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SPICE Tutorial: Creating Netlists for Diff. CMOS Amplifier (ECE 3110, Univ. of Utah) - Pro, Exams of Electrical and Electronics Engineering

University of Utah (The U)Electrical and Electronics Engineering

Prof. R. R. Harrison

A tutorial on using spice for simulating a differential cmos amplifier circuit. It covers creating a new netlist file, adding dc supplies, defining devices and components, and simulating dc operating points, time domain response, ac response, and step response. It also explains how to use the .op, .tran, and .ac commands, and how to plot the results.

Typology: Exams

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Uploaded on 08/30/2009

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Brief Spice Tutorial

ECE 3110, University of Utah, Fall 2002

By now, you have used SPICE in at least one other class. As a result, some familiarity is

assumed. This tutorial will focus on the usage of input files for netlists. Some students

may have experience using only the schematic capture version of PSPICE, but this

tutorial should enable the transition to be less troublesome.

Since you already know the basics, a detailed example of a differential CMOS amplifier

will be simulated and used as the basis of this tutorial.

The following circuit, shown in the figure below, will be simulated in the following

ways: 1) the DC operating points, 2) the time domain response to a sinusoid (transient

test), 3) the AC response (Bode Plot), 4) and the step response.

Figure One: CMOS Differential Amplifier

The first step will be to create a new .cir file. The first line of a netlist file must be a

comment, which is any line beginning with they symbol “*”. The next thing needed is

Discover Exams of Electrical and Electronics Engineering University of Utah (The U)

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Download SPICE Tutorial: Creating Netlists for Diff. CMOS Amplifier (ECE 3110, Univ. of Utah) - Pro and more Exams Electrical and Electronics Engineering in PDF only on Docsity!

Brief Spice Tutorial

ECE 3110, University of Utah, Fall 2002

By now, you have used SPICE in at least one other class. As a result, some familiarity is

assumed. This tutorial will focus on the usage of input files for netlists. Some students

may have experience using only the schematic capture version of PSPICE, but this

tutorial should enable the transition to be less troublesome.

Since you already know the basics, a detailed example of a differential CMOS amplifier

will be simulated and used as the basis of this tutorial.

The following circuit, shown in the figure below, will be simulated in the following

ways: 1) the DC operating points, 2) the time domain response to a sinusoid (transient

test), 3) the AC response (Bode Plot), 4) and the step response.

Figure One: CMOS Differential Amplifier

The first step will be to create a new .cir file. The first line of a netlist file must be a

comment, which is any line beginning with they symbol ì*î. The next thing needed is

the model to use for the transistors. In this case the models were downloaded from the

Sedra & Smith textbook website. By now, your .cir file should contain the following

(note the single * at the beginning):

Differential-pair simulation for SPICE tutorial
ECE 3110, Fall 2002, Dan Clement
Spice MOSFET model from Sedra and Smith book:

.MODEL NMOS NMOS( level=2 vto=1 nsub=1e16 tox=8.5e-8 uo=

cgso=4e-10 cgdo=4e-10 cgbo=2e-10 uexp=0.14 ucrit=5e4 utra=0 vmax=5e4 rsh=
cj=4e-4 mj=2 pb=0.7 cjsw=8e-10 mjsw=2 js=1e-6 xj=1u ld=0.7u )

.MODEL PMOS PMOS( level=2 vto=-1 nsub=2e15 tox=8.5e-8 uo=

cgso=4e-10 cgdo=4e-10 cgbo=2e-10 uexp=0.03 ucrit=1e4 utra=0 vmax=3e4 rsh=
cj=1.8e-4 mj=2 pb=0.7 cjsw=6e-10 mjsw=2 js=1e-6 xj=0.9u ld=0.6u )

The next thing to be added are the DC supplies. In this circuit there is one DC current

supply and two DC voltage supplies.

Define the bias current. Ibias 1 0 200u
Define the DC voltage sources. Vdd 6 0 5V V- 3 0 2.5V V+ 2 0 2.5V Vin 7 2 0V

Note the syntax for the DC sources: Ixxx (or Vxxx) node+ node- value

Note also that we use a ìuî to denote microamps since a lowercase ìuî resembles the

Greek letter mu ( μ).

Now that the bias sources are taken care of, add in the devices and components in the

circuit. For this circuit there are four transistors and one load capacitor.

Note that the name of the input file will be shown in the text box to left of the ìplayî

button. In this case it was called opamp. The simulation should run. If there are errors

you will get a warning dialogue box that pops up. In the bottom left, a summary is

displayed that gives status reports of the simulation. Shown in the figure below is the

result of a successful operating point analysis. There is some information to the right

also, but this information is really only needed for specialized situations which will not

be encountered in this class.

All the simulation data is written to the .out file. The .out file will include whatever

output you specify using .OP or .PRINT commands, a copy of your input file, and other

things. It resembles a log file and you have to look through it to get what you want. In

this case, the operating points will be shown. Here is what it should look like (might be

formatted slightly differently):

**** 09/02/02 22:48:40 ************** PSpice Lite (Mar 2000) *****************

**** SMALL SIGNAL BIAS SOLUTION TEMPERATURE = 27.000 DEG C

NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE ( 1) 2.0150 ( 2) 2.5000 ( 3) 2.5000 ( 4) 2.

