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Pnoise sim with different noise type

VINCENTCHENG

Hi,

I try to study PNOISE currently, and the simple Res+MOS switch+Cap is my schematic.

The switch Fs=1MHz, RES=10Kohm, CAP=1pF.

I found that there are many noise type in PNOISE setting as follow picture:

First, I try "sources" for sim output noise @vo_sc2 in my schematic above.

The sim. results are as follows (V/sqrtHz):

Then, I try "timedomain" for sim output noise @vo_sc2 in my schematic above.

The sim. results are as follows (V^2/Hz):

The results of  different noise type are quite different.

For "sources", we can see the SINC function (sin[x]/x) in the output noise waveform.

But for  "timedomain", the SINC function is not shown.

I would like to know whether noise type should I use for PNOISE simulation?

Thanks.

  • Andrew Beckett

    I doubt you want to be using timedomain . Note that the choices have changed in more recent versions - they are now timeaverage and sampled(jitter). The timedomain (as does the sampled(jitter) mode) works by inserting an ideal sampler at the PSS fundamental rate at the output of the circuit. What that means is that it doesn't make sense to have the pnoise sweep frequency go above half the PSS fundamental, because the ideal sampler would then alias all the noise from higher sidebands into the band 0->0.5MHz (in your case). So you simply won't see the SINC function in this case.

    That requirement is not there if you use "sources" (or the newer "timeaverage") mode. 

    The sources/timeaverage mode gives you an output similar to what you'd see with a spectrum analyser on the output, whereas the timedomain/jitter modes are useful when you want to sample the noise at a particular instant to (for example) compute the jitter (time-variance) of an edge at a switching instant.

    Regards,

    Andrew.

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