Circuits and methods for providing rail-to-rail output with highly linear transconductance performance

Abstract

The circuits and methods of the present invention provide rail-to-rail output stages that cancel the non-linear components of the transconductances of transistors used in the output stages, that allow the idling current in the output stages to be controlled by external current sources and device size ratios, and that enable the idling current in the output stages to be maintained independently of manufacturing processes, temperature, and power supply voltages. The output stages generally comprise a complementary subcircuit, a current mirror and an output driver. The output stages receive an input signal and a bias voltage from an external source and responsively produce a push current that feeds current into a load and a pull current that pulls current from the load. When the push current matches the pull current, the output stages are said to be “idling.” The bias voltage controls the idling current. By mimicking the voltages and currents produced in the output stages using similar components, a bias voltage generation circuit provides a bias voltage that enables the idling point to be maintained in the output stages independently of manufacturing processes, temperature, and power supply voltages.