KR20190021760A - Electroluminescent System And How To Set Reference Voltage Of The Same - Google Patents

Abstract

According to the present invention, an electroluminescent system comprises: a display panel provided with a plurality of pixels, wherein each of the pixels has a driving TFT generating a driving current and an OLED emitting light according to the driving current; a panel driving unit applying a data voltage to a gate electrode of each driving TFT and applying a reference voltage to a source electrode of each driving TFT to emit the OLED; a brightness measuring instrument measuring brightness of a front surface of the display panel while the OLED emits light; a threshold voltage analysis unit generating a luminance map for each color from the measured brightness of the front surface of the display panel and deriving threshold voltage distribution of the driving TFTs for each pixel based on the brightness map for each color; and a reference voltage setting unit changing the reference voltage according to the threshold voltage distribution of the driving TFTs.

Description

TECHNICAL FIELD [0001] The present invention relates to an electroluminescent system and a method of setting the reference voltage,

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

An electroluminescent display device is classified into an inorganic light emitting display device and an organic light emitting display device depending on the material of the light emitting layer. Among them, an active matrix type organic light emitting display device includes an organic light emitting diode (OLED) that emits light by itself, has a high response speed, There is an advantage of a large viewing angle.

The organic light emitting display device arranges the pixels each including the OLED in a matrix form and adjusts the brightness of the pixels according to the gradation of the image data. Each of the pixels includes a driving TFT (Thin Film Transistor) that controls a driving current flowing in the OLED according to a gate-source voltage, and at least one switch TFT for programming a gate-to-source voltage of the driving TFT, The display gradation (luminance) is adjusted by the amount of light emitted by the OLED.

In order to realize a uniform image quality without luminance and color difference between pixels, the driving characteristic of a pixel equal to 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 the pixels, the amount of driving current flowing to the OLED varies, resulting in uneven image quality. To solve this problem, there is known a so-called external compensation technique for sensing the threshold voltage of the driving TFT from each pixel and correcting the digital image data based on the sensing result.

The external compensation technique 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 data voltages to the pixels through the data lines, and is connected to the pixels through the sensing lines to sense the threshold voltage of the driving TFT. Since the sensing circuit includes a plurality of sensing units and a plurality of analog-to-digital converters (ADCs) for individually sensing each of the pixels, its circuit size is large.

As described above, in the case of the OLED display employing the external compensation technique, the chip size of the source driver is large and its cost is increased. Therefore, in compensating the drift characteristic deviation between the pixels, a new method different from the existing external compensation technique is required.

It is an object of the present invention to compensate a threshold voltage deviation of a driving TFT between pixels without a separate sensing circuit and to set a reference voltage applied to a source electrode of the driving TFT in accordance with a threshold voltage distribution of the driving TFT, And to provide a method of setting the reference voltage.

According to an aspect of the present invention, there is provided an electroluminescent display device comprising: a display panel having a plurality of pixels, each pixel having a driving TFT for generating a driving current and an OLED for emitting light according to the driving current; A panel driver for applying a data voltage to the gate electrodes of the driving TFTs and applying a reference voltage to the source electrodes of the driving TFTs to emit the OLEDs; A luminance meter measuring a 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 a driving TFT for the pixels based on the luminance map for each color; And a reference voltage setting unit for changing the reference voltage according to a threshold voltage distribution of the driving TFT.

The reference voltage setting unit sets the result of adding the lowest threshold voltage value and the predetermined voltage margin value in the threshold voltage distribution of the driving TFT to the reference voltage.

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

The electroluminescence system according to the present invention further includes a photographing condition control unit for analyzing a histogram of the front luminance and controlling an exposure time of the luminance meter such that the histogram is within a predetermined confidence interval, Is set to 10% to 90% of the luminance range.

The electroluminescence system according to the present invention analyzes the front luminance and calculates a lower luminance 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 the lower luminance limit value and the upper luminance limit value And a data voltage adjustment unit for determining 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 regulator repeats the recursive function until the value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range to determine the data voltage.

