Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Wed, 05 Jun 2024 00:15:03 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: AD5791 Date: Tue, 04 Jun 2024 17:15:03 -0700 Message-ID: References: User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 55 X-Trace: sv3-wuwQkZUx4d6P/WlpFUv+jhQR/Av6zO9vfB617PA1SwzidBYJtYVpCh/lUN3PD5kgq8wEzRnhaCh8dIT!uLaU/hwIRARI1gt1JsvlBI4XaGrAxVtvVYMGbs/mu7uPO0rpD+QW+phUJFYJw1UAH3s0EjHCylC5!ur/8pg== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 2888 On Tue, 4 Jun 2024 22:58:54 -0000 (UTC), Phil Hobbs wrote: >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. >> >> > >Its quoted rise time is 1us, corresponding to a 3 dB bandwidth of about 350 >kHz, or 550 kHz noise bandwidth. > >With 7.5 nV 1-Hz noise, the total RMS noise should be about 5.6 uV, just >about half a LSB at 10V FS. > >Not that shabby. > >Cheers > >Phil Hobbs Three DACs in parallel with +-16 refs, divided down to +-10, pencils out around 3.2 nv/rthz. I'm going to need a very good preamp to measure the noise, something below 1 nv/rthz. Any ideas?