Displaying gray shades on display panel implemented with active

Abstract

Different gray shades or hues may be displayed in accordance with an active addressing technique that addresses faster responding passive matrix liquid crystal display panels (LCDs) so that video rate, high information content LCDs are perceived as having improved contrast by limiting peak voltage levels across the pixels. A preferred embodiment of the active addressing technique is implemented such that a first set of LCD electrodes is continuously driven with signals each comprising a train of pulses that are periodic in time, have a common period T, are independent of the information to be displayed, and are preferably orthonormal. Multiple column signals are generated from the collective information states of the pixels defined by the overlap with a second electrode pattern. Each column signal is proportional to the sum, obtained by considering each pixel in the column, of the exclusive-or (XOR) products of the logic level of the amplitude of each row signal times the logic level of the information state of the pixel corresponding to that row. Two alternative gray shading techniques provide for intermediate optical states between light and dark states. A frame modulation technique uses several frame periods to control the proportion of time a pixel is light or dark. A pulse width modulation technique subdivides an addressing time interval to control the proportion of time a pixel is light or dark during the addressing time interval. Either technique addresses the pixel to an intermediate optical state.