Patent Publication Number: US-11398182-B2

Title: Display device and method of driving the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0128206 filed in the Korean Intellectual Property Office on Oct. 5, 2020; the Korean Patent Application is incorporated by reference. 
     BACKGROUND 
     (a) Field 
     The technical field relates to a display device and a method of driving the display device. 
     (b) Description of the Related Art 
     A display device typically includes pixels. Image frames to be displayed by the pixels may have different load values. For example, an image frame corresponding to a bright image may have a large load value, and an image frame corresponding to a dark image may have a small load value. 
     According to different load values, the amounts of current required by the pixels may be different. For displaying correct brightness, it is necessary to supply an appropriate amount of current to the pixels corresponding to the load value of the image frame. However, the luminous efficiencies of pixels may be different for different display areas due to process variations of the pixels, and the luminous efficiencies of the pixels may change according to a change in the ambient temperature. 
     If an incorrect amount of current is provided to the pixels, the quality of images displayed by the display device may be unsatisfactory. 
     SUMMARY 
     An object of the present invention is to provide a display device capable of supplying an appropriate current to pixels in response to a process variation of pixels and a change in ambient temperature. 
     An embodiment may be related to a display device. The display device may include a pixel set, a timing controller, a data driver, and a scale factor provider. The pixel set that may include pixels. The pixels may be divided into pixel groups. The timing controller may be electrically connected to the pixel set, may calculate first load values corresponding to an image frame of input image data, and may generate image data by scaling gradation values of the input image data using scale factors. The data driver that may be electrically connected to at least one of the pixel set and the timing controller, may generate data signals corresponding to the image data, and may supply the data signals to the pixel set. The scale factor provider may calculate the first load values and one or more second load values based on temperature data corresponding to a temperature of the pixel set and may generate the scale factors based on the one or more second load values and a common current value flowing through the pixels. 
     The scale factor provider may include a unit target current value generator that generates a unit target current value based on the common current value corresponding to a reference pixel group among the pixel groups. 
     The scale factor provider may include a scale factor generator that generates a target current value based on the unit target current value and the one or more second load values, and generates the scale factors based on the target current value and the common current value. 
     The timing controller may calculate a first load value corresponding to each of the pixel groups. 
     The scale factor provider may include a temperature calculator that calculates predicted temperature data sets for the pixel groups based on the temperature data and the first load values. 
     The scale factor provider may include a load weight calculator that calculates load weights based on the predicted temperature data sets, first weight data sets, and second weight data sets. 
     Each of the first weight data sets may correspond to light emission efficiency values of a corresponding one of the pixel groups. Each of the second weight data sets may correspond to light emission efficiency of the pixels in an associated one of the pixel groups according to the temperature of the pixel set. 
     The load weight calculator may calculate a load weight by multiplying a value from a corresponding second weight data set and a value from a corresponding first weight data set. The value from the corresponding second weight data set may be according to the temperature of the pixel set based on a corresponding predicted temperature data set. 
     The pixel groups may include a first pixel group and a second pixel group. Light emission efficiency for the first pixel group may be higher than light emission efficiency for the second pixel group. A value of the first weight data set for the first pixel group may be smaller than a value of the first weight data set for the second pixel group. 
     A first temperature of the pixel set may be lower than a second temperature of the pixel set. A value of the second weight data set for the first temperature of the pixel set may be larger than a value of the second weight data set for the second temperature of the pixel set. 
     The pixels may include a first pixel including a first light emitting diode, a second pixel including a second light emitting diode, and a third pixel including a third light emitting diode. The load weight calculator may calculate a second weight data set for the first light emitting diode, a second weight data set for the second light emitting diode, and a second weight data set for the third light emitting diode. The second weight data set for the first light emitting diode, the second weight data set for the second light emitting diode, and the second weight data set for the third light emitting diode may be unequal according to the temperature of the pixel set. 
     The load weight calculator may calculate the load weights respectively corresponding to the pixel groups. 
     The scale factor provider may include a load determiner that calculates the one or more second load values based on the first load values and the load weights respectively corresponding to the pixel groups. 
     The load determiner may calculate the one or more second load values by multiplying a corresponding first load value and a corresponding load weight for each of the pixel groups to produce multiplied values and by adding the multiplied values. 
     The pixels include a current sensor that is connected to a first power source line and generates the common current value by sensing a current transmitted through the first power source line. 
