Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-10-12
2004-07-13
Eisen, Alexander (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S211000
Reexamination Certificate
active
06762737
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tone display voltage generating device for supplying a tone display voltage to a tone display element such as a liquid crystal panel and a plasma display panel, and also relates to a tone display device including such a tone display voltage generating device. Particularly, the invention relates to a tone display voltage generating device which switches modes of charging load capacitors of the tone display element via a selecting circuit such as a DA converter, between a rapid charging mode which utilizes a low output impedance circuit such as a buffer and a power-efficient charging mode which does not utilize the buffer, and also relates to a tone display device including such a tone display voltage generating device.
BACKGROUND OF THE INVENTION
FIG. 13
is a block diagram showing an arrangement of a liquid crystal display device of the TFT (Thin Film Transistor) system, which is a representative of the active-matrix variety.
The liquid crystal display device includes a liquid crystal display section and a liquid crystal driving unit (liquid crystal driving circuit) for driving the liquid crystal display section. The liquid crystal display section has a liquid crystal panel
901
of the TFT system. The liquid crystal panel
901
includes a plurality of display unit elements (pixels) which are disposed in a matrix pattern, and a counter electrode (common electrode)
906
.
The liquid crystal driving unit, on the other hand, includes a source driver
902
and a gate driver
903
, each having IC (Integrated Circuit) chips, and a controller
904
and a liquid crystal driving power supply
905
.
The source driver
902
and the gate driver
903
are mounted by a common mounting method in which a TCP (Tape Carrier Package) having the IC chips on a film with a predetermined wiring pattern is mounted on ITO (Indium Tin Oxide) terminals which extend from inside toward the periphery of the liquid crystal panel
901
. In other cases, the IC chips are directly mounted by heat-bonding on the ITO terminals of the liquid crystal panel
901
via an ACF (Anisotropic Conductive Film).
Further, for miniaturization of the liquid crystal display device, the controller
904
, the liquid crystal driving power supply
905
, the source driver
902
, and the gate driver
903
may be packaged into a single chip, or two to three chips. These members are shown in separate form in
FIG. 13
according to their functions.
The controller
904
outputs digital display data (e.g., video signals of R (Red), G (Green), and B (Blue)) indicated by D in FIG.
13
and various control signals indicated by S
1
in
FIG. 13
to the source driver
902
, and outputs various control signals indicated by S
2
in
FIG. 13
to the gate driver
903
. The control signals supplied to the source driver
902
chiefly include a horizontal synchronize signal (latch signal Ls), a start pulse signal, and a clock signal for the source driver. The control signals supplied to the gate driver
903
chiefly include a vertical synchronize signal, and a clock signal for the gate driver. Note that, power supplies for driving the IC chips (gate driver ICs, source driver ICs) are omitted in FIG.
13
.
Further, the liquid crystal driving power supply
905
is for supplying a liquid crystal panel display voltage to the source driver
902
and the gate driver
903
. As the term is used herein, the liquid crystal panel display voltage refers to a reference voltage for generating a tone display voltage.
Externally inputted display data are inputted to the source driver
902
via the controller
904
in the form of display data D of a digital signal. The source driver
902
samples the inputted display data D in a time sequential manner and stores the sampled data before converting it into a tone display voltage by DA (Digital-Analog) conversion in synchronism with a horizontal synchronize signal (latch signal Ls) which is sent from the controller
904
.
The source driver
902
then outputs the resulting tone display analog voltage (tone display voltage) after the DA conversion through the liquid crystal driving voltage output terminals to source signal lines
1004
(see
FIG. 14
) which are provided in the liquid crystal panel
901
.
The following describes a configuration of the liquid crystal panel
901
with reference to FIG.
14
. The liquid crystal panel
901
includes pixel electrodes
1001
, pixel capacitors
1002
, TFTs
1003
as the switching element for switching ON/OFF a voltage applied to the pixels, the source signal lines
1004
, gate signal lines
1005
, and a counter electrode
1006
(corresponds to the counter electrode
906
of
FIG. 13
) of the liquid crystal panel. Note that, in
FIG. 14
, the area indicated by A corresponds to the display unit element of a single pixel.
To the source signal lines
1004
from the source driver
902
of
FIG. 13
is applied a tone display voltage of an intensity according to the display brightness of a target pixel. Meanwhile, to the gate signal lines
1005
from the gate driver
903
of
FIG. 13
is applied a scanning signal, so that the plurality of TFTs
1003
which are disposed in a vertical direction (i.e., direction of extension of the source signal lines
1004
) are switched ON one after another.
While the TFTs
1003
are ON, the tone display voltage is applied from the source signal lines
1004
to the pixel electrodes
1001
which are connected to the drain of the TFTs
1003
. This sets off storing charge in the pixel capacitors
1002
between the pixel electrodes
1001
and the counter electrode
1006
. The TFTs
1003
are then switched OFF (non-select state) at the end of the selection by the gate signal lines
1005
, thus maintaining the applied voltage to the pixel capacitors
1002
. The transmission of light at each display unit element (pixel) is thus varied by this ON/OFF operation according to the level of the applied tone display voltage, thus realizing intended tone display.
FIG.
15
and
FIG. 16
show exemplary waveforms of liquid crystal driving voltages respectively applied to the source signal lines
1004
, the gate signal lines
1005
, and the pixel electrodes
1001
of the liquid crystal panel
901
of FIG.
14
. In FIG.
15
and
FIG. 16
, indicated by
1101
and
1201
are waveforms of the tone display voltage which is outputted from the source driver
902
to the source signal lines
1004
. Further, indicated by
1102
and
1202
are voltage waveforms of the scanning signal outputted from the gate driver
903
to the gate signal lines
1005
for controlling ON/OFF of the TFTs
1003
. Note that, the TFTs
1003
become ON when
1102
or
1202
is at High level, and become OFF when
1102
or
1202
is at Low level.
Further,
1103
and
1203
indicate a potential of the counter electrode
1006
(see FIG.
14
), and
1104
and
1204
are waveforms of a voltage applied to the pixel electrodes
1001
. The following explains how the voltage waveform
1104
(see FIG.
15
and elsewhere) applied to the pixel electrodes
1001
is varied with respect to a given pixel.
First, the TFT
1003
is switched ON when the scanning signal
1102
is at High level, and the pixel capacitor
1002
starts charging (i.e., application of the tone display voltage
1101
). Then, the TFT
1003
is switched OFF as the scanning signal becomes Low level when the voltage of the pixel capacitor
1002
reaches a predetermined voltage level. This voltage level, corresponding to the stored charge in the pixel capacitor
1002
, is maintained until the scanning signal returns to High level. Note that, the voltage waveform indicated by
1204
in
FIG. 16
is also varied in this manner.
Note that, the voltage applied to a liquid crystal material (not shown) is the potential difference (voltage) between the pixel electrode
1001
and the counter electrode
1006
, which is indicated by the areas of oblique lines in FIG.
15
and FIG.
16
.
Further, FIG.
15
and
FIG. 16
are different in the voltage values of the tone display voltages (
1101
,
1201
) appli
Kajihara Noriyuki
Katsutani Masafumi
Watanabe Toshio
Birch & Stewart Kolasch & Birch, LLP
Eisen Alexander
Sharp Kabushiki Kaisha
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