| 摘要 |
An amplifier for combining color difference signals with luminance signals and driving a color image reproducing device includes first and second transistors of opposite conductivity type. Color difference signals are capacitively coupled to the base of the first transistor. The emitter of the first transistor is direct current coupled to the emitter of the second transistor. Luminance signals are coupled to the base of the second transistor. Color signals developed at the collector of the first transistor are coupled to the image reproducing device. The base-emitter junction of the first transistor is also direct current coupled in feedback relation across the collector-base junction of a third transistor of like conductivity type. The emitter of the third transistor is coupled to a gating circuit which couples a reference voltage to the emitter of the third transistor to cause the third transistor to conduct during each horizontal retrace interval. As a result, the emitter of the first transistor is clamped substantially to the reference voltage to thereby determine the operating point of the first transistor. The gating circuit also selectively couples a signal to the emitter of the first transistor to render the image reproducer cut-off during the horizontal trace portion of the vertical retrace interval so that disconcerting horizontal scan lines are not visible during vertical retrace. The gating circuit is arranged so that the signal to cut off the image reproducing device during vertical retrace is disconnected from the emitter of the first transistor during the horizontal retrace intervals so as not to interfere with the clamping operation of the first and third transistors. |
