KR102339647B1 - Display device and data compensation method thereof - Google Patents

Abstract

The display device of the present invention includes a display panel, a logo detection unit, a data compensation unit, and a display panel driving unit. In the display panel, pixels including a plurality of sub-pixels are arranged. The logo detection unit detects logo data from the input image data. The data compensator detects low grayscale data from among the logo data, and adds a preset compensation value to the low grayscale data. The display panel driver writes compensation data to the display panel.

Description

Display device and data compensation method thereof

The present invention relates to a display device and a data compensation method thereof.

Organic Light Emitting Diode Display (hereinafter referred to as "OLED Display"), Liquid Crystal Display Device (LCD), Plasma Display Panel (PDP), Field Emission Display Device ( Various flat panel display devices such as Field Emission Display (FED) are being used.

Since the OLED display device is a self-luminous device, it consumes less power and can be made thinner than a liquid crystal display device that requires a backlight. In addition, the OLED display has a wide viewing angle and a fast response speed. OLED display devices are expanding the market while competing with liquid crystal display devices.

In general, a logo is displayed for a long time, as opposed to a moving picture displayed on a display device being displayed for a short time. The sub-pixels of the area where the logo is displayed maintain the same luminance for a long time, and some sub-pixels among the sub-pixels of the logo area maintain a non-emission state. Since the logo is displayed for a long time compared to the moving picture, a negative shift occurs in the threshold voltage Vth of the driving transistors included in the sub-pixels that do not emit light in the logo area. The OLED display generally includes a method and apparatus for compensating for variations in threshold voltage (Vth) of driving transistors included in sub-pixels. However, when the negative shift phenomenon becomes severe, the threshold voltage compensation method is used. However, normal operation of the driving transistor cannot be expected.

The present invention provides a display device and a data compensation method thereof for improving a negative shift in threshold voltages of driving transistors included in subpixels that do not emit light for a long time.

The display device of the present invention includes a display panel, a logo detection unit, a data compensation unit, and a display panel driving unit. Pixels including a plurality of sub-pixels are arranged on the display panel. The logo detection unit detects logo data from the input image data. The data compensator detects low grayscale data from among the logo data, and adds a preset compensation value to the low grayscale data. The display panel driver writes compensation data to the display panel.

The present invention detects a sub-pixel that does not emit light for a long time and causes the sub-pixel to emit light based on compensation data, thereby improving the negative shift of the threshold voltage of the driving transistor in the sub-pixel.

In addition, the present invention can improve a phenomenon in which the threshold voltage of the driving transistor is negatively shifted while maintaining the color temperature constant by correcting the change in the color temperature of the pixel by the compensation data.

1 is a block diagram illustrating a display device according to an embodiment of the present invention.
2 is a diagram illustrating a pixel structure according to an embodiment of the present invention.
3 is a flowchart illustrating a data compensation method according to an embodiment of the present invention.
4 is a diagram illustrating an example of an image including a logo.
5 and 6 are edge maps illustrating a logo data detection process.
7 is a diagram illustrating an example of sub-pixels including low grayscale data in a pixel.
8 is a diagram illustrating color coordinates for color temperature correction.

The display device of the present invention may be implemented as a flat panel display device such as an OLED display device, a liquid crystal display device (LCD), a plasma display panel (PDP), or a field emission display device (FED). The following embodiments will be mainly described with respect to an OLED display device, but the present invention is not limited thereto.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals refer to substantially identical elements throughout. In the following description, if it is determined that a detailed description of a known function or configuration related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

1 shows a display device according to an embodiment of the present invention.

Referring to FIG. 1 , the display device of the present invention includes a host system 20 , a logo detection unit 30 , a data compensation unit 40 , a display panel 100 , and a display panel driving unit.

The host system 20 provides input image data and timing control signals to the logo detection unit 30 including a system-on-chip having a built-in scaler. The host system 20 may be implemented as any one of a TV (Television) system, a set-top box, a navigation system, a DVD player, a Blu-ray player, a personal computer (PC), a home theater system, and a phone system.

