PLL circuit including a voltage controlled oscillator and a method for controlling a voltage controlled oscillator

• US 6,853,257 B2
• Filed: 05/22/2003
• Issued: 02/08/2005
• Est. Priority Date: 05/29/2002
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Fujitsu Limited
• Inventors: Doi, Takehito, Yonekawa, Masayuki
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US10/443,105
• Publication Number:
  US 20030222726A1
• Time in Patent Office: 628 Days
• Field of Search: 331/1.A, 331/8, 331/10, 331/11, 331 16- 18, 331/25, 331/34, 331/36.R, 331/36.C, 331/36.L, 331/117.R, 331/117.FE, 331/117.D, 331/175, 331/177.R, 331/177.V, 331/179, 331/181
• US Class Current: 331/17
• CPC Class Codes: H03B 2201/025 the means being an electronic switch for switching in or out oscillator elements
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 7/193 the frequency divider/counter comprising a commutable pre-divider, e.g. a two modulus divider

Abstract

A voltage controlled oscillator having a wide oscillation frequency band, desirable carrier-noise characteristic, and desirable linearity of the oscillation frequency relative to a control voltage. The voltage controlled oscillator includes an oscillation unit and a control unit. The oscillation unit generates an output signal having an oscillation frequency corresponding to the control voltage in one of a plurality of oscillation frequency bands. The oscillation unit includes a switching unit for selecting one of the plurality of oscillation frequency bands in accordance with a switching signal. The control unit generates the switching signal in accordance with the control voltage.

Claims

1. A voltage controlled oscillator comprising:

an oscillation unit which generates an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands, wherein the oscillation unit includes;

a fixed inductor;

a variable capacitor connected to the fixed inductor and having a capacitance varied in accordance with the control voltage; and

a fixed capacitor connected in parallel with the variable capacitor;

a plurality of additional inductors;

a plurality of switch circuits connected to the additional inductors to selectively connect the additional inductors in parallel with the fixed inductor in accordance with a switching signal; and

a control unit connected to the switch circuits which generates the switching signal in accordance with the control voltage.

2. The voltage controlled oscillator according to claim 1, wherein the control unit includes a plurality of comparators having different threshold values.

3. The voltage controlled oscillator according to claim 2, wherein each of the comparators has a hysteresis characteristic, in which a rising threshold value is greater than a trailing threshold value.

4. A method for controlling a voltage controlled oscillator, wherein the voltage controlled oscillator includes a fixed inductor and a plurality of additional inductors, the method comprising:

generating an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands;

generating a switching signal in accordance with the control voltage; and

selectively connecting the additional inductors in parallel with the fixed inductor in accordance with the switching signal.

5. The method according to claim 4, wherein the voltage controlled oscillator includes a variable capacitor connected to the fixed inductor and has a capacitance varied in accordance with the control voltage, and a fixed capacitor connected to the variable capacitor, the method further comprising:

setting the oscillation frequency band in accordance with the fixed inductor, the variable capacitor, the fixed capacitor, and at least one of the additional inductors.

6. A PLL circuit comprising:

a voltage controlled oscillator including;

an oscillation unit which generates an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands, wherein the oscillation unit includes;

a fixed inductor;

a variable capacitor connected to the fixed inductor and having a capacitance varied in accordance with the control voltage; and

a fixed capacitor connected in parallel with the variable capacitor;

a plurality of additional inductors;

a plurality of switch circuits connected to the additional inductors to selectively connect the additional inductors in parallel with the fixed inductor in accordance with a switching signal; and

a control unit connected to the switching unit which generates the switching signal in accordance with the control voltage.