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pnoise simulation setup questions (again?)

eeask

Hello, there

I'm simulating the jitter performance of a driven ckt (inverter chain like, e.g.). I'm confused by the simulation setup and like to ask a couple of questions regarding the setup parameters.

 1.  relharmnum

First I set sweeptype=relative and relharmnum=1 and run the simulation. Then I change  relharmnum=0 and compare the output results from 2 simulatoins. It looks like that the difference is very small (smaller than 0.01fs). Per the Q&A from Cadence's support website, if we set  relharmnum=1,we're looking at the frequency

 from f0 + 1Xfstart to f0 + 1Xfstop (f0 is the fundamental frequency and fstart/fstop the sweep frequency range).  1 is the relharmnum.

 I think this is the frequency range exactly of my interest. But I wonder why setting relharmnum=0 didn't really disable the sweep frequency range setting (fstart/fstop), if we just follow the equation as above. The small difference of simulation results show it.

 

2.  fstop

I already explored the previous discussion regarding how to set fstop to simulate a driven ckt. The suggestion is to set it to 1/2 of f0 (fundamental tone frequency). It's consistent with Nyquist sampling theorem. But I like to know if it's in conflict with up/down conversion of noise whose frequency can be N times of f0 (N set by the maxsideband). 

Thanks for clearing my questions and any comments welcomed!

 

 

 

Parents
  • Hi, Andrew

    I’m confused by your answer.

    In an oscillator if we just ignore harmonics of fundamental tone for simplicity, the system can be modeled by thermal/flicker noise mixing with fundamental tone (refer to SpectreRF user guide). The output at the mixer is still wideband noise. Then the wideband noise will be sampled by the ideal sampler in pss/pnoise simulation. If the wideband noise is not band-limited in advance, the aliasing will occur. I guess that there’s something I didn’t get right. Could you clarify how the noise will be calculated in pss/pnoise simulation? Thanks a lot!

    Best
Reply
  • Hi, Andrew

    I’m confused by your answer.

    In an oscillator if we just ignore harmonics of fundamental tone for simplicity, the system can be modeled by thermal/flicker noise mixing with fundamental tone (refer to SpectreRF user guide). The output at the mixer is still wideband noise. Then the wideband noise will be sampled by the ideal sampler in pss/pnoise simulation. If the wideband noise is not band-limited in advance, the aliasing will occur. I guess that there’s something I didn’t get right. Could you clarify how the noise will be calculated in pss/pnoise simulation? Thanks a lot!

    Best
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