Re: AD5791

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