Hi The problem taking that circuit directly to 24 bits is the drift on the output sampling capacitor.
Even with *good* caps and op-amps, holding 16 bits is challenging for times that are dimensioned in milliseconds. Easier if they don't get very warm .. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bruce Griffiths Sent: Tuesday, June 29, 2010 4:34 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] yet another GPSDO design, or so Bob Camp wrote: > Hi > > Are you referring to something like this: > > http://www.electronicsweekly.com/Articles/2008/05/01/43680/fast-settling-syn > chronous-pwm-dac-filter-has-almost-no.htm > > as a synchronous filter for the PWM? > > Bob > > Yes, that is the original article. There's a later one (the link is in the archives) which shows how to use a pair of 16 bit PWM signals in conjunction with such a filter. However there is an error in one of the resistor values. Ulrich built and tested a 24 bit version using a pair of 16 bit PWM signals. Bruce > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Bruce Griffiths > Sent: Tuesday, June 29, 2010 4:07 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] yet another GPSDO design, or so > > Attila Kinali wrote: > >> On Tue, 29 Jun 2010 21:32:10 +1200 >> Bruce Griffiths<[email protected]> wrote: >> >> >> >>> 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. >>> >>> >> I've thought about that, but i'm afraid that this will add too >> much phase noise trough EFC noise. Though, i have not calculated >> how much noise this would generate. >> >> Attila Kinali >> >> > How do you conclude that? > You don't know what the circuit is and you've never tested it. > Ulrich has, and the output noise is very low. > > Bruce > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
