KR20060120766A - Display device and driving method thereof - Google Patents

Abstract

A display device and a driving method thereof are provided to prevent quality degradation of an OLED(Organic Light Emitting Diode) by flowing current corresponding to an input image signal to the OLED even if the threshold voltage of a driving transistor is transited. A display device includes plural pixels comprising plural light emitting elements; a lookup table(610) independently memorizing plural correction reference data(f) by at least three basic colors; a timer(630) generating driving accumulation time(Td) by accumulating the emission time of the light emitting elements; a signal converting unit(620) for generating a correction image signal on the basis of an input image signal, the driving accumulation time output from the timer, and correction reference data sent from the lookup table; and a data driving unit generating data voltage corresponding to the correction image signal sent from the signal converting unit and supplying the data voltage to the pixels.

Description

Display device and driving method thereof {DISPLAY DEVICE AND DRIVING METHOD THEREOF}

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

2 is an equivalent circuit diagram of one pixel of an organic light emitting diode display according to an exemplary embodiment of the present invention.

3 is a cross-sectional view illustrating an example of a cross section of a driving transistor and an organic light emitting diode of one pixel of the organic light emitting diode display illustrated in FIG. 2.

4 is a schematic diagram of an organic light emitting diode of an organic light emitting diode display according to an exemplary embodiment.

FIG. 5 is a block diagram illustrating an example of a signal controller of the OLED display illustrated in FIG. 1.

6 is a schematic diagram of a look-up table of the signal controller shown in FIG. 5.

7 is a block diagram of an organic light emitting diode display according to another exemplary embodiment of the present invention.

FIG. 8 is a block diagram of a signal controller and a gray voltage generator of the OLED display illustrated in FIG. 7.

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

In recent years, with the reduction in weight and thickness of personal computers and televisions, display devices are also required to be lighter and thinner, and cathode ray tubes (CRTs) are being replaced by flat panel displays.

Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), organic light emitting diode displays, and plasma display panels (PDPs). Etc.

In general, in an active flat panel display, a plurality of pixels are arranged in a matrix form, and an image is displayed by controlling the light intensity of each pixel according to given luminance information. Among these, an organic light emitting display is a display device that displays an image by electrically exciting and emitting a fluorescent organic material. The organic light emitting display is a self-emission type, has a low power consumption, a wide viewing angle, and a fast response time of pixels. It is easy.

The organic light emitting diode display includes an organic light emitting diode (OLED) and a thin film transistor (TFT) driving the organic light emitting diode (OLED). The thin film transistor is classified into a polysilicon thin film transistor and an amorphous silicon thin film transistor according to the type of the active layer. The organic light emitting diode display employing the polysilicon thin film transistor has many advantages, and thus is widely used. However, the manufacturing process of the thin film transistor is complicated and thus the cost increases. In addition, it is difficult to obtain a large screen with such an organic light emitting display device.

The organic light emitting diode display employing the amorphous silicon thin film transistor is easy to obtain a large screen, and the number of manufacturing processes is relatively smaller than that of the organic light emitting diode display employing the polycrystalline silicon thin film transistor. However, as the bipolar DC voltage is continuously applied to the control terminal of the amorphous silicon thin film transistor, the threshold voltage of the amorphous silicon thin film transistor is shifted. This causes non-uniform current to flow through the organic light emitting diode even when the same control voltage is applied to the thin film transistor, resulting in deterioration in image quality of the organic light emitting diode display. This shortens the life of the organic light emitting display device.

Therefore, many pixel circuits have been proposed to date to compensate for the transition of the threshold voltage and to prevent deterioration of image quality. However, most pixel circuits include many thin film transistors, capacitors, and wirings, so that the aperture ratio of the pixels is low and is complicated in design.

In addition, even when the threshold voltage shift of the driving transistor is compensated for, the organic light emitting diode may not display the same luminance for each color of the same image data because the lifespan and efficiency of the organic light emitting diode vary with time.

Accordingly, the technical problem to be achieved by the present invention is to simplify the pixel circuit and to increase the aperture ratio of the pixel, and to compensate for the transition of the threshold voltage of the driving transistor to prevent deterioration of image quality and to prevent deterioration of image quality for each color. The present invention provides a display device and a driving method thereof.

