Path: ...!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: AD5791 Date: Wed, 5 Jun 2024 23:15:30 -0000 (UTC) Organization: A noiseless patient Spider Lines: 62 Message-ID: References: <1eb16jdu7858p5h1r74il3rak0bvaoain0@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 06 Jun 2024 01:15:30 +0200 (CEST) Injection-Info: dont-email.me; posting-host="4452f8fae99243d2a53738a137c85186"; logging-data="1233659"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+E90QsfYJluXTDY8KVDvEYKaxb8xZD8rs=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:vl5aazbFoOZOzd5CuP+GoPB+n5Y= Bytes: 3597 On Wed, 05 Jun 2024 14:32:15 -0400, Joe Gwinn wrote: > On Wed, 05 Jun 2024 10:56:18 -0700, john larkin wrote: > >>On Wed, 05 Jun 2024 12:50:59 -0400, Joe Gwinn >>wrote: >> >>>On Tue, 04 Jun 2024 13:56:36 -0700, john larkin wrote: >>> >>>>On Tue, 4 Jun 2024 21:53:13 +0200, Jeroen Belleman >>>> 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. > > . > > For a product instance: > > . 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