about KT/C noise- which is right to calculate the KT/C noise

[lhlbluesky]

kt/c noise

in pipeline ADC, we need to calculate the KT/C noise to decide the value of sampling capacitor; then how to calculate the KT/C noise?

someone says, for fully differential sc opamp, KT/C noise is 2KT/Cs, while someone says, for fully differential sc opamp, KT/C noise is 4KT/Cs,
and which is right? if not, what's the correct answer?

pls help me, i'm confused very much, thanks all.

 

[rfsystem]

Re: about KT/C noise

You add 2 uncorrelated noise sources if the input related voltage is between 2 sampled caps. Because k*T/C is a voltage by square 2*k*T/C is the correct answer. If you normalize to the sum of 2 caps each single ended cap is only half of them. So for sum cap it is 4*k*T/Csum.

Regarding the SNR a differential SC circuit have double the signal voltage range. So SNR is equal for equal cap.

 

[lhlbluesky]

about KT/C noise

thanks rfsystem, but i don't understand well, can you explain more clearly, pls?