[volt-nuts] Precision Reference Supply

[Ulrich Bangert]

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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