| 摘要 |
<p>PURPOSE:To digitally compare a detected voltage and to detect level variation of a reproduced video signal every fixed section by comparing an envelope detecting voltage with each weighted detecting reference voltage and obtaining a count value. CONSTITUTION:An envelope detecting signal Vx of a reproduced video signal obtained in each continuous or periodical fixed section synchronized with a head switching signal in a helical scanning type video tape recorder is inputted to a voltage comparator 8. The voltage Vx is compared with a detecting reference voltage Vf by an OR circuit 8', the compared result is outputted as a binary signal, the high or low periods of binary signals in each field are counted by a counter 9, the count value data are sent, and an up or down pulse is sent to a counter 10. A multiplexer 8'' switches resistors R1-R4 in accordance with the output of a counter 10 and the voltage Vf is weighted and varied. Thereby, digital comparison can be always attained by the output data of the counter 9.</p> |
