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sum of sampled_noise output spectrum, how to access the phase information?

NewScreenName

Hi all,

I am trying to simulate the pnoise of a circuit whose output of interest is then passed through a high pass FIR filter x(n)-x(n-1)+x(n-2)-x(n-3)+x(n-4)-...-x(n-L-1) with L even number.

Because the noise I am interested in, is the one after this filtering process, I have tried to implement this filter in a verilogA model, where I had to put the ignore hidden states option, but the result is I get 0 noise at the output of such model. Is that because the noise is not retained once electrical nets are assigned to variables within the verilog model?

As an alternative, I tried to simulate L cycles of the circuit, performing one pnoise_sampled point for each of these. The idea was to then take the L output noise power spectra and sum/subtract them accordingly to the FIR operation. However this is not yielding expected results. I see the output noise spectrum is not a complex number, therefore I guess it is just showing the absolute values and this would explain why I do not see the expected cancelation of the noise within certain portion of the frequency spectrum.

Is there a way to have a meaningful sum of the output noise at different time points, like for example by accessing the actual output power spectrum with its phase information?

Are there maybe more suitable ways to simulate this? (transient noise would require me very long simulations, so would be the last option if possible

Thank you

Best regards)

  • in reply to ShawnLogan

    Dear ShawnLogan,

    I used a Ts*L period in the pss because I hoped to get the low frequencies filtering discussed above via linear combination of the L sampled noise power. The actual sampling frequency of the ADC is 1/Ts, hence the folding due to sampling, according to me should be limited up to 1/(2*Ts). After the FIR filter action which "averages" or anyway processes the L samples into one result, then the bandwidth limitation would become 1/(2*L*Ts).

    The integration limits you refer to are arbitrary, as they come from a separate testbench used purely to test the noiseSummary functionality on sampled(jitter) pnoise.

  • in reply to Andrew Beckett
    Andrew Beckett said:
    I'm not sure combining the results from different sample points makes sense - if you want to do that, you could use a Verilog-A model to do that

    I will try to follow your suggestion via a model devoid of hidden states and let you know whether it works

    Andrew Beckett said:
    I'll have to check that out to see what happens.

    Thank you very much, it would be much appreciated as I was not able to find further documentation on how to get it working with sampled(jitter) pnoise.

    Best regards

  • in reply to NewScreenName

    Dear NewScreenName,

    NewScreenName said:
    The integration limits you refer to are arbitrary, as they come from a separate testbench used purely to test the noiseSummary functionality on sampled(jitter) pnoise.

    I may have misunderstood your response or perhaps was not clear in my response, but if the minimum "arbitrary" integration limit of 1000 in your noiseSummary() argument is greater than 1/2 the inverse of your pss period, I am concerned the noiseSummary() function will produce an error. The maximum offset frequency for a sampled pnoise analysis is 1/2 the inverse of the pss period. This is distinctly different than in a conventional time-average based pnoise analysis.

    If I am stating something obvious to you, I apologize! I just wanted to make sure we both understood one another's comments!

    Shawn

  • in reply to Andrew Beckett
    Andrew Beckett said:
    I'll have to check that out to see what happens.

    Dear Andrew,

    I was wondering if this issue might be related with having to specify a jitterevent time when trying to use noiseSummary on a noise sampled pnoise? But even if that was the case, I could not find how this could be specified in the noiseSummary function. (However the issue occurs even when only one jittereventtime exists).

    Also, I can access to the noise power spectrum with getData("/out" ?result "pnoise_sample_pm0"), but this cannot be directly passed to the noiseSummary function in place of the ?result parameter, so it is not helpful (unless there is some specific syntax which would allow me to do that?)

    Thank you

    Best regards

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