US Patent 9608576 Apparatus and methods for power amplifier bias circuits

Apparatus and methods for power amplifier bias circuits are disclosed herein. In certain implementations, a power amplifier bias circuit includes a current source configured to generate a reference current, a plurality of reference bipolar transistors, a selection circuit configured to select one or more selected reference bipolar transistors from the plurality of reference bipolar transistors, and a transimpedance amplifier. The one or more selected reference bipolar transistors have a current therethrough that changes in relation to a power amplifier stage bias voltage, and the transimpedance amplifier is configured to control the power amplifier stage bias voltage based on an error current corresponding to a difference between the reference current and the current through the one or more selected reference bipolar transistors.