[time-nuts] Phase noise and jitter

Javier Serrano javier.serrano.pareja at gmail.com
Mon Oct 13 15:15:24 UTC 2008


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


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