Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-09
2001-08-28
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C345S097000
Reexamination Certificate
active
06281866
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a display device in which two rows of picture elements (pixels) can be simultaneously addressed, and to a method of addressing such a display.
DISCUSSION OF THE RELATED ART
FIG. 1
is a schematic view of a liquid crystal display device disposed between two polarising plates
24
,
25
. The liquid crystal display device comprises a transparent substrate
22
on which are provided transparent strobe electrodes S (also known as row or scanning electrodes( which extend parallel to one another. An insulating layer
26
a
is provided over the strobe electrodes S, and an alignment film
27
a
is formed over the insulating layer. The alignment film
27
a
is spaced from a second alignment film
27
b
by spacers
28
and a liquid crystal layer
21
. A second transparent substrate
23
carries transparent data electrodes D (also known as column electrodes), which are parallel to one another and which are perpendicular to the strobe electrodes. The alignment film
27
b
is formed over a second insulating layer
26
b
which itself is formed over the data electrodes D. The electrodes D, S are connected to a drive circuit (not shown).
A pixel Pij if defined by the overlap of the ith strobe electrode and the jth data electrode. In a passive addressing method, the pixel Pij is addressed by applying a strobe voltage to the ith strobe electrode while applying a data voltage to the jth data electrode. The voltage across the pixel is equal to the difference between the strobe voltage and the data voltage.
One example of the voltages that can be used in a method of passively addressing a liquid crystal display are the Joers/Alvey voltage waveforms (P. W. H. Surguy et al, “Ferroelectrics” 122 pp 63-79 (1991)). These voltages are used to drive a display device comprising a layer of ferroelectric liquid crystal (FLC) material which has two stable states—the drive voltage applied across a pixel will either switch the liquid crystal molecules in that pixel from one stable state to the other stable state, or it will not switch the liquid crystal molecules in that pixel.
One example of driving voltages according to the Joers/Alvey scheme is shown in FIGS.
2
(
a
)-
2
(
d
). To address a display, a strobe driving circuit (not shown in
FIG. 1
) will apply a ‘select’ voltage pulse Vs shown in FIG.
2
(
a
) to one strobe electrode, while applying the ‘non-select’ voltage pulse Vn (FIG.
2
(
b
)) to the remaining strobe electrodes. The pixels in the selected row of the display are addressed by a data driving circuit (not shown in FIG.
1
), which will apply either the ‘re-write’ data voltage pulse V
R
(FIG.
2
(
c
)) or the ‘hold’ data voltage pulse V
H
(FIG.
2
(
d
))to the column electrodes. A pixel to which is applied the ‘select’ strobe voltage and the ‘switch’ data voltage will switch from one stable state of the FLC to the other stable state, and all other pixels will not switch. When a row of pixels is selected, the column electrodes can be addressed sequentially or simultaneously After one row of pixels has been addressed, the remaining rows are addressed, one after the other, in the same way.
It is a general object of workers in this field to increase the frame rate f of a display. The frame rate is given by:
F=1/tlb
where &tgr; is the effective row address time, l the number of rows, and b the number of temporal bits required. If l and b are fixed, then the frame rate can only be increased by reducing &tgr;. If two rows could be simultaneously addressed, then &tgr; would, in principle, be halved.
A conventional passively addressed liquid crystal display, such as that shown in
FIG. 1
, could be operated in such a way that two rows of pixels were simultaneously addressed by applying a first select voltage Vs
1
to one strobe electrode and a second select voltage Vs
2
to another strobe electrode. However, this driving method would require four different data voltages. This is because two binary pixels (that is, two pixels each of which has two possible display states) together give four possible combined display states (the two states of each pixel are shown as 1 and 0).
data voltage
V
1
V
2
V
3
V
4
row 1: strobe voltage Vs1
0
1
0
1
row 2: strobe voltage Vs2
0
0
1
1
Although addressing the device in this way would allow two rows of pixels to be addressed simultaneously, in practice, the line address time increases substantially and becomes approximately equal to twice the line address time where the pixels are addressed one row at a time. Accordingly, there is no substantial improvement in the frame rate of which the display is capable. Further, this technique has the disadvantage of doubling the number of distinct data voltages required. In general, the maximum number of possible combined display states for a column of pixels is equal to the number N of different data voltage waveforms that the driving data circuit can supply.
Display devices in which two scanning electrodes can be simultaneously driven are known. For example, JP-A-06 120 324 discloses a device in which a pixel is ‘split’ into three ‘sub-pixels’, with each sub-pixel having a separate scanning electrode. This is to provide a grey-scale display, by providing intermediate display states in which part of the pixel blocks light and part of the pixel transmits light.
In this prior art device, however, it is not possible to address the sub-pixels completely independently. It is only possible to address the following four combinations of sub-pixels: all sub pixels; the first and second sub-pixels; the first sub-pixels; or none of the sub-pixels. It is not possible, for example, for the first and third sub-pixels to be ‘ON’ when the second sub-pixel
2
is ‘OFF’.
Other devices in which a pixel comprises two sub-pixels each having its own scanning electrode are displayed in JP-A-3 206 188 and JP-A-3 206 189. It is again not possible to address the two sub-pixels completely independently from one another in these prior art devices.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a display device comprising a plurality of strobe electrodes characterised by:
a plurality of pairs of data electrodes crossed with the strobe electrodes to define a respective pixel at each overlap of one of the strobe electrodes with one of the pairs of data electrodes;
a strobe signal source for simultaneously supplying X different strobe signals to each group of X electrodes in turn, where X is an integer greater than one; and
a data signal source for supplying any one of a plurality of data signals to the data electrodes such that all combinations of optical states of the X pixels addressed by each group of strobe electrodes and each pair of data electrodes are selectable.
According to a second aspect of the invention, there is provided a method of addressing a display device of the type comprising a plurality of strobe electrodes and a plurality of data electrodes crossed with the strobe electrodes to define a respective pixel at each overlap of one of the strobe electrodes with one of the pairs of data electrodes, the method comprising the steps of:
simultaneously supplying X different strobe signals to each group of X strobe electrodes in turn, where X is an integer greater than one; and
supply any one of a plurality of data signals to the data electrodes such that all combinations of optical states of the X pixels addressed by each group of strobe electrodes and each pair of data electrodes are selectable.
It has been surprisingly found that the use of pairs of data electrodes for each pixel allows multiple strobing of image data to the pixels at an increased frame rate. In particular, strobing several rows at a time is possible with a line address time which may be greater than that required when strobing a single row at a time but which is less than the sum of the line address times which would be required to refresh the rows individually. For instance, where X is equal to tow so that two rows are refreshed at a time, the time required to address a
Mayhew Nicholas
Robinson Michael Geraint
Tombling Craig
Hjerpe Richard
Laneau Ronald
Renner , Otto, Boisselle & Sklar, LLP
Sharp Kabushiki Kaisha
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