Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1993-02-24
1998-05-12
Lao, Lun-Yi
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345209, G09G 336
Patent
active
057512663
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the co-ordinate addressing of liquid crystal cells. Co-ordinate addressing of such cells can be achieved by methods in which each pixel is defined as the area of overlap between one member of a set of row electrodes on one side of the liquid crystal layer and one member of another set of column electrodes on the other side. In an alternative co-ordinate addressing method the liquid crystal is backed by `an active back-plane ` which has a co-ordinate array of electrode pads which are addressed on a co-ordinate basis within the active back-plane, and electrical stimuli are applied to the liquid crystal layer between individual members of this set of electrode pads on one side of the liquid crystal layer and a co-operating front-plane electrode on the other side of the liquid crystal layer. Generally the front-plane electrode is a single electrode, but in some instances it may be subdivided into a number of electrically distinct regions. The active back-plane may be constructed as an integrated single crystal semiconductor structure, for instance of silicon.
This invention relates in particular to the active back-plane addressing of liquid crystal cells whose response to an electrical stimulus is sensitive to the polarity of that stimulus.
In the electrical addressing of liquid crystal cells it is generally important to ensure that no pixels are subject to any significant long term cumulative charge imbalance that could give rise to electrolytic degradation effects within the cell. In the cases of cells whose response is not polarity sensitive, long-term charge balance can often be ensured by using charge-balanced a.c. stimuli throughout, but clearly there are problems in transferring this approach to the addressing of cells whose response is polarisation sensitive because in these circumstances the application of a charge-balanced a.c. stimulus to a pixel may make it make a temporary excursion from its initial state to some other state, but is then likely to restore it once again to its initial state.
In the ensuing description any particular pixel of a co-ordinate array of pixels is identified by its row and column co-ordinates. Whereas in conventional usage of the terms `row` and `column`, rows and columns are respectively identified as horizontally-extending and vertically-extending lines; in this instance these terms are employed in a wider sense that does not imply any particular orientation of the row and column lines with respect to the horizontal, but merely that the sets of row and column lines intersect each other.
According to the present invention there is provided a method of addressing a liquid crystal cell having a co-ordinate array of pixels, wherein data for refreshing the cell is compared with the data existing prior to refresh to determine those pixels which require to have their states changed, and wherein those pixels are accessed by developing a positive, or negative, electric potential difference across those pixels, according into which state they are to be changed, for a predetermined period of time before re-establishing a zero potential difference, whereby no pixel is consecutively accessed twice by the same polarity of potential difference.
According to the present invention there is further provided a method of coordinate addressing a liquid crystal cell that includes a liquid crystal layer which, by the application of oppositely directed electric potential differences across the thickness of the layer, is enabled to be switched between two stable states, which cell is switchable between said two stable states using an active back-plane provided with a co-ordinate array of electrode pads on one side of the liquid crystal layer, which pads co-operate with a front-plane electrode on the other side of the liquid crystal layer to define an associated co-ordinate array of pixels within the liquid crystal layer, wherein data for refreshing the cell is compared, pixel address by pixel address, with pre-existing data currently displayed by the pixels to determin
REFERENCES:
patent: 4062626 (1977-12-01), Kawakami et al.
Wahl, "Experimental driver and addressing techniques for ferroelectric liquid crystal devices", J. of Physics E/Scientific Instruments, vol. 21, No. 5, May, 1988, pp. 460-466.
Birch Martin John
Crossland William Alden
Lao Lun-Yi
Northern Telecom Limited
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