Attila Kinali

  

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: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] 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<bruce.griffiths@xtra.co.nz> 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 -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > >

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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

		Attila Kinali

  

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: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] 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: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] 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<bruce.griffiths@xtra.co.nz> 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 -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

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 > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > >

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 >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

Ah, now I get the basic idea. I'll need to think about it for a while. Many thanks for the links. Chris Stake -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Bruce Griffiths Sent: 30 June 2010 09:08 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] yet another GPSDO design, or so 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 >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.