Patent Publication Number: US-11049444-B2

Title: Display device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0036255 filed in the Korean Intellectual Property Office on Mar. 28, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of some example embodiments of the present invention relate to a display device and a driving method thereof. 
     2. Description of the Related Art 
     As an information technology is developed, an importance of a display device, which is a connection medium between users and information, has been highlighted. Therefore, a display device such as a liquid crystal display device, an organic light emitting diode display device, and a plasma display device has been increasingly used. 
     Each pixel of the organic light emitting diode display may include at least one organic light emitting diode. The organic light emitting diode may degrade as a usage time increases, requiring more driving current to exhibit the same luminance. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background and therefore the information discussed in this Background section does not necessarily constitute prior art. 
     SUMMARY 
     Some example embodiments of the present invention include a display device that may more accurately compensate for a degradation of an organic light emitting diode using a current sensor and a temperature sensor as well as input grayscale values of pixels and a driving method thereof. 
     A display device according to some example embodiments of the present invention includes a display panel including pixels receiving pixel driving currents; a current sensor for measuring an entire driving current diverged into the pixel driving currents; and a temperature sensor for measuring an ambient temperature of the display panel, wherein the display panel includes a degradation compensator that generates output grayscale values for the pixels based on the entire driving current, the ambient temperature, and input grayscale values for the pixels. 
     According to some example embodiments, the pixels may be set into blocks, a number of the blocks may be less than or equal to a number of the pixels, and the degradation compensator may include a block degradation value accumulator that accumulates a block degradation value based on the input grayscale values and a first block temperature to generate a block degradation accumulation value, for each of the blocks. 
     According to some example embodiments, the block degradation value accumulator may update the block degradation accumulation value by multiplying a first block representative value of the input grayscale values and the first block temperature to generate the block degradation value and adding the generated block degradation value to the block degradation accumulation value, for each of the blocks. 
     According to some example embodiments, the degradation compensator may further include a block representative value extractor that extracts a second block representative value based on a first block degradation accumulation value, which is the block degradation accumulation value at a first time, a second block degradation accumulation value, which is the degradation accumulation value at a second time, and a second block temperature, for each of the blocks. 
     According to some example embodiments, the block representative value extractor may divide a difference between the second block degradation accumulation value and the first block degradation accumulation value by the second block temperature to generate the second block representative value, for each of the blocks. 
     According to some example embodiments, the degradation compensator may further include a block current calculator that calculates a block current based on the entire driving current, the second block representative value, and an entire block representative value, for each of the blocks. 
     According to some example embodiments, the block current calculator may calculate the block current so that a ratio of the block current of the entire driving current corresponds to a ratio of the second block representative value of the entire block representative value, for each of the blocks. 
     According to some example embodiments, the degradation compensator may further include a block temperature determiner that determines the first block temperature based on the block current and the ambient temperature, for each of the blocks. 
     According to some example embodiments, the block temperature determiner may determine the first block temperature by adding a value proportional to a difference between a block predicted temperature for the block current and the ambient temperature to the ambient temperature, for each block. 
     According to some example embodiments, the degradation compensator may further include a grayscale converter that converts the input grayscale values to the output grayscale values based on the block degradation accumulation value. 
     According to some example embodiments, the grayscale converter may generate the output grayscale values by adding compensation values to the input grayscale values, and the compensation values are larger as the block degradation accumulation value corresponding to the compensation values is larger. 
     A driving method of a display device according to some example embodiments of the present invention includes: measuring a current that measures an entire driving current provided to a display panel and diverged into pixel driving currents; measuring a temperature that measures an ambient temperature of the display panel; and compensating a degradation that generates output grayscale values for the pixels based on the entire driving current, the ambient temperature, and input grayscale values for the pixels. 
     According to some example embodiments, the pixels may be set into blocks, a number of the blocks may be less than or equal to a number of the pixels, the compensating the degradation may include accumulating a block degradation value that accumulates a block degradation value based on the input grayscale values and a first block temperature to generate a block degradation accumulation value for each of the blocks, and the block degradation value is generated by multiplying a first block representative value of the input grayscale values and the first block temperature, and the block degradation accumulation value is updated by adding the generated block degradation value to the block degradation accumulation value for each of the blocks in the accumulating a block degradation value. 
