KR102379777B1 - Electroluminescent System And How To Set Reference Voltage Of The Same - Google Patents

Abstract

An electroluminescent system according to the present invention comprises: a display panel including a plurality of pixels, each pixel having a driving TFT generating a driving current and an OLED emitting light according to the driving current; a panel driver that applies a data voltage to a gate electrode of each driving TFT and a reference voltage to a source electrode of each driving TFT to emit light; a luminance meter for measuring the luminance of the entire surface of the display panel while the OLED emits light; a threshold voltage analyzer for generating a luminance map for each color from the measured front luminance and deriving a threshold voltage distribution of the driving TFT for the pixels based on the luminance map for each color; and a reference voltage setting unit configured to change the reference voltage according to a threshold voltage distribution of the driving TFT.

Description

Electroluminescent System And How To Set Reference Voltage Of The Same

The present invention relates to an electroluminescent system and a method for setting a reference voltage thereof.

The electroluminescent display device is roughly classified into an inorganic light emitting display device and an organic light emitting display device according to the material of the light emitting layer. Among them, the active matrix type organic light emitting display device includes an organic light emitting diode (hereinafter referred to as "OLED") that emits light by itself, and has a fast response speed, luminous efficiency, luminance and The viewing angle is a big advantage.

The organic light emitting display device arranges pixels including OLEDs in a matrix form and adjusts the luminance of the pixels according to the gray level of image data. Each of the pixels includes a driving TFT (Thin Film Transistor) that controls a driving current flowing through the OLED according to a gate-source voltage, and one or more switch TFTs for programming a gate-sort voltage of the driving TFT, the driving current Adjusts the display gradation (luminance) with the amount of light emitted by the OLED in proportion to .

In order to realize a uniform image quality without a difference in luminance and color between pixels, the driving characteristics of the pixel, such as the threshold voltage (Vth) of the driving TFT, must be the same in all pixels. However, there may be variations in driving characteristics between pixels due to various causes including process variations. If the driving characteristics are different between pixels, the amount of driving current flowing to the OLED will be different, resulting in non-uniformity of image quality. In order to solve this problem, a so-called external compensation technique of sensing the threshold voltage of the driving TFT from each pixel and correcting digital image data based on the sensing result is known.

The external compensation technology requires a sensing circuit for sensing the threshold voltage of the driving TFT. The sensing circuit is mounted on the source driver. The source driver supplies a data voltage to the pixels through data lines, and is connected to the pixels through sensing lines to sense a threshold voltage of the driving TFT. Since the sensing circuit includes a plurality of sensing units and a plurality of analog-digital converters (ADCs) for individually sensing each pixel, the circuit size is large.

As such, in the case of the organic light emitting diode display employing the external compensation technology, the chip size of the source driver is large and the cost thereof is increased. Accordingly, in compensating for the driving characteristic deviation between pixels, a new method different from the existing external compensation technology is required.

An object of the present invention is to compensate for the threshold voltage deviation of the driving TFT between pixels without a separate sensing circuit, but to set the reference voltage applied to the source electrode of the driving TFT according to the threshold voltage distribution of the driving TFT to improve the compensation performance. An object of the present invention is to provide an electroluminescent system and a method for setting a reference voltage thereof.

In order to solve the above object, an electroluminescent system according to the present invention includes: a display panel provided with a plurality of pixels, each pixel having a driving TFT generating a driving current and an OLED emitting light according to the driving current; a panel driver that applies a data voltage to a gate electrode of each driving TFT and a reference voltage to a source electrode of each driving TFT to emit light; a luminance meter for measuring the luminance of the entire surface of the display panel while the OLED emits light; a threshold voltage analyzer for generating a luminance map for each color from the measured front luminance and deriving a threshold voltage distribution of the driving TFT for the pixels based on the luminance map for each color; and a reference voltage setting unit configured to change the reference voltage according to a threshold voltage distribution of the driving TFT.

The reference voltage setting unit sets a result of adding the lowest threshold voltage value and a predetermined voltage margin value among the threshold voltage distributions of the driving TFT as the reference voltage.

The electroluminescent system according to the present invention includes: a compensation value calculator for calculating a compensation value for compensating for a threshold voltage deviation of the driving TFT between the pixels based on the threshold voltage distribution of the driving TFT; a memory for storing the compensation value; and a timing controller correcting the input image data based on the compensation value.