     The display device may include a temperature sensor that generates the temperature data by sensing the temperature of the pixel set. 
     An embodiment may be related to a method of operating a display device. The display device may include a pixel set that includes pixels. The pixels may be divided into pixel groups. The method may include the following steps: calculating one or more first load values corresponding to an image frame of input image data; calculating one or more second load values based on the one or more first load values and temperature data corresponding to a temperature of the pixel set; generating one or more scale factors based on the one or more second load values and a common current value flowing through the pixels; generating image data by scaling gradation values of the input image data using the one or more scale factors; generating data signals corresponding to the image data; and supplying the data signals to the pixels for the pixels to emit light according to the data signals. 
     The generating of the scale factor may include the following steps: generating a unit target current value based on the common current value corresponding to a reference pixel group among the pixel groups; generating a target current value based on the unit target current value and the one or more second load values; and generating the one or more scale factors based on the target current value and the common current value. 
     The calculating of the one or more second load values may include the following steps: calculating predicted temperature data sets for the pixel groups based on the temperature data and the one or more first load values; calculating load weights based on the predicted temperature data sets, first weight data sets, and second weight data sets; and calculating the one or more second load values based on the one or more first load value and the load weights. 
     Each of the first weight data sets may correspond to light emission efficiency values of a corresponding one of the pixel groups. Each of the second weight data sets may correspond to light emission efficiency of the pixels in an associated one of the pixel groups according to the temperature of the pixel set. 
     According to embodiments, a display device may perform a global current control operation in consideration of light emission efficiency of pixels for pixel groups and the light emission efficiency of the pixels according to ambient temperature. Accordingly, an appropriate current may be supplied to the pixels. Advantageously, satisfactory image display quality may be attained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a display device according to embodiments. 
         FIG. 2  is a circuit diagram illustrating a pixel included in the display device of  FIG. 1  according to embodiments. 
         FIG. 3  is a block diagram for explaining a scale factor provider according to embodiments. 
         FIG. 4  is a diagram illustrating a display panel included in the display device of  FIG. 1  according to embodiments. 
         FIG. 5  is a diagram illustrating a reference block set on the display panel of  FIG. 4  according to embodiments. 
         FIG. 6  is a graph for explaining the light emission efficiency of a pixel according to the (ambient) temperature according to embodiments. 
     
    
    
     Each of  FIG. 7A ,  FIG. 7B , and  FIG. 7C  is a graph for explaining a load weight applied for a pixel according to the (ambient) temperature according to embodiments. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Example embodiments are described with reference to the drawings. Various modifications may be made in the described embodiments. 
     In the drawings, similar reference numerals may be used for similar elements, and dimensions may be enlarged for clarity. 
     Terms such as first and second may be used to describe different elements, but the elements should not be limited by the terms. These terms are used for distinguishing one element from another element. For example, a first component may be referred to as a second component, and/or a second component may be referred to as a first component. The description of an element as a “first” element may not require or imply the presence of a second element or other elements. The terms “first,” “second,” etc. may be used to differentiate different categories or sets of elements. For conciseness, the terms “first,” “second,” etc. may represent “first-category (or first-set),” “second-category (or second-set),” etc., respectively. 
     Singular expressions may mean plural expressions unless the context clearly indicates otherwise. 
     The term “connected” may mean “electrically connected” or “electrically connected through no intervening transistor.” The term “insulate” may mean “electrically insulate” or “electrically isolate.” The term “conductive” may mean “electrically conductive.” The term “drive” may mean “operate” or “control.” The expression “an image frame” may mean data for the image frame.” 
       FIG. 1  is a block diagram illustrating a display device according to embodiments. 
     Referring to  FIG. 1 , a display device  1000  may include a display panel  100 , a timing controller  200 , a scan driver  300 , a data driver  400 , a current sensor  500 , a temperature sensor  600 , and a scale factor provider  700 . 
     The display panel  100  (pixel set) may include pixels PX. Each of the pixels PX may be connected to a corresponding data line and a corresponding scan line. A pixel PXij (where i and j are natural numbers) may mean a pixel in which a scan transistor is connected to the i th  scan line SLi and the j th  data line DLj, a pixel PXi(j+1) may mean a pixel in which a scan transistor is connected to the i th  scan line SLi and the j+1 th  data line DL(j+1), and a pixel PX(i+1)j may mean a pixel in which a scan transistor is connected to the i+1 th  scan line SL(i+1) and the j th  data line DLj. 
