KR100589385B1 - Light-emitting display device and method of generating gray voltage - Google Patents

Abstract

The present invention relates to a light emitting display device and a method of generating a gray voltage thereof.

In the present invention, a light emitting display device is formed in a pixel area where a data line and a signal line cross each other, and a pixel circuit including a capacitor, a transistor for supplying a current corresponding to a voltage charged in the capacitor, and a light emitting element is formed. A plurality of gray voltages are generated, and a gray voltage corresponding to a gray level equal to or higher than a set level among the gray voltages is corrected. Then, one gray voltage is selected from the gray voltage and the corrected gray voltage according to the data signal to be supplied to the data line.

According to the present invention, the gray scale voltage correction is performed according to the gamma characteristic of the light emitting display device, thereby improving image display quality.

Organic EL, gradation voltage, gamma correction

Description

LIGHT EMITTING DISPLAY DEVICE AND GRAY VOLTAGE GENERATING METHOD THEREOF}

1 is a conceptual diagram of an organic EL device.

2 is a schematic structural diagram of a light emitting display device according to an embodiment of the present invention.

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

4 is a graph illustrating gamma characteristics of a light emitting display device and a gamma characteristic of a liquid crystal display device according to an exemplary embodiment of the present invention.

5 is a block diagram of a gray voltage generator according to an exemplary embodiment of the present invention.

FIG. 6 is a circuit diagram of the voltage generator shown in FIG. 5.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device, and more particularly, to an organic electroluminescent (EL) display device and a method of generating a gradation voltage thereof.

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 M × N organic light emitting cells. The organic light emitting cell has a structure of an anode (ITO), an organic thin film, and a cathode layer (metal). A conceptual diagram of such an organic EL element is shown in FIG. The electroluminescent organic thin film has a multilayer structure including an emission layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) to improve the light emission efficiency by improving the balance between electrons and holes. It also comprises a separate electron injection layer (Eil injection layer (EIL) and hole injection layer (HIL)).

As such a method of driving the organic light emitting cell, there are a simple matrix method and an active matrix method using a thin film transistor (TFT). In the simple matrix method, the anode and the cathode are orthogonal and the line is selected and driven, whereas the active driving method connects the thin film transistors to each indium tin oxide (ITO) pixel electrode and the capacitance of the capacitor connected to the gate of the thin film transistor. Is driven according to the maintained voltage. In this case, the active driving method is divided into a voltage driving method and a current driving method according to the type of the signal applied to set the voltage to the capacitor.

In the conventional organic EL display device, pixels are formed in an area where the data line and the scan line cross each other, and each pixel is selected according to a signal applied from the scan line and then emits light according to display information applied through the data line.

By the way, in a series of display apparatuses including such an organic EL display device, a gamma characteristic in which the gray level of an image does not linearly change but varies linearly with the voltage level of an image signal (or data signal) appears. These gamma characteristics are different depending on the display device. In a cathode ray tube (hereinafter referred to as a CRT) using phosphor emission by electrons, gamma characteristics of red (hereinafter referred to as R), green (hereinafter referred to as G), and blue (hereinafter referred to as B) are the same. Has In addition, in the liquid crystal display, the color reproducibility is inferior to that of the CRT due to the electro-optical characteristics of the liquid crystal. This is because the gamma characteristics for R, G, and B are different because the liquid crystal transmittance varies with wavelength. Accordingly, the liquid crystal display uses gamma correction voltages to change intervals between voltage levels of the image signal differently. That is, the gamma characteristic is corrected by adding a gamma correction voltage preset so as to have a different level according to the voltage level of the image signal as an offset voltage to the voltage level of the image signal.

However, in the organic EL display device, image display is performed according to light emission of the organic EL element formed for each pixel, and thus gamma characteristics generated in the organic EL display device using the conventional liquid crystal display device or the gamma correction method used in the CRT. Cannot be corrected effectively.

Therefore, the technical problem to be solved by the present invention is to improve the image display quality by causing the gray scale to be linearly changed according to the voltage level of the image signal in the organic EL display device. In particular, it is for efficiently correcting the gamma characteristic of an organic electroluminescence display.

