FM signal oscillator circuit and modulation level control method

An FM signal oscillator circuit comprising:

• a resonator having a variable capacitance diode whose capacitance is set according to a control voltage, the variable capacitance diode changing a resonance frequency of the resonator;
• a driver configured to drive the resonator and providing an FM signal;
• and
• a corrector configured to correct the level of a modulating signal according to resonance-frequency-changing characteristics of the resonator and apply a signal corresponding to the corrected modulating signal and a signal corresponding to the control voltage to the variable capacitance diode, the corrector comprising,
• an operational amplifier configured to amplify the control voltage, and
• a variable gain amplifier configured to amplify the modulating signal according to the amplified control voltage,
• the corrector applying the control voltage and the amplified modulating signal to opposite ends of the variable capacitance diode, respectively.

An FM signal oscillator circuit comprising:

• a resonator having a variable capacitance diode whose capacitance is set according to a control voltage, the variable capacitance diode changing a resonance frequency of the resonator, the resonator including two variable capacitance diodes to form, together with the driver, a differential voltage controlled oscillator;
• a driver configured to drive the resonator and providing an FM signal;
• and
• a corrector configured to correct the level of a modulating signal according to resonance-frequency-changing characteristics of the resonator and apply a signal corresponding to the corrected modulating signal and a signal corresponding to the control voltage to the variable capacitance diode, the corrector comprising,
• a comparator configured to compare a signal corresponding to the control voltage applied to a common cathode of the variable capacitance diodes with a signal corresponding to an anode voltage of the variable capacitance diodes and providing a differential voltage based on the compared voltages, and
• a variable gain amplifier whose amplification gain is changed according to the differential voltage, configured to set the level of the modulating signal.

A modulation level controlling method for an oscillator having a variable capacitance element to provide an FM signal having a center frequency determined by a control signal and modulated by a modulating signal, the method comprising:

• amplifying the control signal;
• amplifying the modulating signal according to a gain determined by the amplified control signal;
• adding the amplified modulating signal to the control signal, to form a sum signal;
• and
• applying the sum signal to the variable capacitance element to control a resonance frequency in the oscillator.

A modulation level controlling method for an oscillator having a variable capacitance element to provide an FM signal having a center frequency determined by a control signal and modulated by a modulating signal, the method comprising:

• amplifying the control signal;
• amplifying the modulating signal according to a gain determined by the amplified control signal;
• and
• superimposing the amplified modulating signal on the control signal in such a way as to maintain a constant modulation gain for an oscillation frequency of the oscillator with respect to the modulating signal, and applying the superimposed signal to the variable capacitance element to control a resonance frequency in the oscillator.

A modulation level controlling method for an oscillator having a variable capacitance element to provide an FM signal having a center frequency determined by a control signal and modulated by a modulating signal, the method comprising:

• extracting a terminal voltage of the variable capacitance element based on the control signal serving as a comparison reference;
• amplifying the modulating signal by a gain determined from the extracted terminal voltage;
• and
• supplying the amplified modulating signal to the oscillator to control a resonance frequency in the oscillator in such a way as to maintain a constant modulation gain for an oscillation frequency of the oscillator with respect to the modulating signal.