KR101588449B1 - Organic Electroluminescent Display Device And Method Of Driving The Same - Google Patents

Abstract

The present invention relates to an organic electroluminescent panel including a light emitting diode and displaying an image; A timing controller for analyzing the video signal corresponding to the video by frame to determine the type of the video; A current measuring unit for measuring a current value of a power supply voltage applied to the light emitting diode in real time and transmitting the measured current value to the timing controller; And a current limiter for limiting a current of the power supply voltage when the image is a still image.

Organic light emitting display, afterimage, current limitation

Description

TECHNICAL FIELD [0001] The present invention relates to an organic electroluminescent display device and a method of driving the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device and a driving method thereof, in which deterioration and afterimage of a light emitting diode are prevented by limiting a current applied to the light emitting diode.

Since the organic electroluminescent display device (OELD device), which is one of the new flat panel displays, is self-emitting type, it has better viewing angle and contrast ratio than a liquid crystal display device and does not require a backlight It is lightweight and thin, and is also advantageous in terms of power consumption. And it is able to drive DC low voltage, has fast response time and is all solid, so it is resistant to external impact, has wide temperature range, and is cheap in terms of manufacturing cost. Such an organic light emitting display may also be referred to as an organic light emitting diode (OLED) device.

Unlike a liquid crystal display device or a plasma display panel (PDP device), the organic light emitting display device is a very simple process, so it can be said that all the devices are deposition and encapsulation devices.

Particularly, in the active matrix type, a voltage for controlling a current applied to a pixel is charged in a storage capacitor, and a voltage is maintained until a next frame signal is applied, Regardless of the number of wirings, a light emission state is maintained while one screen is displayed.

Therefore, in the active matrix system, even if a low current is applied, the same brightness is exhibited, which has the advantages of low power consumption, high definition, and large size.

As a main component of the organic electroluminescent display device, a light emitting diode formed in each pixel and adapted to receive a direct current and emit light corresponding to the current is greater than a current designed for a predetermined time period when a voltage for initial driving is applied And has a characteristic that a current flows and emits light of higher luminance, which will be described with reference to the drawings.

1 is a diagram illustrating an initial light emission characteristic of a light emitting diode of a conventional organic light emitting display device.

1, when a voltage is applied to the light emitting diode so as to have the first luminance (L1) luminance, the current flowing in the light emitting diode gradually increases during the initial first time interval T1, and accordingly, the luminance of the light emitting diode Becomes a second luminance (L2) higher than the first luminance.

Then, during the second time period T2, the current flowing through the light emitting diode gradually decreases to have the desired first luminance L1.

When the first luminance L1 is about 450 nits, the first time interval T1 is about 2 hours and the second luminance L2 for the first luminance L1 of the red, green, (L2-L1) / L1 of the amount of rise of each of the first and second electrodes is about 5%, about 2%, and about 2.5%, respectively.

Further, the larger the voltage applied to the light emitting diode at the initial stage is, the larger the current rise amount and the luminance rise amount become.

The increase in the initial current and the increase in the initial luminance of the light emitting diode cause a deterioration in image quality as the after-image on the still image of the organic light emitting display device, which will be described with reference to the drawings.

2A and 2B are diagrams illustrating first and second stop patterns, respectively, displayed on a conventional organic light emitting display device.

The first pattern of FIG. 2A is a pattern displaying white and black, and the second pattern of FIG. 2B is a pattern of displaying white. In the first pattern, areas A and B represent white and black, In the pattern, both the area A and the area B display white.

However, as shown in FIG. 2B, when the first pattern is continuously displayed for a predetermined time and then the second pattern is displayed, the degree of deterioration of the light emitting diode varies depending on the region, resulting in a residual image.

That is, while the light emitting diode of the A region is applied with a relatively high voltage during the display of the first pattern, the light emitting diode of the B region is further deteriorated by a relatively high initial current rise, Lt; RTI ID = 0.0 > relatively < / RTI > lower initial current rise.

Since the second pattern is displayed after the first pattern display and the lapse of time, the luminance reduction amount of the A region is smaller than the luminance reduction amount of the B region as the degradation rate of the light emitting diode increases, And the area A displays a luminance lower than that of the area B, resulting in a residual image.

In order to prevent the afterglow caused by the rise of the initial current and the increase of the initial luminance, a dimming driving method of reducing the luminance of the light emitting diode after a certain time has elapsed in displaying still images has been proposed.

