US Patent 10003308 Apparatus and methods for power amplifier biasing

Apparatus and methods for power amplifier biasing are disclosed herein. In certain implementations, a power amplifier system includes a power amplifier bias circuit and a power amplifier. The power amplifier bias circuit includes a reference current source that generates a reference current, a bipolar reference transistor, and a transimpedance amplifier that amplifies a difference between a collector current of the bipolar reference transistor and the reference current, and that provides a base bias voltage to a base of the bipolar reference transistor. The power amplifier generates a radio frequency output signal at an output based on amplifying a radio frequency input signal received at an input. The power amplifier includes a bipolar power amplifier transistor including a base biased by the base bias voltage such that the power amplifier has a substantially flat gain response versus time.