Patent ID: 7454176

Claim:
A semiconductor integrated circuit for communication, comprising: a reception-system signal processing circuit; a transmission-system signal processing circuit; a down-convert mixer which combines a receive signal and a carrier wave signal; an up-convert mixer which combines a transmit signal and the carrier wave signal; and a PLL circuit common to transmission/reception, which includes a voltage-controlled oscillator and generates a carrier wave signal corresponding to a reception frequency and a transmission frequency and supplies the same to the two mixers, said semiconductor integrated circuit being operable in a first communication mode for transmitting and receiving signals subjected to phase modulation and amplitude modulation and a second communication mode for transmitting and receiving the signal subjected only to the phase modulation, wherein a frequency band of a loop for the PLL circuit is switched and set so as to be wider than a frequency band in a transmission mode in a reception mode and to be narrower than a frequency band in the reception mode in the transmission mode.