In order to solve this problem, a light emitting display device according to an aspect of the present invention transmits a data current and a plurality of data lines formed in one direction, a plurality of signal lines transferring scan signals and intersecting the data lines, the data lines and the Display panels formed in regions where signal lines cross each other and including a plurality of pixel circuits for displaying an image corresponding to an applied data current; A scan driver supplying a scan signal to the scan line; A data driver supplying a gray voltage corresponding to a data signal to the data line; And a gray voltage generator supplying the gray voltage for each gray level to the data driver, wherein the gray voltage corresponding to the gray level equal to or higher than a set level among the gray voltages is corrected and output.

The gray voltage generator may include a voltage generator configured to generate gray voltages for each gray level; It may include a correction unit for correcting and outputting a gray voltage according to the gray level of the set level or more of the gray voltage output from the voltage generator. The voltage generator may include a plurality of resistors connected in series between a first voltage and a second voltage to generate a plurality of gray voltages. In addition, the correction unit may be made of a differentiator for differentiating and outputting the gray voltage corresponding to the gray level of the predetermined level or more.

According to another aspect of the present invention, a gray voltage generation method includes a capacitor, a transistor configured to supply a current in response to a voltage charged in the capacitor, and a light emitting element formed in a pixel region where the data line and the signal line cross each other. A gray voltage generation method of a light emitting display device having a pixel circuit, the method comprising: a) generating a plurality of gray voltages; b) correcting a gray voltage according to a gray level of a predetermined level or more among the gray voltages; And c) selecting one of the gray voltages and the corrected gray voltages according to the data signal to be supplied to the data line.

Here, in step b), the gray level voltage corresponding to the gray level of the set level or more is differentiated and output, and the set level may be 200 gray levels or more.

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 the middle.

A light emitting display device according to an 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, a light emitting display device according to an exemplary embodiment will be described in detail with reference to FIG. 1. 1 is a schematic plan view of a light emitting display device according to an exemplary embodiment of the present invention.

As shown in FIG. 1, the light emitting display device according to the exemplary embodiment of the present invention includes an organic EL display panel (hereinafter, referred to as a display panel 100), a data driver 200, a scan driver 300, and a gray voltage generator. 400.

The display panel 100 includes a plurality of data lines Y1-Yn extending in the vertical direction, a plurality of signal lines X1-Xm and Z1-Zm extending in the horizontal direction, and a plurality of pixel circuits 110. The signal lines X1-Xm transmit the scan signals for controlling the light emission operation of the pixels to the display panel 100, and the data lines Y1-Yn transfer the data signals to the display panel 100. Here, the pixel circuit 110 includes a capacitor for charging a voltage transferred from a data line, a transistor for supplying a current corresponding to the voltage charged in the capacitor, and a light emitting device that emits light according to the current supplied through the transistor. This structure is a well-known technique and thus detailed description thereof will be omitted.

The data driver 200 applies a data signal to the data lines Y1-Yn. The scan driver 300 sequentially applies a scan signal for selecting a pixel circuit and emitting light to the signal lines X1-Xm. In addition, the gray voltage generator 400 generates a gray voltage whose gamma characteristic is corrected by the data driver 200 and provides the gray voltage to the data driver 200, and the data driver 200 appropriately adjusts the gray voltage according to the applied data signal. Is provided to the display panel 100. Here, when the data driver 200 is a 6-bit data driver, gray levels from 0 to 63 are represented. When the data driver 200 is an 8-bit data driver, gray levels from 0 to 255 can be expressed.

The scan driver 300 and / or the data driver 200 may be electrically connected to the display panel 100 or may be adhesively attached to the display panel 100 to be electrically connected. ) May be mounted in the form of a chip. Alternatively, a flexible printed circuit (FPC) or a film may be mounted on the display panel 100 in the form of a chip or the like, which may be mounted on a COF (chip on flexible board, chip). on film). Alternatively, the scan driver 300 and / or the data driver 200 and / or the gray voltage generator 400 may be directly mounted on the glass substrate of the display panel, which is called a chip on glass (COG) method. It may also be replaced with a driving circuit formed on the glass substrate in the same layers as the signal line, data line and thin film transistor.

In the pixel circuit 110 according to an exemplary embodiment, a pixel circuit of a current driving method or a voltage driving method may be used. 3 illustrates a structure of a pixel circuit of a voltage driving method.

