KR20080057788A - Organic light emitting display - Google Patents

Abstract

An OLED(Organic Light Emitting Display) device is provided to enhance lifetime thereof by preventing the degradation of driving transistors. An OLED device includes signal lines, pixel circuits, and scan and data drivers(120,130). The signal lines include scan lines, data lines, and first and second power lines. The pixel circuits include a switching transistor, a capacitor, a driving transistor, and a light emitting diode. The switching transistor delivers data signals from the data lines according to scan signals from the scan lines. The capacitor receives and stores the data signals from the switching transistor. The driving transistor generates driving currents according to the data signals stored in the capacitor. The light emitting diode, connected between the driving transistor and the first power line, receives the driving currents and executes light emitting operations. The scan driver applies scan signals to the pixel circuits through the scan lines. The data driver applies data signals to the pixel circuit through the data lines and outputs an analog data signal more than 0V and a negative data signal according to the scan signals.

Description

Organic Light Emitting Display

1 is a block diagram illustrating an organic light emitting display device according to an embodiment of the present invention.

2 is a circuit diagram illustrating a pixel circuit of an organic light emitting display device according to an embodiment of the present invention.

3 is a circuit diagram illustrating a data driver according to an exemplary embodiment of the present invention.

4 is a timing diagram illustrating an operation of an organic light emitting display device according to an exemplary embodiment of the present invention.

5 is a timing diagram illustrating an operation of an organic light emitting display device according to another embodiment of the present invention.

The present invention relates to an organic light emitting display device and a driving method thereof.

Recently, the importance of flat panel displays (FPDs) has increased with the development of multimedia. In response, a number of liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), organic light emitting devices (Organic Light Emitting Devices), etc. Branch-type flat panel displays have been put into practical use.

In particular, the organic light emitting display device has a high response time with a response speed of 1 ms or less, low power consumption, and self-emission. In addition, there is no problem in viewing angle, which is advantageous as a moving image display medium regardless of the size of the device. In addition, low-temperature manufacturing is possible, and the manufacturing process is simple based on the existing semiconductor process technology has attracted attention as a next-generation flat panel display device in the future.

In general, an organic light emitting display device is a display device that electrically excites fluorescent organic compounds and emits light, and performs voltage driving or current driving of N × M organic light emitting diodes (OLEDs) arranged in a matrix form. Programming to express an image. The organic light emitting display device may be driven by a passive matrix method and an active matrix method using a thin film transistor. The passive matrix method forms the anode and the cathode to be orthogonal and selects and drives the lines, whereas the active matrix method connects the thin film transistors to each pixel electrode and drives them according to the voltage maintained by the capacitor capacitance connected to the gate electrode of the thin film transistor. do.

The active matrix organic light emitting display device includes pixel circuits including at least a switching transistor, a capacitor, a driving transistor, and a light emitting diode, and the light emitting diode emits light by a driving current generated by the driving transistor.

However, as the organic light emitting display device is used for a long time, the gate electrode of the driving transistor to which the data signal is applied is maintained in a continuous turn-on state, thereby receiving a stress in a positive or negative direction continuously.

This deteriorates the driving transistor and causes a nonuniformity in luminance between the pixel circuits by shifting the threshold voltage of the driving transistor. In addition, an afterimage remains due to the charge accumulated in the gate electrode of the driving transistor, thereby degrading the quality of the screen.

Accordingly, an object of the present invention is to provide an organic light emitting display device which prevents deterioration of a driving transistor and shift of a threshold voltage and improves screen quality.

In order to achieve the above object, the present invention, the present invention, the signal line including the scan line, the data line, the first and second power supply line, from the data line in accordance with the scan signal from the scan line A switching transistor for transmitting a data signal, a capacitor receiving the data signal from the switching transistor and storing the data signal, a driving transistor for generating a driving current according to the data signal stored in the capacitor, and between the driving transistor and the first power line. A pixel circuit including a light emitting diode connected to the driving current to perform a light emitting operation, a scan driver for applying a scan signal to the pixel circuits through scan lines, and a data line to the pixel circuit to which the scan signal is applied. Data driver for applying data signal through The data driver includes an organic light emitting display device that outputs an analog data signal of 0V or more and a negative analog data signal according to a scan signal.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 1, the organic light emitting display device includes a display panel 110, a scan driver 120, a data driver 130, a controller 140, and a power supply 150.

The display panel 110 includes the data lines D1 -Dm arranged in the first direction and the scan lines S1 -Sn and the data lines (D1 -Dm crossing the first direction and arranged in the second direction). )) And the pixel circuits P11 -Pnm positioned in the region where the scan lines S1 -Sn cross each other.

