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Claims  |
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What is claimed is:
1. A drive method for a liquid crystal device comprising the steps of:
(a) applying a scanning signal to each of a plurality of scanning
electrodes comprising a selection signal during a selection period and a
non-selection signal during a non-selection period; and
(b) applying a data signal to each of a plurality of signal electrodes
based on data representing an image having a gray scale to be displayed by
the liquid crystal device;
wherein step (a) further comprises the step of:
(1) grouping the plurality of scanning electrodes into p groups, wherein p
is an integer of at least two;
(2) applying the selection signal substantially simultaneously to the
plurality of the scanning electrodes in one of the p groups and applying
the non-selection signal substantially simultaneously to the plurality of
scanning electrodes in one of the p groups immediately after applying the
selection signal thereto and selecting a level of the selection signal
based on an orthogonal function, wherein the selection signal is
sequentially applied to succeeding groups of the scanning electrodes,
wherein the non-selection signal is sequentially applied to succeeding
groups of the scanning electrode groups immediately after applying the
selection signal thereto, wherein each of the scanning signals has N
selection periods and N non-selection periods per frame, wherein N is a
integer of at least two, and applying the selection signal to each of the
scanning electrodes in each of the N selection periods, and wherein the
orthogonal function has information for determining a level of the
selection signal; and
(c) applying a weighted voltage in accordance with the display data in each
of the selection periods.
2. A drive method according to claim 1, wherein a signal voltage weighted
according to the desired display data is applied to respective ones of the
signal electrodes to achieve a gray scale display.
3. A drive method according to claim 2,
wherein the display data comprises q bits, q being a positive integer,
wherein each of the N selection periods is divided into k intervals in
accordance with the q bits, and
wherein the signal voltage corresponding to the display data of each of the
q bits is applied to the signal electrodes in each of the k intervals to
achieve a gray scale display.
4. A drive method according to claim 2,
wherein the display data comprises q bits, q being a positive integer,
wherein each of the N selection periods is divided further into k portions,
k being a positive integer greater than q, and
wherein at least one of the k portions is allocated to the display data
corresponding to one of the bits to reduce the number of applied voltage
levels.
5. A drive method according to claim 2,
wherein the N selection periods are each divided further into k portions, k
being a positive integer, and
wherein a voltage value of the voltages applied to the signal electrodes in
the k portions are combined over a time duration to display the image
having the gray scale.
6. A drive method according to claim 1, wherein the display data comprises
a plurality of bits, and wherein the weighted voltage comprises a signal
voltage applied to respective ones of the plurality of signal electrodes
having a pulse width modulated in accordance with each of the plurality of
bits to display the image with the gray scale.
7. A drive method according to claim 1, wherein the image is displayed
during one frame period, and wherein a voltage applied to the signal
electrodes is modulated during an interval of plural frame periods to
display the image having the gray scale.
8. A drive method according to claim 1, wherein a scanning voltage weighted
according to the desired display data is applied to the scanning
electrodes to display the image having the gray scale.
9. A drive method according to claim 8,
wherein the display data comprises q bits, q being a positive integer, each
of the N selection periods is divided into k intervals in accordance with
the q bits, and
wherein a scanning voltage corresponding to the display data of each of the
q bits is applied to the scanning electrodes in each of the k intervals to
display the image having the gray scale.
10. A drive method according to claim 8,
wherein the display data comprises q bits, q being a positive integer,
wherein each of the N selection periods is divided into k intervals, k
being a positive integer greater than q, and
wherein at least one of the k intervals are allocated to the display data
corresponding to one of the q bits to reduce a number of applied voltage
levels.
11. A drive method according to claim 8,
wherein the N selection periods are each divided into k intervals, k being
a positive integer, and
wherein the voltage value of the voltages applied to the scanning
electrodes in the k intervals are applied for a predetermined duration to
display the image having the gray scale.
12. A drive method according to any of claims 2-11, wherein the polarity of
the voltages applied to the scanning electrodes is inverted in each frame.
13. A drive method according to claim 8, wherein the image is displayed
during one frame period and wherein the voltages applied to the scanning
electrodes are modulated during a period of plural frames to display the
image having the gray scale.