According to another aspect of the present invention, there is provided a method of setting a reference voltage of an electroluminescent system including a plurality of pixels and a display panel having a driving TFT for generating a driving current and an OLED for emitting light in accordance with the driving current, A panel driving step of applying a data voltage to a gate electrode of a driving TFT and applying a reference voltage to a source electrode of each driving TFT to emit the OLED; A luminance measuring step of measuring 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.

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

Further, according to the present invention, the reference voltage applied to the source electrode of the driving TFT is set according to the threshold voltage distribution of the driving TFT, so that the compensation performance can be remarkably improved without worrying about luminance accumulation due to insufficient compensation margin.

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

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, and the like disclosed in the drawings for describing the embodiments of the present invention are illustrative, and thus the present invention is not limited thereto. Like reference numerals refer to like elements throughout the specification. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Where the terms "comprises", "having", "done", and the like are used in this specification, other portions may be added unless "only" is used. Unless the context clearly dictates otherwise, including the plural unless the context clearly dictates otherwise.

In interpreting the constituent elements, it is construed to include the error range even if there is no separate description.

In the case of a description of the positional relationship, for example, if the positional relationship between two parts is described as 'on', 'on top', 'under', and 'next to' Or " direct " is not used, one or more other portions may be located between the two portions.

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

Like reference numerals refer to like elements throughout the specification.

It is to be understood that each of the features of the various embodiments of the present invention may be combined or combined with each other partially or wholly and technically various interlocking and driving are possible and that the embodiments may be practiced independently of each other, It is possible.

Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The component names used in the following description are selected in consideration of easiness of specification, and may be different from the parts names of actual products.

1 is a block diagram illustrating an electroluminescent system according to an embodiment of the present invention. 2 is a view illustrating a pixel array of an OLED display according to an exemplary embodiment of the present invention. 3 is a diagram illustrating a pixel circuit of an OLED display according to an embodiment of the present invention.

An electroluminescent system according to an embodiment of the present invention is based on an electroluminescent display. An electroluminescent display device includes an inorganic light emitting display device and an organic light emitting display device. In an embodiment of the present invention, an organic light emitting display device is mainly described. The technical idea of the present invention can be applied not only to organic light emitting display devices but also to inorganic light emitting display devices.

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

A plurality of data lines 14 and a plurality of gate lines 15 are intersected with each other in the display panel 10 and the pixels PXL are arranged in a matrix form to constitute a pixel array as shown in FIG.

2, the pixel array is provided with a plurality of horizontal pixel lines L1 to L4, horizontally adjacent on each horizontal pixel line L1 to L4, and each gate line 15 (1) to 15 (4 A plurality of pixels PXL connected in common to the pixels PXL are disposed. Here, each of the horizontal pixel lines L1 to L4 is not a physical signal line but a one-line block of pixels implemented by horizontally neighboring pixels PXL. The pixel array includes first power supply lines 17 for supplying a high potential supply voltage EVDD to the pixels PXL, second power supply lines 16 for supplying a reference voltage Vref to the pixels PXL, May be included. Further, the pixels PXL may be connected to the low potential power supply 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 element 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 EIL). When a power source voltage is applied to the anode electrode and the cathode electrode, holes passing through the HTL and electrons passing through the ETL are transferred to the EML to form excitons. As a result, the light emitting layer (EML) Thereby generating visible light.

Referring to Fig. 3, the driving TFT DT is a driving element for adjusting 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 thereof 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 supply line 16. [ A high potential driving voltage (EVDD) is applied to the drain electrode of the driving TFT (DT) through the first power supply 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 in accordance with the gate signal SCAN to apply the data voltage Vdata to the gate electrode of the drive 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.

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 either a red pixel, a green pixel, a blue pixel, and a white pixel for various color implementations. The red pixel, the green pixel, the blue pixel, and the white pixel can constitute one unit pixel. The color implemented in a unit pixel can be determined according to the emission ratio of the red pixel, the green pixel, the blue pixel, and the white pixel.

