MarcoC wrote on Jul 8th, 2009, 6:04am:Hi Subgold,
sorry for this latency, I was warried by some personal problems last month.
You're right, the folding effect is a basic property and I can't overcome it. But I have seen a strange thing and I'd like to have a confirm.
Simulating only the CA the noise folding is due to reset; but adding a sampler after the CA, the noise folding is due to the sampling operation.
I think in the first case the reset introduces a shape in time, thus a correlation in frequency, showing a folding effect. However, in the second case, the sampler samples the noise out of the reset time and the reset effect vanishes (but the folding due to sampling is introduced).
What do you think about this?
As for the input stray cap I show you my schematics. If you study the noise of this circuit, you will see that the equivalent input noise power is amplified about by (Cpar/Cf)^2, thus the stray capacitance become a key parameter.
hi,
i'm not sure how you simulate the circuit, but adding a sampler will certainly gives different result. anyway, the folding effect doesn't vanish in either case. the sampler shows the noise at a certain time point, but the noise is still folded.
as for the input stray cap, i was talking about the correct functionality, i didn't think of the noise performance. but this noise power amplification is confirmed by correct simulation or just your calculation? i would think the input stray cap doesn't amplify the noise power. instead, it adds one more noise source to the circuit, whose noise power is something like 2kTCpar/Cf^2. it sounds like your Cpar is too large compared with Cf.