14. A drive method according to claim 1, wherein a number of voltage levels
applied to the signal electrodes is reduced by applying a virtual
selection signal to a virtual scanning electrode.
15. A drive method according to claim 1, wherein voltage waveforms applied
to each of the scanning electrodes and signal electrodes are applied in a
predetermined order, wherein the predetermined order is changed within
each frame period.
16. A drive method according to claim 1, wherein voltage waveforms applied
to each of the scanning electrodes and signal electrodes are applied in a
predetermined order, wherein the predetermined order is changed each
succeeding frame period.
17. A drive method according to claim 1, wherein the order of the signal
voltage waveforms applied to each of the signal electrodes is changed each
frame period.
18. A drive method according to claim 1, wherein each of the N selection
periods is further divided into x division periods, x being a positive
integer greater than 1, wherein one field is defined as selecting all of
the scanning electrodes during one division period, and wherein a frame
period is defined as the selection of the scanning electrodes every x
division periods.
19. A drive method according to claim 1, wherein each of the N selection
periods is further divided into z division periods, z being a positive
integer equal to the number of bits in the display data, wherein one field
is defined as selecting all of the scanning electrodes during one division
period, and wherein a frame period is defined as the selection of the
scanning electrodes every z division periods.
20. A drive method according to claim 1, wherein each of the N selection
periods is further divided into z division periods, z being a positive
integer greater than the number of bits in the display data, wherein one
field is defined as selecting all of the scanning electrodes during one
division period, and wherein a frame period is defined as the selection of
the scanning electrodes every z division periods.
21. A drive method according to claim 1, wherein the polarity of the
voltages applied to the scanning electrodes is inverted each frame.
22. A liquid crystal display apparatus comprising:
a liquid crystal matrix panel having n scannin*g electrodes and m signal
electrodes, wherein m is a positive integer and n is an integer of at
least two; and
a driving circuit
(a) for applying a scanning signal to each of the n scanning electrodes
comprising a selection signal during a selection period and a
non-selection signal during a non-selection period; and
(b) for applying a data signal to each of the m signal electrodes based on
data representing an image having a gray scale to be displayed by the
liquid crystal device;
wherein said driving circuit further:
(1) for grouping the plurality of scanning electrodes into p groups,
wherein p is an integer of at least two;
(2) for applying the selection signal substantially simultaneously to the
plurality of the scanning electrodes in one of the p groups and applying
the non-selection signal substantially simultaneously to the plurality of
scanning electrodes in one of the p groups immediately after applying the
selection signal thereto and selecting a level of the selection signal
based on an orthogonal function, wherein the selection signal is
sequentially applied to succeeding groups of scanning electrodes, wherein
the non-selection signal is sequentially applied to succeeding groups of
the scanning electrode groups immediately after applying the selection
signal thereto, wherein each of the scanning signals has N selection
periods and N non-selection periods per frame, wherein N is an integer of
at least two, and applying the selection signal to each of the scanning
electrodes in each of the N selection periods, and wherein the orthogonal
function has information for determining a level of the selection signal;
and
(3) for applying a weighted signal voltage weighted in accordance with
desired display data to respective ones of said signal electrodes in each
of the N selection periods to achieve a gray scale display.
23. A liquid crystal display apparatus comprising:
a liquid crystal matrix panel having n scanning electrodes and m signal
electrodes, wherein m is a positive integer and n is an integer of at
least two; and
a driving circuit
(a) for applying a scanning signal to each of the n scanning electrodes
comprising a selection signal during a selection period and a
non-selection signal during a non-selection period; and
(b) for applying a data signal to each of the m signal electrodes based on
data representing an image having a gray scale to be displayed by the
liquid crystal device;
wherein said driving circuit further:
(1) for grouping the plurality of scanning electrodes into p groups,
wherein p is an integer of at least two;
(2) for applying the selection signal substantially simultaneously the
plurality of the scanning electrodes in one of the p groups and applying
the non-selection signal substantially simultaneously to the plurality of
scanning electrodes in one of the p groups immediately after applying the
selection signal thereto and selecting a level of the selection signal
based on an orthogonal function, wherein the selection signal is
sequentially applied to succeeding groups of scanning electrodes, wherein
the non-selection signal is sequentially applied to succeeding groups of
the scanning electrode groups immediately after applying the selection
signal thereto, wherein each of the scanning signals has N selection
periods and N non-selection periods per frame, wherein N is an integer of
at least two, and applying the selection signal to each of the scanning
electrodes in each of the N selection periods, and wherein the orthogonal
function has information for determining a level of the selection signal;
and
(3) for applying a weighted scanning voltage weighted in accordance with
desired display data to respective ones of said scanning electrodes in
each of the N selection periods to achieve a gray scale display. |
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Claims |
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Description |
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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 of the electrodes in each group being simultaneously
selected each group being sequentially selected for achieving a gray scale
display.