The electroluminescent system according to the present invention further comprises a photographing condition control unit that analyzes the histogram for the front luminance and controls the exposure time of the luminance meter so that the histogram falls within a preset confidence interval, wherein the confidence interval is It is set from 10% to 90% of the luminance range.

The electroluminescent system according to the present invention analyzes the front luminance to calculate a luminance lower limit value corresponding to 10% of the total luminance range and a luminance upper limit value corresponding to 90% of the entire luminance range, and the luminance lower limit value and the luminance upper limit value are calculated. The method further includes a data voltage adjuster configured to determine the data voltage so that a value obtained by subtracting a preset target luminance value from an average luminance value falls within a predetermined range.

The data voltage adjusting unit determines the data voltage by repeating a recursion function until a value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range.

In addition, according to the present invention, the method for setting a reference voltage of an electroluminescent system including a display panel having a plurality of pixels, each pixel having a driving TFT generating a driving current and an OLED emitting light according to the driving current, a panel driving step of applying a data voltage to the gate electrode of the driving TFT and applying a reference voltage to the source electrode of each driving TFT to emit light; a luminance measuring step of measuring the luminance of the entire surface of the display panel while the OLED emits light; a threshold voltage analysis step of generating a luminance map for each color from the measured front luminance and deriving a threshold voltage distribution of the driving TFT for the pixels based on the luminance map for each color; and a reference voltage setting step of changing the reference voltage according to a threshold voltage distribution of the driving TFT.

Since the present invention can compensate for the threshold voltage deviation of the driving TFT between pixels based on a camera without a sensing circuit, effectively compensate the luminance deviation with the threshold voltage deviation without increasing the chip size and manufacturing cost of the source driver. can do.

In addition, the present invention sets the reference voltage applied to the source electrode of the driving TFT according to the threshold voltage distribution of the driving TFT, thereby remarkably improving the compensation performance without worrying about luminance aggregation due to insufficient compensation margin.

1 is a block diagram showing an electroluminescent system according to an embodiment of the present invention.
2 is a diagram illustrating a pixel array of an organic light emitting diode display according to an exemplary embodiment of the present invention.
3 is a diagram illustrating a pixel circuit of an organic light emitting diode display according to an exemplary embodiment of the present invention.
FIG. 4 is a diagram for explaining an operation of compensating a threshold voltage for a pixel A and a pixel B when a data voltage is applied to all pixels based on an arbitrarily set reference voltage.
5 shows that there is a luminance deviation between panel A and panel B.
6 shows that the threshold voltage distribution is different between panel A and panel B.
FIG. 7 shows that a compensation margin is insufficient in a specific panel due to a threshold voltage deviation between the panels when the reference voltage is set to be the same.
8 is a diagram illustrating a method of setting a reference voltage of an electroluminescent system according to an embodiment of the present invention.
9 and 10 are diagrams for explaining an operation of the shooting condition control unit of FIG. 1 .
11 and 12 are diagrams for explaining an operation of the data voltage adjusting unit of FIG. 1 .
13 is a diagram for explaining an operation of the threshold voltage analyzer of FIG. 1 .
14 to 16 are diagrams for explaining an effect obtained by setting a reference voltage according to a threshold voltage distribution.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be embodied in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative and the present invention is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'next to', etc., 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

Although first, second, etc. are used to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present invention.

Like reference numerals refer to like elements throughout.

Each feature of the various embodiments of the present invention may be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each embodiment may be implemented independently of each other or may be implemented together in a related relationship. may be

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. The component names used in the following description are selected in consideration of the ease of writing the specification, and may be different from the component names of the actual product.

1 is a block diagram showing an electroluminescent system according to an embodiment of the present invention. 2 is a diagram illustrating a pixel array of an organic light emitting diode display according to an exemplary embodiment of the present invention. 3 is a diagram illustrating a pixel circuit of an organic light emitting diode display according to an exemplary embodiment of the present invention.

An electroluminescent system according to an embodiment of the present invention is based on an electroluminescent display device. The electroluminescent display device includes an inorganic light emitting display device and an organic light emitting display device, and in the embodiment of the present invention, the organic light emitting display device will be mainly described. The technical idea of the present invention may be applied to an inorganic light emitting display device as well as an organic light emitting display device.

