I am trying to simulate a Capacitive Transimpedance Amplifier (CTIA), being used to integrate a photodiode current.  Basically, a CTIA is just an op-amp with a capacitor in feedback to integrate (and a reset switch, which shorts this capacitor to clear the integration).  The reset is periodic.

Can a PNOISE simulation be used in this circuit to test the CTIA 1/f noise, and more importantly, to simulate the effect of a CDS downstream at removing 1/f noise?  I have read the paper on simulating SC circuits using PNOISE and PAC.

So far, I have been unsuccessful at getting a output PSD that shows the effect of the CDS (suppression of 1/f noise in low frequencies).  I am starting to question my methods.  

It could also be the circuit, I suppose, but I tried solving the gain from the op-amp inputs (where input-referred noise would appear) to the output, using a PAC analysis, and it correctly shows almost complete suppression of low frequency, so I don't understand why PNOISE would tell me that that op-amps's input transistor is still contributing the majority of noise (as 1/f), and why that 1/f noise has a classic 1/f shape despite CDS.  It should have a zero at DC, I would expect.

Thanks,
Ben