| 摘要 |
PURPOSE:To facilitate the integration of the circuit, to reduce the cost and the circuit volume by providing a pattern matching circuit, the first and the second counters, and a control signal outputting circuit which execute the muting based on the discrete value of the counters. CONSTITUTION:The pattern matching circuit 103, when a chronizing separation signal B is inputted, outputs an output pulse shown by C in the figure in case when it judges that a normal horizontal synchronizing signal is present by measuring the width of the pulse. A horizontal free running circuit 101 is made operating in synchronization with the horizontal period of a composite video signal by the output 101 shown by C as long as the normal horizontal synchronizing signal 301 is present in the composite video signal, but outputs a self-reset pulse 110 shown by D to reset itself if the said output 110 lacks during a noise period 303 in order not to lose its synchronization with the horizontals period of the composite video signal.
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