Patent ID: 7356092

Claim:
A communication semiconductor integrated circuit device, comprising: a transmitting oscillator including at least constituent elements excluding inductance elements, which are formed over a semiconductor chip; a first external terminal which is coupled to the transmitting oscillator for outputting a signal generated by the transmitting oscillator therethrough; a phase detection circuit which compares a phase of a reference signal and a phase of a feedback signal, and which is coupled to the transmitting oscillator for controlling the transmitting oscillator in accordance with the phase difference; a second external terminal which receives a signal supplied from outside that is related to an output of the transmitting oscillator; and a signal combinational circuit which is coupled to the second external terminal and which combines the signal inputted through the second external terminal and a signal having a predetermined frequency, wherein the signal combinational circuit comprises: a differential circuit including a pair of differential input terminals, and attenuation means that attenuates the signal input to the second external terminal, wherein the attenuated signal is provided between one differential input terminal of the signal combinational circuit and the second external terminal, and the other differential input terminal of the signal combinational circuit is connected to a third external terminal via elements identical to elements that constitute the attenuation means, and wherein the signal combinational circuit is coupled to the phase detection circuit for providing the feedback signal.