A/D CONVERTER WITH INTEGRATED BIASING FOR A MICROPHONE

摘要

A combination of an electret microphone (1) and a sigma-delta A/D converter (9, 5, 7, 8). The sigma-delta A/D converter has a DC feedback loop (8) which provides the bias current (IDC) for the junction FET (2) of the electret microphone. In this way the signal current from the FET (2) can be injected directly into the input integrator (9) of the sigma-delta A/D converter without the need of signal resistors in series with the FET (2).