Phase locked circuit

• US 20080180143A1
• Filed: 08/08/2006
• Published: 07/31/2008
• Est. Priority Date: 08/09/2005
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: NOMURA, Masataka, SHIGEMORI, Mikio
• Granted Patent: US 7,541,849 B2
• Time in Patent Office: Days
• US Class Current: 327/156
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A phase locked circuit includes a locked loop circuit having a phase comparator, a voltage controlled oscillator, and a variable frequency divider which divides a clock signal f_vco output from the voltage controlled oscillator by n and outputs it. Additionally, the phase locked circuit includes a band pass filter part which is coupled to an output side of the voltage controlled oscillator via a switching part. A frequency division ratio setting signal to be input into the variable frequency divider is input as a switching signal into the switching part so as to switch a frequency of the clock signal f_vco output from the voltage controlled oscillator. As synchronizing with switching of the frequency, the switching part switches a plurality of band pass filters provided to the band pass filter part and couples to the voltage controlled oscillator.

Claims

1. A phase locked circuit, comprising;

a locked loop circuit

includes including a phase comparator and a voltage controlled oscillator,

wherein the locked loop circuit and outputs an output signal of the voltage controlled oscillator,

the phase comparator outputs a phase difference signal which corresponds to a phase difference between a reference signal input from an outside and a feedback signal based on the output signal of the voltage controlled oscillator,

a frequency of the output signal of the voltage controlled oscillator is controlled on the basis of the phase difference signal, and

at least one band pass filter is provided to an output side of the locked loop circuit.

2. The phase locked circuit according to claim 1, wherein

the locked loop circuit includes a variable frequency divider, and

the variable frequency divider outputs the feedback signal obtained through dividing the output signal of the voltage controlled oscillator by a frequency division ratio which is changed on the basis of a switching signal for an output frequency, the switching signal coming from the outside, the locked loop circuit outputs an output signal having one of a plurality of mutually different frequencies predetermined on the basis of the switching signal for the output frequency, and

the band pass filter part has a plurality of band pass filters which correspond to the plurality of predetermined frequencies which are different from each other.

3. The phase locked circuit according to claim 2, wherein

a switching part which couples the band pass filter corresponding to the frequency of the output signal of the locked loop circuit to the voltage controlled oscillator is provided between the locked loop circuit and the band pass filter part.

4. The phase locked circuit according to claim 1, wherein

the output signal of the voltage controlled oscillator is diffused in a predetermined frequency band.

5. The phase locked circuit according to claim 1, wherein

the band pass filter is a surface acoustic wave filter.

6. The phase locked circuit according to claim 1, wherein

the band pass filter is a surface acoustic wave filter having quartz crystal as a piezoelectric material.

7. The phase locked circuit according to claim 1, wherein

an amplifier is provided to an output side of the band pass filter part.