An oscillator, includes an amplifier circuit including a semiconductor element having a first constant potential as reference potential for a power supply voltage, a variable capacitance element, a piezoelectric resonator, and a capacitance circuit constituting a closed circuit with the piezoelectric resonator. The amplifier circuit and the variable capacitance element are connected in series to provide a series circuit. The capacitance circuit connects the capacitance elements in a plurality of numbers in series. A connecting midpoint of the series connection is connected to a circuit for the first constant potential. Two connecting midpoints other than the midpoint of the closed circuit are used as connecting points to connect the series circuit and the closed circuit in parallel.
1. An oscillator, comprising:
an amplifier circuit;
a first variable capacitance element, a control voltage being connected to a first end of the first variable capacitance element and a reference voltage being connected to a second end of the first variable capacitance element between the second end of the first variable capacitance and an input of the amplifier circuit;
a second variable capacitance element, the control voltage being connected to a first end of the second variable capacitance element and the reference voltage being connected to a second end of the second variable capacitance element between the second end of the second variable capacitance and an output of the amplifier circuit;
a piezoelectric resonator;
a capacitance circuit constituting a closed circuit with the piezoelectric resonator; and
a series circuit, the series circuit including the amplifier circuit, the first variable capacitance element, and the second variable capacitance element connected in series and the series circuit and the closed circuit being connected in parallel.
2. The oscillator according to claim 1 , the first variable capacitance element and the second variable capacitance element being voltage-controlled variable capacitance elements.
3. The oscillator according to claim 2 , further comprising a resistance connected between the input and the output of the amplifier circuit.
4. The oscillator according to claim 1 , the capacitance circuit including a third variable capacitance element.
5. The oscillator according to claim 1 , the reference voltage being ground, and the amplifier circuit being an inverter amplifier circuit of a single power supply including an earth terminal.
6. The oscillator according to claim 1 , the amplifier circuit being an NPN type transistor, and an emitter of the transistor being connected to ground.