Referring to FIG. 1, the panel driving units 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 for driving the data lines 14 connected to the pixels PXL and a gate driver 15 for driving the gate lines 15 connected to the pixels PXL 13).

1, the source driver 12 converts input image data (DATA) received from the timing controller 11 into a data voltage (Vdata) for each frame and supplies the data voltage (Vdata) (14). The source driver 12 outputs the data voltage Vdata using a digital to analog converter (DAC) that converts the input image data DATA to a gamma compensation voltage.

The source driver 12 does not need 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 and a plurality of analog-to-digital converters (ADC) for individually sensing each of the pixels, 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 can reduce the number of output channels of the source driver 12 to the number of data lines by distributing the data voltages output through one output channel from the source driver 12 to the plurality of data lines. The multiplexer can be omitted depending on the resolution and usage of the display device.

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 and supplies the gate voltage Vdata to the horizontal pixel Lines L1 to Ln are selected. The gate driver 13 may be formed directly on the substrate of the display panel 10 together with the pixel array in a gate-driver In Panel (GIP) process, but is not limited thereto. The gate driver 13 may be manufactured in an IC type and then 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 from a host (not shown) and timing signals synchronized with the digital data (DATA). 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 TV 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 can multiply the input frame frequency by i times and control the operation timing of the panel driving units 12 and 13 at a frame frequency of the input frame frequency x i (i is a positive integer larger than 0) Hz. The input frame frequency is 60 Hz in the National Television Standards Committee (NTSC) system and 50 Hz in the PAL (Phase-Alternating Line) system.

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 and DE received from the host, And generates a gate timing control signal GDC for controlling the operation timing.

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 transfer 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, a gate output enable signal, and the like. 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 the frame period every frame period and is input to the shift register of each gate driver 13. [ The gate start pulse controls the start timing at which the gate signal SCAN is output every frame period. The gate shift clock is input to the shift register of the gate driver 13 to control the shift timing of the shift register.

In addition, the electroluminescent system according to the embodiment of the present invention does not have a separate sensing circuit and includes a luminance meter 20, a threshold voltage analyzer 20, and a threshold voltage analyzer 20 to compensate the threshold voltage deviation of the driving TFT DT between the pixels PXL. A reference voltage setting unit 24, a compensation value calculation unit 26, a memory 28, a photographing condition control unit 30, and a data voltage adjustment unit 32. The reference voltage setting unit 24,

Referring to FIG. 1, the luminance meter 20 measures the luminance of the entire surface of the display panel 10 while the OLED of the pixels PXL emits light. The luminance meter 20 may be implemented with 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 supplies the driving TFTs for the pixels PXL The threshold voltage distribution of the transistor DT is derived.

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 analyzer 22, May be supplied to the pixels PXL via the second power supply lines 16. [ The reference voltage setting section 24 sets the reference voltage Vref applied to the source electrode of the driving TFT DT in accordance with the threshold voltage distribution of the driving TFT DT to improve the compensation performance.

1, the compensation value calculation section 26 calculates the compensation value of the threshold voltage of the drive TFT DT between the pixels PXL based on the threshold voltage distribution of the drive TFT DT derived from the threshold voltage analysis section 22. [ And calculates a compensation value for compensating for the deviation. The compensation value can be calculated to be larger at a pixel larger than a pixel having a relatively small threshold voltage of the driving TFT DT. The compensation value calculation section 26 may be incorporated in the timing controller 11. [

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

1, the timing controller 11 corrects the input image data (DATA) based on the compensation value stored in the memory 28, thereby correcting the threshold voltage deviation of the driving TFT DT between the pixels PXL The luminance deviation can be compensated. The driving current flows less in a pixel larger than a pixel having a small threshold voltage of the driving TFT DT. Therefore, if 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 the large driving current, the luminance deviation due to the threshold voltage deviation of the driving TFT (DT) Can be reduced.

