| 摘要 |
PURPOSE:To obtain a correct signal being removed noise by forming a window signal relative to a synchronous signal based on a counting value corresponding to an average cycle of a synchronous signal. CONSTITUTION:A reproducing synchronous signal S1 conducting to an input terminal 1 is supplied to an input gate circuit 2, resets a cycle counter 4 and the counter 4 counts up a clock CLK till a next signal. A count value D1 of this counter 4 is compared with an average count value D2 of a horizontal cycle near to a latch circuit 13 in respect of a largeness in a comparison circuit 5. When D1<D2, a setting value obtained from a setting change over circuit 9 is added to the output value D2 of the latch circuit 13 as it is. When D1>D2, the setting value is subtracted from the latch output value D2. A value to be latched finally shows a cycle of an average reproducing horizontal synchronization signal, is added to a window value D4 giving an allowance and an added value D5 is supplied to a window signal generating circuit 15. A window signal S7 is fed to a window gate circuit 16, a signal S2 is gated and a correct horizontal synchronization pulse S8 of a constant time duration is obtained.
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