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    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

    •   Alt24th June 2008, 02:17

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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.



    •   Alt24th June 2008, 21:15

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    ktc noise

    Maybe this will help.


    2 members found this post helpful.

    •   Alt24th June 2008, 21:36

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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.



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    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 op-amp, 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



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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.



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    flipā€around sampleā€andā€hold

    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 (flip-around).

    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 op-amp input transistors) in noise calculation.

    Thanks for your time
    Regards
    Sachin



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