Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-03-27
2001-11-20
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000
Reexamination Certificate
active
06320566
ABSTRACT:
This application claims the benefit of Korean Application P97-16428, filed in Korea on Apr. 30, 1997, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for driving a liquid crystal display device (LCD), and more particularly, to a driving circuit for dot inversion method using a line inversion mechanism and single bank mode.
2. Discussion of the Related Art
Cathode ray tubes (CRT) are widely used in display devices, such as television sets and display monitors for computers because CRTs can easily reproduce color and have high response speed. However, CRTs are too large and heavy, and consume too much power to be portable. Because of this, it is desirable to replace CRTs with other types of display. To overcome the above mentioned disadvantages of the CRT, a considerable amount of research and development has been conducted to design alternative types of display, such as liquid crystal displays, plasma display panels, and so on. Among them, a liquid crystal display is one of the most widely used devices. This is because the LCD does not have the bulky electron gun as is sed with the CRT, and the LCD can be applied to a thin television set that is mounted on the wall. Furthermore, the LCD can be applied to a portable display device, such as a note-book computer, because the power consumption is very low. Accordingly, the LCD can be driven by a battery.
The schematic structure of a conventional LCD is shown in
FIGS. 1 and 2
.
FIG. 1
shows the perspective view, and
FIG. 2
shows the structure of the lower panel. The LCD includes an upper panel
21
, which has a polarization plate
20
, a color filter
22
, and a common electrode
23
; a lower panel
25
, which has thin film transistors (TFTs)
13
and pixel electrodes
26
; and a liquid crystal material
24
inserted between the upper panel
21
and the lower panel
25
. The lower panel
25
further includes a plurality of scan lines
14
and a plurality of data lines
15
. The scan lines
14
and the data lines
15
perpendicularly cross each other. At the area surrounded by the neighboring scan lines and data lines, the pixel electrode
26
is formed. At each of the intersections of the scan lines and data lines, the TFT
13
is formed. Each of the area surrounded by the neighboring scan lines and data lines is called a pixel. Thus, one pixel includes the pixel electrode
26
, the common electrode
23
, and the liquid crystal material
24
in between. In addition, the lower panel
25
has a data driver IC
11
connected to the data lines
15
and a scan driver IC
10
connected to the scan lines
14
(FIG.
2
).
The TFT includes a gate electrode, a source electrode and a drain electrode. The gate electrode is connected to the scan line, the source electrode is connected to the data line, and the drain electrode is connected to the pixel electrode. The drain electrode and the source electrode are connected with a semiconductor layer. The TFT works as a switch that passes a data voltage applied to the data line to the drain electrode when a scan voltage is applied to the gate electrode through the scan line. The data voltage applied to the drain electrode is applied to the pixel electrode connected to the drain electrode.
As shown in
FIG. 2
, video data is applied from a controller
17
to the data driver IC
11
. The video data includes grey scaled data of red (R), green (G), and blue (B), which are applied to the corresponded pixel electrodes
26
. The data driver IC
11
latches the video data that come from the controller IC
17
until all the data of one line are inputted. Then, the video data of one line is transferred to the data line at once. At that time, the scan driver IC
10
applies a scan voltage to the scan line
14
connecting TFTs
13
to reproduce the video images at the pixel electrodes according to the scan signal of the controller
17
.
An example of the TFT is explained with reference to FIG.
3
.
FIG. 3
shows a cross-sectional view of the TFT. A gate electrode
30
is formed on the lower substrate
25
, and a gate insulating layer
31
is formed thereon. An active layer
34
made of amorphous silicon or polysilicon, for example, is formed on the gate insulating layer opposite the gate electrode
30
. Source and drain electrodes
32
,
33
are connected to both sides of the active layer
34
through an ohmic contact layer
36
(or n
+
layer). A protective layer
35
is formed over the resultant structure. Finally, pixel electrode
26
made of transparent conductive material, such as indium tin oxide (ITO), is formed on the protective layer
35
to be connected to the drain electrode
33
through a contact hole made in the protective layer
35
.
When the scan voltage is applied to a scan line, all the TFTs connected to the scan line are turned on. Accordingly, the video data applied to the data lines are sent to the pixel electrode through the TFTs. Therefore, a voltage is applied to each pixel electrode. On the other hand, constant voltage is applied to the common electrode. Accordingly, a voltage difference is formed between the pixel electrode and the common electrode, and an electric field is formed by the voltage difference. The arrangement (or orientation) of the liquid crystal molecules between the pixel and common electrodes is changed according to the electric field, modulating the amount of light transmission at the pixel. Thus, there are differences in light transmission between the pixel applied with a data voltage and the pixel not applied with a data voltage. Using these properties of pixels, the LCD works as a display device.
Generally, an LCD uses one of the line inversion, the column inversion, and the dot inversion methods, according to the phase of the applied signal voltage. In the line inversion, as shown in
FIGS. 4
a
and
4
b,
the polarity of voltage applied to the pixel electrodes is reversed at every scan line (row). In the column inversion, as shown in
FIGS. 5
a
and
5
b,
the polarity of voltage applied to the pixel electrodes is reversed at every data line (column). In the dot inversion method, as shown in
FIGS. 6
a
and
6
b,
the polarity of voltage is reversed at every row and column.
FIGS. 4
a,
5
a,
and
6
a
represent the phases of the common electrode voltages in a particular frame, and
FIGS. 4
b,
5
b,
and
6
b
represent the phases of the pixel electrode voltages in the same frame. In the next frame, these phases are reversed. The reason for changing the phase of signal is that if the applied voltages to the common and pixel electrodes are the same value in the entire respective electrodes, then the liquid crystal is heated, and the quality of the picture screen deteriorates.
In the line and column inversion method, a flicker problem occurs. The reason is the following. When a scan line signal is “HIGH,” all the TFTs connected to the scan line are turned on, and the data signals are sent to the pixel electrodes from the source electrodes connected to the data lines. Then, the liquid crystal is driven by the voltage difference between the pixel electrode and the common electrode. When the scan line signal is “LOW”, all the TFTs connected to the scan line are turned off. At that time, the voltage applied to the pixel electrodes remains in the pixel electrode, so the liquid crystal is still in the same condition, and the display signals are maintained. However, the stored signal voltage in the pixel electrode is reduced by &Dgr;V by coupling capacitors (Cgs), which are formed between the scan lines and data lines. Since the voltage in the pixel electrodes are not maintained constant, the display has a flicker problem.
In the dot inversion method, the flicker problem does not occur because the neighboring pixels have the different polarity in signal. If the first pixel is applied with a positive signal, the second pixel (neighboring pixels) is applied with a negative signal. At the next period, the first pixel has a negative signal and the second pixel has a positiv
Kumar Srilakshmi
LG Electronics Inc.
Morgan & Lewis & Bockius, LLP
Saras Steven
LandOfFree
Driving circuit for liquid crystal display in dot inversion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Driving circuit for liquid crystal display in dot inversion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Driving circuit for liquid crystal display in dot inversion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2597817