[time-nuts] is there a "best bet" advanced hobbyist buildable GPSDOdesign?
bruce.griffiths at xtra.co.nz
Wed Dec 12 02:32:36 EST 2007
michael taylor wrote:
> You have made similar comments about I believe the same approach in
> the past. I was wondering if you have ever sketched out a schematic,
> even if only rough. Perhaps with a few suggested components to try
> (i.e. DAC, Op-Amp) that would be a good starting point for anyone who
> wanted to prototype and evaluate the performance of this approach.
> It is beyond my elementary design abilities to convert your
> description into a well implemented design on my own, but I would be
> interested in try to at least see if I could construct an unit using
> these suggested techniques.
The analog circuitry for a sigma-delta DAC is attached.
The input is optically isolated using a high speed low jitter CMOS
optocoupler (Avago produce an equivalent device) to break low frequency
Similarly an RF transformer should be used to couple the OCXO output to
the Digital board breaking another potential low frequency ground loop.
The task of the microprocessor firmware is to generate the delta sigma 1
bit input data for the optocoupler.
Alternatively one of Analog devices chip scale transformer isolators
could be used.
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