[time-nuts] DAC performance [WAS: Papers on timing for lunar laser ranging]

Bob kb8tq kb8tq at n1k.org
Sun Jul 16 19:10:51 EDT 2017


> On Jul 16, 2017, at 6:33 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> On 7/16/2017 1:51 PM, Bob kb8tq wrote:
>> Hi
>> One gotcha with any ADC or DAC is going to be the reference. There, you are in the same
>> “get what you pay for” dilemma. Stable and noisy, can do. Quiet and not very stable, can do.
>> Both stable and quiet, not so easy if you want it cheap.
>> Noise can also be the sigma delta ADC’s weak point. Even at slow rates, some of them need
>> a lot of averages to quiet down.
> The reference initially used in the E1938A turned out to be too noisy/unstable.  It was non trivial to find an upgrade.  The
> HP Smart Clocks of 20 years ago were limited in their performance
> by the reference used.
> Has there been much improvement in references in the intervening
> 20 years?

They still don’t seem to have the hysteresis problem licked. Yes, you can do an oversized reference
and take care of the issue. More or less that’s what you would have done 20 years ago.


> Rick N6RK

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