Re: [time-nuts] 31bit ADC, 1000 samples per second
31-bit is 186dB... with what do you compare that device? What kind of reference is needed? On Sun, Dec 9, 2012 at 11:18 PM, Bob Camp li...@rtty.us wrote: Hi It's the big brother of the ADS127x parts that I mentioned a little while back. I'm sure it works quite well. The 127x's are fine parts. The internal filtering combined with the chopper is a very nice combination. Bob On Dec 9, 2012, at 5:13 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
In message CAL8XPmN8PbcSEfmRCiude+sYCX3kawBF6h4T0=n0n0emxlx...@mail.gmail.com, Azelio Boriani writes: 31-bit is 186dB... with what do you compare that device? What kind of reference is needed? It's not 31 noise-free bits, but the SNR is in the 120-130dB territory. -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
31 bits is just a convenient word size that comes out of the on-chip filter, and does not really relate to performance. Better to look at SNR which, at worst case, is 120dB in high-res mode. That indicates performance just under 20 bits, typical for better monolithic sigma-delta converters. Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. Bob LaJeunesse From: Azelio Boriani azelio.bori...@screen.it To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Mon, December 10, 2012 9:39:30 AM Subject: Re: [time-nuts] 31bit ADC, 1000 samples per second 31-bit is 186dB... with what do you compare that device? What kind of reference is needed? On Sun, Dec 9, 2012 at 11:18 PM, Bob Camp li...@rtty.us wrote: Hi It's the big brother of the ADS127x parts that I mentioned a little while back. I'm sure it works quite well. The 127x's are fine parts. The internal filtering combined with the chopper is a very nice combination. Bob On Dec 9, 2012, at 5:13 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
I see that there is a high resolution 130dB mode too that can give 21 bits @ 250 samples per second, good for very slow, high resolution DMTD (but also very stable voltage reference and ADC temperature, seems very challenging). On Mon, Dec 10, 2012 at 4:26 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: 31 bits is just a convenient word size that comes out of the on-chip filter, and does not really relate to performance. Better to look at SNR which, at worst case, is 120dB in high-res mode. That indicates performance just under 20 bits, typical for better monolithic sigma-delta converters. Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. Bob LaJeunesse From: Azelio Boriani azelio.bori...@screen.it To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Mon, December 10, 2012 9:39:30 AM Subject: Re: [time-nuts] 31bit ADC, 1000 samples per second 31-bit is 186dB... with what do you compare that device? What kind of reference is needed? On Sun, Dec 9, 2012 at 11:18 PM, Bob Camp li...@rtty.us wrote: Hi It's the big brother of the ADS127x parts that I mentioned a little while back. I'm sure it works quite well. The 127x's are fine parts. The internal filtering combined with the chopper is a very nice combination. Bob On Dec 9, 2012, at 5:13 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Hi What is atypical about these parts is: 1) The excellent noise performance inside 10 Hz 2) The built in Nyquist filters The first is very impressive compared to just about anything else out there. The second is available in some, but not all similar parts. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Robert LaJeunesse Sent: Monday, December 10, 2012 10:27 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 31bit ADC, 1000 samples per second 31 bits is just a convenient word size that comes out of the on-chip filter, and does not really relate to performance. Better to look at SNR which, at worst case, is 120dB in high-res mode. That indicates performance just under 20 bits, typical for better monolithic sigma-delta converters. Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. Bob LaJeunesse From: Azelio Boriani azelio.bori...@screen.it To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Mon, December 10, 2012 9:39:30 AM Subject: Re: [time-nuts] 31bit ADC, 1000 samples per second 31-bit is 186dB... with what do you compare that device? What kind of reference is needed? On Sun, Dec 9, 2012 at 11:18 PM, Bob Camp li...@rtty.us wrote: Hi It's the big brother of the ADS127x parts that I mentioned a little while back. I'm sure it works quite well. The 127x's are fine parts. The internal filtering combined with the chopper is a very nice combination. Bob On Dec 9, 2012, at 5:13 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
rlajeune...@sbcglobal.net said: Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. The initial post called it TI's ADS1282 geophone ADC. I'm pretty sure that the geologists using geophones don't care about super low frequencies so they probably won't care if the reference changes due to temperature shifts. Some geologists do care about super low frequencies. That would be continental drift. -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Hi When your sound source is a thumper truck, you do indeed care about some pretty low frequencies. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Monday, December 10, 2012 1:33 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 31bit ADC, 1000 samples per second rlajeune...@sbcglobal.net said: Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. The initial post called it TI's ADS1282 geophone ADC. I'm pretty sure that the geologists using geophones don't care about super low frequencies so they probably won't care if the reference changes due to temperature shifts. Some geologists do care about super low frequencies. That would be continental drift. -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