     According to some example embodiments, the compensating the degradation may further include extracting a block representative value that extracts a second block representative value based on a first block degradation accumulation value, which is the block degradation accumulation value at a first time, a second block degradation accumulation value, which is the degradation accumulation value at a second time, and a second block temperature for each of the blocks, and the second block representative value is generated by dividing a difference between the second block degradation accumulation value and the first block degradation accumulation value by the second block temperature for each of the blocks in the extracting a block representative value. 
     According to some example embodiments, the compensating the degradation may further include calculating a block current that calculates a block current based on the entire driving current, the second block representative value, and an entire block representative value for each of the blocks. 
     According to some example embodiments, the block current may be calculated so that a ratio of the block current of the entire driving current corresponds to a ratio of the second block representative value of the entire block representative value for each of the blocks in the calculating a block current. 
     According to some example embodiments, the compensating the degradation may further include determining a block temperature that determines the first block temperature based on the block current and the ambient temperature for each of the blocks. 
     According to some example embodiments, the first block temperature may be determined by adding a value proportional to a difference between a block predicted temperature for the block current and the ambient temperature to the ambient temperature for each block in the determining a block temperature. 
     According to some example embodiments, the compensating the degradation may further include converting a grayscale that converts the input grayscale values to the output grayscale values based on the block degradation accumulation value. 
     According to some example embodiments, the output grayscale values may be generated by adding compensation values to the input grayscale values in the converting a grayscale, and the compensation values are larger as the block degradation accumulation value corresponding to the compensation values is larger. 
     A display device and a driving method thereof according to some example embodiments of the present invention can more accurately compensate for a degradation of an organic light emitting diode using a current sensor and a temperature sensor as well as input grayscale values of pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for illustrating a display device according to some example embodiments of the present invention. 
         FIG. 2  is a drawing for illustrating a pixel according to some example embodiments of the present invention. 
         FIG. 3  is a drawing for illustrating a driving method of a pixel shown in  FIG. 2 . 
         FIG. 4  is a drawing for illustrating a degradation compensator according to some example embodiments of the present invention. 
         FIG. 5  is a drawing for illustrating a case where pixels are set into blocks according to some example embodiments. 
         FIG. 6  is a drawing for illustrating an operation of a block representative value extractor according to some example embodiments. 
         FIG. 7  is a drawing for illustrating an operation of a block degradation value accumulator according to some example embodiments. 
         FIG. 8  is a drawing for illustrating an operation of a grayscale converter according to some example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to accompanying drawings, various example embodiments of the present invention will be described in more detail so that those skilled in the art can more easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the example embodiments described herein. 
     In order to more clearly illustrate example embodiments of the present invention, parts that are not related to the description are omitted, and the same or similar constituent elements are given the same reference numerals throughout the specification. Therefore, the above-mentioned reference numerals can be used in other drawings. 
     In addition, because the size and thickness of each configuration shown in the drawing are arbitrarily shown for better understanding and ease of description, example embodiments of the present invention are not necessarily limited to the illustrated one. In the drawings, the dimensions of layers and regions are exaggerated for clarity of illustration. 
       FIG. 1  is a drawing for illustrating a display device according to some example embodiments of the present invention. 
     Referring to  FIG. 1 , a display device DD according to some example embodiments of the present invention includes a display panel  10 , a current sensor  17 , and a temperature sensor  18 . The display panel  10  may include a timing controller  11 , a data driver  12 , a scan driver  13 , a emission driver  14 , a pixel unit  15 , and a degradation compensator  16 . 
     The display panel  10  may include pixels PXij receiving pixel driving currents. The pixel driving current of each pixel PXij may determine a light emitting luminance of an organic light emitting diode included in each pixel PXij. 
     The current sensor  17  may measure an entire driving current that diverges into pixel driving currents. The entire driving current may refer to an entire current flowing from a first power line to a second power line in the pixel unit  15  (see  FIGS. 2 and 4 ). According to some example embodiments, the current sensor  17  may be disposed to directly measure the entire current flowing from the first power line to the second power line. 
