Multisim Tutorial Using Bipolar Transistor Circuit¶ Updated February 10, 2014. This is a quick tutorial for teaching students of ELEC 2210 how to use Multisim for bipolar transistor circuit simulation. It is written such that no prior Multisim knowledge is required. Multisim is the preferred SPICE circuit simulator for use in EE-331. The current version that is installed on the general purpose computers in the EE Department is 11.0. Multisim was originally developed by Electronics Workbench in Canada, along with the companion printed circuit board (PCB) layout tool Ultiboard. Jul 05, 2018 Trusted Windows (PC) download Multisim 10.0.1. Virus-free and 100% clean download. Get Multisim alternative downloads.

A program that takes electronic circuit design from the real world into the digital world

NI Multisim allows you to design an electronic circuit right on your computer. It is simple and easy to use, making it great for educators and students. NI Multisim includes all kinds of electronic components in its huge database.

Electronic circuit design made easy

It’s hard to find anything better for designing, analyzing, and developing electronic circuits. NI Multisim is a perfict fit for electronic engineers and technicians alike.

Within the NI Multisim database, you can find everything you need for building electronic circuits. As well as the electronic circuits, there is a predefined schema. It also includes VHDL, SPICE simulation, and a PCB generator.

It is simple for beginners and students because of its fully integrated environment. You’ll find plenty of useful information within NI Multisim. You can model and amend more difficult concepts easily. It is possible to manipulate and navigate the program layout to your specific needs.

You can use NI Multisim for finding errors with your circuit plan, too. This feature is excellent because you can learn from any mistakes you make in a cost-free environment. Yes, if you happen to break anything you create in this program, you don’t have to spend money on new parts! NI Multisim models prototypes, and checks that your design idea is robust. This is a huge time saver for users and helps develop your circuit building capabilities.

Finally, you can load tons of extra modules you may need for certain processes within your circuit. This is especially useful if you want to program microcontrollers using ASM or C methods.

Where can you run this program?

This program is designed to run on Windows only. It is currently not available for Mac OS or Linux.

Is there a better alternative?

No, there is no better alternative. Regardless of whether you are a complete beginner without any experience using SPICE or an expert on the subject, this program is for you. Circuit Simulator, QUCS, and Ktechlab may run on other OS’s, but they are not as capable or user-friendly.

Our take

NI Multisim is the best solution for electronic circuit design. It’s full of features, and free to use. The program is great for knowledge development. It is useful throughout your career in circuit building.

Should you download it?

Yes, download it now. NI Multisim is simple to use, and although it looks a little out of date, this simplicity is its power.

Highs

• Little tech knowledge required
• Designed for beginners
• Powerful

Lows

• Processes can be slow
• Cluttered appearance
• Time-consuming installation

NI Multisimfor Windows

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Updated February 10, 2014

This is a quick tutorialfor teaching students of ELEC 2210 how touse Multisim for bipolar transistor circuit simulation.It is written such thatno prior Multisim knowledge is required.

My experience with teaching SPICE and Multisim in ELEC2210is that live tutorials done in classturned out to be most effectivecompared to written tutorial and video tutorials, andthat is what we will rely on in the later partof this class for CMOS circuits.I will still provide screenshots embeddedin the notes of relevant chapters.

With Multisim, there is not a free version,this makes teaching in classroom more difficult.If you have purchased student version, you can bring your laptopto class.

Multisim is available in ECE 308 and310 computer labs, with Elvis drivers.It is also available in the basementcollege of engineering computer labs, it may not havethe Elvis drivers.This likely means all other engineering computer labs shouldalso have it, e.g. in Shelby or Aerospace labs.

It is in some case easier to use thanother SPICE based simulators,e.g. Pspice,butcan be harder to use in other cases.One practical reason for usingMultisim is that it supportsvirtual instruments simulation,which will be useful asthe new 2210 labs use the new NI ELVIS II+ prototypecircuit board.

2.1. Goal¶

1. Introduction to using Multisim for SPICE like circuit simulation
2. Schematic capture
3. Analysis setup with DC sweep examples
4. Nested sweeps (use source 2)
5. Output inspection using grapher
6. Bipolar transistor model parameter editing
7. Understand bipolar transistor I-V characteristics

2.3. Getting Started¶

First, launch Multisim from programs - this will vary depending onyour PC configuration, an example of starting Multisim is given below:

The design environment should pop up as follows:

Figure 2: menus of Multisim design environment

A new design file, with a default named “Design 1”, is created witha blank schematic sheet, also named “Design 1”.On the left is the navigation pane.

Note the standard components toolbars, the virtual components toolbar, and thevirtual instruments toolbars. For teaching purpose, we will first use virtualcomponents.Unfortunately, by default, the virtual components toolbar is not shown, so we will needto turn that on as follows:

These toolbars will come in handy in placing components, and save a lot oftyping, scrolling, searching and clicking.

