Low Voltage, Low Power, Inverter-Based Switched-Capacitor Delta-Sigma Modulator

Abstract

An operational transconductance amplifier (OTA) is a major building block and consumes most of the power in switched-capacitor (SC) circuits, but it is difficult to design low-voltage OTAs in scaled CMOS technologies. Instead of using an OTA, this paper proposes an inverter-based SC circuit and its application to low-voltage, low-power delta-sigma (DeltaSigma) modulators. Detailed analysis and design optimizations are also provided. Three inverter-based DeltaSigma modulators are implemented for an implantable pacemaker, a CMOS image sensor, and an audio codec. The modulator-I for an implantable pacemaker achieves 65-dB peak-SNDR for 120-Hz bandwidth consuming 0.73 muW with 1.5 V supply. The modulator-II for a CMOS image sensor implemented with 320-channel parallel ADC architecture achieves 63-dB peak-SNDR for 8-kHz bandwidth consuming 5.6 muW for each channel with 1.2-V supply. The modulator-III for an audio codec achieves 81-dB peak-SNDR with 20-kHz bandwidth consuming 36 muW with 0.7-V supply. The prototype DeltaSigma modulators achieved high power efficiency maintaining sufficient performances for practical applications.