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 FIG. 49
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.sub.1 -Y.sub.m are oriented on substrate 2 in the vertical
direction and a plurality of row electrodes X.sub.1 -X.sub.n are formed on
substrate 3 in substantially the horizontal direction to form a matrix.
Each intersection of column electrodes Y.sub.1 -Y.sub.m and row electrodes
X.sub.1 -X.sub.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 panel mentioned above. In such a
method, a selected voltage or non-selected voltage is sequentially applied
to each of row electrodes X.sub.1 -X.sub.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.sub.-X.sub.n is known as one frame period, indicated in FIGS. 43A-E as
time period F. Typically the frame period is approximate 1/60th 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.sub.1 -X.sub.n, a
data signal representing an ON or OFF voltage is applied to column
electrodes Y.sub.1 -Y.sub.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. 43A-E, a conventional multiplex drive
method of a simple matrix type liquid crystal and more specifically the
amplitude selective addressing scheme is shown therein. Such a
conventional drive method is not intended to provide the features of
achieving a gray scale display. FIGS. 43A-C show the row selection voltage
waveforms that are applied in sequence to row electrodes X.sub.1, X.sub.2
. . . X.sub.n, respectively. More particularly, in time period t.sub.1, a
voltage pulse having a magnitude of V.sub.1 is applied to row electrode
X.sub.1, and a voltage of zero is applied to electrodes X.sub.2 -X.sub.n ;
in time period t.sub.2, a voltage pulse having a magnitude of V.sub.1 is
applied to row electrode X.sub.2 and a voltage of zero is applied to
electrodes X.sub.1 and X.sub.3 -X.sub.n and in time period t.sub.n,
V.sub.1 is applied to row electrode X.sub.n and a voltage of zero is to
electrodes X.sub.1 -X.sub.n-1. In other words, a voltage pulse having a
magnitude of V.sub.1 is applied to only one row electrode X.sub.i in time
t.sub.i. Typically, t.sub.i is approximately 69 .mu.seconds and V.sub.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.sub.1 -t.sub.n or one frame period F.
FIG. 43D shows the waveform applied to column electrode Y.sub.1, and FIG.
43E shows the synthesized voltage waveform applied to the pixel 7.sub.1,1
formed at the intersection of the column electrode Y.sub.1 and the row
electrode X.sub.1. As shown therein, during time period t.sub.1, a voltage
pulse having a magnitude of V.sub.1 is applied to row X.sub.1 and a
voltage pulse of -V.sub.2 is applied to column electrode Y.sub.1.
Typically, V.sub.2 is approximately 1.6 volts. The resultant voltage at
pixel 7.sub.1,1 is (V.sub.1 -V.sub.2). This synthesized voltage is
sufficient to turn pixel 7.sub.1,1 to its ON state.
As noted above this conventional driving method does not display an image
having a gray scale. Furthermore, another 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
parent patent application Ser. No. 08/148,083, filed Nov. 4, 1993, is
directed to a method driving a liquid crystal panel comprising the steps
of sequentially selecting a group of a plurality of row electrodes during
a selection period, simultaneously selecting the row electrodes comprising
the group, and dividing and separating the selection period into a
plurality of intervals within one frame period.
In another 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 apply a row selection
voltage to more than one row electrode.