     According to some example embodiments, when it is not possible to dispose the current sensor  17  to directly measure the entire current flowing from the first power line to the second power line, the current sensor  17  may be disposed to measure a current provided to the pixel unit  15  or a current provided to an entire display panel  10 . Because most of power of the display panel  10  is consumed in the pixel unit  15 , the current sensor  17  may indirectly measure the entire driving current. That is, example embodiments of the present invention may be implemented with only one current sensor  17 . 
     The temperature sensor  18  may measure an ambient temperature of the display panel. That is, example embodiments of the present invention may be implemented with only one temperature sensor  18 . 
     The timing controller  11  may receive grayscale values and control signals for an image frame from an external processor. The timing controller  11  may render grayscale values corresponding to a specification of display device  10 . For example, the external processor may provide a red grayscale value, a green grayscale value, and a blue grayscale value for each unit dot. However, for example, when the pixel unit  15  is a pentile structure, adjacent unit dots share pixels, so that each grayscale value may not correspond to one pixel. In this case, a rendering of grayscale values is required. When one grayscale value corresponds to one pixel, a rendering of grayscale values may be unnecessary. Grayscale values that are rendered or not rendered may be provided to the degradation compensator  16  as input grayscale values. In addition, the timing controller  11  may provide control signals suitable for each of the data driver  12 , the scan driver  13 , the emission driver  14 , and the degradation compensator  16 , and the like for displaying the image frame. 
     The degradation compensator  16  may generate output grayscale values for the pixels PXij based on the entire driving current, the ambient temperature and input grayscale values for the pixels PXij. The degradation compensator  16  may provide the generated output grayscale values directly to the data driver  12  or indirectly to the data driver  12  through the timing controller  11 . A detailed description of the degradation compensator  16  will be given later with reference to  FIG. 4 . 
     According to some example embodiments, some or all of the degradation compensator  16  may be configured integrally with the timing controller  11 . For example, some or all of the degradation compensator  16  may be configured in the form of an integrated circuit with the timing controller  11 . According to some example embodiments, some or all of the degradation compensator  16  may be implemented in software in the timing controller  11 . According to some example embodiments, the degradation compensator  16  may be implemented in software or hardware in an external processor. 
     The data driver  12  may generate data voltages to provide to data lines D 1 , D 2 , D 3 , and Dn using the output grayscale values and control signals. For example, the data driver  12  may sample the output grayscale values using a clock signal and apply data voltages corresponding to the output grayscale values to the data lines D 1 -Dn for each pixel row. The n may be an integer greater than zero. 
     The scan driver  13  may receive a clock signal and a scan start signal from the timing controller  11  and generate scan signals to be provided to the scan lines S 1 , S 2 , S 3 , and Sm. For example, the scan driver  13  may sequentially provide scan signals with a pulse of a turn-on level to the scan lines S 1 -Sm. For example, each scan stage circuit of the scan driver  13  may be configured in the form of a shift register, and generate scan signals in a manner that sequentially transmits the scan start signal with a pulse of turn-on level to the next scan stage circuit according to a control of a clock signal. The m may be an integer greater than zero. 
     The emission driver  14  may receive a clock signal, a emission stop signal, and the like from the timing controller  11  to generate emission signals to be provided to emission lines E 1 , E 2 , E 3 , and Eo. For example, the emission driver  14  may sequentially provide emission signals with a pulse of a turn-off level on the emission lines E 1 -Eo. For example, each emission stage circuit of the emission driver  14  may be configured in the form of a shift register, and generate emission signals in a manner that sequentially transmits the emission stop signal with a pulse of turn-on level to the next emission stage circuit according to a control of a clock signal. The o may be an integer greater than zero. 
     The pixel unit  15  includes pixels. Each pixel PXij may be connected to the corresponding data line, scan line and emission line. In addition, the pixels PXij may be connected to a common first power line and second power line being common to each other. The i and j may be natural numbers. The pixel PXij may refer to a pixel of which the scan transistor is connected to the i-th scan line and the j-th data line. 
       FIG. 2  is a drawing for illustrating a pixel according to some example embodiments of the present invention. 
     Referring to  FIG. 2 , the pixel PXij may include transistors M 1 , M 2 , M 3 , M 4 , M 5 , M 6 , and M 7 , a storage capacitor Cst, and an organic light emitting diode OLED. 
