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I know that the opposite is possible i.e. using 2 DAC's to get a higher quality output, but is it possible with ADC's?

John Am
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  • And your premise isn't correct either; [you can't combine two DACs to double their resolution](https://electronics.stackexchange.com/questions/72176/cascade-dacs-to-get-higher-resolution). –  May 08 '17 at 22:52
  • @duskwuff If you check Microchip mcp4822 there is documented an application to get a 24-bit DAC by combining 2 12-bit channels of a DC. – John Am May 08 '17 at 23:04
  • To do that with DAC or with ADCs requires that the device dealing with the most significant bits has an accuracy equal to of the LSB of the whole system - most ADC/DAC only have an accuracy of about 1LSB or slightly better referenced to its own bit length. – Kevin White May 08 '17 at 23:45
  • I assume you are talking about http://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf That is not what you call a well-thought-out app note. The specification of "a digital value in the range 0-4096" ought to be a tipoff. What the app note fails to mention is that the two resistors must have a resistance ratio accurate to the unit DAC dynamic range. So, even for the 1000:1 ratio implied, this means resistors matched to 0.1%, and a full 24-bit unit would require matching to 0.024%. Worse, the interpolation is not consistent, but varies with the level of the major DAC. – WhatRoughBeast May 09 '17 at 03:01
  • your error should go down by one lsb, but double rez? nope... – dandavis May 09 '17 at 03:31
  • I suggest you digitize with one 10_bit ADC, convert that code into analog with a 20_bit DAC (so the INL is very good) and then subtract that from the original input, to generate a residue. Amplify that reside 1024X, and run thru a 2nd 10_bit ADC. Then you'll likely need some logic to implement a mild error correction. This was used decades ago by Computer Labs in Greensboro NC, to produce 10bit 10 MegaSample/sec ADCs. That product was about the size of a kid's lunchbox. – analogsystemsrf May 09 '17 at 04:39
  • Just over-sample thousands of times and you'll make a 20 bit ADC from a 10 bit ADC. You don't need multiple ADCs to do this. – Andy aka May 09 '17 at 07:30

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I know that the opposite is possible i.e. using 2 DAC's to get a higher quality output, but is it possible with ADC's?

generally no.

that means in some cases it is doable. For example, for adc's with external reference.

dannyf
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