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# Simulating Analog Circuit using OrCAD

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#### pavan garate

##### Member level 3
Hi..

I want to learn the software "OrCAD 16.6 Lite" version. I want to design various applications of OP-Amp such as Inverting & Non-inverting Amplifiers, Differentiator, Integrator, etc.

I designed the schematic of inverting amplifier using "OrCAD Capture CIS Lite". But I don't understand how to give the AC signal as the input. Please help me. It will be helpful to me if someone guides me stepwise from the beginning.

I'm new to this software & hence don't know much about it.

##### Full Member level 4
in part there is ac source and other sources such as sin wave.

pavan garate

### pavan garate

Points: 2

#### pavan garate

##### Member level 3
in part there is ac source and other sources such as sin wave.

Thanks.

I found the voltage source as VSTIM/SOURCSTM. But when I simulate the circuit, I get an error as-
ERROR(ORNET-1110): Part V1 has no 'STIMULUS' property

What should I do?

##### Full Member level 4
you should define initial parameters for ac source such as amplitude and frequency. right click on that and define parameters.

pavan garate

### pavan garate

Points: 2

#### mvaseem

##### Full Member level 2
If you want to do transient analysis (means wrt time) with constant voltage, sine or pulse - choose vdc, vsin, vpulse respectively.
If you want to do AC analysis (means wrt freq) choose vac.

pavan garate

### pavan garate

Points: 2

#### pavan garate

##### Member level 3
you should define initial parameters for ac source such as amplitude and frequency. right click on that and define parameters.

Thanks. I found the voltage sources in the SOURCE library. I have few more doubts:

1) For the sine wave voltage source VSIN, we need to specify four parameters as VOFF, VAMPL, FREQ and AC. What does the parameter AC stands for?

2) How can I generate a square wave signal at the input?

3) After simulation, the input and output waveforms are shown in the same graph. How can I separate the graphs for input and output waveforms?

#### mvaseem

##### Full Member level 2
1) AC parameter is used only when you want to do AC analysis (wrt freq). VSIN can be used for both transient (time domain) as well as AC analysis. If you are doing only transient analysis, leave this blank. For AC analysis provide AC=1, then the o/p voltage would represent gain wrt freq.
2) Use VPULSE. Provide pulse width with half value of time period. Provide high, low voltages, rise time,fall time as desired.
3) You need to add new plot. Go to menu Plot->Add plot to window. Now insert one trace to this new plot.

Points: 2

### Endolith

Points: 2

#### pavan garate

##### Member level 3
1) AC parameter is used only when you want to do AC analysis (wrt freq). VSIN can be used for both transient (time domain) as well as AC analysis. If you are doing only transient analysis, leave this blank. For AC analysis provide AC=1, then the o/p voltage would represent gain wrt freq.
2) Use VPULSE. Provide pulse width with half value of time period. Provide high, low voltages, rise time,fall time as desired.
3) You need to add new plot. Go to menu Plot->Add plot to window. Now insert one trace to this new plot.

Thanks a lot mvaseem...

But I'm still not able to generate the square wave input. I want the square wave with following parameters:
High voltage = 1 V
Low voltge = -1 V
Time period of one pulse = 1 sec
Rise time, fall time and delay = 0 sec (i.e. very small)

So, I used the VPULSE with following specifications:
V1 = 1
V2 = -1
TD = 1u
TR = 1u
TF = 1u
PW = 0.5
PER = 0

I simulated the circuit from 0 sec to 10 sec with the step of 0.1 sec. But I got only one square pulse upto 1 sec. After 1 sec, it is a straight line of 1 V.

What should I do?

I'm just trying to design a basic integrator circuit using OPAmp for the square wave input.

What is the parameter "PER" of VPULSE?

#### mvaseem

##### Full Member level 2
PER is the time period. Provide PER=1 and you are done.

You can further minimize the delay and rise fall time, if you want. Delay (TD) can be given as 0. Rise/fall time can be made in nano, pico range.

pavan garate

### pavan garate

Points: 2

#### pavan garate

##### Member level 3
PER is the time period. Provide PER=1 and you are done.

You can further minimize the delay and rise fall time, if you want. Delay (TD) can be given as 0. Rise/fall time can be made in nano, pico range.

Thanks a lot. It solved all my problems.

Now I want to design Log Amplifier and Antilog Amplifier using Diode as well as Transistor. I designed Log Amplifier using Diode as well as Transistor but both times I got the error: Missing model

What values should be specified for the Diode and Transistor?

How to find their reverse saturation currents to determine the output voltage for Log Amplifier and Antilog Amplifier?

Thanks again.

#### mvaseem

##### Full Member level 2
Looks like either you are choosing the parts from wrong library or your model library is not properly configured.
Can you post the pspice out file (file which shows the error).

#### pavan garate

##### Member level 3
Looks like either you are choosing the parts from wrong library or your model library is not properly configured.
Can you post the pspice out file (file which shows the error).

