Electro-luminescence display with divided power supply lines

Details Electro-luminescence display with divided power supply lines Electro-luminescence display with divided power supply lines

2000-08-15

2002-04-30

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Plural power supplies

Plural cathode and/or anode load device

C345S060000

Reexamination Certificate

active

06380688

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electro-luminescence display (ELD), and more particularly to an ELD wherein a voltage supply line is divided into a plurality of voltage supply lines, and thereby reduce the number of pixels connected to each voltage supply line.
2. Description of the Related Art
An ELD is a device that is luminous by recombining electrons injected from an external source to a luminescent layer. The luminescent layer can be made from electro-luminescent (EL) materials with holes.
Because the ELD is luminous by the recombination of the injected electrons and holes, a back light is not required. This permits a display panel to be thinner and allows power consumption to remain low.
As a result, ELD has been the subject of growing interest in the field of displays. In particular, an organic ELD, in which the luminescent layer is formed from organic EL materials has received attention due to its advantages. The advantages include requiring a low driving voltage, having a high luminous efficiency, and allowing manufacture by a low temperature process.
typical active ELD has a number of scanning electrode lines crossing a number of data electrode lines. The ELD also includes a number of pixels, each of which is formed at the crossing. A voltage supply line is also supplied to each pixel, and the voltage supply lines are insulated from both the scanning electrode and data electrode lines. Each pixel includes a switching device comprising a thin film transistor (TFT), a driver, a storage capacitor, and an EL device.
FIG. 1
is a circuit diagram of a pixel array of a conventional ELD. In
FIG. 1
, the active matrix array has M×N pixels
10
, where M and N are integers. Each pixel
10
includes a switching transistor Q
s
, a driving transistor Q
d
, a capacitor C, and an EL device E
d
.
A gate of the switching transistor Q
s
is connected to a scanning electrode line
12
and a source of Q
s
is connected to a data electrode line
14
. A drain of Q
s
. is connected to a gate of the driving transistor Q
d
. A source of Q
d
is connected to a first voltage supply V
dd
via a first power supply line
16
, and a drain of Q
d
is connected to an anode of the EL device E
d
.
A cathode of the EL device E
d
is connected to a second voltage supply V
ss
via a second power supply line
18
. It should be noted that all connections to V
ss
are common to all EL devices E
d
. The EL device E
d
includes at least one luminescent layer (not shown) made from an organic EL material, between the anode and the cathode.
Finally, the capacitor C is connected between the gate and the source of the driving transistor Q
d
as shown.
operation of the conventional ELD having the configuration as shown in
FIG. 1
is as follows. A desired row of pixels is selected by applying a signal to a corresponding scanning electrode line
12
. This applies a voltage to the gates of the desired switching transistors Q
s
to turn on the selected switching transistors Q
s
.
Then a desired pixel
10
is selected by applying a signal to a corresponding data electrode line
14
. This applies a voltage to the gate of the desired driving transistor Q
d
to turn on the selected driving transistor Q
s
.
When the driving transistor is turned on, current is allowed to flow between the first and second voltage supplies V
dd
and V
ss
through the EL device E
d
. This in turn allows the EL device E
d
to become luminous by the recombination of electrons and holes in the luminescent layer.
The capacitor C maintains the data signal level until the next time the data signal is applied.
FIG. 2
is a schematic diagram of the conventional ELD. The conventional ELD includes a pixel array
20
, a data driving circuit
21
, a gate driving circuit
23
, first and second voltage supply terminals
25
and
27
, and first and second power supply lines
29
and
31
.
The pixel array
20
has the configuration as shown in FIG.
1
. The array
20
is arranged to be electrically connected to the data driving circuit
21
and the gate driving circuit
23
at the periphery thereof (not shown). The data driving circuit
21
and the gate driving circuit
23
are connected to the data electrode lines
14
and the scanning electrode lines
12
, respectively, which are in turn connected to the pixel array
20
, as shown in FIG.
1
.
The first and second voltage supplies V
dd
and V
ss
are applied to the first and second voltage supply terminals
25
and
27
, respectively, which are in turn connected to the first and second power supply lines
29
and
31
, respectively, as shown in FIG.
2
. And as shown in
FIG. 1
, the first and second power supply lines are connected to each pixel
10
of the pixel array
20
. It should be noted again that the cathodes of EL devices E
d
serve as a common electrode.
When a particular pixel
10
of the conventional ELD is driven, the pixel
10
receives the first and second supply voltages V
dd
and V
ss
through the first and second voltage supply terminals
25
and
27
, respectively. As a result, current flows through the first and second power supply lines
29
and
31
, again respectively. Only a minute amount of current is required to make the pixel
10
luminous.
However, the conventional ELD suffers from at least the following problem. Even though each pixel requires a small amount of current, the sum of current required to drive all pixels can be significant. It can be significant enough to generate significant amounts of heat and thus to melt the supply lines and damage the luminescent layers of the pixels. In both cases, the reliability of the ELD is compromised. This problem becomes more acute as the ELD becomes larger and as the resolution of the display is increased.
SUMMARY OF THE INVENTION
Accordingly, is an object of the present invention to provide an electro-luminescence display capable of preventing or minimizing heat generation caused by a current flowing through the first and second power supply lines, and thereby improve its reliability.
To achieve these and other objects of the invention, an electro-luminescence display according to an embodiment of the present invention includes a pixel array having a number of pixels. Each pixel includes an electro-luminescence device having a luminescent layer made from an electro-luminescent material. The electro-luminescence device also includes an anode electrode and a cathode electrode serving as a common electrode for the ELD. The ELD may be an active matrix type.
The display also includes a gate driving circuit and the data driving circuit, being connected, via a plurality of scanning electrode lines and a plurality of data electrode lines, respectively, to the pixel array, to selectively drive each pixel.
The display further includes first and second voltage supply terminals to which first and second supply voltages are applied, from an external circuit for example. First and second power supply lines couple the first and second voltage supply terminals with the pixel array.
Each first power supply line supplies a subset of the pixels with the first supply voltage. Likewise, each second power supply line supplies another subset of the pixels with the second supply voltage.


REFERENCES:
patent: 5990629 (1999-11-01), Yamada et al.
patent: 6064158 (2000-05-01), Kishita et al.
patent: 6154187 (2000-11-01), Kim
patent: 6271812 (2001-08-01), Osada et al.

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