[time-nuts] yet another GPSDO design, or so

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jun 30 08:03:30 UTC 2010


Chris

All the details are in the article:
http://www.edn.com/contents/images/6607197.pdf

However it would be best to read the article posted by Bob Camp first:


Bruce

Chris Stake wrote:
> Hi Bruce,
> This sounds like a promising idea, please could you expand on the
> synchronous filter technique? I have seen some articles about how such
> filters can be used to "clean up" the data from rotating machinery for
> vibration analysis etc. but I don't follow how they can be used in a PWM
> application.
> Regards
> Chris Stake
>
>
>
> Its possible to build a 24 bit resolution D/A using a synchronously
> filtered PWM circuit.
> A pair of PWM outputs and a few relatively low precision resistors and
> capacitors together with a low noise low drift reference are required.
> The technique takes advantage of the fact that the required EFC voltage
> changes slowly and isnt updated at a highg rate.
> The synchronous filter technique eliminates the very long time constant
> RC filters required with an asynchronously filtered PWM waveform.
>
> Bruce
>
>
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