Strange Noise Issue of Passie Swicthed Capcitor Circuit

[sharezhao]

Strange Noise Issue of Passive Swicthed Capcitor Circuit


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.

 

[helpmejerry]

HI sharezhao,

I believe that you will need to include the kT/C noise of the SC circuit to calculate the proper result.

BR Jerry

 

[sharezhao]

Hi helpmyjerry, Thanks, Here is my Calculation:

 

[helpmejerry]

Hi sharezhao,

Please have a look at this articles **broken link removed** http://www.designers-guide.org/Forum/Attachments/schrier_tcas1_SC.pdf, hope it helps.

BR Jerry

 

[sharezhao]

Hi helpmyjerry
Thanks for your reply. The materials you provided is useful. I read them many times before. The problem is solved. The passive case is a little different from active integrator. So if anyone interested, please contact my. LOL