For a battery-powered design (3 to 3.6V), I'd like to use a sensor that outputs a small, low-power AC voltage signal. To sample this signal, an ADC is used (this ADC is also powered by the battery), where currently the voltage is boosted by a DC source to prevent the sensor's output signal from going below 0V.
To replace this DC source, I figured a voltage regulator that's about 1/2 of the supply voltage (~1.6V) would work. However, there's a concern that as the device's battery drains from 3.6V to 3V, the ADC may read different values due to a fixed regulated voltage used to boost the sensor's AC signal.
Would it be possible or even a good idea to have a regulated DC voltage that is always half of whatever the supply voltage is (i.e.: half of 3.6V, half of 3.3V, half of 3V, etc.)?
The following solution is what would have fully answered my question:
1) By feeding multiple batteries in series to a 3.6V voltage regulator, there would be less concern about the ADC reading different values due to a draining battery supply.
2) A decoupling capacitor / high-pass-filter (from Harry Svensson's response), would remove any inherent DC components in the AC signal.
3) A voltage divider would bias the decoupled AC signal to guarantee that the AC signal would always be centered at half the voltage supply. I think the lower resistance also affects the high-pass filter cutoff frequency.
4) A voltage reference would ensure that the ADC's measurements are less affected by any possible fluctuations in the V+ voltage supply.