Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-03-29
2001-06-26
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06252573
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a driving apparatus and a driving method for a liquid crystal display having a plurality of row electrodes and column electrodes. More particularly, the invention relates to such an apparatus and a method in which the row electrodes are divided into groups, each group being sequentially selected and the row electrodes within each group being simultaneously selected.
BACKGROUND OF THE INVENTION
Matrix liquid crystal displays such as, twisted nematic (TN) and super twisted nematic (STN), are known in the art. Reference is made to FIGS.
21
(
a
)-(
e
) and
22
in which a conventional matrix liquid crystal display is provided. A liquid crystal panel generally indicated as
1
is composed of a liquid crystal layer
5
, a first substrate
2
and a second substrate
3
for sandwiching the liquid crystal layer
5
therebetween. A group of column electrodes Y
1
-Y
m
are oriented on substrate
2
in the vertical direction and a plurality of row electrodes X
1
-X
n
are formed on substrate
3
in substantially the horizontal direction to form a matrix. Each intersection of column electrodes Y
1
-Y
m
and row electrodes X
1
-X
n
forms a display element or pixel
7
. Display pixels
7
having the open circle indicate an ON state and those pixels having a blank indicate an OFF state.
A conventional multiplex driving based on the amplitude selective addressing scheme is known to one of ordinary skill in the art as one method of driving the liquid crystal cells mentioned above. In such a method, a selected voltage or non-selected voltage is sequentially applied to each of row electrodes X
1
-X
n
individually. That is, a selection voltage is applied to only one row electrode at a time. In the conventional driving method, the time period required to apply the successive selected or non-selected voltage to all the row electrodes X
1
-X
n
is known as one frame period, indicated in FIGS.
21
(
a
)-(
e
) as time period F. Typically the frame period is approximate {fraction (1/60)}th of a second or 16.66 milliseconds.
Simultaneously to the successive application of the selected voltage or the non-selected voltage to each of the row electrodes X
1
-X
n
, a data signal representing an ON or OFF voltage is applied to column electrodes Y
1
-Y
m
. Accordingly, to turn a pixel
7
e.g, the area in which the row electrode intersects the column electrode, to the ON state, an ON voltage is applied to a desired column electrode when the row electrode is selected.
Referring specifically to FIGS.
21
(
a
)-(
e
), a conventional multiplex drive method of a simple matrix type liquid crystal and more specifically the amplitude selective addressing scheme are shown therein. FIGS.
21
(
a
)-(
c
) show the row selection voltage waveforms that is applied in sequence to row electrodes X
1
, X
2
. . . X
n
, respectively. More particularly, in time period t
1
, a voltage pulse having a magnitude of V
1
is applied to row electrode X
1
, and a voltage of zero is applied to electrodes X
2
-X
n
; in time period t
2
, a voltage pulse having a magnitude of V
1
is applied to row electrode X
2
and a voltage of zero is applied to electrodes X
1
and X
3
-X
n
; and in time period t
n
, V
1
is applied to row electrode X
n
and a voltage of zero is to electrodes X
1
-X
n−1
. In other words, a voltage pulse having a magnitude of V
1
is applied to only one row electrode X
i
in time t
i
Typically, t
i
is approximately 69 &mgr;seconds and V
1
is approximately 25 volts. As will be apparent to one who has read this description, all of the row electrodes are sequentially selected in time periods t
1
-t
n
or one frame period F.
FIG.
21
(
d
) shows the waveform applied to column electrode Y
1
, and FIG.
21
(
e
) shows the synthesized voltage waveform applied to the pixel 7
1,1
formed at the intersection of the column electrode Y
1
and the row electrode X
1
. As shown therein, during time period t
1
, a voltage pulse having a magnitude of V
1
is applied to row X
1
and a voltage pulse of −V
2
is applied to column electrode Y
1
. Typically, V
2
is approximately 1.6 volts. The resultant voltage at pixel 7
1,1
is −(V
1
−V
2
). This synthesized voltage is sufficient to turn pixel 7
1,1
to its ON state.
One known problem with this method is that in order to select and drive the one line of the row electrodes, a relatively high voltage is required to provide good display characteristics, such as, contrast and low distortion. These conventional displays, requiring such a high voltage, also consume relatively more energy. When such displays are used in portable devices, they are supplied with electrical energy by, for example, batteries. As a result of the higher energy consumption, the portable devices have relatively shorter times of operation before the batteries require replacement and/or recharging.
Various attempts have been made to overcome this problem. For example, it has been suggested in “A Generalized Addressing Technique for RMS Responding Matrix LCDs,” 1988
International Display Research Conference
, pp. 80-85 to simultaneously applying a row selection voltage to more than one row electrode.
As shown in FIGS.
23
(
a
)-(
d
), a conventional method for driving a liquid crystal display by simultaneously selecting a group of more than one row electrode is shown. As shown therein, the n row electrodes are divided in j groups of row electrodes, each group comprising, for example, two row electrodes. In this example, row electrodes X
1
, X
2
; X
3
, X
4
; and X
n−1
, X
n
, each form a group of row electrodes.
Referring again to FIG.
23
(
a
), that figure illustrates row selection voltage waveforms applied simultaneously to both row electrodes X
1
and X
2
in time periods t
1
and t
2
and a voltage of zero is applied to row electrodes X
1
and X
2
in the remaining time periods of frame period F. Similarly, FIG.
23
(
b
) indicates the row selection voltage waveforms applied to row electrodes X
3
and X
4
, during time periods t
3
and t
4
and a voltage of zero is applied to row electrodes X
3
and X
4
in the other time periods of frame period F. FIG.
23
(
c
) illustrates the voltage waveform applied to column electrode Y
1
, and FIG.
23
(
d
) indicates the synthesized voltage waveform applied to the pixel 7
1,1
. Generally, t
1
, t
2
, . . . t
n
=69 &mgr;seconds, V
1
is approximately 17.6 volts and V
2
is approximately 2.3 volts.
As shown in the example of FIGS.
23
(
a
)-(
d
) every two row electrodes are selected in sequence. In the first selection sequence, two row electrodes, X
1
and X
2
, are selected and row selection voltage waveforms such as that shown in FIG.
23
(
a
) are applied to each row electrode. At the same time, the designated column voltage, which is described below, is applied to each column electrode, Y
1
to Y
m
. Next, row electrodes X
3
and X
4
are simultaneously selected with substantially the same type of waveform voltages as that described above. At the same time, the column voltages Y
1
to Y
m
are applied to each column electrode. One frame period represents the selection of all row electrodes, X
1
to X
n
. In other words, a complete image is displayed during one frame.
As will be explained hereinbelow, when h row electrodes are simultaneously selected, the voltage waveforms that apply the row electrodes described above use 2
h
row-select patterns. In the example illustrated in FIGS.
23
(
a
)-(
d
), the number of row electrodes simultaneously selected is two, thus the number of row select patterns is 2
2
or 4.
Moreover, the column voltages applied to each column electrode Y
1
to Y
m
provide the same number of pulse patterns as that of the row select pulse patterns. That is, there are 2
h
pulse patterns. These pulse patterns are determined by comparing the states of pixels on the simultaneously selected row electrodes i.e., whether the pixels are ON or OFF, with the polarities of the voltage pulses applied to row electrode.
In this example, as shown in the previously
Iino Shoichi
Ito Akihiko
Brier Jeffery
Seiko Epson Corporation
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