JPS57149970A - Phase comparing circuit - Google Patents

Abstract

PURPOSE:To exercise stable phase comparison control even during a period when a phase difference between two input signals is extremely large, by performing switching to an output voltage similar to that during phase coincidence if the input signals are extremely out of phase. CONSTITUTION:A horizontal synchronizing pulse, which contains a jitter, extracted by a synchronizing signal separating circuit 5 on the basis of a signal reproduced from a disk 2 with a reproducing stylus 1 is compared with a phase comparator with a horizontal synchronizing signal, which contains no jitter, outputted by a synchronizing signal generator 8 according to a reproduced tracking signal. On the basis of the resulting comparison voltage, the tracking of the stylus 1 is controlled through an arm stretcher 10. Once this generator 8 generates a vertical blanking pulse, a switch 11 is changed over to apply the stretcher 10 with a cntrol voltage similar to that during phase coincidence from a power source 12. Therefore, even during a vertical flyback period when two comparison inputs are greatly out of a phase, a failure in control, etc., never occurs and stable control is exercised.