Patent Publication Number: US-10325547-B2

Title: Display device and method of compensating degradation of a display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 USC § 119 to Korean Patent Application No. 10-2015-0118259, filed on Aug. 21, 2015 in the Korean Intellectual Property Office (KIPO), the content of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments of the present invention relate to a display device. 
     2. Description of the Related Art 
     An organic light emitting display device displays an image using an organic light emitting diode. The organic light emitting diode and a driving transistor that transfers a current to the organic light emitting diode may degrade over time as the organic light emitting diode and the driving transistor are utilized. Thus, over time the organic light emitting display device may not display an image with the intended luminance due to degradation of the organic light emitting diode or degradation of the driving transistor. 
     A related art organic light emitting display device provides a reference voltage to each of a plurality of pixels, senses a current flowing through each of the pixels in response to the reference voltage, and calculates an amount of the degradation of the organic light emitting diode or an amount of the degradation of the driving transistor based on a sensed current. That is, the related art organic light emitting display device may include a relatively complex (or, complicated) current sensing configuration to sense the current of each of the pixels. 
     The above information disclosed in this Background section is only to enhance the understanding of the background of the invention, and therefore it may contain information that does not constitute prior art. 
     SUMMARY 
     Example embodiments of the present invention relate to a display device. For example, some embodiments of the present invention relate to a display device and a method of compensating degradation of a display panel. 
     Some example embodiments include a display device that includes a relatively simple current sensing configuration. 
     Some example embodiments provide a method of compensating for degradation (or, luminance degradation) of a display panel that can correctly (or, accurately) compensate for degradation of the display panel. 
     According to example embodiments, a display device includes: a display panel comprising a pixel; a current sensor configured to measure a driving current provided to the display panel; and a timing controller configured to calculate a reference driving current and a degradation ratio of the pixel based on first image data provided to the display panel and to compensate second image data based on the driving current, the reference driving current, and the degradation ratio of the pixel. 
     According to some embodiments, the display device further includes a power supply configured to provide first and second power voltages to the display panel through first and second power supply lines, wherein the current sensor is configured to measure the driving current that is returned from the display panel to the power supply through the second power supply line. 
     According to some embodiments, the first image data comprises frame images, and the timing controller is configured to generate average image data based on the frame images and to calculate the reference driving current and the degradation ratio based on the average image data. 
     According to some embodiments, the degradation ratio represents a ratio of an amount of luminance degradation of the pixel to an amount of luminance degradation of the display panel. 
     According to some embodiments, the timing controller is configured to calculate the degradation ratio based on a total sum of grayscales included in the first image data and a grayscale for the pixel among the grayscales. 
     According to some embodiments, the timing controller is configured to calculate an average grayscale based on grayscales included in the first image data and to calculate the reference driving current based on the average grayscale. 
     According to some embodiments, the timing controller comprises a look-up table comprising respective real driving current values for each of average grayscales of the first image data and is configured to determine the reference driving current by selecting one of the real driving current values based on the average grayscale. 
     According to some embodiments, the timing controller is configured to calculate a degradation current based on the reference driving current and the driving current. 
     According to some embodiments, the timing controller is configured to calculate a pixel degradation current of the pixel based on the degradation ratio and the degradation current. 
     According to some embodiments, the timing controller is configured to calculate an offset grayscale of the pixel based on the pixel degradation current, and the offset grayscale is added to a grayscale for the pixel included in the first image data. 
     According to some embodiments, the timing controller is configured to calculate a compensation grayscale curve that includes a degradation compensation value of the pixel for each of grayscales based on the offset grayscale. 
     According to some embodiments, the timing controller is configured to compensate the second image data based on the degradation compensation curve. 
     According to some embodiments, the timing controller is configured to compensate a degradation prediction profile based on the degradation current, and the degradation prediction profile comprises a luminance degradation rate of the display panel with time. 
     According to some embodiments, the timing controller is configured to calculate a degradation time constant, which represents a change of the degradation current with time, based on the degradation current and to compensate the degradation prediction profile based on the degradation time constant. 
     According to some embodiments of the present invention, a display device includes: a display panel comprising a pixel; a current sensor configured to measure a driving current provided to the display panel; and a timing controller configured to calculate a reference driving current based on first image data provided to the display panel, to calculate a degradation current based on the driving current and the reference driving current, and to compensate a degradation prediction profile based on the degradation current, wherein the degradation prediction profile comprises a luminance degradation rate of the display panel with time. 
     According to some embodiments, the timing controller is configured to calculate a degradation time constant, which represents a change of the degradation current with time, based on the degradation current and to compensate the degradation prediction profile based on the degradation time constant. 
     According to some embodiments, the timing controller is configured to compensate second image data based on a compensated degradation prediction profile. 