Referring to FIG. 1 , an electroluminescent system according to an embodiment of the present invention includes a display panel 10 including pixels PXL, and panel drivers 12 and 13 for driving signal lines connected to the pixels PXL. , and a timing controller 11 for controlling the panel drivers 12 and 13 .

In the display panel 10 , a plurality of data lines 14 and a plurality of gate lines 15 cross each other, and the pixels PXL are arranged in a matrix form to form a pixel array as shown in FIG. 2 .

Referring to FIG. 2 , the pixel array includes a plurality of horizontal pixel lines L1 to L4, horizontally adjacent to each horizontal pixel line L1 to L4, and each gate line 15(1) to 15(4). )), a plurality of pixels PXL commonly connected to each other are disposed. Here, each of the horizontal pixel lines L1 to L4 does not mean a physical signal line, but a pixel block equivalent to one line implemented by horizontally adjacent pixels PXL. The pixel array includes first power lines 17 for supplying the high potential power voltage EVDD to the pixels PXL, and second power lines 16 for supplying the reference voltage Vref to the pixels PXL. may be included. Also, the pixels PXL may be connected to the low potential power voltage EVSS.

Each of the pixels PXL includes an OLED as shown in FIG. 3 , a driving TFT DT, a switch TFT ST, and a storage capacitor Cst.

Referring to FIG. 3 , an OLED is a self-luminous device that emits light according to a driving current. The OLED includes an anode electrode connected to the source electrode of the driving TFT DT, a cathode electrode connected to the low potential power supply voltage EVSS, and an organic compound layer provided between the anode electrode and the cathode electrode. The organic compound layer includes a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (Electron Injection Layer, EIL). When a power voltage is applied to the anode and cathode electrodes, holes passing through the hole transport layer (HTL) and electrons passing through the electron transport layer (ETL) are moved to the light emitting layer (EML) to form excitons, and as a result, the light emitting layer (EML) is produces visible light.

Referring to FIG. 3 , the driving TFT DT is a driving device that adjusts the driving current to the gate-source voltage Vgs. The gate electrode of the driving TFT DT is connected to the first node N1 , and the source electrode is connected to the second node N2 . A reference voltage Vref is applied to the source electrode of the driving TFT DT through the second power line 16 . Then, the high potential driving voltage EVDD is applied to the drain electrode of the driving TFT DT through the first power line 17 .

Referring to FIG. 3 , the switch TFT ST is turned on/off according to the gate signal SCAN to control the current flow between the data line 14 and the first node N1 . The switch TFT ST is turned on according to the gate signal SCAN to apply the data voltage Vdata to the gate electrode of the driving TFT DT. The switch TFT ST has a gate electrode connected to the gate line 15 , a drain electrode connected to the data line 14 , and a source electrode connected to the first node N1 .

Referring to FIG. 3 , the storage capacitor Cst is connected between the first node N1 and the second node N2 to maintain the gate-source voltage Vgs of the driving TFT DT for a predetermined time. .

Each of these pixels PXL may be any one of a red pixel, a green pixel, a blue pixel, and a white pixel to implement various colors. A red pixel, a green pixel, a blue pixel, and a white pixel may constitute one unit pixel. A color implemented in a unit pixel may be determined according to emission ratios of a red pixel, a green pixel, a blue pixel, and a white pixel.

Referring to FIG. 1 , the panel drivers 12 and 13 write input image data DATA to the pixels PXL of the display panel 10 . The panel drivers 12 and 13 include a source driver 12 driving the data lines 14 connected to the pixels PXL, and a gate driver 12 driving the gate lines 15 connected to the pixels PXL. 13) is included.

Referring to FIG. 1 , the source driver 12 converts input image data DATA received from the timing controller 11 every frame into a data voltage Vdata, and then converts the data voltage Vdata to data lines. (14) is supplied. The source driver 12 outputs the data voltage Vdata using a digital-to-analog converter (DAC) that converts the input image data DATA into a gamma compensation voltage.

The source driver 12 does not require a sensing circuit for sensing the threshold voltage of the driving TFT DT for each pixel. Since the source driver 12 does not include a plurality of sensing units for individually sensing each pixel and a plurality of analog-digital converters (ADC), a separate sensing circuit is mounted with a circuit size of the source driver 12 . It is small compared to when it is made, and the manufacturing cost is low.