     The pixels PX may be connected to a first power source line VDDL and a second power source line VSSL. The pixels PX may receive a voltage of the first power source through the first power source line VDDL, and a voltage of the second power source through the second power source line VSSL. The voltage of the first power source and the voltage of the second power source may drive the pixels PX, and the voltage level of the first power source may be higher than the voltage level of the second power source. For example, the voltage of the first power source may be a positive voltage, and the voltage of the second power source may be a negative voltage. 
     The pixels PX may be commonly connected to the first power source line VDDL. The pixels PX may be commonly connected to the second power source line VSSL. The pixels PX may be connected to different second power source lines. The pixels PX may be connected to different first power source lines. 
     The display panel  100  is divided into pixel groups, including pixel groups BLKa and BLKb. Each of the pixel groups BLKa and BLKb may include at least one pixel. For example, the first pixel group BLKa may include the pixels PXij and PX(i+1)j, and the second pixel group BLKb may include a pixel PXi(j+1). 
     The timing controller  200  may receive input image data IDATA and a control signal CS from an external source. The control signal CS may include a synchronization signal, a clock signal, and the like. The input image data IDATA may include (data for) at least one image frame. 
     The timing controller  200  may generate a first control signal SCS (scan control signal) and a second control signal DCS (data control signal) based on the control signal CS. The timing controller  200  may supply the first control signal SCS to the scan driver  300  and may supply the second control signal DCS to the data driver  400 . 
     The first control signal SCS may include a scan start signal, a clock signal, and the like. The scan start signal may control the timing of the scan signal. The clock signal included in the first control signal SCS may be used to shift the scan start signal. 
     The second control signal DCS may include a source start signal, a clock signal, and the like. The source start signal may control a sampling start point of data. The clock signal included in the second control signal DCS may control a sampling operation. 
     The timing controller  200  may calculate a frame load value FL 1  (first load value) corresponding to each image frame of the input image data IDATA. The frame load value FL 1  may correspond to gradation values of the image frame. For example, as the sum of the gradation values of the image frame increases, the frame load value FL 1  of a corresponding image frame may increase. 
     For example, the frame load value FL 1  may be 100 in a full-white image frame, and the frame load value FL 1  may be 0 in a full-black image frame. The full-white image frame may mean an emission image frame with maximum luminance in which all pixels PX of the display panel  100  are set to maximum gradations (white gradations) to emit light. The full-black image frame may mean a non-emission image frame in which all pixels PX of the display panel  100  are set to the lowest gradations (black gradations). The frame load value FL 1  may be in a range of 0 to 100. 
     The timing controller  200  may calculate the frame load value FL 1  for each of the pixel groups of the display panel  100 . The frame load value FL 1  may include frame load values corresponding to each of the pixel groups BLKa and BLKb. 
     The timing controller  200  may provide the calculated frame load value FL 1  to the scale factor provider  700 , and may scale the gradation values of the input image data IDATA using a scale factor SF received from the scale factor provider  700 . The scale factor SF may be applied commonly to all pixels PX of the display panel  100 . The gradation values of the input image data IDATA may be scaled at the same rate based on the scale factor SF. 
     The timing controller  200  may generate the image data DATA by rearranging the input image data IDATA obtained by scaling the gradation values, and may provide the generated image data to the data driver  400 . 
     The scan driver  300  may receive the first control signal SCS from the timing controller  200 , and may provide the scan signals to the scan lines SL 1 , SL 2 , SL 3  to SLn (where n is natural number) based on the first control signal SCS. For example, the scan driver  300  may sequentially provide the scan signals to the scan lines SL 1  to SLn. If the scan signals are sequentially provided, the pixels PX are selected in units of horizontal lines (or in units of pixel rows), and the data signal may be supplied to the selected pixels PX. A scan signal may be set to a gate-on voltage (low voltage or high voltage) such that a transistor included in each of the pixels PX and receiving the scan signal is turned on. 
     The data driver  400  may receive the image data DATA and the second control signal DCS from the timing controller  200 , and may supply the data signals (data voltages) corresponding to the image data DATA to the data lines DL 1 , DL 2 , DL 3  to DLm (where m is natural number) in response to the second control signal DCS. The data signals supplied to the data lines DL 1  to DLm may be supplied to the pixels PX selected by the scan lines. The data driver  400  may supply the data signals to the data lines DL 1  to DLm in synchronization with the scan signal. 
