Simplified Class AB Control Circuits for Rail to Rail Output Stages of Operational Amplifiers

Abstract

A new approach to solving the problem of class AB control of rail to rail output stages is presented. Step by step five simple class AB control circuits will be discussed, showing the advantages of 'common mode feed parallel'. One of the control circuits has been implemented in a simplified two stage OPAMP with a 2.5MHz bandwith, rail to rail output range and an input common mode range down to the negative rail. A photomicrograph as well as measurement results of a semicustom design are included.