A multiplexer (not shown) may be further disposed between the source driver 12 and the data lines 14 of the display panel 10 . The multiplexer divides the data voltage output from the source driver 12 through one output channel into a plurality of data lines, thereby reducing the number of output channels of the source driver 12 compared to the number of data lines. The multiplexer may be omitted depending on the resolution and use of the display device.

Referring to FIG. 1 , the gate driver 13 supplies the gate signal SCAN to the gate lines 15 in a line-sequential manner under the control of the timing controller 11 , so that the data voltage Vdata is charged in a horizontal pixel. Select the line (L1~Ln). The gate driver 13 may be directly formed on the substrate of the display panel 10 together with the pixel array through a gate-driver in panel (GIP) process, but is not limited thereto. After the gate driver 13 is manufactured as an IC type, it may be bonded to the display panel 10 through a conductive film.

Referring to FIG. 1 , the timing controller 11 receives digital data DATA of an input image and timing signals synchronized therewith from a host (not shown). The timing signals may include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a dot clock signal DCLK, and a data enable signal DE. The host may be any one of a television (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 timing controller 11 multiplies the input frame frequency by i to control the operation timing of the panel drivers 12 and 13 with a frame frequency of the input frame frequency×i (i is a positive integer greater than 0) Hz. The input frame frequency is 60 Hz in the NTSC (National Television Standards Committee) scheme and 50 Hz in the PAL (Phase-Alternating Line) scheme.

The timing controller 11 includes a data timing control signal DDC for controlling the operation timing of the source driver 12 based on the timing signals Vsync, Hsync, DE received from the host, and the gate driver 13 . A gate timing control signal GDC for controlling the operation timing is generated.

The data timing control signal DDC includes a source start pulse, a source sampling clock, and a source output enable signal. The source start pulse controls the sampling start timing of the source driver 12 . The source sampling clock is a clock for shifting the data sampling timing. If the signal transmission interface between the timing controller 11 and the source driver 12 is a mini LVDS (Low Voltage Differential Signaling) interface, the source start pulse and the source sampling clock may be omitted.

The gate timing control signal GDC includes a gate start pulse, a gate shift clock, and a gate output enable signal. In the case of the GIP circuit, the gate output enable signal (Gate Output Enable) may be omitted. The gate start pulse is generated at the beginning of each frame period and is input to the shift register of each of the gate drivers 13 . The gate start pulse controls the start timing at which the gate signal SCAN is output in every frame period. The gate shift clock is input to the shift register of the gate driver 13 to control shift timing of the shift register.

In addition, the electroluminescence system according to the embodiment of the present invention does not include a separate sensing circuit, and the luminance meter 20 and the threshold voltage analyzer are used to compensate for the threshold voltage deviation of the driving TFT DT between the pixels PXL. 22 , a reference voltage setting unit 24 , a compensation value calculating unit 26 , a memory 28 , a photographing condition control unit 30 , and a data voltage adjusting unit 32 .

Referring to FIG. 1 , the luminance meter 20 measures the luminance of the entire surface of the display panel 10 while the OLEDs of the pixels PXL emit light. The luminance meter 20 may be implemented as a camera.

Referring to FIG. 1 , the threshold voltage analyzer 22 generates a luminance map for each color from the front luminance measured by the luminance meter 20 , and a driving TFT for pixels PXL based on the luminance map for each color The threshold voltage distribution of (DT) is derived.

Referring to FIG. 1 , the reference voltage setting unit 24 changes the reference voltage Vref according to the threshold voltage distribution of the driving TFT DT derived from the threshold voltage analysis unit 22 , and the reference voltage Vref. may be supplied to the pixels PXL through the second power lines 16 . The reference voltage setting unit 24 sets the reference voltage Vref applied to the source electrode of the driving TFT DT according to the threshold voltage distribution of the driving TFT DT to increase compensation performance.

Referring to FIG. 1 , the compensation value calculator 26 calculates the threshold voltage of the driving TFT DT between pixels PXL based on the threshold voltage distribution of the driving TFT DT derived from the threshold voltage analyzer 22 . A compensation value for compensating for the deviation is calculated. The compensation value may be calculated to be larger in a pixel having a larger threshold voltage than a pixel having a relatively small threshold voltage of the driving TFT DT. The compensation value calculator 26 may be built into the timing controller 11 .

