Patent ID: 7012470

Claim:
A communication semiconductor integrated circuit, comprising: a DA converter circuit which DA-converts a modulating code; a voltage-controlled oscillator circuit; a phase comparator which detects a phase difference between an oscillation output of the voltage-controlled oscillator circuit and a reference clock signal; and a control voltage generating circuit which generates a voltage corresponding to the phase difference detected by the phase comparator and applies the voltage to the voltage-controlled oscillator circuit as a first control voltage, said voltage-controlled oscillator circuit being controlled by the first control voltage to thereby generate a frequency signal used as a carrier, and the voltage-controlled oscillator circuit being controlled by a second control voltage based on an output of the DA converter circuit to thereby frequency-modulate the carrier and output a modulated carrier, a frequency adjustment/control circuit which measures the frequency of the oscillation output of the voltage-controlled oscillator circuit and generates a signal corresponding to the measured value by referring to a pre-set target value, wherein a reference current value of the DA converter circuit is changed based on the signal generated by the frequency adjustment/control circuit to thereby correct a frequency of the oscillation output of the voltage-controlled oscillator circuit, and wherein the frequency adjustment/control circuit includes: a frecquency measuring circuit which measures the oscillation output of the voltage-controlled oscillator circuit or a frequency of a signal obtained by dividing the oscillation output; and an arithmetic circuit which calculates a correction value from the value measured by the frequency measuring circuit and the target value.