Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1995-03-01
1998-08-11
Chow, Dennis-Doom
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 89, G09G 336
Patent
active
057933472
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the addressing of ferroelectric liquid crystal displays or FLCDs, and in particular to a method of addressing a matrix-type liquid crystal cell to produce grey levels.
DESCRIPTION OF THE RELATED ART
A matrix-type liquid crystal cell comprises a matrix of pixels defined by the intersection of row and column electrodes mounted on opposing substrates. One known method of addressing such a cell includes the features set forth in the preamble of claim 1 and is disclosed in GB-A-2146473.
In the known method, which employs so-called blank before write, signals applied to the column electrodes, or data signals, take two forms, either "on" or "unchanged". Synchronised with these signals are signals which are applied to the row electrodes: "select" or "non-select". Furthermore "blank" signals are periodically applied to the row electrodes. At any one time, only one row electrode has the "select" signal applied to it; all the remaining row electrodes have the "non-select" signal applied to them.
The addressing scheme operates in the following manner. Data signals are applied to the column electrodes in order to create the desired pattern in the row of pixels corresponding to the row electrode to which the select signal is applied. The arrangement is such that this row will previously have been blanked by the application to the corresponding electrode of the blanking signal. This has the effect of setting that row into a particular state, usually the dark (or "off") state.
Addressing methods are also disclosed in EP-A-0337780, EP-A-0370649 and EP-A-0394903.
In such a system, it is a requirement to maintain dc compensation, or charge balancing. This necessitates both the "on" and "unchanged" data signals having no net dc component, and preferably also the sum of the blanking, select and non-select signals having no net dc component.
Known methods of generating grey levels include spatial dither, temporal dither and threshold variation techniques. Spatial dither involves the subdivision of each pixel into separate areas which can be switched individually. This has the disadvantage of increasing the complexity of the display by the electrode patterning and interconnection required. Temporal dither, wherein a pixel is addressed with different data several times per picture to create a perceived grey has the disadvantage of requiring high speed electronics which limits the maximum size of the display. Threshold variation involves the division of each pixel into a plurality of regions having different switching thresholds, such that a particular addressing signal may switch only some of the regions giving a grey effect. This technique is complicated by the fact that its operation requires more than two data voltage levels.
This invention seeks to alleviate these disadvantages.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of addressing a matrix of pixels which are defined by areas of overlap between members of a first set of electrodes on one side of a layer of ferroelectric material, and members of a second set of electrodes which cross the members of the first set, on the other side of the material, in which method unipolar blanking signals are applied to the members of the first set of electrodes to effect blanking before unipolar select signals are applied thereto one by one to effect addressing of the corresponding pixels by simultaneously applying a selected charge-balanced bipolar data waveform to each member of the second set of electrodes, the data waveforms each comprising pulses of two respective voltage levels, characterized in that the data waveforms are selected from data waveforms of at least first, second and third forms which, when combined with select signals, produce resultant waveforms of a first kind which causes switching of substantially the entire pixel, a second kind which leaves substantially the entire pixel unswitched, and a third kind which causes switching of part of the pixel, respectively, a
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Central Research Laboratories Limited
Chow Dennis-Doom
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