[time-nuts] Performance verification for time counters

Magnus Danielson magnus at rubidium.dyndns.org
Wed Nov 29 16:45:30 EST 2017

Hi Leo,

On 11/29/2017 10:24 PM, Leo Bodnar wrote:
> I am looking for an established and widely accepted procedure for verifying performance of high resolution time counters.


> 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?

This is not very useful in practice, except for certain tests.

> 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

Using an oscillator to syntesize a somewhat offset frequency works very 
well and is established. If you have a frequency synthesizer that you 
can lock to 10 MHz you should be just fine. If you set it to 9,999 MHz 
the period will be 100,010 ns, that is 10 ps larger than the 10 MHz. 
While you may not trigger on each occurrence, the time difference sweeps 
through the full range of time relationships within 1 ms and then it 
re-occurs. By collecting lots of samples, you can histogram in 10 ps 
bins and make analysis. It is also trivial to measure RMS performance.
Set the synthesis for 9,9999 MHz for 1 ps sweep.

Proven in battle. You can use relatively cheap equipment for this.

Some relatively cheap DDS-board may pull this off too.

> 3) Trusted pulse generator with high resolution delay adjustment fed from the same master clock as the counter

This works too. I think it may be hard to push it very deeply down. I 
have 50 ps and 5 ps resolution versions for this purpose. May be a 
complementary solution to the offset generator above.

> 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.

I hope that you can feel inspired to quickly locate the equipment needed.

Good luck and report back on your progress!


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