KR20060000357A - Organic electroluminescence display device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display device, and more particularly, to an organic light emitting display device capable of compensating for a defect or deviation caused by abnormal device characteristics of a driving transistor.

      According to an exemplary embodiment, an organic light emitting display device includes: a plurality of pixel areas formed in an area where a plurality of scan lines and a plurality of data lines cross each other; A switching transistor configured to transfer a data voltage applied to the data line in response to a selection signal applied to the scan line; A capacitor for maintaining the data voltage for a predetermined time; At least two driving transistors supplying a current to the organic light emitting diode in response to the data voltage input to the gate through the switching transistor; And an organic light emitting device connected to the at least two driving transistors, wherein a current supplied to the organic light emitting device is a sum of output currents of the at least two driving transistors.

Driving transistor, organic EL

Description

Organic electroluminescence display device

1 is a conceptual diagram of an organic electroluminescent device.

2 is an equivalent circuit diagram of a pixel circuit of a conventional voltage writing method.

3 is a schematic plan view of an organic EL display device according to an embodiment of the present invention.

4 is an equivalent circuit diagram of a pixel circuit according to an exemplary embodiment of the present invention.

5 is a drain current characteristic diagram when the same gate voltage is applied to the first and second driving transistors.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel display, and more particularly, to an organic electroluminescent display (hereinafter referred to as an "organic EL") display device capable of compensating for a defect or deviation caused by abnormal device characteristics of a driving transistor.

In general, an organic EL display device is a display device for electrically exciting a fluorescent organic compound to emit light, and is capable of displaying an image by voltage driving or current driving N × M organic light emitting cells arranged in a matrix form.

Such an organic light emitting cell has a diode characteristic and is also called an organic light emitting diode (OLED). As shown in FIG. 1, the organic light emitting cell has a structure of an anode (ITO), an organic emitting layer (EML), and a cathode electrode layer (metal). Electron transport layer (ETL), electron injecting layer (ETL), hole transport layer (HTL), hole injection layer (hole) It consists of a multilayer structure including an injecting layer (HIL). These organic light emitting cells are arranged in an N × M matrix to form an organic EL display panel.

The organic EL display panel is driven by a passive matrix method and an active matrix method using a thin film transistor (hereinafter, referred to as TFT). Passive matrix schemes form anodes and cathodes orthogonal and select lines to drive, whereas active matrix schemes connect thin film transistors to each indium tin oxide (ITO) pixel electrode and are held by capacitor capacitance connected to the thin film transistor's gate. It is driven according to the voltage.

FIG. 2 is a diagram representatively showing one of the N × M pixel circuits of the display panel of the organic EL display device.

As shown in Fig. 2, the pixel circuit includes an organic EL element OLED, two transistors M1 and M2 and a capacitor Cst. The transistors M1 and M2 are formed of PMOS transistors.

In the driving transistor M2, a source is connected to the power supply voltage Vdd, and a capacitor Cst is connected between the gate and the source. The capacitor Cst maintains the gate-source voltage V _GS of the transistor M2 for a period of time. The switching transistor M1 transfers the data voltage from the data line Dm to the transistor M2 in response to the selection signal from the current scan line Sn.

In the organic EL element OLED, a cathode is connected to the reference voltage Vss and emits light corresponding to a current applied through the driving transistor M2. Here, the reference power supply VSS connected to the cathode of the organic EL element OLED is a voltage having a lower level than the power supply voltage Vdd, and a ground voltage or the like may be used.

At this time, the current flowing through the organic EL element OLED is represented by Equation 1 below.

Where I _OLED is the current flowing through the organic EL element OLED, Vgs is the voltage between the gate and the source of the driving transistor M2, Vth is the threshold voltage of the driving transistor M2, Vdata is the data voltage, and β is a constant value. Indicates.

As shown in Equation 1, according to the pixel circuit shown in FIG. 2, a current corresponding to the applied data voltage Vdata is supplied to the organic EL element OLED, and the organic EL element OLED corresponds to the supplied current. ) Will emit light.

However, the organic EL display device as described above does not operate the driving transistor M2 so that a current corresponding to the data voltage cannot be applied to the organic EL element so that light cannot be emitted or a characteristic variation of the driving transistor M2 is desired. There was a problem that it does not emit light of brightness.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above-described problems, and to compensate for defects or deviations caused by abnormal device characteristics of a driving transistor in an organic EL display device so that a light emitting display operation is normally performed.

