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Elective 3 ECE Computer Aided Design

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Machine Problem #02

Semiconductor Devices Analysis Using WinSpice (Part 1)

Objectives

1. Simulate active devices such as diodes and bipolar transistor circuits using WinSpice.

2. Use the transient, DC and AC analysis tools of WinSpice

Introduction

As stated before, WinSpice can simulate semiconductor devices such as diodes, BJTs,

MOSFETs, etc. These devices require two pieces of information to be described in a netlist. First is the

node information, where, just like the passive components, you assign nodes at the terminals of these

devices. Refer to the Spice Manual for specific details. The second piece of information is the model

statement. The model statement describes internal device parameters and physics which determines the

small and large signal behavior of these devices.

WinSpice can perform different types of analysis: DC, AC and transient. The DC analysis portion

of SPICE determines the DC operating point of the circuit with inductors shorted and capacitors opened.

The DC analysis options are specified on the .DC, .TF, and .OP control lines. A DC analysis is

automatically performed prior to a transient analysis to determine the transient initial conditions, and prior

to an AC small-signal analysis to determine the linearized, small-signal models for non-linear devices. If

requested, the DC small-signal value of a transfer function (ratio of output variable to input source), input

resistance, and output resistance is also computed as a part of the DC solution. The DC analysis can

also be used to generate DC transfer curves: a specified independent voltage or current source is

stepped over a user-specified range and the DC output variables are stored for each sequential source

value.

The AC small-signal portion of SPICE computes the AC output variables as a function of

frequency. The program first computes the DC operating point of the circuit and determines linearized,

small-signal models for all of the non-linear devices in the circuit. The resultant linear circuit is then

analysed over a user-specified range of frequencies. The desired output of an AC small-signal analysis is

usually a transfer function (voltage gain, transimpedance, etc.). If the circuit has only one AC input, it is

convenient to set that input to unity and zero phase, so that output variables have the same value as the

transfer function of the output variable with respect to the input.

The transient analysis portion of SPICE computes the transient output variables as a function of

time over a user-specified time interval. The initial conditions are automatically determined by a DC

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analysis. All sources which are not time dependent (for example, power supplies) are set to their DC

value. The transient time interval is specified on a .TRAN control line.

There are other analysis that can be performed using WinSpice but we will concentrate mostly on

these three analyses.

This is the first of the two parts on the exercises on semiconductor analysis using WinSpice. Inthis particular exercise, we will simulate diode and obtain the current-voltage characteristics of a bipolar

junction transistor.

Procedure:

A. Diode circuit Transient analysis

1. Create the SPICE netlist of the circuit shown below.

Refer to the SPICE manual on the details of defining source voltages and resistors. Note that the

voltage source is a sinusoidal source, hence its SPICE card must be

V1 SIN(0 10 1k 0 0)

Interpret the SPICE card above.

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2. For the diode, use the following syntax:

D

where NA is the node assigned to the anode, NK to the cathode, model name is the reference

name to be used by the diode in the .model statement and the rest are optional parameters, details

V1

10 Vpk

1kHz

0

D1

1N4001

R1

5

V210 V

R210

D21N4001

R3

5

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of which are in the manual. Use 1N4001 as the model name and supply this model statement to the

SPICE netlist.

.MODEL 1N4001 d (

+IS=3.19824e-08 RS=0.0428551 N=2 EG=0.784216

+XTI=0.504749 BV=53 IBV=0.0001 CJO=4.67862e-11+VJ=0.4 M=0.469632 FC=0.5 TT=8.86839e-06

+KF=0 AF=1 )

Although the circuit uses two diodes, you do not need to specify two .model statements. Just use identical

model names for the two diodes in their circuit description and the model statement will be applied to both.

