Single-chip A/D converter for digital microphones with on-chip preamplifier and time-domain noise isolation

A 1-bit sigma-delta modulator (SigmaDeltaM) with an on-chip preamplifier for digital electret microphones has been implemented. A differential gm-opamp-RC preamplifier eliminates the traditional single-ended JFET interface and is integrated with an on-chip SigmaDeltaM by removing all external components. The proposed time-domain noise isolation technique preserves circuit performance under a single power supply condition. The prototype implemented in a 0.18 mum CMOS technology achieves a 78 dB dynamic range and 62 dB peak signal-to-noise+distortion ratio (both A-weighted) with a current consumption of 450 muA under a 1.8 V supply.