As shown in FIG. 45A-D, a conventional method for driving a liquid crystal
display is provided by simultaneously selecting a group of more than one
row electrode. 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.sub.1, X.sub.2 and X.sub.3
and X.sub.4, X.sub.5 and X.sub.6 form first and second groups of row
electrodes, respectively.
Referring again to FIG. 45A, that figure illustrates row selection voltage
waveforms applied simultaneously to both row electrodes X.sub.1, X.sub.2
and X.sub.3 in time periods t.sub.11 -t.sub.18 and a voltage of zero is
applied to row electrodes X.sub.1, X.sub.2 and X.sub.3 in the remaining
time periods of frame period F. Similarly, FIG. 45B indicates the row
selection voltage waveforms applied to row electrodes X.sub.4, X.sub.5 and
X.sub.6, during time periods t.sub.21 -t.sub.28 and a voltage of zero is
applied to row electrodes X.sub.4, X.sub.5 and X.sub.6 in the other time
periods of frame period F. FIG. 45C illustrates the voltage waveform
applied to column electrode Y.sub.1, and FIG. 45D indicates the
synthesized voltage waveform applied to the pixel 7.sub.1,1. Generally,
t.sub.11, t.sub.12, . . . t.sub.j,n =34.5 .mu.seconds, V.sub.1 is
approximately 17.6 volts and V.sub.2 is approximately 2.3 volts.
As shown in the example of FIGS. 45A-D, every three row electrodes are
selected in sequence. In the first selection sequence, two row electrodes,
X.sub.1, X.sub.2 and X.sub.3, are selected and row selection voltage
waveforms such as that shown in FIG. 45A 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.sub.1 to Y.sub.m.
Next, row electrodes X.sub.4, X.sub.5 and X.sub.6 are simultaneously
selected with substantially the same type of waveform voltages as that
described above. At the same time, the column voltages Y.sub.1 to Y.sub.m
are applied to each column electrode. One frame period represents the
selection of all row electrodes, X.sub.1 to X.sub.n. In other words, a
complete image is displayed during one frame.
As will be explained hereinbelow, when h row electrodes are simultaneously
elected, the voltage waveforms that apply the row electrodes described
above use 2.sup.h row-select patterns. In the example illustrated in FIGS.
45A-D, the number of row electrodes simultaneously selected is two, thus
the number of row select patterns is 2.sup.3 or 8.
Moreover, the column voltages applied to each column electrode Y.sub.1 to
Y.sub.m provide the same number of pulse patterns as that of the row
select pulse patterns. That is, there are 2.sup.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 described FIGS. 45A-D, when row
electrodes X.sub.1, X.sub.2 and X.sub.3 are selected and row voltages such
as those in FIG. 45A and FIG. 46A are applied thereto and when the pixels
on row electrodes X.sub.1, X.sub.2 and X.sub.3 are ON, ON and OFF,
respectively, as shown in FIG. 44, the voltage waveform applied the column
electrode is voltage waveform Y.sub.1 shown in FIG. 45C.
The above-mentioned column voltage waveform Y.sub.1 is determined as
follows. At first, each pixel simultaneously selected is defined to have a
first value of 1 when the voltage applied by the row electrode to the
corresponding selected pixel is positive or a first value of 0 when the
row electrode is negative. In the example shown in FIGS. 45A-D, the
voltage ON/OFF patterns applied to the three simultaneously selected row
electrodes X.sub.1, X.sub.2, and X.sub.3 are shown in the following table
using values of 1 and 0 for ON and OFF pixel states, respectively.
TABLE A
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X.sub.1 0 0 0 0 1 1 1 1
X.sub.2 0 0 1 1 0 0 1 1
X.sub.3 0 1 0 1 0 1 0 1
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Each of the selected pixels is defined to have a second value of 1 when the
display state is ON or a second value of 0 when display state is OFF. The
first value is compared to the second value bit-by-bit, the number of
mismatches, i.e., when the first value does not equal the second value, is
calculated. When the number of mismatches for the simultaneously selected
rows is zero, -V.sub.Y2 is applied; when 1, -V.sub.Y1 is applied; when 2,
V.sub.Y1 is applied; and when 3, V.sub.Y2 is applied. In this example the
ratio of V.sub.Y1 to V.sub.Y2 is 1:3.