1, when the reference voltage Vref is set according to the threshold voltage distribution of the drive TFT DT, the image pickup condition control unit 30 and the data voltage adjustment unit 32 are configured such that the data voltage Vdata exceeds the compensation margin To increase the reliability of compensation.

Since the luminous efficiency of each of the pixels PXL may be different from each other, the luminance of the pixel PXL may be measured by changing the camera photographing condition or by determining the applied data voltage Vdata through a recursive function. It is possible to increase the reliability of the luminance information and improve the accuracy of the compensation.

1, the photographing condition control unit 30 analyzes the histogram of the front luminance inputted 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.

1, the data voltage regulator 32 analyzes the front luminance input from the luminance meter 20 and calculates a lower luminance 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 the data voltage (Vdata) can be determined such that a value obtained by subtracting a preset target luminance value from an 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 embedded in the source driver 12. [

FIGS. 4 to 7 are diagrams for explaining a compensating margin shortage when a threshold voltage deviation is compensated by using a camera as a comparative example of the present invention.

4 shows a threshold voltage compensation operation for pixel A and pixel B when applying a data voltage to all the pixels based on the 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).

4, the camera-based compensation method generates compensation values V _{comp, A} , V _{comp, B of the} pixels A and B according to a preset target curve C in order to compensate for the threshold voltage deviation . The target curve C is set between curve A for pixel A and curve B for pixel B. [ In order for the threshold voltage Vth_A of the pixel A to be fitted to the target curve C, the curve A must be shifted to the right. In order for the threshold voltage Vth_B of the pixel B to fit the target curve C, the curve B must 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 larger than 0, (-) compensation value is difficult to implement unlike the (+) compensation value.

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

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

As shown in FIG. 7, the output voltage range of the source driver includes a gradation representation period between the first voltage (VA) and the second voltage (VB) and a gradation representation period between the second voltage (VB) . The gradation representation interval is a voltage interval for expressing an input image, and the compensation margin interval is a voltage interval for compensating 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. 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 accumulation and luminance uniformity lowering. The reason why the compensation margin of the panel A is insufficient is that the reference voltage Vref is set to 0 V in the same manner as the panel B regardless of the threshold voltage distribution of the driving TFT.

8 is a view illustrating a reference voltage setting method of an electroluminescent system according to an embodiment of the present invention. FIGS. 9 and 10 are views for explaining the operation of the photographing condition control unit of FIG. 11 and 12 are views for explaining the operation of the data voltage control unit of FIG. 13 is a diagram for explaining the operation of the threshold voltage analyzing unit of FIG.

Referring to FIGS. 1 and 8, a reference voltage setting method of an electroluminescence system according to the present invention includes setting a reference voltage Vref as a default value to pixels PXL using panel driving units 12 and 13, And applies an arbitrary data voltage Vdata to the pixels PXL (S1, S2). Accordingly, the OLED of the pixels PXL is caused to emit by the driving current corresponding to the gate-source voltage Vgs of the driving TFT DT, that is, "Vdata-Vref".

Referring to FIGS. 1 and 8, a reference voltage setting method of an electroluminescence system according to the present invention measures the brightness of the entire surface of a display panel while the OLED emits light using a luminance meter 20 (S3).

Referring to FIGS. 1 and 8, a reference voltage setting method of an electroluminescence system according to the present invention is a method of setting a reference voltage, which is input from a luminance meter 20 using a photographing condition controller 30 and a data voltage adjuster 32, The camera photographing condition is changed so as 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 luminance measurement value to accurately determine the threshold voltage distribution. This will be described in detail as follows.

Referring to FIG. 9, a reference voltage setting method of an electroluminescence system according to the present invention includes analyzing a histogram of a front luminance inputted from a luminance meter 20 using a photographing condition controller 30, And controls the exposure time of the luminance meter 20 so as to fall within the confidence interval. Here, the confidence interval may be set to 10% (LSL) to 90% (USL) of the entire brightness range as shown in FIG. The lower luminance limit value " LSL " corresponds to the lower 3σ of the entire pixel luminance data, and the upper luminance limit value "USL " corresponds to the upper 3σ of the entire pixel luminance data. By controlling the exposure time of the luminance meter 20, the reliability of the front luminance measurement value input from the luminance meter 20 can be increased.

