By marrying the new AD5791 20 bit DAC from Analog Devices with the LTZ1000(A), a variable 0 to 7.2 VDC adjustable voltage refence is possible with 1 ppm accuracy and resolution.  Not a trivial design considering thermoelectric and noise issues but certainly possible ( see http://maxmcarter.com/vref/faq.html for details).  I currently use the surplus HP 3458A voltage reference board from John Daly with the ESI RV722 Kelvin Varley divider for my precision reference source.  I am working on a little more complex design for a 0 to 10.000000 volt precison reference using the AD5791 for my own use.  Has anyone else looked into the device? Randy Evans

Randy, while I have no experience at all with the AD5791 I would like to draw your attention to the fact that even higher reolution monotonic DACs are easily constructed from "normal" microcontroller's PWM outputs. Well, of course you need some additional electronics like in http://www.electronicsweekly.com/Articles/2008/10/30/44817/dc-accurate-32-bi t-dac-achieves-32-bit-resolution.htm but this stuff really works! And, the term "easily" of course refers to the principle and the things you are refering to > Not a trivial design considering thermoelectric > and noise issues but certainly possible are indeed not trivial. I have built a 24 Bit DA out of a AVRMEGA128 (you don't need such a big one, anything with two 16 bit PWM channels will do) and have used it to set the EFC voltage of an OCXO in an GPSDO. Worked very vell and the only noise that I was able to measure on the output was the lf noise of my reference (a LT1021 in this case) down-divided by the downscaling ratio of the DAC. Thermoelectric effects are a different issue, of course. Best regards Ulrich Bangert > -----Ursprüngliche Nachricht----- > Von: volt-nuts-bounces@febo.com > [mailto:volt-nuts-bounces@febo.com] Im Auftrag von Randy Evans > Gesendet: Samstag, 24. April 2010 06:23 > An: volt-nuts@febo.com > Betreff: [volt-nuts] Precision Reference Supply > > > By marrying the new AD5791 20 bit DAC from Analog Devices > with the LTZ1000(A), a variable 0 to 7.2 VDC adjustable > voltage refence is possible with 1 ppm accuracy and > resolution.  Not a trivial design considering thermoelectric > and noise issues but certainly possible ( see > http://maxmcarter.com/vref/faq.html for details).  I > currently use the surplus HP 3458A voltage reference board > from John Daly with the ESI RV722 Kelvin Varley divider for > my precision reference source.  I am working on a little more > complex design for a 0 to 10.000000 volt precison reference > using the AD5791 for my own use.  Has anyone else looked into > the device? > > Randy Evans > > > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Correction! You need at least 3 PWM channels, sorry for my mistake. Ulrich Bangert > -----Ursprüngliche Nachricht----- > Von: volt-nuts-bounces@febo.com > [mailto:volt-nuts-bounces@febo.com] Im Auftrag von Ulrich Bangert > Gesendet: Samstag, 24. April 2010 14:55 > An: 'Discussion of precise voltage measurement' > Betreff: Re: [volt-nuts] Precision Reference Supply > > > Randy, > > while I have no experience at all with the AD5791 I would > like to draw your attention to the fact that even higher > reolution monotonic DACs are easily constructed from "normal" > microcontroller's PWM outputs. Well, of course you need some > additional electronics like in > > http://www.electronicsweekly.com/Articles/2008/10/30/44817/dc- > accurate-32-bi > t-dac-achieves-32-bit-resolution.htm > > but this stuff really works! And, the term "easily" of course > refers to the principle and the things you are refering to > > > Not a trivial design considering thermoelectric > > and noise issues but certainly possible > > are indeed not trivial. I have built a 24 Bit DA out of a > AVRMEGA128 (you don't need such a big one, anything with two > 16 bit PWM channels will do) and have used it to set the EFC > voltage of an OCXO in an GPSDO. Worked very vell and the only > noise that I was able to measure on the output was the lf > noise of my reference (a LT1021 in this case) down-divided by > the downscaling ratio of the DAC. Thermoelectric effects are > a different issue, of course. > > Best regards > Ulrich Bangert > > > -----Ursprüngliche Nachricht----- > > Von: volt-nuts-bounces@febo.com > > [mailto:volt-nuts-bounces@febo.com] Im Auftrag von Randy Evans > > Gesendet: Samstag, 24. April 2010 06:23 > > An: volt-nuts@febo.com > > Betreff: [volt-nuts] Precision Reference Supply > > > > > > By marrying the new AD5791 20 bit DAC from Analog Devices > > with the LTZ1000(A), a variable 0 to 7.2 VDC adjustable > > voltage refence is possible with 1 ppm accuracy and > > resolution.  