     According to some example embodiments of the present invention, transistors are shown as P-type transistors, but a person of an ordinary skill in the art may configure a pixel circuit with the same function as an N-type transistor. Hereinafter, it is assumed that the transistors are configured of p-type transistors. 
     A first electrode of the storage capacitor Cst may be connected to the first power line ELVDD and a second electrode of the storage capacitor Cst may be connected to a gate electrode of the transistor M 1 . 
     A first electrode of the transistor M 1  may be connected to a second electrode of a transistor M 5 , a second electrode of the transistor M 1  may be connected to a first electrode of the transistor M 6 , and a gate electrode of the transistor M 1  may be connected to the second electrode of the storage capacitor Cst. The transistor M 1  may be referred to as a driving transistor. The transistor M 1  determines an amount of a pixel driving current flowing between a first power line ELVDD and a second power line ELVSS according to a potential difference between the gate electrode and a source electrode. 
     A first electrode of the transistor M 2  may be connected to the data line Dj, a second electrode of the transistor M 2  may be connected to the first electrode of the transistor M 1 , and a gate electrode of the transistor M 2  may be connected to a current scan line Si. The transistor M 2  may be referred to as a switching transistor, a scan transistor, and the like. The transistor M 2  pulls and inputs a data voltage of the data line Dj to the pixel PXij when a scan signal of a turn-on level is applied to the current scan line Si. 
     A first electrode of the transistor M 3  may be connected to the second electrode of transistor M 1 , a second electrode of transistor M 3  may be connected to the gate electrode of transistor M 1 , and a gate electrode of transistor M 3  may be connected to the current scan line Si. The transistor M 3  connects the transistor M 1  in a diode form when a scan signal of a turn-on level is applied to the current scan line Si. 
     A first electrode of the transistor M 4  may be connected to the gate electrode of transistor M 1 , a second electrode of the transistor M 4  may be connected to an initialization voltage line, and a gate electrode of the transistor M 4  may be connected to a previous scan line S(i−1). According to some example embodiments, the gate electrode of the transistor M 4  may be connected to another scan line. The transistor M 4  transmits the initialization voltage VINT to the gate electrode of the transistor M 1  when a scan signal of a turn-on level is applied to the previous scan line S(i−1), thereby initializing a charge amount of the gate electrode of the transistor M 1 . 
     A first electrode of the transistor M 5  may be connected to the first power line ELVDD, a second electrode of the transistor M 5  may be connected to the first electrode of transistor M 1 , and a gate electrode of the transistor M 5  may be connected to a emission line Ei. A first electrode of the transistor M 6  may be connected to the second electrode of transistor M 1 , a second electrode of the transistor M 6  may be connected to an anode of the organic light emitting diode OLED, and a gate electrode of the transistor M 6  may be connected to the emission line Ei. The transistors M 5  and M 6  may be referred to as a light emitting transistor. When a emission signal of a turn-on level is applied to the transistors M 5  and M 6 , the transistors M 5  and M 6  form a path of a pixel driving current between the first power line ELVDD and the second power line ELVSS to light the organic light emitting diode OLED. 
     A first electrode of the transistor M 7  may be connected to the anode of the organic light emitting diode OLED, a second electrode of the transistor M 7  may be connected to the initialization voltage line, and a gate electrode of the transistor M 7  may be connected to the current scan line Si. According to some example embodiments, the gate electrode of transistor M 7  may be connected to another scan line. For example, the gate electrode of transistor M 7  may be connected to the previous scan line S(i−1) or a scan line before the previous scan line, the next scan line (e.g., i−1-th scan line) or a scan line after the next scan line. The transistor M 7  transmits the initialization voltage to the anode of the organic light emitting diode OLED when a scan signal of a turn-on level is applied to the current scan line Si, thereby initializing a charge amount stored in the organic light emitting diode OLED. 
     The anode of the organic light emitting diode OLED may be connected to the second electrode of the transistor M 6  and the cathode of the organic light emitting diode OLED may be connected to the second power line ELVSS. The organic light emitting diode OLED is taken as an example embodiment of the present invention, but a degradable inorganic light emitting diode, a quantum dot light emitting diode, or the like may be provided in the pixel PXij in another example embodiment. 
       FIG. 3  is a drawing for illustrating a driving method of a pixel shown in  FIG. 2 . 
