KR20070084958A - Driving method for light emitting display device and light emitting display device the same - Google Patents

Abstract

A light emitting display device and a driving method thereof are provided to extend the lifespan of the display device by selectively driving top and bottom light emitting units using switches which are connected to the top and bottom light emitting units. A light emitting display device includes a substrate, a pixel circuit, and a switching unit. The pixel circuit, which is formed on the substrate, includes top and bottom light emitting units(Top,Bottom) electrically connected to two or more electrodes. The switching unit is electrically connected to the top and bottom light emitting units, and inputs high and low signals to the top and bottom light emitting units. The switching unit includes first to fourth switches(SW1,SW2,SW3,SW4), each of which is connected to a cathode of the top and bottom light emitting units.

Description

Driving Method and Light Emitting Display Device and Light Emitting Display Device the same}

1 is a view for explaining a general organic light emitting device.

2 is a circuit diagram of a conventional organic light emitting display device.

3 is a circuit diagram of an electroluminescent display device driven by a driving method of the present invention.

4 is a diagram illustrating a driving method for driving the electroluminescent display of FIG. 3.

5 is a view showing a waveform according to the driving method of FIG.

6 is a schematic view of an electroluminescent display device according to the present invention.

<Explanation of symbols on main parts of the drawings>

SW1: first switch section SW2: second switch section

SW3: third switch section SW4: fourth switch section

The present invention relates to a method of driving an electroluminescent display and an electroluminescent display.

In the organic light emitting device, electrons and holes are injected into the light emitting layer from an electron injection electrode and a hole injection electrode, respectively, and an exciton in which the injected electrons and holes combine is excited. The device emits light when it falls from the ground state to the ground state.

The organic light emitting diode is classified into a passive matrix organic light emitting diode (PMOELD) and an active matrix organic light emitting diode (AMOELD) according to a driving method.

In general, an organic light emitting display device is capable of representing an image by driving voltage or current by driving N × M organic light emitting cells.

Hereinafter, an organic light emitting display device according to the related art will be described with reference to the accompanying drawings.

1 is a view for explaining a general organic light emitting device.

As shown in FIG. 1, a general organic light emitting cell structure has a structure of an anode (ITO), an organic thin film, and a cathode (Metal).

In detail, the organic thin film has a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), and an electron to improve the emission efficiency by improving the balance between electrons and holes. Consists of a multi-layer structure including an electron transport layer (ETL) and an electron injection layer (EIL).

The organic light emitting cell formed as described above has a simple matrix method in which the anode and the cathode are orthogonal to each other according to an addressing method, and a line is selected and driven, and the transistor TFT and the capacitor C are connected to each anode ( It can be classified into an active matrix method which is connected to the pixel electrode of ITO and is driven by maintaining the voltage by the capacitor capacitance. Here, it may be divided into a voltage application method and a current application method according to the type (voltage or current) of the signal applied to the driving circuit.

FIG. 2 is a conventional active matrix for driving a transistor in an organic light emitting diode, and is representatively showing one of N × M pixels as a voltage applying pixel circuit.

Referring to FIG. 2, a current driving type driving transistor Mb is connected to an organic light emitting diode (OLED), and supplies a current to emit light of the organic light emitting diode OLED. .

The current amount of the driving transistor Mb is controlled by the data voltage applied through the switching transistor Ma. At this time, a capacitor C for maintaining the applied voltage for a predetermined period is connected between the source and the gate of the driving transistor Mb.

An nth select signal line Select [n] is connected to a gate of the driving transistor Ma, and an mth data line Data [m] is connected to a source side.

Referring to the operation of the pixel having such a structure, as shown in FIG. 2, when the switching transistor Ma is turned on by the selection signal Select [n] applied to the gate of the switching transistor Ma, the data line The data voltage VDDD is applied to the gate (node A) of the driving transistor Mb through Data [m]. A current flows through the organic light emitting diode OLED through the driving transistor Mb corresponding to the data voltage VDD applied to the gate to emit light.

