Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-11-27
2003-07-15
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000, C345S098000, C345S100000, C345S204000, C345S211000
Reexamination Certificate
active
06593905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of controlling a liquid crystal display panel (LCD panel), and more particularly to a driving method and a circuit for recycling charges on display electrodes using adjacent scan line control signals, thereby reducing the power consumption and lowering the time required for charging and discharging of the display electrode.
2. Description of the Related Art
FIG. 1
(PRIOR ART) schematically shows an equivalent circuit of the conventional thin film transistor liquid display panel (hereafter referred to as TFT-LCD). As shown in the figure, the liquid crystal display panel is composed of the cross-connected data electrodes (D
1
, D
2
, D
3
, . . . and Dy) and the scan electrodes (G
1
, G
2
, . . . and Gx), each pair of the data electrodes and the scan electrodes can be used to control a display cell. For example, data electrode D
1
and scan electrode G
1
can be used to control the display cell
100
. As shown in the figure, the equivalent circuit of display cell
100
(the same for other display cells) include a thin film transistor
10
for controlling, a storage capacitor Cs and a liquid crystal capacitor Clc constructed by the display electrode and the common electrode. The gate and the drain of the thin film transistor
10
are connected to scan electrode G
1
and data electrode D
1
respectively. The video signal carried by the data electrode D
1
can be written to the display cell
100
by controlling the conducting state of the thin film transistor
10
using the scan signal carried by the scan electrode G
1
.
Scan driver
3
sends out the scan signal on the scan electrode G
1
, G
2
, . . . Gx sequentially, according to scan control signals. When one of the scan electrode is scanned, the thin film transistors corresponding to this scanned scan electrode are turned on and the thin film transistors corresponding to other scan electrodes are turned off. When the thin film transistors of the display cells on a row are turned on, data driver
2
sends corresponding video signal (gray level) to y display cells on the row through data electrode D
1
, D
2
, and Dy according to the image data to be displayed. When scan driver
3
finishes the scanning of the x scan lines, the display of a single video frame is done. The scanning of the scan lines described above is performed repeatedly, thereby displaying subsequent video frames.
According to the relationship between the common electrode voltage VCOM and the sent video signals on the data electrode, the polarities of the sent video signals on the data electrodes can be positive or negative relative to the common electrode voltage VCOM.
FIG. 2
(PRIOR ART) schematically shows the relationship between the common electrode voltage VCOM and the video signals of different polarities. As shown in
FIG. 2
, the positive video signals are positioned between common electrode voltage VCOM and the system high voltage VDD. According to the gray level represented by the positive video signal, the actual voltage is positioned between voltages Vp
1
and Vp
2
(in general, the closer the positive video signal to the common electrode voltage, the lower its gray level). In contrast, the negative video signals are positioned between common electrode voltage VCOM and the system low voltage VSS. According to the gray level represented by the negative video signal, the actual voltage is positioned between voltage Vn
1
and Vn
2
(Similarly, the closer the negative video signal to the common electrode voltage, the lower the gray level it corresponds to). When the positive video signal and the negative video signal corresponding to the same gray level have the same visual effect theoretically.
To prevent the liquid crystal molecules being subjected to a voltage bias of single polarity and therefore shortening the life of the liquid crystal molecules, a single display cell in the general TFT-LCD is driven by video signals of opposite polarities in the odd-numbered video frames and even-numbered video frames.
There are four driving schemes to achieve the above-described requirement, including frame-inversion, line-inversion, column-inversion and dot-inversion.
FIG. 3A
(PRIOR ART) shows the pattern of the polarities of the video signals received by the display cells in the frame-inversion driving scheme. As shown in
FIG. 3A
, two diagrams show the patterns of the polarities of the video signals received by each display cell in the area defined by data electrodes Dn−1, Dn, Dn+1 and scan electrodes Gm−1, Gm, Gm+1 in an odd-numbered video frame and an even-numbered video frame, respectively. In the left diagram, which-is corresponding to the odd-number video frame, all video signals are positive (denoted by “+”). On the other hand, in the right diagram corresponding to the even-numbered video frame, all video signals are negative (denoted by “−”). The frame-inversion driving scheme uses video signals of different polarities in adjacent video frames for all display cells.
FIG. 3B
(PRIOR ART) shows the pattern of the polarities of the video signals in the line-inversion driving scheme. The difference between FIG.
3
A and
FIG. 3B
lies in that the display cells of the same row (the same data line) in the same video frame receive video signals of the same polarity, however the display cells of the adjacent rows receive video signals of the opposite polarity.
FIG. 3C
(PRIOR ART) shows the pattern of the polarities of the video signals in the column-inversion driving scheme. The arrangement of the video signal polarities in
FIG. 3C
is similar to that in FIG.
3
B. The display cells of the same columns (the same data lines) in the same video frame receive the video signals of the same polarity, and the display cells of the adjacent columns receive video signals of the opposite polarity.
FIG. 3D
(PRIOR ART) shows the pattern of the polarities of the video signals in the dot-inversion driving scheme. In the dot-inversion driving scheme, if one display cell is driven by the positive video signal, the four display cells adjacent to this display cell are driven by the negative video signals.
FIG. 4
(PRIOR ART) shows a circuit diagram of a portion of the conventional liquid crystal display panel, including data electrodes (Dn−1, Dn and Dn+1), scan electrodes (Gm−1, Gm) and the corresponding display cells. When the scan signal appears on the scan electrode Gm−1, the thin film transistors connected to scan electrode Gm−1 are turned on and the video signals on data electrodes Dn and Dn+1 can be coupled to the display electrodes of the corresponding display cells. When the scan signal appears on scan electrode Gm, thin film transistors TFT
1
and TFT
2
connected to scan electrode Gm are turned on and the video signals on data electrodes Dn and Dn+1 can be coupled to the display electrodes P
1
and P
2
of the corresponding display cells.
Assume that the circuit shown in
FIG. 4
adopts the dot-inversion or column-inversion driving scheme for determining the polarities of various video signals.
FIG. 5
(PRIOR ART) shows a timing diagram of the signals in display electrodes P
1
and P
2
and scan electrodes Gm−1 and Gm. Pulses
20
and
21
in the scan electrode Gm−1 indicate the scanning of the scanning line corresponding to scan electrode Gm−1 in two adjacent video frames, respectively. Pulses
30
and
31
in the scan electrode Gm indicate the scanning of the scanning line corresponding to scan electrode Gm in the corresponding video frames, respectively. Each scan signals
20
,
21
,
30
and
31
can turn on the connected thin film transistors, thereby coupling the video signals on the data electrodes to the corresponding display electrodes.
The operation is described as follows by using scan electrode Gm as an example. Before the scan signal
30
is sent (before time t
1
), the video signal coupled to the display electrode P
1
is positive (between voltages Vp
1
and Vp
2
),
AU Optronics Corp.
Dharia Prabodh
Ladas & Parry
Shalwala Bipin
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