It is 31 bits with no missing codes. Usually missing codes is of concern in feedback systems, but I don't see the use in a geophone. Perhaps they will average the digital signal further to reduce the noise, hence the noisy bits. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) On Mon, Dec 10, 2012 at 2:19 PM, li...@lazygranch.com wrote: It is 31 bits with no missing codes. Usually missing codes is of concern in feedback systems, but I don't see the use in a geophone. Perhaps they will average the digital signal further to reduce the noise, hence the noisy bits. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Am 10.12.2012 21:53, schrieb Didier Juges: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) With that much noise it is really guaranteed that no code will be missing. :-) Gerhard ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
How long does it take to prove it? And what's the point? On Mon, Dec 10, 2012 at 3:04 PM, Gerhard Hoffmann dk...@arcor.de wrote: Am 10.12.2012 21:53, schrieb Didier Juges: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) With that much noise it is really guaranteed that no code will be missing. :-) Gerhard __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Regarding feedback loops, I had a brain fart. I mean monotonic and no missing codes, not no missing codes in general. I think it was Fluke or Analog that had a small booklet on understanding data converter specifications. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Hi I suspect you can prove it mathematically. You could also just sit there and watch what it puts out for a year or so. With a reasonable ramp it likely would put out all codes. That's not to say you could prove they are in order, only that you saw all 4 billion codes. More or less: 1,000 samples a second, 4 billion codes - you need 4 million seconds if everything works perfectly. 10X that number is probably adequate to catch them all. Bob On Dec 10, 2012, at 3:53 PM, Didier Juges shali...@gmail.com wrote: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) On Mon, Dec 10, 2012 at 2:19 PM, li...@lazygranch.com wrote: It is 31 bits with no missing codes. Usually missing codes is of concern in feedback systems, but I don't see the use in a geophone. Perhaps they will average the digital signal further to reduce the noise, hence the noisy bits. ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Integrating converters including delta-sigma converters can be no missing codes by design without being able to take advantage of the full resolution that implies. Integral nonlinearity, drift, and noise will limit the usable resolution. On Mon, 10 Dec 2012 15:08:38 -0600, Didier Juges shali...@gmail.com wrote: How long does it take to prove it? And what's the point? On Mon, Dec 10, 2012 at 3:04 PM, Gerhard Hoffmann dk...@arcor.de wrote: Am 10.12.2012 21:53, schrieb Didier Juges: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) With that much noise it is really guaranteed that no code will be missing. :-) Gerhard ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
The gain drift is specified at 2ppm per degree C. There are provisions for a calibration cycle but that requires external multiplexing. On Mon, 10 Dec 2012 07:26:55 -0800 (PST), Robert LaJeunesse rlajeune...@sbcglobal.net wrote: . . . typical for better monolithic sigma-delta converters. Nonetheless 20 bits indicates a matching reference would have to hold 1PPM over temperature, no simple task. Bob LaJeunesse ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
I agree, but there is a difference between something that you should be able to achieve by design and being able to prove it, or even if it's useful in practice. In a case like this, the wide span between resolution and effective bits makes me wonder what's the point of advertising the former other than bragging rights? On Mon, Dec 10, 2012 at 3:38 PM, David davidwh...@gmail.com wrote: Integrating converters including delta-sigma converters can be no missing codes by design without being able to take advantage of the full resolution that implies. Integral nonlinearity, drift, and noise will limit the usable resolution. On Mon, 10 Dec 2012 15:08:38 -0600, Didier Juges shali...@gmail.com wrote: How long does it take to prove it? And what's the point? On Mon, Dec 10, 2012 at 3:04 PM, Gerhard Hoffmann dk...@arcor.de wrote: Am 10.12.2012 21:53, schrieb Didier Juges: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) With that much noise it is really guaranteed that no code will be missing. :-) Gerhard ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
In message tilcc892a6ntfk64t2nljm92idr92df...@4ax.com, David writes: The gain drift is specified at 2ppm per degree C. There are provisions for a calibration cycle but that requires external multiplexing. That's the really smart thing about this particular chip: You can drive the geophone calibration signal in through the second input and out onto the first, which eliminates the external calibration mux and the errors that usually cause. And yes, in seismology you do care about frequencies from 0.1Hz and up (0.01Hz if you're involved with the CTBT) and most voltage references will be stable enough for that. For longer term you calibrate your entire system, starting with the geophone, so the voltage reference is caught that way. -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
In message camqqfunudahc9rdrk0g8hxo_kohs+bndeilnqspq1_b2nqk...@mail.gmail.com , Didier Juges writes: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) No missing codes is guaranteed by the design, you'd have to screw up the digital filters to come out with missing codes. That's not impossible to do, but the fix is simple: sufficient precision in the filters, hence the 31 bits. The 32nd bit is an overrange bit btw, if it tracks the sign bit you're fine, if it is inversed you are out of range. Smart detail. -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
