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Measurements >> Phase Noise and Jitter Measurements >> Some questions about Ken's paper: Predicting......
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Message started by lunren on May 27^th, 2006, 1:44am

Title: Some questions about Ken's paper: Predicting......
Post by lunren on May 27^th, 2006, 1:44am

Dear all,

I am a new comer to this forum. Let me first give my honest thanks to Ken for his great works. Recently, I read the paper by Ken"Predicting the phase noise and jitter of PLL-Based frequency synthesizers", It is really a wonderful work for pll disigners. Afer reading the paper, however, I am confused by some questions maybe due to my short knowledge. I know Ken is very busy, so I hope other experienced experts who read the paper can give me some hints.
1) with pss and pnoise analysis, I ploted the phase noise curve. In fact the curve is L not S_phi, My first question is how can I get a curve of S_phi?
2) with the curve of L, acorrding to Ken's paper "Predicting the phase noise ...", page 33, we can calculate the jitter of the circuit for example a VCO. But I am confused by the fact that: when I used L=-71dBc/Hz at 100KHz from the carrier (f₀=409MHz), the jitter is 3.39ps; when I used L=-42dBc at 10KHz from the carrier (f₀=409MHz), the jitter is 9.59ps. I am confused by the way to calculate jitter according to Ken's paper. Which one can I accept as my jitter? What's the exact meaning of the jitter culculated from equation(74)? It is the period jitter just at the offset frequency "point" or some thing else?
3) I find another paper about conversion from phase noise to jitter. http://www.maxim-ic.com/appnotes.cfm/appnote_number/3359. From the paper, the jitter is calculated by integrating _L from for example f₁ to f₂. What's the difference between Ken's method and maxim's?

Title: Re: Some questions about Ken's paper: Predicting..
Post by Ken Kundert on May 31^st, 2006, 7:32am

1) See (27).
2) if your jitter changes based on which offset frequency you use, it is an indication that flicker noise is present, which invalidates the formula used to predict jitter. In fact, even the metric used to characterize jitter is invalid when flicker noise is present.
3) I don't know. I'll try to take a look at this paper and get back to you.

-Ken

Title: Re: Some questions about Ken's paper: Predicting..
Post by lunren on Jun 1^st, 2006, 12:42am

Dear Ken,

Thank you a lot for your explanation. According to your answer, I reread your papers and some related materials today. I also resimulated my VCO. I got the phase noise plot (please see attachment). The phase noise ramp down by -30dB/dec until about 1MHz. Offset frequency above 1MHz, the slope of the phase noise increases to some value but still smaller than -20dB/dec. The phase noise becomes flat above 10MHz. Normally the phase noise caused by the white noise proportional to 1/f². But in my simulation result, there is no abvious area where the phase noise is proportional to 1/f². Does this mean the flicker noise dominates too much than the white noise in my VCO over a wide frequency band?

Title: Re: Some questions about Ken's paper: Predicting..
Post by swicap on Jul 24^th, 2006, 12:11am

3). The formula in ken's paper gives short term periods rms jitter,
and Maxim's application note is used to predict long term periods rms jitter.

Title: Re: Some questions about Ken's paper: Predicting..
Post by David Lee on Aug 8^th, 2006, 10:40pm

2) In Ken's paper, (74) gives rms period jitter for a VCO, caused by thermal noise and shot noise. This does not include the effect of 1/f noise.
3) There are many different PLL jitter specs. To understand the relationship among them, have a look at:
David C. Lee, "Analysis of Jitter in Phase-Locked Loops",
IEEE Transactions on Circuits and Systems II, Volume 49, No 11, Nov 2002, Pages 704-711