I've been wondering if there is a simple means of extracting a DC signal from an AC+DC signal for the purpose of providing a small DC supply to a CMOS device.
Essentially the signal I'm considering is a DC microphone bias supplied to an electret microphone. The electret mic will add its own small signal AC, and this will pass through some circuit that requires the DC bias only, leaving the microphone AC undistorted to be passed to another part of the circuit uneffected. The rest of the audio chain is passive, and no external supply is available other than the 2.5V - 5.0V DC microphone bias superimposed with audio AC.
I'd like to add a small CMOS comparator (or similar) that requires a DC supply, and the microphone bias is the only DC source available for the CMOS device supply. Usually removing the DC from a signal is straight forward with a DC block capacitor, but any thoughts how to do this DC extraction simply without effecting the audio signal ??