The logo detection unit 30 detects logo data based on input image data provided from the host system 20 .

The data compensator 40 detects low grayscale data from the logo data, and generates compensation data by adding a compensation value to the low grayscale data. Since the compensation value is preset to a value greater than '0', all pixels in which logo data are written emit light. As a result, it is possible to improve a phenomenon in which the threshold voltage of the driving transistor DT is significantly negatively shifted in the sub-pixels that do not emit light for a long time in the logo image.

The data compensator 40 generates correction data by adding a correction value to image data other than the low grayscale data among the logo data. The correction data corrects a change in the color temperature of a pixel by writing the compensation data.

The data compensation unit 40 provides compensation data converted from logo data and compensation data to the timing controller 110 . In addition, the data compensator 40 provides input image data other than the logo data to the timing controller 110 .

The logo detecting unit 30 and the data compensating unit 40 may be built in the host system 20 or the timing controller 110 .

A plurality of data lines 14 and a plurality of gate lines 15 cross each other in the pixel array of the display panel 100 . The data line 14 corresponds to the number of pixel columns, and each data line 14 includes data voltage supply lines 14A and reference voltage lines 14B. The gate line 15 corresponds to the number of pixel rows, and each gate line 15 includes a scan line 15A and a sense line 15B. The pixel array of the display panel 100 includes pixels arranged in a matrix to display an input image. Each of the pixels includes a red (Red, R) subpixel, a green (G) subpixel, and a blue (Blue, B) subpixel. Each of the pixels may further include a white (W) sub-pixel.

Each of the subpixels includes an organic light emitting diode (OLED), one or more thin film transistors (TFTs), a driving TFT, a capacitor, etc. The organic light emitting diode (OLED) includes a hole injection layer (HIL). ), a hole transport layer (HTL), a light emitting layer (Emission layer, EML), an electron transport layer (Electron transport layer, ETL), and an electron injection layer (Electron Injection layer, EIL) such as organic compound layers have a stacked structure. The organic light emitting diode (OLED) generates light when electrons and holes combine in the light emitting layer. In addition, each of the sub-pixels may further include an internal compensation circuit. The internal compensation circuit includes one or more switch TFTs and one Compensate for the characteristic change of the driving TFT by including the above capacitor.

The display panel driver includes a timing controller 110 , a data driver 120 , and a gate driver 130 . The display panel driver writes the compensation data obtained by converting the input image data and the logo data into the pixels of the display panel 100 .

The timing controller 110 receives input image data in which the logo data is modulated by the data compensator 40 . Also, the timing controller receives timing signals synchronized with input image data. The timing signals include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, and a dot clock CLK. The timing controller 110 transmits input image data to the data driver 102 .

The timing controller 110 controls operation timings of the data driver 120 and the gate driver 130 based on timing signals synchronized with the input image data. The timing controller 110 synchronizes the data driver 120 and the gate driver 130 by generating a data timing control signal and a gate timing control signal based on the timing signals. The data timing control signal defines the operation timing and output timing of the data driver 120 . The gate timing control signal defines the operation timing and output timing of the gate driver 130 .

The data driver 120 converts the input image data received from the timing controller 110 into an image data voltage, and converts the compensation data and the correction data into the compensation data voltage and the correction data voltage. The data driver 120 outputs the image data voltage, the compensation data voltage, and the compensation data voltage to the data voltage supply line 15A.

The gate driver 104 supplies a gate pulse synchronized with the output voltage of the data driver 102 to the gate lines 15 under the control of the timing controller 110 . The gate driver 104 sequentially shifts the gate pulse to sequentially select pixels into which data is written in line units.

2 is a diagram illustrating a pixel structure according to the present invention.

Referring to FIG. 2 , each of the pixels P includes an organic light emitting diode OLED, a driving transistor DT, a first transistor T1 , a second transistor T2 , and a storage capacitor Cst.

The organic light emitting diode OLED has an anode electrode connected to the second node N2 and a cathode electrode connected to the low potential power supply EVSS.

