Patent ID: 8565344

Claim:
A transmission circuit for outputting a transmission signal, comprising: a control section for determining whether to switch an operation mode of the transmission circuit to a quadrature modulation scheme or a polar modulation scheme, based on power information, and outputting a vector signal which includes I and Q signals when the operation mode of the transmission circuit is the quadrature modulation scheme, and outputting an amplitude signal and a phase signal when the operation mode of the transmission circuit is the polar modulation scheme; an amplitude phase modulation section for amplitude-phase modulating the vector signal outputted by the control section; a first variable gain amplifier for amplifying an output signal from the amplitude phase modulation section with a first gain; a regulator for outputting a voltage in accordance with the amplitude signal outputted by the control section; a phase modulation section for phase-modulating the phase signal outputted by the control section; a second variable gain amplifier for amplifying an output signal from the phase modulation section with a second gain; a power amplifier for receiving a predetermined direct-current voltage supplied thereto and amplifying an output signal from the first variable gain amplifier using the supplied predetermined direct-current voltage when the operation mode of the transmission circuit is the quadrature modulation scheme, and for receiving the voltage in accordance with the amplitude signal supplied thereto by the regulator and amplifying an output signal from the second variable gain amplifier using the supplied voltage when the operation mode of the transmission circuit is the polar modulation scheme; and a bias circuit for outputting a bias control signal to the power amplifier, wherein the power amplifier comprises: a first input terminal to which the direct-current voltage or the voltage in accordance with the amplitude signal is supplied; a second input terminal to which the output signal from the first variable gain amplifier or the output signal from the second variable gain amplifier is inputted; and a third input terminal to which the bias control signal is inputted, and the control section controls switching of the operation mode of the transmission circuit so that at least one of the first input terminal and the second input terminal is prevented from being in a no input state.