In the conventional method of driving a display device using the organic light emitting device having the above structure, when the light emitting device is driven by driving the thin film transistor, deterioration of the organic material occurs due to the voltage applied to the light emitting device, thereby resulting in a luminance lifetime. There was a problem of rapidly decreasing.

An object of the present invention for solving the above problems is to improve the life of the double-sided display device including a current-driven organic light emitting device, and to selectively emit light in the upper and lower by connecting a switch to the upper and lower light emitting portion A driving method and an electroluminescent display are provided.

According to an aspect of the present invention, there is provided a method of driving an electroluminescent display device, the first switch being electrically connected to an upper light emitting part of a pixel circuit part including an upper light emitting part and a lower light emitting part electrically connected to two or more electrodes. Applying an on signal to the part and applying an on signal to the second switch part electrically connected to the lower light emitting part to emit an upper light emitting part, or a third switch part electrically connected to the lower light emitting part The method may include applying an on signal and applying an on signal to the fourth switch unit electrically connected to the upper light emitting unit to emit the lower light emitting unit.

Here, the first, second, third and fourth switch parts are connected to the cathodes of the upper and lower light emitting parts.

Herein, when the first and third switch units are turned on, they are electrically connected to the ground voltage, and when the second and fourth switch units are turned on, they are electrically connected to the reference voltage.

Here, the reference voltages connected to the second and fourth switch units are relatively higher than the power supply voltages applied to the anodes of the upper and lower light emitting units.

Here, in the upper light emitting step, as the first and second switch parts are turned on, a voltage higher than the voltage applied to the anode of the lower light emitting part is applied to the cathode of the lower light emitting part so that a reverse voltage is applied to the third and fourth switches. Wealth is off.

Here, in the lower light emitting step, as the third and fourth switch parts are turned on, a voltage higher than the voltage applied to the anode of the upper light emitting part is applied to the cathode of the upper light emitting part so that a reverse voltage is applied to the first and second switches. Wealth is off.

Here, an anode of the upper and lower light emitting parts includes a thin film transistor part commonly connected to a source or a drain, and the upper part is operated by operating conditions of the first, second, third and fourth switch parts in a state where the thin film transistor part is turned on. Or to selectively emit light downward.

Here, the light emitting layers of the upper and lower light emitting parts are formed of an organic material.

On the other hand, the electroluminescent display device according to the present invention, a substrate; A pixel circuit part formed on the substrate, the pixel circuit part including an upper light emitting part and a lower light emitting part electrically connected to two or more electrodes; And a switching unit electrically connected to upper and lower light emitting units formed in the pixel circuit unit, and configured to input a high signal and a low signal to the upper and lower light emitting units.

Here, the switching unit is formed of first, second, third and fourth switch units connected to the cathodes of the upper and lower light emitting units.

Here, when the first and third switch units are On, they are electrically connected to the ground voltage formed in the switching unit, and when the second and fourth switch units are On, they are electrically connected to the reference voltage formed in the switching unit. Will be.

Here, the reference voltages connected to the second and fourth switch units are relatively higher than the power supply voltages applied to the anodes of the upper and lower light emitting units.

Here, an anode of the upper and lower light emitting parts includes a thin film transistor part commonly connected to a source or a drain, and the upper part is operated by operating conditions of the first, second, third and fourth switch parts in a state where the thin film transistor part is turned on. Or to selectively emit light downward.

Here, the light emitting layers of the upper and lower light emitting parts are formed of an organic material.

Specific details of other embodiments are included in the detailed description and drawings.

<Method for Driving Electroluminescent Display>

3 is a diagram illustrating a circuit configuration of an electroluminescent display device driven by a driving method of the present invention, FIG. 4 is a view showing a driving method for driving an electroluminescent display device of FIG. 3, and FIG. 5 is FIG. 4. Figure is a view showing a waveform according to the driving method.

As shown in FIG. 3, an electroluminescent display device driven by a driving method of the present invention includes an upper light emitting part Top and a lower light emitting part electrically connected to two or more electrodes formed in one pixel. Although not included, the pixel circuit unit is formed on the substrate. Here, the top and bottom light emitting parts (Top, Bottom) is a hole injection layer (HIL: Hole Injecting Layer), hole transport layer (HTL: Hole Transport Layer), in order to improve the light emission efficiency by improving the balance between electrons and holes It is composed of organic material layer including EML: Emitting layer, ETL: Electron Transport Layer and EIL: Electron Injecting Layer.

