| 摘要 |
PURPOSE:To prevent, without fail, the change of a base point electric potential at the time of non-inputting the compound video signal due to the variance on the manufacture of an electric current amplifying ratio beta of the transistor for clamping by calculating and flowing in the base electric current necessary to the base of the transistor for clamping, and removing the influence of a change of the base electric current due to the variance of the electric current amplifying ratio beta. CONSTITUTION:At a corrector side of a transistor 24, to calculate a necessary base electric current from the corrector electric current, a transistor 42 equal to a transistor 24 is installed serially, the electric current, which flows at a transistor 46, is applied to the base of the transistor 24, and the base electric current, which the transistor 24 needs, is applied. As this result, even when the compound video signal applied to an input terminal 34 goes to be a non- input condition, the base electric current, which flows at the transistor 24, is forcibly applied by the base electric current from the transistor 42, and therefore, the change of the P point electric potential due to the variance of the electric current amplifying ratio beta of the transistor 24 can be suppressed without fail.
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