Input-switching voltage-controlled oscillator and PLL-controlled oscillator

• US 20030076184A1
• Filed: 10/23/2002
• Published: 04/24/2003
• Est. Priority Date: 10/24/2001
• Status: Active Grant

• Current Assignee: Nihon Dempa Kogyo Company Limited
• Original Assignee: Nihon Dempa Kogyo Company Limited
• Inventors: Oita, Takeo
• Granted Patent: US 6,791,421 B2
• Time in Patent Office: Days
• US Class Current: 331/176
• CPC Class Codes: H03B 5/368 the means being voltage variable capacitance diodes
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/14 for assuring constant frequency when supply or correction voltages fail or are interrupted

Abstract

A PLL-controlled oscillator that can be suitably used for such purposes as a jitter filter in an optical transmission system includes an input voltage-switching control oscillator as a voltage-controlled oscillator (VCO). The input voltage-switching control oscillator includes: an oscillation closed loop that is provided with a variable-voltage capacitance element; and a switch for interchangeably selecting one of a plurality of voltages in accordance with a selection signal and applying the selected voltage as a control voltage to the variable-voltage capacitance element.

Claims

1. An input-switching voltage-controlled oscillator, comprising:

an oscillation closed-loop provided with a variable-voltage capacitance element; and

a switch for selecting one of a plurality of voltages in accordance with a selection signal and applying said selected voltage as a control voltage to said variable-voltage capacitance element.

2. The voltage-controlled oscillator according to claim 1, wherein a crystal unit is included in said oscillation closed loop and said voltage-controlled oscillator is constituted as a voltage-controlled crystal oscillator.

3. The voltage-controlled oscillator according to claim 2, wherein a first voltage of said plurality of voltages is a voltage that is obtained by applying a signal corresponding to a phase difference between a reference signal and an output signal of said voltage-controlled oscillator to a low-pass filter.

4. The voltage-controlled oscillator according to claim 3, wherein a second voltage of said plurality of voltages is a voltage that is separate from said first voltage and that is supplied from a dc voltage source.

5. The voltage-controlled oscillator according to claim 3, further comprising a detector for detecting presence or absence of said reference signal and outputting said selection signal, wherein said first voltage is selected when said reference signal is received as input.

6. The voltage-controlled oscillator according to claim 4, further comprising a detector for detecting presence or lack of said reference signal and outputting said selection signal, wherein said first voltage is selected when said reference signal is received as input, and said second voltage is selected when said reference signal is lacked.

7. An input-switching voltage-controlled oscillator comprising:

a variable-voltage capacitance element to which a control signal is applied;

a capacitor; and

a switch for selecting one of said variable-voltage capacitance element and said capacitor according to a selection signal and inserting the selected one into an oscillation closed loop.

8. The voltage-controlled oscillator according to claim 7, wherein said oscillation closed loop includes a crystal unit and said voltage-controlled oscillator is constituted as a voltage-controlled crystal oscillator.

9. The voltage-controlled oscillator according to claim 8, wherein said control voltage is a voltage that is obtained by applying a signal corresponding to a phase difference between a reference signal and an output signal of said voltage-controlled oscillator to a low-pass filter.

10. The voltage-controlled oscillator according to claim 9, further comprising a detector for detecting presence or lack of said reference signal and outputting said selection signal, wherein said variable-voltage capacitance element is selected when said reference signal is received as input and said capacitor is selected when said reference signal is lacked.

11. A PLL-controlled oscillator comprising:

a phase comparator for detecting phase difference between a reference signal and an output signal;

a low-pass filter connected to an output of said phase comparator for outputting a control voltage;

an oscillation means for generating said output signal;

a selection means for, in accordance with a selection signal, making a transition between a first state in which the oscillation means is caused to oscillate at an output frequency that changes in accordance with said control voltage and a second state in which said oscillation means is caused to oscillate at an output frequency that is unaffected by said PLL-control signal.

12. The PLL-controlled oscillator according to claim 11, wherein said oscillation means includes at least a variable-voltage capacitance element to which said control voltage is applied in said first state and a crystal unit.

13. The PLL-controlled oscillator according to claim 11, further comprising a detection means for detecting presence or lack of said reference signal and outputting said selection signal.