[time-nuts] PRS-10 findings
magnus at rubidium.dyndns.org
Wed May 30 10:48:04 EDT 2007
From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] PRS-10 findings
Date: Thu, 31 May 2007 02:27:09 +1200
Message-ID: <465D89BD.8000106 at xtra.co.nz>
> Poul-Henning Kamp wrote:
> > In message <email@example.com>, 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-
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