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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jun 30 04:07:31 EDT 2010


Here's a link to a pdf version of the synchronously filtered low ripple 
pwm dac:

http://www.edn.com/contents/images/6553625.pdf

Bruce

Bruce Griffiths wrote:
> 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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>
>
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