3 is a diagram illustrating a change in luminance of a still image in a conventional organic light emitting display device.

As shown in FIG. 3, when the dimming driving method is applied to the organic light emitting display device in order to prevent the afterimage due to the increase in the initial luminance on the still picture, The luminance of the light emitting display device is reduced from the third luminance L3 to the fourth luminance L4. For example, the third and fourth luminance L3 and L4 are about 400 nits and about 200 nit, respectively, The 3-hour interval T3 may be about 6 minutes.

Since the luminance of the light emitting diode is reduced, the initial current rise and the initial luminance rise also decrease, resulting in reduction of the afterimage occurrence.

However, even in the case of such a dimming driving method, there is a problem that the luminance increases when the light emission continues for a certain time at the fourth luminance L4 after the third time period T3.

For example, when about one hour has elapsed after the third time interval T3, the fourth luminance L4 is increased by about 1 to 2%. The luminance increase of the light emitting diode causes a residual image again.

In order to prevent an afterimage due to an increase in an initial current of the light emitting diode and an increase in an initial luminance, an aging process for driving the organic light emitting display device for a predetermined period of time under a predetermined condition is further performed.

However, in such an aging process, since the light emitting diode is driven for several tens to several hundreds of hours, the manufacturing time and manufacturing cost are increased, and the practical life of the light emitting diode is shortened.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above problems, and it is an object of the present invention to provide an organic light emitting display device in which when a still image is displayed at the beginning of driving, To prevent an afterimage due to an initial current rise and an initial luminance rise of the organic EL element, and to improve image quality.

According to an aspect of the present invention, there is provided an organic light emitting display comprising: an organic electroluminescent panel including a light emitting diode and displaying an image; A timing controller for analyzing the video signal corresponding to the video by frame to determine the type of the video; A current measuring unit for measuring a current value of a power supply voltage applied to the light emitting diode in real time and transmitting the measured current value to the timing controller; And a current limiter for limiting a current of the power supply voltage when the image is a still image.

The organic light emitting display includes a frame memory for storing the video signal of a previous frame and providing the video signal to the timing controller, and a table for a current corresponding to the average gradation and the average gradation for each frame of the video signal, And a timing controller.

The timing control unit compares the video signal of the previous frame with the video signal of the current frame to determine that the video is the still video, and if the current value of the power source voltage of the current frame is greater than the current value of the previous frame The current corresponding to the average gradation of the current frame may be extracted from the table and the current limiter may be controlled to be set to an upper limit value of the current of the power source voltage.

The organic electroluminescence panel includes a substrate, first to m-th gate lines, first to n-th data lines, first to n-th power lines, and first to n- And a first transistor, a second transistor, and a storage capacitor formed in the pixel region, wherein the light emitting diode is connected to each of the first to the n-th power wiring through the second transistor, And may be applied to each of the first to the n-th power wiring lines.

The organic light emitting display device may further include a gate driver for supplying a gate signal to the first to m-th gate lines, and a data driver for supplying a data signal to the first to the n-th data lines .

According to another aspect of the present invention, Comparing the video signal of the previous frame with the video signal of the current frame;

Supplying a power supply voltage to the organic electroluminescent panel in which a current corresponding to an average gray level of the video signal of the current frame is set to an upper limit value when the video signal of the previous frame is identical to the video signal of the current frame; And a step of causing the light emitting diode of the organic electroluminescent panel to emit light using the power supply voltage.

Here, the step of comparing and judging the identity between the video signal of the previous frame and the video signal of the current frame may be continued for a frame longer than the reference number.

The driving method of the organic light emitting display device may further include: measuring a current value of the power supply voltage supplied to the organic light emitting panel in real time; Comparing a current value of the power source voltage of the previous frame with a current value of the power source voltage of the current frame when the video signal of the previous frame is identical to the video signal of the current frame; If the current value of the power source voltage of the current frame is greater than the current value of the power source voltage of the previous frame, And extracting a current corresponding to the average gradation of the signal.

As described above, in the organic light emitting display according to the present invention, the type of an image is determined by analyzing a video signal for each frame, and when it is determined that the current is increased by measuring a current flowing through the organic electroluminescent panel By restricting the current to a predetermined upper limit value, it is possible to prevent an initial afterimage due to an increase in an initial current of the light emitting diode and an increase in an initial luminance, to improve an image quality, and to reduce a manufacturing time and a manufacturing cost by omitting an additional step .

