Fully differential folded cascode CMOS operational amplifier having adaptive biasing and common mode feedback circuits

摘要

An adaptive biasing circuit is combined to a fully differential cascode operational amplifier ("OP AMP") to eliminate the effect of a slew rate, thereby increasing the operation speed of the OP AMP while maintaining a high DC voltage gain. A common mode feedback circuit with a large input common mode voltage range is also connected to the OP AMP, thereby maximizing a linear output voltage swing range. The common mode feedback circuit comprises a nMOS input stage differential amplifier and a pMOS input stage differential amplifier which are connected in parallel, and a push-pull CMOS amplifier for converting current outputs from the nMOS and the pMOS input stage differential amplifiers to an output voltage signal. The adaptive bias circuit comprises an operational transconductance amplifier, two current subtractor circuits and four output transistors.