According to an aspect of the present invention, a display device includes a plurality of pixels each including a plurality of light emitting elements, a lookup table that independently stores a plurality of correction reference data for at least three primary colors, and A signal for generating a corrected video signal based on a timer for generating a driving cumulative time that accumulates the light emission time of the light emitting device, an input video signal, the accumulated driving time from the timer, and the correction reference data from the lookup table. And a data driver for generating a data voltage corresponding to the corrected image signal from the signal converter and supplying the data voltage to the pixel.

The signal converter may independently correct the input image signal for each of the at least three primary colors to generate the corrected image signal.

According to another aspect of the present invention, there is provided a method of driving a display device including a light emitting device and a lookup table, including: accumulating light emission time of the light emitting device, and correcting reference data from the lookup table according to an input image signal and the accumulated time. Extracting, generating a corrected image signal based on the input image signal, the accumulated time, and the correction reference data, and emitting the light emitting element according to the corrected image signal. The data includes at least three basic color correction reference data.

The generating of the corrected image signal may include generating the corrected image signal by independently correcting the input image signal for each of the at least three primary colors.

According to another aspect of the present invention, there is provided a display device including a plurality of pixels each including a plurality of light emitting elements, a lookup table for storing a plurality of correction gamma data, and a timer for generating a driving accumulated time accumulating light emission time of the light emitting elements. A gamma data generator for generating digital gamma data based on the driving accumulated time from the timer and the gamma data for correction from the lookup table, at least one corresponding to the digital gamma data from the gamma data generator And a data driver for generating a data voltage corresponding to an image signal based on the gray voltage set from the gray voltage generator and supplying the data voltage to the pixel.

The gray voltage generator may include a digital to analog converter for converting the digital gamma data into the gray voltage set.

The gray voltage generator may further include a register that stores the digital gamma data.

The at least one gray voltage set may include three gray voltage sets.

The three gray voltage sets may correspond to the pixels displaying three primary colors.

The data driver may divide the set of gray voltages and supply a gray voltage corresponding to the image signal among the divided gray voltages as the data voltage to the pixel.

The pixel may include a driving transistor for supplying current to the light emitting device and a switching transistor for transmitting the data voltage to the driving transistor.

The driving transistor and the switching transistor may include amorphous silicon.

The pixel may further include a capacitor that charges the data voltage.

According to another aspect of the present invention, a method of driving a display device including a pixel including a light emitting element and a lookup table includes accumulating light emission time of the light emitting element and correcting gamma data from the lookup table according to the accumulated time. Generating digital gamma data based on the accumulated time and the correction gamma data, analog converting the digital gamma data to generate at least one gray voltage set, an image signal and the gray voltage Generating a data voltage based on the set, and emitting the light emitting element according to the data voltage.

The correction gamma data may include at least three primary gamma correction data.

The at least one gray voltage set may include three gray voltage sets respectively corresponding to the pixels displaying three primary colors.

The generating of the data voltage may include dividing the set of gray voltages and selecting a gray voltage corresponding to the image signal among the divided gray voltages.

DETAILED DESCRIPTION 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.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a portion of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only when the other part is "right on" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

A display device and a driving method thereof according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, an organic light emitting diode display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1 and 2.

1 is a block diagram of an organic light emitting diode display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of one pixel of the organic light emitting diode display according to an exemplary embodiment of the present invention.

As shown in FIG. 1, an organic light emitting diode display according to an exemplary embodiment of the present invention includes a display panel 300, a scan driver 400, a data driver 500, and a data driver 500 connected thereto. Connected gray voltage generator 800 and a signal controller 600 for controlling the gray voltage generator 800.

The display panel 300 includes a plurality of signal lines G ₁ -G _n , D ₁ -D _m , and a plurality of pixels Px connected to the plurality of signal lines G ₁ -G _n , D ₁ -D _m , which are arranged in a substantially matrix form. Include.

The signal line includes a plurality of scan signal lines G ₁ -G _n transmitting the scan signals and data lines D ₁ -D _m transferring the data signals. The scan signal lines G ₁ -G _n extend substantially in the row direction and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction and are substantially parallel to each other.

2, each pixel (Px), for example, scanning signal lines (G _i) and the data lines (D _j) in the pixel includes an organic light emitting diode (LD), a driving transistor (Qd), a capacitor which is connected (Cst), and the switching transistor (Qs).