Output File for log amplifier using transistor:-

**** 08/24/14 22:42:05 ****** PSpice Lite (October 2012) ****** ID# 10813 ****

** Profile: "SCHEMATIC1-lgar" [ D:\Softwares\My OrCAD Circuits\logampr-pspicefiles\schematic1\lgar.sim ]

**** CIRCUIT DESCRIPTION

******************************************************************************

** Creating circuit file "lgar.cir"
** WARNING: THIS AUTOMATICALLY GENERATED FILE MAY BE OVERWRITTEN BY SUBSEQUENT SIMULATIONS

*Libraries:
* Profile Libraries :
* Local Libraries :
* From [PSPICE NETLIST] section of C:\SPB_Data\cdssetup\OrCAD_PSpice/16.6.0/PSpice.ini file:
.lib "nomd.lib"

*Analysis directives:
.TRAN 0 100ms 0 10ms SKIPBP
.PROBE64 V(alias(*)) I(alias(*)) W(alias(*)) D(alias(*)) NOISE(alias(*))
.INC "..\SCHEMATIC1.net"

**** INCLUDING SCHEMATIC1.net ****
* source LOGAMPR
.EXTERNAL OUTPUT PORTLEFT-L
E_U1 PORTLEFT-L 0 VALUE {LIMIT(V(0,N00191)*1E6,-15V,+15V)}
R_R1 N00175 N00191 1k TC=0,0
Q_Q1 N00191 0 PORTLEFT-L
--------------------------------\$
ERROR(ORPSIM-16407): Missing model
V_V1 N00175 0 DC 2Vdc AC 2Vac

**** RESUMING lgar.cir ****
.END

Output File for log amplifier using diode:-

**** 08/24/14 22:45:15 ****** PSpice Lite (October 2012) ****** ID# 10813 ****

** Profile: "SCHEMATIC1-lgar" [ D:\Softwares\My OrCAD Circuits\logampr-pspicefiles\schematic1\lgar.sim ]

**** CIRCUIT DESCRIPTION

******************************************************************************

** Creating circuit file "lgar.cir"
** WARNING: THIS AUTOMATICALLY GENERATED FILE MAY BE OVERWRITTEN BY SUBSEQUENT SIMULATIONS

*Libraries:
* Profile Libraries :
* Local Libraries :
* From [PSPICE NETLIST] section of C:\SPB_Data\cdssetup\OrCAD_PSpice/16.6.0/PSpice.ini file:
.lib "nomd.lib"

*Analysis directives:
.TRAN 0 100ms 0 10ms SKIPBP
.PROBE64 V(alias(*)) I(alias(*)) W(alias(*)) D(alias(*)) NOISE(alias(*))
.INC "..\SCHEMATIC1.net"

**** INCLUDING SCHEMATIC1.net ****
* source LOGAMPR
.EXTERNAL OUTPUT PORTLEFT-L
E_U1 PORTLEFT-L 0 VALUE {LIMIT(V(0,N00191)*1E6,-15V,+15V)}
R_R1 N00175 N00191 1k TC=0,0
V_V1 N00175 0 DC 2Vdc AC 2Vac

**** RESUMING lgar.cir ****
.END

JOB CONCLUDED

**** 08/24/14 22:45:15 ****** PSpice Lite (October 2012) ****** ID# 10813 ****

** Profile: "SCHEMATIC1-lgar" [ D:\Softwares\My OrCAD Circuits\logampr-pspicefiles\schematic1\lgar.sim ]

**** JOB STATISTICS SUMMARY

******************************************************************************

Total job time (using Solver 1) = 0.00

I just want to learn the basics of OrCAD for designing Log and Antilog amplifiers. So you can take any input value. Also tell me how to supply proper inputs to such circuits.

Thanks.

#### mvaseem

##### Full Member level 2
Looks like BJT used has no model name specified.
The BJT instance in your netlist is having E,B,C connections. Thereafter model name is missing.
You can re-instantiate BJT from bipolar.olb. Not sure which olb to be used for demo version.
There is lot of material available for log amplifiers on web. I think the challenge would be to find saturation currents of BJT/DIODES to perform theoretical calculations.

pavan garate

### pavan garate

Points: 2

#### pavan garate

##### Member level 3
Looks like BJT used has no model name specified.
The BJT instance in your netlist is having E,B,C connections. Thereafter model name is missing.
You can re-instantiate BJT from bipolar.olb. Not sure which olb to be used for demo version.
There is lot of material available for log amplifiers on web. I think the challenge would be to find saturation currents of BJT/DIODES to perform theoretical calculations.

Which MOSFETs are generally used to design the normal circuits in OrCAD? In the TRANSISTOR library, there are many such components.

#### mvaseem

##### Full Member level 2
If you are using demo version - there is library called breakout.olb.
You can use generic MOS, BJT (mbreakn, mbreakp, qbreakn, qbreakp).
You can configure MOS W,L values on the instance properties. You can also set the LEVEL (BSIM model to be used by simulator).

pavan garate

### pavan garate

Points: 2

#### pavan garate

##### Member level 3
If you are using demo version - there is library called breakout.olb.
You can use generic MOS, BJT (mbreakn, mbreakp, qbreakn, qbreakp).
You can configure MOS W,L values on the instance properties. You can also set the LEVEL (BSIM model to be used by simulator).

I'm now able to use the MOSFETs.

Can you please tell me in detail how to change the W & L values? I have the technology file of 90 nm which I used for the TANNER tool. Can I use the same file with OrCAD? How should I specify the technology file in OrCAD?

Thanks again..

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