[time-nuts] ADC sample voting algorithm?

Scott Stobbe scott.j.stobbe at gmail.com
Wed Oct 5 21:05:06 EDT 2016

It sounds like once in awhile your sampling something else too. Ground
bounce of a 10 MHz buffer, or something coupling onto your phase detector,
or running your adc at the edge of a timing spec?

How large would the outlier be in mV?

On Wednesday, 5 October 2016, Nick Sayer via time-nuts <time-nuts at febo.com>

> This is tangentially on topic, I suppose. It’s for my GPSDO.
> I notice periodically that the phase measurements seem “noisy.” You can
> see that over the course of several seconds the value doesn’t change, then
> it jumps a bunch and then comes right back.
> My theory at the moment is that sampling the ADC multiple times in a row
> might help, but then what’s the best way to (quickly) pick which sample to
> use?
> The mean would allow a bad sample undue influence.
> At the moment, I’ve coded taking 3 samples, averaging them and picking the
> sample that is closest to the mean. If I’m right, and two of the samples
> happen to be very close to each other and a third is an outlier, then that
> seems like it would eliminate it.
> I guess what I want is the mode, but with 3 samples, that’s going to be
> poorly defined (if at all).
> Anyone have any suggestions (besides a larger sample size)?
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