The driving transistor DT controls the current Ioled flowing through the organic light emitting diode OLED according to the gate-source voltage Vgs. The driving transistor DT includes a gate electrode connected to the first node N1 , a drain electrode connected to the high potential power EVDD, and a source electrode connected to the second node N2 .

The storage capacitor Cst is connected between the first node N1 and the second node N2 .

The first transistor ST1 is switched according to the scan signal SCAN to apply the data voltage supplied from the data voltage supply line 14A to the first node N1 . The first transistor ST1 includes a gate electrode connected to the scan line 15A, a drain electrode connected to the data voltage supply line 14A, and a source electrode connected to the first node N1 .

The second transistor ST2 is switched according to the sense signal SENSE, and applies the initialization voltage Vref supplied from the reference line 14B to the second node N2. In addition, the second transistor ST2 is switched according to the sense signal SENSE, and the threshold voltage Vth sensing voltage of the driving transistor DT is applied to the ADC (not shown). The gate electrode of the second transistor ST2 is connected to the second gate line 15B, the drain electrode is connected to the second node N2, and the source electrode is connected to the reference line 14B.

A method of compensating for the threshold voltage Vth of the driving transistor DT in the sub-pixels having such a structure will be described below.

During the initialization period, a high level scan signal SCAN is provided through the scan line 15A, and a high level sense signal SENSE is provided through the sense line 15B, so that the first and second transistors T1, T2) are all turned on. The first transistor T1 is turned on in response to the scan signal SCAN, the data voltage received from the data line 14A is applied to the gate electrode of the driving transistor DT, and the source of the driving transistor DT is applied. An initialization voltage received from the reference voltage line 15B is applied to the electrode. As a result, the potential between the gate-source electrode of the driving transistor DT is constantly initialized.

During the sensing period following the initialization period, the reference voltage line 14B is disconnected from the reference voltage source (not shown) and connected to an analog-to-digital converter (not shown). In a state in which the source electrode of the driving transistor DT is floating, the driving transistor DT operates when the gate-source voltage of the driving transistor is greater than or equal to the threshold voltage Vth, and an analog-to-digital converter connected to the reference voltage line 14B ( (not shown) senses the threshold voltage of the driving transistor DT. The analog-to-digital converter provides the sensed voltage to the timing controller 110 , and the timing controller 110 converts the sensed voltage into sensed data.

The period for acquiring the sensed data may be performed in a non-display section disposed at the front end of the image display section or at the rear end of the image display section. In this case, the non-display section disposed at the front end of the image display section refers to a section from immediately after driving power is applied until an image is displayed, and the non-display section disposed at the rear end of the image display section is immediately after image display is finished. It refers to the section from until the driving power is cut off. Alternatively, the period for acquiring the sensing data may be acquired during a blank period of the display period.

Even if the threshold voltage of the driving transistor DT is compensated in this way, the threshold voltage Vth of the driving transistor DT may remain negatively shifted. When the threshold voltage Vth of the driving transistor DT is negatively shifted, the driving transistor may operate even when the potential difference between the gate and the source of the driving transistor DT is '0'V. As a result, the driving transistor DT operates even in a state in which a driving voltage is not applied, so that the sub-pixel emits light in an undesired state.

In the present invention, compensation data is generated to improve the negative shift of the threshold voltage Vth of the driving transistor DT, and the sub-pixels are emitted using the compensation data.

3 is a flowchart illustrating a data compensation method according to an embodiment of the present invention, and FIG. 4 is a diagram illustrating an example of an image including a logo. 5 and 6 are diagrams illustrating an example of an edge map, and FIG. 7 is a diagram illustrating an example of low grayscale subpixels. And FIG. 8 is a diagram illustrating color coordinates for temperature compensation.