The control unit 140 outputs a control signal to the scan driver 120, the data driver 130, and the power supply unit 150, and the power supply unit 150 controls the first power lines in accordance with the control signal of the control unit 140. A voltage necessary for driving the display panel 110 is output through 160: VDD1-VDDm and the second power lines 170: VSS1-VSSn.

The scan driver 120 outputs a scan signal to scan lines S1 -Sn connected to the scan driver 120 according to a control signal of the controller 140. As a result, the pixel circuits P11 -Pnm located in the display panel 110 are selected in response to the scan signals S1 -Sn.

The data driver 130 may correspond to the data signals through the data lines D1 -Dm connected to the data driver 130 in synchronization with the scan signal output from the scan driver 120 according to the control signal of the controller 140. Applied to the pixel circuits 110. Accordingly, the display panel 110 displays an image image by emitting light from the pixel circuits P1 -Pnm in response to the data signals.

Hereinafter, the structure of the pixel circuit and the data driver of an organic light emitting display device according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

2 is a circuit diagram illustrating a pixel circuit of an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 2, the pixel circuit transmits a data signal from the data line Dm in response to a selection signal from the scan line Sn, and a data signal received through the switching transistor T2. A capacitor Cst for storing the voltage, a driving transistor T2 for generating a driving current according to the data signal stored in the capacitor Cst, and a light emitting operation according to the driving current, and connected to the first power line VDD. Organic light emitting diodes (OLED).

The gate electrode of the driving transistor T2 is connected to the drain electrode of the switching transistor T1 to receive a data signal, and the driving transistor T2 is connected to the second power line VSS connected to the source electrode and the data signal. The driving current corresponding to the difference is generated and supplied to the organic light emitting diode OLED connected to the drain electrode.

The amount of current flowing through the organic light emitting diode OLED can be expressed as follows.

Here, K is a constant, Vgs is the difference between the source-gate voltage of the driving transistor, and Vth is the threshold voltage of the driving transistor.

3 is a circuit diagram illustrating a data driver according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the data driver includes an output buffer 130a for supplying an analog data signal of 0V or higher in response to a digital data signal input from the outside, and a negative voltage supply unit 130b for supplying a negative voltage.

Here, the negative voltage supply unit 130b includes at least one control transistor Ts, the source electrode of the control transistor Ts is connected to the negative power line Voff, and the drain electrode is connected to the data line. The gate electrode of the control transistor Ts is connected to the control line AZ.

Therefore, when a control signal is applied through the control line AZ, the control transistor Ts is turned on to supply a negative voltage to the data line through the negative power line Voff.

4 is a timing diagram illustrating a method of driving an organic light emitting display device according to an embodiment of the present invention. Hereinafter, a driving method of an organic light emitting display device according to an exemplary embodiment of the present invention having the above structure will be described with reference to FIGS. 1 to 4.

1 to 4, the scan driver 120 applies a scan signal having a high level to the pixel circuits P11-Pnm through the scan lines S1..Sn according to the vertical synchronization signal Vsync. Is authorized.

In this case, a digital data signal corresponding to each gray is input to the data driver 130. When a digital data signal of 'gray 1' or more is input, the output buffer 130a of the data driver 130 corresponds to each digital data signal. A positive voltage, which is an analog data signal, is output to the pixel circuit P11-Pnm through the data lines D1 -Dm.

The switching transistor T1 receiving the scan signal through the scan line Sn transfers a data signal, which is a positive voltage, received through the data line Dm to the gate electrode and the capacitor Cst of the driving transistor T2. . The driving transistor T2 receives the data signal and generates a driving current corresponding to the difference between the ground voltage and the data signal applied from the second power line Vss connected to the source electrode, and transfers the driving current to the organic light emitting diode OLED. In addition, the organic light emitting diode OLED performs a corresponding light emitting operation.

At this time, when the digital data signal input to the data driver 130 is a digital data signal corresponding to 'gray 0', the controller 140 applies a high level control signal through the control line AZ, and the data driver ( The negative power supply 130b of 130 supplies a data signal having a negative voltage to the data lines D1 -Dm.

When a negative voltage is supplied through the data line Dm, it is transferred to the gate electrode of the driving transistor T2 through the switching transistor T1. As a result, the gate electrode of the driving transistor T2 in which the positive stress is accumulated may be refreshed by applying a negative voltage. At this time, since the voltage difference Vgs between the gate and source electrodes of the driving transistor T2 is equal to or less than 0, the driving transistor T2 does not generate a driving current, and the organic light emitting diode OLED stops emitting light.

