Electro-luminescent display and driving method thereof

Details Electro-luminescent display and driving method thereof Electro-luminescent display and driving method thereof

2000-08-18

2003-06-24

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Plural power supplies

Plural cathode and/or anode load device

C345S076000, C345S077000

Reexamination Certificate

active

06583577

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
This application claims priority from Korean Patent Application No. P1999-40743 filed on Sep. 21, 1999, the entirety of which is hereby incorporated by reference for all purposes as if fully set forth therein.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electro-luminescent display and a driving method thereof, more particularly, to an active type matrix electro-luminescent display and a driving method thereof.
2. Discussion of Related Art
An electro-luminescent display (hereinafter abbreviated ELD) is a display device which uses electro-luminescence of excited molecules generated from recombined electrons and holes which are injected outside the ELD. The thickness of an ELD is greatly reduced compared to other displays because it does not require a back light. It also can decrease power consumption compared to other displays. Therefore, the ELD has been focused upon as a next generation display.
FIG. 1
shows a general schematic equivalent circuit of a unit cell in ELD. Referring to
FIG. 1
, a pixel region is defined by a gate line G and a data line D crossing each other. And a power supply line L is arranged in parallel with the data line D. Alternatively, the power supply line L may be arranged to be parallel with the gate line G. The pixel region includes a switching device T
1
, a driving device T
2
, a storage capacitor C, and an electro-luminescent (EL) diode EL.
A gate, a source, and a drain of the switching device T
1
are connected to the gate line G, the data line D, and another gate of the driving device T
2
, respectively. And a drain and a source of the driving device T
2
are connected to an anode + of the EL diode EL and the power supply line L, respectively.
The storage capacitor C is connected between the gate of the driving device T
2
and the power supply line L. And, a cathode − of the EL diode EL is connected to a terminal
10
of a common electrode.
The operation of the above-mentioned ELD is explained in the following description.
If the gate line G connected to the switching device T
1
is selected to be turned on by a gate driver (not shown in the drawing), a data signal from the data line D connected to the switching device T
1
is stored in the storage capacitor. On the other hand, if the switching device T
1
is turned off, a voltage of the storage capacitor is maintained as it is until the gate line G is selected again.
In this case, the storage capacitor C keeps the voltage applied between the gate and source of the driving device T
2
. Thus, a source current depending on the gate voltage of the driving device T
2
is transferred to the common electrode
10
through the driving device T
2
and the EL diode EL from the power supply line L, thereby resulting in the luminescence of the EL diode. Thus, the driving device T
2
, which reacts on a selection signal applied selectively to the gate line G and the data line D, controls the current flowing from the power supply line L through the driving device T
2
.
The current of the EL diode EL is controlled by the driving device T
2
, and the EL diode EL emits light with a brightness corresponding to the current flowing through it. For instance, if a predetermined gate voltage is applied to the gate of the driving device T
2
, the level of the current flowing through the driving device T
2
is determined and the other current flowing through the EL diode EL is fixed in accordance with the current of the driving device T
2
.
FIG. 2
shows a circuit of an ELD according to a related art, wherein pixels emitting red, green, and blue light R, G, and B, respectively are arranged on a substrate.
The basic structures of the respective pixels are the same as those explained in FIG.
1
. Thus, the description of the same parts will be skipped in the following description.
Referring to
FIG. 2
, a plurality of pixel regions are defined by a plurality of gate lines G
1
, G
2
, . . . , and data lines D
1
, D
2
, . . . crossing one another. And, a plurality of power supply lines L
1
, L
2
, L
3
, . . . are arranged in parallel with the data lines D
1
, D
2
, D
3
, . . . Alternatively, the power supply lines may be arranged in parallel with the gate lines.
A plurality of the power supply lines L
1
, L
2
, L
3
, . . . formed in the respective pixel regions are connected to a single wire
20
in common, thereby receiving commonly a voltage from an extra power source voltage terminal
21
.
Each of the pixel regions is equipped with a switching device T
1
, a driving device T
2
, a storage capacitor C, and an EL diode EL. A reference numeral
22
designates a common electrode terminal connecting the respective EL diodes EL in common.
Each of the pixels may be defined by “R”, “G”, and “B” pixels emitting red, green, and blue light, respectively according to the luminescent colors emitted by the respective EL substances constructing each EL diode EL. The R, G, and B pixels are arranged as a unit.
The unit constructed with the R, G, and B pixels determine a certain color to be displayed by the combination of the three colors. The display is designed to produce colors, and the selection of a white color depends on various environmental conditions. Producing the white color from combination of the basic colors of R, G, and B (hereinafter abbreviated ‘white balance’) depends on the chromaticity and the brightness of the basic colors.
However, the respective EL diodes of the R, G, and B pixels, as shown in
FIG. 3
, exhibit a variety of brightness characteristics, depending upon the current.
Namely, when the same current flows through the respective pixels, the EL diodes R-EL, G-EL, and B-EL of the R, G, and B pixels produce different brightness levels.
Moreover, the respective brightness of the red, blue, and green lights required for the white balance of the ELD are different from one another due to the different EL substances constructing the EL diode.
Therefore, the ELD according to the related art is unable to produce colors properly, provided that the same driving waveform is applied to the respective pixels.
Namely, when the same data driving waveform is applied to the R, G, and B pixels, as is the case with a liquid crystal display using color filters, it is impossible to meet the brightness required for the respective pixels due to the different brightness of the respective EL substances constructing the EL diode according to the respective currents.
Therefore, the related art requires a driver which drives the R, G, and B pixels independently, thereby making the design of a data driving circuit of the ELD complicated, and increasing the product cost thereof.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electro-luminescent display and a driving method thereof that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electro-luminescent display and a driving method thereof which provides a simplified data driving circuit, as well as a simplified fabricating method thereof, by improving the construction which enables it to produce fine colors despite applying the same data driving waveform to the respective R, G, and B pixels.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes a gate line, first to third data lines defining first to third pixel regions, respectively, the first to third data lines crossing with the gate line, first to third power supply lines passing through the first

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