The driving transistor Qd is a three-terminal element whose control terminal is connected to the switching transistor Qs and the capacitor Cst, the input terminal is connected to the driving voltage Vdd, and the output terminal is the organic light emitting diode LD. )

A switching transistor and also a three-terminal device (Qs) The control terminal and the input terminal of each of the scanning signal lines (G _i) and the data lines (D _j) is connected to the output terminal is a capacitor (Cst) and the driving transistor (Qd) It is connected.

The capacitor Cst is connected between the switching transistor Qs and the driving voltage Vdd, and charges and maintains the data voltage from the switching transistor Qs for a predetermined time.

An anode and a cathode of the organic light emitting diode LD are connected to the driving transistor Qd and the common voltage Vcom, respectively. The organic light emitting diode LD displays an image by emitting light at different intensities according to the magnitude of the current I _LD supplied from the driving transistor Qd. The magnitude of the current I _LD depends on the magnitude of the voltage Vgs between the control terminal and the output terminal of the driving transistor Qd.

The switching and driving transistors Qs and Qd are composed of n-channel field effect transistors (FETs) made of amorphous silicon or polycrystalline silicon. However, these transistors Qs and Qd may also be p-channel field effect transistors (FETs), in which case the p-channel field effect transistors (FETs) and n-channel field effect transistors (FETs) are complementary to each other. ), The operation and voltage and current of the p-channel field effect transistor (FET) are opposite to that of the n-channel field effect transistor (FET).

Next, the structure of the driving transistor Qd and the organic light emitting diode LD of the organic light emitting diode display illustrated in FIG. 2 will be described in detail with reference to FIGS. 3 and 4.

3 is a cross-sectional view illustrating an example of a cross section of a driving transistor and an organic light emitting diode of one pixel of the organic light emitting diode display illustrated in FIG. 2, and FIG. 4 is an organic light emitting diode display according to an exemplary embodiment of the present invention. A schematic diagram of a light emitting diode.

The control electrode 124 is formed on the insulating substrate 110. The control terminal electrode 124 is an aluminum-based metal such as aluminum (Al) or an aluminum alloy, a silver-based metal such as silver (Ag) or a silver alloy, a copper-based metal such as copper (Cu) or a copper alloy, and molybdenum (Mo) And a molybdenum-based metal such as molybdenum alloy, chromium (Cr), titanium (Ti), and tantalum (Ta) are preferably made. However, the control terminal electrode 124 may have a multilayer structure including two conductive films (not shown) having different physical properties. One of the conductive films is made of a low resistivity metal such as an aluminum-based metal, a silver-based metal, or a copper-based metal to reduce signal delay or voltage drop. On the other hand, other conductive films are made of other materials, particularly materials having excellent physical, chemical and electrical contact properties with indium tin oxide (ITO) and indium zinc oxide (IZO), such as molybdenum-based metals, chromium, titanium, tantalum, and the like. Good examples of such a combination include a chromium bottom film, an aluminum (alloy) top film, and an aluminum (alloy) bottom film and a molybdenum (alloy) top film. However, the control terminal electrode 124 may be made of various various metals and conductors. The control terminal electrode 124 is inclined with respect to the surface of the substrate 110 and its inclination angle is 20-80 °.

An insulating layer 140 made of silicon nitride (SiNx) is formed on the control terminal electrode 124.

On the insulating layer 140, a semiconductor 154 made of hydrogenated amorphous silicon (amorphous silicon is abbreviated a-Si), polycrystalline silicon, or the like is formed.

On the semiconductor 154, a pair of ohmic contacts 163 and 165 made of a material such as n + hydrogenated amorphous silicon doped with a high concentration of silicide or n-type impurities are formed.

Side surfaces of the semiconductor 154 and the ohmic contacts 163 and 165 are inclined with respect to the substrate 110 surface, and the inclination angle is 30-80 °.

An input electrode 173 and an output electrode 175 are formed on the ohmic contacts 163 and 165 and the insulating layer 140. The input terminal electrode 173 and the output terminal electrode 175 are preferably made of refractory metals such as chromium, molybdenum-based metals, tantalum, and titanium. It may have a multi-layer structure including a low resistance material upper layer (not shown) disposed thereon. Examples of the multilayer structure include a double layer of chromium or molybdenum (alloy) lower layer and an aluminum upper layer, and a triple layer of molybdenum (alloy) lower layer-aluminum (alloy) interlayer-molybdenum (alloy) upper layer. Like the control terminal electrode 124, the input terminal electrode 173 and the output terminal electrode 175 are also inclined at an angle of about 30-80 degrees.