Here, the top and bottom light emitting parts (Top and Bottom) are configured in a circuit with a storage capacitor (not shown) to drive at least one thin film transistor unit (driving device) and each light emitting unit for a predetermined time in one pixel. These are electrically connected.

Here, the upper and lower light emitting parts (Top, Bottom) may be the anode electrode of each light emitting part is connected to the source or drain of the thin film transistor unit (driving device).

On the other hand, the present invention by using only the top and bottom light emitting portion (Top, Bottom) active circuit type electroluminescent device by circuit passively configured a matrix type electroluminescent device or a thin film transistor (driving device) and a storage capacitor (not shown) Of course, it is possible to drive the display device formed.

As shown in FIG. 4, the driving method of the electroluminescent display device using the electroluminescent device as described above is as follows, and a signal applied according to the driving method is referred to FIG. 5.

First, the upper light emitting step S402 may include a first switch electrically connected to an upper light emitting part Top of a pixel circuit part including an upper light emitting part Top and a lower light emitting part Bottom that are electrically connected to two or more electrodes. Applying an on signal to the part SW1 and applying an on signal to the second switch part SW2 electrically connected to the bottom light emitting part Bottom to emit the top light emitting part Top; to be.

Here, the third switch unit SW3 and the fourth switch unit SW4 are in an off state.

Accordingly, the top light emitting unit Top emits light to represent an image toward the top.

Subsequently, in the lower light emitting step S404, an on signal is applied to the third switch unit SW3 electrically connected to the lower light emitting unit Bottom, and the fourth switch is electrically connected to the upper light emitting unit Top. The lower light emitting unit Bottom is emitted by applying an on signal to the unit SW4.

Here, the first switch unit SW1 and the second switch unit SW2 are in an off state.

Accordingly, the top light emitting unit Top is turned off, and the bottom light emitting unit Bottom emits light to represent an image toward the bottom.

Here, the first, second, third, and fourth switch parts SW1, SW2, SW3, and SW4 are connected to cathodes of the upper and lower light emitting parts Top and Bottom.

Here, when the first and third switch units SW1 and SW3 are turned on, they are electrically connected to the ground voltage GND, and when the second and fourth switch units SW2 and SW4 are turned on. It is electrically connected to the reference voltage Vrev. On the other hand, the reference voltage Vrev connected to the second and fourth switch units SW2 and SW4 is relatively higher than the power supply voltage applied to the anodes of the upper and lower light emitting units Top and Bottom.

Accordingly, in the upper light emitting step S402, as the first and second switch parts SW1 and SW2 are turned on, a voltage higher than the voltage applied to the anode of the lower light emitting part Bottom is lowered. Is applied to the cathode at the bottom to form a reverse voltage.

In addition, in the lower light emitting step S404, as the third and fourth switch parts SW3 and SW4 are turned on, a voltage higher than the voltage applied to the anode of the upper light emitting part Top is applied to the upper light emitting part Top. Is applied to the cathode to form a reverse voltage.

On the other hand, when the electroluminescent display device is an active matrix type, the upper and lower light emitting parts Top and Bottom are driving thin film transistors (drive elements) and first, second, third and fourth switch parts formed in the pixel. Depending on the operating conditions of (SW1, SW2, SW3, SW4), selective light emission is performed at the top or bottom. However, in the case of the passive matrix type, the first, second, third and fourth switch units SW1, SW2, SW3, and the upper and lower light emitting scan wirings connected to the upper and lower light emitting portions Top and Bottom are connected. SW4) may be connected to selectively emit light to an upper side or a lower side.

In addition, while the upper light emitting step (S402) and the lower light emitting step (S404) is described above, they can be selected to emit the upper light emitting portion, or to emit the lower light emitting portion, or may emit the upper and lower light emitting portion at the same time, This is selectable according to the operating conditions of the first to fourth switch units SW1, SW2, SW3, and SW4.

