[time-nuts] GPSDO control loops and correcting quantization error

David davidwhess at gmail.com
Fri Sep 14 23:18:13 UTC 2012


On Fri, 14 Sep 2012 15:08:53 -0700, Hal Murray
<hmurray at megapathdsl.net> wrote:

>djl at montana.com said:
>> Michael: Actually implementing a 16 bit DAC to its 1-bit minimum resolution
>> will be headache enough. You will gain a real education in good grounding
>> practice, shielding, power supply stability and noise, and other Murphy
>> intrusion. A 32 bit DAC IMHO, is impossible, and that's the name of that
>> tune. 
>
>The trick for this application is that you don't need full accuracy over the 
>full range of the DAC.  All you need is roughly linear and stable around the 
>operating point.  The PLL will take care of any offset.  Any gain error is 
>just a minor change to the overall gain.

One thing you sure want is a DAC that is monotonic.  Differential
nonlinearity larger than the least significant bit can cause some
rather peculiar servo loop problems.



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