Referring to FIG. 11, a reference voltage setting method of an electroluminescence system according to the present invention includes analyzing a front luminance input from the luminance meter 20 using a data voltage adjustment unit 32, The luminance upper limit value LSL and the luminance upper limit value USL corresponding to 90% of the total 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 The data voltage Vdata can 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 recursive function until the value obtained by subtracting the target luminance value from the average luminance value belongs to the predetermined range (? K) as shown in FIG. 12, Can be determined. When the data voltage Vdata is determined using the recursive function, the reliability of the front luminance measurement value input from the luminance meter 20 can be increased. On the other hand, since the OLED luminous efficiencies of the red pixels, the green pixels, the blue pixels, and the white pixels are different from each other, the data voltage Vdata can be determined differently for each color.

Referring to FIGS. 1 and 8, a reference voltage setting method of an electroluminescence system according to the present invention generates a luminance map for each color from a front luminance measured by a luminance meter 20 using a 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).

The reference voltage setting method of the electroluminescence system according to the present invention is a method of setting the threshold voltage distribution in accordance with the brightness of the red, green, blue, and blue colors based on the front luminance measured by the luminance meter 20, A brightness map is generated for each white color (S61).

The reference voltage setting method of the electroluminescence system according to the present invention converts the brightness map for each color into a voltage domain and calculates an average value (Vdata_in) of the applied data voltage (Vdata) for each color (S62, S63).

The reference voltage setting method of the electroluminescence system according to the present invention calculates a voltage upper limit value Vdata_out (Vdata_out) of the entire pixel voltage distribution (corresponding to the upper limit luminance value "USL "

The reference voltage setting method of the electroluminescence system according to the present invention is a method of setting the reference voltage 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 voltage (Vdata) The threshold voltage value Vth_LSL is calculated (S65).

1 and 8, the reference voltage setting method of the electroluminescence system according to the present invention changes and sets the reference voltage Vref according to the threshold voltage distribution of the driving TFT by using the reference voltage setting unit 24 S7). A reference voltage setting method of an electroluminescence system according to the present invention is a method of setting a reference voltage (Vref) to a result obtained by adding a lowest threshold voltage value (Vth_LSL) and a predetermined voltage margin value (NBTis Margin Value) Setting.

FIGS. 14 to 16 are diagrams for explaining the effect obtained by setting the reference voltage according to the threshold voltage distribution. FIG.

The reference voltage setting method of the electroluminescence system according to the present invention is a method of setting the reference voltage Vref based on the lowest threshold voltage Vth_A among the threshold voltage distributions of the pixels having the best threshold voltage characteristics, (Positive Bias Driving) can be performed in the whole gradation display period, and a pixel in which the threshold voltage is shifted in the negative (-) direction can be compensated. For example, in the present invention, the reference voltage Vref is set on the basis of 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. Then, the present invention generates the compensation values (V _{comp, B} , V _{comp, C} ) of the pixels B and C in accordance with the target curve A. In order for the threshold voltage Vth_A of the pixel B to be fitted to the target curve A, the curve B must be shifted to the left. Then, in order for the threshold voltage Vth_C of the pixel C to be fitted to the target curve A, the curve C must 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 positive value and the compensation value V _{comp, C} of the pixel C for shifting the curve C to the left is also + ) Value. Since the output voltage range of the source driver is greater than zero, the (+) compensation values can be fully implemented.

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 TFTs for the panel A and the panel B is set as a reference Setting the reference voltages Vref_A and Vref_B to the threshold voltages of the panels A and B satisfies all the voltage margins allocated to the threshold voltage compensation. In other words, according to the present invention, by setting the reference voltage for each panel in consideration of the threshold voltage characteristic of each panel, it is possible to solve the luminance aggregation problem due to insufficient compensation margin and to increase the luminance uniformity.

