Patent ID: 7463876

Claim:
A communication semiconductor integrated circuit including a transmission oscillation circuit for generating a transmission signal having a predetermined frequency, a first variable gain amplifier circuit for amplifying a signal outputted by said transmission oscillation circuit, a phase control loop having an amplitude detection circuit and for controlling a phase of the transmission signal outputted by said transmission oscillation circuit, and an amplitude control loop for controlling a gain of said first variable gain amplifier circuit to control an amplitude of the transmission signal outputted by said first variable gain amplifier circuit, said communication semiconductor integrated circuit executing calibration of said amplitude control loop, comprising: a second variable gain amplifier circuit disposed on a feedback path of said amplitude control loop which feeds back a signal conformable to an output level of the transmission signal to said amplitude detection circuit; and a third variable gain amplifier circuit disposed on a forward path extending from said amplitude detection circuit to said first variable gain amplifier circuit; wherein upon execution of said calibration, a gain of said second variable gain amplifier circuit is varied in a state where a first value for setting a gain of said first variable gain amplifier circuit is given to said first variable gain amplifier circuit to thereby detect a gain of said second variable gain amplifier circuit at the time when an output of said second variable gain amplifier circuit is equal to a predetermined value, the gain of said second variable gain amplifier circuit is varied in a state where a second value for setting the gain of said first variable gain amplifier circuit is given to said first variable gain amplifier circuit to thereby detect a gain of said second variable gain amplifier circuit at the time when the output of said second variable gain amplifier circuit is equal to a predetermined value and decide a gain of said third variable gain amplifier circuit on the basis of a difference between said detected two gains of said second variable gain amplifier circuit.