( 5) 2.5010 ( 6) 5.0000 ( 7) 2.

VOLTAGE SOURCE CURRENTS NAME CURRENT

Vdd -2.000E- V- 0.000E+ V+ 0.000E+ Vin 0.000E+

TOTAL POWER DISSIPATION 1.00E-03 WATTS

Note that the DC voltages are printed, along with the node number. The power

consumption is also summarized.

Now that the circuit is up and working, the rest of the analysis is easy. The next item to

simulate is the transient (time-domain) response to a sinusoid. The Vin voltage source

will be defined as a sine wave at 10kHz. The following code defines the voltage source

and type of analysis desired:

Define the input sine wave (transient, time domain) *Vin 7 2 sin(0 15mV 10kHz)
Run the transient test: *.tran .1u 400u 0 .1u
request that all nodes be probed *.probe

Here is the syntax for the sine wave:

Vxxx node+ node- sin(DC_VALUE PEAK FREQUENCY)

The syntax for the .TRAN analysis command:

.tran plot_time_step time_stop time_to_start_plot_at calculation_time_step

The AC response will be simulated next. Itís basically the same procedure as before

except for an AC sinusoidal source and a .ac command. Note that an input voltage

amplitude of 1V is used so that the transfer function equivalent to the output voltage

(Vout/1 = Vout). Here is the code:

Define the input sine wave (ac, frequency domain, use 1 Volt to make H(s) easier) Vin 7 2 AC 1
Run the AC test: .ac dec 500 1 10G
request that all nodes be probed .probe

.end

Once again, here is the syntax:

AC sine wave:

Vxxx node+ node- AC magnitude

.AC command:

.ac analysis_type(dec for log space) number_points_per_decade start_f end_f

Add the above code to the .cir file, but this time comment out the transient sinusoidal

source, and the .tran command line. Only one type of analysis can be requested in a

simulation, with the exception of .op. To comment out a line, put a * character in front of

the comment. If you use this method of commenting out the other analyses, you can use

one netlist for each simulation type, making it very fast and easy to finish and to switch

back and forth.

Run the simulation. When the blank plot is displayed, go to the plot menu and select

ìadd plot to windowî. Now there are two sets of graphs available. Click the mouse on

the top graph so that SEL>> is displayed on the y-axis. Open the add trace dialogue as

before, except this time click on the DB() function from the right hand side list. After

you click on DB(), click on V(4). This will apply the DB() function to the output voltage,

V(4). Click OK. This will plot the magnitude portion of your Bode plot.

To plot the phase, click on the lower graph so that SEL>> is shown on the y-axis. Open

the add trace dialogue again and select the P() function and then on V(4). This will plot

the phase of your Bode plot. Before you click ok, in the bottom text area, after P(V(4)),

type in ñ180. This will subtract 180 degrees from the phase. This is needed because the

amplifier is an inverting amplifier, and the true phase response needs to start at 0 degrees.

You should always report the phase this way. Click OK. The graph should look like

this:

The transient portion will stay the same as the sine wave was. Everything else is the

same.

For reference, the entire input file used is repeated here for clarity. Note that it is

currently set up for the square wave simulation.

Differential-pair simulation for SPICE tutorial
ECE 3110, Fall 2002, Dan Clement
Spice MOSFET model from Sedra and Smith book:

.MODEL NMOS NMOS( level=2 vto=1 nsub=1e16 tox=8.5e-8 uo=

cgso=4e-10 cgdo=4e-10 cgbo=2e-10 uexp=0.14 ucrit=5e4 utra=0 vmax=5e4 rsh=
cj=4e-4 mj=2 pb=0.7 cjsw=8e-10 mjsw=2 js=1e-6 xj=1u ld=0.7u )

.MODEL PMOS PMOS( level=2 vto=-1 nsub=2e15 tox=8.5e-8 uo=

cgso=4e-10 cgdo=4e-10 cgbo=2e-10 uexp=0.03 ucrit=1e4 utra=0 vmax=3e4 rsh=
cj=1.8e-4 mj=2 pb=0.7 cjsw=6e-10 mjsw=2 js=1e-6 xj=0.9u ld=0.6u )

Define the bias current. Ibias 1 0 200u
Define the DC voltage sources. Vdd 6 0 5V V- 3 0 2.5V V+ 2 0 2.5V
Add the transistors in *input pair first: M1 5 3 1 0 NMOS L=2u W=50u M2 4 7 1 0 NMOS L=2u W=50u *Now the current mirror devices M3 5 5 6 6 PMOS L=10u W=93.5u M4 4 5 6 6 PMOS L=10u W=93.5u
Capacitive load Cload 4 0 5p
Define the input sine wave (transient, time domain) *Vin 7 2 sin(0 15mV 10kHz) Vin 7 2 pulse(0 15m 0 1n 1n 50u 100u)
Define the input sine wave (ac, frequency domain, use 1 Volt to make H(s) easier)

*Vin 7 2 AC 1

Request the DC operating point to be output to .out file .OP
Run the transient test: .tran .1u 400u 0 .1u
Run the AC test: *.ac dec 500 1 10G
request that all nodes be probed .probe

.end

SPICE Tutorial: Creating Netlists for Diff. CMOS Amplifier (ECE 3110, Univ. of Utah) - Pro, Exams of Electrical and Electronics Engineering

Related documents

Partial preview of the text

Download SPICE Tutorial: Creating Netlists for Diff. CMOS Amplifier (ECE 3110, Univ. of Utah) - Pro and more Exams Electrical and Electronics Engineering in PDF only on Docsity!

