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24th June 2008, 02:17 #1
kt/c noise
Dear Friends
I would be grateful if someone could explain the KT/C noise (input referred) contribution of Sampling Capacitor (CS) and feedback capacitor (CF) for the standard two capacitor S/H implementation (not the flip around architecture).
Regards
Sachin

24th June 2008, 02:17

24th June 2008, 21:15 #2
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sample and hold circuit
I did not remake the derivation but the path is the following:
Have a RC low pass filter. The R is the noise source with 4kT*R. The RC filters so that the power noise density get filtered by 1/(1+omega^2). If you integrate that up to infinity over frequency you get the expression above.

24th June 2008, 21:36 #3
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ktc noise
Maybe this will help.
2 members found this post helpful.

24th June 2008, 21:36

25th June 2008, 01:42 #4
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switched capacitor noise
the noise contribution from the sampling capacitor is 2*k*T/Cs, where two times are from sampling phase and integrating phase. the noise contribution from feedback capacitor is 2*k*T*Cf/Cs² due to capacitance divider.

25th June 2008, 06:07 #5
sample and hold capacitor
Thank you for your comments.
Dear Jiangxb
I have an amplifier circuit. It is not an integrator. In phase 1, the capacitor CS samples the input via a switch. In phase 2, the charge is transfered to another capacitor CF (feedback capacitor). This capacitor, along with the opamp, hold the charge.
Please have a look at the image and suggest your views on the KT/C noise.
Looking forward to hear from you.
Regards
Sachin

25th June 2008, 06:07

25th June 2008, 06:32 #6
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kt c noise
well, the noise contribution only comes from the switches connected with the sampling capacitor Cs, it's 2*k*T/Cs.

25th June 2008, 08:01 #7
flipāaround sampleāandāhold
Dear JiangXB
Thanks for your response. I agree with you that the KT/C noise should equal "KT/Cs".
I am slightly confused about the KT/C noise presented in the following document (page 242). Please note that this is a different SH architecture (fliparound).
http://kabuki.eecs.berkeley.edu/~cli...sis/thesis.pdf
The figure referred to in this analysis is as below:
If time permits, please have a look and let me know the reason of including CGS (parasitic gate to source capacitance of the opamp input transistors) in noise calculation.
Thanks for your time
Regards
Sachin
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