      According to an exemplary embodiment, an organic light emitting display device includes: a plurality of pixel areas formed in an area where a plurality of scan lines and a plurality of data lines cross each other; A switching transistor configured to transfer a data voltage applied to the data line in response to a selection signal applied to the scan line; A capacitor for maintaining the data voltage for a predetermined time; At least two driving transistors supplying a current to the organic light emitting diode in response to the data voltage input to the gate through the switching transistor; And an organic light emitting device connected to the at least two driving transistors, wherein a current supplied to the organic light emitting device is a sum of output currents of the at least two driving transistors.

Here, the at least two driving transistors are characterized in that the source is commonly connected to the voltage power source, the gate is commonly connected to the switching transistor, the drain is commonly connected to the pixel electrode of the organic light emitting device.

In addition, the at least two drive transistors are characterized in that they have the same conductivity type.

In addition, the at least two driving transistors are connected in parallel to each other.

The at least two driving transistors may share the capacitors with each other.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification. When a part is connected to another part, this includes not only a directly connected part but also an electrically connected part with another element in between.

A light emitting display device, a pixel circuit, and a driving method thereof according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings. The light emitting display device described below is an organic light emitting display device having an organic light emitting cell, but the light emitting display device according to the present invention is not limited thereto.

First, an organic EL display device according to an embodiment of the present invention will be described in detail with reference to FIG. 3 is a schematic plan view of an organic EL display device according to an embodiment of the present invention.

As shown in FIG. 3, the organic EL display device includes an organic EL display panel 100, a scan driver 200, and a data driver 300.

The organic EL display panel 100 includes a plurality of data lines D1 -Dm extending in a column direction, a plurality of scanning lines S1 -Sn extending in a row direction, and a plurality of pixel circuits 110.

The data lines D1 -Dm transmit a data signal representing an image signal to the pixel circuit 110, and the scan lines S1 -Sn transfer a selection signal to the pixel circuit 110. The pixel circuit 110 is formed in a pixel area defined by two neighboring data lines D1 -Dm and two neighboring scan lines S1 -Sn.

The scan driver 200 sequentially applies a selection signal to the scan lines S1 -Sn, and the data driver 300 applies a data voltage corresponding to the image signal to the data lines D1 -Dm.

The scan driver 200 and / or the data driver 300 may be electrically connected to the display panel 100, and may be attached to a tape carrier package (TCP) adhered to the display panel 100 and electrically connected to the display panel 100. It may be mounted in the form of a chip. Alternatively, the display panel 100 may be mounted in a flexible printed circuit (FPC) or a film that is adhered to and electrically connected to the display panel 100 in the form of a chip. Alternatively, the scan driver 200 and / or the data driver 300 may be directly mounted on the glass substrate of the display panel, or may be replaced with a driving circuit formed of the same layers as the scan line, the data line, and the thin film transistor on the glass substrate. It may be mounted directly.

FIG. 4 is a pixel circuit according to an embodiment of the present invention for driving an organic EL display device using a TFT, and representatively illustrates a pixel circuit connected to a data line Dm and a scan line Sn among NxM pixel circuits. It is.

As shown in FIG. 4, the pixel circuit 110 includes an organic EL element OLED, three transistors M1, M2, and M3 and a capacitor Cst. The transistors M1, M2, M3 are formed of PMOS transistors.

The switching transistor M1 receives the data voltage from the data line Dm, whose gate is connected to the current scan line Sn and connected to the source in response to a selection signal from the current scan line, to the first or second driving transistors M2 and M3. Pass to the gate of.

In the first driving transistor M2, a source is connected to the power supply voltage Vdd, and a capacitor Cst is connected between the gate and the source.

The second driving transistor M3 also has a source connected to the power supply voltage Vdd and a capacitor Cst connected between the gate and the source. That is, the source, gate, and drain of the first driving transistor M2 and the second driving transistor M3 are connected in common.

The capacitor Cst maintains the gate-source voltage V _GS of the first and second driving transistors M2 and M3 for a predetermined period of time.

In the organic EL device OLED, a cathode is connected to the reference voltage Vss, and an anode is commonly connected to the drains of the first and second driving transistors M2 and M3 to connect the first and second driving transistors M2 and M3. It emits light corresponding to the sum of the currents applied through. The amount of current is controlled by the data voltage applied through the switching transistor M1.