     First, a data voltage DATA (i−1)j for a previous pixel row is applied to the data line Dj and a scan signal of a turn-on level (e.g., a low level) is applied to a previous scan line S(i−1). 
     Because a scan signal of a turn-off level is applied to the current scan line Si, the transistor M 2  is in a turn-off state, and the data voltage DATA (i−1)j for the previous pixel row is prevented from being pulled and input into the pixel PXij. 
     At this time, because the transistor M 4  is turned on, the initializing voltage is applied to the gate electrode of the transistor M 1  to initialize the charge amount. Because a emission signal of a turn-off level is applied to the emission line Ei, the transistors M 5  and M 6  are turned off and a light emission of an unnecessary organic light emitting diode OLED according to an application process of the initialization voltage is prevented. 
     Next, a data voltage DATAij for a current pixel row is applied to the data line Dj, and a scan signal of a turn-on level is applied to the current scan line Si. As a result, the transistors M 2 , M 1 , and M 3  are turned on, and the data line Dj and the gate electrode of the transistor M 1  are electrically connected. Therefore, a compensation voltage that subtracts the threshold voltage of the transistor M 1  from the data voltage DATAij is applied to the second electrode of the storage capacitor Cst, and the storage capacitor Cst stores a difference between a voltage of the first power line ELVDD and the compensation voltage. 
     At this time, because the transistor M 7  is turned on, the anode of the organic light emitting diode OLED is connected to an initialization voltage line, and the organic light emitting diode OLED is precharged or initialized with a charge amount corresponding to a voltage difference between the initialization voltage and a voltage of the second power line. 
     Thereafter, as a emission signal of a turn-on level is applied to the emission line Ei, the transistors M 5  and M 6  are turned on and an amount of a pixel driving current flowing the transistor M 1  is controlled according to a charge amount stored in the storage capacitor Cst so that a pixel driving current flows to the organic light emitting diode OLED. The organic light emitting diode OLED emits light until a emission signal of a turn-off level is applied to the emission line Ei. 
       FIG. 4  is a drawing for illustrating a degradation compensator according to some example embodiments of the present invention,  FIG. 5  is a drawing for illustrating a case where pixels are set into blocks,  FIG. 6  is a drawing for illustrating an operation of a block representative value extractor,  FIG. 7  is a drawing for illustrating an operation of a block degradation value accumulator, and  FIG. 8  is a drawing for illustrating an operation of a grayscale converter. 
     Referring to  FIG. 4 , the degradation compensator  16  according to some example embodiments of the present invention may generate output grayscale values OG for the pixels PXij based on an entire driving current IE, an ambient temperature TPA, and input grayscale values IG for the pixels PXij. 
     For example, the degradation compensator  16  may include a block degradation value accumulator  161 , a block representative value extractor  162 , a block current calculator  163 , a block temperature determiner  164 , and a grayscale converter  165 . 
     Referring to  FIG. 5 , pixels PX 1 , PX 2 , and PX 3  may be set or partitioned into blocks BL 1 , BL 2 , and BL 3 . The number of blocks BL 1 , BL 2 , and BL 3  may be less than or equal to the number of pixels PX 1 , PX 2 , and PX 3 . For example, each of blocks BL 1 , BL 2 , and BL 3  may be set or partitioned to include one or more pixels PX 1 , PX 2 , and PX 3 . When each of blocks BL 1 , BL 2 , and BL 3  includes only one of the pixels PX 1 , PX 2 , and PX 3 , that is, the number of blocks BL 1 , BL 2 , and BL 3  is equal to the number of pixels PX 1 , PX 2 , and PX 3 , accurate degradation compensation may be achieved, but costs for a data storage and a computation may increase. When each of blocks BL 1 , BL 2 , and BL 3  includes two or more of the pixels PX 1 , PX 2 , and PX 3 , that is, the number of blocks BL 1 , BL 2 , and BL 3  is less than the number of pixels PX 1 , PX 2 , and PX 3 , costs for a data storage and computation decrease, but accurate degradation compensation may not be achieved. A manufacturer of the display device DD may determine a size of the blocks BL 1 , BL 2 , and BL 3  in view of this trade-off relationship. 
