Automatic beam limiter circuit

Abstract

An automatic beam limiter circuit (ABL circuit) calculating an average of a video signal at least a portion of the video signal is provided. After a converter circuit converts an analog signal, which is generated from the video signal, to a digital signal, a horizontal and a vertical average circuits calculate a horizontal and vertical averages of the digital signal at least a portion of the digital signal. The portion of the digital signal is a scanned line of the digital signal on a CRT. A comparison circuit compares a first calculation value calculated between a reference value and the vertical average with a second calculation value calculated between the reference value and the horizontal average, and outputs a first comparison signal and a second comparison signal based on the comparison results. A gain control circuit produces a gain control signal for adjusting the brightness/contrast in response to the first comparison and second comparison signals. Advantageously, the automatic beam limiter circuit is capable of efficiently preventing a frame delay in controlling the brightness/contrast of the video signal and the rapid increase of beam current when a black field is rapidly changed into a white field.

Dependencies are inferred from the claim text.