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NNTP-Posting-Date: Tue, 04 Jun 2024 20:56:36 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: AD5791
Date: Tue, 04 Jun 2024 13:56:36 -0700
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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.