2.4. Schematic Capture¶

2.4.1. Placing Components¶

2.4.1.1. Real versus Virtual Components¶

Any part that can be placed onto the schematic is called a component.There are real as well asvirtual components:

• real component is tied to a part you can buy, and they haveproperties that cannot be changed, e.g. beta of a transistor.They also have a known and fixed physical size, whichwill be important to consider if we were to build a printed-circuit-board (PCB).We will need to use realcomponent whensimulating a circuit with a part we use in the physical lab, e.g. the 2N3904bipolar transistor.
• virtual component is for simulation only.For instance, a virtual transistor can have any beta, e.g. 100, 200, or 10, or4.2210 is we so wish.We can simulate designs with continuous even hypothetical values ofparameters.Virtual component is also particularly useful forlearning and teaching, since we canuse simplified model parameters to facilitate comparison betweenfirst order theory and circuit simulation.

2.4.1.2. Procedures¶

One can in general use the component toolbar for finding components.For this tuorial, let us use the virtual component toolbar.

Let us now place a few components so that we can simulate the output curvesof a bipolar transistor.

1. Place a virtual NPN transistor as follows:

2. Place a DC current source which we will use to supply base current as follows:

   Figure 5: place the base current source

   The latest Multisim version has removed “VIRTUAL” from the name ofthe virtual parts. The picture was taken with a previous version.

3. Place a DC voltage source, which we will use to set the collector-to-emitter voltage VCE, as follows:

4. Last but not least, place ground as follows:

   Figure 7: place ground

5. Select and move around your components to your liking.

   1. Click a single compoent to select it. Esc to deselect it.
   2. Hold Shift, then click to select multiple components.

DC Voltage Source is DC Power Source in Multism

The DCvoltagesource is actually called DCpowersource. If youhad used the search feature, and typed in DCvoltagesource, the search wouldhave returned no result.

Always Place Ground!

Ground is under Power_sources in Multisim.Like other SPICE based circuit simulators, it is mandatory tohave the proper ground which is the reference point for allthe nodal voltages simulated.This ground is known as the 0 node in most SPICE based simulators.

2.4.2. Wiring¶

Wiring is both particularly simple and particularlydifficult in Multisim. The chanceis that you will first find the wiringsimple or simpler than other programs you used before,at least forsimple circuits.Whenthe cursor is close to the unconnected end of any component,it will change into a small black connection dot and crosshair.A click on the end of the component starts the wiring.Move the cursor to where you want it to be connected.The routing of the wire isby default automatic, but manual adjustment is possible.

A very important limitation is thatone of the two pins or component ends you are trying towire together must be unconncted.If both pins are connected, which can easily occur,you will encounter problem of existing connections beingbroken as new wiring is added.I encoutered theproblem within 3 minutes of learning Multisim the first time, Spring 2011, in evaluating Multisim and NI Elvis for our then potential ECE lab upgrade.Fortunately a solution was found, which we willaddress in another tutorial. For now I want youto be aware of this issue in case you encounter it.

To alleviate the problem, I recommend you to always findand click an unconnected component terminal first for wiring.

Wire your components together as follows:

Figure 8: schematic for forced IB output curve simulation

2.4.3. Use Better Net Names¶

A good circuit simulation practice is to name the circuit nodes (nets) meaningfully.By default, all nodes are named numerically or with someconventions only understood bythe program itself.In this case, we want to rename the base node b, and the collector node c.That way, we later can refer to the base voltage by v(b) in expressions so wedo not have to try to remember that node 2 is the base node.Later on in CMOS complex logic gates where we can have 20 or 30 nets, it will notbe even possible to try to remember the meanings of all nets by number.

The best way to look at all the nets information is through the Nets tab inthe Spreadsheet view as shown below:

Just click on a net name to make changes, this includes name and color. The color changewill be necessary later on. For now, let us just make name changes as follows:

Figure 10: procedures of changing net name

Your schematic now looks like:

2.4.4. Change Component Values¶

Often the default component values need to be changed.For instance, the transistor model parameters need to bechanged, which we will discuss in greater detail below.For now, we notice the default value for the current source we useto drive the base is 1A, which is too much for most if not alltransistors. Let us change that to 1uA instead to begin with.In general, double clicking a component opens up a window forchanging values of its properties. Try this on the base current source:

Figure 12: schematic with meaningful net names for 1uA base current

Let us use the default transistor model parameters to proceed withI-V simulation. We will come back to transistor model soon.