On Mon, 10 Dec 2012 23:01:49 +, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message tilcc892a6ntfk64t2nljm92idr92df...@4ax.com, David writes: The gain drift is specified at 2ppm per degree C. There are provisions for a calibration cycle but that requires external multiplexing. That's the really smart thing about this particular chip: You can drive the geophone calibration signal in through the second input and out onto the first, which eliminates the external calibration mux and the errors that usually cause. I see now from the data sheet that the 3000 ppm typical gain mismatch applies between the PGA gain settings and not between the multiplexor input channels so you can use the internal multiplexor for external calibration. The other instrumentation delta-sigma ADCs I am familiar with do a gain and offset calibration for every conversion which knocks the drift down by an order of magnitude unless you disable that feature. And yes, in seismology you do care about frequencies from 0.1Hz and up (0.01Hz if you're involved with the CTBT) and most voltage references will be stable enough for that. Voltage reference 1/f noise will be a problem but only because the ADS1282 input stage is already chopped allowing that kind of sensitivity at low frequencies. Competing instrumentation delta-signal converters have the same problem if you consider that a problem. For longer term you calibrate your entire system, starting with the geophone, so the voltage reference is caught that way. What they need is a ratiometric geophone . . . :) ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Hi It's not at all uncommon for the seismic guys to go a bit uber-nuts on clean supplies and references. Bob On Dec 10, 2012, at 7:54 PM, David davidwh...@gmail.com wrote: On Mon, 10 Dec 2012 23:01:49 +, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message tilcc892a6ntfk64t2nljm92idr92df...@4ax.com, David writes: The gain drift is specified at 2ppm per degree C. There are provisions for a calibration cycle but that requires external multiplexing. That's the really smart thing about this particular chip: You can drive the geophone calibration signal in through the second input and out onto the first, which eliminates the external calibration mux and the errors that usually cause. I see now from the data sheet that the 3000 ppm typical gain mismatch applies between the PGA gain settings and not between the multiplexor input channels so you can use the internal multiplexor for external calibration. The other instrumentation delta-sigma ADCs I am familiar with do a gain and offset calibration for every conversion which knocks the drift down by an order of magnitude unless you disable that feature. And yes, in seismology you do care about frequencies from 0.1Hz and up (0.01Hz if you're involved with the CTBT) and most voltage references will be stable enough for that. Voltage reference 1/f noise will be a problem but only because the ADS1282 input stage is already chopped allowing that kind of sensitivity at low frequencies. Competing instrumentation delta-signal converters have the same problem if you consider that a problem. For longer term you calibrate your entire system, starting with the geophone, so the voltage reference is caught that way. What they need is a ratiometric geophone . . . :) ___ 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
If it *was* missing codes in reality, it would not be the first time TI made that kind of mistake. One of their not so early multi-slope integrating converters was advertised to *not* return both plus zero and minus zero which was a big feature at the time . . . but it did. Almost nobody noticed that error for years. On Mon, 10 Dec 2012 16:28:52 -0600, Didier Juges shali...@gmail.com wrote: I agree, but there is a difference between something that you should be able to achieve by design and being able to prove it, or even if it's useful in practice. In a case like this, the wide span between resolution and effective bits makes me wonder what's the point of advertising the former other than bragging rights? On Mon, Dec 10, 2012 at 3:38 PM, David davidwh...@gmail.com wrote: Integrating converters including delta-sigma converters can be no missing codes by design without being able to take advantage of the full resolution that implies. Integral nonlinearity, drift, and noise will limit the usable resolution. On Mon, 10 Dec 2012 15:08:38 -0600, Didier Juges shali...@gmail.com wrote: How long does it take to prove it? And what's the point? On Mon, Dec 10, 2012 at 3:04 PM, Gerhard Hoffmann dk...@arcor.de wrote: Am 10.12.2012 21:53, schrieb Didier Juges: I do not understand how anyone can guaranty no missing codes when the lower 11 bits are essentially noise? (31 bits resolution versus 20 effective bits) With that much noise it is really guaranteed that no code will be missing. :-) Gerhard ___ 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] 31bit ADC, 1000 samples per second
I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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.
Re: [time-nuts] 31bit ADC, 1000 samples per second
Hi It's the big brother of the ADS127x parts that I mentioned a little while back. I'm sure it works quite well. The 127x's are fine parts. The internal filtering combined with the chopper is a very nice combination. Bob On Dec 9, 2012, at 5:13 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: I'm doing some work with a couple of geophones (long story...) and stumbled across TI's ADS1282 geophone ADC. It has some pretty amazing specs for low frequencies, and having played with the EVAL board for an evening here in my lab, I'm pretty impressed. People working with close-in phase-noise measurements may want to consider this chip... -- 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.
