ADC question  - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: April 08, 2013, 10:41:02 pm
content: can i take 2 10 bit ADCs on my 16 bit DAC than use like a few opamps (or opamps and zeners or whatever i come up with) to split the voltage between 2 of the ADCs to get an 17 bit ADC? (2 times the resolution)im using a quad 16 bit DAC and 3 of them are used i would like to use the last one for this and because its already using like 20 opamps one more dual or quad pack wont add much to the final cost at alli dont see anything inherently wrong with doing this and worse case i can just not-populate and reflash but i was wondering if any of you can see anything wrong with this or if there is an already established method for doing this?it hit 100 here today ( F ... tho i cant tell the difference it was 55 here 2 days ago) so my brain is not all here excuse me if im being daft

author: ve7xen
author_rank: Super Contributor
timestamp: April 08, 2013, 10:54:18 pm
content: You could oversample and decimate to get more resolution, if you're not already running the ADC as fast as you can. I'm not aware of any easy way to get more resolution by fiddling with the signal, other than making sure it's properly scaled to the input range of the ADC.

author: kxenos
author_rank: Frequent Contributor
timestamp: April 08, 2013, 11:04:01 pm
content: You and beefeater london dry gin got me puzzled but I think you can double the resolution by adding 2 DACs. In tests that I have made some years ago, the result was not good because the splitting circuit was not adequate for the required precision. But I guess you can have a go. Cheers!

author: c4757p
author_rank: Super Contributor
timestamp: April 08, 2013, 11:12:38 pm
content: You're going to have to be damn careful to get anything useful with 17 bits of resolution. If you're measuring up to 5V, that's38 uV increments. Can the circuit you're using to shift stuff around do it without introducing 38 uV offsets?Quote from: kxenos on April 08, 2013, 11:04:01 pmDouble the resolution, sure, but remember that that's only one additional bit. Is it worth the additional circuitry, effort and second DAC, when you could just get a DAC with one bit higher resolution?

author: BiOzZ
author_rank: Regular Contributor
timestamp: April 08, 2013, 11:58:27 pm
content: sorry guys i ended up ridding of the need to use one of the ADCs by changing the micro and just chose a dual 16 bit DAC so this is not needed any morebut thanks anyway ill keep that in mind for the future!

author: LukeW
author_rank: Frequent Contributor
timestamp: April 12, 2013, 09:08:28 am
content: Yeah... if you've got a 16-bit ADC chip, then you need careful, well-designed PCB layout, power supply design, decoupling caps, stable clean reference voltages, decoupled analog and digital grounds and power rails and appropriate signals coming in from the analog front end etc. in order to get 16 bits of usable resolution.If somebody gets a 16-bit ADC chip and just sticks it on a breadboard or something with wires hanging around everywhere without clean power supply and reference filtering and decoupling etc. then sure it will work - but it might only have, say, 12 bits of usable resolution with the last 4 bits buried below the noise. So if that's the case, they might as well just use a cheaper 12-bit ADC.

author: ddavidebor
author_rank: Super Contributor
timestamp: April 12, 2013, 03:58:21 pm
content: Quote from: BiOzZ on April 08, 2013, 10:41:02 pmJust switch the two signal one at the times!

author: ejeffrey
author_rank: Super Contributor
timestamp: April 12, 2013, 04:20:25 pm
content: This is how 'half flash' ADCs work. They measure coarsely with an ADC, then use a DAC and opamps to subtract off the measured value and amplify the residual then feed that to an ADC to get fine resolution.It takes careful design to get right. The first ADC must still be accurate enough for the full resolution, and you have to carefully match the DAC and ADCs. I think you made the right choice to get a pre-built 16 bit ADC.