Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1996-05-30
1998-04-14
Hjerpe, Richard
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 60, 345 97, G09G 303
Patent
active
057397988
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of addressing a matrix of pixels which are defined by areas of overlap between the members of a first set of electrodes on one side of a layer of material and members of a second set of electrodes, which cross the members of the first set, on the other side of the layer of material. The material is electrically addressable to change an optical property thereof from one stable state to another stable state. Each member of the first set of electrodes comprises first and second subelectrodes which are, at opposing edges thereof, connected by a layer of resistive material at least in the pixel areas. In the method, for each electrode of the first set, a blanking pulse of a given polarity is applied to the subelectrodes thereof and thereafter a predetermined strobe signal is applied to a subelectrode thereof whilst a data signal having a chosen amplitude is applied to each electrode of the second set in parallel. The predetermined strobe signals are applied to the respective electrodes of the second set in succession.
A method of the above general kind is disclosed in EP-A- 224243 and EP-A 276864. In the known method, when a strobe signal is applied to one subelectrode of an electrode of the first set the other subelectrode of that electrode is maintained at zero voltage. The result is that a voltage gradient is created between the two subelectrodes, that is, across each corresponding pixel. Thus, it can be arranged that the electric field across the layer of material of each pixel varies from one edge to the opposing edge from a level which is above the switching threshold of the material to a level which is below the threshold. The choice of data waveforms simultaneously applied to each member of the second set of electrodes determines where the switching threshold is crossed and thus how much of the corresponding pixel is switched from the blanked state. For a material such as ferroelectric liquid crystal material where the stable states are light-transmissive and non light-transmissive states for the corresponding pixel if the material is situated between crossed polarizers, the brightness level or grey level of each pixel can be controlled in this way.
A problem with such a method is that the switching threshold of the material may vary with temperature. In large matrices such as displays, for example, the temperature may vary considerably from one edge of the matrix to the center. Thus, the amount of a selected pixel which is switched by a given waveform may vary across the matrix, making control of the grey level unreliable.
It is an object of the present invention to alleviate the problems of the known prior art.
According to the present invention there is provided a method in which the predetermined strobe signals each comprise a pre-pulse and a main pulse which are of the opposite polarity to the blanking pulses. Each time a predetermined strobe signal is applied to a subelectrode, an auxiliary strobe signal is applied to the other subelectrode of the same electrode, which auxiliary strobe signal comprises a pre-pulse of the same polarity as the blanking pulses and a main pulse of the opposite polarity to the blanking pulses. Each data signal is also of chosen polarity and, when of non-zero amplitude, comprises a first pulse which coincides with the pre-pulses of the corresponding predetermined and auxiliary strobe signals and a second pulse which coincides with the main pulses of the predetermined and auxiliary strobe signals. The first and second pulses having mutually opposite polarities, in that the magnitudes of the main pulses of the predetermined and auxiliary strobe signals are, by equal amounts, respectively greater than and less than the switching threshold of the material at a predetermined working temperature. The magnitudes of the pre-pulses of the predetermined and auxiliary strobe signals are equal to the magnitude of the first pulse of a data signal which has an amplitude such that the second pulse thereof has a magnitude which is equal to the differe
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Acosta Joseph
Central Research Laboratories Limited
Hjerpe Richard
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