Not a trivial design considering thermoelectric > > and noise issues but certainly possible ( see > > http://maxmcarter.com/vref/faq.html for details).  I > > currently use the surplus HP 3458A voltage reference board > > from John Daly with the ESI RV722 Kelvin Varley divider for > > my precision reference source.  I am working on a little more > > complex design for a 0 to 10.000000 volt precison reference > > using the AD5791 for my own use.  Has anyone else looked into > > the device? > > > > Randy Evans > > > > > > > > > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

I was aware of the article you referenced and the scheme does work good( I built a variant of the circuit) but it does have a bit of ancillary electronics around it and does require some precision resistors, particularly if you try to go beyond 20 bits of resoution, and filtering can be a burden if you want reasonable settling time.  It is also limited to a DC reference due to low frequency fitlering requirements. One big advantage of the AD5791 is that not only can you generate a DC reference but you can also use it to generate an AC voltage reference of 400, 1000, or 10K Hz, for example. Randy Evans ----- Original Message ---- From: Ulrich Bangert <df6jb@ulrich-bangert.de> To: Discussion of precise voltage measurement <volt-nuts@febo.com> Sent: Sat, April 24, 2010 5:55:19 AM Subject: Re: [volt-nuts] Precision Reference Supply Randy, while I have no experience at all with the AD5791 I would like to draw your attention to the fact that even higher reolution monotonic DACs are easily constructed from "normal" microcontroller's PWM outputs. Well, of course you need some additional electronics like in http://www.electronicsweekly.com/Articles/2008/10/30/44817/dc-accurate-32-bi t-dac-achieves-32-bit-resolution.htm but this stuff really works! And, the term "easily" of course refers to the principle and the things you are refering to > Not a trivial design considering thermoelectric > and noise issues but certainly possible are indeed not trivial. I have built a 24 Bit DA out of a AVRMEGA128 (you don't need such a big one, anything with two 16 bit PWM channels will do) and have used it to set the EFC voltage of an OCXO in an GPSDO. Worked very vell and the only noise that I was able to measure on the output was the lf noise of my reference (a LT1021 in this case) down-divided by the downscaling ratio of the DAC. Thermoelectric effects are a different issue, of course. Best regards Ulrich Bangert > -----Ursprüngliche Nachricht----- > Von: volt-nuts-bounces@febo.com > [mailto:volt-nuts-bounces@febo.com] Im Auftrag von Randy Evans > Gesendet: Samstag, 24. April 2010 06:23 > An: volt-nuts@febo.com > Betreff: [volt-nuts] Precision Reference Supply > > > By marrying the new AD5791 20 bit DAC from Analog Devices > with the LTZ1000(A), a variable 0 to 7.2 VDC adjustable > voltage refence is possible with 1 ppm accuracy and > resolution.  Not a trivial design considering thermoelectric > and noise issues but certainly possible ( see > http://maxmcarter.com/vref/faq.html for details).  I > currently use the surplus HP 3458A voltage reference board > from John Daly with the ESI RV722 Kelvin Varley divider for > my precision reference source.  I am working on a little more > complex design for a 0 to 10.000000 volt precison reference > using the AD5791 for my own use.  Has anyone else looked into > the device? > > Randy Evans > > >      > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.