[time-nuts] Comparing Reference Accuracy

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri May 23 01:52:25 EDT 2008

Stanley Reynolds wrote:
> Bruce
> This counter may be close : http://www.psplc.com/datasheets/vigo/VOITC-200.pdf
> or http://ztc.wel.wat.edu.pl/kalisz/T-2300R.pdf
> Stanley

Much better but still inadequate for characterising good oscillators, at 
least for short averaging times.

Its actually not too difficult to achieve 25ps or better resolution with 
a suitable interpolator.

You can actually achieve better resolution with an analog phase comparator.
The only constraints being that the frequency difference between the 2 
sources being compared isnt too large and that such comparators have 
deadbands towards the end of the range.
The latter constraint can be overcome by using a pair of linear phase 
comparators driving the second with one of the signals in quadrature 
with the corresponding input to the first comparator.


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