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US 4,902,105 AGranted
Liquid crystal display device
AssigneeU.S. Philips Corporation
InventorsTheodorus L. Welzen, Adrianus J. S. M. De Vaan
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AssigneeU.S. Philips Corporation
InventorsTheodorus L. Welzen, Adrianus J. S. M. De Vaan
Estimating the term…
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.
A method of driving a display device having at least one display cell, said method comprising the steps of
A display device comprising a liquid crystal display having at least one polariser, which liquid crystal display comprises two parallel supporting plates having facing surfaces spaced a distance d from each other and on one surface of which a pattern of line electrodes is provided and on the other surface of which a pattern of column electrodes is provided, the line electrodes crossing the column electrodes and the crossings forming a matrix of display cells, a layer of a nematic liquid crystal with a cholesteric addition being present between the supporting plates, the liquid crystal having a positive dielectric anisotropy and a natural pitch p, in which the ratio d/p has a value between 0.5 and 1, the said surfaces provided with an orientation layer which gives the average direction of the longitudinal axis of the liquid crystal molecules (director) over the layer thickness d a rotation increasing to a value between .pi. and 2.pi. radians and gives the molecules at one surface an angle of tilt between 0.degree. and 70.degree. and those at the other surface an angle of tilt between 5.degree. and 70.degree. with respect to the respective surfaces, the device further comprising a line scanning circuit for scanning, within a frame time t.sub.f, periodically the line electrodes with a line selection pulse, and a column selection circuit for applying data pulses to the column electrodes during a time that a line electrode is scanned for selecting those display cells which are to be switched from a first condition to a second condition differing optically from the first, characterized in that the line selection pulses, the data pulses and the frame time t.sub.f are chosen such that:
Dependencies are inferred from the claim text.