KR101126349B1 - Oled - Google Patents

Abstract

The present invention relates to a load effect compensation device of an organic light emitting display device for preventing deterioration due to load effects occurring in a large organic light emitting display device.

According to an embodiment of the present invention, a load effect correction unit for correcting an image signal according to an amount loaded on a screen, and converting a data pulse for inputting the corrected image signal into a data line of an organic light emitting diode are applied to the data line of the organic light emitting diode. A load effect compensation device of an organic light emitting display device having a data driver is provided.

Accordingly, since the image signal value is corrected without changing the panel structure or the process conditions, the luminance can be kept constant regardless of the load amount.

Description

Load effect compensation device for organic light emitting display device

1 is a schematic plan view of a typical active matrix type organic light emitting display device.

2 is an equivalent circuit diagram of the pixel circuit of FIG.

3 is a screen state diagram illustrating screen degradation caused by a load effect of a conventional organic light emitting display device.

4 is a diagram illustrating a rod configuration of a conventional organic light emitting display device.

FIG. 5 is a graph illustrating luminance values according to amounts of image signals having the same gray scale values loaded on a screen; FIG.

6 is a conceptual graph of a load effect compensation device of an organic light emitting display device according to an embodiment of the present invention;

7 is a block diagram of a load effect compensation device of an organic light emitting display device according to an embodiment of the present invention.

FIG. 8 is a table of compensation coefficients for each APL step according to each grayscale stored in the lookup table storage of FIG. 7. FIG.

9 is a view for explaining an example of correcting an image signal received by a load effect corrector, an APL calculator, and a lookup table storage;

The present invention relates to a load effect compensation device of an organic light emitting display device for preventing deterioration due to load effects occurring in a large organic light emitting display device.

An organic light emitting device (OLED) is a self-light emitting device that emits a fluorescent material by recombination of electrons and holes. The organic light emitting display device using the same is faster than the passive light emitting device requiring a separate light source, such as a liquid crystal display device, the response speed is fast, the DC driving voltage is low and ultra-thin film is possible to be applied to the wall-mounted or portable.

Such an organic light emitting diode is divided into a passive matrix organic light emitting diode (PMOLED) and an active matrix organic light emitting diode (AMOLED) using TFTs as a method of driving an OLED light emitting cell. Can be. A simple matrix type organic light emitting diode (PMOLED) is formed so that an anode and a cathode are orthogonal, and a line is selected and driven, whereas an active matrix organic light emitting diode (AMOLED) connects a TFT and a capacitor to each of the ITO pixel electrodes to form a capacitor. It is a driving method to maintain the voltage by the capacitance.

1 is a schematic plan view of a general active matrix organic light emitting display device.

Referring to FIG. 1, a general active matrix type organic light emitting display device has a plurality of pixel circuits 11 formed in an OLED panel 10. The OLED panel 10 is electrically connected to the scan driver 12 and the data driver 14.

The scan driver 12 sequentially outputs the selection signals through the scan lines S1, S2, S3, S4 ..... Sn, and the data driver 14 outputs the data lines D1, D2, D3 ... Dn. A data voltage representing an image signal is outputted through < RTI ID = 0.0 > 1, < / RTI >

That is, the OLED panel 10 is branched from the data driver 14 to a plurality of data lines D1, D2, D3,..., Dn and branched from the scan driver 12 to select images. A plurality of scanning lines S1, S2, S3, ..., Sn for transmitting? Are arranged so as to cross each other, and a pixel circuit 11 is formed at each intersection point of the scanning line and the data line.

FIG. 2 is an equivalent circuit diagram of the pixel circuit of FIG. 1.

Referring to FIG. 2, in the pixel circuit 11 of the organic light emitting display device, an image signal is transmitted to a data line Dn branched from the data driver 14, and a scan line Sn branched from the scan driver 12. The selection signal is transmitted to The second thin film transistor M2 transfers data to the capacitor Cst according to the selection signal of the scan line Sn, and the capacitor Cst stores and stores the applied data. The first thin film transistor M1 supplies the current from the power supply line Vdd to the organic light emitting diode OLED according to the data applied to the capacitor Cst, thereby emitting the organic light emitting diode OLED.

Referring to the operation of the pixel circuit 11 of the organic light emitting display described above in detail, when the second thin film transistor M2 is turned on by the selection signal Select applied to the gate of the first thin film transistor M1, The data voltage Vdata is applied to the gate of the first thin film transistor M1 through the data line Vdata. In addition, a current flows through the first thin film transistor M1 to the organic light emitting diode OLED in response to the data voltage Vdata applied to the gate, thereby emitting light.

