Phase-locked loop circuit

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 lead-in start signal generating circuit for generating a lead-in start signal in response to the index signal input at the start of an operation;
• a loop filter for smoothing the output signal of the phase comparator;
• a controlled oscillator for oscillating at a frequency in accordance with the output signal of the loop filter;
• a frequency divider for generating the reference signal having the minimum phase difference with respect to the index signal when the lead-in start signal is input, feedback-inputting the reference signal to the phase comparator, generating the reference signal by dividing the output signal of the controlled oscillator by a predetermined frequency dividing rate N (where N is a positive integer) when the output signal of the controlled oscillator is input, and feedback-inputting the reference signal to the phase comparator;
• an unlock detecting circuit for detecting the 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 the unlock detecting signal and inputting a predetermined signal to the controlled oscillator.

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 lead-in start signal generating circuit for generating a lead-in start signal in response to the index signal input at the start of an operation;
• a loop filter for smoothing the output signal of the phase comparator;
• a controlled oscillator for oscillating at a frequency in accordance with the 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 generating the reference signal having the minimum phase difference with respect to the index signal when the lead-in start signal is input, feedback-inputting the reference signal to the phase comparator, generating the reference signal by dividing the output signal of the controlled oscillator by a predetermined frequency dividing rate N (where N is a positive integer) when the output signal of the controlled oscillator is input, and feedback-inputting the reference signal to the phase comparator;
• an unlock detecting circuit for detecting the 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 the unlock detecting signal and inputting a predetermined signal to the controlled oscillator.