Amplifier having linear input-output characteristics and high efficiency

Claim 1

An amplifier for amplifying a high frequency signal comprising: an input impedance matching circuit having an input end and an output end; an output impedance matching circuit having an input end and an output end; an FET having a gate connected to the output end of said input impedance matching circuit for receiving a high frequency signal having a power for amplification by said FET and a drain connected to the input end of said output impedance matching circuit; and a gate voltage control circuit for controlling a gate voltage applied to the gate of said FET in response to the power of the high frequency signal, an output of said gate voltage control circuit being connected to a junction of the output end of said input impedance matching circuit and the gate of said FET, said gate voltage control circuit comprising a diode having an anode and a cathode, the anode being connected to the gate of said FET, a capacitor connected between the cathode of said diode and ground, and a gate bias setting circuit having an output terminal connected to the junction of the cathode of said diode and said capacitor for outputting a control voltage in response to the power of the high frequency signal.