cczhang wrote on Oct 23^rd, 2009, 1:07am:


Of course, you can. All you need is an ac analysis and the capability to draw the imaginary part of the loop gain vs. the real part.

cczhang wrote on Oct 23^rd, 2009, 1:39am:


I am afraid you are not very familiar with the subject - and therefore, it´s not easy to explain in detail the meaning resp. simulation alternatives for loop gain. I am not working with Cadence, but with a lot of other simulation programs - nevertheless I am sure that you can ask cadence to plot IM(L(s)) if L(s) is the loop gain.  And than you can change the x-axis to show R(L(s)). And this gives you the NYQUIST plot.
I repeat: At first you have to become familiar with the term loop gain - and how to simulate it. This item has been discussed very often in this forum.
Regards + good luck.

Hi

If you just want results for some application purpose and this simulation is not specific to just cadence ;  then i think you can do this better at MAT-LAB simmulink. Mat lab has built in function for Feedback loop gain.

For 'gain' : It is the measure of ability of a system to increase its output (Power , Amplitude) with respect to Input.
For 'Loop gain' :  If this gain is controlled by some feed back then it is called loop gain.

Remember adding Loop to some system decreases its overall gain.

Nyquist Criterion :  It tells whether the system under consideration is stable or not and if not stable what changes can be done to make it stable !

This is actually dealing with complex variables in terms of systems  ;)
and Plotting results.



thanks