First, for data compensation according to the present invention, the logo detection unit 30 detects logo data from input image data. The logo data detected by the logo detection unit 30 is an image written in sub-pixels located in a still image image that does not change for a long time in addition to image data written in sub-pixels located in the logo image 31 shown in FIG. 4 . contains data. The logo data may be detected by comparing sizes of image data included in successive image frames. For example, the logo detection unit 30 calculates a difference between successive image data, and distinguishes between image data in which the calculated difference is less than or equal to a threshold and image data exceeding the threshold. FIG. 5 shows an example of an edge map indicating whether a difference between successive image data exceeds a threshold, and shows an edge map of area 'A' shown in FIG. 4 . As shown in FIG. 5 , the logo detection unit 30 assigns a weight of '1' to image data whose size change is equal to or less than the threshold, and does not give a weight to image data whose size change is greater than the threshold. 6 is an edge map showing a result of repeating this comparison of image data n times or more. The logo detection unit 30 determines image data in which the weight of the edge map is equal to or greater than a certain value as logo data (S301, S303).

The data compensator 40 detects low grayscale data in the logo data. When the sub-pixels emit light with a low gray scale for a long time, there is a great concern that the threshold voltage Vth of the driving transistor DT included in the sub-pixels may be negatively shifted. The data compensator 40 detects image data in which the threshold voltage Vth of the driving transistor DT is negatively shifted as low grayscale data as described above. A threshold value serving as a reference for detecting low grayscale data may be set in consideration of panel characteristics and user needs. In the case where the threshold voltage Vth of the driving transistor DT is compensated only for sub-pixels with a high probability that a negative shift phenomenon remarkably occurs due to the user's visibility, the data compensator 40 sets the threshold to '0'. can be set to That is, the data compensator 40 may detect a grayscale value that does not emit light as the low grayscale data.

7 is a diagram illustrating an example of sub-pixels detected as low grayscale data according to colors displayed by the pixels. FIG. 7 shows an example of low grayscale data in a RWGB type display panel in which each pixel includes an R sub-pixel, a W sub-pixel, a G sub-pixel, and a B sub-pixel.

When any one of the three primary colors is displayed in the RWGB display panel, only the corresponding sub-pixel emits light and the other three sub-pixels do not emit light. For example, as shown in FIG. 7A , only the R sub-pixel is emitted from a pixel displaying red, and other sub-pixels do not emit light. And, as shown in (b) of FIG. 7, the pixel displaying green emits light of the G sub-pixel, and the pixel displaying blue color as in (c) emits only the sub-pixel B. As shown in FIG. Accordingly, in the pixel shown in FIG. 7A , image data written in the W subpixel, the G subpixel, and the B subpixel is detected as low grayscale data. Similarly, in the pixel shown in FIG. 7B, image data written in the R subpixel, W subpixel, and B subpixel is detected as low grayscale data. In addition, in the pixel shown in FIG. 7C , image data written in the R subpixel, the W subpixel, and the G subpixel is detected as low grayscale data.

When displaying a white image in the RWGB method, any other sub-pixel other than the W sub-pixel may be emitted. The simplest way for a pixel to display a white image is to emit only the W sub-pixel, but other sub-pixels are emitted to increase the overall luminance or adjust the color temperature according to the characteristics of the device to which the display panel is applied and the user's request. FIG. 7(d) shows pixels displaying white color by emitting light of R sub-pixels and B sub-pixels in addition to the W sub-pixels. Accordingly, in the pixel shown in FIG. 7D, the image data written in the G sub-pixel is detected as low grayscale data (S305).

After detecting the low grayscale data, the data compensator 40 generates compensation data C_DATA_L by adding the compensation value c to the low grayscale data DATA_L as shown in Equation 1 below.

[Equation 1]

C_DATA_L = DATA_L +c

The compensation value c is preset to a luminance value that does not affect visibility. For example, if the amount of change in luminance that does not affect visibility in a display panel having a specific resolution is 1 nit, the compensation value c may be set to a value capable of displaying 1 nit of luminance ( S307)

The display panel driver writes the compensation data generated by the data compensator 40 to the display panel. As a result, in the display panel, all sub-pixels in the logo image 31 emit light. Accordingly, even when the logo image 31 is displayed for a long time, it is possible to improve a phenomenon in which the driving transistors DT of the sub-pixels that do not emit light in the logo image 31 are negatively shifted for a long time.

Even if the compensation value c is set within a range that does not affect visibility, the color temperature of the pixel may change because the luminance changes due to the compensation data C_DATA_L.