Conventionally, when driving an organic light emitting display device, a positive data signal is always applied to the gate electrode of the driving transistor T2. When the black data signal corresponding to 'gray 0' is applied, a 0 V data signal is applied. Therefore, charges are stored in the gate electrode T2 of the driving transistor due to the positive electrical stress in the positive direction, thereby shifting the threshold voltage or leaving afterimages due to the electrical stress.

Therefore, in the organic light emitting display device according to an exemplary embodiment of the present invention, when a gray data, that is, a digital data signal corresponding to black data is input to the data driver, the organic light emitting display device applies a data signal having a negative voltage to the driving transistor. The electrical stress of the driving transistor accumulated in the positive direction is eliminated.

The negative voltage may be a negative voltage that is equal to or less than the off voltage Voff of the driving transistor T2.

In general, since the ground voltage VSS is applied to the source electrode of the driving transistor T2, when the data signal of OV is applied to the gate electrode of the driving transistor T2, the voltage between the source and gate electrodes of the driving transistor T2 is changed. The difference Vgs is O, so that no current flows through the organic light emitting diode OLED.

However, since the off voltage of the driving transistor T2 substantially made of amorphous silicon is -5 to -10V, even if OV is applied to the gate electrode of the driving transistor T2, a current of several tens of nA flows. This causes the organic light emitting diode (OLED) to emit light even when the OV, which is black data, is applied, thereby increasing the black gradation to lower the contrast ratio of the screen.

Accordingly, the data driver of the organic light emitting display device according to an embodiment of the present invention includes a negative power supply to relieve stress of the driving transistor and to turn off the driving transistor so that leakage current does not occur when black data is applied. Supply a negative voltage below the voltage.

As a result, the electrical stress accumulated in the gate electrode of the driving transistor T2 can be eliminated without losing display time, and the contrast ratio can be prevented by preventing leakage current from occurring in the organic light emitting diode OLED when the black data is input. Can improve.

 5 is a timing diagram illustrating a method of driving an organic light emitting display device according to another embodiment of the present invention.

Hereinafter, a method of driving an organic light emitting display device according to another exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3 and 5.

In another embodiment of the present invention, one frame is divided into two subframes sub1 and sub2. The first subframe sub1 is an interval for display, and the second subframe sub2 is an interval for refreshing the driving transistor T2, and a scan signal is applied to each subframe.

1 to 3 and 5, in the first subframe sub1, the scan driver 120 sequentially applies a scan signal having a high level to the scan lines according to the vertical synchronization signal Vsync. .

In this case, a digital data signal corresponding to each gray is input to the data driver 130, and the output buffer 130a of the data driver 130 outputs an analog data signal of 0V or more corresponding to each digital data signal. The scan signal is output to the applied pixel circuit through Dm).

The switching transistor T1 of the pixel circuit receiving the scan signal through the scan line Sn receives a data signal that is a positive voltage received through the data line Dm, and the gate electrode and the capacitor Cst of the driving transistor T2. To pass on. The driving transistor T2 receives the data signal and generates a driving current corresponding to the difference between the ground voltage and the data signal applied from the second power line Vss connected to the source electrode, and transfers the driving current to the organic light emitting diode OLED. In addition, the organic light emitting diode OLED performs a light emitting operation corresponding thereto.

Next, in the second subframe sub2, the scan driver 120 applies a scan signal having a high level through the scan lines S1..Sn. Here, the scan driver 120 may not uniformly supply scan signals to the scan lines S1..Sn, but may uniformly supply scan signals to all scan lines.

In this case, the controller 140 applies a high level control signal through the control line AZ, and the negative voltage supply unit 130b of the data driver 130 outputs a negative voltage through the data line.

Accordingly, all scan lines are selected by the scan signal, and a negative voltage is supplied to the gate electrode of the driving transistor T2 of all the pixel circuits during the second subframe sub1. As a result, the electrical stress of the driving transistor accumulated in the positive direction is solved, and the degradation of the driving transistor and the shift of the threshold voltage can be prevented.

However, since a data signal having a negative voltage is applied during the second subframe sub1, each pixel circuit is maintained in a black state until the data signal is applied in the first subframe sub1 of the next frame. .

Therefore, the display time of the pixel circuits Pn1-Pnm connected to the last scan line is reduced in state than the pixel circuits P11-P1m connected to the first scan line in the current frame, and if the above operation is repeated, As a result, the display time deviation between the pixel circuits connected to each scan line becomes more serious.

