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

Chris Stake stake at btinternet.com
Tue Jun 29 20:53:26 UTC 2010

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
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.


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