Liquid crystal colour displays

Claim 2

A liquid crystal display comprising a liquid crystal cell (6) capable of rotating the plane of plane polarised liaht Jassing there for observing the ON and OFF states of the cell (6), the cell (6) comprising two spaced transparent slides (9, 10) each bearing an electrode structure (12a, 12b, 13) containing a layer (14) of a nematie or a cholesteric liquid crystal material having a cholesteric pitch greater than twice the layer (14) thickness and a dielectric anisotrophy which changes between positive and negative values at a critical frequency (f c ) of applied electrical signals, a source (19) of low frequency (f 1 ) electrical signals and a source (20) of high frequency (f h ) electrical signals, where f h >> f c >> f l characterised by control logic (18) for causing application of signals f l and fh in sequence to the cell (6) with a space between the end of the signal f l and the beginning of the signal f h whereby the liquid crystal material adepts a uniform twist in the call when driven to an OFF state

Claim 3

A liquid crystal display characterised by a cathode ray tube (1) having a screen (8) which is capable, when energised, of emitting light in at least a first and a second narrow range of wavelengths, field scan circuitry (3, 17) for providing at leasta first and a second field image on the screen (8) in sequence and related to different input means (15), at least a first and second colour selective polariser (4, 5) each having a selective transmission at different ones of the peak waveleng the emitted by the screen (8) and arranged with their optical axis at an angle to one another, a liquid crystal cell (6) capable of rotating the plane of plane polarised light passing there through and transmitting polarised light without such rotation dependent on electrical signals applied to the cell, the cell (6) itself comprising two parallel spaced transparent slides (9, 10) bearing transparent electrode structures (12a, 12b, 13) on their opposing inner faces and a layer of nematic or cholesteric liquid crystal material (14) between the slides, the layer material (14) having a cholesteric pitch greater than twice the layer thickness end a dielectric anisetropy which changes between positive and negative values at a critical frequency, f , of applied electrical signals, a source (19) of electrical signals of frequency, f l , less than fc, a source (20) of electrical signals of frequency, f h , greater than f c , means (18) for alternately applying the signals f l and f h to the cell in synchronism with different fields of images displayed on the screen, delay means (18) for providing a delay between removal of f l from the cell and applications of f h to the cell so that liquid crystal molecules may rotate from a position normal to the liquid crystal layer, timing means (18) for controlling the application of signals f l and f h and timing means (18) for limiting application of signals f. whereby reverse tilt within the layer is avoided, the arrangement being such that a required display is shown as successive fields of different images and observed as an image in two or more colours, and the liquid crystal material adopts a uniform molecular twist after each application of signal f h .

Claim 4

A liquid crystal display characterised by a cathode ray tube (1) having a screen (8) which is capable, when energised, of emitting light in at least a first and a second narrow range of wavelengths, field scan circuitry (3, 17) for providing at leasta first and a second field image on the screen (8) in sequence and related to different input means (15), at least a first and second colour selective polariser (4, 5) each having a selective transmission at different ones of the peak waveleng the emitted by the screen (8) and arranged with their optical axis at an angle to one another, a liquid crystal cell (6) capable of rotating the plane of plane polarised light passing there through and transmitting polarised light without such rotation dependent on electrical signals applied to the cell, the cell (6) itself comprising two parallel spaced transparent slides (9, 10) bearing transparent electrode structures (12a, 12b, 13) on their opposing inner faces and a layer of nematic or cholesteric liquid crystal material (14) between the slides, the layer material (14) having a cholesteric pitch greater than twice the layer thickness end a dielectric anisetropy which changes between positive and negative values at a critical frequency, f , of applied electrical signals, a source (19) of electrical signals of frequency, f l , less than fc, a source (20) of electrical signals of frequency, f h , greater than f c , means (18) for alternately applying the signals f l and f h to the cell in synchronism with different fields of images displayed on the screen, delay means (18) for providing a delay between removal of f l from the cell and applications of f h to the cell so that liquid crystal molecules may rotate from a position normal to the liquid crystal layer, timing means (18) for controlling the application of signals f l and f h and timing means (18) for limiting application of signals f. whereby reverse tilt within the layer is avoided, the arrangement being such that a required display is shown as successive fields of different images and observed as an image in two or more colours, and the liquid crystal material adopts a uniform molecular twist after each application of signal f h .

Claim 5

A liquid crystal display according to claim 2 characterised in that the signal f h is applied to the cell (6) during kickback of the liquid crystal molecules.

Claim 6

A liquid crystal display according to claim 2 characterised in that the control means (18) can vary the lengths and timing of signals f l and f h applied to the cell (6).

Claim 7

A liquid crystal display according to claim 2 characterised in that the input means each represent a different image.

Claim 8

A liquid crystal display according to claim 2 characterised in that the input means each represent a different colour of the same image.

Claim 9

A liquid crystal display according to claim 2 characterised by means for heating the liquid crystal material (14).

Claim 10

A liquid crystal display according to claim 7 chanracterised in that the heating means are the electrodes (12a, 12b, 13) in the cell (6).

Claim 11

A liquid crystal display according to claim 7 characterised in the heating means comprises an electrically resistive layer in thermal contact with the outside of the cell (6).

Claim 12

A liquid crystal display according to claim 2 characterised in that the cell (6) is connected in a parallel resonant circuit ( 12 , C B , L) resonant at about f h .