Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-08-06
2004-10-19
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000
Reexamination Certificate
active
06806858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electro-optical apparatus and a method of driving an electro-optical material that allow display with less unevenness in luminance, a driving circuit therefor, an electronic apparatus, and a display apparatus.
2. Description of Related Art
Generally, in a passive-matrix liquid crystal apparatus, a plurality of scanning electrodes are formed on one substrate and a plurality of signal electrodes are formed on the other substrate, and liquid crystal is held between the substrates as an electrooptical material. Pixels are arranged respectively in association with intersections of the scanning electrodes and the signal electrodes so as to form a matrix. The intensity level of each pixel is determined according to a potential difference between associated scanning electrode and signal electrode.
MLS (Multi-Line Selection) driving, in which a plurality of scanning electrodes are simultaneously selected in a period and the selection period is divided into a plurality of sub-periods within a frame, can be used to drive the above apparatus. In MLS driving, a selection voltage is applied to a pixel a plurality of times in a frame, so that change is luminance of a pixel that is turned on for display is reduced compared with a method in which a selection voltage is applied only once in a frame, serving to avoid reduction in contrast. In the following description, the sub-periods into which one frame is divided will be referred to as fields.
A case where a liquid crystal panel having 4S scanning electrodes is driven by MLS driving is considered below. In this example, it is assumed that four scanning electrodes are simultaneously selected. In the following description, a set of scanning electrodes that are selected simultaneously will be referred to as a scanning electrode group. In this example, S scanning electrode groups G
1
, G
2
, . . . GS exist. Furthermore, the first scanning electrodes Y
1
, Y
5
, . . . Yk+1, . . . in the respective scanning electrode groups will be referred to as first scanning electrodes R
1
, the second scanning electrodes Y
2
, Y
6
, . . . Yk+2, . . . in the respective scanning electrode groups as second scanning electrodes R
2
, the third scanning electrodes Y
3
, Y
7
, . . . Yk+3, . . . in the respective scanning electrode groups as third scanning electrodes R
3
, and the fourth scanning electrodes Y
4
, Y
8
, . . . Yk+4, . . . in the respective scanning electrode groups as fourth scanning electrodes R
4
.
In MLS driving, either a positive voltage +V
3
or a negative voltage −V
3
with reference to a reference voltage VC is selected and applied to scanning electrodes. Each frame is divided into a first field f
1
, a second field f
2
, a third field f
3
, and a fourth field f
4
, and the scanning electrode groups are sequentially selected in each of the fields.
FIG. 18
is a chart showing polarities of scanning electrode voltage in MLS driving. In
FIG. 18
, “+1” indicates selection of +V
3
as a scanning electrode voltage, whereas “−1” indicates selection of −V
3
as a scanning electrode voltage. Furthermore, sets of polarities of selection voltages to be applied respectively to the first to fourth scanning electrodes R
1
to R
4
that are selected simultaneously will be referred to as first to fourth scanning patterns P
1
to P
4
, and sets of scanning patterns will be referred to as scanning pattern sets. In the example shown in
FIG. 18
, a column corresponds to a scanning pattern, and a set of the first column to the fourth column corresponds to a scanning pattern set. For example, if the first to fourth scanning patterns P
1
to P
4
are sequentially used in the first to fourth fields f
1
to f
4
, voltage applied to the first scanning electrodes R
1
is +V
3
in the first field f
1
, +V
3
in the second field f
2
, −V
3
in the third field f
3
, and +V
3
in the fourth field f
4
.
Signal electrode voltages are selected from +V
2
, −V
2
, +V
1
, −V
1
, and VC. A relationship among the potentials +V
3
, −−V
3
, +V
2
, −V
2
, +V
1
, −V
1
, and VC is shown in FIG.
19
. Signal electrode voltages are selected based on the number of mismatches between a scanning pattern and a pattern of display data D (hereinafter referred to as a display pattern). If display data D to be displayed on a pixel is off (black) for “0” and on (white) for “1,” “0” is associated with “−1” and “1” is associated with “+1.”
FIG. 20
is a chart showing an example of selection of signal electrode voltages. In this example, +V
2
is selected as a signal electrode voltage if the number of mismatches between scanning pattern and display pattern is “4,” +V
1
is selected as a signal electrode voltage if the number of mismatches is “3,” VC is selected as a signal electrode voltage if the number of mismatches is “2,” −V
1
is selected as a signal electrode voltage if the number of mismatches is “1,” and −V
2
is selected as a signal electrode voltage if the number of mismatches is “0.”
It can be assumed, as an example, that display pattern corresponding to the first to fourth scanning electrodes R
1
to R
4
is “−1, −1, −1, −1.” Since the first scanning pattern P
1
is “+1, −1, +1, +1,” the number of mismatches is “3.” Accordingly, if display pattern is “−1, −1, −1, −1” as shown in
FIG. 20
, +V
1
is selected as a signal electrode voltage.
If a combination of polarities of scanning electrode voltages simultaneously selected are such that only one of four is mismatched as described above, for example, when all pixels on a signal electrode are off, the signal electrode voltage forms a waveform Q
1
shown in
FIG. 21
, whereby +V
1
is applied uniformly throughout one frame. On the other hand, if all pixels on a signal electrode are on, the signal electrode voltage forms a voltage waveform Q
2
shown in
FIG. 21
, whereby −V
1
is applied uniformly throughout one frame.
Accordingly, variation in voltages applied to pixels in a non-selection period is eliminated. That is, if a combination of polarities of scanning electrode voltages simultaneously selected is such that only one of four is mismatched, variation in signal electrode voltages is reduced when displaying black text in white background, which is most typical, or when displaying white text in black background.
In MLS driving, however, signal electrode voltages are selected according to a combination of scanning pattern and display pattern. Thus, signal electrode voltages are fixed to a specific pattern in relation to a specific display pattern.
FIG. 22
shows an example of display pattern. In this example, black is displayed at pixels indicated by oblique lines while white is displayed at the other pixels, the display pattern shown in
FIG. 22
being repeated in the rightward direction and in the downward direction. Signal electrode voltages are selected according to a table shown in FIG.
20
.
In this case, the first to fourth columns from the left always display “white.” Thus, display pattern of these columns is always “+1, +1, +1, +1,” so that voltages at the signal electrodes X
1
to X
4
are always −V
1
. On the other hand, the fifth to eighths columns from the left repeatedly displays “white, white, white, black, and black, black, black, white.” Thus, display pattern of G
1
and G
3
in these columns is always “+1, +1, +1, −1,” so that voltages at the signal electrodes X
5
to X
8
are always VC or −V
2
.
Display pattern of G
2
and G
4
in these columns is always “−1, −1, −1, +1,” so that voltages at the signal electrodes X
5
to X
8
are always VC or +V
2
. That is, voltages at the signal electrodes X
1
to X
4
are always −VC, whereas voltages at the signal electrodes X
5
to X
8
are always VC or ±V
2
Ito Akihiko
Kurumisawa Takashi
Yamazaki Sugura
Mengistu Amare
Oliff & Berridg,e PLC
Patel Nitin
Seiko Epson Corporation
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