Patent ID: 7340227

Claim:
A wireless communication system comprising: a radio frequency power amplifier which amplifies a transmission signal; a transmission power detection circuit which detects a transmission power of the transmission signal that amplified by the radio frequency power amplifier; and a control circuit which receives information on a transmission level from a base station to control transmission power and which restricts an increase in the transmission power when judging from a detection output detected by the transmission power detection circuit that transmission power exceeds specified maximum transmission power, wherein the transmission power detection circuit comprises: a rectifying detection part that comprises plural differential amplifiers coupled in series that each include a differential transistor pair of which emitters are connected in common and to the base terminals of which a signal to be detected is inputted, and smoothing capacitors each coupled to common emitter terminals of a differential transistor pair constituting each differential amplifier; a dummy amplifier having a construction similar to the differential amplifiers; a coefficient circuit that generates a first voltage obtained by multiplying emitter voltage of differential transistors of the dummy amplifier by a prescribed coefficient; and a subtraction circuit that generates a second corresponding to the difference between a third voltage obtained by synthesizing outputs detected by the plural differential amplifiers and the first voltage adjusted by the coefficient circuit, wherein the transmission power detection circuit is increased in the linearity of the detection output over a wider range by the plural differential amplifiers connected in series than by a single differential amplifier, and outputs the second voltage obtained by compensating the temperature dependence of the differential amplifiers by the temperature dependence of the dummy amplifier from the subtraction circuit.