The pixel circuit 110 includes an organic EL element OLED, a driving transistor M1, a switching transistor M1, and a capacitor C1. The driving transistor M1 is connected to the organic EL element OLED to supply current for emitting light, and the amount of current of the driving transistor M1 is controlled by the data voltage applied through the switching transistor M2. At this time, a capacitor C1 for maintaining the applied voltage for a predetermined period is connected between the source and the gate of the transistor M1. The structure of the pixel circuit according to the exemplary embodiment of the present invention is not limited to that shown in FIG. 3.

The light emitting display device according to the embodiment of the present invention having such a structure has the following gamma characteristics.

4 illustrates gamma characteristics of a light emitting display device and a gamma characteristic of a liquid crystal display device according to an exemplary embodiment of the present invention. FIG. 4A is a graph showing gamma characteristics of the liquid crystal display device, and FIG. 4B is a graph showing gamma characteristics of the organic EL device.

As shown in FIG. 4A, it can be seen that the liquid crystal display has lower linearity and higher gray level. However, as shown in (b) of FIG. 4, the organic EL display device has only non-linear characteristics such as diode characteristic curves, and upper gray scales (for example, 200 or more gray scales) have linear characteristics.

Therefore, in the exemplary embodiment of the present invention, the gray scale characteristic of the organic EL display apparatus is corrected using the gray scale voltage device used in the liquid crystal display based on the difference in gamma characteristics.

That is, the gray voltage device of the liquid crystal display generates gray voltage for each gray level in consideration of the non-linear characteristics of the lower gray level and the upper gray level. However, since the organic EL display device is nonlinear in the lower gradation but the upper gradation is linear in nature, when the gradation voltage device of the liquid crystal display is applied to the organic EL display as it is, the display of the upper gradation is not naturally performed. In consideration of this, in the exemplary embodiment of the present invention, the gray voltage device used in the liquid crystal display device is used, and the gray voltage corresponding to the upper gray level is corrected to be output in accordance with the linear characteristics of the organic EL display device.

To this end, the gray voltage generator according to the embodiment of the present invention has a structure as shown in FIGS. 5 and 6.

5 is a block diagram of a gray voltage generator according to an exemplary embodiment of the present invention, and FIG. 6 is a circuit diagram of the voltage generator 41 shown in FIG. 5.

As shown in FIG. 5, the gray voltage generator 400 according to an exemplary embodiment of the present invention corresponds to a voltage generator 41 for generating a corresponding gray voltage for each gray level, and a gray level equal to or higher than a set level among the generated gray voltages. And a correction unit 42 for differentiating and outputting the voltage.

As illustrated in FIG. 5, the voltage generator 41 includes a plurality of resistor strings R1 to Rn + 1 for generating a plurality of gray voltages V1 -Vn and a plurality of resistors connected in parallel to the contacts of the resistors forming the resistor string. Of capacitors C1 to Cn.

In the resistor string, a plurality of resistors R1 to Rn + 1 are connected in series between a first voltage VDD and a second voltage VSS applied from the outside to generate a plurality of gray voltages. The contact between (VDD) and each resistor becomes a V1 to Vn gray voltage corresponding to each gray level. Here, the gray scale voltage is varied according to the time constants of the resistors R1 to Rn + 1 and the capacitors C1 to Cn. In particular, the gray scale voltage is generated for each gray scale by adjusting the resistance of each resistor.

Since the voltage generator 41 operates in the same way as the gray voltage device used in the liquid crystal display, it generates a gray voltage according to a secondary functional gamma characteristic as shown in FIG. However, as shown in FIG. 4B, in the organic EL display device, since the gamma characteristic is linear, that is, linear function at a predetermined level, for example, higher gray level than 200 gray level, the primary functional gamma is applied to the gray level above the predetermined level. The gray voltage generated by the voltage generator 41 is corrected to generate a gray voltage according to the characteristic. That is, for grayscales above a predetermined level, the grayscale voltage output according to the nonlinear gamma characteristic is corrected to generate the grayscale voltage according to the linear gamma characteristic.

