Javier Serrano wrote: > Dear nuts, > > I would like to know if there is a clear explanation somewhere with > considerations on how to choose an upper frequency limit when integrating > phase noise to find jitter. Let's say I'm interested in the raw jitter > measurement which comes from integrating phase noise without applying any > filter to it. For a given application, I can easily understand that I can > define a lower integration limit if the time spans I'm interested in are > shorter than some value. For example, we run a synchrotron with a 1.2 second > cycle time. Phase noise in our clocks below say 0.1 Hz should be of no > concern since it is "common mode" to all the triggers we define within any > given cycle using counts of the clock we are characterizing (incidentally I > am also interested in your comments on how a phase noise measurement would > fare against Allan deviation in this frequency area). I have a bit more > trouble with the upper frequency limit. Am I right in saying that the right > answer in principle is to integrate to infinity but due to Physics the phase > noise will at some offset fmax be so low that the contribution of > integrating from fmax to infinity would be negligible? How can I then work > out experimentally which is the value of this fmax? Maybe extrapolating the > slope of the curve I measure using for example a low bandwidth PLL > technique? Thanks for any insight. > > Cheers, > > Javier > Javier
You could do that but the resultant integrated phase noise will be quite large and you should take into account the finite bandwidth of the signal processing/distribution system. In practice all amplifiers (buffers, isolation etc), comparators etc have a finite bandwidth which rolls of the response to input phase noise as well as limiting the devices own contributions to high offset phase noise. A typical high quality 10MHz ultra low phase noise distribution amplifier may only have a 3db bandpass of to 1 - 20MHz and a corresponding 100MHz distribution amplifier may have a bandpass of perhaps 80-120MHz. Typical high end instruments for measuring Allan deviation may only have a bandwidth of a few Hz. Even logic devices have a finite gain bandwidth in the transition region. The Allen deviation can be calculated from the phase noise if the phase noise is known for all frequencies of interest. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
