Low Voltage Differential Input Stage With Improved CMRR and True Rail-to-Rail Common Mode Input Range

A scheme for low voltage rail-to-rail operation with improved common mode rejection ratio is introduced. It can operate with single supply voltages close to a transistor´s threshold voltage and it is very compact and power efficient. It is based on a differential amplifier with floating gate input transistors featuring dynamical adjustment of a floating gate biasing voltage. This reduces significantly common mode voltage variations at the input terminals of the differential pair. The implementation of single ended two stage class AB operational amplifiers based on this scheme is discussed. Experimental results of a test chip in 0.5 mum CMOS technology that validates the proposed scheme are presented.