For example, when the pulse waveforms shown in FIG. 45A are applied to row
electrodes X.sub.1, X.sub.2 and X.sub.3, a column voltage having the
waveform of Y.sub.1 is applied. For time period t.sub.11, the column
voltage is determined as follows. The pixels formed at the intersections
of column electrode Y.sub.1 and rows electrodes X.sub.1, X.sub.2 and
X.sub.3 are in the ON, ON and OFF states, respectively. For the purposes
of this discussion, these pixels will be referred to as the first, second
and third pixels, respectively. In other words, the first pixel has a
second value of 1, the second pixel has a second value of 1 and the third
pixel has a second value of 0 (zero) . Those pixels assume the first
values, as shown in Table A. Referring to the first pixel, since the first
value is 0 and the second value is 1, there is a mismatch. With regard to
the second pixel, the first value is 0 and the second value is 1, thereby
also forming a mismatch. Finally, referring to the third pixel, the first
value is 0 and the second value is also 0, thereby forming a match.
Accordingly, the number of mismatches is determined to be 2. Therefore, a
voltage of V.sub.Y1 is applied to the column electrode in time t.sub.11.
The row select pattern of the voltage applied to the row electrodes
X.sub.1, X.sub.2, and X.sub.3 in time t.sub.12 is OFF-OFF-ON. The number
of mismatches during this time period is three. Therefore, voltage
V.sub.Y2 is applied as the second pulse to column electrode Y.sub.1.
Similarly, V.sub.Y1 is applied as the third pulse, -V.sub.Y1 as the fourth
pulse. Thus the following pulses are, in sequence, -V.sub.Y2, V.sub.Y1,
-V.sub.Y1, -V.sub.Y1 are applied to the column electrode.
The next three row electrodes X.sub.4 -X.sub.6 are then selected, and when
the voltage shown in FIG. 47B is applied to these row electrodes X.sub.4
-X.sub.6, a column voltage of the voltage level corresponding to the
number of mismatches between the on/off states of the pixels at the
intersections of row electrodes X.sub.4 -X.sub.6 and the column electrode
and the on/off states of the voltage row select patterns applied to the
row electrodes X.sub.4 -X.sub.6 as shown in FIG. 45C is applied.
The voltage waveforms generated based on these values for application to
the row electrodes are shown in FIG. 46A. The waveform shown in FIG. 46A,
however, contains dispersions in the frequency component, which can result
in display uniformity when applied. In other words, the applied voltage
waveforms, which include the following different frequency components:
X1: 4.multidot..DELTA.t, 4.multidot..DELTA.t
X2: 2.multidot..DELTA.t, 4.multidot..DELTA.t, 2.multidot..DELTA.t
X3: 2.multidot..DELTA.t, 2.multidot..DELTA.t, 2.multidot..DELTA.t,
2.multidot..DELTA.t
Such differences in frequency appear to cause distortion of the displayed
image.
The waveforms modified by reordering the array to eliminate the bias in the
frequency component is shown in FIG. 46B. The prior art example shown in
FIG. 45A-D can also utilize these waveforms.
However, when a driving method, such as shown in FIG. 48A or B is used to
drive a liquid crystal display panel, the pulse width of each pulse
becomes narrower. That is particularly true when the number of
simultaneously selected row electrodes increases. In other words, there is
an exponential increase in the number of bit word patterns with each pulse
width becoming narrower. The narrower pulse width leads to possible
rounding when the waveform is applied to pixel and/or crosstalk may occur.
These distortions are particularly apparent when a gray scale display is
attempted.
In another example, values 1 and -1 are used for the positive and negative
selection pulses of the row voltage waveform, and -1 and 1 are used for
the ON and OFF display data states of pixel, respectively, and the column
voltage waveform is set according to the difference between the number of
matches and the number of mismatches, values of 1 or -1 can be used for
either, and the column voltage waveform can be set using only the number
of matches or the number of mismatches without calculating the difference
between the number of matches or the number of mismatches.
