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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: AD5791
Date: Thu, 06 Jun 2024 19:38:12 -0700
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On Thu, 6 Jun 2024 22:19:22 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 2024-06-06 13:57, john larkin wrote:
>> On Thu, 06 Jun 2024 10:15:45 -0700, boB <boB@K7IQ.com> wrote:
>> 
>>> On Tue, 04 Jun 2024 10:48:00 -0700, john larkin <jl@650pot.com> 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.
>>>
>>>
>>> Nice part but costs way too much for any products we make.
>>>
>>> boB
>> 
>> What do you make?
>> 
>> We live on the lunatic fringe of electronics, things that are really
>> hard to do, things with extreme exponents. It makes money because it
>> has little competition, but the money is a side effect. I do it
>> because it's fun.
>> 
>> There must be something cool that we can do with a 1 PPM accurate DAC.
>> 
>> TI has a 20-bit delta-sigma DAC that's about $12, but it's only linear
>> to 15 PPM. I don't understand how a d-s DAC or ADC can even be that
>> good. It would seem to need femtosecond edge accuracies inside.
>> 
>
>I expect that the deterministic part of the jitter gets pushed out to 
>high frequency by the noise shaping.
>
>Random jitter you'd have to deal with by averaging.
>
>Cheers
>
>Phil Hobbs

I was thinking about rise/fall time asymmetry, changing average values
as duty cycles squirm all over the place.