FYI, for others who is interested in the reference. 1. Jitter in ring oscillators McNeill, J.A.; Solid-State Circuits, IEEE Journal of Volume 32, Issue 6, June 1997 Page(s):870 - 879 2. Ali Hajimiri, S. Limotyrakis, and Thomas H. Lee, "Jitter and Phase Noise in Ring Oscillators," IEEE Journal of Solid-State Circuits, June 1999, p. 790-804. [Paper] 3. T. H. Lee and A. Hajimiri, ?Phase Noise in Oscillators, A Tutorial,? Invited Paper, IEEE Journal of Solid-State Circuits, vol. 34, no. 3, pp. 326-336, March 2000 Cheers, Yafei --- "Tang, George" <George.Tang@xxxxxxx> wrote: > Alfred,=20 > > See comments in [[[[[ ]]]]]. =20 > > George=20 > > > -----Original Message----- > From: Alfred P. Neves > [mailto:al.neves@xxxxxxxxxxx]=20 > Sent: Wednesday, March 21, 2007 11:07 PM > To: weirsi@xxxxxxxxxx; Tang, George; > si-list@xxxxxxxxxxxxx > Subject: RE: [SI-LIST] Re: Jitter transfer vs. > accumulation > > George, > > > >{{{{{Alfred made the initial postulate that > open-loop VCO has rms=20 > >jitter governed by his funny equation Y=3DmX + b, > where Y is the rms=20 > >jitter, X is the time duration of measurement, and > m > 0. This shows=20 > >that as time goes to infinity, the rms jitter of > the open-loop VCO also > > >goes to infinity. > > No George, this is not what I said. It is the > autocorrelation record of > the VCO that increases linearly on a log-log plot, > where the axis are > log(RMS jitter) and log(time interval length), where > this is not to be > confused with an RMS jitter or whether it is bounded > or not. =20 > > [[[[[Amazing. If your autocorrelation record for > the open-loop VCO > looks like Y=3DmX + b, you have either invented a > random-noise-free > environment (congratulations to you,) or your > environment is so bad that > it is completely dominated by deterministic > modulation so you cannot > take clean measurements at all. My guess is that > the latter case is the > truth. ]]]]]]]=20 > > > I already > provided numerous references regarding this and can > also provide > numerous measurements for several VCO's to > illustrate VCO RMS jitter > characteristics versus measurement interval. We > have used this analysis > 100's of times for closed (and open loop) PLL > analysis to determine the > PLL loop bandwidth and peaking in the PLL loop > response. =20 > > [[[[[Like I said before, we do not see this problem > in our measurements. > The VCO RMS jitter is bounded, and so is the PLL RMS > jitter. The RJ > distribution takes on a true Gaussian waveform. In > addition to that, we > test our communication channels (including TX, RX, > &PLL) for weeks with > no errors. All our measurements fairly closely > match up with the system > BER predicted by the model simulation. We do not > see the problems that > you are fighting with. ]]]]]=20 > > > You can also > use this analysis to analyze jitter problems like > spurious response due > to charge pump leakage, power supply junk like > switching noise or HF > digital, XTALK in the substrate, SSO, and jitter > multiplication from PLL > to PLL. The basis for this analysis is work by John > McNeil in > collaboration with Analog Devices in the mid 90's - > have you read the > reference already provided, I can send you a copy if > need be? I didn't > originate the concept, just use the practical > elements to analyze PLL's > and VCO's. Before you belittle this, become > dismissive, or make any > more personally targeted comments it may behoove you > to do a bit of > homework. And once again, you are asked to > significantly raise the > level of your professionalism in your > communications. =20 > > > He further claimed that with the feedback loop > of=20 > >the PLL, the rms jitter became bounded. You don't > think Alfred was=20 > >crazy enough to make the mistake of comparing phase > jitter of VCO to=20 > >the RMS jitter of the PLL, do you? That will be > comparing apples to=20 > >bananas, let alone oranges > > No, I did not say this either. The reference was > regarding the > autocorrelation record, NOT any comment regarding > characteristics of VCO > RMS jitter. A VCO has certain properties: It has > poor frequency > stability, it is temperature sensitive, it is not > WSS (wide sense > stationary), it has a LOT of low frequency jitter > due to numerous 1/f > noise sources, it also has unbounded RMS jitter, but > the estimate of the > RMS jitter is difficult to measure since: Measure > the RMS of a VCO > over a certain time T, remeasure the RMS jitter > later over the same time > interval and you will arrive at a different RMS > number since it is not a > stationary process. Sample size really has little > to do with this. > BTW, do you have data on "stable" VCO's in terms of > PPM frequency drift > versus time, after you claim the temperature > stabilizes in 1-2 hours. > > [[[[[If the RMS RJ of the VCO is unbounded, the > closed-loop PLL will > never be fully stable since the feedback has finite > correction > capability. The only way the PLL can be fully > stable is that the RMS > jitter of the VCO HAS TO BE BOUNDED. We measure the > PLL for say 20 > minutes on day one and another 20 minutes on day 2 > and day 3, and the > Peak-to-Peak jitter and RMS jitter for each day > matches the results of > the other days down to 0.1ps range. To say that the > VCO and/or the PLL > has unbounded RMS jitter will be a tough tough sell, > since you will > never be able to get this kind of repeatability > otherwise. ]]]]]]=20 > > > NOW, place the VCO into a PLL loop that is locked on > a stable input > signal, the VCO accumulated phase jitter is shaped > by the PLL loop > response. The RMS RJ jitter measured (using some > RJ-DJ extraction) will > be unbounded - by definition. =20 > > [[[[[Why? What equipment do you use to give you > such results? ]]]]] > > The resulting PLL accumulated jitter, > phase jitter, or autocorrelation record will not > continue to increase > past a value related to the PLL loops bandwidth, > however (assuming the > loop is stable). =20 > > > [[[[[Phase jitter is bounded?? What equipment shows > that! ]]]]]] > > This is due to the intrinsic PLL loop gain. =20 > > [[[[[No, you are wrong, again. Even when the PLL is > in the locked > operation, the feedback can only correct the VCO > jitter within the loop > bandwidth. Beyond that, the feedback cannot do > anything, period. When > the overall PLL output RMS jitter is measured to be > bounded across all > frequencies, then the VCO RMS jitter *must also be > bounded across all > frequencies*. =20 > > On the other hand, phase jitter for a locked PLL is > unbounded due to > probability of random events. ]]]]] > > > My point is that the way to deal with both VCO's and > the VCO-PLL > === message truncated === ____________________________________________________________________________________ Expecting? Get great news right away with email Auto-Check. Try the Yahoo! 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