Patent ID: 6940323
Filing Date: 2005-09-06
Classification: H03L

Abstract:
1. A phase locked loop circuit, comprising a phase comparator for comparing phases of an index signal and a reference signal and outputting a signal in accordance with the phase difference; a loop filter for smoothing the output signal of the phase comparator; a controlled oscillator for oscillating at a frequency in accordance with an output signal of the loop filter; a limiter provided on a path from the output side of the phase comparator to the input side of the controlled oscillator for limiting the level of signals on the path in a predetermined range of phase differences and setting a large gain; a frequency divider for dividing an output signal of the controlled oscillator by a predetermined frequency dividing rate N (where N is a positive integer), generating the reference signal and feedback-inputting the reference signal to the phase comparator; an unlock detecting circuit for detecting unlocking of a phase lock based on the index signal and the reference signal or based on the output signal of the phase comparator and for outputting an unlock detecting signal; and a switch unit for shutting up the output signal of the loop filter based on a PLL operational signal and inputting a predetermined signal to the controlled oscillator.