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How to derive edge phase noise from Output Noise in sampled Pnoise simulation

mxm14

I m driving a buffer with a clock of 7 GHz, launching a pss simulation and  pnoise sampled at the rising edge of the output ( threshold set at 0). 

I obtained the following graph for output noise and edge phase noise

the two spectra differs of 13dB that i suppose be the power of the carrier since i consider:

dbC= 10log( Pnoise/Pc)= 10logPnoise - 10log(Pc)= Output Noise Spectrum -10log(Pc)

so 10log(Pc)=13dB

if I plot the spectrum of the rms output clock i obtain:

so if i consider Pc=Vrms^2 i  have

10log(Pc)= -7.87dB

It s not clear for me how the edge phase noise is obtained....What i m doing wrong?

 

Parents

  • Edge Phase Noise is related to Jitter. If you want to compare it to Sampled Pnoise, you need to take into account the slope of the signal at the threshold crossing as well.

    Edge Phase Noise has been defined in a way so that it can be directly used in formulas that were originally developed for the SSB Phase Noise of sinusoidal oscillators. 

Reply

  • Edge Phase Noise is related to Jitter. If you want to compare it to Sampled Pnoise, you need to take into account the slope of the signal at the threshold crossing as well.

    Edge Phase Noise has been defined in a way so that it can be directly used in formulas that were originally developed for the SSB Phase Noise of sinusoidal oscillators. 

Children
  • in reply to Frank Wiedmann

    Dear mxm14,

    As Frank correctly notes, the phase noise computation involves the entire waveform whereas the edge jitter examines the sampled noise at a threshold. There is an application note entitled "Why is pnoise sampled(jitter) different than pnoise timeaverage on a driven circuit?" that might be of interest to aid your understanding. Using the example it provides for a driven inverter (similar to your driven inverter), I have compared their result with your result. Note that the edge phase noise is different when the threshold is defined for the rising and falling edges.

    I hope this helps.

    Shawn

    Figure 1

    pastedimage1678873557298v1.pdf

  • in reply to ShawnLogan

    Shawn, I don't think that this is the problem here. He is already looking at sampled pnoise, not timeaverage.

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