As described above, the present invention connects two switches to the cathode electrodes of the upper and lower light emitting units, respectively, in order to improve the life of the double-sided display device including the current-driven organic light emitting diode, one to the ground Allow connection to any voltage. Accordingly, when the electroluminescent display including the current driven light emitting device is driven, a reverse voltage can be applied to the light emitting unit, thereby reducing trapped charge, thereby improving driving life and brightness. .

<Electroluminescent Display>

6 is a schematic view of an electroluminescent display device according to the present invention.

As illustrated in FIG. 6, the electroluminescent display device 600 according to the present invention includes an upper light emitting part Top and a lower light emitting part electrically connected to two or more electrodes formed in one pixel 620. A pixel circuit unit 630 including a is formed on the substrate 610.

Here, the top and bottom light emitting parts (Top, Bottom) is a hole injection layer (HIL: Hole Injecting Layer), hole transport layer (HTL: Hole Transport Layer), in order to improve the light emission efficiency by improving the balance between electrons and holes It is composed of organic material layer including EML: Emitting layer, ETL: Electron Transport Layer and EIL: Electron Injecting Layer.

Here, the upper and lower light emitting parts (Top, Bottom) are configured in a circuit with a thin film transistor (driving device) configured in one pixel 620 and a storage capacitor (not shown) to drive each light emitting part for a predetermined time or more. And they are electrically connected.

In addition, the first, second, third, and fourth switch parts may be electrically connected to the upper and lower light emitting parts Top and Bottom of the pixel circuit part 630 formed on the substrate 610. And a switching unit 640 formed of (SW1, SW2, SW3, SW4).

Here, the first, second, third, and fourth switch parts SW1, SW2, SW3, and SW4 are connected to cathodes of the upper and lower light emitting parts Top and Bottom.

In addition, the first and third switch units SW1 and SW3 are electrically connected to the ground voltage GND formed in the switching unit 640, and the second and fourth switch units SW2 and SW4 are connected to the switching unit ( It is electrically connected to the reference voltage Vrev formed at 640.

Here, the reference voltages Vrev connected to the second and fourth switch units SW2 and SW4 are relatively higher than the power supply voltages applied to the anodes of the upper and lower light emitting units Top and Bottom.

Here, the upper and lower light emitting parts Top and Bottom are driving thin film transistor parts (driving elements) and first, second, third and fourth switch parts SW1, SW2, SW3, and SW4 formed in the pixel 620. By the driving of the light is emitted to the top or bottom. Here, the first, second, third and fourth switch parts SW1, SW2, SW3, and SW4 must satisfy the above-described operating conditions while the thin film transistor part (driving device) is turned on.

In the electroluminescent display device 600 as described above, when the first and second switch units SW1 and SW2 are turned on when the upper light is emitted, the electroluminescent display device 600 is higher than the voltage applied to the anode of the bottom light emitting unit Bottom. The reverse voltage source is applied so that a voltage is applied to the cathode of the bottom light emitting unit Bottom.

At this time, the third and fourth switch units SW3 and SW4 are in an off state.

Subsequently, when the lower emission is performed, as the third and fourth switch units SW3 and SW4 are turned on, a voltage higher than the voltage applied to the anode of the upper emission unit Top is increased. Apply a reverse voltage source to the cathode.

At this time, the first and second switch units SW1 and SW2 are in an off state.

Accordingly, when the electroluminescent display including the current driven light emitting device is driven, a reverse voltage can be applied to the light emitting unit, thereby reducing trapped charge, thereby improving driving life and brightness. .

On the other hand, the present invention is formed as an active matrix type electroluminescent device by circuit-forming the thin film transistor and the storage capacitor in the upper and lower light emitting portion, it is of course also applicable to passive matrix type electroluminescent device formed of the upper and lower light emitting portion. .

In addition, although the switching unit is described as being formed externally, it can be formed on the substrate on which the electroluminescent element is formed.

In addition, although the upper emission and the lower emission are described in the above, they may be selected to emit the upper emission part or emit the lower emission part, and the upper and lower emission parts may emit light at the same time, which is the first to fourth switch parts. It can be selected according to the operating conditions of (SW1, SW2, SW3, SW4).

