Hi The one I'm building up is a ADS1278
http://focus.ti.com/lit/ds/symlink/ads1278.pdf There are others in the series with fewer inputs. As with a lot of converters, there isn't a whole lot of data on them. Bob On Jun 28, 2010, at 2:49 PM, Didier Juges wrote: > Bob, > > Do you have a part number to suggest a quick glance a the TI web site did not > show up any parts in that category... > > I found a Cirrus Logic ADC with chopper front end and good low noise specs, > CS5530. > > It's a 24 bit ADC but the ENB (noise free) drops to 15 at 1ksample/sec. Even > at the lowest rate, it only has 19 bits noise free, so I assume digital > filtering would be required to obtain 24 bits of resolution. > > Didier > > > ------------------------ Sent from my BlackBerry Wireless thingy while I do > other things... > > -----Original Message----- > From: Bob Camp <li...@rtty.us> > Sender: time-nuts-boun...@febo.com > Date: Mon, 28 Jun 2010 13:18:32 > To: Discussion of precise time and frequency measurement<time-nuts@febo.com> > Reply-To: Discussion of precise time and frequency measurement > <time-nuts@febo.com> > Subject: Re: [time-nuts] EFC tracking > > Hi > > TI has a line of ADC's that drop a chopper stabilization loop around a fairly > normal 24 bit "audio ADC" part. Their claimed benefit is that they take down > the level of flicker noise and DC drift present in audio only parts. > > Since most of the "interesting" stuff on an EFC is long time span, flicker > noise is indeed something to be concerned about. > > Bob > > > On Jun 27, 2010, at 3:07 AM, Poul-Henning Kamp wrote: > >> In message <hmebkhfeacmnlmhiafdneegponac.jmi...@pop.net>, "John Miles" >> writes: >> >>>> That is actually a very debatable proposition, a lot of them are >>>> tracking types that conveniently cover up any lack of linearity >>>> on the analog side of the fence. >>> >>> Can you elaborate on that? Linearity is linearity - wouldn't it ultimately >>> show up in the card's IMD specs? >> >> That would sort of assume there were relevant specs provided. >> >> The Audio ADC's are provided with audio relevant specs, which are >> not the specs you would care about in the suggested application. >> >> Broadly speaking, the important ability for a audio ADC is to be >> able to capture the top 16 significant bits of a continuous signal >> in an approx 24 bit space, sort of like a 16b*2^8b floating point >> format. >> >> Concerns like long term stability top out at "30 seconds", whereas >> woodoo-concerns like clock-jitter has gotten all the snakeoil >> recently. >> >> And then there are the features that really will totally get >> you in this application: autozero features, that are built with >> the assumption that any DC on the ADC should be compensated out. >> >> These ADC's are great for sound and they are almost perfect for Ham's >> SDR experiements. >> >> But they are not and will never be 7∏ digit 200 ksps instrumentation >> grade ADCs. >> >> You can get a brand new china-style DVM with USB port for approx >> 150USD on ebay, and as other said, you can get a HP3456A for as >> little as 50USD, but would need a GPIB-USB converter. >> >> By the time you have fixed a long term reference for your soundcard, >> which likely entails a buried zener chip, a totally new input >> section and a thermally controlled enclosure, you will have spent >> many times that, and still get a performance much worse than the >> HP3456A. >> >> So if the objective is to learn about analog/digital converters >> and their ailments: go for it. >> >> If the objective is to measure the EFC voltage over the long term, >> hit ebay, find instrument built for such purposes and move on. >> >> Poul-Henning >> >> -- >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >> p...@freebsd.org | TCP/IP since RFC 956 >> FreeBSD committer | BSD since 4.3-tahoe >> Never attribute to malice what can adequately be explained by incompetence. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.