In the organic EL display, a gray level of a predetermined level or more is Y = aX ² Differentiation is necessary because it has the linear function of Y = aX + b rather than the quadratic function of + bX + C. Then Y '= 2aX + B, and Y' / 2 = aX + B to make 2aX aX in the variable. Therefore, the equation that should be varied is (Y / 2) '= (1/2) (aX ² + bX + C) (dx / dy), so at least one resistor and differentiator are required. Therefore, the compensator 42 according to an exemplary embodiment of the present invention may be formed of a differentiator for differentiating a gray voltage corresponding to a gray level of a predetermined level or more output from the voltage generator 41, and a resistance formed at the differentiator and an input terminal side. have.

In the light emitting display device as described above, the voltage generator 41 of the gray voltage generator 400 generates different gray voltages according to the resistance value based on the input voltage. That is, the resistor columns R1 to Rn + 1 divide the first voltage VDD and the second voltage VSS to generate a plurality of gray voltages V1 to Vn. Since the gray voltages V1 to Vn output as described above are voltages generated based on nonlinear gamma characteristics, such as a liquid crystal display, the correction unit 42 has a linear gamma characteristic with respect to grayscale voltages corresponding to gray levels of a predetermined level or more. The gray voltage output from the voltage generator 41 is corrected and outputted such that the voltage according to the output is output. That is, the gradation voltage of the predetermined level or more output from the voltage generator 41 is differentially processed and outputted, and the gradation voltage for the gradation smaller than the predetermined level is output without being differentially processed as it is. .

The gray voltage generated as described above is provided to the data driver 200, and the data driver 200 selects the gray voltage according to a data signal provided from a controller (not shown) and provides it to the display panel 100. do. Accordingly, light emission of each pixel is performed based on the gradation voltage corrected according to the gamma characteristic of the organic EL display device, thereby achieving accurate image display.

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. For example, the gray voltage generator as described above may be applied to the light emitting display device having the scan driver or the data driver in a dual form.

As described above, according to the present invention, the image display quality can be improved by correcting the gray level linearly according to the voltage level of the image signal according to the characteristics of the light emitting display device.

Claims (11)

A plurality of data lines which carry data currents and are formed in one direction, A plurality of signal lines that transmit scan signals and cross the data lines; A display panel formed in an area where the data line and the signal line cross each other and including a plurality of pixel circuits for displaying an image corresponding to an applied data current; A scan driver supplying a scan signal to the scan line; A data driver supplying a gray voltage corresponding to a data signal to the data line; And A gray voltage generator supplying a gray voltage for each gray level to the data driver. Including; A light emitting display device in which gray level voltages corresponding to gray levels equal to or greater than a set level among the gray level voltages are corrected and output. The method of claim 1 The gray voltage generator A voltage generator which generates a gray voltage for each gray level; A correction unit for correcting and outputting a gray voltage according to a gray level of a predetermined level or higher among the gray voltages output from the voltage generator A light emitting display device comprising a. The method of claim 2 The voltage generator includes a plurality of resistors connected in series between a first voltage and a second voltage to generate a plurality of gray voltages. The method of claim 2 The voltage generator is a light emitting display device that generates a gray level voltage for each gray level according to the same gamma characteristics as a liquid crystal display. The method of claim 2 And the corrector is a differentiator for differentiating and outputting a gray voltage corresponding to a gray level equal to or higher than the set level. The method of claim 5 The correction unit further comprises a resistor connected to the input terminal of the differentiator. The method of claim 1 The pixel circuit A capacitor charging the voltage provided from the data line; A transistor for supplying a current corresponding to the voltage charged in the capacitor; And Light emitting device that emits light according to the current through the transistor A light emitting display device comprising a. The method of claim 1 The light emitting device is an organic EL device. A gray voltage is formed in the pixel area where the data line and the signal line cross each other, and a pixel circuit including a capacitor, a transistor supplying a current corresponding to the voltage charged in the capacitor, and a light emitting element is formed. In the way a) generating a plurality of gradation voltages; b) correcting a gray voltage according to a gray level of a predetermined level or more among the gray voltages; And c) selecting one of the gray voltage and the corrected gray voltage according to the applied data signal and supplying the gray voltage to the data line; A gray voltage generation method of a light emitting display device comprising a. The method of claim 9 B) generating a gray voltage of the light emitting display device by differentiating the gray voltage corresponding to the gray level of the predetermined level or more. The method of claim 9 The gray level voltage generation method of the light emitting display device, wherein the set level is 200 gray levels.

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