Hi, all: I design a full differential OPA whose CMFB is switch capacitance circuit.
Because the switch capacitance circuit, I do not know how to process the ac analyse.

Paul,

I assume you meant to say that if you replace the switch-cap parts with equivalent resistors you can then simulate using an AC analysis not a PAC analysis.

If you have SpectreRF (as you say), you can then simulate using PSS/PAC with the circuit as is (I expect).

I'm sure it was just a typo, but just thought I'd check (with my pedant's hat on).

Regards,

Andrew.