[time-nuts] GPS noise reduction

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 6 07:29:24 EDT 2008

From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] GPS noise reduction
Date: Sun, 06 Apr 2008 14:30:52 +1200
Message-ID: <47F835DC.50404 at xtra.co.nz>

> If one uses an ADC to sample say a 1MHz sinewave (produced by dividing 
> down the OCXO frequency and low pass filtering) on the PPS edge then 
> subnanosecond resolution combined with the ability to make software 
> corrections of the sawtooth error is possible.

A refined method is to use a sine and a cosine, since these have their worst
slope errors when the other has its best. But you can get far on just a sine.

A classic method is to count time in a coarse clock and then produce an error
signal which is integreated into a capacitor and then either converted into a
longer pulse using a much lower discharge current. Another method is to use an
ADC and then only clear the capacitor. Either way allows for easy access to
x10 to x100 increase in time resolution. Really a handfull of stuff being not
that exclusive and esquicit. Reaching for 1 ns to 100 ps resolution is doable.


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