A 0.2-mW CMOS ΣΔ modulator for speech coding with 80 dB dynamic range

Abstract

A CMOS /spl Sigma//spl Delta/ modulator for speech coding with continuous-time loopfilter is presented. Compared to switched-capacitor implementations, the relaxed bandwidth requirements of the active elements of the loopfilter reduce the power consumption. Furthermore, the need for an antialiasing filter at the modulator input is eliminated. A fourth-order, 64/spl times/ oversampling /spl Sigma//spl Delta/ modulator for application in portable telephones was designed and shows 80 dB dynamic range over the 300-3400 Hz voice bandwidth. Its input is directly connected to the microphone (maximum 40 mV/sub RMS/). Total harmonic distortion (THD) is below -70 dB at 95 /spl mu/A current consumption from a 2.2 V supply voltage. The active die area of the modulator is 0.5 mm/sup 2/ in a standard 0.5-/spl mu/m CMOS process.