     The block degradation value accumulator  161  may accumulate block degradation values based on input grayscale values IG and a first block temperature TP 1  for each of blocks BL 1 , BL 2 , and BL 3  to generate a block degradation accumulation value. 
     For example, the block degradation value accumulator  161  may update the block degradation accumulation value by multiplying a first block representative value of the input grayscale values IG and a first block temperature TP 1  to generate a block degradation value and adding the generated block degradation value to a block degradation accumulation value for each of the blocks BL 1 , BL 2 , and BL 3  (see Equation 1).
 
ACD( n )=ACD[ n− 1]+BRV1[ n ]*TP1  [Equation 1]
 
     Here, ACD [n−1] may be a block degradation accumulation value up to the n−1-th image frame, BRV 1  [n] may be a first block representative value in the n-th image frame, and TP 1  may be a first block temperature TP 1 . ACD [n] may be a block degradation accumulation value up to the n-th image frame. 
     For example, the first block representative value may be a value obtained by applying weight values to the input grayscale values IG of the corresponding block and dividing by the number of the input grayscale values IG. For example, when weight values of the input grayscale values IG are equal to 1, a representative value may mean an average value. 
     In Equation 1, BRV 1  [n]*TP 1  may be a block degradation value. That is, the larger the first block representative value BRV 1  [n] in the n-th image frame and the larger the first block temperature TP 1 , the larger the block degradation value in the n-th image frame. The block degradation value may correspond to the degree of degradation of the organic light emitting diodes included in the pixels included in the corresponding block. When an organic light emitting diode is degraded, more driving current is required to emit light at the same level of luminance. 
     Because the block degradation value accumulator  161  must store degradation data over an entire life-span of the display device DD, degradation data needs to be simplified. For example, the block degradation value accumulator  161  may store a block degradation accumulation value at the current time, and may not store a block degradation accumulation value at the past time, the first block representative value of each image frame, and the first block temperature TP 1 . 
     As shown in  FIG. 6 , the block degradation accumulation value increases with time. 
     The block representative value extractor  162  may extract a second block representative value BRV 2  based on a first block degradation accumulation value ACD 1  which is the block degradation accumulation value at a first time t 1 , a second block degradation accumulation value ACD 2  which is the block degradation accumulation value at a second time t 2 , and a second block temperature TP 2  for each of the blocks BL 1 , BL 2 , and BL 3 . 
     For example, the block representative value extractor  162  may generate the second block representative value BRV 2  by dividing a difference between the second block degradation accumulation value ACD 2  and the first block degradation accumulation value ACD 1  by the second block temperature TP 2  to for each of the blocks BL 1 , BL 2 , and BL 3  (See Equation 2).
 
BRV2=(ACD2( t 2)−ACD1( t 1))/TP2  [Equation 2]
 
     Here, BRV 2  may be the second block representative value, ACD 2  (t 2 ) may be the second block degradation accumulation value at the second time t 2 , ACD 1  (t 1 ) may be the first block degradation accumulation value at the first time t 1 , and TP 2  may be the second block temperature TP 2 . 
     If the block degradation value of the n-th image frame is reflected in the block degradation accumulation value at the second time t 2 , the block degradation value of the n−1-th image frame is reflected in the block degradation accumulation value at the first time t 1 , and the second block temperature TP 2  is equal to the first block temperature TP 1  in Equation 1, BRV 2  in Equation 2 becomes equal to BRV 1  [n] in Equation 1. That is, according to some example embodiments, the block representative value extractor  162  may accurately extract the block representative value from the block degradation value accumulator  161  including only information on the block degradation accumulation value. 
     However, according to the specification of a product, the block degradation value of the n-th image frame may be reflected in the block degradation accumulation value at the second time t 2 , and the block degradation value of the n−2-th image frame may be reflected in the block degradation accumulation value at the first time t 1  or a time before the first time t 1 . That is, an interval with which the block representative value extractor  162  samples the block degradation accumulation value from the block degradation value accumulator  161  may be more than an interval of two image frame. In this case, the second block representative value BRV 2  may be mismatched with the first block representative value BRV 1  [n] of Equation 1, but the display device DD may be designed so that this mismatch may be acceptable for calculating the block temperature. 
     The block current calculator  163  may calculate a block current IB based on the entire driving current IE, the second block representative value BRV 2  and the entire block representative value for each block BL 1 , BL 2 , and BL 3 . 