Brief Spice Tutorial

ECE 3110, University of Utah, Fall 2002

By now, you have used SPICE in at least one other class. As a result, some familiarity is

assumed. This tutorial will focus on the usage of input files for netlists. Some students

may have experience using only the schematic capture version of PSPICE, but this

tutorial should enable the transition to be less troublesome.

Since you already know the basics, a detailed example of a differential CMOS amplifier

will be simulated and used as the basis of this tutorial.

The following circuit, shown in the figure below, will be simulated in the following

ways: 1) the DC operating points, 2) the time domain response to a sinusoid (transient

test), 3) the AC response (Bode Plot), 4) and the step response.

Figure One: CMOS Differential Amplifier

The first step will be to create a new .cir file. The first line of a netlist file must be a

comment, which is any line beginning with they symbol ì*î. The next thing needed is

the model to use for the transistors. In this case the models were downloaded from the

Sedra & Smith textbook website. By now, your .cir file should contain the following

(note the single * at the beginning):

The next thing to be added are the DC supplies. In this circuit there is one DC current

supply and two DC voltage supplies.

Note the syntax for the DC sources: Ixxx (or Vxxx) node+ node- value

Note also that we use a ìuî to denote microamps since a lowercase ìuî resembles the

Greek letter mu ( μ).

Now that the bias sources are taken care of, add in the devices and components in the

circuit. For this circuit there are four transistors and one load capacitor.

Note that the name of the input file will be shown in the text box to left of the ìplayî

button. In this case it was called opamp. The simulation should run. If there are errors

you will get a warning dialogue box that pops up. In the bottom left, a summary is

displayed that gives status reports of the simulation. Shown in the figure below is the

result of a successful operating point analysis. There is some information to the right

also, but this information is really only needed for specialized situations which will not

be encountered in this class.

All the simulation data is written to the .out file. The .out file will include whatever

output you specify using .OP or .PRINT commands, a copy of your input file, and other

things. It resembles a log file and you have to look through it to get what you want. In

this case, the operating points will be shown. Here is what it should look like (might be

formatted slightly differently):

Note that the DC voltages are printed, along with the node number. The power

consumption is also summarized.

Now that the circuit is up and working, the rest of the analysis is easy. The next item to

simulate is the transient (time-domain) response to a sinusoid. The Vin voltage source

will be defined as a sine wave at 10kHz. The following code defines the voltage source

and type of analysis desired:

Here is the syntax for the sine wave:

Vxxx node+ node- sin(DC_VALUE PEAK FREQUENCY)

The syntax for the .TRAN analysis command:

.tran plot_time_step time_stop time_to_start_plot_at calculation_time_step

The AC response will be simulated next. Itís basically the same procedure as before

except for an AC sinusoidal source and a .ac command. Note that an input voltage

amplitude of 1V is used so that the transfer function equivalent to the output voltage

(Vout/1 = Vout). Here is the code:

Once again, here is the syntax:

AC sine wave:

Vxxx node+ node- AC magnitude

.AC command:

.ac analysis_type(dec for log space) number_points_per_decade start_f end_f

Add the above code to the .cir file, but this time comment out the transient sinusoidal

source, and the .tran command line. Only one type of analysis can be requested in a

simulation, with the exception of .op. To comment out a line, put a * character in front of

the comment. If you use this method of commenting out the other analyses, you can use

one netlist for each simulation type, making it very fast and easy to finish and to switch

back and forth.

Run the simulation. When the blank plot is displayed, go to the plot menu and select

ìadd plot to windowî. Now there are two sets of graphs available. Click the mouse on

the top graph so that SEL>> is displayed on the y-axis. Open the add trace dialogue as

before, except this time click on the DB() function from the right hand side list. After

you click on DB(), click on V(4). This will apply the DB() function to the output voltage,

V(4). Click OK. This will plot the magnitude portion of your Bode plot.

To plot the phase, click on the lower graph so that SEL>> is shown on the y-axis. Open

the add trace dialogue again and select the P() function and then on V(4). This will plot

the phase of your Bode plot. Before you click ok, in the bottom text area, after P(V(4)),

type in ñ180. This will subtract 180 degrees from the phase. This is needed because the

amplifier is an inverting amplifier, and the true phase response needs to start at 0 degrees.

You should always report the phase this way. Click OK. The graph should look like

this:

The transient portion will stay the same as the sine wave was. Everything else is the

same.