Design of a Switched-Mode Operational Amplifier Operating With a 0.5V Supply Voltage

This work presents a novel design of a switched-mode operational amplifier (SMOA). It consists of two stages. The first stage is a low supply voltage operational amplifier. It utilizes common mode feedback techniques to eliminate current sources and increase the output voltage swing. The second stage is a pulse width modulator (PWM) which transforms the output signal information from voltage to time domain. This results in increasing the voltage swing and reducing the distortion issues that conventional operational amplifiers suffer from. Multi-phase techniques were employed to attenuate the PWM distortion components and increase linearity. The 10-phase SMOA circuit proposed in this work was implemented and simulated using Hspice circuit simulator. It uses 28nm CMOS technology and operates from a 0.5V supply voltage and a 500MHz PWM frequency. It consumes 1.5mW while achieving a 740mV peak-to-peak differential output voltage swing with -43.9dB total harmonic distortion (THD) and 44.7dB spurious free dynamic range (SFDR) when a 1MHz input frequency is used.