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

[Hal Murray]

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.

This thread started with "16 bit PWM DAC".  I think that matches the 
requirements.

I would expect a problem area would be filtering the PWM output.  Anything 
you don't filter out will turn into close in spikes.  It might be fun to try 
to measure them.

64K/72 MHz is about 1 ms.   32bits at 72 MHz is 60 seconds.

Has anybody compared DDS style DACs with PWM?  The idea is to spread the 
pulses out to make the filtering easier.  Instead of 1111100000, you would 
get to work with 1010101010


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