hi, all

I think it is common sense that we use pmjitter to simulate VCO phase noise, due to the modulated noise by the oscillator signal, if buffer/divider is followed. But after reading ken's paper about cyclostationary noise, I still have some questions about the pnoise noise type.

1.  characterizing the modulated noise at the threshold using pmjitter is for characterizing the cyclostationary noise due to the following stage, like buffer. Can i take it this way? if no, why?

2. if so, i think both fmjitter and modulated can also do the job, for they use the two-sweep approach and one of them is based on correlated type, which is also a way to characterize cyclostationary noise, according to ken's paper in page 20. Am I right? if yes, what is the difference between fmjitter and pmjitter?

3. according to one of ken's post years ago, the dominant source of phase variation is due to oscillator phase noise, which is slow and the same for all signals and can be measured using either sources or time-domain. But in my opinion, the noise here is still cyclostationary noise and should be simulated using time-domain or pmjitter. is it right？

regards,
Hao

I wouldn't recommend it. See http://www.designers-guide.org/Forum/YaBB.pl?num=1158924743 and http://www.designers-guide.org/Forum/YaBB.pl?num=1158788102.

Right. Modulated and fmjitter pnoise analyses only examine a single sideband on both sides of the signal and are only suitable for sinusoidal signals with a small bandwidth.

It means that only the frequencies around the fundamental of your signal will be taken into account for the result, but not the harmonics. It is like having a narrow bandpass filter around the fundamental frequency of your signal.

Well, the bandpass-filtered signal is different from the original one, so it's no surprise that the jitter is also different.

Which of the two results is relevant for you depends on how you are going to use the output signal. If you are going to use a narrow bandpass filter to obtain a sinusoidal signal, fmjitter or modulated gives you the correct information. If you are going to use the output signal directly to trigger some other circuit having a certain threshold voltage, then the pmjitter result is relevant for you.