| 摘要 |
PURPOSE:To reduce the frequency fluctuation of a VCO in a vertical signal period even in a reception mode of an abnormal NTSC signal and to secure the satisfactory lock in a vertical flyback time, by using a phase wave detector which delivers the same output as that obtained when the period phase of a vertical synchronizing signal has coincidence. CONSTITUTION:A phase wave detector 7 which is controlled by a vertical synchronizing signal is provided to a synchronizing oscillator. The horizontal and vertical signal input terminals 11 and 12 are connected to the detector 7. The phase difference is detected by gate circuits 23 and 24 of the detector 7 and at the fall of an input pulse, and this detection output is converted into a direct current by MOS transistors TR25 and 26, and this conversion output is applied to an LPF8 to prevent the frequency component higher than a prescribed frequency of the output. This output is applied to a VCO9. The vertical synchronizing signal given from an output terminal 13 of the VCO9 is applied to the detector 7 via a programmable counter 10. Thus the frequency fluctuation of the VCO9 even in a reception mode of a non-NTSC signal such as a video signal, etc., and the satisfactory lock is secured in a vertical flyback time. |