     Since the image data DATA is generated based on the input image data IDATA obtained by scaling the gradation values with the scale factor SF, the data driver  400  may supply the data signals corresponding to the scaled gradation values to the data lines DL 1  to DLm. For example, the data driver  400  may apply a data signal corresponding to the scaled gradation value of the pixel PXij to the j th  data line DLj, and may apply a data signal corresponding to the scaled gradation value of the pixel PXi(j+1) to the j+1 th  data line DL(j+1). 
     The current sensor  500  may be connected to the first power source line VDDL connected commonly to the pixels PX. The current sensor  500  may supply a global current value GC (common current value) to the scale factor provider  700  by sensing a current through the first power source line VDDL. The global current value GC may correspond to a current supplied commonly to all pixels PX through the first power source line VDDL. The current sensor  500  may sense a current through the second power source line VSSL via a connection to the second power source line VSSL connected commonly to the pixels PX. 
     The display device  1000  emits light of a pixel group that is set as a reference pixel group among the pixel groups. The current sensor  500  may sense a current through the first power source line VDDL, generate the global current value GC, and supply the generated global current value GC to the scale factor provider  700 . The scale factor provider  700  may store a unit target current value corresponding to the global current value GC on a memory. 
     A storage operation of the unit target current value may be performed once when the display device  1000  is turned on. The timing and the number of times of storing the unit target current value may be set according to embodiments. 
     The scale factor provider  700  may generate a target current value based on the unit target current value and the frame load value FL 1 , and may generate the scale factor SF by comparing the global current value GC provided from the current sensor  500  and the target current value. For example, the scale factor provider  700  may determine a ratio between the target current value and the global current value GC as the scale factor SF. For example, the scale factor provider  700  may determine the scale factor SF such that if the global current value GC is greater than the target current value, the gradation values of the pixels PX are scaled smaller. As another example, the scale factor providing unit  700  may determine the scale factor SF such that if the global current value GC is smaller than the target current value, the gradation values of the pixels PX are scaled larger. The above-described driving process may be referred to as global current management GCM. 
     The light emission efficiency levels of the pixels PX may be different due to process variations of the pixels PX. For example, the light emission efficiency levels of light emitting diodes (for example, light emitting diode emitting red light, light emitting diode emitting green light, light emitting diode emitting blue light, and the like) included in the pixels PX may be different. The light emission efficiency levels of the pixels PX may be different according to ambient temperature of the display device  1000 . For example, the light emitting diodes included in the pixels PX may have different light emission efficiency levels according to the ambient temperature. The light emission efficiency level of a pixel PX may mean the light emission luminance of the pixel PX in relation to a current supplied to the pixel PX. When the display device  1000  (scale factor provider  700 ) performs a global current control operation regardless of the different light emission efficiency levels of the pixels PX, the current supplied to the pixels PX may not be optimal, such that the pixels PX may emit light with a luminance different from the target luminance. 
     In order to compensate for variations in the light emission efficiency levels of the pixels PX, the display device  1000  (and/or scale factor provider  700 ) may determine the scale factor SF in consideration of the variations of the light emission efficiency levels of the pixels PX. 
     The temperature sensor  600  may generate temperature data TD by sensing the ambient temperature of the display device  1000  (and/or display panel  100 ). The temperature sensor  600  may provide the temperature data TD to the scale factor provider  700 . 
     The scale factor provider  700  may calculate a correction load value (second load value) using the temperature data TD from the temperature sensor  600  and may apply a weight to the frame load value FL 1  based on the light emission efficiency level for each of the pixel groups stored on the memory and the light emission efficiency levels of the pixels PX according to temperature. 
     The scale factor provider  700  may generate the target current value based on the correction load value and the unit target current value. For example, the scale factor provider  700  may generate the target current value by multiplying the correction load value and the unit target current value. The scale factor provider  700  may generate the scale factor SF based on the global current value GC and the target current value provided from the current sensor  500 . 
     The display device  1000  (and/or scale factor provider  700 ) may perform the global current control operation in consideration of the light emission efficiency level of each pixel group and the light emission efficiency levels of the pixels PX according to the ambient temperature. Advantageously, an appropriate current may be supplied to the pixels PX in consideration of the process variations of the pixels PX and a change in ambient temperature. 
     The scale factor provider  700  may be implemented in a separate integrated chip (IC) different from the timing controller  200 . All or part of the scale factor provider  700  may be integrated with the timing controller  200  in the same IC. All or part of the scale factor provider  700  may be implemented in software in the timing controller  200 . 