As described above, since the present invention can compensate for the threshold voltage deviation of the driving TFTs between the pixels based on the camera without using the sensing circuit, it is possible to reduce the threshold voltage deviation The luminance deviation can be effectively compensated.

Further, according to the present invention, the reference voltage applied to the source electrode of the driving TFT is set according to the threshold voltage distribution of the driving TFT, so that the compensation performance can be remarkably improved without worrying about luminance accumulation due to insufficient compensation margin.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, 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 drive unit 20: luminance meter
22: threshold voltage analysis unit 24: reference voltage setting unit
26: compensation value calculation unit 28: memory
30: photographing condition control section 32: data voltage adjusting section

Claims (12)

A display panel having a plurality of pixels, each pixel having a driving TFT for generating a driving current and an OLED emitting light in accordance with the driving current;
A panel driver for applying a data voltage to the gate electrodes of the driving TFTs and applying a reference voltage to the source electrodes of the driving TFTs to emit the OLEDs;
A luminance meter measuring a 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 a driving TFT for the pixels based on the luminance map for each color; And
And a reference voltage setting unit for changing the reference voltage according to a threshold voltage distribution of the driving TFT. The method according to claim 1,
Wherein the reference voltage setting unit includes:
And sets a result of adding the lowest threshold voltage value and a predetermined voltage margin value among the threshold voltage distributions of the driving TFTs to the reference voltage. The method according to claim 1,
A compensation value calculation unit for calculating a compensation value for compensating 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
And a timing controller for correcting the input image data based on the compensation value. The method according to claim 1,
Further comprising a photographing condition control unit for analyzing a histogram of the front luminance and controlling an exposure time of the luminance meter such that the histogram falls within a predetermined confidence interval,
Wherein the confidence interval is set to 10% to 90% of the entire luminance range. The method according to claim 1,
Calculating a lower limit value of luminance corresponding to 10% of the entire luminance range and an upper luminance limit value corresponding to 90% of the entire luminance range by analyzing the front luminance, And a data voltage regulator for determining the data voltage so that a value obtained by subtracting the value falls within a predetermined range. 6. The method of claim 5,
Wherein the data voltage adjusting unit determines the data voltage by repeating a recursive function until a value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range. A reference voltage setting method of an electroluminescence system including a plurality of pixels and a display panel having a driving TFT for generating a driving current and an OLED for emitting light in accordance with the driving current,
A panel driving step of applying a data voltage to gate electrodes of the driving TFTs and applying a reference voltage to source electrodes of the driving TFTs to emit the OLEDs;
A luminance measuring step of measuring 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
And a reference voltage setting step of changing the reference voltage according to a threshold voltage distribution of the driving TFT. 8. The method of claim 7,
The reference voltage setting step may include:
And sets a result of adding the lowest threshold voltage value and a predetermined voltage margin value among the threshold voltage distributions of the driving TFTs to the reference voltage. 8. The method of claim 7,
A compensation value calculation step of calculating a compensation value for compensating 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
And correcting the input image data based on the compensation value. 8. The method of claim 7,
Further comprising a photographing condition control step of analyzing a histogram of the front luminance and controlling an exposure time of the luminance meter such that the histogram falls within a predetermined confidence interval,
Wherein the confidence interval is set to 10% to 90% of the entire brightness range. 8. The method of claim 7,
Calculating a lower limit value of luminance corresponding to 10% of the entire luminance range and an upper luminance limit value corresponding to 90% of the entire luminance range by analyzing the front luminance, And a data voltage adjustment step of determining the data voltage so that a value obtained by subtracting the value falls within a predetermined range. 12. The method of claim 11,
Wherein the data voltage adjusting step determines the data voltage by repeating a recursive function until a value obtained by subtracting the target luminance value from the average luminance value falls within the predetermined range.

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