| 摘要 |
PURPOSE:To obtain a synchronizing clock signal, by detecting an average value of a phase difference signal obtained by comparing an input TV signal with a signal which is obtained by frequency division of an oscillation output signal and controlling a variable phase shifter in accordance with this detection output to shift the phase of the oscillation output. CONSTITUTION:The phase difference between a horizontal synchronizing signal HD and a horizontal synchronizing signal, which is formed by counting down and frequency-dividing the pulse signal having a standard clock cycle of a crystal control oscillator 3 by a counter 2, is obtained, and a discrete value indicating its time difference is supplied to an averaging means 4 so that it is integrated for a proper time. An average value is obtained in the averaging means 4 for such time that the influence of a minute frequency fluctuation, etc. in a short time of the crystal oscillator 3 is eliminated, and a representative value of the phase difference is impressed to a phase shifter 5, and the phase of an oscillation output clock pulse signal from the oscillator 3 to the phase shifter 5 is shifted by a quantity corresponding to this phase difference, and a synchronizing clock signal CK synchronized with the input horizontal synchronizing signal HD with respect to phase is taken out. |
