From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] PRS-10 findings Date: Thu, 31 May 2007 02:27:09 +1200 Message-ID: <[EMAIL PROTECTED]>
> Poul-Henning Kamp wrote: > > In message <[EMAIL PROTECTED]>, Peter Vince writes: > > > > > >> I have seen something similar with my 53132A. I was checking > >> on the delay variation of an amplifier distributing 10 MHz, and > >> noticed a regular sinusoidal pattern, about a third of a nanosecond > >> peak-to-peak, with a period of about 70 seconds. > >> > > > > > A manifestation of the effects of slowly sweeping through a range of > start and stop interpolator values so that the interpolator integral and > and differential non linearities become apparent? Yes. I have been pointing toward such tests earlier. One should recall that the deviations is not only from non-linear effects, but also from highly linear effects such as cross-talk between channels which help to cause biases in channels. Similar cross-talk towards the internal clocks should be expected. There can be many causes of such cross-talk, so due care needs to be considered throughout the design. > Strictly the difference between the nonlinearities of the start and stop > interpolators becomes visible. > The resultant variation of around 300ps pp are well within the > specifications for the counter. > > Almost any kind of interference will cause such anomalies and the > > closer the frequencies are to a multiple of each other, the longer > > the period will be. > > > > It is quite common for the frequency difference between the counters > > internal X-tal and the measued frequency to show up like that once > > you start to measure down in the nanosecond end of things. > > > > The HP5370 has a rather heavyhanded piece of electronics that > > eliminate this effect with a jitter based approach and as far as I > > have been able to measure, it works. > > > > > Not quite true the HP5370 has a whole host of anomalies like > differential linearity errors of 100psec or more for certain time > interval ranges, at least according to its designers. > The identified causes are: > Crosstalk between microstriplines used for each channel (effective only > when the affected signals are simultaneously active near a trigger > point) and modulation of the internal 200MHz reference by the mixer > outputs (always present with a quasi period of ~5.02ns). This matches my experience too, altought not with the 5370. I would also expect there to be some interaction with the interpolators. There always are. Ground-bounce is certainly a reason for crosstalk which causes such non- linearities. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts