| 摘要 |
PURPOSE:To detect and separate correctly a synchronizing signal by detecting the period of the transmitted synchronizing signal at the reception side and masking and detecting the synchronizing signal over a period while the synchronizing signal is not transmitted based on the detected period. CONSTITUTION:The transmitted synchronizing signal Sr is detected by a detection circuit 65 to obtain a pulse P65. A clock CLK of a prescribed frequency is fed to a counter 71. The interval between two consecutive signals Sr is detected by counting the clock. Comparator circuits 72, 73 compare the interval Q71 of the signals Sr with the permitted lower limit TL or the upper limit TH, an output P72 being logical 1 is extracted from the comparator circuit 72 at Q71>=TL and an output P73 being logical 1 at Q71>=TH is extracted from the comparator circuit 73. AND circuits 74, 75 mask a noise pulse Pn. A D flip-flop 77 and a monostable multivibrator 78 form a pseudo pulse P65 when the pulse P65 is missing. A delay circuit 76 is used for correcting time.
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