Title: Beam control circuit for diode-gun type camera tubes

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Abstract: A beam control circuit which instantaneously increases beam current just sufficiently to discharge a highlight, utilizes the fact that a substantially linear relationship exists between the grid current and the available beam current of a diode-gun camera tube. A tube grid control circuit provides means for calibrating the relationship between the incoming signal current and the available beam current. A highlight enable circuit coupled to the grid control circuit is pre-biased whereby the beam current of the tube is maintained at a constant value as long as the video signal current remains within its normal operating range, i.e., there are no highlights in the viewed scene. However, when the video signal current increases above the pre-bias level, as in the presence of a highlight, the highlight enable circuit conducts to cause a corresponding increase in the beam current of the tube, wherein the beam current maintains a pre-calibrated, substantially constant margin above the video signal current which is just sufficient to discharge the highlight.


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