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Message started by neoflash on Jul 14th, 2011, 10:58pm

Title: Noise of S/H in Sampling Phase
Post by neoflash on Jul 14th, 2011, 10:58pm
This is the S/H stage in pipelined ADC. I have a question about this noise analysis.

After the sampling phase, all charges on the Cs will be transferred to Ch.

The question is that whether the switch (3) contribute noise to the result. I have read some article and saying that it doesn't. I'm confused and feel it should impact since the noise charge is stored on Cs bottom plate .

Hope people can suggest and provide reference, thanks!

Title: Re: Noise of S/H in Sampling Phase
Post by raja.cedt on Jul 15th, 2011, 12:07am
hello,
where is switch 3 here?
Up to my knowledge every switch wil contribute noise, so when you sample there is some noise charge will be accumulated on Cs, and when hold it will get deposited on Ch. This is roughly kt*c1/c2^2, in addition to this there kt/ch on holding cap.

Thanks.

Title: Re: Noise of S/H in Sampling Phase
Post by thechopper on Jul 15th, 2011, 5:37am
Hi,

Both switches 1 and 3 will contribute to sampled noise on Cs. Moreover you could consider both of them as a single switch, thus a single thermal noise source with an ideal resistor in series.
As a consequence the sampled noise power will be KT/Cs, which is independent of the Ron from switch 1 and switch 3 added.
Bottom line: both switches contribute but the noise power is not Ron dependent.

Hope this helps
Tosei

Title: Re: Noise of S/H in Sampling Phase
Post by neoflash on Jul 15th, 2011, 9:24am
Switch 3 is the switch in the middle labeled with (3).


raja.cedt wrote on Jul 15th, 2011, 12:07am:
hello,
where is switch 3 here?
Up to my knowledge every switch wil contribute noise, so when you sample there is some noise charge will be accumulated on Cs, and when hold it will get deposited on Ch. This is roughly kt*c1/c2^2, in addition to this there kt/ch on holding cap.

Thanks.

Title: Re: Noise of S/H in Sampling Phase
Post by neoflash on Jul 15th, 2011, 11:43am
From simulation, the total noise appear at Ch in hold phase is 2*KT/C no matter Ron(1,2,3)'s value.

Just another good example of KT/C theory. It is just that this complex network and sample/hold charge transfer make it look so blurred.

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