| 摘要 |
PURPOSE:To stably detect a direct current level included in a composite video signal with a good accuracy by generating a positive, a negative or zero values from a constant value generating means and accumulating and adding to a reference level stored in an accumulating means. CONSTITUTION:The digital video signal Sin is compared with the reference level stored in the accumulating device 8 by a comparator 2 and the output signal of the comparator 2 changes over a selection switch 7. It is outputted according to the relation in scale between the signal Sin and the reference level from the constant value generator 3. The values of the positive S0, the negative S1 or the zero S2 are added to the reference level stored in the accumulating device 8 by an adder 9, the added result is stored in a memory circuit 10 again as the reference level, and the reference level changes so as to follow the signal Sin. To the constant value generator 3, control signals corresponding to the horizontal and vertical fly-back signals of the signal Sin are supplied from terminals 11, 12 and the direct current level during a video signal period of the composite video signal can be detected. The reference level stored in the accumulating device 8 is outputted as the signal Sr corresponding to the direct current level included in the composite video signal.
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