Patent ID: 7518449
Filing Date: 2009-04-14
Classification: H03F

Abstract:
1. A Doherty amplifier, comprising: a Doherty amplification circuit including a distributor for dividing an input signal, a class AB or B carrier amplifier for amplifying one of the signals divided by the distributor, a peak amplifier for amplifying the other of the signals divided by the distributing means, and a combiner for combining an output signal from the carrier amplifier with an output signal from the peak amplifier; and an active bias circuit including an average power detector for detecting a voltage value representing an average power of the input signal, an envelope detector for detecting an envelope of the input signal, a threshold calculator for calculating a lower-side limiting value of the envelope detected by the envelope detector based on the voltage value detected by the average power detector, and a voltage limiter for limiting the envelope detected by the envelope detector below a predetermined value, wherein a bias voltage corresponding to the average power of the input signal is applied to the Doherty amplification circuit.