2.4.5. General Editing¶

Much of the usual editing key bindings inother computer programs will work in Multisim, including:

• Ctrl + C for copy
• Ctrol + X for cut
• Ctrl + V for paste
• Delete for delete
• Ctrl + Z for undo
• Ctrl + Y for redo
• Ctrl + S for saving

When multiple instances of an existing component, e.g. ground, or a voltage source,are needed. We can use Copy and Paste.

2.5. DC Sweep Analysis¶

While Multisim provides “instruments” like simulation, which we will coverlater,these “instruments” often have limitations. We can have morecontrol or flexibility using Analysis under Simulate.This is close to the Analysis in other SPICE based simulators.

One of the best ways of understandingoperation of a transistor or a circuitis to examine how an output of interestresponds to an excitation change.For the NPN transistor in question,we want to examine how the output current, in this case,the collector current, changes when the collector-emitter voltage VCE, whichis set by V1, sweeps say from 0 to 1V for a given fixed base current of 1uA we setearlier.This can be achieved by sweeping V1, and doing a DCanalysis at each V1.

2.5.1. Single Source Sweep¶

The procedures of V1 (VCE) sweep for a given I1 (IB) are as follows:

1. From the main menu,select Simulate -> Analyses -> DCSweepas follows:

2. Set the AnalysisParameters tab as follows:

   Figure 14: dc sweep setting for Ic-Vce curvesimulation under a single Ib input

3. Click the Output tab, select I(Q1[IC]),click Add to add it toSelectedvariableforanalysis as shown below:

   Figure 15: dc sweep output tab setting for Ic-Vce curve simulation

4. Click Simulate, a grapher window will pop up after simulation is complete,showing the output we selected earlier, IC of Q1:

5. You can change the black background by clicking on thefollowing icon as shown below:

   Figure 17: how to change background of a graph

   Figure 18: Ic-Vce curve simulated for Ib=1uA with white background

Practice

Plot out VBE and VBC on another graph. Note that emitter is grounded.You will need to use expressions to calculate VBC.

Solution

In Grapher, select from menu,Graph -> AddtracesfromLatestSimulationResults.A new window pops up. Check Tonewgraph. Add expressions. Your resultshould look like:

Figure 19: Vbe and Vbc, two junction biases as a function of VCE for Ib=1uA

In this case, having meaningful net names greatly simplifiesconstruction of expressions.

2.5.2. Nested Two Level Sweep¶

We have obtained a graph of IC vs VCE for a given IB.Next, we would like to know how this curve changes as base current change.What we need to do is to repeat the above DC sweep of V1for different values of I1 which controls IB.

To achieve this, just go back to the Analysisparameters tab,and check usesource2. Then set the start, stop and increment ofthe 2nd source, I1 in this case, as shown below:

Figure 20: how to make nested two level DC sweep,IC-VCE for multiple IB as example

The result is a family of IC-VCE curves for the specified basecurrents:

Note

The red rectangles are added, not from the grapher.

The legends at the bottom indicate values ofthe 2nd source, in this case, I1 or IB.

Tab name and title can both be changed.You can zoom vertically, horizontally using the zooming tools.

2.6. Device Modeling¶

2.6.1. Why Modeling¶

There is no question that computer simulations usingSPICE like programs such as Multisim are absolutely necessary.The accuracy of circuit simulation, however, is only asgood as the accuracy of the device models used internallyto describe device electrical characteristics.

The biggest pitfall of circuit simulation islack of necessary attention to device modeling.Far too often, students and engineers simplyassume the models they have downloaded from the Internet or obtained by other meansarecorrect for the devices they are using to build circuits, meaningthe models can faithfully reproduce measured electrical characteristics, atleast for the biasing condition and frequency of operation in question.Sadly, in most cases, such models are NOT carefully calibrated againstmeasured electrical characteristics.

Extracting or sometimes adjusting parameters ofa device model to match measurement is essential. Once we havea calibrated device model, our circuit simulation results will bepretty accurate. One of my research areas is device modeling, which includesnot only extracting model parameters to match measured data, but also developingphysics based new models when existing models simply fail to work, no matter howparameters are extracted. My most recent project on device modeling is to successfullydevelop new transistor models to enable integrated circuit design over thewide temperature range from 43K to 393K. The models were used todesign integrated electronics that can operate in space as is without warm boxes.

So what if I do not have a good model? Likely the simulation result is justgarbage. Many people call this garbageingarbageout.

In our lecture I have made an effort in explainingthe solid-state physics basis of bipolar transistor and developingthe essential I-V equations that are at the heart ofbipolar transistor models used in all circuit simulators.You are equipped with the knowledge to understand the essential transistor modelequations and list of parameters.