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

FIG. 4 is a schematic view showing an organic light emitting display according to an embodiment of the present invention, and FIG. 5 is a detailed view of a current measuring unit and a current limiting unit of an organic light emitting display according to an embodiment of the present invention.

4 and 5, the organic light emitting display device 110 includes an organic electroluminescence panel 120 for displaying an image, a gate signal and a data signal to the organic electroluminescence panel 120, A timing control unit 150 for supplying a gate control signal, a data control signal and an RGB signal to the gate driving unit 130 and the data driving unit 140, A storage unit 160 for storing a current value corresponding to the current value and providing it to the timing controller 160, and a frame memory unit 170 for storing the video signal on a frame-by-frame basis.

The organic electroluminescence panel 120 includes first through m-th gate lines GL1 through GLm, first through n-th data lines DL1 through DLn, and first through n-th data lines DL1 through DLn, Power lines PL1 to PLn are formed and a first transistor T1, a second transistor T2, a storage capacitor Cst, and a light emitting diode Del are formed in each pixel region P.

Here, the first to the n-th data lines DL1 to DLn may be sequentially and repeatedly connected to the pixel regions for displaying red, green, and blue.

Although not shown, the organic electroluminescent panel 120 may be formed by forming devices such as a gate wiring, a data wiring, a transistor, a storage capacitor, and a light emitting diode on a first substrate through deposition, photolithography, The second substrate may be formed by laminating the first substrate so as to cover the elements of the first substrate or by forming an element such as a gate wiring, a data line, a transistor, and a storage capacitor on the first substrate through vapor deposition or photolithography, May be formed by bonding the first and second substrates so that the elements of the first and second substrates face each other after the first and second substrates are formed on the second substrate.

The gate electrode and the source electrode of the first transistor T1 are connected to the gate lines GL1 to GLm and the data lines DL1 to DLn respectively and the drain electrode of the first transistor T1 is connected to the gate electrode of the second transistor T2 And is connected to the gate electrode.

The source electrode of the second transistor T2 is connected to the power lines PL1 to PLn and the storage capacitor Cst is connected between the gate electrode of the second transistor T2 and the power lines PL1 to PLn.

The light emitting diode Del is connected to the drain electrode of the second transistor T2.

The first transistor T1 serves as a switching element for supplying a data signal supplied through the data lines DL1 to DLn to the second transistor T2 according to a gate signal supplied through the gate lines GL1 to GLm The second transistor T2 is a driving element for supplying a power supply voltage supplied through the power lines PL1 to PLn to the light emitting diode Del in accordance with a data signal applied to the gate electrode through the first transistor .

Accordingly, a different power supply voltage VDD depending on the data signal is supplied to the light emitting diode Del, thereby enabling various gray scales to be displayed.

In FIG. 4, two transistors T1 and T2 are formed in one pixel region P, but in another embodiment, three or more transistors may be formed in one pixel region.

The gate driver 130 generates a gate signal using the gate control signal supplied from the timing controller 150 and supplies the generated gate signal to the first to m-th gate lines GL1 to GLm, respectively.

The data driver 140 generates a data signal using the data control signal and the RGB signal supplied from the timing controller 150 and supplies the generated data signal to the first to the nth data lines DL1 to DLm, And supplies the power supply voltage VDD to the first to the n-th power wiring lines PL1 to PLn.

The data driver 140 includes a current measuring unit 142 for measuring the current flowing through the first to nth power lines PL1 to PLn of the organic electroluminescent panel 120, And the current limiting unit 144 for limiting the intensity of the current flowing through the first to the n-th power wiring lines PL1 to PLn of the first to n-th power lines PL1 to PLn.

The current measuring unit 142 measures the current flowing through the power wiring of the organic electroluminescence panel 120 in real time and provides the result to the timing controller 150. The current measuring unit 142 measures the current flowing through the power wiring of the organic light emitting panel 120 in the red, The current flowing through the corresponding power wiring can be measured.

The current limiting unit 144 limits the current of the power supply voltage VDD supplied to the power wiring of the organic electroluminescence panel 120 to the upper limit value in accordance with the current limiting signal supplied from the timing controller 150, , Green, and blue pixel regions (P), respectively.

For example, when it is assumed that the first to third power lines PL1 to PL3 correspond to the red, green, and blue pixel regions P, respectively, the current limiting portion 144 is connected to the first to third power lines PL1 Green and blue current conversion circuits 144a, 144b, and 144c connected to one ends of the red, green, and blue current conversion circuits 144a, 144b, and 144c, respectively. And 144c, and a conversion circuit 142a connected to both ends of the resistor 142b.

