Phase-locked loop circuit

• US 20060139106A1
• Filed: 11/09/2005
• Published: 06/29/2006
• Est. Priority Date: 12/24/2004
• Status: Active Grant

• Current Assignee: Socionext Inc.
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Okamoto, Kouji, Dosho, Shiro, Morie, Takashi, Yamada, Yuji, Sogawa, Kazuaki
• Granted Patent: US 7,298,219 B2
• Time in Patent Office: Days
• US Class Current: 331/16
• CPC Class Codes: H03L 7/0898 the source or sink current values being variable H03L7/0896 takes precedence
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: H03L 7/1976 using a phase accumulator for controlling the counter or frequency divider

Abstract

The phase-locked loop circuit includes a gain setting circuit for setting a gain of a voltage controlled oscillator, and a time-constant setting circuit for setting a time constant, which is determined by the amount of current in a charge pump circuit and a capacitance value of a loop filter. The gain setting circuit sets the gain to a predetermined value, and the time-constant setting circuit sets the time constant to a predetermined value, whereby the loop band width of the phase-locked loop circuit is set to a desired value.

Claims

1. A phase-locked loop circuit comprising:

a gain setting circuit for setting a gain of a voltage controlled oscillator; and

a time-constant setting circuit for setting a time constant, which is determined by the amount of current in a charge pump circuit and a capacitance value of a loop filter.

2. The circuit of claim 1, further comprising a temperature-compensation circuit for adjusting the amount of current in the charge pump circuit in accordance with temperature changes.

3. The circuit of claim 1, wherein the gain setting circuit includes:

a switching section for switching inputs into the voltage controlled oscillator;

a gain measurement section for measuring the gain based on a difference between outputs produced from the voltage controlled oscillator in response to a first voltage and a second voltage, respectively, which are input into the voltage controlled oscillator by the switching section;

a gain setting section for setting the gain in accordance with a supplied control signal; and

a gain control section for generating the control signal based on a difference between the gain measured by the gain measurement section and an expected value.

4. The circuit of claim 1, wherein the time-constant setting circuit includes:

a dummy charge pump circuit for performing push-pull operation in accordance with a first signal and a second signal;

a capacitor for receiving a current output from the dummy charge pump circuit;

a signal generation section for generating the first and second signals based on a voltage produced in the capacitor;

a frequency measurement section for measuring a frequency of either the first or second signal;

a current setting section for setting the amount of current in the dummy charge pump circuit and the amount of current in the charge pump circuit in accordance with a supplied control signal; and

a current control section for generating the control signal based on a difference between the frequency measured by the frequency measurement section and an expected value.

5. The circuit of claim 4, further comprising a temperature-compensation circuit for outputting a current which increases in amount according to temperature changes,

wherein the current setting section sets the amount of the current in the dummy charge pump circuit and the current in the charge pump circuit based on the current output from the temperature-compensation circuit.

6. The circuit of claim 2, wherein the temperature-compensation circuit includes:

a diode;

a resistor connected in series to the diode; and

a current mirror circuit for receiving a current passing through the resistor,

wherein a constant voltage is applied to the diode and the resistor.