Understanding noise & ENOB ADC - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: February 09, 2015, 08:25:41 am
content: 1. I am using ADS1248, 24 bit delta sigma adc.2. I have attached a datasheet page explains rms & pp noise for different PGA & sampling rates3. What does it signify.e.g with PGA = 128 & SPS = 2000 , uRMS = 1uV & uPP = 6.48uV.Does that mean my actual signal if less than 6.48uV than it can embed in noise & data sampled is not correct?And data samples should always be greater than 6.48uV for correct sampling.(considering only internal noise at this time)4. I have noticed that even if for SPS = 2000 , for PGA = 1 there is more noise than PGA = 128.But ENOB are more for PGA = 1 rather than PGA = 128?Shouldn't it be other way around?5. Is there any AN or reference data where i can understand all parameters of typical delta sigma adc

author: coppice
author_rank: Super Contributor
timestamp: February 09, 2015, 08:49:51 am
content: Quote from: Vindhyachal.takniki on February 09, 2015, 08:25:41 amAt 2000samples/second and x1 gain the noise represents 31.42uV at the input.At 2000samples/second and x128 gain the noise represents 1uV at the input.If you raise the gain by 128, and the noise voltage only drops to about 1/32 of the original, I'd say your adding about 4 times as much noise to your signal at x128. Clearly this converter adds a lot of the noise after the gain, as the SNR stays more or less constant from x1 to x32. Its only at x64 and x128 that the SNR falls.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: December 28, 2017, 05:43:43 am
content: i found myself looking at some ADC out of curiosityas usual, i lack fundamental understanding about them. i have some questions similar to this very old thread.1) am i right to assume that it is possible to characterize the INL errors of a ADC and compensate for it? eg by using a very accurate voltage ladder?2) and if INL is compensated, it makes more economical sense to choose a lowest noise ADC (more ENOB?) than lowest INL?(the table in pic is very rough collected data. esp with my shallow understanding, esp max112xx ENOB i think is weird)if for example i use MAX11200 and managed to compensate for INL, it would be a "instrument" that makes more sense than LTC2400? in terms of more noiseless ENOB?

author: coppice
author_rank: Super Contributor
timestamp: December 28, 2017, 05:50:11 am
content: Quote from: 3roomlab on December 28, 2017, 05:43:43 amYou can characterise the INL errors at one temperature, but they won't remain the same as the temperature changes. They might also change over time.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: December 28, 2017, 06:00:20 am
content: Quote from: coppice on December 28, 2017, 05:50:11 amyes indeed i saw that, and since most ADC include an internal temperature measurement. i assume they did it also for the possibility of improving compensation.and so i assume there could be a huge set of compensating data and math to fix INLbut do ppl really do it? (esp looking at resistor TC thread, where andreas measure resistor tempco?)the better question i suppose is, does anyone here do characterization on their ADC to zero out the INL?

author: danadak
author_rank: Super Contributor
timestamp: December 28, 2017, 11:00:01 am
content: This might be useful -http://www.analog.com/media/en/training-seminars/tutorials/MT-003.pdfRegards, Dana.

author: David Hess
author_rank: Super Contributor
timestamp: December 28, 2017, 12:41:02 pm
content: The ENOB depends on dynamic range. Operating with a higher input gain lowers the input noise level but decreases the maximum signal range even even more so fewer bits are available.Some ADCs, like the Linear Technology LTC2400 series, have a very predictable INL even over temperature allowing it to be easily corrected.