[time-nuts] Performance verification for time counters

Bob kb8tq kb8tq at n1k.org
Wed Nov 29 16:52:36 EST 2017


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.


> 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
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