Quote:If we use fixed time step solver in signal flow model simulator and set analysis time step lesser than time resolution of jitter,
we can never miss jitter in FFT.
Suppose, if the accuracy of discrete time simulator is 1ps,
& we upsample the waveform, be it square or sine, at less than 1ps,
then i dont think we are missing anything.
Since for taking FFT, we are sampling at rate higher than the accuracy of the simulator. I think that's what
Pancho meant by
Quote:we have to set analysis time step lesser than time resolution of jitter.
Then i agree with what
Pancho said.
But, obviously this method requires unnecessary upsampling at such high frequency in the Post-Processing Phase generating large no. of timepoints.
If
Ken says, Spectre employs a better algo taking only transition timepoints into consideration, then it's worth it.
Speaking alongwith the on-going but digressed discussion,
Ken, if you say, taking a FFT directly over VCO/FDN to determine phase noise is incorrect, then while doing transient noise simulations on PLLs, when we take DFT of the output clock to obtain phase noise PSD, IS THAT INCORRECT TOO ??
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Mayank.