The input terminal electrode 173 and the output terminal electrode 175 are separated from each other and positioned on both sides of the control terminal electrode 124. The control terminal electrode 124, the input terminal electrode 173, and the output terminal electrode 175 together with the semiconductor 154 form a driving transistor Qd, the channel of which is output with the input terminal electrode 173. It is formed in the semiconductor 154 between the terminal electrodes 175.

The ohmic contacts 163 and 165 exist only between the semiconductor 154 below and the input terminal electrode 173 and the output terminal electrode 175 thereon, and serve to lower the contact resistance. The semiconductor 154 has an exposed portion without being covered by the input terminal electrode 173 and the output terminal electrode 175.

A passivation layer 180 is formed on the input terminal electrode 173, the output terminal electrode 175, the exposed portion of the semiconductor 154, and the insulating layer 140. The passivation layer 180 is made of an inorganic insulator such as silicon nitride (SiNx) or silicon oxide (SiO ₂ ), an organic insulator, or a low dielectric insulator. Preferably, the dielectric constant of the low dielectric constant insulator is 4.0 or less, for example, a-Si: C: O, a-Si: O: F, etc., which are formed by plasma enhanced chemical vapor deposition (PECVD). Among the organic insulators, the protective layer 180 may be formed by having photosensitivity, and the surface of the protective layer 180 may be flat. In addition, the passivation layer 180 may be formed as a double layer structure of the lower inorganic layer and the upper organic layer so as to protect the exposed portion of the semiconductor 154 while utilizing the advantages of the organic layer. In the passivation layer 180, a contact hole 185 exposing the output terminal electrode 175 is formed.

The pixel electrode 190 is formed on the passivation layer 180. The pixel electrode 190 is physically and electrically connected to the output terminal electrode 175 through the contact hole 185 and may be formed of a transparent conductive material such as ITO or IZO, or a metal having excellent reflectivity of aluminum or silver alloy. Can be.

The partition 361 is further formed on the passivation layer 180. The partition 361 defines an opening by surrounding a periphery of the pixel electrode 190 like a bank and is made of an organic insulating material or an inorganic insulating material.

An organic light emitting member 370 is formed on the pixel electrode 190, and the organic light emitting member 370 is trapped in an opening surrounded by the partition wall 360.

As illustrated in FIG. 4, the organic light emitting member 370 has a multilayer structure including auxiliary layers for improving the light emission efficiency of the light emitting layer EML in addition to the light emitting layer EML. The secondary layer contains an electron transport layer (ETL) and hole transport layer (HTL) to balance electrons and holes, and an electron injecting layer to enhance injection of electrons and holes. (EIL) and hole injecting layer (HIL). Subsidiary layers may be omitted.

The auxiliary electrode 382 is formed on the partition wall 360 in the same pattern as the partition wall 360 and made of a conductive material having a low specific resistance such as metal.

The common electrode 270 to which the common voltage Vcom is applied is formed on the partition 361, the organic light emitting member 370, and the auxiliary electrode 382. The common electrode 270 is made of a reflective metal including calcium (Ca), barium (Ba), aluminum (Al), silver (Ag), or the like, or a transparent conductive material such as ITO or IZO.

The opaque pixel electrode 190 and the transparent common electrode 270 are applied to a top emission organic light emitting display device that displays an image in an upper direction of the display panel 300. The opaque common electrode 270 is applied to a bottom emission organic light emitting display device that displays an image in a downward direction of the display panel 300.

The pixel electrode 190, the organic light emitting member 370, and the common electrode 270 form the organic light emitting diode LD shown in FIG. 2, and the pixel electrode 190 is an anode and the common electrode 270 is a cathode. In contrast, the pixel electrode 190 becomes a cathode and the common electrode 190 becomes an anode. The organic light emitting diode LD emits light of one of the primary colors according to the material of the organic light emitting member 370. Examples of the primary colors include three primary colors of red, green, and blue, and display a desired color as the spatial sum of the three primary colors.

The auxiliary electrode 382 is in contact with the common electrode 270, and serves to prevent the signal transmitted to the common electrode 270 from being distorted.

