[volt-nuts] Precision Reference Supply

[Ulrich Bangert]

Correction!

You need at least 3 PWM channels, sorry for my mistake.

Ulrich Bangert

> -----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
> 
> 
> 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 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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