Liquid crystal display device

Claim 3

A method according to claim 1, wherein said voltage pulses of value ±Vc are formed as modulated pulses, said modulated pulses being modulated by a pulse duration of picture information for said liquid crystal display device.

Claim 4

A method according to claim 1 or claim 2, wherein said frame time t f is at most approximately 30 msec.

Claim 5

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 π and 2π radians and gives the molecules at one surface an angle of tilt between 0° and 70° and those at the other surface an angle of tilt between 5° and 70° with respect to the respective surfaces, the device further comprising a line scanning circuit for scanning, within a frame time t 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 f are chosen such that: a display cell in the stationary "on" condition shows a transmission which is formed by the superposition of a maximum background level T b1 and a maximum response having a peak height T 1 ; a display cell in the stationary "off" condition shows a transmission which is formed by the superposition of a minimum background level T b2 and a minimum response having peak height T 2 , T 1 being larger than or equal to 0.5 (T b1 -T b2 ) for a display cell which is switched from the stationary "off" condition to the stationary "on" condition.

Claim 6

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 π and 2π radians and gives the molecules at one surface an angle of tilt between 0° and 70° and those at the other surface an angle of tilt between 5° and 70° with respect to the respective surfaces, the device further comprising a line scanning circuit for scanning, within a frame time t 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 f are chosen such that: a display cell in the stationary "on" condition shows a transmission which is formed by the superposition of a maximum background level T b1 and a maximum response having a peak height T 1 ; a display cell in the stationary "off" condition shows a transmission which is formed by the superposition of a minimum background level T b2 and a minimum response having peak height T 2 , T 1 being larger than or equal to 0.5 (T b1 -T b2 ) for a display cell which is switched from the stationary "off" condition to the stationary "on" condition.

Claim 7

A display device as claimed in claim 4, characterized in that a display cell which is switched from the stationary "off" condition to the stationary "on" condition shows a transmission response which during the first occuring frame time is equal to that of each of the subsequent frame times.

Claim 8

A display device as claimed in claim 4 or 5, characterized in that the ratio d/p is approximately 0.75, the director over the layer thickness d shows a rotation increasing to 3/2π radians and the layer thickness d is smaller than 8 microns.

Claim 9

A display device as claimed in claim 4 or 5, characterized in that the front supporting plate and the rear supporting plate comprise a polariser.

Claim 10

A display device as claimed in claim 4 or 5, characterized in that it comprises a first liquid crystal display and a second liquid crystal display placed behind the first, the front supporting plate of the first display and the rear supporting plate of the second display comprising a polariser, a common polariser being present between the two displays.

Claim 11

A display device as claimed in claim 7, characterized in that a reflector is provided on the polariser of the rear supporting plate.

Claim 12

A display devide as claimed in claim 4, characterized in that the line scanning circuit provides line selection pulses of the voltage V 1 , the column selection circuit provides data pulses of the voltage ±V c , and that during line scanning, selected scanned display cells convey a voltage V 1 +V c , non-selected scanned display cells convey a voltage V 1 -V c and all the cells not scanned convey a voltage ±V c .

Claim 13

A display device as claimed in claim 4, characterized in that the data pulses are formed as pulses which are modulated in pulse duration by the picture information.