Referring to the operation of the pixel circuit according to the exemplary embodiment of the present invention, when the switching transistor M1 is turned on by the selection signal applied from the scan driver 200 to the gate of the switching transistor M1, the data driver ( The data voltage from 300 is applied to the gates of the first and second driving transistors M2 and M3 through the data line Dm. The sum of output currents of the first driving transistor M2 and the second driving transistor M3 is supplied to the organic EL element OLED to emit light in correspondence with the data voltage applied to the gate.

In this case, the current flowing through the first driving transistor M2 or the second driving transistor M3 is determined by the characteristics of the first and second driving transistors, which will be described with reference to FIG. 5.

5 illustrates drain current characteristics when the same gate voltage is applied to the first and second driving transistors.

When the same gate voltage is applied to the first and second driving transistors M2 and M3, the drain current curve is displayed as shown in FIG. 5 according to the drain current amounts of the first and second driving transistors M2 and M3. For example, when the gate voltages of the first and second driving transistors M2 and M3 are 5 V, it can be seen that the drain current amount of the second driving transistor M3 is greater than that of the first driving transistor M2. The reason why such a drain current characteristic appears is that it is impossible to manufacture the driving transistor such that the same drain current characteristic for the same gate voltage appears in the driving transistor manufacturing process.

In the pixel circuit as shown in FIG. 4, the sum of the drain currents of the first driving transistor and the second driving transistor flows to the organic EL element OLED in response to the data voltage applied to the gate. Therefore, it is possible to compensate for variations due to non-uniform device characteristics of the driving transistor.

In FIG. 4, two driving transistors M2 and M3 have been described, but two or more, that is, three, four, ... n driving transistors may be connected in parallel. Therefore, at least two driving transistors according to an embodiment of the present invention. However, it is preferable to provide two driving transistors in terms of aperture ratio.

Hereinafter, a case in which any one of the first and second driving transistors M2 and M3 is not operated will be described with reference to FIG. 4.

According to the exemplary embodiment of the present invention, when one of the two driving transistors M2 and M3 is not operated due to a defective element, the other driving transistor operates as the driving transistor to drain the current. To (OLED).

In detail, when the switching transistor M1 is turned on by the selection signal applied from the scan driver 200 to the gate of the switching transistor M1 in FIG. 4, the data line Dm from the data driver 300. The data voltage is applied to the gates of the first and second driving transistors M2 and M3 through. In addition, a current flows through the first driving transistor M2 and the second driving transistor M3 in response to the data voltage applied to the gate to emit light. In one of the two driving transistors M2 and M3, for example, when the first driving transistor M2 does not operate due to a defective element, the conventional pixel circuit as shown in FIG. 2 does not allow drain current to flow. In the pixel circuit according to the exemplary embodiment of the present invention as shown in FIG. 4, the light does not emit light to the pixel, but the second driving transistor M3 flows the drain current corresponding to the data voltage to the organic EL element OLED. The light emission causes the element defect of the first driving transistor M3 to be compensated for.

As described above, according to the present invention, by further including one driving transistor in a conventional pixel circuit, even when one driving transistor is not operated, the other driving transistor can operate to emit light, thereby driving the driving transistor. It is possible to reduce the occurrence of dark pixels due to the defect of.

As described above, according to the present invention, the amount of current flowing through the organic light emitting device can be distributed to at least two driving transistors to compensate for the deviation caused by the variation of device characteristics of the driving transistor.

Further, according to the present invention, when any one of the driving transistors is not operated, a current is applied to the organic light emitting element through the other normal driving transistor so that light emits light, so that the operation of the organic EL display device can be more stable.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (5)

A plurality of pixel areas formed in areas where a plurality of scan lines and a plurality of data lines cross each other; A switching transistor configured to transfer a data voltage applied to the data line in response to a selection signal applied to the scan line; A capacitor for maintaining the data voltage for a predetermined time; At least two driving transistors supplying a current to the organic light emitting diode in response to the data voltage input to the gate through the switching transistor; An organic light emitting device connected to the at least two driving transistors, And the current supplied to the organic light emitting element is a sum of output currents of the at least two driving transistors. The method of claim 1, The at least two driving transistors of which the source is commonly connected to a power supply voltage, a gate is commonly connected to the switching transistor, and a drain is commonly connected to the pixel electrode of the organic light emitting device. The method of claim 1, And the at least two driving transistors have the same conductivity type. The method of claim 1, And at least two driving transistors are connected in parallel to each other. The method of claim 1, And at least two driving transistors share the capacitors with each other.

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