Crystal oscillator

• US 20030025567A1
• Filed: 07/23/2002
• Published: 02/06/2003
• Est. Priority Date: 07/24/2001
• Status: Active Grant

• Current Assignee: Nihon Dempa Kogyo Company Limited
• Original Assignee: Nihon Dempa Kogyo Company Limited
• Inventors: Asamura, Fumio, Kubo, Kuichi
• Granted Patent: US 6,861,915 B2
• Time in Patent Office: Days
• US Class Current: 331/158
• CPC Class Codes: H03B 2201/0266 the means comprising a transistor
• CPC Class Codes: H03B 5/368 the means being voltage variable capacitance diodes

Abstract

A crystal oscillator has a quartz-crystal unit, a first oscillating capacitor connected between a first end of the crystal unit and a reference potential point, a second oscillating capacitor connected between a second end of the crystal unit and the reference potential point, a CMOS inverter connected parallel to the crystal unit, and a feedback resistor connected across the inverter. The crystal oscillator can easily be incorporated into integrated circuits and has an increased variable oscillation frequency range. The crystal oscillator also has an adjustable capacitive assembly having selectable capacitances which is connected parallel to a combined capacitor comprising the first and the second oscillating capacitors.

Claims

1. A crystal oscillator comprising:

a crystal unit;

a first oscillating capacitor connected between a first end of the crystal unit and a reference potential point;

a second oscillating capacitor connected between a second end of the crystal unit and the reference potential point; and

an adjustable capacitive assembly having selectable capacitances which is connected parallel to a combined capacitor comprising the first and second oscillating capacitors.

2. The crystal oscillator according to claim 1, wherein the adjustable capacitive assembly comprises:

a first capacitor; and

a series-connected circuit connected parallel to the first capacitor, the series-connected circuit comprising a second capacitor and a switching element connected in series to the second capacitor.

3. The crystal oscillator according to claim 1, further comprising an amplifier for maintaining oscillation in a resonance loop comprising the crystal unit and the first and second oscillating capacitors.

4. The crystal oscillator according to claim 2, wherein the switching element comprises a MOSFET.

5. The crystal oscillator according to claim 1, wherein at least one of the first and second oscillating capacitors comprises a voltage-variable capacitive element.

6. The crystal oscillator according to claim 5, further comprising means for applying a control voltage to a cathode of the voltage-variable capacitive element.

7. The crystal oscillator according to claim 5, further comprising an amplifier for maintaining oscillation in a resonance loop comprising the crystal unit and the first and second oscillating capacitors.

8. The crystal oscillator according to claim 1, further comprising a voltage-variable capacitive element inserted in at least one of circuits between the first oscillating capacitor and the first end and between the second oscillating capacitor and the second end.

9. The crystal oscillator according to claim 8, wherein the adjustable capacitive assembly comprises:

a first capacitor;

a series-connected circuit connected parallel to the first capacitor; and

a first switching element short-circuiting opposite ends of the adjustable capacitive assembly;

the series-connected circuit comprising a second capacitor and a second switching element connected in series to the second capacitor.

10. The crystal oscillator according to claim 9, wherein each of the first and second switching elements comprises a MOSFET.

11. The crystal oscillator according to claim 8, further comprising:

means for applying a first control voltage to an anode of the voltage-variable capacitive element; and

means for applying a second control voltage to a cathode of the voltage-variable capacitive element.

12. The crystal oscillator according to claim 8, further comprising an amplifier for maintaining oscillation in a resonance loop comprising the crystal unit, the first and second oscillating capacitors, and the voltage-variable capacitive element.