| 摘要 |
PURPOSE:To make it unnecessary to provide separately a clamp voltage source, and also to obtain a stable DC voltage clamping circuit, by constituting said circuit so that a potential difference of two outputs of the first differential amplifier is amplified by the second differential amplifier, is fed back to the first differential amplifier, and DC signal voltage fetched from the first differential amplifier is clamped. CONSTITUTION:An output which amplifies difference voltage of two outputs of the first differential amplifier 1 is obtained in a P point, and this output is returned to the first differential amplifier 1 by negative feedback. Said operation is executed when a pulse is provided to a terminal B and a current flows to the collector of a transistor Q6, and since an amplification degree of the second differential amplifier 2 is very large, the collector DC voltage of a transistor Q1 and transistor Q2 becomes equal. Also, when the terminal B is in a section of an ''L'' level, an operation of the differential amplifier 2 is stopped, the charge accumulated in a capacitor C2 is held, and the potential is maintained. A video signal is fetched from the collector of the transistor Q2, and its pedestal voltage is clamped to desired clamp voltage. |