Referring back to FIG. 1, the gray voltage generator 800 generates a gray voltage set (or a reference gray voltage set) related to the luminance of the pixel Px.

The scan driver 400 is connected to the scan signal lines G ₁ -G _n of the display panel 300 to combine a high voltage Von for turning on the switching transistor Qs and a low voltage Voff for turning off the switching transistor Qs. Is applied to the scan signal lines G ₁ -G _n .

The data driver 500 is connected to the data lines D ₁ -D _m of the display panel 300 to apply one gray voltage from the gray voltage generator 800 as a data voltage to the pixel Px. However, when the gray voltage generator 800 does not provide all the voltages for all grays, but only the reference gray voltages, the data driver 500 divides the reference gray voltages to generate gray voltages for all grays. Among them, the data voltage is selected and then applied to the pixel Px.

The scan driver 400 or the data driver 500 may be mounted directly on the display panel 300 in the form of at least one driver integrated circuit chip, or mounted on a flexible printed circuit film (not shown). The display panel 300 may be attached to the display panel 300 in the form of a tape carrier package (TCP). Alternatively, the scan driver 400 or the data driver 500 may be integrated in the display panel 300.

The signal controller 600 controls operations of the scan driver 400, the data driver 500, and the like, and corrects an image signal.

Next, the operation of the organic light emitting diode display will be described in detail.

The signal controller 600 is configured to control the input image signals R, G, and B and their display from an external graphic controller (not shown), for example, a vertical synchronization signal Vsync and a horizontal synchronization signal ( Hsync, main clock MCLK, and data enable signal DE are provided. The signal controller 600 properly processes the image signals R, G, and B according to the operating conditions of the display panel 300 based on the input image signals R, G, and B and the input control signal, and scan control signals CONT1. ) And the data control signal CONT2, and the like, the scan control signal CONT1 is sent to the scan driver 400, and the data control signal CONT2 and the processed image signal DAT are the data driver 500. Export to).

The scan control signal CONT1 includes a vertical synchronization start signal STV for instructing the start of scanning of the high voltage Von and at least one clock signal for controlling the output of the high voltage Von.

The data control signal CONT2 is a load signal LOAD and a data clock for applying a corresponding data voltage to the horizontal synchronization start signal STH indicating the start of input of the image data DAT and the data lines D ₁ -D _m . Signal HCLK and the like.

The data driver 500 receives the image data DAT for one row of pixels according to the data control signal CONT2 from the signal controller 600, and selects each of the gray voltages from the gray voltage generator 800. By selecting the gray scale voltage corresponding to the image data DAT, the image data DAT is converted into the corresponding data voltage and then applied to the corresponding data lines D ₁ -D _m . Alternatively, the data driver 500 may divide the reference gray voltage from the gray voltage generator 800 to generate a gray voltage by itself and apply it to the data lines D ₁ -D _m as data voltages.

The scan driver 400 is applied to the scanning signal lines (G ₁ -G _n), the high voltage (Von) according to the scan control signal (CONT1) from the signal controller 600 connected to the scanning signal lines (G ₁ -G _n) The control transistor and the capacitor Cst of the driving transistor Qd are turned on through the switching transistor Qs, which turns on the switching transistor Qs, and thus the data voltage applied to the data lines D ₁ -D _m is turned on. Applied to the capacitor Cst charges this data voltage. Since the voltage charged in the capacitor Cst is maintained for one frame even when the scan signal becomes the low voltage Voff and the switching transistor Qs is turned off, the control terminal voltage of the driving transistor Qd is kept constant.

The driving transistor Qd sends an output current I _LD whose amplitude is controlled according to the data voltage to the organic light emitting diode _LD , and the organic light emitting diode LD increases in intensity according to the magnitude of the current I _LD . The image is displayed by emitting light differently.

After one horizontal period (or "1H") (one period of the horizontal synchronization signal Hsync and the data enable signal DE), the data driver 500 and the scan driver 400 perform the same operation with respect to the pixels in the next row. Repeat. In this manner, the high voltage Von is sequentially applied to all the scan signal lines G ₁ -G _n during one frame to apply the data voltage to all the pixels.

Next, image signal correction of the signal controller of the organic light emitting diode display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 5 and 6.