You might wonder how can a generic virtual transistor model representany transistor? I wondered as a sophomore student. The answer is it cannotpossibly do so. The so-called realcomponent transistors often use the sametransistor model equations, but with different model parameters extracted for thattransistor. However, the general paractice of serious designers is to stillcalibrate its model parameters against measurement. If calibration is not possible, at leastwe want to find out if the simulation matches measurement for characteristicsof interest.

As a first step towards successful circuit simulation,we want to know how to find out what device modelis used in our simulator, andhow to modify model parameters. We can for instance, measuretransistor’s forward beta BF and reverse beta BR, saturation current IS, andput them into Multisim, rather than relying onthe generic default values for bipolar transistor.

2.6.2. Editing Model Parameter in Multisim¶

To edit model parameters of a transistor,

1. double click the transistor

2. click Editmodel

   Figure 22: how to edit transistor model parameters

The first entry in the model parameter table is IS, thesaturation current.The second entry is BF, forward beta.The third entry is NF, foward ideality factor, incorrectly called“forward current emission coefficient”.You can also see the reverse beta BR and reverse ideality factor NR.

As you can see, a transistor model has many more parameters than what we usein hand analysis.

You can edit a model parameter’s value here.

You may use several different transistors in the same design. Theywill need to have different model parameters.It is important to know what parameters each transistor use.

The most convenient way of examining the models and/or model parameters eachtransistor uses is to view the netlist.

On main menu, select view -> SpiceNetlistViewer.A window of the netlist pops up. You can copy the netlist to clipboard.The netlist for the above circuit is shown below:

You may notice that the parameter list is not as long asin the model parameter table we saw earlier.This is simply because only parameters withvalues different from the default values needto be stated.If a parameter is not shown, it takes on the default value.

2.7. Homework Problems and Solutions¶

The best way to learn is to experiment yourself. Below are some homework problems. You will needto use expression.

2.7.1. Homework Problems¶

Use Virtual NPN, edit model such that IS=1e-15, BF=200, BR=10. Read (and follow) the new tutorial first.Complete the following simulations and plotting tasks. You need to create a circuit schematic thatis designed to complete the required simulations first. You can also read mistakes made by past students given below at the end ofthis tutorial.

1. Simulate IC and IB as a function of VBE when VBC is set to zero.Range of VBE is from 0.2 to 1.0 V in step of 0.01V.Use log scale for y-axis (current axis).This type of plot is known as Gummel Plot widely usedin experimentally characterizing transistors.

   Your circuit schematic should look like this for Gummel plotsimulation:

   Figure 23: schematic for simulating Gummel characteristics

2. Using the simulation results of the previous step,plot out beta as a function of VBE, defined as the ratio of IC to IB using expressions.

   Comment on if the beta simulated is consistent with BF value you put in.

3. Simulate IC as a function of VCE for several VBE values.VBE is from 0.65 to 0.7V, in step of 0.01V. VCE is from 0 to 3V, in step of 0.001V.Note VCE sweep is primary, i.e. the first source to be swept.

   Indicate the forward bias region and saturation region on the IC-VCE output plot. Your circuit should look like this:

   Figure 24: schematic for simulating forced-VBE (or voltage drive) output characteristics

   Your output should look like the graph below, but your numbers will be different:

   Figure 25: sample plots of forced-VBE (or voltage drive) output characteristics

   You will need to use VBE as source 2.This type of plot is known as forced VBE output plot.

4. Simulate IC as a function of VCE for various IB values.This is known as forced IB output characteristics.IB is from 0.1uA to 1uA, in step of 0.1uA. VCE is from 0 to 1.5V in 0.01V step.

   Indicate the forward bias region and saturation region on the IC-VCE plot.

Need screen shots of:

1. schematic
2. model parameter list, you can attach the netlist for this
3. analysis parameter settings
4. all simulation result plots with proper labels

Multisim 14

2.7.2. Mistakes and Solutions¶

Below are mistakes I have seen in helpingstudents debug Multisim simulation.

Multisim Live

1. Incorrect circuit configuration. For instance, VCB is placed between C and E.

2. Use default values for components. For instance, when you add a voltage source and use it for VCB, the default 12V is toohigh, and breaks down the transistor.

3. Plot out currents, IB and IC, and ratio of IC/IB all together. In general, this does not make sense. Use new graph as shownabove for VBE and VBC plotting in forced-IB output circuit.

4. An expression, e.g. beta = ic/ib, must be created. An example of how to do this is:

   Figure 26: how to create a new trace using expressions after a simulation

5. Use default labels. Default labels are often voltage even if you are plotting currents. Change them manually to avoid confusion.

   Figure 27: forward mode Gummel plot, i.e. IC and IB versus VBE. VBC=0

6. Your beta (IC/IB) should look like htis:

   Figure 28: how to create and add a new trace using expressions after a simulation