Voltage-controlled oscillator, high-frequency module, and communication apparatus

• US 20030231074A1
• Filed: 05/12/2003
• Published: 12/18/2003
• Est. Priority Date: 05/28/2002
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Shinoda, Satoshi, Nishida, Hiroshi, Sakamoto, Koichi, Baba, Takahiro, Fujidai, Masanori
• Granted Patent: US 6,836,191 B2
• Time in Patent Office: Days
• US Class Current: 331/177.00V
• CPC Class Codes: H03B 5/18 with frequency-determining element comprising distributed inductance and capacitance
• CPC Class Codes: H03B 5/1847 the active element in the amplifier being a semiconductor device
• CPC Class Codes: H03B 5/1864 the frequency-determining element being a dielectric resonator
• CPC Class Codes: H03B 5/368 the means being voltage variable capacitance diodes

Abstract

A voltage controlled oscillator includes a resonant circuit which is connected with an active circuit. In the resonant circuit, a variable capacitance diode is connected with a resonator via a transmission line, and a capacitive circuit is connected in parallel with the variable capacitance diode. By setting the length of the transmission line to an appropriate value ranging from, for example, about one quarter to about one half of the wavelength of the resonant frequency, the frequency change width can increase, while maintaining the frequency linearity because of connection of the capacitive circuit.

Claims

1. A voltage-controlled oscillator comprising:

a resonant circuit; and

an active circuit for amplifying a signal output from the resonant circuit;

wherein said resonant circuit includes a resonator having a predetermined resonant frequency, a variable capacitance diode connected to the resonator for shifting the resonant frequency according to a control voltage, a transmission line connected between the resonator and the variable capacitance diode, and a capacitive circuit connected in parallel with the variable capacitance diode.

2. A voltage-controlled oscillator according to claim 1, wherein the capacitive circuit includes an open stub which includes another transmission line having one end connected between the variable capacitance diode and the transmission line and the other end which is open.

3. A voltage-controlled oscillator according to claim 1, wherein the capacitive circuit includes a capacitor which is connected in parallel with the variable capacitance diode.

4. A voltage-controlled oscillator according to claim 1, wherein the capacitive circuit has a smaller capacitance than the variable capacitance diode, and the transmission line has a length ranging from about one quarter to about one half of the wavelength of the resonant frequency of the resonant circuit.

5. A voltage-controlled oscillator according to claim 1, wherein the resonator is defined by a dielectric resonator.

6. A voltage-controlled oscillator according to claim 1, wherein the active circuit includes a field-effect transistor.

7. A voltage-controlled oscillator according to claim 1, wherein the resonant circuit includes a resonator, a variable capacitance diode, a transmission line, and a capacitive circuit.

8. A voltage-controlled oscillator according to claim 7, wherein the resonator includes at least one of a microstrip line and a dielectric resonator.

9. A voltage-controlled oscillator according to claim 7, wherein one end of the resonator is connected with the active circuit.

10. A voltage-controlled oscillator according to claim 7, wherein the variable capacitance diode is connected with one end of the resonator via the transmission line.

11. A voltage-controlled oscillator according to claim 7, wherein the variable capacitance diode has a cathode connected with the transmission line and an anode that is grounded.

12. A voltage-controlled oscillator according to claim 7, wherein a variable capacitance of the variable capacitance diode varies according to the control voltage applied to the cathode thereof, causing the resonant frequency of the resonator to be shifted.

13. A voltage-controlled oscillator according to claim 7, wherein the transmission line is connected between the resonator and the variable capacitance diode.

14. A voltage-controlled oscillator according to claim 7, wherein the capacitive circuit is connected in parallel with the variable capacitance diode.

15. A voltage-controlled oscillator according to claim 7, wherein the capacitive circuit has a constant capacitance and the capacitance of the capacitive circuit is set to a value that is smaller than the capacitance of the variable capacitance diode.

16. A high-frequency module comprising the voltage-controlled oscillator according to claim 1.

17. A communication apparatus comprising the voltage-controlled oscillator according to claim 1.