Hi there,

I am designing a Fully differential single stage opamp with normal resistor divided CMFB, using Cadence 0.18um.

While simulating the opamp with resistor divided CMFB i get a gain of 65db and 200Mhz UGBW. And the results from Transcient analysis is fine.
But when the circuit's resistor in CMFB is replaced by Switched capacitor  and PSS and PAC analysis were done, PAC yield me same gain and UGBW. I am happy in it...

When annotated my dc opearting points by PSS, it  looked exact as in ac and tran analysis. i am happy in it....BUT..

During PSS i applied input frequency of 100Mhz and Clock freq also 100Mhz. I know for PSS (according to Ken) only clock (no input) is applied. After PSS i have to do PAC. But u see...PAC needs an input. How is it possible to run PSS followed by PAC (one requiring no input and other requiring input) at teh same time. I dont know what i understood is wrong...pls correct me if i have gone wrong.

My tran analysis and transient response using PSS looked different.

PSS reponse showed me the output sinusoidal waveform to be distorted and outputs were not differential. they looked almost similar?

Can i see the transient waveform which i got by Tran analysis using PSS?

Since i got same gain and BW (but different Tran response) using normal ac, tran and PAC, PSS, can i ensure that both my circuits are identical?

I am looking forward for ur great help...please respond .

regards
Sajam