A 250mV 77dB DR 10kHz BW SC ΔΣ Modulator Exploiting Subthreshold OTAs

Abstract

This paper presents a high-resolution ΔΣ modulator which is capable of operation under supply voltage as low as 250mV. A novel subthreshold inverter-based OTA is proposed and exploited in the switched-capacitor (SC) integrators, permitting a satisfied noise-shaping performance in the 4th-order feed-forward topology. With each stage's coefficient optimized, the integrators' internal swings and the distortion power stemming from OTAs' gain nonlinearity are minimized. Implemented in a 0.13μm CMOS with an OSR of 64 and a sampling frequency (fs) of 1.28MHz, this design achieves a measured DR of 77.0dB, SNDR of 73.3dB, and SFDR of 85.0dB over a 10kHz bandwidth. To the best of authors' knowledge, it appears to be the converter with highest SNDR observed among sub -0.5V designs.