Azelio Boriani wrote:
Also you need a super ultra fantastic voltage reference for a 32bit DAC.
Not really, the reference only needs to have low noise and good short
term stability.
Long term drift in the reference voltage will be corrected by the
feedback loop.
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.
However the noise associated with the timing resolution doesn't average
down so quickly.
If such noise is random than at best it is reduced by SQRT(10) by
averaging 10 measurements.
There is no real substitute for lower noise, higher resolution measurements.
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.
Bruce
On Fri, Sep 14, 2012 at 8:52 PM, Chris Albertson
<albertson.ch...@gmail.com>wrote:
On Fri, Sep 14, 2012 at 11:21 AM, Michael Tharp
<g...@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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