| 摘要 |
PURPOSE:To reduce the number of parts and to constitute an IC easily by providing the titled circuit with an input circuit for comparing a vertically synchronizing separation signal with a threshold to be switched in accordance with the output of signal presence or absence detection, an oscillated pulse counting circuit and a signal presence or absence detection output circuit. CONSTITUTION:A vertical synchronizing separation signal 3 is transmitted to a differential amplifier 19 through an integrating circuit 18 and compared with a threshold voltage 24 determined by resistors 20-22 and a Tr23 and its output 25 is supplied to the set input of an S-RFF26 with a clear terminal and clear terminals of TFFs 27, 28 through a Tr36. The TFFs 27, 28 constitute binary counting circuits, a vertical oscillation pulse 8 is inputted to the input of the 1st FF27 and its output 29 is connected to the input of the succeeding FF28. The outputs 29, 30 of the FFs 27, 28 are AND-processed by an AND gate 31 and its output 32 is inputted to the clear terminal of an FF26. The output 17 of the FF26 is a tuning detection output.
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