Patent ID: 6700945
Filing Date: 2004-03-02
Classification: H03L

Abstract:
A phase lock loop circuit for switching a division ratio of a variable divider to carry out a fractional division, comprising:a voltage control oscillator; a variable divider for varying a division ratio of an output of a voltage control oscillator in response to a divider control signal; an operation unit for previously calculating divider control data to obtain a division number corresponding to an output frequency; a divider switching memory circuit for writing the divider control data and reading the data every time an output of the variable divider is generated, to set a division value of the variable divider; a phase comparator for phase comparing the output of the variable divider with a reference frequency; and a low-pass filter for inputting an output of the phase comparator and removing a high frequency component; wherein said voltage control oscillator changes an oscillation frequency through an output of said low-pass filter, and wherein said variable divider switches a division ratio to obtain an average division number (N+L/A), where N, L and A are integers.