Patent ID: 8170171

Claim:
A communication semiconductor integrated circuit, comprising: a digital control oscillator capable of controlling an oscillatory frequency of an oscillation signal based on an oscillator tuning word which is a digital value; a counter which counts a wave number of the oscillation signal and outputs a count value; a time to digital converter which outputs a phase difference value between a reference signal and the oscillation signal as a digital value; a first computing element which adds the count value and the phase difference value and outputs a first computed value as an addition result; a second computing element which adds set frequency data obtained by dividing a carrier frequency by a reference frequency of the reference signal and modulation frequency data obtained by dividing a modulation frequency by the reference frequency, and outputs a second computed value as an addition result; a third computing element which subtracts the second computed value from the first computed value and outputs a third computed value as a subtraction result, the third computed value being a phase error; a loop filter which outputs a normalized control value obtained by filtering the third computed value; a first multiplier which outputs a carrier frequency control value obtained by multiplying an output of the loop filter by a first coefficient; a second multiplier which outputs a modulation frequency control value obtained by multiplying the modulation frequency data by a second coefficient; and a fourth computing element which adds the carrier frequency control value and the modulation frequency control value, and outputs the oscillator tuning word as an addition result, wherein the second coefficient “Km” has a relationship of: Km=Kc+A×F mod/ F ref where “Kc” is the first coefficient, “A” is a correction term as a real number, “Fmod” is the modulation frequency, and “Fref” is the reference frequency.