FIG. 5 is a block diagram illustrating an example of a signal controller of the OLED display illustrated in FIG. 1, and FIG. 6 is a schematic diagram of a lookup table of the signal controller illustrated in FIG. 5.

As shown in FIG. 5, the signal controller 600 includes a lookup table 610, a signal converter 620, and a timer 630.

The timer 630 generates a driving accumulated time Td that accumulates the time that the organic light emitting diode LD emits light by supplying power to the organic light emitting diode display, and provides the accumulated time Td to the lookup table 610 and the signal converter 620. do.

The lookup table 610 receives the driving cumulative time Td from the input image signals R, G, and B and the timer 630, and extracts the correction reference data f corresponding thereto to the signal converter 620. send.

Obtaining and storing all the driving accumulated time Td and the corrected image signals for all the input image signals R, G, and B in the lookup table 610 is time- and spatially difficult, and thus, the accumulated accumulation time of a predetermined unit ( The corrected video signal is obtained only for the video signal of Td) and a predetermined unit and stored in the lookup table 610 as the correction reference data f, and the time and the video signal therebetween are stored in the lookup table 610. A correction video signal is calculated by interpolation using the surrounding four correction reference data f.

For example, as shown in FIG. 6, the lookup table 610 is represented by a matrix, the driving accumulation time Td is displayed in units of 100 hours on the vertical axis, and the image signals R, G, and B are on the horizontal axis. Is indicated in 8 gradation units. The correction reference data f is stored where these drive accumulation times Td and the video signals R, G, and B intersect. The correction reference data f is a correction image signal capable of outputting a current I _LD corresponding to the input image signals R, G, and B even when the threshold voltage of the driving transistor Qd changes as the driving time elapses. to be. For example, if the driving cumulative time Td is 300 hours and the input video signal is 24 gradations (hereinafter referred to as (300, 24)), the correction reference data f becomes "30". Such correction reference data f is obtained by experiment.

The lookup table 610 supplies to the signal converter 620 four calibration reference data f to which the input image signals R, G, and B and the driving accumulation time Td belong. For example, in FIG. 6, if the driving cumulative time Td is 250 hours and the input image signal is 20 gradations, the four reference data f for correction are (200, 16), (200, 24), (300, 16), And reference data f for correction corresponding to (300, 24).

The signal converter 620 interpolates based on the input image signals R, G, and B, the accumulated driving time Td from the timer 630, and four correction reference data f from the lookup table 610. After generating the image data (DAT) by using and to send to the data driver 500. Linear interpolation and the like can be used as the interpolation method.

As described above, the correction reference data is stored in the lookup table and interpolated according to the accumulated driving time to generate a corrected image signal, so that the current corresponding to the input image signals R, G, and B even when the threshold voltage of the driving transistor Qd transitions. May be generated, thereby compensating for the luminance change of the organic light emitting diode LD.

In addition, the lookup table 610 may store the correction reference data f for each RGB, and independently correct the input image signals R, G, and B for each RGB. In this way, even if the efficiency of the organic light emitting diode LD changes individually for each RGB over time, the RGB pixel may display a constant luminance.

Although the display device according to an exemplary embodiment of the present invention has been described with the unit of the accumulated driving time of the lookup table 610 as 100 hours and the gradation unit of the image signal as 8 gradations, the time unit and the gradation unit may be changed. The size does not necessarily have to be regular. Although the video signal has been described as being 6 bit 64 gradations, it may be 8 bit 256 gradations or 10 bit 1024 gradations.

In addition, although the display device according to the embodiment of the present invention has been described as displaying an image using a so-called voltage programming method of applying a data voltage to a capacitor Cst as a data signal indicating a gray level, the present invention is not limited thereto. The image may be displayed by using a so-called current programming method of applying a data current as a data signal.

Next, an organic light emitting diode display according to another exemplary embodiment of the present invention will be described in detail with reference to FIGS. 7 and 8.

7 is a block diagram of an organic light emitting diode display according to another exemplary embodiment. FIG. 8 is a block diagram of a signal controller and a gray voltage generator of the organic light emitting diode display illustrated in FIG. 7.

As illustrated in FIG. 7, the organic light emitting diode display according to the present exemplary embodiment includes a display panel 300, a scan driver 400 connected thereto, a data driver 501, and a gray voltage generator 801 connected to the data driver 501. And a signal controller 601 for controlling them.