       FIG. 2  is a circuit diagram illustrating a pixel included in the display device of  FIG. 1  according to embodiments. 
     Referring to  FIG. 2 , the pixel PXij includes transistors T 1  and T 2 , a storage capacitor Cst, and a light emitting diode LD. 
     The circuit may include N-type transistors. The circuit may include P-type transistors. The circuit may include at least one P-type transistor and at least one N-type transistor. For a P-type transistor, the amount of current conducted may increase when a voltage difference between the gate electrode and a source electrode increases in a negative direction. For an N-type transistor, the amount of current conducted may increase when the voltage difference between the gate electrode and the source electrode increases in the positive direction. A transistor may be a thin film transistor (TFT), a field effect transistor (FET), or a bipolar junction transistor (BJT). 
     A first transistor T 1  may be connected between the first power source line VDDL and the light emitting diode LD, and the gate electrode may be connected to a first node N 1 . The first transistor T 1  may control an amount of current flowing from the first power source line VDDL to the second power source line VSSL via the light emitting diode LD in response to the voltage of the first node N 1 . The first transistor T 1  may be referred to as a driving transistor. 
     The second transistor T 2  may be connected between the data line DLj and the first node N 1 , and the gate electrode may be connected to the scan line SLi. When the scan signal is supplied to the scan line SLi, the second transistor T 2  is turned on such that the data line DLj and the first node N 1  may be electrically connected to each other. Accordingly, the data signal may be transmitted to the first node N 1 . The second transistor T 2  may be referred to as a scan transistor. 
     The storage capacitor Cst may be connected between the first node N 1  corresponding to a gate electrode of the first transistor T 1  and a second electrode of the first transistor T 1 . The storage capacitor Cst may store a voltage corresponding to the voltage difference between the gate electrode and the second electrode of the first transistor T 1 . 
     A first electrode (anode electrode or cathode electrode) of the light emitting diode LD may be connected to the second electrode of the first transistor T 1 , and a second electrode (cathode electrode or anode electrode) of the light emitting diode LD may be connected to the second power source line VSSL. The light emitting diode LD may generate light with a predetermined luminance in response to the amount of current (driving current) supplied from the first transistor T 1 . 
     The light emitting diode LD may be an organic light emitting diode. The light emitting diode LD may be an inorganic light emitting diode such as a micro light emitting diode or a quantum dot light emitting diode. The light emitting diode LD may include organic and inorganic materials. In  FIG. 2 , it the pixel PXij includes a single light emitting diode LD. The pixel PXij may include a plurality of light emitting diodes, and the light emitting diodes may be connected in series, parallel, or series-parallel. 
     The voltage of the first power source may be supplied to the first power source line VDDL, and the voltage of the second power source may be applied to the second power source line VSSL. The voltage of the first power source may be greater than the voltage of the second power source. 
     If the scan signal of a turn-on level (e.g., logical high level) is applied through the scan line SLi, the second transistor T 2  is turned on. At this time, a voltage corresponding to the data signal applied to the data line DLj may be stored in the first node N 1  (first electrode of storage capacitor Cst). 
     A driving current corresponding to a voltage difference between the first electrode and a second electrode of the storage capacitor Cst may flow between the first electrode and the second electrode of the first transistor T 1 . Accordingly, the light emitting diode LD may emit light with a luminance level corresponding to the data signal. 
     The global current value GC provided by the current sensor  500  of  FIG. 1  may be a value obtained by summing driving current values flowing through all pixels PX of the display panel  100 . Since the magnitude of the data signals is adjusted by scaling the gradation values corresponding to the scale factor SF generated by the scale factor provider  700  of  FIG. 1 , the driving current values of the pixels PX may be adjusted. 
     The structures of pixel PXij of  FIG. 2  may be applied to other pixels of the display panel  100 . The pixel PXij may further include a transistor which electrically connects the second electrode of the first transistor T 1  and a first electrode of the light emitting diode LD and/or a first electrode of the first transistor T 1  and the first power source line VDDL when being turned on by an emission control signal. The pixel PXij may further include a sensing transistor that senses the voltage or current applied to the second electrode of the first transistor T 1  or the first electrode of the light emitting diode LD and transmits the sensed current to the sensing line when being turned on by a sensing signal supplied through a separate sensing line. 
