[volt-nuts] Precision Reference Supply
df6jb at ulrich-bangert.de
Sat Apr 24 13:00:36 UTC 2010
You need at least 3 PWM channels, sorry for my mistake.
> -----Ursprüngliche Nachricht-----
> Von: volt-nuts-bounces at febo.com
> [mailto:volt-nuts-bounces at 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
> 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
> 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 at febo.com
> > [mailto:volt-nuts-bounces at febo.com] Im Auftrag von Randy Evans
> > Gesendet: Samstag, 24. April 2010 06:23
> > An: volt-nuts at 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
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