| 摘要 |
PURPOSE:To supply always a clamping electric potential set at the time of no signals to a sink chip of a compound video signal by detecting a change of a clamping electric potential as a changing part of one side transistor VBE of a pair of a current mirror and compensating by other side transistor VBE. CONSTITUTION:A collector electric current of Q7 is supplied to an emitter of Q8 through a current mirror circuit composed of Q9 and Q10 by a collector of a transistor Q7, and a clamping electric potential goes to be an emitter electric potential VEQ7 of Q7. A compound video signal is impressed to an input terminal T2, the compound video signal is outputted from an emitter of Q1 to an output terminal T1, but in a sink chip electric potential VEQ7 at a base of Q1, a charging electric current ic is supplied through current mirror circuits of Q9 and Q10 to an emitter of Q8, and therefore, the influence to VEQ7 can be excluded. Next, the change of a clamping electric potential, which occurs at a V period of the compound video signal, can be detected as the change of VBE7, the electric current increased part, which occurs by the detection, is supplied to the emitter of Q8 through a current mirror circuit and can be absorbed at VBE8.
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