Possible Salvage scheme for the Xmega adc

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I've read most all the relevant posts, and there seem to be real issues with the internal 1v ref, and the internal Vref/2 for differential measurements. To get full 12 bit resolution and stable readings, has anyone tried an external 2v or 2.5v ref in addition to using an externally supplied Vref/2 to a -diff input, and taking readings in signed differential mode?

Thanks!

Tom Pappano
Tulsa, Oklahoma

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According to new XMEGA errata, there are the following problems with internal 1v Vref:

ATxmega128a1:

Quote:
When operating at below 0°C and using internal 1.0V reference the RMS noise will be up 4 LSB, Peak-to-peak noise up to 25 LSB.

ATxmega256a3, ATxmega192A3, ATxmega128A3, ATxmega64A3, ATxmega16A4, ATxmega32A4:
Quote:
In signed mode INL is increased to:
– 6 LSB for reference voltage below 1.1V when VCC is above 3.0V.
– 20 LSB for ambient temperature below 0 degree C and reference voltage below 1.3V.
In unsigned mode, the INL is increased up to a factor of 3 for the conditions above.

Ozhan KD
Knowledge is POWER