       FIG. 3  is a block diagram for explaining the scale factor provider according to embodiments.  FIG. 4  is a diagram illustrating the display panel included in the display device of  FIG. 1  according to embodiments.  FIG. 5  is a diagram for explaining the reference pixel group in the display panel of  FIG. 4  according to embodiments.  FIG. 6  is a graph for explaining light emission efficiency levels of a pixel according to temperature values according to embodiments. Each of  FIG. 7A ,  FIG. 7B , and  FIG. 7C  is a graph for explaining load weight values applied for a pixel according to temperature values. 
     The display device  1000  (and/or scale factor provider  700 ) may set at least one among the pixel groups as the reference pixel group in order to perform a unit target current value (UTC) storage operation. 
     Referring to  FIG. 4 , the pixels PX of the display panel  100  may be divided into a plurality of pixel groups BLK 11 , BLK 12 , BLK 13 , BLK 14 , BLK 15 , BLK 21 , BLK 22 , BLK 23 , BLK 24 , BLK 25 , BLK 31 , BLK 32 , BLK 33 , BLK 34 , and BLK 35 . Each of the pixel groups BLK 11  to BLK 35  may include at least one pixel. The total number of pixel groups BLK 11  to BLK 35  may be equal to or smaller than the total number of pixels of the display panel  100 . 
     By dividing the display panel  100  into pixel groups BLK 11  to BLK 35  having the same size, the pixel groups BLK 11  to BLK 35  may include the same number of pixels. In embodiments, all or some of the pixel groups BLK 11  to BLK 35  may share one or more pixels, and/or some of the pixel groups BLK 11  to BLK 35  may include more pixels than other pixel groups. 
       FIG. 4  illustrates that the display panel  100  is divided into 15 pixel groups BLK 11  to BLK 35 . The display panel  100  may be divided into fewer or more pixel groups, such as 100 pixel groups. 
     Referring back to  FIG. 3 ,  FIG. 4 , and  FIG. 5 , when the display device  1000  is turned on, the display device  1000  may emit light from the reference pixel group RBLK among the pixel groups BLK 11  to BLK 35 . The reference pixel group RBLK may correspond to the pixel group BLK 23  located at the center of the display panel  100 . The reference pixel group RBLK may be set at other positions. For example, the reference pixel group may be a pixel group located outside the display panel  100 . As another example, two or more of the pixel groups BLK 11  to BLK 35  may be set as the reference pixel group. 
     The pixels included in the reference pixel group RBLK may emit light at the highest gradation level (for example, the white gradation level), and the remaining pixel groups may not emit light (for example, remaining at the black gradation level). 
     At this time, the current sensor  500  may generate the global current value GC by sensing a current flowing through the first power source line VDDL, and may provide the global current value GC to a unit target current value generator  760  of the scale factor provider  700 . 
     The unit target current value generator  760  may generate a unit target current value UTC corresponding to the global current value GC. For example, the unit target current value generator  760  may store the global current value GC as the unit target current value UTC on a second memory  770 . As illustrated in  FIG. 4  and  FIG. 5 , one of the 15 pixel groups BLK 11  to BLK 35  (for example, the pixel group BLK 23 ) is set as the reference pixel group RBLK. When the display device  1000  is turned on, the pixels included in the reference pixel group RBLK may emit light with the highest gradation, and the remaining pixel groups do not emit light. Therefore, the global current value GC may be equal to the unit target current value UTC multiplied or divided by approximately 6.67%, or 1/15, based on the full-white image frame. When the display panel  100  is divided into 100 pixel groups, one of the 100 pixel groups which is set as the reference pixel group may emit light with the highest gradation, and the remaining pixel groups do not emit light. Therefore, the global current value GC may be equal to the unit target current value UTC multiplied or divided by 1%, or 1/100 based on the full-white image frame. 
     In an embodiment, the unit target current value UTC may be generated when the display device  1000  is turned on, may be stored on/in a second memory  770  of the scale factor provider  700 , and may be used during a display period of image frames of the display device  1000  afterwards. 
     The scale factor provider  700  may generate the scale factor SF in consideration of variations of the light emission efficiency levels of the pixels PX for pixel groups and variations of the light emission efficiency levels of the pixels PX according to the ambient temperature. 
     The scale factor provider  700  may include a temperature calculator  710 , a load weight calculator  720 , a first memory  730 , a load determiner  740 , a scale factor generator  750 , the unit target current value generator  760 , and the second memory  770 . The unit target current value generator  760  may generate the unit target current value UTC corresponding to the global current value GC, and the second memory  770  may store the unit target current value UTC. 