FIGS. 47A, A', B and C depict another example of a conventional method for
driving a liquid crystal display by simultaneously selecting a group of
more than one row electrode. 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.sub.1, X.sub.2 ;
X.sub.3, X.sub.4 ; and X.sub.n-1, X.sub.n, each form a group of row
electrodes.
Referring again to FIG. 47A, that figure illustrates row selection voltage
waveforms applied simultaneously to both row electrodes X.sub.1 and
X.sub.2 in time periods t.sub.1 and t.sub.2 and a voltage of zero is
applied to row electrodes X.sub.1 and X.sub.2 in the remaining time
periods of frame period F. Similarly, FIG. 47A'indicates the row selection
voltage waveforms applied to row electrodes X.sub.3 and X.sub.4, during
time periods t.sub.3 and t.sub.4 and a voltage of zero is applied to row
electrodes X.sub.3 and X.sub.4 in the other time periods of frame period
F. FIG. 47B illustrates the voltage waveform applied to column electrode
Y.sub.1, and FIG. 47C indicates the synthesized voltage waveform applied
to the pixel 7.sub.1,1. Generally, t.sub.1, t.sub.2, . . . t.sub.n =69
.mu. seconds, V.sub.1 is approximately 17.6 volts and V.sub.2 is
approximately 2.3 volts.
As shown in the example of FIGS. 47A, A' B and C every two row electrodes
are selected in sequence. In the first selection sequence, two row
electrodes, X.sub.1 and X.sub.2, are selected and row selection voltage
waveforms such as that shown in FIG. 47A 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.sub.1 to Y.sub.m.
Next, row electrodes X.sub.3 and X.sub.4 are simultaneously selected with
substantially the same type of waveform voltages as that described above.
At the same time, the column voltages Y.sub.1 to Y.sub.m are applied to
each column electrode. As explained above, one frame period represents the
selection of all row electrodes, X.sub.1 to X.sub.n.
As will be explained hereinbelow, when h row electrodes are simultaneously
selected, the voltage waveforms that apply the row electrodes described
above use 2.sup.h row-select patterns. In the example illustrated in FIGS.
47A, A', B and C the number of row electrodes simultaneously selected is
two, thus the number of row select patterns is 2.sup.2 or 4.
Moreover, the column voltages applied to each column electrode Y.sub.1 to
Y.sub.m provide the same number of pulse patterns as that of the row
select pulse patterns. That is, there are 2.sup.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 described FIGS. 47A, A' B and C
when row electrodes X.sub.1 and X.sub.2 are selected and row voltages such
as those in FIG. 47A and FIG. 48A are applied thereto and when the pixels
on row electrodes X.sub.1 and X.sub.2 are ON and OFF, respectively, the
voltage waveform applied the column electrode is voltage waveform Y.sub.a
shown in FIG. 48B. When the pixels are OFF and ON, respectively, the
column voltage waveform Y.sub.b is applied to the column electrode. In
another example, when the pixels are both ON, a voltage waveform Y.sub.c
is applied to the column electrode. Finally, when both pixels are OFF, the
a column voltage waveform Y.sub.d is applied to the column electrode.
The above-mentioned column voltage waveforms Y.sub.a -Y.sub.d are
determined as follows. At first, each pixel simultaneously selected is
defined to have a first value of 1 when the voltage applied by the row
electrode to the corresponding selected pixel is positive or a first value
of -1 when the row electrode is negative. Each of the selected pixels is
defined to have a second value of -1 when the display state is ON or a
second value of 1 when display state is OFF. The first value is compared
to the second value bit-by-bit, the difference between the number of
matches, i.e., when the first value equals the second value, and the
number of mismatches, i.e., when the first value does not equal the second
value, is calculated. When the difference between the number of matches
and mismatches for the simultaneously selected rows is two, V.sub.2 is
applied; when 0, V.sub.0 is applied; and when -2, -V.sub.2 is applied.
For example, when the pulse waveforms shown in FIG. 47A are applied to row
electrodes X.sub.1 and X.sub.2, a column voltage having the waveform of
Y.sub.a is applied. This column voltage is determined as follows. The
pixels formed at the intersections of column electrode Y.sub.1 and rows
electrodes X.sub.1 and X.sub.2 are in the ON and OFF states, respectively.
