| 摘要 |
PROBLEM TO BE SOLVED: To improve both a lock-up time and an S/N. SOLUTION: The phases of reference signals and internal signals outputted by a frequency divider 11 are compared in a phase comparator 11, and when a phase difference is within a prescribed range, lock detection signals are outputted from a lock detection circuit 12. When the signals are supplied to a charge pump 13, an output current is switched to be small by a changeover switch SW and the time for charging or discharging a loop filter 14 is prolonged. Thus, a noise band is narrowed and the S/N is improved. While lock-up is not performed and the lock detection signals are not supplied, the output current of the charge pump 13 is large and the lock-up time is reduced. |
