[time-nuts] Allan variance by sine-wave fitting

[Ralph Devoe]

Hi,
       The fitting routine only takes up 40 uS of the 1 sec interval
between measurements, as shown in Fig. 1 of the paper. This is less than
10(-4) of the measurement interval. It just determines the phase difference
at the start of every second. I don't think the filtering effect is very
large in this case.
        The interesting thing is that good results are achievable with such
a short fitting interval. One way to think of it is to treat the fitting
routine as a statistically optimized averaging process. Fitting 40 uS, that
is 4096 points at 10 ns/point,  should reduce the noise by a factor of 64
(roughly). The single shot timing resolution of the ADC is about 10 pS (see
Fig. 4), so dividing this by 64 brings you down into the 100's of fs range,
which is what you see.

Ralph