For the purposes of this discussion, these pixels will be referred to as
the first and second pixels, respectively. In other words, the first pixel
has a second value of -1 and the second pixel has a second value of 1.
During the period t.sub.a, the first pixel has a first value of -1 and the
second pixel has a first value of -1, since the row voltages X.sub.1 and
X.sub.2 are both -V.sub.1. Referring to the first pixel, since the first
value is -.sub.1 and the second value is -1, there is a match. With regard
to the second pixel, the first value is -1 and the second value is 1,
thereby forming a mismatch. The difference between the number of
mismatches and matches is 1-1 or zero. Therefore, a voltage of 0 (zero) is
applied to the column electrode in time t.sub.a. Next, concerning the
pulse waveforms of the time interval t.sub.b, the applied voltage of row
electrode X.sub.1 is positive and the applied voltage of row electrode
pulse X.sub.2 is negative. Using a similar analysis as described above,
the number of matches is zero and the number of mismatches is 2. Thus,
-V.sub.2 volts will be applied to the second half of time interval
t.sub.1.
As should now be apparent, the first values in time interval t.sub.c in
FIG. 47A are -1 and 1 because the applied voltage of row electrode X.sub.1
is negative and the applied voltage of row electrode X.sub.2 is positive.
When these are compared with the second values of the first and second
pixels of -1 and 1, the number of matches is two and the number of
mismatches is zero. The difference between the number of matches and the
number of mismatches is 2. Thus, the column voltage of V.sub.2 volts will
be applied in time interval t.sub.c.
In time interval t.sub.d, the applied voltage of row electrodes X.sub.1 and
X.sub.2 are both positive. Thus, the first values are 1 and 1. When
compared to the pixel states of -1 and 1, the number of matches is 1 and
the number of mismatches is 1, thus the difference between the number of
matches and the number of mismatches is zero. Accordingly, zero volts will
be applied to Y.sub.a for the time interval t.sub.d.
A summary of this analysis for time periods t.sub.a, t.sub.b, t.sub.c and
t.sub.d, is shown in Table B below:
TABLE B
______________________________________
t.sub.a
t.sub.b t.sub.c
t.sub.d
______________________________________
pixel
1 - ON
first value -1 1 -1 1
second value -1 -1 -1 -1
match yes no yes no
mismatch no yes no yes
2 - OFF
first value -1 -1 1 1
second value 1 1 1 1
match no no yes yes
mismatch yes yes no no
no. of matches
1 0 2 1
no. of mismatches
1 2 0 1
difference 0 -2 2 0
column voltage
0 -V.sub.2 V.sub.2
0
______________________________________
As is readily apparent, the column voltage Y.sub.a corresponds to the
column voltage pattern and is applied to the column to place the first
pixel in its ON state and the second pixel in its OFF state.
As for the other column voltage waveforms, Y.sub.b to Y.sub.d, the voltages
are selected under the same criteria as described above and are summarized
in Tables C, D and E hereinbelow:
TABLE C
______________________________________
t.sub.a
t.sub.b t.sub.c t.sub.d
______________________________________
pixel
1 - OFF
first value -1 1 -1 1
second value 1 1 1 1
match no yes no yes
mismatch yes no yes no
2 - ON
first value -1 -1 1 1
second value -1 -1 -1 -1
match yes yes no no
mismatch no no yes yes
no. of matches 1 2 0 1
no. of mismatches
1 0 2 1
difference 0 -2 2 0
column voltage 0 -V.sub.2
V.sub.2
0
Column Voltage Applied = Y.sub.b
______________________________________
TABLE D
______________________________________
t.sub.a
t.sub.b t.sub.c
t.sub.d
______________________________________
pixel
1 - ON
first value -1 1 -1 1
second value -1 -1 -1 -1
match yes no yes no
mismatch no yes no yes
2 - ON
first value -1 -1 1 1
second value -1 -1 -1 -1
match yes yes no no
mismat | | |
