Automatic beam current control with an envelope detector for a color television camera tube with a stripe filter

摘要

A feedback control loop for controlling the intensity of a scanning electron beam of an image pickup tube of a color TV camera which is especially useful in a single tube color TV camera with a stripe filter, comprises an envelope detector for detecting the envelope of an output video signal derived from the image pickup tube. An envelope signal from the envelope detector is then compared with a reference threshold by a comparator so that a voltage applied to a control grid of the pickup tube is controlled in accordance with the amplitude of the envelope signal, thereby increasing the intensity of the scanning electron beam applied to a portion of a photoelectric converting layer when the brightness at the portion is high. As a result, an ideal multi-color output video signal is obtained irrespective of the brightness of a subject to be taken even if the intensity of the scanning electron beam is usually set to a relatively low value. In one embodiment, a circuit for amplifying high-frequency components of the output video signal is employed for compensating for a modulation characteristic of typical pickup tubes having a poor high frequency response.