Updated February 10, 2014

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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. Download Multisim Blue 14 free – Schematic capture, simulation, PCB design, and BOM. NI Multisim 14 represents a best-in-class engineering design experience, both in the classroom and in the laboratory performing SPICE simulation or measurements on prototypes. With strong roots as an exploratory virtual electronics workbench, Multisim has.

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¶

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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.

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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

2.7.2. Mistakes and Solutions¶

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

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

So here is the tutorial, where I will discuss how you can get started with Multisim, which is one of the best electronic circuit simulator software available and will also discuss how you can simulate electronic circuits using the software.

From our smartphones to the computer that we use, and every other electronic gadget to accomplish a lot of small tasks, there is one thing in common. They all have electronic circuits, which include microprocessors, microcontrollers and small other circuits that help the gadgets do the magic. If you are into Electronics, a professional, hobbyist or a student, playing with electronic circuits is something that you have to do almost every single day and things might not go perfectly every time. In the worst-case, the circuit might go out on smoke and at other times, you might not get the appropriate output for which you have designed the circuit. Yes, life seems frustrating at times!

That’s when simulation plays an important role. If you are reading this article, you might already know about what simulation is all about, but let me explain it in one line. Simulation is a kind of a virtual arrangement where you can have an idea of how a system will function when it is implemented in real life. That’s the simplest definition of simulation and it varies depending upon what you want to simulate. So if you are working with electronics, simulation can save both your money and time and help you check whether you are getting the appropriate outputs before you can proceed with actually building a circuit from scratch. Just in case things don’t go as planned, you can again make the necessary modifications and find out whether it is working, to give your circuit a final shot.

What is Ni-MultiSim?

The NI Multisim is a simulation software for professionals, students and Educational purpose. It is a complete package to perform different exercises on electronic circuits. Multisim has an integrated chain of tools for circuit detection, simulation and layout allows the interdisciplinary use of the product. Seamless integration with NI Multisim optimizes the design experience, ensuring you can easily transfer schematics to PCB design and effortlessly annotate changes between layout and capture. With a comprehensive component library of components, whose characteristics correspond to the real components, circuits from analogue and digital circuit technology, mechatronics, microcontroller technology, Function generator, oscilloscope, logic or spectrum analyzer, in combination with interactive components, simulation are possible.

It is available in multiple editions, the Multisim for Education comes with 30+ intuitive simulated instruments, 20+ easy-to-configure analyses, and interactive components. Educational entities can use this circuiting software to teach analogue and digital circuit technology and power electronics in classroom and laboratory exercises. Students can retrieve designs from NI Multisim interactive SPICE-based simulation or from scratch using parts from the built-in Ultiboard database.

Available in two versions Mutlisim for Education and Multisim for Designers, of course, the designer one comes with extra features and capabilities such as 19,000+ Components Verified by Semiconductor Manufacturers; advanced Power Design With MOSFETs and IGBTs From NXP and International Rectifier; Multisim and Ultiboard Training Classes and more…

Before purchasing the Trial version is available to experience it.

MultiSim Supported Operating Systems:

• Windows 10
• Windows 7 (SP1) 32-bit
• Windows 7 (SP1) 64-bit
• Windows 8.1
• Windows Embedded Standard 7 (SP1)
• Windows Server 2008 R2 (SP1) 64-bit
• Windows Server 2012 R2 64-bit

Downloading, installing and using Multisim

Step 1: You can purchase and get a license for Multisim from here, and if you already have a license, you can download a copy or trial version of Multisim from here.

Step 2: Once downloaded, the installation of Multisim is the same as the installation of other Windows programs.
So, after the installation of the program is complete, it is time I should talk about how you can start stimulating your electronic circuits.

Step 3: Just open NI Multisim from your desktop or simply by searching for the same on your Windows start menu.

Step 4: I will show you, how you can build and simulate a half-wave rectifier using Multisim. A half-wave rectifier is the most rudimentary circuit to convert AC or alternating current to DC or direct current.
I will not keep any kind of filters and other sophistication within the circuit, as I just want to show you, how you can deal with circuits on Multisim, and proceed with even bigger projects.

Step 5: In this circuit, for making a half-wave rectifier, I will need 5 elements, a diode, an AC voltage source, a resistor as the load; a ground, and the cathode ray oscilloscope (CRO) or simply an oscilloscope.

Step 6: Let me start by adding the necessary elements for making the circuit. Simply use the shortcut key combination ‘Ctrl+W’ or click on ‘Component…’ under the ‘Place’ tab to find a list of elements that is available within the program.

Step 7: I will recommend you to use the shortcut key combination as it will be handy, and adding electronic components is something that you will need every time on Multisim.

Step 8: Just type in the element that you need, in the search box, and add the appropriate element to your circuit. I am adding the four elements by searching for them in the search box. I am using a 1 k Ohm or a 1,000 Ohm resistor as a load. You can even use a different value.

Step 9: If you can’t find the element that you are looking for, just select the appropriate group to find the element. For example, if you are looking for a transformer, just select the group ‘TRANSFORMER’ and place the appropriate one.

Step 10: To add the elements, just select the element you want to add and click on ‘OK’. Now drop it anywhere within the area as per your requirements.

Step 11: Once you are done adding all the elements, simply click on ‘Close’ to exit the component window, and proceed with connecting the elements.

Step 12: Now simply connect the ends, as per your circuit diagram, by clicking on one end of the element, and then by releasing the click, where it is to be connected.

Step 13: Keep doing this, unless your circuit is complete. My half-wave rectifier is complete now.

Step 14: To start simulating the circuit, click on the ‘Run’ button, or simply hit the ‘F5’ button.

Step 15: Depending upon your circuit, you can see the output in a digital display, voltmeter, ammeter, or any other element. My output will be on the oscilloscope, and to find that, I will have to double-click to see the wave-form.
Here is the output wave-form, which is the same as the output generated by a half-wave rectifier.
You can even adjust the scale and get the output exactly the way you will see in a lab, with the abundance of options that are available in the oscilloscope window.

Step 16: To stop the simulation, just click on the ‘Stop’ button. You can even ‘Pause’ the simulation in between if you want to.

Step 17: You can even double-click on most elements to change the parameters. For example, you can double click on the ‘AC Voltage’ element to change the peak voltage, frequency, damping factor, delay, phase, and other perimeters.

You can repeat the same with other elements in the circuit, as well.

Multisim is a pretty powerful program, and you can even simulate the microcontroller-based circuits, as well, with Multisim. I will cover them in the coming days for sure.

Well, the simulation on Multisim might not be 100% accurate, as the electronic components available in the market aren’t perfect. Multisim will automatically implement the most common inaccuracies on the components. For example, the forward voltage drop on a real diode is around 0.7 Volt, and it automatically applies that, when you simulate circuits. Depending upon how complex a circuit is, it might consume significant CPU resources for the complete simulation to run effortlessly.

However, you can even remove the inaccuracies like, remove the 0.7 Volt voltage drop and change it to an ideal diode, just in case you need it under certain circumstances.
When you are actually making an electronic circuit, there are different things that come into play, which include, the resistance of the wires that you are using, connection faults, temperature differences, and many other things.
Hence, Multisim is the perfect tool to find whether your circuit is overall functional. Multisim is however only available for Windows, which is kind of disappointing for Linux and macOS users.

So that was all about how you can install and use Multisim on your computer. Do you have any questions? Feel free to comment on the same below.

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