| 摘要 |
PURPOSE:To separate a stable and highly accurate composite synchronizing signal from a weak composite signal or a strong signal by using a comparator so as to allow its threshold voltage to be changed in response to the amplitude of an inputted video composite signal. CONSTITUTION:A means potential of a television composite signal is nearly at a common potential at a point A by selecting the time constant C1R1 larger the pulse width of a vertical synchronizing signal. A gate of an analog switch 2 is opened during the synchronizing signal period to charge a capacitor C2. A potential (point B) of the capacitor C2 keeps a negative peak voltage (synchronizing signal voltage), which is divided by a resistor through a voltage follower 3 to form a threshold voltage of a comparator 4. The threshold voltage (at point C) has a value between the potential of the synchronizing signal and a common potential, it is used as a reference voltage and the synchronizing signal is separated by the comparator 4. The analog switch 2 is switched again by using the separated synchronizing signal. The time constant C2R2 is set to a value far larger than the period of the horizontal synchronizing signal.
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