Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1995-03-08
1997-05-13
Saras, Steven
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 94, 345 97, G09G 336
Patent
active
056297181
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of addressing a matrix-type liquid crystal cell including liquid crystal material which is electrically settable to first and second stable optical states, the cell comprising a plurality of pixels which are defined by areas of overlap between members of a first set of electrodes on one side of the material and members of a second set of electrodes, which cross the first set, on the other side of the material, in which method the pixels are addressed in lines, the addressing of each line comprising (a) applying an erase signal having a given polarity to the corresponding electrode of the first set while applying at least one charge-balanced bipolar data signal to each electrode of the second set, thereby setting any pixel of the line which is not already in the first state to that state, and (b) subsequently applying a strobe signal having an opposite polarity to said given polarity to the corresponding electrode of the first set while applying a charge-balanced bipolar data signal to each electrode of the second set, thereby selectively setting to the second state any pixel of the line for which the data signal applied to the corresponding electrode of the second set has a given form. The invention also relates to optical modulator apparatus for implementing such a method.
A known such method is disclosed in GB-A-214473. In this known method, the data signal comprises first and second successive portions of opposite polarities. When the data signal has the given form the strobe signal coincides with that one of these portions which has the given polarity, so that the magnitude of the signal applied across the corresponding pixel is the sum of the magnitudes of the strobe and data signals. GB-A-214473also discloses an addressing method in which the data signal comprises first, second and third portions, the polarity of the second portion being opposite to that of the first and third portions. In this last method the strobe signal coincides with the second portion of the data signal and is bipolar, making it unnecessary to employ an erase signal to ensure that all pixels of a line are initially in the first state. In both these known methods the product of the time for which the data signal has one polarity and its amplitude when it has this polarity is equal to the product of the time for which it has the other polarity and its amplitude when it has this other polarity. The data signal is therefore balanced; in itself it has no net effect on any given pixel.
The maximum addressing speed when using such methods is limited by the length of the erase signal (if present) and the length of the strobe signal; each has to be present for a sufficient time to ensure that the relevant pixels are actually set to the first and second states respectively, this process taking a finite time. When the first of the known methods referred to above is used, the length of the strobe signal is equal to the length of one of the two (equal-length) portions of the data signal i.e. to half the length of the complete data signal, and when the second of these known methods is used the length of the active portion of the strobe signal is equal to half the length of the second portion of the data signal, which corresponds to one quarter of the length of the complete data signal.
It is an object of the invention to allow the minimum length of a complete data signal in a method as defined in the opening paragraph to be reduced, thereby increasing the maximum permissible addressing speed.
According to one aspect the invention provides a method as defined in the first paragraph which is characterised in that when said data signal has said given form it comprises first, second and third successive portions in which it has said given polarity, said opposite polarity and said given polarity respectively, the amplitude of the second portion being less than the amplitude of the strobe signal, the end of the first portion coinciding with or occurring before the start of the strobe signal, the end of the second
REFERENCES:
patent: 5091723 (1992-02-01), Kanno et al.
patent: 5264839 (1993-11-01), Kanno et al.
Central Research Laboratories Limited
Chang Kent
Saras Steven
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