The data compensator 40 may generate correction data by compensating the basic image data in order to correct the color temperature change due to the compensation data C_DATA_L. The basic image data refers to image data of sub-pixels to which image data other than the low grayscale data DATA_L among logo data is applied. For example, basic image data in the pixel shown in FIG. 7A is image data written in the R sub-pixel. And in the pixel shown in (b) of FIG. 7, basic image data is image data written in the G sub-pixel, and in the pixel shown in (c), basic image data is image data written in the B sub-pixel, (d) In the pixel shown in ), the basic image data is image data written to the R sub-pixel, W sub-pixel, and B sub-pixels.

The data compensator 40 generates correction data A_DATA_S by adding a correction value to the basic image data DATA_S as shown in Equation 2 below. The correction value is calculated by multiplying the basic image data DATA_S by the gain value g. The gain value g may be stored in a lookup table (not shown) as a preset value.

[Equation 2]

A_DATA_S = DATA_S + DATA_S * g

A process in which the data compensator 40 performs color temperature correction of pixels based on [Equation 2] will be described with reference to the color coordinates of FIG. 8 .

When the subpixel to which the low grayscale data detected in step S305 is written is the G subpixel as shown in FIG. 5D , the data compensator 40 applies the compensation value c to the G subpixel G. add up As the luminance of the G sub-pixel G increases due to the compensation data C_DATA_L, the color temperature of the pixel shown in FIG. In order to correct the change in the y value of the color coordinate, the data compensator 40 generates correction data A_DATA_S by correcting the image data of the B sub-pixel B, which is the basic image data DATA_S. When the luminance of the B sub-pixel B is increased by the correction data A_DATA_S, the x-coordinate value and the y-coordinate value of the white color coordinate are decreased. The data compensator 40 generates correction data A_DATA_S of the R subpixel R to compensate for the decrease in the x-coordinate value and the y-coordinate value in the color coordinate.

As described above, the data compensation method of the present invention can improve the negative shift of the threshold voltage Vth of the driving transistor DT by writing the compensation data C_DATA_S to the sub-pixel. Also, in the data compensation method of the present invention, the color temperature of the pixel can be prevented from being changed due to the compensation data C_DATA_S by writing the correction data A_DATA_S to the sub-pixel.

Those skilled in the art from the above description will be able to see that various changes and modifications are possible without departing from the technical spirit of the present invention. Accordingly, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

20: host system 30: logo detection unit
40: data compensation unit 100: display panel
110: timing controller 120: data driver
130: gate driver

Claims (10)

a display panel in which pixels composed of a plurality of sub-pixels are arranged;
a logo detection unit for detecting logo data from input image data;
Among the logo data, logo data whose image data is '0' is detected as low grayscale data, and a compensation value corresponding to a grayscale greater than '0' and less than '1' nit is added to the low grayscale data. a data compensator to generate compensation data; and
and a display panel driver configured to write the compensation data to the display panel.
delete delete The method of claim 1,
The data compensator detects image data other than the low grayscale data as basic image data in order to compensate for the color temperature change of the pixels due to the compensation data, and corrects the basic image data to generate corrected image data Device. 5. The method of claim 4,
The data compensator generates a correction value by multiplying the basic image data by a preset gain value, and generates the corrected image data by adding the correction value to the basic image data. detecting logo data from input image data;
detecting logo data in which image data is '0' among the logo data as low grayscale data;
generating compensation data by adding a compensation value corresponding to a grayscale greater than '0' and less than '1' nits to the low grayscale data; and
and converting the compensation data into a compensation data voltage and providing the compensation data to a display panel.
delete delete 7. The method of claim 6,
After generating the compensation data, image data other than the low grayscale data is detected as basic image data, and the basic image data is corrected to compensate for the color temperature change of the pixels due to the compensation data. Data compensation method of the display device further comprising the step of generating. 10. The method of claim 9,
The step of generating the corrected image data is
generating a correction value by multiplying the basic image data by a preset gain value; and
and adding the correction value to the basic image data.

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