At this time, the voltage Vgs_n between the source and gate of the first thin film transistor M1 becomes the difference between the voltage Vdd of the power line and the data voltage Vn transferred through the second thin film transistor M2, and the first thin film transistor ( M1) supplies the organic light emitting diode OLED with a current corresponding to the square of the difference between the source-gate voltage and the threshold voltage Vth of the transistor. This may be expressed as Equation 1 below.

I _OLED = β (Vgs_n-Vth) ²

Here, I _OLED is a current flowing through the organic light emitting diode, Vgs_n is a voltage between the source and the gate of the transistor M1, Vth is a threshold voltage of the first thin film transistor M1, and β is a constant value. Where Vgs_n is Vdd-Vn.

As shown in Equation 1, according to the pixel circuit 11 shown in FIG. 2, the current I _OLED corresponding to the applied data voltage Vn is supplied to the organic light emitting diode OLED, and the supplied current. In response to this, the organic light emitting diode OLED emits light.

However, there is a problem in that image quality deterioration occurs due to a load effect in which luminance decreases when the number of loads increases due to the large area of the organic light emitting display device.

3 is a screen state diagram illustrating screen degradation due to a load effect of a conventional organic light emitting display device.

Referring to FIG. 3, in the conventional organic light emitting display device, a luminance decreases as a load increases, that is, a load effect occurs. That is, the luminance value measured when 5% of the screen size (right edge screen of FIG. 3B) emits light when the gray scales are all 256 RGB is measured when 100% of the screen size (right edge screen of FIG. 3B) emits light. It was larger than one luminance value.

4 is a diagram illustrating a rod configuration of a conventional organic light emitting display device.

Referring to FIG. 4, when only A pixels, B pixels, and C pixels of FIG. 4 emit light, 5%, 50%, and 100% of the screen size emit light when P _a , P _b , and P _c are respectively emitted. Each power was P _a , P _a + P _b , P _a + P _b + P _c . Theoretically, if the power is increased infinitely to increase the brightness, the brightness may be relatively increased. However, in the organic light emitting display device, power consumption is no longer increased by saturating the power in consideration of power consumption and efficiency. This limiting power consumption was to protect the display device and to keep the power consumption constant.

5 is a graph illustrating luminance values according to amounts of image signals having the same gray scale values loaded on a screen.

Referring to FIG. 5, since power consumption is kept constant by saturating power, luminance decreases even when the average picture level or video picture level increases. The decrease in luminance due to the load effect becomes larger as the organic light emitting display becomes larger and becomes an important factor that hinders the large area of the organic light emitting display.

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a load effect compensation device of an organic light emitting display device capable of maintaining a constant luminance regardless of the load amount without changing the panel structure or the process conditions. There is a purpose.

In order to achieve the above object, the present invention is a load effect correction unit for correcting the image signal according to the amount loaded on the screen, and converts the corrected image signal into a data pulse to be input to the data line of the organic light emitting device A load effect compensation device of an organic light emitting display device having a data driver applied to a data line of an electroluminescent device.

At this time, the load level calculation unit for calculating the load level of the received video signal and the compensation coefficient of the load levels according to each gray level are stored in advance, and corresponding to the load level of the received video signal calculated by the load level calculation unit. The apparatus may further include a look-up table storage unit which passes the compensation coefficient to the load effect correction unit, and the load effect correction unit may correct the image signal using the compensation coefficient.

In addition, the compensation coefficient of the load levels according to each gray level is the same as the following equation, and the load effect correction unit may correct the image signal by subtracting the compensation coefficient from the image signal.

α is a compensation coefficient of a load level according to each gradation, x is a measured luminance value of a load level according to each gradation, and y is a measured luminance value of a specific load level according to the gradation.

In addition, the measured luminance value of the specific load level of y may be the minimum luminance value of the final load level.

In addition, the image signal corrected by the load effect correction unit may be expressed as in the following equation.

Here, γ is an image signal corrected by the load effect correction unit, β is a received image signal which is not corrected, and α is a compensation factor of a load level according to each gray level.

In addition, the gamma correction unit may further have a gamma correction unit for correcting the image signal before the image signal is corrected by the load effect correction unit.

In addition, the half-toning unit may further include a half-toning unit which halftones the image signal corrected by the load effect correction unit using either error diffusion or dithering and inputs the data signal to the data driver.

In addition, the lookup table storage unit calculates a compensation coefficient by calculating some load levels for each gray level by the above equations, but calculates a compensation coefficient for the remaining unloaded load levels by using an interpolation method ( interpolation).

In addition, the load level may be an average picture level (APL) of the video signal.

