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Simulators >> RF Simulators >> question on pnoise sim theory
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Message started by dog1 on Apr 9^th, 2019, 12:35pm

Title: question on pnoise sim theory
Post by dog1 on Apr 9^th, 2019, 12:35pm

Hello all,

I have a question about the pnoise simulation.

I understand that in frequency domain, the switching system should translate noise in the following way:

cross correlate the noise source spectra with the model of the system large signal behavior (eg. square or sin signal in a mixer)

However, I read in the manuel that the pnoise is actually "a time-average of the noise at the output is computed as a spectral density versus frequency". This I could not understand, because it looks to me that "the model of the system large signal behavior" as mentioned previously is different from "a time-average of the system transfer function at each bias point in a period".

For example, for a simple mixer, "the model of the system large signal behavior" could be a square wave, while at each time point, this simple model results in a transfer with infinite BW, thus the "time-averaged" version also having infinite BW.

I don't know where goes wrong. Could anybody help me? Thanks.

Title: Re: question on pnoise sim theory
Post by Ken Kundert on Apr 11^th, 2019, 12:41pm

SpectreRF performs a detailed noise analysis including all correlations, and then presents the time-average of the noise. So the time-averaging only occurs after the noise leaves the circuit and is being processed for display.

This is very analogous to the case where you are observing the noise of a circuit with a spectrum analyzer. The circuit processes the noise including the effect of all correlations, and the result is observed by the spectrum analyzer when then computes the time-average of the noise before displaying it.

-Ken

Title: Re: question on pnoise sim theory
Post by dog1 on Apr 12^th, 2019, 2:19am

Hello Ken,

Thanks very much for your reply. Now it is clear for me:)

Best regards,

Chen