Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-09-03
2004-05-04
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S099000
Reexamination Certificate
active
06731266
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a display device, and an apparatus and method for driving the display device. More particularly, the present invention relates to a thin film transistor liquid crystal display (TFT-LCD), and an apparatus and method for driving the TFT-LCD.
(b) Description of the Related Art
TFT-LCDs apply an electric field to liquid crystal material having anisotropic dielectricity and injected between two substrates to form a liquid crystal layer. The two substrates are arranged substantially in parallel having a predetermined gap therebetween, and the amount of light permeating the substrates is controlled by the intensity of the electric field applied to the liquid crystal material. Because of the many advantages of the TFT-LCD—low power consumption, thin profile and low weight, high resolution and others—the CRT, which is presently the most widely used display configuration, is being replaced by this flat panel display technology in many areas.
FIG. 1
shows a schematic view of a general TFT-LCD. The TFT-LCD includes an LCD panel
10
, a gate driver
20
, a data driver
30
, and a timing generator
40
. A plurality of gate lines G are formed on the LCD panel
10
, and a plurality of data lines D are formed insulated from and crossing the gate lines G. A TFT
12
is formed in each pixel defined by the crossing of gate lines G and the data lines D. A gate electrode, source electrode, and drain electrode of each TFT
12
are connected respectively to one of the gate lines G, one of the data lines D, and a pixel electrode (not shown). Liquid crystal material is injected between a substrate (TFT substrate) on which the above elements are formed and a substrate (common electrode substrate) on which are formed common electrodes. The two substrates and the liquid crystal material injected between the two substrates act as a capacitor Cl.
The gate driver
20
applies a gate ON/OFF voltage to the gate lines G to turn the TFTs ON or OFF. The gate ON voltage is applied sequentially to one of the gate lines G such that the TFTs connected to the gate lines G are turned ON in sequence. Further, the data driver
30
applies a gray voltage to the data lines D. Finally, the timing generator
40
receives from a graphic controller (not shown) a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a clock signal CLK, and a data signal DATA, and outputs a variety of timing control signals to the gate driver
20
and the data driver
30
.
The operation of the TFT-LCD structured as in the above will be described hereinafter.
The gate ON voltage is applied to the gate electrodes via the gate lines G such that the TFTs
12
are turned ON, after which the gray voltages, representing image signals, are applied to the source electrodes through the data lines D and then transmitted to the drain electrodes. As a result, the gray voltages are transmitted to the pixel electrodes, and electric fields are formed by a potential difference between the pixel electrodes and the common electrodes. An intensity of the electric field is controlled by the magnitude of the gray voltage, and the amount of light permeating the substrates is determined by this level of the electric field intensity.
As the size of the conventional TFT-LCD increases, the increased parasitic capacitance of the data lines prevents the gray voltages from sufficiently charged to the data lines. As a result, an inadequate gray voltage is transmitted to each of the pixels. To improve charge characteristics of the data lines, a method of precharging each data line to a predetermined voltage level is used in a conventional TFT-LCD.
In the conventional TFT-LCD, image data corresponding to an (n)th horizontal line (pixel line) are sampled and the sampled data are written on each of the data lines. When writing of the sampled (n)th data, image data corresponding to an (n+1)th horizontal line are sampled. Data lines are precharged in an interval between data writing times (data enable intervals) of the (n)th horizontal line and the (n+1)th horizontal line.
U.S. Pat. Nos. 5,426,447 and 5,510,807 disclose the above data line precharging methods. In these inventions, the data lines are precharged in an interval (i.e. invalid data interval) between the data enable interval of the (n)th horizontal line and the data enable interval of the (n+1)th horizontal line as described above. Also, a block addressing method is used in these inventions. In block addressing, a single pixel line is divided into blocks, each having many data lines, and each block is sequentially selected. For example, in a display device having 640 data lines, after the data lines are divided into 10 blocks each having 64 data lines, each block is selected within a single horizontal interval such that image data are written to the data lines within the selected block.
FIG. 2
shows a diagram used to describe the conventional precharging method in which precharging is performed in the interval (i.e., the invalid data interval) between the data enable intervals of the (n)th horizontal line and the (n+1)th horizontal line. A valid data interval shown in
FIG. 2
refers to the interval during which sampled image data is written on one horizontal line. In the conventional precharging method, precharging is performed only between valid data intervals (data enable intervals). That is, precharging is performed during invalid data intervals P
1
and P
2
. Accordingly, if the invalid data intervals P
1
and P
2
are not long enough, various problems may result.
Namely, in the conventional precharging method, since all the data lines must be precharged to a desired voltage level within the relatively short precharging interval, an extremely large amount of current is necessary for precharging, giving much stress to a current driving capability of the system. For example, in a color XGA display having 1024×3 (R,G,B) data lines, if a parasitic capacitance of each data line is 80 pF, a large capacitance of 1024×3×80 pF=245.7 nF must be charged within a maximum allowable time of approximately 4.6 &mgr; sec to one horizontal line. Further, in the conventional precharging method, since precharging is performed in the intervals (invalid data intervals) between adjacent data enable intervals, if adjacent data intervals overlap without invalid data intervals, data lines can not be precharged.
On the other hand, a method is used in larger TFT-LCDs in which after gate blocks are selected, gate ON signals are applied to each gate line within the selected block. Such a TFT-LCD structure is disclosed in U.S. Pat. Nos. 5,028,916, 4,714,921, and 5,426,447. However, these inventions require many bus lines in a gate driver structure, increasing a circuit area of the gate drivers and resulting in line open defects during the manufacture of the gate driver.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a display device, and an apparatus and a method for driving the display device that reduce a current level needed for precharging, allowing a high degree of margin for a precharging signal generator design, and making it possible to be applied to systems having a limited valid data interval.
It is another object of the present invention to provide a display device, and an apparatus and a method for driving the display device that reduce the number of required bus lines and a circuit area of a gate driver, thereby preventing line defects.
To achieve the above objects, the present invention provides a display device (e.g., a liquid crystal display), and an apparatus and a method for driving the display device. The LCD includes an LCD panel comprising a plurality of gate lines, a plurality of data lines insulated from and intersecting the gate lines, and a plurality of TFTs each having a gate electrode connected to one of the gate lines and a source electrode connected t
McGuireWoods LLP
Piziali Jeff
Samsung Electronics Co,. Ltd.
Shalwala Bipin
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