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

6 is a conceptual graph of a load effect compensation device of an organic light emitting display device according to an embodiment of the present invention.

As can be seen from FIG. 6, a load effect compensator of an organic light emitting display device according to an exemplary embodiment of the present invention is referred to as a load amount or an average resolution (APL) for each gray level. Increases, the image signal is corrected to have a constant luminance value, for example, a minimum luminance value, regardless of the APL. In FIG. 6, in the case of the conventional organic light emitting display device, the brightness decreases as the APL increases, causing the load effect. In FIG. 6, B represents the organic light emitting display device according to the embodiment of the present invention. It has the minimum luminance value regardless of the APL.

7 is a block diagram of a load effect compensation device of an organic light emitting display device according to an embodiment of the present invention.

Referring to FIG. 7, a load effect compensator 20 of an organic light emitting display device according to an embodiment of the present invention may include a gamma correction unit 22, a load effect correction unit 24, an APL calculation unit 26, It has a lookup table storage unit 28. In addition, the load effect compensator 20 includes a half toning unit 30, a data alignment unit 32, and a data driver 34.

The gamma correction unit 24 gamma corrects an image signal input to a data line, for example, grayscale values A ₁ , A ₂ , A ₃ .... A _N-2 , A _N-1 , A _N. do. That is, gamma correction is to exponentially grayscale values of the video signal as shown in Equation (2).

Is a gamma correction value of the gray value of the video signal, b is a gray value of the video signal, 255 is a gray value of the highest video signal, and a is a gamma constant.

The load effect correcting unit 26 outputs an image signal, for example, grayscale values A ₁ , A ₂ , A ₃ ... A _N-2 , A _N-1 , A _N according to the APL of each gray Correct it using the compensation factor. The load effect correction unit 26 converts the grayscale values of the video signal as shown in Equation 3 below.

In Equation 3, γ is a gray value of the image signal corrected by the road effect correction unit, β is a gray value of the gamma-corrected image signal, and α is a compensation coefficient of the APL according to each gray level.

The lookup table storage unit 26 stores the compensation coefficients of the APL according to each gray level in advance. In order to calculate the compensation coefficient β of the APL according to each gray level, first, the APL step for each gray level is divided into APL0 to APL1023 into 1024 steps. Thereafter, luminance values per frame for each gray level are measured for each APL step. For example, if the resolution is 640 x 480 RGB at 256 gradations, the minimum APL0 of a specific gradation is the luminance value when all screens are emitted at that specific gradation value, for example 100 gradations, 921,600, and the maximum APL1023 is 100 gradations. The luminance value obtained when 5% of the entire screen was emitted is 46,080. The maximum APL1023 is defined as the luminance value when 5% of the entire screen is emitted because it is considered to have the same luminance value at 0 to 5% emission.

After measuring the luminance value of each APL step of a specific gradation, the compensation coefficient of the APL step of a specific gradation is calculated by the following Equation 4, and the compensation coefficient is stored in the lookup table storage unit 26.

α is a compensation coefficient of APL according to each gray level, x is a luminance value (Lumi_APL_X) measured for each APL step according to each gray level, and y is a measured luminance value (Lumi_APL1023) of the maximum APL step for the corresponding gray level.

8 is a table of compensation coefficients for each APL step according to each gray level stored in the lookup table storage unit 26. As a result, when the gradation value of the video signal and the APL step of the video signal per frame are determined, the lookup table storage unit 26 passes the compensation coefficient to the load effect correction unit 24 using these values. At this time, the compensation coefficient α is larger as the APL step is lower. A large compensation coefficient α means that a large amount of luminance correction should be performed, and a correction of the gray value of the image signal should also be large.

The APL calculator 28 determines an APL step by calculating an APL for the received video signal. The APL step is determined by summing the gradation values of the image signals per frame for the entire screen and then comparing them with a predetermined APL.

When the APL step of the image signal received by the APL calculation unit 28 is determined, the load effect correction unit 24 retrieves a compensation coefficient for the gray level value of each pixel of the received image signal from the lookup table storage unit 26. And the received video signal is corrected. Then, the corrected video signal for each pixel of the video signal is obtained.

FIG. 9 is a diagram for explaining an example of correcting an image signal received by the load effect corrector 24, the APL calculator 28, and the lookup table storage 26.

Referring to FIG. 9, the gamma corrected video signal value of the APL500 in the gamma correction unit 22 is 200.10, the measured luminance value of the APL500 is 500 cd / m 2, and the measured luminance value of the APL1023 is the maximum APL step. In the case of 200 cd / m 2, the compensation coefficient is “0.4” when calculated according to Equation 5 below. This compensation coefficient is already stored in the lookup table 26.

