Differential ADC and a 0 to 10V Input Signal - Page 1
Forum section: electronics / general

author: luky315
author_rank: Regular Contributor
timestamp: July 01, 2022, 11:10:36 am
content: Is it better to "simply" attenuate and buffer a 0 to 10V input signal before measuring it with a 0 to 2.5V ADC (16bit, 100ksps with differential inputs) or is it beneficial to use the differential input of the ADC with a single ended to diff. amplifier (attenuator) like the LTC6363? How do you decide which input stage is more suitable?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 01, 2022, 11:21:52 am
content: It depends on the ADC. Some ADCs need a differential driven signal to use there full input range. Another point is that the INL of some ADC is better with differential drive.The single ended drive is usually simpler. So if differential drive does not provide a significant advantege one can use a single ended signal.

author: iMo
author_rank: Super Contributor
timestamp: July 02, 2022, 05:30:49 am
content: FYI - I've been currently messing with a vintage ADuC845 (2x 24bit SD ADC). Tried all possible settings for the 0-10V usage. Using 2.5V Vref, and an 1:5 resistive divider at the input. Gain set such the input range is +/-2.56V bip or 0-2.56V unip. Floating input voltage (a 10V ref) battery powered. The input ADC voltage is therefore +/- 2V when applied bipolar, or 0-2V unipolar. Internal ADC calibration (zero and gain) made before a measurement. Buffered, chopped, 50Hz rejection, 5.3 smps.Lessons learned so far - with unipolar you cannot go to 0V. The minimum voltage is something like 0.3V over agnd. That applies for any diff ADCs afaik.With bipolar I can go +/-10V, the resolution and stddev is 2x worse than with unipolar, there is a difference between the positive and negative 10V readings in my ADC, however, like 300uV (probably INL as specified max 15ppm of FS) but with modern ADCs it could be smaller, hopefully.

author: luky315
author_rank: Regular Contributor
timestamp: July 02, 2022, 07:19:16 am
content: What would be the "best" solution for measuring a 0 to 10V signal (maybe with some overrange? -0.5 to 10.5V) with 100ksps and > 100 db SINAD?

author: iMo
author_rank: Super Contributor
timestamp: July 02, 2022, 07:25:19 am
content: What is your ADC?

author: luky315
author_rank: Regular Contributor
timestamp: July 02, 2022, 02:02:07 pm
content: I haven't finaly chosen my ADC yet, at the moment I have a MCP3561, but there is room for improvement...

author: tszaboo
author_rank: Super Contributor
timestamp: July 02, 2022, 02:40:58 pm
content: Depends on what you want to do. How fast you are measuring. If the DC accuracy is important or you just want to measure AC signals. How much digital processing you want to do. And how much noise you have on the signal. Or how much you are willing to spend of the passive parts, if you need high accuracy parts with good tempco.Differential measurement has the benefit of having +3dB amplitude, but you need more electronics to drive it.TI has a handbook on how to connect ADCs. And you should consider a bunch of things before asking the question.

author: MasterT
author_rank: Frequent Contributor
timestamp: July 02, 2022, 03:03:19 pm
content: You can't get 100dB SiNaD at 100 ksps with mcp3561, check DS FIGURE 2-10: SINAD vs. OSR External VREF.

author: iMo
author_rank: Super Contributor
timestamp: July 02, 2022, 06:32:36 pm
content: You would need a good SAR ADC for required 100k samples per second and >100dB SINAD, imho..

author: Kleinstein
author_rank: Super Contributor
timestamp: July 02, 2022, 08:47:22 pm
content: Quote from: imo on July 02, 2022, 06:32:36 pm100 dB SINAD at 100 khz needs a good ADC. There are also a few modern SD ADCs to get there, but not many. One example would be the relatively new AD4134, though probably overkill.High end audio ADCs may be an option, if 192 kSPS is OK.With an SAR ADC one may have to plan with an even higher sampling rate and downconversion to 100 kSPS to allow for a realistic anti aliasing filter.