[time-nuts] Code for phase noise and allan variance

Magnus Danielson cfmd at bredband.net
Mon Jun 27 18:40:37 EDT 2005

From: Matt Ettus <boyscout at gmail.com>
Subject: [time-nuts] Code for phase noise and allan variance
Date: Mon, 27 Jun 2005 15:22:25 -0700
Message-ID: <ad9f7823050627152273d400cd at mail.gmail.com>


> Does anyone have code which will take an amplitude vs. time input
> stream and output phase noise and/or allan variance?

I guess you could do it that way, but really, it would be alot of data at a
high sampling rate to make any usefullness. The single-shot resolution is just
one of the limiting parameters and a sampled system has a bandwidth limitation
(good old Nyquist) which also puts a limitation on single-shot resolution.
I would say that slope estimation would make a poor indicator.

Allen variance is calculated from accurate time samples rather than amplitude
samples. Time interval counting is really the best way to reduce data, and it
must be back-to-back (which is possible with sampled data, but much of the
data is just waste of time and storage). Much of the pre-processing would be
to convert the sampled stream into time interval counts anyway. Basically doing
the trigger point detection and time estimates in software.

Lets just say that I'm sceptical. Time Interval Counters isn't rocket science
and nor is ADCs, but they are very different animals for very different needs.

However, performing very accurate timed ADC is in itself a very interesting


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