The display panel 300 includes a plurality of signal lines G ₁ -G _n , D ₁ -D _m , and a plurality of pixels Px connected to the plurality of signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. Include.

Since the display panel 300 and the scan driver 400 according to the present exemplary embodiment are substantially the same as the display panel 300 and the scan driver 400 according to the previous embodiment, detailed description thereof will be omitted.

The signal controller 601 controls operations of the scan driver 400 and the data driver 501, and generates and provides digital gamma data DGD to the gray voltage generator 801.

The gray voltage generator 801 generates three reference gray voltage sets VGR, VGG, and VGB related to the luminance of the pixel Px based on the digital gamma data DGD from the signal controller 601. The three reference gray voltage sets VGR, VGG, and VGB each have three basic colors (for example, red (R), green (G), and blue (B)) emitting pixels (hereinafter referred to as RGB pixels). It is provided independently. However, instead of the three reference gray voltage sets VGR, VGG, and VGB, only one reference gray voltage set may be generated, or four or more reference gray voltage sets may be generated when the basic color is four or more colors.

The data driver 501 is connected to the data lines D ₁ -D _m of the display panel 300 to divide the reference gray voltages VGR, VGG, and VGB from the gray voltage generator 801 for each RGB pixel, thereby dividing the entire grayscale voltages. A gray voltage for the gray is generated, and a gray voltage of the image data DAT is selected and applied to the pixel Px as a data voltage.

Then, the signal controller 601 and the gray voltage generator 801, which can compensate for the transition of the threshold voltage of the driving transistor Qd and prevent the deterioration of image quality for each color, will be described in more detail with reference to FIG. 8. do.

Referring to FIG. 8, the signal controller 601 includes a lookup table 611, a gamma data generator 621, and a timer 631.

The timer 631 generates a driving accumulation time Td that accumulates the time that the organic light emitting diode LD emits light by supplying power to the organic light emitting diode display, and provides the accumulated time Td to the gamma data generator 621.

The lookup table 611 stores gamma data for each RGB pixel correction corresponding to a predetermined time. The gamma data for correction is a set of reference gradation voltages for compensating for the threshold voltage of the driving transistor Qd or changing the efficiency of the organic light emitting diode LD according to color over time, thereby displaying a constant luminance for each color. Corresponds to. The gamma data for correction are obtained in advance by experiment or the like.

The gamma data generation unit 621 reads the correction gamma data corresponding to the driving accumulated time Td from the lookup table 611 to perform predetermined signal processing to generate digital gamma data DGD.

Obtaining and storing the optimal RGB gamma data for all the driving accumulated time Td in the lookup table 611 is time- and spatial-intensive. Therefore, the optimum gamma data for the driving accumulated time Td of a predetermined unit is obtained in advance and stored in the lookup table 611 as gamma data for correction. Then, the digital gamma data DGD is calculated by interpolation using the correction gamma data stored in the lookup table 611 for the time between them.

Alternatively, the elapsed time and the optimal gamma data at this time can be obtained in advance based on a change in luminance of a predetermined unit over time and stored in the lookup table 611. The gamma data may be extracted based on the driving accumulated time Td and the elapsed time to generate digital gamma data DGD.

The gray voltage generator 801 includes RGB digital-to-analog converters 810, 820, and 830, and the RGB digital-to-analog converters 810, 820, and 830 convert the digital gamma data (DGD) to RGB for reference. The gray voltage set VGR, VGG, and VGB are generated and exported to the data driver 501. The gray voltage generator 801 may include a register (not shown) that stores the digital gamma data DGD. The RGB digital-to-analog converters 810, 820, and 830 may be made in various forms, and the number of digital-to-analog converters may be reduced by using a sample-holding circuit (not shown).

As such, by generating an independent gamma curve for each RGB over time, luminance may be maintained for each RGB pixel even when the threshold voltage of the driving transistor Qd changes or the efficiency of the organic light emitting diode LD changes.

The gray voltage generator 801 may generate a gray voltage set for all grays instead of the reference gray voltage set. In this case, the data driver 501 does not need a separate voltage dividing circuit, and may select a gray voltage corresponding to the image data DAT from the gray voltage set.

In addition, if necessary, the gray voltage generator 801 may generate only one reference gray voltage set instead of three reference gray voltage sets.

