Very simple circuit. Suppose only the resistor produce thermal noise. Phi1 lasts mTs. Now want to calculate the Continuous time output Noise PSD. My calculation is as:
Devided into two phase, then add together.
First during Phi1
The output is continuous time noise produced by resistor. KTRn, then divided by two capacitor.

During Phi 2, only the sampled noise, all the PSD are folded back to low frequency. The value is only related to the Cap and Clock frequency.

At last, add two together.

But the simulation result is different from my calculation. Large than my calculation. I was wondering where is the problem with my calculation?

Thank you for your time.

The noise is 4KT(c1+cl1)/(cl1*cl1).