| 摘要 |
PURPOSE:To promptly stabilize an oscillation frequency by once opening a loop filter when a signal to indicate a discontinuous point is inputted, resetting an oscillator and making the oscillator follow the loop filter immediately after the discontinuous point. CONSTITUTION:A phase comparator 2 makes a horizontal synchronizing signal H-SYNC into one input and makes the output signal of a voltnge control oscllator VCO 1 into the other input, and outputs the phase difference between the both input signals. The output of the comparator 2 is inputted to a loop filter 3 through a switch 4, and the VCO 1 is controlled, and a signal to synchronize with the signal H-SYNC is outputted by the output. When a signal S to indicate the discontinuous point is inputted, while the VCO 1 is reset, the switch 4 is opened for a short time, and the output of the comparator 2 is not inputted to the VCO 1. Immediately after that, the switch 4 is turned on, and after the completion of a discontinuous point signal S, the phase comparison is restarted immedintely. Thus, the signal to follow the signal H-SYNC can be obtained immediately after the discontinuous point. |
