TI's new ADS127L21 could be the next best precision ADC after ADI's AD4x30-24 - Page 1
Forum section: electronics / general

author: laichh
author_rank: Regular Contributor
timestamp: August 14, 2023, 08:39:25 am
content: Well, the typical INL of 0.4 ppm of FS not is really impressive in shine of ADI AD4x30-24 (0.1 ppm of FS typical), but at a fraction of what the ADI cost.https://www.ti.com/product/ADS127L21

author: ch_scr
author_rank: Frequent Contributor
timestamp: August 17, 2023, 09:32:11 am
content: Looking at the datasheets, the zero / offset error vs temperature is very close between the two (looming physical limits probably) at typical 50nV/°C vs 35nV/°C for the AD4030.More interesting maybe the gain error vs temperature: typical 0.5ppm/°C (1ppm max) with the TI part vs. 0.025 ppm/°C for AD.Haven't looked further yet, but for DC precision that's quite a difference in temperature sensitivity there?

author: miro123
author_rank: Frequent Contributor
timestamp: August 18, 2023, 08:17:52 am
content: General - My observation for that past 5..7 years.1. Nice to see development in this area. - performance from major manufacture went up.2. The two major manufacture have chosen different way - Analog/LT choose performance while TI - versatility and easy integration.3. High performance components becomes difficult to handle for home hobbyist. The modern components are approaching the physicals limits. New package is needed4. The border between different adc architecture is narrowed. - e.g. ads127l21 is multibit 3-th order sigma delta while AD4x30 got the oversampling principe from SD converters.On topicThe two components are not comparable1. different architecture2. different performance parameters.3. different features for different market.4. Number A from manufacture A is not equal to number A from manufacture B . different manufacture measure the parameters on different way and conditions.ADS12721 can be compared with already great AD7177-2Personal thoughtsI don't care about gain error temperature drift r typical 0.5ppm/°C (1ppm max) with the TI part vs. 0.025 ppm/°C for AD. I cannot design analogue frontend with lower than 0.5ppm/K drift.

author: MasterT
author_rank: Frequent Contributor
timestamp: August 18, 2023, 10:06:32 am
content: Quote from: miro123 on August 18, 2023, 08:17:52 amI think the same, both ADC unbuffered, so all those numbers INL, uV bla-bla has no practical meanings w/o analog front-end.Get ad127-l-11 for evaluation, now can't find OPA to interface w/o significant lose SNR or linearity or both. Even passive components seems play a big role.

author: ch_scr
author_rank: Frequent Contributor
timestamp: August 18, 2023, 11:08:24 am
content: Quote from: miro123 on August 18, 2023, 08:17:52 amSure, but if you do that, would you rather take an additional 0.5ppm/°C hit or an insignificant 0.025ppm/°C one? Even if you have 5ppm/°C frontend, an additional 10-20% hit is noticeable.In general, to get any of these numbers, the rest of the system has to support it, quite the challenge no doubt!

author: laichh
author_rank: Regular Contributor
timestamp: August 18, 2023, 12:04:32 pm
content: QuoteTry THS2630 + LT5400https://www.ti.com/product/THS2630https://www.analog.com/en/products/lt5400.html

author: MasterT
author_rank: Frequent Contributor
timestamp: August 18, 2023, 01:25:10 pm
content: THS2630 is wrong choise:QuoteRegarding recommended by TI THS4551 (page 100 Figure 9-8. ADS127L21 Circuit Diagram) I see in DSInput bias current drift (5) 3.3 (typ) nA/C, than alone produce x 1.5k = ~5 uV/C. And it's just "basic buffer" with input impedance 1.5k, to get it up at least to 10 MOhms, 5uV likely jump to 50

author: iMo
author_rank: Super Contributor
timestamp: August 18, 2023, 03:49:37 pm
content: In past I did a simulation with a simple bootstrapped opamp (2 opapmps + 2 transistors + 2 zeners) with following 10:1 divider (LT5400 9+9+1+1k) feeding a differential ADC input. You would need a floating +15/-15V source. The simulation showed it could be applicable for ~7digits.https://www.eevblog.com/forum/projects/simple-dc-afe-for-adc-chips-with-unipolar-diff-inputs/msg2143462/#msg2143462

author: exe
author_rank: Unknown
timestamp: August 18, 2023, 04:43:36 pm
content: Only one channel