Ferroelectric liquid crystal displays with digital greyscale

Details Ferroelectric liquid crystal displays with digital greyscale Ferroelectric liquid crystal displays with digital greyscale

1996-10-29

1999-05-18

Nguyen, Chanh

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

345 97, G09G3/36

Patent

active

059054824

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to the multiplex addressing of bistable liquid crystal displays with greyscale, particularly ferroelectric liquid crystal displays.
2. Discussion of Prior Art
Liquid crystal display devices are well known. They typically comprise a liquid crystal cell formed by a thin layer of a liquid crystal material held between two glass walls. These walls carry transparent electrodes which apply an electric field across the liquid crystal layer to cause a reorientation of the molecules of liquid crystal material. The liquid crystal molecules in many displays adopt one of two states of molecular arrangement. Information is displayed by areas of liquid crystal material in one state contrasting with areas in the other state. One known display is formed as a matrix of pixels or display elements produced at the intersections between column electrodes on one wall and line (or row) electrodes on the other wall. The display is often addressed in a multiplex manner by applying voltages to successive line and column electrodes.
Liquid crystal materials are of three basic types, nematic, cholesteric, and smectic each having a distinctive molecular arrangement.
The present invention concerns ferroelectric smectic liquid crystal materials. Devices using this material form the surface stabilised ferroelectric liquid crystal (SSFLC) device. These devices can show bistability, ie the liquid crystal molecules, more correctly the molecular director, adopt one of two aligned states on switching by positive and negative voltage pulses and remain in the switched state after removal of the voltage. The two states can appear as dark (black) and light (white) areas on a display. This bistable behaviour depends upon the surface alignment properties and chirality of the material.
A characteristic of SSFLCs is that they switch on receipt of a pulse of suitable voltage amplitude and length of time of application, ie pulse width, termed a voltage time product V.t. Thus both amplitude and pulse width need to be considered in designing multiplex addressing schemes.
There are a number of known systems for multiplex addressing ferroelectric displays: see for example article by Harada et al 1985 S.I.D. Paper 8.4 pp 131-134, and Lagerwall et al 1985 I.D.R.C. pp 213-221. See also GB 2,173,336-A, and GB 2,173,629-A. Multiplex addressing schemes for SSFLCs employ a strobe waveform that is applied in sequence to lines but not necessarily to successive lines simultaneously with data waveforms applied to eg column electrodes.
There are two basic types of addressing. One uses two fields of addressing with a first strobe (eg positive strobe) in a first field, followed by a second strobe (eg negative strobe) in a second field; the two fields making up a frame which is the time taken to completely address a display. The other type of addressing uses a blanking pulse to switch all pixels in one or more lines to say a black state, followed by a single strobe pulse applied sequentially to each line for selectively switching pixels in that line to a white state. In this blanking addressing system the frame time is the time required to blank plus the time taken to strobe all the lines.
The bistability property, together with the fast switching speed, makes SSFLC devices suitable for large displays with a large number of pixels or display elements. Such ferroelectric displays are described for example in;- N. A. Clark and S. T. Lagerwall. Applied Physics Letters Vol 36. No 11 pp 889-901. Jun. 1980; GB-2.166.256-A; U.S. Pat. No. 4,367,924; U.S. Pat. No. 4,563,059; patent GB-2,209,610; R. B. Meyer et al. J Phys Lett 36, L69, 1975.
For many displays two visible states only are required, ie an ON state and an OFF state. Examples of such displays include alpha numeric displays and line diagrams. There is now an increasing requirement for a plurality of visible states between the ON and OFF states, ie a plurality of different contrast levels. Such different levels are termed greyscales. Ideally th

REFERENCES:
patent: 4367924 (1983-01-01), Clark et al.
patent: 4563059 (1986-01-01), Clark et al.
patent: 5048246 (1991-09-01), Inaba et al.
patent: 5398042 (1995-03-01), Hughes
patent: 5469281 (1995-11-01), Katakura et al.
patent: 5497173 (1996-03-01), Hughes
Clark, Noel A. et al., "Submicrosecond Bistable Electro-Optic Switching in Liquid Crystals", Appl. Phys. Lett. vol. 36, No. 11, Jun. 1, 1980, pp. 899-901.
Harada, T. et al., "An Application of Chiral Smectic-C Liquid Crystal to a Multiplexed Large-Area Display", SID 85 Digest, Paper 8.4, 1985, pp. 131-134.
Kuniyasu, Seiyu et al., "The Strength of Rubbing Worked on Polyimide Films . . . ", Japanese Journal of Applied Physics, vol. 27, No. 5, May, 1988, pp. 827-829.
Lagerwall, S.T. et al., "Ferroelectric Liquid Crystals for Displays", 1985 International Display Research Conference, pp. 213-221.
Le Pesant, J.P. et al., "Ferroelectric Optical Switching of Chiral Smectic C Liquid Crystal Mixtures", Proc. 4.sup.th IDRC, 1984, pp. 217-220.
Meyer, R.B. et al., "Ferroelectric Liquid Crystals", Le Journal De Physique-Lettres, Tome 36, Mar. 1975, pp. L-69-L-71.

Affiliated with

Also associated with

Rating

Ferroelectric liquid crystal displays with digital greyscale does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ferroelectric liquid crystal displays with digital greyscale, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ferroelectric liquid crystal displays with digital greyscale will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1763111