Design considerations for common-mode feedback circuits in fully-differential operational transconductance amplifiers with tuning

Abstract

Power consumption, chip area, feedback loop gain, parasitic capacitance and nonlinearity of three popular common-mode feedback (CMF) circuits used in operational amplifiers are analyzed and compared. One of them is chosen as a candidate for CMF in fully differential operational transconductance amplifiers (OTAs). Three improved versions of this circuit that can be used in an OTA without leading to DC offset caused by the always unavoidable tuning are proposed. Simulation results show that the improved circuits reduce the DC offset from 0.6 V to nearly zero for the whole tuning range. >