Patent ID: 7605656

Claim:
An operational amplifier with a rail-to-rail common-mode input and output range comprising: a first voltage generator for generating a first supply voltage; a second voltage generator for generating a second supply voltage; a differential input stage, for receiving an input signal, comprising: a first differential pair comprising a first positive input terminal, a first negative input terminal, a first positive output terminal, and a first negative output terminal; and a second differential pair comprising a second positive input terminal, a second negative input terminal, a second positive output terminal, and a second negative output terminal; a summing circuit, coupled to the differential input stage and comprising a first current output terminal and a second current output terminal, for outputting a summation result of output signals of the first positive output terminal, the first negative output terminal, the second positive output terminal, and the second negative output terminal; and a push-pull output stage, coupled to the summing circuit, for outputting an amplification signal, comprising: an output terminal for outputting the amplification signal; a source coupled circuit, comprising a first terminal coupled to the first current output terminal of the summing circuit and a second terminal coupled to the second current output terminal of the summing circuit, for generating a control voltage according to currents of the first current output terminal and the second current output terminal; a first output transistor comprising a source electrode coupled to the first voltage generator, a drain electrode coupled to the output terminal, and a gate electrode, coupled to the first terminal of the source coupled circuit, for controlling the first output transistor according to the control voltage of the source coupled circuit; and a second output transistor comprising a source electrode coupled to the second voltage generator, a drain electrode coupled to the output terminal, and a gate electrode, coupled to the second terminal of the source coupled circuit, for controlling the second output transistor according to the control voltage of the source coupled circuit.