A low-power continuous-time ΔΣ modulator for Electret microphone applications

A continuous-time delta-sigma modulator that maybe used as an interface for Electret microphones is presented. The third order modulator comprises a single-ended-to-differential-converter integrated inside the loop-filter with a single-ended high-impedance input, an RC integrator on the first stage and Gm-C integrators for the other stages. Gm-C integrators comprise highly-linear low-power transconductances. The modulator has been designed and fabricated in the TSMC 0.18um technology for audio application (300Hz–10kHz) with a single supply voltage of 1.8V and a single-ended input signal with a peak of 125mV. The measured dynamic range of the modulator is 86dB with a power consumption of 240uA.