General Electric Company

Harold L Herz

David P Benfey

Sam S Jobes

William C Wheeler

John D Jordan

John S Prince

Edward P Coleman, Jr

A video brightness control system for high performance CRT displays including a buffer amplifier for receiving high speed video information and applying it to a gain control variable resistor serving as a contrast control. An ambient light sensor drives a nonlinear amplifier to provide an ambient light signal which is in proportion to the logarithm of the ambient light level over a wide range. A manual brightness control potentiometer is adjustable to provide a constant brightness signal. The video information signal, the ambient light signal, and the manual brightness control signal are added together by a summing device, with the resultant signal approximating a logarithmic characteristic. The output of the summing device is applied to a gamma correction amplifier which drives a video driver amplifier, the video amplifier, in turn, drives the CRT. The gamma correction amplifier and video driver in combination with the video transfer function of the CRT approximates an exponential transfer function, thereby creating CRT screen brightness which is an antilogarithmic function of the total video signal appearing at the gamma correction amplifier input. This results in automatic brightness control as a function of ambient light level, minimum interaction between brightness and contrast controls, and a gamma characteristic which provides a reasonable approximation to the variation of brightness difference threshold of the eye.

Brightness control system for CRT video display

A high voltage power supply of the flyback type typically used in cathode ray tube displays or TV receivers operates in synchronism with the scan rate frequency of display and may either be self-synchronizing, externally synchronized, or externally directly driven. The power supply has a relatively high efficiency (75%), regulates three output voltages to within .+-.0.1% against source voltage variations and regulates its highest level voltage output to within .+-.0.1% against source voltage and load variations.

High voltage power supply

Growing community of inventors

Binghamton, NY, United States of America

Harold L Herz