| 摘要 |
PURPOSE:To make it possible to obtain stably a binary output signal, by obtaining a variable threshold signal, which follows white-and-black level fluntuation, by an envelope detecting circuit and by comparing this variable threshold signal and a video signal amplified to a prescribed level. CONSTITUTION:The video signal picked up by camera 20 is subjected to differential amplification in 21 and is amplified to a prescribed level by 22. Envelope detecting circuit 23 eliminates transfer clock components of the video signal synchronized with transfer clocks, and envelope detecting circuits 24 and 26 follow upper level fluctuation and lower level fluctuation of the output signal respectively, and envelope detecting circuit 25 synthesizes respective signals of circuits 24 and 26, thus obtaining a variable threshold signal following white-and-back level fluctuation. Further, the variable threshold signal following white-and-back level fluctuation and the video signal amplified to a prescribed level are compared with each other by comparator 27, so that a binary output signal can be obtained stably. |
