Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2003-05-16
2004-06-29
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169400, C345S076000, C345S079000
Reexamination Certificate
active
06756742
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a driving device and a driving method for a flat panel display. In particular, the present invention relates to a driving device and a driving method to decrease the switching frequency of a data chip, which provides the addressing voltage of the data electrodes of a flat panel display, by changing the scanning order of the scanning electrodes.
2. Description of the Related Art
Flat panel display comprises liquid crystal display (LCD), organic light-emitting display (OLED), and plasma display panel (PDP), etc. The advantages of the plasma display panel are small size, good display performance, and high reliability. Thus, PDP is often used in current electric equipment.
The current method of driving a plasma display panel is achieved through a plurality of subfield-display operations, which altogether constitute a full frame-display operation. For example, a picture frame in a plasma display panel with 256 gray levels may comprise eight subfields SF
0
~SF
7
as shown in FIG.
1
A. Each subfield-display operation comprises steps of resetting, addressing, and sustaining the display signal. Specifically, a plasma display panel is driven by a driving signal which comprises an erasing period, a addressing period, and a sustaining period. During the erasing period, residual ions of each illuminant cell of a PDP are erased using a voltage pulse having a pulse width shorter than a sustaining pulse. During the addressing period, external data are input using a voltage pulse having a voltage higher than a sustaining pulse of the erasing period. During the sustaining period, an AC voltage of a constant frequency is applied to avoid an ignition miss or incorrect display and to obtain a correct power margin.
FIG. 1B
shows a cross section of a conventional PDP structure, and
FIG. 1C
shows a schematic top view of the data and scanning electrodes of the same PDP. As shown in
FIG. 1B
, a PDP is constructed by joining a front glass substrate
1
with a rear glass substrate
2
, wherein data electrodes
3
for inputting external data are formed on the surface of the front glass substrate
1
that opposes the rear glass substrate
1
. Furthermore, a plurality of ribs
4
is defined on the data electrodes
3
to form illuminant cells. A plurality of sustaining electrodes
7
and scanning electrodes
8
in parallel direction, on the other hand, are formed on the surface of the rear glass substrate
2
that opposes the front glass substrate
1
, wherein the above-mentioned data electrodes
3
are formed perpendicular to both the sustaining electrodes
7
and the scanning electrodes
8
.
In addition, the surfaces of both the sustaining electrodes
7
and scanning electrodes
8
are coated with a dielectric layer
6
(such as a MgO layer) for protecting the surfaces of the electrodes. Furthermore, a fluorescent material
5
(such as phosphorous) is deposited between ribs (where the illuminant cells reside) for illumination to occur as soon as a voltage is applied. As shown in
FIGS. 1C and 1D
, a typical conventional plasma display panel comprises a plurality of row plasma display units (represented by L
1
~L
N
). Each row display unit has one of the plurality sustaining electrodes
7
(represented by a corresponding X
1
~X
N
), one of the plurality of parallel scanning electrodes
8
(Y
1
~Y
N
); for example, the first row display unit L
1
comprises the first sustaining electrode X
1
, and the first scanning electrode Y
1
. The plurality of illuminant cells of the first row display unit L
1
is driven by the X
1
, Y
1
simultaneously during the sustaining period. The plurality of data electrodes
3
(A
1
~A
M
) are disposed perpendicular to both the sustaining electrodes
7
(X
1
~X
N
) and the scanning electrodes
8
(Y
1
~Y
N
). Each of the sustaining electrodes
7
(X
1
~X
N
) is connected to the others and thereby the electrodes can be driven synchronously. In contrast, each of the scanning electrodes
8
(Y
1
~Y
N
) is separately connected from the other electrodes so as to actuate each of the electrodes independently. Thus, external data are input to each illuminant cell of the plasma display panel via the data electrodes
3
(D
1
~D
M
) by controlling both the sustaining electrodes
7
(X
1
~XN) and the scanning electrodes
8
(Y
1
~Y
N
).
FIG. 2
is a driving signal diagram of various electrodes of the plasma display panel shown in
FIGS. 1B
,
1
C, and ID, which are driven according to the method of a prior art. Accordingly, a plasma display panel is driven by a driving signal comprising an erasing period, an addressing period, and a sustaining period. During the erasing period, a very short pulse VW of a high voltage is applied to all of the sustaining electrodes
7
(including X
1
~X
N
), and all of the scanning electrodes
8
(including Y
1
~Y
N
) are connected to the ground Vg, so as to remove the remaining residual ions. At this point, no data electrodes
3
(including D
1
~D
M
) are yet driven. During the addressing period, a bias V
K
is applied to all of the sustaining electrodes
7
(including X
1
~X
N
), so the scanning electrodes
8
(Y
1
~Y
N
) can input external data sequentially via the data electrodes
3
(D
1
~D
M
) based on an addressing signal VY. At this point, the scanning electrodes
8
(Y
1
~Y
N
) are connected to a row address decoder (not shown in the figure) to receive an addressing signal, and the data electrodes
3
(D
1
~D
M
) are connected to external data to precede write operations. During the sustaining period, a periodic voltage pulse Vs is alternately applied to the sustaining electrodes
7
(X
1
~X
N
) and the scanning electrodes
8
(including Y
1
~Y
N
) to maintain the luminance of the illuminant cells.
During the addressing period, conventional method enables the scanning electrodes according to the subfield data in a fixed order, and the data chip provides the addressing voltage to the data electrodes corresponding to the driven scanning electrodes. However, the number of the switching cell of the data chip is directly proportional to the used power, because there is a parasitical capacitor Cd between the electrodes. When the voltage between the electrodes is raised to V
dd
, the consumed power is (½)C
d
V
dd
2
. Moreover, when the voltage between the electrodes returns to a low level, the consumed power is (½)C
d
V
dd
2
again. The consumed power increases the temperature of the data chip, especially when the subfield data is interleaved scanning, and the temperature may reaches 100° C., which wastes power and decreases the life of the data chip.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a driving device and a driving method for a flat panel display, which analyzes the characteristic of the subfield before addressing, and addresses the electrodes in a suitable order to decrease the voltage switching frequency of the data chip.
Moreover, another object of the present invention is to provide a driving device and a driving method for a flat panel display, which detects the output current of the power supply to the flat panel display. When the output current exceeds a predetermined value, the scanning order of the flat panel display is changed to decrease the output current, such that the voltage switching frequency of the data chip is decreased.
To achieve the above-mentioned object, the present invention provides a driving method for a flat panel display. First, an image signal is transformed to frame data. Next, a characteristic data of the frame data is obtained. Next, a scanning order of the first electrodes is determined according to the characteristic data. Next, scanning electrodes are driven in the scanning order during the addressing period. Finally, the data electrodes corresponding to the first electrodes are driven to perform the addressing operation.
Moreover, the present invention provides a driving method for a flat panel display comprising a power supply, first electrodes, and second electrod
Lyu Li-Ru
Tsai Chung-Kuang
Au Optronics Corp.
Vu David
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