US Patent 7496333 Transmission circuit and communication apparatus employing the same

A small-size transmission circuit is provided which outputs a transmission signal having high linearity independently of a magnitude of an output power, and operates with high efficiency. A signal generating section generates quadrature data based on input data. A computation section compares an amplitude component of the quadrature data with a predetermined amplitude threshold value, and outputs an amplitude signal, a first phase signal, and a second phase signal. A regulator outputs a voltage controlled depending on the amplitude signal. An angle modulation section and an angle modulation section angle-modulate the phase signal to output first and second angle-modulated signals. An amplitude modulation section and an amplitude modulation section amplitude-modulate the first and second angle-modulated signals using a voltage controlled depending on the amplitude signal to output the angle-modulated and amplitude-modulated signals as a first modulated signal and a second modulated signal. A combining section combines the first and second modulated signals to output a transmission signal.