[time-nuts] 31bit ADC, 1000 samples per second

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Dec 10 23:07:06 UTC 2012

In message <CAMQqFunUDaHC9rdrK0g8HXO_KoHS+bndeiLNqSPQ1_b2NqKoHA at mail.gmail.com>
, Didier Juges writes:

>I do not understand how anyone can guaranty no missing codes when the lower
>11 bits are essentially noise? (31 bits resolution versus 20 effective bits)

No missing codes is guaranteed by the design, you'd have to screw up the
digital filters to come out with missing codes.

That's not impossible to do, but the fix is simple: sufficient precision
in the filters, hence the 31 bits.

The 32nd bit is an overrange bit btw, if it tracks the sign bit
you're fine, if it is inversed you are out of range.

Smart detail.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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