CIRCUIT FOR DETECTING PRESENCE OR ABSENCE OF VIDEO SIGNAL RECEPTION,申请号JP19840103649-传众专利搜索

CIRCUIT FOR DETECTING PRESENCE OR ABSENCE OF VIDEO SIGNAL RECEPTION

申请公布号：JPS60248082(A)

申请号：JP19840103649

申请日期：1984.05.24

申请公布日期：1985.12.07

申请人：

HITACHI SEISAKUSHO KK

发明人：ITAGAKI TSUGIO

分类号：H03J7/02;H04N5/44

主分类号：H03J7/02

摘要：PURPOSE:To attain stable operation even if a reception signal level is low at a weak electric field by providing two criterion values deciding the presence or the absence of video signal reception and using the criterion values depending on the direction of increase/decrease in the count value. CONSTITUTION:Two threshold levels are selected as, e.g., two positions of 20% duty ratio and 80% duty ratio. When an output of a detecting number count circuit 9 is increasing and the level exceeds the position of 80%, it is decided as absence of signal and when the said output is decreasing and the level is decreased to a value below the position of 20%, it is decided as presence of signal. When an output of the circuit 9 changes increasing, it is not decided as absence of signal only with a level exceeding the position of 20% and it is decided as absence of signal when the level exceeds the position of 80%. Two criterion values deciding the presence/absence of signal are prepared depending on the output of the circuit 9 in this way and a hysteresis characteristic is given to the result of decision, so as to ensure the operation.