To solve this problem, the organic light emitting display device according to another exemplary embodiment of the present invention supplies a scan signal according to a first scan order in an odd frame and scans in a second scan order different from the first scan order in an even frame. Supply the signal.

That is, if the scan signals are sequentially supplied from the first scan line to the nth scan line in the first frame, the scan signals are sequentially supplied from the nth scan line to the first scan line in the second frame. That is, the scan signal is supplied in the reverse order.

Therefore, the display time of the pixel circuits connected to the first scan line is longest in the first frame, but the display time of the pixel circuits connected to the last scan line is longest in the second frame.

That is, the driving method of the organic light emitting display device according to another embodiment of the present invention can prevent the display time from being changed between pixel circuits connected to each scan line due to the refresh through the second subframe sub1. There is an effect that can improve the quality of the screen.

The negative voltage may be a negative voltage less than or equal to the off voltage Voff of the driving transistor T2. As a result, the electrical stress accumulated in the driving transistor can be sufficiently solved, and the contrast ratio can be improved by preventing leakage current from flowing through the organic light emitting diode OLED during the second subframe.

As described above, the organic light emitting display device according to the exemplary embodiment of the present invention can prevent the degradation of the driving transistor and the shift of the threshold voltage by applying a negative voltage to the gate electrode of the driving transistor. In addition, the driving method of the organic light emitting display device according to an embodiment of the present invention has the effect of increasing the contrast and refreshing the driving transistor without losing display time.

In addition, the driving method of the organic light emitting display device according to another embodiment of the present invention can refresh the driving transistor for each frame while maintaining the display time of each pixel circuit uniformly, thereby reducing the lifespan and screen of the organic light emitting display device. There is an effect to improve the quality of.

In the embodiments of the present invention, the data driver includes an output buffer and a negative voltage supply, but the present invention is not limited thereto. The data driver includes a negative voltage supply, that is, an output buffer capable of outputting a negative voltage. It may also include.

 While the invention has been shown and described with reference to certain preferred embodiments, the invention is not so limited, and the invention is not limited to the scope and spirit of the invention as defined by the following claims. It will be readily apparent to one of ordinary skill in the art that various modifications and variations can be made.

The present invention has the effect of preventing the deterioration of the driving transistor to increase the life of the organic light emitting display device and improve the quality of the screen.

Claims (9)

Signal lines including scan lines, data lines, first and second power lines; A switching transistor which transfers the data signal from the data line according to the scan signal from the scan line, a capacitor which receives the data signal from the switching transistor and stores it, and generates a driving current according to the data signal stored in the capacitor Pixel circuits including a driving transistor configured to be connected to the driving transistor and the first power line, and a light emitting diode receiving the driving current to perform a light emitting operation; A scan driver which applies a scan signal to the pixel circuits through the scan lines; And A data driver configured to apply a data signal to the pixel circuit to which the scan signal is applied through the data line; And the data driver outputs an analog data signal of 0V or more and a negative analog data signal according to the scan signal. The method of claim 1, The data driving unit includes an output buffer for outputting an analog data signal of OV or more and a negative voltage supply unit for outputting a negative analog data signal. The method of claim 2, The negative voltage supply unit includes at least one control transistor, a negative voltage line connected to a source electrode of the control transistor, and a control line connected to a gate electrode of the control transistor, And a control signal is applied to the control line, and the control transistor is turned on to apply a negative voltage to the pixel circuit through a data line connected to a drain electrode of the control transistor. The method of claim 3, And the data driver is configured to apply the negative data signal to the pixel circuit through the negative power supply unit when the digital signal is a digital signal corresponding to gray zero. The method of claim 3, One frame is divided into a first subframe for display and a second subframe for refresh, And the data driver is configured to apply a negative data signal from the negative voltage supply unit to the subpixel during the second subframe. The method of claim 5, The scan driver sequentially supplies scan signals to the scan lines during the first subframe, and uniformly supplies scan signals to the scan lines during the second subframe. The method of claim 6, The scan driver supplies a scan signal to the scan lines according to a first scan order during a first subframe of an odd numbered frame, and differs from the first scan order to the scan lines during a first subframe of an even numbered frame. An organic light emitting display device for supplying a scan signal in a second scanning order. The method of claim 7, wherein And the first scan order and the second scan order are opposite to each other. The method according to claim 4 or 5, And the negative voltage supply unit supplies a negative voltage equal to or less than an off voltage of the driving transistor.

Images