Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-04-08
2001-01-23
Saras, Steven J. (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S103000, C345S094000
Reexamination Certificate
active
06177917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for driving the same.
2. Description of the Related Art
Methods for driving a liquid crystal display device include a voltage averaging method (see “Ekisyo no Saisin Gijyutu (Latest Technology of Liquid Crystal)” published by Kogyo Chosakai Publishing Co., Ltd., p. 106) and a method for simultaneously selecting and driving a plurality of rows (see T. N. Ruckmongathan, Conf. Record of 1988 International Display Research Conference, p. 80 (1988); T. J. Scheffer and B. Clifton, 1992 SID Digest of Technical Papers XXIII, p. 228 (1992); and S. Ihara et al., 1992 SID Digest of Technical Papers XXIII, p. 232(1992)).
The basic principle of the voltage averaging method and the method for simultaneously selecting and driving a plurality of rows is as follows: A voltage waveform for each scanning electrode corresponding to an orthogonal matrix such as a unit matrix and a Walsh matrix is formed. Moreover, a voltage waveform for each signal electrode is formed by orthogonal transformation of display data based on the orthogonal matrix. Then, the resultant voltage waveforms are respectively applied to each scanning electrode and each signal electrode, and a voltage waveform corresponding to the difference in a voltage waveform between the scanning electrode and the signal electrode is applied to a liquid crystal panel on an intersection by intersection basis of the scanning electrodes and the signal electrodes. Thus, inverse transformation of the display data is performed on the display panel, whereby an image is displayed.
In a liquid crystal display device driven by the above-mentioned methods, a voltage waveform on each signal electrode and on each scanning electrode is distorted by reduction in sharpness or by induction at a changing point in the waveform, causing crosstalk between electrodes.
In the case where a DC voltage is continuously applied to a liquid crystal layer of the liquid crystal panel, liquid crystal will be degraded by decomposition. Accordingly, the liquid crystal panel is driven using an alternating voltage waveform of each signal electrode and each scanning electrode (this driving method is, hereinafter, referred to as an alternating driving method). In the case of the alternating driving method, crosstalk is generated significantly when a polarity of a voltage waveform changes.
Hereinafter, display on a liquid crystal panel as shown in
FIG. 5
by the voltage averaging method and the alternating driving method will be described by way of example.
This liquid crystal panel has 10×5 dot display with signal electrodes X
1
through X
10
and scanning electrodes Y
1
through Y
5
being located perpendicular to each other. In
FIG. 5
, a white circle represents a pixel in an ON state, whereas a shaded circle represents a pixel in an OFF state. When the liquid crystal panel has the display as shown in
FIG. 5
, signals as shown in
FIG. 6
are supplied to drive the liquid crystal panel.
In the liquid crystal panel, the scanning electrodes Y
1
through Y
5
are sequentially scanned during each frame period in synchronization with a horizontal synchronizing signal shown in (a) of FIG.
6
. An alternating driving signal shown by (b) of
FIG. 6
is inverted at time t
1
and t
2
of respective frame periods.
Each voltage waveform on the signal electrodes X
1
through X
10
is inverted in response to the inversion of the alternating driving signal. Referring to
FIG. 5
, all of the pixels on the signal electrode X
4
are ON. Therefore, the voltage waveform on the signal electrode X
4
shown by (c) of
FIG. 6
indicates ON during a frame period, and is inverted at time t
1
when the alternating driving signal is inverted. For the signal electrode X
5
, only one pixel in a first row is ON, whereas the remaining pixels in second through fifth rows are OFF. Accordingly, the voltage waveform on the signal electrode X
5
shown by (d) of
FIG. 6
indicates ON corresponding to the pixel in the first row, while indicating OFF corresponding to the pixels in the second through fifth rows. This voltage waveform is inverted at time t
1
.
Similarly, each voltage waveform on the scanning electrodes Y
1
through Y
5
is also inverted in response to the inversion of the alternating driving signal. For example, the voltage waveform on the scanning electrode Y
1
shown in (e) of
FIG. 6
is at a low level at the beginning of the first frame, while attaining a high level at the beginning of the next frame period after time t
1
.
As a result, a voltage waveform shown in (f) of
FIG. 6
is applied to the pixel at the intersection of the signal electrode X
4
and the scanning electrode Y
1
, whereas a voltage waveform shown in (g) of
FIG. 6
is applied to the pixel at the intersection of the signal electrode X
5
and the scanning electrode Y
1
.
However, in the case where such crosstalk as mentioned above is present, these voltage waveforms will become as shown in (a) through (g) of FIG.
7
.
In this case, a voltage waveform on the scanning electrode Y
1
as shown in (e) of
FIG. 7
is distorted at time t
1
and t
2
when the alternating driving signal is inverted. The reason for this will be described in the following in terms of time t
1
. Before time t
1
, pixels in the 8 columns of the signal electrodes X
1
through X
4
and X
7
through X
10
are ON, whereas pixels in the 2 columns of the signal electrodes X
5
and X
6
are OFF. In other words, the signal electrodes X
1
through X
4
and X
7
through X
10
have a positive potential, whereas the signal electrodes X
5
and X
6
have a negative potential. Accordingly, positive charges corresponding to 6 dots, the difference in number between the pixels in the ON state and in the OFF state are charged between the scanning electrode Y
1
and the signal electrodes. A potential on each of the signal electrodes X
1
through X
10
is inverted in polarity at time t
1
. Therefore, these positive charges are discharged through a resistance of the scanning electrode Y
1
. Thereafter, negative charges corresponding to 6 dots are charged between the scanning electrode Y
1
and the signal electrodes through the resistance of the scanning electrode Y
1
. As a result, the voltage waveform on the scanning electrode Y
1
is distorted. Similarly, a voltage waveform on each of the scanning electrodes Y
2
through Y
5
is also distorted. Since the distortion generation mechanism at time t
2
is the same as that at time t
1
except for the polarity, description thereof will be omitted.
For example, when the voltage waveform on the scanning electrode Y
1
as shown in (e) of
FIG. 7
is distorted, a voltage waveform at the pixel at the intersection of the signal electrode X
4
and the scanning electrode Y
1
as shown in (f) of
FIG. 7
is also distorted. Similarly, the voltage waveforms on the other scanning electrodes Y
2
through Y
5
are also distorted, and the voltage waveforms at the remaining pixels on the signal electrode X
4
are also distorted. Therefore, effective voltages applied to the pixels on the signal electrode X
4
are reduced, causing reduction in luminance of each pixel on the signal electrode X
4
.
In addition, a voltage waveform at the pixel at the intersection of the signal electrode X
5
and the scanning electrode Y
1
as shown in (g) of
FIG. 7
is distorted, and an effective voltage applied to the pixel is increased. Similarly, the voltage waveforms at the other pixels on the signal electrode X
5
are also distorted, and effective voltages applied to the pixels are increased. As a result, luminance of each pixel on the signal electrode X
5
is increased.
Thus, luminance of each pixel on the signal electrode X
4
is reduced, whereas luminance of each pixel on the scanning electrode X
5
is increased. As a result, vertical stripe lines appear on the display screen.
In order to eliminate such crosstalk, Japanese Laid-Open Publication No. 64-29899 (or see P. Maltese, Eurodisplay Digest, p. 15 (1980)), for example
Imai Masahiro
Koizumi Takashi
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Saras Steven J.
Sharp Kabushiki Kaisha
Spencer William C.
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