PSS + PSTB for Buck converter

What happens if you do pss+pac for the converter + PWM generator (E0 in your circuit) by adding a vdc source at the PWM ramp generator and make its PAC magnitude as 1. Do you see any gain from the pac source to the output? As per theory this should give you the frequency response of the converter and PWM circuit.

As part of debugging I actually did a simple tb with only the ramp and i/p passed through a comparator to generate a PWM waveform. To my surprise, I found that the pac gain from i/p to PWM o/p is giving '0'.

I guess the problem lies here itself....!!

I suggest that you take a look at https://designers-guide.org/forum/YaBB.pl?num=1189658426 and check if (too) ideal components in your circuit are causing this effect. Please also note Ken's remark at https://designers-guide.org/forum/YaBB.pl?num=1107716368/53#53 : "To get PAC to work on a behavioral comparator model you need a transition region where the gain is finite, and the PSS analysis must put some points down in that region." Of course, this also applies to PSTB and PXF.

Thanks Frank.. Understood the issue.
I guess simplis supports analysis period op. point analysis (pop) and (p)ac for these type of circuits.
Is there any hack I can use in cadence to get the results similar to simplis?

According to my experience, PAC, PXF and PSTB usually work very well if the circuit is built with real devices (transistors etc.) and does not use ideal components or Verilog-A models. If you want to use such ideal components, you need to make sure that the conditions I mentioned above are satisfied.

Out of curiosity I tried this out. For some reason I am unable to attach images to this post. They are at this link. 

The gain from dc to dc (0th harmonic conversion) should be 0.5. But it is all over the place The results depend slightly on the number of harmonics, but doesn’t make much difference.

Bottomline: Greed is bad! Limiting yourself to a total gain of ~ 100 is OK.

Nagendra

Did you check how well the condition mentioned above is satisfied? 

Frank Wiedmann said:

"To get PAC to work on a behavioral comparator model you need a transition region where the gain is finite, and the PSS analysis must put some points down in that region."

How many points did you get in the transition region for the different values of Gcomp? You can find this out by double-clicking on the trace in ViVA and selecting both "Turn On Symbols" and "Show All Points".

Did you check how well the condition mentioned above is satisfied? 

Frank Wiedmann said:

"To get PAC to work on a behavioral comparator model you need a transition region where the gain is finite, and the PSS analysis must put some points down in that region."

How many points did you get in the transition region for the different values of Gcomp? You can find this out by double-clicking on the trace in ViVA and selecting both "Turn On Symbols" and "Show All Points".