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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: AD5791
Date: Wed, 5 Jun 2024 23:15:30 -0000 (UTC)
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On Wed, 05 Jun 2024 14:32:15 -0400, Joe Gwinn wrote:

> On Wed, 05 Jun 2024 10:56:18 -0700, john larkin <jl@650pot.com> wrote:
> 
>>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.
> 
> It might be easier to buy a 1ppm voltage reference and calibrate against
> that.
> 
> .<https://en.wikipedia.org/wiki/Voltage_reference>
> 
> For a product instance:
> 
> .<https://voltagestandard.com/001%25-10v-reference>  costs $140.
> 
> Joe Gwinn

Or if you're short of funds but feeling lucky:

https://www.ebay.co.uk/itm/386121438204?
itmmeta=01HZNARNCPT8774B3GGG71T3CA&hash=item59e6a193fc:g:KnAAAOSwBWZlA~l-
&itmprp=enc%3AAQAJAAAA4I%2Fd68mFhvvQ5uDzWpxhkKg5vNDFXKoaX71I7C%2Bqi4X1gEOSl%2ByQi%2Byb2yOKfSu2%2FGOYQPxHJw1jBRs3MIV3zJSRqR7pVAm8aYNVy7wLMnKjXWFN3KSHr6bKCyxJl7bSItVlod4JvVGDybNaYHAoGlJYiRk5MoLu6Ts%2F2qgn36iLDRdrEx31hJOeg1QyKcHTImNsukRBOP7Yl22Bx9YxUiHUfAOCZM815wKloAqWtkq7q7XeVxFJa2zzbrTD68SkZelbZjGcClZiCAa0c3nS8z3CkRuQ%2FXFCitVqwxvlZ2a6%7Ctkp%3ABFBM1Nbiqv1j