Referring to FIG. 1 , the memory 28 stores the compensation value calculated by the compensation value calculation unit 26 . The memory 28 may be implemented as a non-volatile memory in which stored contents are maintained even when the system power is turned off. As an example, the memory 28 may be a flash memory.

Referring to FIG. 1 , the timing controller 11 corrects the input image data DATA based on the compensation value stored in the memory 28 , thereby causing a threshold voltage deviation of the driving TFT DT between the pixels PXL. It is possible to compensate for the luminance deviation. A smaller driving current flows in a pixel having a large threshold voltage of the driving TFT DT compared to a pixel having a small threshold voltage. Accordingly, when the image data DATA applied to the pixel having a small driving current is corrected to be larger than the image data DATA applied to the pixel having a large driving current, the luminance deviation due to the threshold voltage deviation of the driving TFT DT is reduced. can be reduced

Referring to FIG. 1 , when the imaging condition controller 30 and the data voltage adjuster 32 set the reference voltage Vref according to the threshold voltage distribution of the driving TFT DT, the data voltage Vdata exceeds the compensation margin. This is to increase the reliability of compensation by not doing so.

Since the luminous efficiency of each of the pixels PXL may be different from each other, it is measured by the luminance meter 20 by changing the camera shooting condition or determining the applied data voltage Vdata through a recursive function. It is possible to increase the reliability of the obtained luminance information, thereby increasing the accuracy of compensation.

Referring to FIG. 1 , the photographing condition controller 30 analyzes the histogram of the front luminance input from the luminance meter 20 and controls the exposure time of the luminance meter 20 so that the histogram falls within a preset confidence interval. do.

Referring to FIG. 1 , the data voltage adjusting unit 32 analyzes the front luminance input from the luminance meter 20 to determine the luminance lower limit value corresponding to 10% of the entire luminance range and the luminance upper limit value corresponding to 90% of the total luminance range. The data voltage Vdata may be determined such that a value obtained by subtracting a preset target luminance value from the average luminance value of the luminance lower limit value and the luminance upper limit value falls within a predetermined range. The data voltage adjusting unit 32 may be built into the source driver 12 .

4 to 7 are diagrams for explaining a phenomenon of insufficient compensation margin when compensating for a threshold voltage deviation based on a camera as a comparative example of the present invention.

4 shows a threshold voltage compensation operation for the pixel A and the pixel B when a data voltage is applied to all pixels based on an arbitrarily set reference voltage. In FIG. 4 , the horizontal axis represents the gate-source voltage (Vgs) of the driving TFT, and the vertical axis represents the driving current Ioled.

Referring to FIG. 4 , the camera-based compensation method generates compensation values (V _comp,A , _Vcom,B ) of each pixel (A,B) according to a preset target curve C to compensate for a threshold voltage deviation. . A target curve C is established between curve A for pixel A and curve B for pixel B. In order to fit the threshold voltage Vth_A of the pixel A to the target curve C, the curve A needs to be shifted to the right. And, in order to fit the threshold voltage Vth_B of the pixel B to the target curve C, the curve B needs to be shifted to the left. The compensation value (V _comp,B ) of the pixel B for causing the curve B to shift to the left is a (+) value. On the other hand, the compensation value (V _comp,A ) of the pixel A for causing the curve A to shift to the right is a negative value. Since the output voltage range of the source driver is greater than 0, it is difficult to implement a (-) compensation value unlike a (+) compensation value.

FIG. 5 shows that when the same gate-source voltage is applied to all pixels, a luminance deviation between the panels A and B occurs. And, FIG. 6 shows that the threshold voltage distribution is different between panel A and panel B. FIG. 7 shows that a compensation margin is insufficient in a specific panel due to a threshold voltage deviation between the panels when the reference voltage is set to be the same.

Referring to FIGS. 5 and 6 , when the threshold voltage distribution is different between panels A and B, when the same gate-source voltage is applied to panels A and B, a luminance deviation occurs between panels A and B. The luminance of the panel A having a relatively high threshold voltage is darker than the luminance of the panel B having a relatively low threshold voltage. In order to compensate for the luminance deviation, the compensation value of the panel A having a large threshold voltage needs to be increased compared to the compensation value of the panel B.

