[time-nuts] Performance verification for time counters
Bob kb8tq
kb8tq at n1k.org
Wed Nov 29 21:52:36 UTC 2017
Hi
The “simple / easy / quick” approach is a pps generated by source with a small frequency
offset. If your objective is 5 ps, both your reference and your offset source will need to do
better than that. While that sounds like it’s specific to this technique, it’s actually a more
general constraint.
Just how hard this is depends a bit on your definition of jitter. Since you are looking at 1 second,
ADEV with a tau = 1 second *might* be a reasonable measure. If it is, then you need two sources
that are well below 5x10^-12 at one second. That eliminates most signal generators and many
atomic standards. This gets you to using things like Masers or some pretty good OCXO’s. Tuning
a Maser for a low offset is doable. Tuning an OCXO … maybe not so much.
Bob
> On Nov 29, 2017, at 4:24 PM, Leo Bodnar <leo at leobodnar.com> wrote:
>
> I am looking for an established and widely accepted procedure for verifying performance of high resolution time counters.
>
> I have designed a time stamping counter for qualifying 1PPS signal performance against external reference (e.g. 10MHz master clock.)
>
> Simple design verification check I am doing at the moment is gating random selection of master clock edges back into device's signal input and letting the device measure this test signal offset against its reference clock - which, for ideal design, should result in zero offset (modulo 100ns.) My results are roughly in line with what I expect to see http://leobodnar.com/balloons/NTP/time-sampler-test1.png
>
> Now, what would be recognised procedure for sweeping external input pulse delay over few hundred ns in a controlled, measurable and repeatable way?
>
> I can see few naïve approaches:
> 1) Using selectively gated (or divided) reference clock followed by adjustable delay line. E.g. something like mechanically adjusted delay lines used in HP test sets. Or, perhaps, calibrated rigid coax sections?
> 2) Slightly offset another master clock (e.g. second Rb oscillator) gated in a similar way but without delay line, followed by statistical data analysis
> 3) Trusted pulse generator with high resolution delay adjustment fed from the same master clock as the counter
>
> I am looking for something with ~10ps accuracy, 100ns+ range, and reasonably low jitter (~5ps or better.)
> It is possible that the range needs to be split up (e.g. fixed rigid coax delay line followed by a mechanically adjust section.)
>
> This is a low budget fun project so something simple and common sense is preferred to "price on application" NIST traceable equipment.
>
> Thanks!
> Leo
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the Time-nuts_lists.febo.com
mailing list