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

[Azelio Boriani]

Also you need a super ultra fantastic voltage reference for a 32bit DAC.
Anyway, yes, in my GPSDO the controller has 3 levels: at startup is fast,
then slow and then very slow. The levels trigger when the precision
estimate is 10E-9 and 10E-11. If you have a resolution of 10nS then take 10
averages and your resolution will be 1nS and so on. When I switch level,
the number of averages is increased too but this leads to a slower DAC
update rate. This is the problem: now I'm trying to figure out if the
corrective action can be "predicted" (Kalman filtering) and applied at the
same speed.

On Fri, Sep 14, 2012 at 8:52 PM, Chris Albertson
<albertson.chris at gmail.com>wrote:

> On Fri, Sep 14, 2012 at 11:21 AM, Michael Tharp
> <gxti at partiallystapled.com> wrote:
>
> > Finally, do people think a 16 bit DAC is adequate or should I consider
> > building a 32-bit one? I looked at a few designs when putting this
> together
> > but decided to keep it simple until things were up and running.
>
> Having a 32-bit DAC would give you enough range so that you could drop
> in any OCXO you might have.  But if you can have trimmer resisters to
> selected for your specif OCXO then 16-bits should be enough.   If it
> were me, I'd want the DAC steps to be smaller than what the phase
> detector can measure.     Said another way a 32-bit DAC might
> eliminate the need for scale and offset trimmer resistors.
>
> Chris Albertson
> Redondo Beach, California
>
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