The operation of the organic light emitting diode display according to the present exemplary embodiment is largely similar to the operation of the organic light emitting diode display of the foregoing embodiment, and many features of the organic light emitting diode display of FIGS. 1 to 6 described above are described in FIGS. 7 and 8. It can also be applied to the device.

As described above, according to the present invention, the correction reference data is stored in the look-up table and the correction image signal is generated according to the driving accumulation time, so that a current corresponding to the input image signal can flow to the organic light emitting diode even when the threshold voltage of the driving transistor is shifted. Therefore, deterioration in image quality of the organic light emitting diode can be prevented. In addition, by storing reference data for RGB correction in a look-up table and independently correcting an input image signal for each RGB, RGB pixels may display a constant luminance even if the efficiency of the organic light emitting diode changes individually for each RGB over time.

In addition, by independently correcting the gray-level voltage for each RGB according to the driving accumulation time, the RGB pixel may display a constant luminance even when the threshold voltage of the driving transistor is shifted or the efficiency of the organic light emitting diode is changed.

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.

Claims (17)

A plurality of pixels each comprising a plurality of light emitting elements, Look-up table for independently storing a plurality of correction reference data for at least three primary colors, A timer for generating a driving accumulation time accumulating the light emission time of the light emitting device; A signal converter for generating a corrected video signal based on an input video signal, the driving cumulative time from the timer, and the correction reference data from the lookup table, and A data driver configured to generate a data voltage corresponding to the corrected image signal from the signal converter and supply the data voltage to the pixel Display device comprising a. In claim 1, And the signal converter is configured to independently correct the input image signal for each of the at least three primary colors to generate the corrected image signal. A driving method of a display device including a light emitting element and a lookup table, Accumulating light emission time of the light emitting device; Extracting reference data for correction from the lookup table according to an input image signal and the accumulated time; Generating a corrected video signal based on the input video signal, the accumulated time, and the correction reference data; and Emitting light to the light emitting device according to the corrected video signal Including; The correction reference data includes at least three primary color correction reference data Method of driving the display device. In claim 3, The generating of the corrected image signal may include generating the corrected image signal by independently correcting the input image signal for each of the at least three primary colors. A plurality of pixels each comprising a plurality of light emitting elements, Look-up table for storing a plurality of correction gamma data, A timer for generating a driving accumulation time accumulating the light emission time of the light emitting device; A gamma data generation unit for generating digital gamma data based on the driving accumulated time from the timer and the correction gamma data from the lookup table; A gray voltage generator for generating at least one gray voltage set corresponding to the digital gamma data from the gamma data generator, and A data driver which generates a data voltage corresponding to an image signal based on the set of gray voltages from the gray voltage generator and supplies the data voltage to the pixel; Display device comprising a. In claim 5, The gray voltage generator includes a digital to analog converter for converting the digital gamma data into the gray voltage set. In claim 6, The gray voltage generator further includes a register configured to store the digital gamma data. In claim 6, The at least one gray voltage set includes three gray voltage sets. In claim 8, And the three gray voltage voltage sets respectively correspond to the pixels displaying three primary colors. In claim 6, And the data driver divides the set of gray voltages and supplies the gray voltages corresponding to the image signals among the divided gray voltages as the data voltages to the pixel. In claim 6, The pixel includes a driving transistor for supplying current to the light emitting element and a switching transistor for transferring the data voltage to the driving transistor. In claim 11, And the driving transistor and the switching transistor include amorphous silicon. In claim 11, The pixel further includes a capacitor charging the data voltage. A driving method of a display device including a pixel including a light emitting element and a look-up table, Accumulating light emission time of the light emitting device; Extracting gamma data for correction from the lookup table according to the accumulated time; Generating digital gamma data based on the accumulated time and the correction gamma data; Analog converting the digital gamma data to generate at least one gray voltage set; Generating a data voltage based on an image signal and the gray voltage set; and Emitting light to the light emitting device according to the data voltage Method of driving a display device comprising a. The method of claim 14, The correction gamma data includes at least three primary gamma correction gamma data. The method of claim 14, The at least one gray voltage set includes three gray voltage sets respectively corresponding to the pixels displaying three primary colors. The method of claim 14, The generating of the data voltage includes dividing the set of gray voltages and selecting a gray voltage corresponding to the image signal among the divided gray voltages.

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