     The temperature calculator  710  may receive the temperature data TD from the temperature sensor  600 , and may receive the frame load value FL 1  from the timing controller  200 . The timing controller  200  may calculate a frame load value FL 1  for each of the pixel groups BLK 11  to BLK 35 . 
     The temperature calculator  710  may calculate predicted temperature data BTD for each of the pixel groups BLK 11  to BLK 35  based on the temperature data TD and the frame load value FL 1  calculated for the corresponding pixel group of the pixel groups BLK 11  to BLK 35 . Temperatures of the pixel groups BLK 11  to BLK 35  of the display panel  100  may be different according to the frame load values FL 1 . For example, the temperature of a pixel group having a high frame load value FL 1  may be higher than the temperature of a pixel group having a low frame load value FL 1 . 
     The temperature calculator  710  may include a lookup table in which values of the predicted temperature data BTD corresponding to predetermined frame load values FL 1  are stored. Accordingly, the temperature calculator  710  may calculate the predicted temperature data BTD corresponding to the frame load value FL 1  for each of the pixel groups BLK 11  to BLK 35  using the lookup table. 
     The load weight calculator  720  may calculate a load weight LW using the predicted temperature data BTD from the temperature calculator  710  and using first weight data BLW and second weight data TLW from the first memory  730 . 
     The first weight data BLW may correspond to the light emission efficiency of each of the pixel groups BLK 11  to BLK 35 . The light emission efficiency levels for the pixel groups BLK 11  to BLK 35  may be different due to process variations. The light emission efficiency levels of the light emitting diodes (for example, light emitting diode emitting red light, light emitting diode emitting green light, light emitting diode emitting blue light, and the like) included in the pixels PX may be different for the pixel groups BLK 11  to BLK 35 . The first weight data BLW may include the weight data BLW 1  according to the light emission efficiency for the red gradation, the weight data BLW 2  according to the light emission efficiency for the green gradation, and the weight data BLW 3  according to the light emission efficiency for the blue gradation corresponding to the pixel groups BLK 11  to BLK 35 . As the light emission efficiency for the same supply current is high, the pixels PX may emit light with high luminance. Accordingly, for each of the pixel groups BLK 11  to BLK 35 , as the light emission efficiency of each of the red gradation, the green gradation, and the blue gradation is high, the weight data BLW 1 , the weight data BLW 2 , and the weight data BLW 3  may be small. The first weight data BLW corresponding to the pixel group having the minimum light emission efficiency for each of the red gradation, the green gradation, and the blue gradation may have a value of 1. The first weight data BLW corresponding to the remaining pixel groups may have a value corresponding to the respective light emission efficiency levels with reference to the light emission efficiency of the pixel group having the minimum light emission efficiency. As an example, when the pixel group having the minimum light emission efficiency has 6 cd/A for the red gradation, the weight data BLW 1  corresponding to the pixel group having the minimum light emission efficiency may have a value of 1, and the weight data BLW 1  corresponding to the pixel group having 6.6 cd/A may have a value of approximately 0.91, or 6/6.6. 
     A test current corresponding to the input image data IDATA of each of the red gradation, the green gradation, and the blue gradation is applied to each of the pre-shipment pixel groups BLK 11  to BLK 35  of the display panel  100 . At this time, the light emission efficiency of the red gradation, the green gradation, and the blue gradation corresponding to each of the pixel groups BLK 11  to BLK 35  may be measured based on the measured light emission luminance. The first weight data BLW may be stored on the first memory  730  in a form of a lookup table. 
     The second weight data TLW may correspond to the light emission efficiency of a pixel according to the ambient temperature. The light emission efficiency for a first pixel including a first light emitting diode emitting the red light, the light emission efficiency for a second pixel including a second light emitting diode emitting the green light, and the light emission efficiency for a third pixel including a third light emitting diode emitting the blue light may be different according to the ambient temperature. The second weight data TLW may be stored on the first memory  730  in the form of a lookup table. 
     Referring to  FIG. 6 , the light emission efficiency levels (unit: cd/A) for light emitting diodes according to the ambient temperature (temperature unit, □C) are illustrated. The light emission efficiency levels corresponding to the first light emitting diode emitting the red light, the second light emitting diode emitting the green light, and the third light emitting diode emitting the blue light are illustrated. 
