Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: AD5791 Date: Fri, 7 Jun 2024 14:28:18 -0400 Organization: A noiseless patient Spider Lines: 71 Message-ID: <6a51813e-c633-2ac7-b47d-bc38f8e7953e@electrooptical.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Fri, 07 Jun 2024 20:28:19 +0200 (CEST) Injection-Info: dont-email.me; posting-host="0045d7fa27721880bbbbbdce3da44235"; logging-data="2298206"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19BuEi9nqLt4ySFZ6RhzF5r" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.0 Cancel-Lock: sha1:iNKr9w0r2d2w4G6bCp7PO3qvN6E= In-Reply-To: Bytes: 3563 On 2024-06-06 22:38, john larkin wrote: > On Thu, 6 Jun 2024 22:19:22 -0400, Phil Hobbs > wrote: > >> On 2024-06-06 13:57, john larkin wrote: >>> On Thu, 06 Jun 2024 10:15:45 -0700, boB wrote: >>> >>>> On Tue, 04 Jun 2024 10:48:00 -0700, 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. >>>> >>>> >>>> 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. > Yeah, part of which is deterministic and part random. DAC noise shaping AIUI makes the the DS sum run in a limit cycle even for a fixed code, so that most of the switching junk is up at high frequency where it's easier to filter out. However, I'm not a delta-sigma expert. (They call them sigma-deltas for some reason--possibly related to gang insignia.) ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com