As shown in FIG. 7 , the output voltage range of the source driver includes a grayscale expression section between the first voltage VA and the second voltage VB and a compensation margin section between the second voltage VB and the third voltage VC. includes The grayscale expression section is a voltage section for expressing an input image, and the compensation margin section is a voltage section for compensating for a threshold voltage deviation between pixels. As an example, the first voltage V-A may be 0V, the second voltage V-B may be 10V, and the third voltage V-C may be 16V. In addition, the reference voltage Vref may be 0V.

In this case, the voltage margin allocated to the threshold voltage compensation of the panel A may be insufficient. If the compensation margin is insufficient, compensation may be insufficient, resulting in luminance aggregation and poor luminance uniformity. The reason why the compensation margin of panel A is insufficient is that the reference voltage Vref is set to 0V, the same as that of panel B, regardless of the threshold voltage distribution of the driving TFT.

8 is a diagram illustrating a method of setting a reference voltage of an electroluminescent system according to an embodiment of the present invention. 9 and 10 are diagrams for explaining the operation of the shooting condition control unit of FIG. 1 . 11 and 12 are diagrams for explaining the operation of the data voltage controller of FIG. 1 . 13 is a diagram for explaining an operation of the threshold voltage analyzer of FIG. 1 .

1 and 8 , in the method for setting the reference voltage of the electroluminescent system according to the present invention, the reference voltage Vref is set to the pixels PXL by using the panel drivers 12 and 13 as a default value. is applied, and an arbitrary data voltage Vdata is applied to the pixels PXL (S1 and S2). Accordingly, the OLEDs of the pixels PXL emit light by the driving current corresponding to the gate-source voltage Vgs of the driving TFT DT, that is, “Vdata-Vref”.

1 and 8 , in the method for setting the reference voltage of the electroluminescent system according to the present invention, the luminance of the entire surface of the display panel is measured while the OLED emits light by using the luminance meter 20 ( S3 ).

1 and 8 , in the method for setting the reference voltage of the electroluminescent system according to the present invention, the front luminance input from the luminance meter 20 is preset by using the photographing condition control unit 30 and the data voltage adjustment unit 32 . The camera shooting conditions are changed to fall within the set confidence interval, or the applied data voltage Vdata is adjusted (S4, S5).

This is to increase the reliability of the front-side luminance measurement to accurately determine the threshold voltage distribution. This will be described in detail as follows.

Referring to FIG. 9 , in the method for setting the reference voltage of the electroluminescent system according to the present invention, the histogram of the front luminance input from the luminance meter 20 is analyzed using the shooting condition control unit 30, and the histogram is set in advance. Control the exposure time of the luminance meter 20 to fall within the confidence interval. Here, the confidence interval may be set to 10% (LSL) to 90% (USL) of the entire luminance range as shown in FIG. 10 . The luminance lower limit value “LSL” corresponds to the lower 3σ of all pixel luminance data, and the luminance upper limit value “USL” corresponds to the upper 3σ of all pixel luminance data. If the exposure time of the luminance meter 20 is controlled, the reliability of the front luminance measurement value input from the luminance meter 20 can be improved.

Referring to FIG. 11 , the reference voltage setting method of the electroluminescent system according to the present invention uses the data voltage adjuster 32 to analyze the front luminance input from the luminance meter 20 and corresponds to 10% of the entire luminance range. The luminance lower limit value (LSL) and the luminance upper limit value USL corresponding to 90% of the entire luminance range are calculated, and the average luminance value {(LSL+USL)/2} of the luminance lower limit value LSL and the luminance upper limit value USL is used in advance. The data voltage Vdata may be determined such that a value obtained by subtracting the set target luminance value falls within a predetermined range (≤k).

To this end, the data voltage adjusting unit 32 repeats the recursion function until the value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range (≤k) as shown in FIG. ) can be determined. If the data voltage Vdata is determined using the recursive function, the reliability of the front luminance measurement value input from the luminance meter 20 may be improved. Meanwhile, since OLED luminous efficiencies of red pixels, green pixels, blue pixels, and white pixels are different from each other, the data voltage Vdata may be determined differently for each color.

1 and 8, in the method of setting the reference voltage of the electroluminescent system according to the present invention, a luminance map for each color is generated from the front luminance measured by the luminance meter 20 using the threshold voltage analyzer 22, , a threshold voltage distribution of the driving TFT for the pixels is derived based on the luminance map for each color (S6).

