Differential output amplifier input stage with rail-to-rail common mode input range

摘要

An amplifier having a rail-to-rail common mode input range that can be used in low voltage power supply applications includes differential input and output stages, the output stage having first and second current paths. First and second output duplicating circuits are respectively connected in parallel with the first and second current paths in the differential output stage to duplicate the differential output. A circuit for detecting a common-mode voltage difference is provided between nodes of the first and second output duplicating circuits for developing a current related to the common-mode voltage difference. A current mirror circuit is connected to receive the current related to the common-mode voltage difference for controlling the current in the first and second current paths in the differential output stage. The circuit for detecting a common-mode voltage difference between nodes of the first and second output duplicating circuits can be established by a transistor that senses only common-mode current. The transistor has a control element connected to the nodes in the output duplicating circuits and a current path to a supply voltage.