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the above-described technical configuration of the present invention may be embodied in other specific forms by those skilled in the art to which the present invention pertains without changing its technical spirit or essential features. It will be appreciated that it may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is shown by the claims below, rather than the above detailed description. Also, it is to be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

According to the above-described configuration of the present invention, two switches are connected to the cathode electrodes of the upper and lower light emitting units to improve the lifespan of the double-sided light emitting display device including the current-driven organic light emitting diode, one of which is connected to ground. Allow connection to any voltage. As a result, it is possible to reduce the trapped charge that occurs when the electroluminescent display including the current driven light emitting device is driven, thereby improving driving life and luminance.

Claims (14)

An on signal is applied to a first switch part electrically connected to the upper light emitting part of the pixel circuit part including an upper light emitting part and a lower light emitting part electrically connected to two or more electrodes, and electrically connected to the lower light emitting part. By applying an on signal to the second switch unit to emit the upper light emitting portion, An electric field for applying an on signal to a third switch electrically connected to the lower light emitting part, and applying an on signal to a fourth switch electrically connected to the upper light emitting part to emit light of the lower light emitting part A method of driving a light emitting display device. The method of claim 1, And the first, second, third and fourth switch units are connected to the cathodes of the upper and lower light emitting units. The method of claim 2, When the first and third switch unit is turned on (on) is electrically connected to the ground voltage, When the second and fourth switch unit is turned on (on) it is electrically connected to the reference voltage of the electroluminescent display device Driving method. The method of claim 3, And a reference voltage connected to the second and fourth switch units is a voltage higher than a power supply voltage applied to the anodes of the upper and lower light emitting units. The method of claim 2, wherein in the upper light emitting step, As the first and second switch parts are turned on, a voltage higher than the voltage applied to the anode of the lower light emitting part is applied to the cathode of the lower light emitting part so that a reverse voltage is applied, and the third and fourth switch parts are turned off ( Off) driving method of the electroluminescent display device characterized in that. The method of claim 2, wherein in the lower light emitting step, As the third and fourth switch parts are turned on, a voltage higher than the voltage applied to the anode of the upper light emitting part is applied to the cathode of the upper light emitting part so that a reverse voltage is applied, and the first and second switch parts are turned off ( Off) driving method of the electroluminescent display device characterized in that. The method of claim 1, An anode of the upper and lower light emitting parts includes a thin film transistor part commonly connected to a source or a drain, and under the operating conditions of the first, second, third and fourth switch parts in the state where the thin film transistor part is turned on. A method of driving an electroluminescent display device characterized by selectively emitting light to an upper side or a lower side. The method of claim 1, The light emitting layers of the upper and lower light emitting parts are formed of an organic material. Board; A pixel circuit part formed on the substrate, the pixel circuit part including an upper light emitting part and a lower light emitting part electrically connected to two or more electrodes; And And a switching unit electrically connected to the upper and lower light emitting units formed in the pixel circuit unit, and configured to input a high signal and a low signal to the upper and lower light emitting units. The method of claim 9, wherein the switching unit, And a first switch, a second switch, a third switch, and a fourth switch connected to the cathodes of the upper and lower light emitting parts. The method of claim 10, When the first and third switch units are turned on, the first and third switch units are electrically connected to ground voltages formed at the switching unit. When the second and fourth switch units are turned on, the first and third switch units are electrically connected to reference voltages formed at the switching unit. Electroluminescent display device characterized in that connected to. The method of claim 11, And a reference voltage connected to the second and fourth switch units is a voltage higher than a power supply voltage applied to the anode of the upper and lower light emitting units. The method of claim 9, An anode of the upper and lower light emitting parts includes a thin film transistor part commonly connected to a source or a drain, and under the operating conditions of the first, second, third and fourth switch parts in the state where the thin film transistor part is turned on. The electroluminescent display device characterized by selectively emitting light to the top or bottom. The method of claim 9, The light emitting layers of the upper and lower light emitting parts are formed of an organic material.

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