     For example, the block current calculator  163  calculates the block current IB so that a ratio of the block current IB of the entire driving current IE may correspond to a ratio of the second block representative value BRV 2  of the entire block representative value for each blocks BL 1 , BL 2 , and BL 3 .
 
IB=IE*(BRV2/EBRV)  [Equation 3]
 
     Here, IB is the block current, IE is the entire driving current, BRV 2  is the second block representative value, and EBRV is the entire block representative value. 
     As described above, the entire driving current IE may refer to the entire current flowing from the first power line ELVDD to the second power line ELVSS in the pixel unit  15 . The pixels PXij may be connected to the first power line ELVDD and the second power line ELVSS to be common to each other. 
     In addition, as described above, when the current sensor  17  cannot be disposed to directly measure the entire current flowing from the first power line ELVDD to the second power line ELVSS, the current sensor  17  may be disposed to measure a current provided to the pixel unit  15  or a current provided to the entire display panel  10 . In this case, the measured entire driving current IE may be mismatched with the entire driving current IE of Equation 3, but the display device DD may be designed so that this mismatch may be acceptable for calculating the block current. For example, the entire driving current IE may be obtained by excluding a current amount that is expected to be consumed from another element except for the pixel unit  15  from the measured current value. 
     In addition, when the interval with which the block representative value extractor  162  samples the block degradation accumulation value from the block degradation value accumulator  161  may more than an interval of two image frame as described above, the entire driving current IE may be a value accumulated more than an interval of two image frame. 
     An entire block representative value may be a value obtained by adding weight values to the second block representative values of the entire blocks BL 1 , BL 2 , and BL 3 . For example, when the weight values are all 1, the entire block representative value may be a sum of the second block representative values of the second blocks of BL 1 , BL 2 , and BL 3 . 
     The block temperature determiner  164  may determine a first block temperature TP 1  based on a block current IB and an ambient temperature TPA for each of blocks BL 1 , BL 2 , and BL 3 . 
     For example, the block temperature determiner  164  may determine the first block temperature TP 1  by adding a value which is proportional to a difference between a block predicted temperature for the block current IB and an ambient temperature TPA to the ambient temperature TPA for each block BL 1 , BL 2 , and BL 3  (see Equation 4).
 
TP1=TPA+( K *(TPE−TPA))  [Equation 4]
 
     Here, TP 1  is the determined first block temperature TP 1 , TPA is the ambient temperature TPA, K is a proportional constant, and TPE is the block predicted temperature. 
     The block prediction temperature TPE may be determined by referring to a look up table LUT based on the block current IB. Alternatively, the block prediction temperature TPE may be determined by another algorithms. 
     Different block currents IB may flow and the first block temperature TP 1  may be changed depending on a luminous efficiency of the display panel  10  even with the same input grayscale values IG. Therefore, the accurate first block temperature TP 1  can be obtained by referring to the block current IB as well as the input grayscale values IG according to some example embodiments of the present invention. 
     In addition, some example embodiments of the present invention may be implemented with only one current sensor  17  and one temperature sensor  18 . 
     The block degradation value accumulator  161  may update the third block degradation accumulation value ACD 3  at the third time t 3  by adding the block degradation value to the second block degradation accumulation value ACD 2  at the second time t 2  through Equation 1. 
     The grayscale converter  165  may convert the input grayscale values IG to the output grayscale values OG based on a third block degradation accumulation value ACD 3 . 
     For example, the grayscale converter  165  may generate the output grayscale values OG by adding compensation values CPV to the input grayscale values IG. The compensation values CPV may be larger as the corresponding third block degradation accumulation value ACD 3  is larger. In other words, the degradation of an organic light emitting diode OLED may be compensated by adding a larger compensation value CPV to the input grayscale value IG. 
     The drawing and the detailed description of the present invention referred to above are descriptive sense only and are used for the purpose of illustration only and are not intended to limit the meaning thereof or to limit the scope of the invention described in the claims. Accordingly, a person having ordinary skill in the art will understand from the above that various modifications and other equivalent embodiments are also possible. Therefore, the real protective scope of the present invention shall be determined by the technical scope of the accompanying claims, and their equivalents.