This correction coefficient is passed to the load effect correction unit 24, and the load effect correction unit 24, which has received the compensation coefficient, calculates the corrected image signal value 120.06 according to the following expression (6).

Referring to FIG. 7 again, the half toning unit 30 halftons the image signal corrected by the load effect correction unit 24 by at least one method of error diffusion or dithering. . That is, the half toning unit 30 halftons the decimal value of the data signal value corrected by Equation 3 consisting of an integer value and a decimal value, for example, 120.06 (120 is an integer value and 0.06 is a decimal value). It is reflected in the integer of the next video signal value. In this way, since the decimal value of the previous video signal value is passed to the next video signal value, data distortion can be prevented by reflecting the next data signal value without discarding the decimal value of the video signal.

The data sorter 32 arranges the data in time according to the organic light emitting display device.

Finally, the data driver 34, a data arranging unit 32 to the data line for receiving a time alignment value of the video signal by _{(D 1, D 2, D} 3 .... D N-2, D N- ₁ , D _N ) is supplied with a data driving pulse for the finally corrected image signal value to drive the organic light emitting diode OLED.

As described above, since the image signal is corrected by using the load effect compensation device of the organic light emitting display device according to an embodiment of the present invention, it is generated according to the large area of the organic light emitting display device without improving the panel structure or manufacturing process. It can prevent the load effect.

As mentioned above, although an embodiment of the present invention has been described with reference to the drawings, the present invention is not limited thereto.

In the above embodiment, the gamma correction is performed before the image signal value is corrected. However, since the gamma correction unit 22 does not exist, the load effect correction unit 24 directly corrects the image signal value without the gamma correction. It may be.

In addition, in the above embodiment, the load effect correcting unit 24 has been described as half-toning in the half-toning unit 30 to prevent data distortion after correcting the image signal value, but the half-toning unit 30 in the image signal The value may be input to the data driver 32 without halftoning.

In addition, in the above embodiment, the load level is described as being APL, but the present invention is not limited thereto and may have any value that can distinguish the load level according to the load amount.

As described above, it is to be understood that the technical structure of the present invention can be embodied in other specific forms without departing from the spirit and essential characteristics of the present invention.

Therefore, it should be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, It is intended that all changes and modifications derived from the equivalent concept be included within the scope of the present invention.

As described above, the present invention corrects the image signal value without changing the panel structure or the process conditions, so that the luminance can be kept constant regardless of the load amount. Accordingly, it is possible to prevent the deterioration of image quality due to the load effect caused by the increased load amount.

As a result, the present invention has the effect that the large area of the organic light emitting display device can be increased.

Claims (9)

A load effect correction unit for correcting the video signal according to the amount loaded on the screen; A load level calculator configured to calculate a load level of the received video signal; A look-up table storage unit which stores a compensation coefficient of load levels according to each gray level in advance and passes the compensation coefficient corresponding to the load level of the received image signal calculated by the load level calculator to the load effect correction unit; And And a data driver converting the image signal corrected by the load effect correction unit into a data pulse to be input to the data line of the organic light emitting diode and applying the data signal to the data line of the organic light emitting diode. The load effect correction unit corrects an image signal by using the compensation coefficient, The compensation coefficient of the load levels according to each gray level is represented by Equation 7 below, and the load effect correction unit corrects the image signal by subtracting the compensation coefficient from the image signal. Compensation device.

α is the compensation coefficient of the load level according to each gradation, x is the measured luminance value of the load level according to each gradation, and y is the measured luminance value of the specific load level according to the gradation. delete delete The method of claim 1, And the measured luminance value of the specific load level of y is a minimum luminance value of the final load level. The method of claim 4, wherein And the image signal corrected by the load effect correcting unit is expressed by Equation (8).

Here, γ is an image signal corrected by the load effect correction unit, β is a received image signal that is not corrected, and α is a compensation factor of a load level according to each gray level. The method according to claim 1 or 4, And a gamma correction unit for gamma correcting the video signal before correcting the video signal by the load effect correcting unit. The method of claim 5, And a half toning unit for half-toning the corrected image signal by one of error diffusion or dithering and inputting the corrected image signal by the load effect correction unit to the data driver. The method of claim 1, The lookup table storage unit calculates a compensation coefficient by calculating some load levels for each gray level by the equation (7), and interpolation using the compensation coefficients obtained by calculating the compensation coefficients for the remaining unloaded load levels. A load effect compensation device of an organic light emitting display device, characterized in that obtained by (). The method of claim 5, The load level compensation device of the organic light emitting display device, characterized in that the load level is the APL (Average Picture Level) of the image signal.

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