Referring to FIG. 13, the process of deriving the threshold voltage distribution will be described in detail. The method for setting the reference voltage of the electroluminescent system according to the present invention is based on the front luminance measured by the luminance meter 20, red, green, blue, A luminance map is generated for each white (S61).

In the method for setting the reference voltage of the electroluminescent system according to the present invention, the luminance map for each color is converted into a voltage domain, and the average value Vdata_in of the applied data voltage Vdata for each color is calculated (S62 and S63).

In the method for setting the reference voltage of the electroluminescent system according to the present invention, the voltage upper limit value (corresponding to the luminance upper limit value “USL”) (Vdata_out) of the entire pixel voltage distribution is calculated from the result converted into the voltage domain ( S64 ).

The method for setting the reference voltage of the electroluminescent system according to the present invention is the lowest value corresponding to the luminance lower limit value (LSL) by subtracting the voltage upper limit value (Vdata_out) of the entire pixel voltage distribution from the average value (Vdata_in) of the applied data voltages (Vdata) for each color. A threshold voltage value Vth_LSL is calculated (S65).

1 and 8, in the method of setting the reference voltage of the electroluminescent system according to the present invention, the reference voltage Vref is changed and set according to the threshold voltage distribution of the driving TFT using the reference voltage setting unit 24 ( S7). In the method for setting a reference voltage of an electroluminescent system according to the present invention, the result of adding the lowest threshold voltage value (Vth_LSL) and a predetermined voltage margin value (NBTis Margin Value) among the threshold voltage distributions of the driving TFT is used as the reference voltage (Vref). set

14 to 16 are diagrams for explaining an effect obtained by setting a reference voltage according to a threshold voltage distribution.

In the method of setting the reference voltage of the electroluminescent system according to the present invention, as shown in FIG. 14, the reference voltage Vref is set based on the lowest threshold voltage value (Vth_A) among the threshold voltage distribution of the pixel having the best threshold voltage characteristic, that is, the driving TFT. Because it is set, positive bias driving is possible in the entire grayscale expression section, and even pixels whose threshold voltage is shifted in the (-) direction can be compensated. For example, in the present invention, as shown in FIG. 14 , the reference voltage Vref is set based on the threshold voltage value Vth_A of the pixel A having the best threshold voltage characteristic, and the curve A for the pixel A is selected as the target curve A do. In addition, the present invention generates compensation values (V _comp,B , V _comp,C ) of each pixel (B,C) according to the target curve A. In order to fit the threshold voltage Vth_A of the pixel B to the target curve A, the curve B needs to be shifted to the left. And, in order to fit the threshold voltage Vth_C of the pixel C to the target curve A, the curve C needs to be shifted to the left. The compensation value (V _comp,B ) of the pixel B for shifting the curve B to the left is a (+) value, and the compensation value (V _comp,C ) of the pixel C for shifting the curve C to the left is also (+) ) is the value. Since the output voltage range of the source driver is greater than 0, (+) compensation values can be sufficiently implemented.

Also, referring to FIGS. 15 and 16 , when the threshold voltage distribution is different between the panel A and the panel B, the lowest threshold voltage value Vth_A among the threshold voltage distributions of the driving TFT for each of the panels A and B is the reference. When the reference voltages Vref_A and Vref_B are set to , the voltage margins allocated to the threshold voltage compensation of panels A and B are all sufficient. That is, the present invention can solve the problem of luminance aggregation due to insufficient compensation margin and increase luminance uniformity by setting the reference voltage for each panel in consideration of the threshold voltage characteristics for each panel.

As described above, in the present invention, since the threshold voltage deviation of the driving TFT between pixels can be compensated for based on a camera without a sensing circuit, the threshold voltage deviation can be reduced without increasing the chip size and manufacturing cost of the source driver. It is possible to effectively compensate for the luminance deviation.

In addition, the present invention sets the reference voltage applied to the source electrode of the driving TFT according to the threshold voltage distribution of the driving TFT, thereby remarkably improving the compensation performance without worrying about luminance aggregation due to insufficient compensation margin.

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.

