A 300mV-Supply Standard-Cell-Based OTA with Digital PWM Offset Calibration

This paper introduces a fully digital pulse-width-modulation (PWM) based calibration technique intended to dynamically compensate the input offset voltage due to process and mismatch in Ultra Low Voltage (ULV) Digital-Based Operational Transconductance Amplifiers (DB-OTA). Post-layout simulations on a DB-OTA circuit in 180nm featuring the proposed calibration technique demonstrate that process and mismatch related offset voltage can be effectively compensated by varying the duty cycle of a square wave signal with minimum performance overhead. The proposed OTA consumes just 7.34nW while driving a capacitive load of 80pF with a Total Harmonic Distortion lower than 2.26% at 100mV input signal swing. The total silicon area is 1,700 um^2.