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Simulators >> RF Simulators >> Noise type in Pnoise for VCO phase noise simulation
https://designers-guide.org/forum/YaBB.pl?num=1385467183

Message started by Hao Yan on Nov 26^th, 2013, 3:59am

Title: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Nov 26^th, 2013, 3:59am

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

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Nov 27^th, 2013, 9:17pm

as far as i know, analyses of fmjitter and modulated are the same. Maybe i can simply the first two questions into one, which is whether or not the fmjitter( or modulated) is applicable in phase noise simulation of oscillator with buffer/divider as the following stage?

does anyone has a clue about this? or anyother thread i can get to?

thanks in advance!
Hao

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Frank Wiedmann on Nov 28^th, 2013, 1:12am

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.

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Nov 28^th, 2013, 4:34am

hi, Frank,

thanks for your attention. i've read these threads. But i still have two questions to be confirmed.

1. Modulated (fmjitter) has done correlated-type simulation to simulate cyclostationary noise. But the simulation is done over the whole period instead of the threshold-crossing point, which is not suitable with divider or buffer followed. right?

2. Ken has talked about two kinds of phase variation in oscillator and the first one, due to oscillator phase noise, is slow and the same over one period and can be simulated using sources. But I think the output noise of the sole oscillator is still cyclostationary noise and should not use sources. or am i take it wrong?

best regards,
Hao

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Frank Wiedmann on Nov 28^th, 2013, 5:15am

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.

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Nov 28^th, 2013, 6:26am

hi, Frank,

thanks again for your help! but i'm sorry i can't quite follow you here...

what do you mean by "examine a single sideband on both sides of the signal"? and is sinusoidal signal ideally a one-tone signal? i don't understand what's a sinusoidal signal with small bandwidth.

thanks,
Hao

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Frank Wiedmann on Nov 28^th, 2013, 7:23am

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.

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Nov 28^th, 2013, 7:36am

oh, i see~

but in this case, I think the phase noise result from fmjitter/modulated would be better than that from pmjitter, as it just takes the fundamental part into consideration.

but in my design which is a cross-coupled LC VCO, the fmjitter result is about 1.5 dBc worse than the pmjitter. do you have any idea about this？

best regards！
Hao

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Frank Wiedmann on Nov 29^th, 2013, 12:26am

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.

Title: Re: Noise type in Pnoise for VCO phase noise simulation
Post by Hao Yan on Dec 2^nd, 2013, 4:04am

Thank you, Frank!

i think it's clear for me about how to set up my simulation. thank you very much!

wish you a good day!
Hao