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NNTP-Posting-Date: Wed, 05 Jun 2024 16:51:00 +0000
From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: AD5791
Date: Wed, 05 Jun 2024 12:50:59 -0400
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On Tue, 04 Jun 2024 13:56:36 -0700, john larkin <jl@650pot.com> wrote:

>On Tue, 4 Jun 2024 21:53:13 +0200, Jeroen Belleman
><jeroen@nospam.please> wrote:
>
>>On 6/4/24 19:48, john larkin wrote:
>>> https://www.analog.com/en/products/ad5791.html
>>> 
>>> That's an amazing part. 20 bit DAC with 1 PPM accuracy and 0.05 PPM
>>> per degree C tempco.
>>> 
>>> My main gripe is its 3.4K output impedance, which makes a lot of
>>> Johnson noise. I suppose I could run a bunch in parallel.
>>> 
>>
>>But you can power the chip from +/-16V and the LSB can be in
>>the 25uV ballpark. The Johnson noise of 7.5nV/rtHz doesn't
>>seem so bad then, does it?
>>
>>Jeroen Belleman
>
>That helps some. +-14v is about the limit on the references. We'd have
>to divide down to get our +-10v range back, and that would need some
>crazy stable resistors.
>
>Looks like the other way to get the noise down would be to parallel a
>number of DACs. Times 8 channels! Ballpark $100 per DAC, which is
>actually feasible.
>
>It will of course need crazy-low-noise hyper-stable references.
>
>I wonder how ADI tests these parts. I can't buy a 1 PPM accurate DVM.

Aren't 6.5-digit DMMs exactly 1PPM?

Joe Gwinn