Bias circuit design for bipolar power amplifier linearity improvement

摘要

A bias circuit (2) for a power amplifier (1) comprises a first bipolar transistor (9) arranged to form a current mirror with a bipolar power transistor (8) of the power amplifier (1). The base of the first bipolar transistor (9) is coupled to a first resistor (11), which is in series with a second resistor (10), the second resistor (10) representing an output terminal of the bias circuit (2) for coupling to the base of the bipolar power transistor (8). A second bipolar transistor (12) is coupled via its emitter to the junction of the first (11) and second (10) resistors and is adapted to control the impedance at the junction of the first (11) and second (10) resistors such that the impedance of the bias circuit (2) at the output terminal is substantially dependent on the value of the second resistor (10) alone.