Each of the red, green and blue current conversion circuits 144a, 144b and 144c may be a current source type digital to analog converter (DAC), and the conversion circuit may be an analog to digital converter ADC).

The converting circuit 142a of the current measuring unit 142 can measure the current flowing through the first to third power lines PL1 to PL3 by measuring the voltage drop in the resistor 142 of the voltage VGP, And transmits the measured current value to the timing controller 150.

The red, green, and blue current conversion circuits 144a, 144b, and 144c receive the red, green, and blue current limiting signals from the timing controller 150 and apply the red, green, and blue current limiting signals to the first to third power lines PL1 to PL3 And limits the current of the power supply voltage VDD to the red, green, and blue upper limit values.

The timing controller 150 generates a gate control signal, a data control signal, and an RGB signal from the external system, and supplies the gate control signal, the data control signal, and the RGB signal to the gate driver 130 and the data driver 140.

The storage unit 160 stores the current value for each color corresponding to the average gradation, and the frame memory unit 170 stores the image signal of the previous frame.

In particular, the timing controller 150 determines whether the video signal is a still image or a moving image by analyzing the video signal for each frame and checks whether the measured current value supplied from the current measuring unit 142 is abnormal .

If it is determined that the current value measured in the current frame is larger than the current value measured in the previous frame, the timing controller 150 calculates an average gray level of the video signal of the current frame, The current values of red, green, and blue are extracted from the storage unit 160.

Further, the timing control section 150 supplies the current limiting section 144 with red, green, and blue current limit signals for specifying the extracted current value as the current upper limit value for red, green, and blue.

For this purpose, the storage unit 160 stores a table for each of red, green, and blue gradations that have been optically compensated in consideration of luminance and chromaticity coordinates, and a current value corresponding to the corresponding gradation. An EEPROM (electrically erasable programmable read only memory ).

Also, the frame memory 170 may continuously update and store the video signal of the previous frame, and may be configured as a synchronous dynamic random access memory (SDRAM).

In the organic light emitting display having such a structure, when a still image is displayed, a current value flowing through the organic electroluminescent panel is actually measured to check for an abnormality, and when the measured current value increases, an initial current rise occurs The initial current rise and the initial luminance increase can be suppressed by restricting the current of the power supply voltage supplied to the organic electroluminescence panel to the upper limit value by using the table of the average gradation and the current value judged and set in advance, It is possible to prevent degradation of image quality.

And, since the additional aging step can be omitted, the process can be simplified and the manufacturing time and manufacturing cost can be reduced.

A driving method of such an organic light emitting display will be described with reference to the drawings.

FIG. 6 is a flowchart illustrating a method of driving an organic light emitting display according to an embodiment of the present invention, which will be described with reference to FIGS. 4 and 5. FIG.

6, the frame memory unit 170 of the organic light emitting display device 110 stores a video signal of a previous frame in a video signal received from an external system (st200) The control unit 150 compares the video signal of the previous frame of the frame memory unit 170 with the video signal of the current frame transmitted from the external system (step 202).

If the video signal of the previous frame and the video signal of the current frame are different from each other but different from each other, the timing controller 150 determines that the video to be displayed is not a still video but a moving picture frame count (st204) and drives the organic light emitting display device 110 in a normal mode in which the current of the power supply voltage VDD of the power wiring is not limited (st206) .

The timing controller 150 continues the comparison of the video signal of the previous frame with the video signal of the current frame during a frame of a predetermined reference number N to check whether the video to be displayed is a still video, Before the reference number N is reached, the organic light emitting display device 110 is driven in the normal mode (st206).

That is, when the video signal of the previous frame is the same as the video signal of the current frame, the timing control unit 150 increments the frame count by "1" (st210) and compares the current frame count with the reference number N st210).

As a result of the comparison, if the current frame count is less than the reference number N, the timing controller 150 drives the organic light emitting display device 110 in the normal mode (st206) N), the timing controller 150 receives the current value of the current frame flowing from the current measuring unit 142 to the power lines PL1 to PLn, compares the current value with the current value of the previous frame, and determines whether the current increases st212).

As a result of the determination, if the current value does not rise, the timing controller 150 determines that the initial current rise and the initial brightness increase do not occur in the light emitting diode Del, and the organic light emitting display device 110 is driven in the normal mode (ST206).

