Patent ID: 7609123

Claim:
A direct modulation type voltage-controlled oscillator for oscillating a signal in which a carrier wave component is modulated by a modulated wave component, the direct modulation type voltage-controlled oscillator comprising: a first variable capacitor section having a first terminal and a second terminal, the first variable capacitor section including a variable capacitor whose capacitance value varies in accordance with a potential difference between a control voltage, corresponding to the carrier wave component, which is fed to the first terminal and a first reference voltage applied to the second terminal; a second variable capacitor section having a first terminal and a second terminal, the second variable capacitor section including a variable capacitor whose capacitance value varies in accordance with a potential difference between a control voltage, corresponding to the modulated wave component, which is fed to the first terminal and a second reference voltage applied to the second terminal; and a voltage setting section operable to set the control voltage corresponding to the modulated wave component based on the second reference voltage, wherein the voltage setting section includes: an offset circuit operable to detect an intermediate capacitance value in the second variable capacitor section and to generate, based on the second reference voltage, a third reference voltage corresponding to the intermediate capacitance value; a resistance located between the offset circuit and the first terminal of the second variable capacitor section, the third reference voltage passing through the resistance prior to being received at the first terminal of the second variable capacitor section; and a capacitor located before the first terminal of the second variable capacitor section, the capacitor being operable to pass only an AC component included in the modulated wave component to the first terminal of the second variable capacitor section.