Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-08
2002-06-18
Nguyen, Chanh (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000
Reexamination Certificate
active
06407728
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device operable with an in plane switching mode and a method of driving the same.
It has been known that one of active material liquid crystal display devices is operable in in-plane switching mode, wherein liquid crystal molecules are switched in horizontal direction by applying an electric field to the liquid crystal molecules in the horizontal direction. The electric field is generated between two electrodes formed in a substrate in which thin film transistors are formed. This in-plane switching mode active material liquid crystal display device has, for example, been used for displays or monitors of computers such as note-type personal computers.
FIG. 1
is a circuit diagram illustrative of an equivalent circuit of a first conventional in-plane switching mode active material liquid crystal display device. The first conventional in-plane switching mode active material liquid crystal display device comprises a data driver circuit
1510
, a gate driver circuit
1520
and a liquid crystal display panel
1530
which is connected to the data driver circuit
1510
and the gate driver circuit
1520
. The liquid crystal display panel
1530
has an array of pixels
1540
which are aligned in matrix throughout the liquid crystal display panel
1530
. The liquid crystal display panel
1530
also has a plurality of data lines
1531
which extend in parallel to each other in a first direction for transmission of data to the pixels
1540
. The data lines
1531
are connected to the data driver circuit
1510
. The liquid crystal display panel
1530
also has a plurality of gate lines
1533
which extend in parallel to each other but in a second direction perpendicular to the first direction along which the data lines
1531
extend. The gate lines
1533
are provided for transmission of gate control signals to the pixels
1540
. The gate lines
1533
are connected to the gate driver circuit
1520
. The pixels
1540
are positioned at crossing points of the data lines
1531
and the gate lines
1533
. The liquid crystal display panel
1530
also has a single column-common electrode line
1532
which extends in parallel to each other but in the first direction perpendicular to the second direction along which the gate lines
1533
extend.
Each of the pixels
1540
is represented by a square-shaped broken line in FIG.
1
. Each of the pixels
1540
further comprises a pixel transistor
1541
, a storage capacitor
1542
, a pixel electrode
1543
and a column-common electrode
1544
. The pixel transistor
1541
comprises a thin film transistor formed in a substrate. The pixel transistor
1541
in each of the pixels
1540
has a gate electrode which is connected to corresponding one of the gate lines
1533
. The pixel transistor
1541
in each of the pixels
1540
has a source electrode which is connected to corresponding one of the data lines
1531
. The storage capacitor
1542
is connected between a drain electrode of the pixel transistor
1541
and a ground line. The pixel electrode
1543
in each of the pixels
1540
is connected to the drain electrode of the pixel transistor
1541
. The column-common electrode
1544
in each of the pixels
1540
is connected to the single column-common electrode line
1532
, so that an external voltage may be applied through the single column-common electrode line
1532
to the column-common electrode
1544
in each of the pixels
1540
. The data lines
1531
are driven by the data driver circuit
1510
. The gate lines
1533
are driven by the gate driver circuit
1520
.
FIG. 2
is a timing chart illustrative of waveforms of a horizontal synchronizing signal Hsync, a column-common electrode potential Com, a first data line potential D
1
of first one of adjacent two data lines, a second data line potential D
2
of second one of the adjacent two data lines, a first gate line potential G
1
of first one of adjacent two gate lines, and a second gate line potential G
2
of second one of the adjacent two gate lines to explain the driving method of the first conventional in-plane switching mode active material liquid crystal display device of FIG.
1
.
The following descriptions are operations of writing image signals into pixels of the first conventional in-plane switching mode active material liquid crystal display device of FIG.
1
. Pulse signals are sequentially outputted from output terminals of the gate driver circuit
1520
in synchronizing with the horizontal synchronizing signals Hsync of the image signal. The data driver circuit
1510
is operated to fetch the image signals with one horizontal time period unit in order to output the image signals onto the data lines
1531
. Each pulse signal outputted from the gate driver circuit
1520
is transmitted on one of the gate lines
1533
, whereby the pixel transistor
1541
having the gate electrode connected to the one of the gate lines
1533
turns ON, during which an image signal voltage Vvc outputted from the data driver circuit
1510
is applied through the pixel transistor
1541
into the pixel electrode
1543
. On the other hand, a column-common voltage Vcom is applied to the column-common electrode
1544
through the single column-common electrode line
1532
. Namely, the pixel electrode
1543
has the image signal voltage Vvc, whilst the column-common electrode
1544
has the column-common voltage Vcom. A potential difference of Vvc−Vcom is generated between the pixel electrode
1543
and the column-common electrode
1544
. Namely, the pixel
1540
has the potential difference of Vvc−Vcom, which generates an electric field to be applied to liquid crystal molecules positioned between the pixel electrode
1543
and the column-common electrode
1544
. The liquid crystal molecules are therefore switched.
The foregoing operations are repeated for one frame unit thereby to obtain a two-dimensional image.
The image signals to be applied to the pixel electrode are required to be changed in polarity with reference to the column-common electrode potential in every frame units. Namely the polarity inversion driving is carried out to the data driver circuit
1510
in order to obtain or secure a highly accurate intensity of the electric field applied to applied to the liquid crystal molecules. By contrast to the polarity inversion driving, if a direct current electric field would be applied to the liquid crystal molecules, an electrolysis of the liquid crystal molecules is caused to generate ions in the liquid crystal molecules, whereby the generated ions generate local electric fields which displaces the intensity of the electric field applied between the pixel electrode and the column-common electrode.
The above described in-plane switching mode active matrix liquid crystal display requires a higher driving voltage by 6 V than that of a twisted nematic mode active matrix liquid crystal display. In order to accomplish the polarity inversion driving, a high voltage of not less than 12 V is required to be applied to the liquid crystal panel.
Further, it is required for realizing intermediate gray scale display of full color with 256-gray scales that the accuracy of the voltage level applied to the pixel electrode is within ±several tens mV. The data driver circuit
1510
is required to have a high quality performance like that an output voltage range is not less than 12 V, and an error in voltage level of the output voltage is within ±several tens mV.
If the display is applied to the liquid crystal display panel having a resolution of extended graphics array (1024×768), the number of the output terminals of the data driver circuit is not less than 1024. It is thus required to suppress variations in output voltage level of those output terminals within ±several tends mV.
The above described conventional in plane switching mode active matrix liquid crystal display has he following problems.
The first problem is that i
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