3. Obtain the waveform across R2 using transient analysis. The syntax for transient analysis

.tran

tstep is the printing or plotting increment for line printer output; tstop is the final time and tstart

is the initial time; uic is used when you want your transient analysis to start at the initial conditions

defined for components. For details of the usage, refer to manual. For this exercise use the syntax

.tran 1u 6m

What does this SPICE card mean?

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4. To obtain the waveform across R2, use the .plot or .print function of the SPICE. Add the following SPICE

card to your netlist.

.plot tran V(2) *this is assuming that you assigned R2 at nodes 2 and 0

This causes the SPICE to plot the results of the transient analysis at the specified node. V(2) is the output variable

in this case. You can place as many output variables as you like, separated by spaces.

What is the difference between the .plot and .print command?

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5. Save your netlist, not forgetting the .end statement at the last line. Then run the netlist using WinSpice.

6. WinSpice would then compute for the results of the analysis. If this takes long, just press the ESC button. Then a

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plot will appear. This is the output voltage waveform at the node you have specified in your netlist. Copy and

paste the waveform on a separate sheet of paper. To copy and paste the plot on an open word processor

document, on the plot itself, click on Edit, Copy, and then paste this on the open word processor document. Based

on this plot, what kind of circuit is this?________________________________.

Briefly discuss the operation of the circuit in relation to its output waveform.

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7. Determine the peak value of the voltage at this node. This can be done by zooming in to the peak of the waveform

or printing the results in an external file. Record the value below:

Peak Voltage Value

8. Edit your netlist to obtain the waveform of the current passing through R2. To do this, insert a voltage source in

series to R2. Name this VR2. Then assign your output variable as I(VR2). The plot that will come out is the

waveform of the current flowing through R2. Copy and paste this waveform on a separate sheet. Then obtain the

peak current value from this waveform. Record the value below.

Peak Current Value

9. On a separate netlist, repeat steps 6 through 8 with D2 reversed in polarity. How does this compare to the

previous results. Why is this so?

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Peak Voltage Value

Peak Current Value

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10. Discuss the use of transient analysis in WinSpice.

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11. Do a research on diode parameters as stated in the model statement. Attach this on a separate sheet

of paper.

B. Bipolar Junction Transistor Simulation Current-Voltage Characteristics

12. Write a SPICE netlist for the circuit below

Use the following model statement for the transistor

.MODEL 2N2222A npn

+IS=2.04566e-13 BF=296.463 VAF=10 BR=0.481975

+RB=3.99688 RE=0.0857267 RC=0.428633

+CJE=1.09913e-11 VJE=0.99 MJE=0.23

+TF=2.96787e-10 CJC=3.1941e-11 VJC=0.4

+MJC=0.85 CJS=0 VJS=0.75 MJS=0.5

Leave the value of VCC blank. Set the value of IBB to 10 uA and RB to 10 megaohms. Also add a

zero-voltage source called Vic to measure the collector current.

13. Do a DC analysis on the circuit to obtain its voltage-current characteristics. To do this, add the SPICE

card below.

.dc VCC 0 5 0.1

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This will cause the SPICE to vary the values of VCC while computing for the output variable. The

current voltage characteristic of a BJT is identified by the relationship between the collector-emitter

voltage (VCE) and the collector current (IC). In the circuit, VCC = VCE and therefore we can plot the

VCE versus IC transfer function by adding the SPICE card

.plot DC I(VIc)

14. Run the simulation. Paste the plot on a separate sheet of paper. Interpret this plot.

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15. We can obtain this current-voltage characteristics for various values of the base current. Edit your

netlist to do this, obtaining the current-voltage characteristics for 10 uA, 20 uA, 30 uA, 40 uA and 50

uA base currents. Write the SPICE card for the DC analysis below and paste the resulting plot on a

separate sheet of paper.

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16. Do a research on the different parameters of the BJT as stated in the model statement. Include the

things you found out about these parameters and relate them to the plots you obtained in steps 14

and 15. Attach this on a separate sheet of paper.

References

WinSpice3 Users Manual by Mike Smith, 2004