When the current value increases, the timing controller 150 determines that the initial current rise and the initial luminance rise have started to occur in the light emitting diode Del, and calculates the average gradation of the video signal of the current frame, Green, and blue, respectively, corresponding to the average gradation of the video signal of the current frame (step 214), supplies the calculated current value to the current restricting section 144, and outputs the calculated current value Value to the upper limit value of the power supply voltage VDD applied to the power lines PL1 to PLn.

Finally, the organic light emitting display device 110 is driven in the normal mode or the current limited mode with respect to the video signal of the current frame, and then this process is repeated for the video signal of the next frame.

As described above, in the organic light emitting display device 110 according to the embodiment of the present invention, the video signals are compared frame by frame to determine whether the video signals are still or moving images. When the video signals are discriminated as still images, When it is determined that the current flowing through the organic light emitting display panel is measured in real time and the current measurement current is increased, the current of the power supply voltage applied to the power wiring of the organic electroluminescence panel is limited to the upper limit value by using the table of the average gradation and current stored in advance .

Therefore, the current flowing in the light emitting diode Del does not rise above the upper limit value, and it is possible to prevent the initial afterimage due to the initial current rise and the initial luminance increase.

The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an initial light emitting characteristic of a light emitting diode of a conventional organic light emitting display. FIG.

FIGS. 2A and 2B are diagrams illustrating first and second stop patterns displayed on a conventional organic light emitting display device, respectively. FIGS.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an organic light emitting display.

4 is a schematic view showing an organic light emitting display device according to an embodiment of the present invention.

5 is a detailed view of a current measuring unit and a current limiting unit of an organic light emitting display according to an embodiment of the present invention.

6 is a flowchart illustrating a method of driving an organic light emitting display according to an exemplary embodiment of the present invention.

Claims (8)

An organic electroluminescent panel including a light emitting diode and displaying an image; A timing controller for analyzing the video signal corresponding to the video by frame to determine the type of the video; A current measuring unit for measuring a current value of a power supply voltage applied to the light emitting diode in real time and transmitting the measured current value to the timing controller; And And a current limiting unit for limiting the current of the power supply voltage when the image is a still image, And an organic electroluminescent display device. The method according to claim 1, A frame memory for storing the video signal of the previous frame and providing the video signal to the timing controller; and a storage unit for storing a table for a current corresponding to the average gradation and the average gradation for each frame of the video signal, The organic electroluminescent display device comprising: 3. The method of claim 2, Wherein the timing controller compares the video signal of the previous frame with the video signal of the current frame to determine that the video is the still video if the current video signal of the current frame is identical to the video signal of the current frame, And controls the current limiter so as to extract a current corresponding to the average gradation of the current frame from the table and to set the current corresponding to the average current gradation of the current frame to an upper limit value of the current of the power supply voltage when the current is greater than the current value of the power supply voltage. The method of claim 3, The organic electroluminescence panel includes a substrate, a gate wiring, a data wiring, and a power wiring formed on the substrate so as to intersect with each other to define a pixel region, and a gate electrode formed on the gate wiring and the data wiring, A second transistor having a gate electrode, a source electrode, and a drain electrode connected to the drain electrode, the power wiring, and the light emitting diode of the first transistor, A gate electrode, and a storage capacitor connected to the power wiring, wherein the light emitting diode is connected to the power wiring through the second transistor, and the power source voltage is applied to the power wiring. 5. The method of claim 4, A gate driver for supplying a gate signal to the gate line, and a data driver for supplying a data signal to the data line. Storing a video signal of a previous frame; Comparing the video signal of the previous frame with the video signal of the current frame; Supplying a power supply voltage to the organic electroluminescent panel in which a current corresponding to an average gray level of the video signal of the current frame is set to an upper limit value when the video signal of the previous frame is identical to the video signal of the current frame; And Wherein the light emitting diode of the organic electroluminescence panel emits light using the power supply voltage And driving the organic light emitting display device. The method according to claim 6, Wherein the comparison of the video signal of the previous frame with the video signal of the current frame is continued for at least a reference number of frames. 8. The method of claim 7, Measuring a current value of the power supply voltage supplied to the organic electroluminescence panel in real time; Comparing a current value of the power source voltage of the previous frame with a current value of the power source voltage of the current frame when the video signal of the previous frame is identical to the video signal of the current frame; If the current value of the power source voltage of the current frame is greater than the current value of the power source voltage of the previous frame, Extracting a current corresponding to the average gradation of the signal And a driving method for driving the organic light emitting display device.

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