Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-07-08
2002-12-31
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S092000, C345S094000
Reexamination Certificate
active
06501455
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a driving device and driving method of a liquid crystal display device for improving display quality of a liquid crystal display device of a simple matrix type.
BACKGROUND OF THE INVENTION
In a conventional liquid crystal display device of a simple matrix type, as shown in
FIG. 10
, a segment side driving circuit (segment driver)
72
and a common side driving circuit (common driver)
73
are connected to a liquid crystal panel
71
. To the segment side driving circuit
72
and the common side driving circuit
73
are connected a power source circuit
74
and a controller
75
. The power source circuit
74
supplies power to the segment side driving circuit
72
and the common side driving circuit
73
. The controller
75
sends various control signals to the segment side driving circuit
72
and the common side driving circuit
73
.
The controller
75
gives the segment side driving circuit
72
display data, a data latch clock for taking in the display data, a horizontal synchronizing signal, and an alternating signal for driving the liquid crystal panel
71
in AC. The controller
75
gives the common side driving circuit
73
a horizontal synchronizing signal, an alternating signal, and a vertical synchronizing signal for recognizing a start of a screen.
The power source circuit
74
supplies voltages of V
BH
and V
BL
to the segment side driving circuit
72
, and voltages of V
H
, V
C
, and V
L
to the common side driving circuit
73
. The liquid crystal panel
71
constitutes a simple matrix arrangement by segment electrodes X
1
, X
2
, X
3
, . . . , and X
m
and common electrodes Y
1
, Y
2
, Y
3
, . . . , and Y
n
, and a liquid crystal cell
76
constitutes a pixel at the intersection of the segment electrodes and the common electrodes.
FIG. 11
shows an internal structure of the conventional segment side driving circuit
72
. The segment side driving circuit
72
includes a shift register
77
, a data latch
78
, a line latch
79
, a level shifter
80
, and a liquid crystal driving output circuit
81
. In the case where the segment side driving circuit
72
has, for example,
240
outputs, the display data of
240
lines are serially inputted to the shift register
77
in synchronization with the data latch clock. The display data then are converted into parallel data in the shift register
77
, and are latched in the data latch
78
and accumulated therein.
When data of the number of column electrodes of the liquid crystal panel
71
are accumulated, the horizontal synchronizing signal (LP) is inputted, and the display data accumulated are latched by the line latch
79
. The display data then are converted by the level shifter
80
from a logic voltage level to a liquid crystal driving voltage level to be inputted to the liquid crystal driving output circuit
81
. The liquid crystal driving output circuit
81
outputs a driving output voltage to the segment electrodes X
1
, . . . , and X
240
of the liquid crystal panel
71
in accordance with the display data inputted from the level shifter
80
and in accordance with the alternating signal (FR).
FIG. 12
shows operations of the prior art. For convenience, the explanation will be given through the case where the number of common electrodes Y (scanning electrodes) is, for example, seven, that is, the case where the alternating signal is switched per seven scanning periods.
A common output voltage V
Y
applied to the common electrodes Y as scanning electrodes receives the vertical synchronizing signal and outputs, in accordance with the horizontal synchronizing signal and the alternating signal from a head line, either V
H
level or V
L
level when the electrodes are selected, and outputs V
C
level when the electrodes are not selected (non-select period). A segment output voltage V
X
applied to the segment electrodes X as data electrodes is selected as one of V
BH
and V
BL
levels in accordance with the display data and the alternating signal, and the whole output of a single scanning electrode is applied in parallel to the segment electrodes X.
In the liquid crystal panel
71
, a potential difference between the segment electrodes X and the common electrodes Y is applied to each pixel, and display or non-display is decided in accordance with an effective value of the potential difference in a single frame period, which is the time required to display one screen. In the prior art, the display color or gradation on the liquid crystal panel
71
is slightly different depending on display data or display pattern even by comparison within the same ON display or OFF display.
The following describes one example of luminous non-uniformity generated by display data.
{circle around (1)} As shown in
FIG. 13
, in the case of a whole screen ON display, the segment output voltage from each segment side driving circuit
72
is maintained at a constant voltage level unless the alternating signal is changed.
The effective voltage V
effA
of voltage V
A
applied to the liquid crystal cell
76
as a pixel of the liquid crystal panel
71
is represented by a difference between a potential of a segment output waveform and a potential of a common output waveform.
{circle around (2)} As shown in
FIG. 14
, in the case of a stripe display in which display data repeats ON and OFF per scanning line, the segment output voltage from each segment side driving circuit
72
is outputted with alternating and repeating V
BH
and V
BL
levels per fall of the horizontal synchronizing signal even when the alternating signal is not changed.
The effective voltage V
effB
of voltage V
B
applied to the liquid crystal cell
76
as a pixel of the liquid crystal panel
71
is represented by a difference between a potential of a segment output waveform and a potential of a common output waveform.
The difference between {circle around (1)} and {circle around (2)} is that the number of changes of the output level of the segment output waveform per unit time is different. When the output level changes, the output waveform is blunted by such factors as the capacitance of the liquid crystal cell
76
, the electrode resistance of the electrodes of the liquid crystal panel
71
, and the output resistance of the driving circuits
72
and
73
, and therefore when the number of changes of the output level is large, the effective voltage is reduced by blunted waveform.
Thus, even when there are the same numbers of ON display pixels and OFF display pixels, the effective voltage V
effB
, in which the number of changes of the output level of the segment output waveform is made larger, satisfies the relationship of V
effB
<V
effA
relative to the effective voltage V
effA
. As a result, by this reduction in effective voltage, luminous non-uniformity called shadowing is generated on the display screen.
The following describes an example of luminous non-uniformity generated when the alternating signal is switched.
{circle around (3)} As shown in
FIG. 15
, in the case of a whole screen ON display in which the alternating signal is switched at least once in a single frame period, the segment output voltage from the segment side driving circuit
72
is outputted with alternating and repeating V
BH
and V
BL
levels in accordance with the alternating signal. When the alternating signal is switched, all the segment output voltages are switched at once from (a) V
BH
to V
BL
or from (b) V
BL
to V
BH
. Here, distortion due to a voltage shift is generated on the common electrodes Y, which are scanning electrodes facing the segment electrodes X with the liquid crystal therebetween, in accordance with the ratio of the change [(a) and (b)] in the segment electrodes X.
The effective voltage V
effC
of voltage V
C
applied to the liquid crystal cell
76
which is a pixel of the liquid crystal panel
71
is represented by a difference between a potential of the segment output waveform and a potential of the common output waveform.
{circle around (4)} As shown in
FIG. 16
, in the case of a partially OFF block dis
Birch Stewart Kolasch & Birch
Hjerpe Richard
Nguyen Kimnhung
Sharp Kabushiki Kaisha
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