RADIO FREQUENCY POWER AMPLIFIER FOR CELLULAR TELEPHONES

摘要

A bias circuit (28) having a relatively long time constant improves the linearity of a radio frequency power amplifier (22) of a spread spectrum mobile telephone by causing a power transistor (52) of the amplifier to operate in class A or AB mode. The power amplifier thus derives an output signal that is a substantial replica of the spread spectrum input signal for all amplitudes of the input signal. The bias circuit has transistors (72, 76) connected in a feedback circuit which tends to oscillate to affect the amplifier operation. A low pass filter (78, 80) connected to the transistors suppresses the tendency. An interstage high pass matching circuit between a linear amplifier (24) that drives the power amplifier includes a series capacitor (32) and an inductor (35) connected between an output terminal of the linear amplifier (24) and a DC power supply terminal (31).