10: display panel 11: timing controller
12, 13: panel driving unit 20: luminance meter
22: threshold voltage analysis unit 24: reference voltage setting unit
26: compensation value calculation unit 28: memory
30: shooting condition control unit 32: data voltage control unit

Claims (12)

a display panel including a plurality of pixels, each pixel having a driving TFT generating a driving current and an OLED emitting light according to the driving current;
a panel driver that applies a data voltage to the gate electrode of each driving TFT and a reference voltage to the source electrode of each driving TFT to emit light;
a luminance meter for measuring the luminance of the entire surface of the display panel while the OLED emits light;
a threshold voltage analyzer for generating a luminance map for each color from the measured front luminance and deriving a threshold voltage distribution of the driving TFT for the pixels based on the luminance map for each color; and
and a reference voltage setting unit configured to change the reference voltage according to the lowest threshold voltage value among the threshold voltage distributions of the driving TFT. The method of claim 1,
The reference voltage setting unit,
An electroluminescent system for setting a result of adding a lowest threshold voltage value and a predetermined voltage margin value among the threshold voltage distributions of the driving TFT as the reference voltage. The method of claim 1,
a compensation value calculator calculating a compensation value for compensating for a threshold voltage deviation of the driving TFT between the pixels based on the threshold voltage distribution of the driving TFT;
a memory for storing the compensation value; and
The electroluminescent system further comprising a timing controller for correcting the input image data based on the compensation value. The method of claim 1,
Further comprising a photographing condition control unit that analyzes the histogram for the front luminance and controls the exposure time of the luminance meter so that the histogram falls within a preset confidence interval,
The confidence interval is an electroluminescent system that is set to 10% to 90% of the entire luminance range. The method of claim 1,
The front luminance is analyzed to calculate a luminance lower limit value corresponding to 10% of the entire luminance range and a luminance upper limit value corresponding to 90% of the entire luminance range, and a preset target luminance value from the average luminance value of the luminance lower limit value and the luminance upper limit value The electroluminescent system further comprising a data voltage adjusting unit for determining the data voltage so that a value obtained by subtracting a value falls within a predetermined range. 6. The method of claim 5,
The data voltage adjusting unit determines the data voltage by repeating a recursion function until a value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range. In the method for setting a reference voltage of an electroluminescent system including a display panel including a plurality of pixels, each pixel having a driving TFT generating a driving current and an OLED emitting light according to the driving current,
a panel driving step of applying a data voltage to the gate electrode of each driving TFT and applying a reference voltage to the source electrode of each driving TFT to emit light;
a luminance measuring step of measuring the luminance of the entire surface of the display panel through a luminance meter while the OLED emits light;
a threshold voltage analysis step of generating a luminance map for each color from the measured front luminance and deriving a threshold voltage distribution of the driving TFT for the pixels based on the luminance map for each color; and
and a reference voltage setting step of changing the reference voltage according to the lowest threshold voltage value among the threshold voltage distributions of the driving TFT. 8. The method of claim 7,
In the step of setting the reference voltage,
A reference voltage setting method of an electroluminescent system for setting a result of adding a lowest threshold voltage value and a predetermined voltage margin value among the threshold voltage distributions of the driving TFT as the reference voltage. 8. The method of claim 7,
a compensation value calculation step of calculating a compensation value for compensating for a threshold voltage deviation of the driving TFT between the pixels based on the threshold voltage distribution of the driving TFT;
storing the compensation value in a memory; and
The reference voltage setting method of the electroluminescent system further comprising the step of correcting the input image data based on the compensation value. 8. The method of claim 7,
A photographing condition control step of analyzing the histogram for the front luminance and controlling the exposure time of the luminance meter so that the histogram falls within a preset confidence interval,
The confidence interval is a reference voltage setting method of an electroluminescent system that is set to 10% to 90% of the entire luminance range. 8. The method of claim 7,
The front luminance is analyzed to calculate a luminance lower limit value corresponding to 10% of the entire luminance range and a luminance upper limit value corresponding to 90% of the entire luminance range, and a preset target luminance value from the average luminance value of the luminance lower limit value and the luminance upper limit value The method of setting a reference voltage of an electroluminescent system further comprising the step of adjusting the data voltage to determine the data voltage so that the value obtained by subtracting the value falls within a predetermined range. 12. The method of claim 11,
The data voltage adjustment step repeats a recursion function until a value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range to determine the data voltage.

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