U.S. Philips Corporation

Theodorus L Welzen

Adrianus J De Vaan

A liquid crystal display device which comprises two supporting plates spaced a distance d from each other the which a pattern of line and column electrodes, respectively, is provided on the facing surfaces and form a matrix of display cells. A mixture of a nematic liquid crystal with a cholesteric addition is present between the supporting plates. The mixture has a positive dielectric anisotropy and a natural pitch p such that the ratio d/p has a value between 0.5 and 1. The cell support surfaces comprise an orientation layer which gives the director over the layer thickness d a rotation between .pi. and 2.pi. radians with, the director at one surface enclosing an angle of tilt between 0.degree. and 70.degree. and at the other surface an angle of tilt between 5.degree. and 70.degree.. Data voltages are applied to the column electrodes and line selection pulses are applied to the line electrodes. The line selection voltage, the data voltage and the frame time are chosen to provide a display cell in the stationary 'on' condition during the frame time show a transmission which is formed by the superposition of a background level T.sub.b1 and a peak response with peak height T.sub.1, while a display cell in the stationary 'off' condition during the frame time shows a transmission which is formed by the superposition of a background level T.sub.b2 and a peak response having peak height T.sub.2, and a display cell which is switched from the stationary 'off' condition to the stationary 'on' condition to reach the 'on' condition via a transmission-response curve which is formed by the superposition of a background level and a peak response having final values T.sub.b1 and T.sub.1, respectively, T.sub.1 being larger than or equal to 0.5 (T.sub.b1 -T.sub.b2). The display device shows fast switching times with a large multiplex ratio and has a contrast with a small dependence on the viewing angle.

Liquid crystal display device

In a low drive voltage display device having a matrix structure, the number of rows to be addressed is selected to be smaller than is possible on the ground of threshold steepness. The required selection voltages can then be selected to be considerably lower than the voltages in accordance with the Alt & Pleshko addressing scheme.

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Eindhoven, Netherlands

Theodorus L Welzen