Patent ID: 7474166

Claim:
A PLL frequency synthesizer circuit integrated on a semiconductor integrated circuit, comprising: a voltage-controlled oscillator circuit provided with a capacitor, an inductor, and a variable capacitor element for oscillating using the resonance frequencies of the capacitor and inductor, for outputting the oscillation frequency signal of the variable capacitor element; a negative feedback loop circuit configured to comprise the voltage-controlled oscillator circuit, capable of looping the signal output from the voltage-controlled oscillator circuit and performing a frequency acquisition operation for adjusting the frequency of the signal to a desired locking frequency; a tuning circuit, connected to the loop circuit to receive the signal output, for performing tuning so that the oscillation frequency approaches the locking frequency, by modulating the capacitance value of the capacitor of the voltage-controlled oscillator circuit prior to the frequency acquisition operation; and a reference potential application circuit for selectively applying a reference potential to the variable capacitor element of the voltage-controlled oscillator circuit during the tuning operation performed by the tuning circuit, the reference voltage application circuit is configured to switch between two types of electrical potentials to be applied to the variable capacitor element of the voltage-controlled oscillator circuit during the tuning operation.