METHOD AND APPARATUS FOR GRAY-SCALE GAMMA CORRECTION FOR ELECTROLUMINESCENT DISPLAYS

摘要

A circuit and method of driving a display panel requiring gray scale control wherein the voltage applied to a row of pixels is equal to the sum of voltages of opposite sign with respect to ground applied respectively to the row electrode and column electrodes whose intersection with the row defines the pixels. Gray scale is realized through modulation of the voltage applied to the column electrodes. Typically for video application, 256 individual gray levels are required corresponding to luminance levels ranging from zero (no emissive luminance) to full luminance. The required luminance for each gray level is not a linear function of the gray level number but rather corresponds to an approximate quadratic function of this number. The present invention facilitates generation of luminance values for each gray level that approximates this functional dependence (i.e. Gamma corrected) with a non-linear voltage ramp terminated by a digital clock having 256 (8 bit) resolution. The voltage at the ramp termination is held at a constant value and fed to the output buffer of the gray scale drivers for the display columns.

主权项

1. A gray scale column driver circuit for an alternating current dielectric electroluminescent display comprising rows, columns that intersect the rows and pixels at the intersections of said rows and columns, said column driver circuit comprising:
a counter receiving video signal gray level data and in response counting for a time interval proportional to said gray level data; a non linear analogue voltage ramp generator connected to said counter, said non linear analogue voltage ramp generator outputting a ramping voltage during said time interval, wherein said ramping voltage conforms to a curve having an initial convex portion followed by a concave portion, wherein said initial convex portion conforms to a negative second derivative with respect to said time interval, and wherein said concave portion conforms to a positive second derivative with respect to said time interval; and a column driver receiving the ramping voltage and in response applying driving pulses to the columns of said dielectric electroluminescent display, wherein said ramping voltage determines a maximum voltage of the alternating polarity driving pulses applied to the columns of said dielectric electroluminescent display.