Voltage controlled oscillator

A voltage controlled oscillator that makes an oscillatory frequency variable in accordance with a control voltage, comprising a crystal resonator and a control voltage supply terminal through which a control voltage is applied, wherein

• a first resistor and a first capacitor are connected in series on a line of the crystal resonator and the control voltage supply terminal,
• a cathode of a first variable-capacitance diode is connected between the first resistor and the first capacitor, and an anode of the first variable-capacitance diode is grounded,
• a parallel-connected circuit is disposed between the first capacitor and the crystal resonator, the parallel-connected circuit including a second variable-capacitance diode and a second capacitor connected in series, and a coil, which are connected in parallel,
• a point between the first capacitor and the parallel-connected circuit on an input side is grounded via a second resistor, and
• a digital potentiometer is disposed to apply a fixed voltage to a point between a cathode of the second variable-capacitance diode and the second capacitor, the digital potentiometer being equipped with a function of a Q dump resistor.

A voltage controlled oscillator that makes an oscillatory frequency variable in accordance with a control voltage, comprising a crystal resonator and a control voltage supply terminal through which a control voltage is applied, wherein

• a first capacitor and a second capacitor connected in parallel, and a first resistor are connected in series on a line of the crystal resonator and the control voltage supply terminal,
• a first variable-capacitance diode is disposed between the first resistor and the first and the second capacitors,
• a point between the first and the second capacitors and an anode of the first variable-capacitance diode is grounded via a second resistor,
• a parallel-connected circuit on an input side is connected between the first resistor and a cathode of the first variable-capacitance diode, the parallel-connected circuit including a third capacitor and a coil connected in series, a second variable-capacitance diode, and a Q dump resistor, which are connected in parallel, and the parallel-connected circuit on an output side is grounded.