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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: AD5791
Date: Wed, 05 Jun 2024 10:56:18 -0700
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On Wed, 05 Jun 2024 12:50:59 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

>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

I think the best I've seen is something like 4 PPM.  For north of
$14K.