Power control circuit for transmission apparatus

摘要

A modulated signal from an orthogonal modulator is supplied to a mixer, and a second local oscillating signal from a second local oscillator is supplied through a variable gain amplifier to the mixer. A transmission signal from the mixer is supplied through a step-attenuator (ATT) to a power amplifier, and further supplied through a directional coupler and an isolator to an antenna. A signal from the directional coupler is supplied through a detector to a comparator, and a reference voltage from a reference voltage setting unit is supplied to the comparator. An output from the comparator is supplied to a control unit of the variable gain amplifier and a gain is thereby controlled such that a DC voltage from the detector and the reference voltage from the reference voltage setting unit become equal to each other. Further, an attenuation amount of the step-attenuator is set by an attenuation amount setting unit in accordance with a transmission output control signal from a base station.