     As illustrated in  FIG. 6 , at 0° C., the light emission efficiency corresponding to the second light emitting diode is 10 cd/A, the light emission efficiency corresponding to the first light emitting diode is 7 cd/A, and the light emission efficiency corresponding to the third light emitting diode is 5 cd/A. As the temperature increases, the light emission efficiency corresponding to each light emitting diode may decrease. For example, at 100° C., the light emission efficiency corresponding to the second light emitting diode is 7.5 cd/A, the light emission efficiency corresponding to the first light emitting diode is 6 cd/A, and the light emission efficiency corresponding to the third light emitting diode is 4.5 cd/A. Since materials included in light emitting diodes are different, the degrees of decrease in the light emission efficiency according to the increment of the temperature may be different for the light emitting diodes. 
     The second weight data TLW may include the weight data TLW 1  corresponding to the first light emitting diode, the weight data TLW 2  corresponding to the second light emitting diode, and the weight data TLW 3  corresponding to the third light emitting diode. Weight change rates according to temperature of the second weight data TLW may be different for different light emitting diodes. 
     Referring to  FIG. 7A ,  FIG. 7B , and  FIG. 7C , at 100° C., all the weight data TLW 1 , the weight data TLW 2 , and the weight data TLW 3  may have a value of 1; at 0° C., the weight data TLW 1  may have a value of 0.7, the weight data TLW 2  may have a value of 0.6, and the weight data TLW 3  may have a value of 0.9. At a temperature (for example, 100° C.) corresponding to the minimum light emission efficiency for each of the light emitting diodes, the second weight data TLW may have the value of 1; below the temperature of the minimum light emission efficiency, the second weight data TLW may be determined by applying different weight change rates for different light emitting diodes. 
     The load weight calculator  720  may calculate the load weight LW corresponding to each of the pixel groups BLK 11  to BLK 35  based on the predicted temperature data BTD, the first weight data BLW, and the second weight data TLW. 
     The load weight calculator  720  may calculate the weight for each of the red gradation, the green gradation, and the blue gradation of a pixel group by multiplying the corresponding one of the weight data TLW 1 , the weight data TLW 2 , and the weight data TLW 3  according to the temperature of the pixel group based on the predicted temperature data BTD for one pixel group among the pixel groups BLK 11  to BLK 35  and the corresponding one of the weight data BLW 1 , the weight data BLW 2 , and the weight data BLW 3  of the pixel group, and may calculate the load weight values LW of the pixel group by multiplying the weights for the red gradation, the green gradation, and the blue gradation. The load weight calculator  720  may calculate the load weight LW corresponding to each of the pixel groups BLK 11  to BLK 35  by applying light emission efficiency variations for the pixel groups BLK 11  to BLK 35  and variations of the light emission efficiency for the light emitting diodes according to the ambient temperature. 
     Referring to  FIG. 3 , the load determiner  740  may receive the frame load value FL 1  for each of the pixel groups BLK 11  to BLK 35  from the timing controller  200 , and may receive the load weight LW for each of the pixel groups BLK 11  to BLK 35  from the load weight calculator  720 . 
     The load determiner  740  may calculate a correction load value FL 2  based on the frame load value FL 1  and the load weight LW. For example, the load determiner  740  may calculate the correction load value FL 2  by multiplying the frame load value FL 1  and the load weight LW for each of the pixel groups BLK 11  to BLK 35 , and adding all the multiplied values. 
     The scale factor generator  750  may determine the target current value based on the unit target current value UTC and the correction load value FL 2  received from the unit target current value UTC and the load determiner  740 . For example, the scale factor generator  750  may determine the target current value by multiplying the unit target current value UTC and the correction load value FL 2 . The scale factor generator  750  may generate the scale factor SF by comparing the target current value with the global current value GC received from the current sensor  500 . For example, the scale factor generator  750  may determine a ratio between the target current value and the global current value GC as the scale factor SF. 
     The display device  1000  (and/or scale factor provider  700 ) may perform the global current control operation in consideration of light emission efficiency variations for the pixel groups BLK 11  to BLK 35  and light emission efficiency variations of the pixels PX according to the ambient temperature. Accordingly, an appropriate current may be supplied to the pixels PX. Advantageously, the display device  1000  may display images with satisfactory quality. 
     The embodiments described above are illustrative. Practical embodiments can be implemented with various combinations, changes, environments, and/or modifications within the scope defined by the appended claims.