KR100670172B1 - Light emitting display device and gray voltage adjusting method thereof - Google Patents

Abstract

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

In the present invention, a display panel is formed in a pixel region where the data line and the signal line intersect, a display panel in which a capacitor, a transistor for supplying a current corresponding to a voltage charged in the capacitor, and a pixel circuit including a light emitting element are formed. And a driver, a scan driver, and a voltage generator. Here, the gray voltage generator generates a plurality of gray voltages, and corrects the gray voltages according to the set gamma correction coefficients. Here, the gamma correction coefficient is increased from low gray to high gray.

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 ADJUSTING METHOD THEREOF}

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

2 is an exemplary diagram illustrating a gamma correction coefficient for each gray according to an exemplary embodiment of the present invention.

3 is a structural diagram of a gray voltage generator of FIG. 1.

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 display device and a method of correcting a gray voltage.

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). The organic thin film has a multilayer structure including an emission layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) in order to improve the emission efficiency by improving the balance between electrons and holes. It also includes a separate electron injection layer (EIL) and a 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 devices including such an organic EL display device, a gamma characteristic in which the gray level of an image does not change linearly but nonlinearly in accordance with the voltage level of the image 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 achieved by the present invention is to improve the image display quality so that the gray scale changes linearly in accordance with 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 signal 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 corrected according to the set gamma correction coefficient to the data driver, wherein the gamma correction coefficient is increased from low gray to high gray.

The gray voltage generator may include a resistor string including a plurality of resistors connected in series between a first voltage and a second voltage to generate a plurality of gray voltages; It may include a correction unit consisting of a plurality of capacitors connected to the contact between the respective resistors to correct the gray voltage. Here, the time constants of the resistor and the capacitor may vary according to the gamma correction coefficient.

According to another aspect of the present invention, a gray voltage correction method includes a capacitor, a transistor configured to supply a current in response to a voltage charged in the capacitor, formed in a pixel region where a data line and a signal line cross each other, and a light emitting device. A method of correcting a gray voltage of a light emitting display device having a pixel circuit, the method comprising: a) generating a plurality of gray voltages; b) respectively correcting the gray voltages according to a set gamma correction coefficient; And c) selecting one gray voltage from among the corrected gray voltages according to the applied data signal and supplying the gray voltage to the data line, wherein the gamma correction coefficient is increased from low gray to high gray.

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 attached to 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 exemplary embodiment of the present invention, since the gamma curve representing the gamma characteristic of the organic EL display device has the diode characteristic, the gamma correction coefficient is different for each gray level. That is, in low gradation, the gamma correction coefficient is made smaller by reducing the gamma correction coefficient, and the gamma correction coefficient is made larger by increasing the gamma correction coefficient from the low gradation to the high gradation so that the gamma correction is made at a wider interval. For example, in the case of 256 gray levels, the gamma correction coefficient may be set as shown in FIG. 2. 2 is an exemplary diagram illustrating a gamma correction coefficient for each gray according to an exemplary embodiment of the present invention.

Based on the gamma correction characteristic, the gray voltage generator may be configured as follows.

3 illustrates a structure of a gray voltage generator according to an exemplary embodiment of the present invention. As shown in FIG. 3, the gray voltage generator 400 includes a resistor string 410 for generating a plurality of gray voltages V1 -Vn and a beam connected to the resistor string 410 to correct the gray voltage. It consists of the government (20).

The resistance column 410 is a plurality of resistors R1 to Rn + 1 connected in series between the first voltage VDD and the second voltage VSS applied from the outside to generate a plurality of gray voltages. The contact between the first voltage VDD and each of the resistors becomes a V1 to Vn gray voltage.

The correction unit 420 includes a plurality of capacitors C1 to Cn connected in parallel to each of the resistors R1 to Rn + 1 to correct the gray voltage generated at each contact point.

Here, the time constants of the resistors R1 to Rn + 1 and the capacitors C1 to Cn become gamma correction coefficients for correcting the gray scale voltage, and the resistors R1 to satisfy the characteristics as shown in FIG. The resistance values of ˜Rn + 1 and the capacitances of the capacitors C1 to Cn are set.

According to this structure, the resistor strings R1 to Rn + 1 divide the first voltage VDD and the second voltage VSS to generate a plurality of gray voltages V1 to Vn, and thus, the generated gray voltages. V1 to Vn are corrected and output by capacitors C1 to Cn connected to the contacts of the respective resistors. The gamma corrected gray voltages V1 to Vn are 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) to display the display panel ( 100). 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 (6)

A plurality of data lines 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, the display panel including a plurality of pixel circuits configured to display an image corresponding to a data current according to an applied gray voltage; A scan driver supplying a scan signal to the signal line; A data driver supplying a gray voltage corresponding to a data signal to the data line; And A gradation voltage generator for supplying the gradation voltage corrected according to the set gamma correction coefficient to the data driver. Wherein the gamma correction coefficient is increased from a low gray level to a high gray level. The method of claim 1 The gray voltage generator A resistor string comprising a plurality of resistors connected in series between the first voltage and the second voltage to generate a plurality of gray voltages; A compensator comprising a plurality of capacitors connected to the contacts between the resistors to correct the gray voltage; A light emitting display device comprising a. The method of claim 2 And a time constant of the resistor and the capacitor according to the gamma correction coefficient. 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; Light emitting device that emits light according to the current through the transistor A light emitting display device comprising a. The method of claim 4 The light emitting device is an organic EL device. The gray voltage correction of the light emitting display device is formed in the pixel region where the data line and the signal line intersect, and the 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 gray voltages for each gray level; b) respectively correcting the gray voltages according to a set gamma correction coefficient; And c) supplying one gray voltage among the corrected gray voltages to the data line according to an applied data signal The gamma correction coefficient of claim 2, wherein the gamma correction coefficient is increased from a low gray level to a high gray level.

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