I am doing the stability analysis (need to look at the amplitude response, phase response and phase delay) of an electronic circuit which will drive a DC motor (ofcourse its a closed loop system). The input to the circuit varies from +10 V to -10V and circuit contain opamp ELH0041. I am using ORCAD PSPICE for the modeling and would like to know, what kind of source model I can use for this analysis and what kind of analysis I should select from PSPICE.
Any inputs on this will be highly appreciated
You should perform AC analysis and make sure your input voltage source has "AC" property and it's value is set = 1. This analysis will enable you to analyze circuit response in frequency domain. You can observe gain & phase at desired output node in per unit terms. You may need to replace complex sub circuit models (if used in circuit) by equivalent small signal model for successful AC analysis. In short - this would give you bode plot at point of interest in you circuit. One can configure a circuit to be open loop or close loop.
In reply to alokt:
Thanks alot for your reply. I used a VAC soucre from PSPICE library for the analysis with 1Vac. The DC offset value (Vdc) was set to zero.This shows zero output from the source after the analysis. When I changed offset value to 1Vdc , the output became 1V, but analysis results were reversed. Do we really need to give a DC offset value for the frequency response analysis?
In reply to madhuraj:
Generally speaking, DC bias should not be needed or it should not have impact on overall stability. However this can be confirmed for a given circuit only. Change in output as standalone point of observation, may not be meaningful from stability point of view, one need to observer GAIN/Phase margin at the point where loop is being closed.
I am also interested in phase delay. Can I do it in Pspice?
I assume you mean phase lag at output. Yes, You can use one of the following methods
- plot P(V(out)) in PSpice wave form viewer. This would plot phase of V(out) in degrees
use Phase .. marker from PSpice>Markers>Advance Marker menu and place it at appropriate node
Use Bode Plot... from PSpice>Markers>Plot Window Template
Thanks alot for your kind reply.
Actually my problem here is I need to plot the phase delay (in microseconds) over frequency.
By plotting the phase at the input and output I may be able to see the phase shift, but to see the actual delay,(As u know, phase shift = -Omega X Time delay), is there any way I can get a plot of this delay directly,