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Regarding PNOISE results obtained from Spectre-RF

sarfraz

Hi,
What sort of spectral density is obtained when we do Pnoise analysis in Spectre-RF.
Is it power spectral density of phase or is it power spectral density of voltage?

Best Regards
Sarfraz

  • Hi Sarfraz,

    It is power spectral density of voltage (or current, depending on how you have probed the output in the pnoise analysis). This can then easily be converted to phase noise (in dBc using the phaseNoise calculator function - use the direct plot form in ADE to do this easily).

    Strictly speaking this gives you output noise in dBc rather than phase noise, but for most oscillators the PM part is dominant and so it's the same as the phase noise. If you want true separation of the AM and PM parts of the noise, you can use noiseType=modulated (at the bottom of the pnoise form) to extract PM and AM parts (as well as being able to see the noise in both the lower and upper sideband).

    Regards,

    Andrew
  • Thanks Andrew for the quick response,

    I tried simulation with  noiseType=modulated.

    What I found is that it decomposes the results into AM, PM, USB and LSB?

    Now I have a question, correct me if I am wrong:  When we need the power spectral density (PSD) for phase we should take into account the noise contribution of amplitude modulation as it is converted into phase modulation?

    So what I conclude is that with Spectre-RF we will not be able to see PSD of phase with all noise sources included; As from phase noise simulation with noiseType=sources, we get the PSD for voltage (which as you pointed out in your reply, will be close the PSD of phase for oscillator kind of circuit) and with noiseType=modulated we can individual contribution of AM and PM.

    Best Regards

    Sarfraz
  • Hi Sarfraz,

    If you're interested in the phase-modulated noise at the output, then the PM output from "modulated" mode is what you want. This will include _all_ noise contributions (be they am or pm at source) and tell you the phase modulated content at the output.

    Regards,

    Andrew

  • In Spectre 6.1, in the Pnoise simmulator, modulated noise type. Do you know if the PM noise is SSB or DSB. I'm trying to figure out if my results are 3db greater than they should be. I'm only interested in SSB

  • If you look at the PM output it's DSB (because it is using both sidebands to compute the AM and PM components), if you look at either the USB or LSB output it's SSB. At least that's what I think it should be - checking such an old version is hard (and makes little sense for me to check).

    Note that spectre 6.1 is pretty old - I would strongly advise against using a version of the simulator that is probably 7 years or so old - I can't quite remember the date ranges for MMSIM61. SSince then we've had 6.2, 7.0, 7.1, 7.2, 10.1, 11.1 and 12.1 (so 7 major new versions of the simulator).

    Regards,

    Andrew.

  •  Hi Angel,

    L(f) is defined as a single sideband entity and in the phase noise results I have obtained in IC 6.1 the pnoise output reflects this definition. I hope I understood your question correctly!

     

    Shawn

  • Thank you for the quick response. My apologies, I am using cadence 6.1 and MMSIM 11.1. So just to verify for this version when I run PNOISE, noise type ->modulated. PM = DSB, AM =DSB, LSB = SSB, USB = SSB? Therefore, if I'm interested in SSB PM the results I see are actually 3db higher than they should be? Thank you for the help.

  • The definition of modulated AM and PM noise in Cadence was changed some time ago, see http://www.designers-guide.org/Forum/YaBB.pl?num=1309258199/27#27 .

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