel oscilloscope and logic analyzer displays.
The “Save” button allows you to save the measured data to either a .BOD text file or a .TDM binary file.
The “Set” button allows you to determine the resolution of the displayed data (i.e., the total number of data
points that the Bode plotter will collect).
9.3
Using the Bode Plotter
For this example you will examine the frequency response of an RC low-pass filter. The frequency
response of a filter is the output voltage referenced to the input voltage. First, build the circuit shown in
Figure 9-9.
75
Using Multisim®: An Introductory Tutorial
Figure 9-9: Low-Pass Filter Circuit
Next, select the Bode plotter tool from the instrument bar and place it above the circuit as shown in Figure
9-10.
Figure 9-10: Placing the Bode Plotter
The reference voltage of the filter, Vin, connects to the input of the Bode plotter. Connect the Bode plotter
input to Vin by connecting the IN “+” terminal to the Vin junction and the IN “–” terminal to ground. Your
circuit should look like that in Figure 9-11.
Figure 9-11: Reference Voltage Connected to Input of Bode Plotter
The output of the filter, Vout, connects to the output of the Bode plotter. Connect the Bode plotter output to
Vout by connecting the OUT “+” terminal to the Vout junction and the OUT “–” terminal to ground. Your
circuit should now look like that in Figure 9-12.
76
Section 9 - The Bode Plotter
Figure 9-12: Filter Output Connected to Output of Bode Plotter
The Bode plotter will measure the magnitude and phase of the output Vout relative to the input Vin.
The next step is to configure the Bode plotter. Double-click the Bode plotter to open the enlarged view and
set the Bode plotter settings to those in Table 9-1.
Table 9-1: Bode Plotter Settings
Mode
Magnitude
Phase
Horizontal
Vertical
Log
F: 1 MHz
I: 1 Hz
Log
F: 1 MHz
I: 1 Hz
Log
F: 20 dB
I: −80 dB
Lin
F: 0 deg
I: –90 deg
Now, simulate the circuit and examine the frequency response.
1.
Set the Mode setting to “Magnitude”.
2.
Click the Run switch to simulate the circuit and wait for the Bode plotter to display the plot.
3.
Click the Run switch to stop the simulation. The display should look similar to Figure 9-13. As
you should see, the magnitude of the output decreases as the frequency increases and C1 appears
more and more as a short. Below a certain frequency, called the –3 dB point or corner frequency,
the magnitude levels out.
Figure 9-13: Bode Plot Magnitude Display
4.
Right-click the magnitude cursor to open the right-click menu and select “Set Y_Value =>”.
5.
Enter “–3” for the value to find the –3 dB point for the filter. The display should now look similar
to Figure 9-14. As the display status bar shows, the corner frequency is about 159 Hz.
77
Using Multisim®: An Introductory Tutorial
Figure 9-14: Bode Plotter with Repositioned Magnitude Cursor
6.
Change the Mode setting to “Phase”. The display should look similar to Figure 9-15. As you should
see, the phase of the RC circuit changes from 0° at low frequency to –90° at high frequency.
Figure 9-15: Example Bode Plotter Phase Display
7.
Right-click the phase cursor to open the right-click menu and select “Set Y_Value =>”.
8.
Enter “–45” for the value, which should correspond to the corner frequency of the filter. The display
should now look similar to Figure 9-16. As the display status bar shows, the –45° frequency is about
159 Hz.
Figure 9-16: Bode Plotter with Repositioned Phase Cursor
9.
78
Try experimenting by changing the values of C1 and R1 and determine how this affects the Bode
plotter results. Then try exchanging the positions of C1 and R1 and see how this affects the results.