> However, if you have a front end that only selects part of the voltage,=20
> (say 1V -> 1/1024 =3D ~1mV) that is of interest to you then you can=20
> achieve 1mV or higher. For instance, if the battery is at 3V, you can=20
> just monitor the 2.5-3.5 range using an opamp to amplify (and level=20
> shift if necessary) so the full range of the ADC is used

IIRC the absolute resolution of a 10-bit PIC ADC is 500uV (although
you may wish to consult Microchip AN1152, "Achieving Higher ADC
Resolution Using Oversampling")

Using an external 14- or 16-bit ADC would be a lot simpler than
tracking the battery with a Vref+/Vref- window to make the most of
the inherent 500uV granularity of the internal ADC, which I think
are mostly 10-bit or 12-bit but I've not researched that

Joe

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