     According to some embodiments of the present invention, in a method of compensating a degradation of a display panel, the method includes: measuring a driving current provided to the display panel that comprises a pixel; calculating a degradation current based on the driving current and first image data that is provided to the display panel; calculating a pixel degradation current of the pixel based on the first image data and the degradation current; and compensating second image data based on the pixel degradation current. 
     According to some embodiments, calculating the degradation current includes: calculating a reference driving current based on the first image data; and calculating the degradation current based on a difference between the driving current and the reference driving current. 
     According to some embodiments, calculating the pixel degradation current includes: calculating a degradation ratio of the pixel based on the first image data; and calculating the pixel degradation current of the pixel based on the degradation current and the degradation ratio of the pixel. 
     Therefore, a display device according to example embodiments may correctly compensate for degradation (or, luminance degradation) of a display panel by sensing a total driving current of the display panel using a relatively simple current sensing configuration (e.g., employing one-channel current sensing technique) and by calculating a compensation grayscale (or, compensation data) for each of pixels based on the total driving current and input data that is provided to the display panel. 
     In addition, a method of compensating degradation of a display panel may correctly compensate for luminance degradation of the display panel (or, degradation of each of pixels) by calculating a degradation ratio of each of the pixels based on input data and by calculating a compensation grayscale for each of the pixel based on a calculated degradation ratio and a total driving current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative, non-limiting example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a display device according to some example embodiments of the present invention. 
         FIG. 2  is a diagram illustrating an example of a current sensor included in the display device of  FIG. 1 . 
         FIG. 3  is a diagram illustrating an example of a timing controller included in the display device of  FIG. 1 . 
         FIG. 4A  is a diagram illustrating an example of a first look-up table included in the timing controller of  FIG. 3 . 
         FIG. 4B  is a diagram illustrating an example of a second look-up table included in the timing controller of  FIG. 3 . 
         FIG. 4C  is a diagram illustrating an example of average image data generated by the timing controller of  FIG. 3 . 
         FIG. 4D  is a diagram illustrating another example of average image data generated by the timing controller of  FIG. 3 . 
         FIG. 4E  is a diagram illustrating an example of a degradation ratio table generated by the timing controller of  FIG. 3 . 
         FIG. 4F  is a diagram illustrating an operation of compensating unit included in the timing controller of  FIG. 3 . 
         FIG. 4G  is a diagram illustrating an example of a pixel degradation current generated by the timing controller of  FIG. 3 . 
         FIG. 4H  is a diagram illustrating an example of a compensation grayscale table generated by the timing controller of  FIG. 3 . 
         FIG. 5  is a diagram illustrating an example of a compensation grayscale curve generated by the timing controller of  FIG. 3 . 
         FIG. 6  is a flowchart illustrating a method of compensating degradation of a display panel according to some example embodiments of the present invention. 
         FIG. 7  is a flowchart illustrating an example in which a degradation current is calculated by the method of  FIG. 6 . 
         FIG. 8  is a flowchart illustrating an example in which a pixel degradation current is calculated by the method of  FIG. 6 . 
         FIG. 9  is a diagram illustrating an example of the timing controller included in the display device of  FIG. 1  according to some example embodiments of the present invention. 
         FIG. 10  is a diagram illustrating an example of a degradation predicting profile generated by the timing controller of  FIG. 9 . 
         FIG. 11  is a flowchart illustrating a method of compensating degradation of a display panel according to some example embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, aspects of example embodiments of the present invention will be explained in more detail with reference to the accompanying drawings, in which like reference numbers refer to like elements throughout. The present invention, however, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments herein. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the aspects and features of the present invention to those skilled in the art. Accordingly, processes, elements, and techniques that are not necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present invention may not be described. Unless otherwise noted, like reference numerals denote like elements throughout the attached drawings and the written description, and thus, descriptions thereof will not be repeated. In the drawings, the relative sizes of elements, layers, and regions may be exaggerated for clarity. 
     It will be understood that, although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present invention. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of explanation to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or in operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the example terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it can be directly on, connected to, or coupled to the other element or layer, or one or more intervening elements or layers may be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layers, it can be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and “including,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     As used herein, the term “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of “may” when describing embodiments of the present invention refers to “one or more embodiments of the present invention.” As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. Also, the term “exemplary” is intended to refer to an example or illustration. 
     The electronic or electric devices and/or any other relevant devices or components according to embodiments of the present invention described herein may be implemented utilizing any suitable hardware, firmware (e.g. an application-specific integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of these devices may be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of these devices may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on one substrate. Further, the various components of these devices may be may be a process or thread, running on one or more processors, in one or more computing devices, executing computer program instructions and interacting with other system components for performing the various functionalities described herein. The computer program instructions are stored in a memory which may be implemented in a computing device using a standard memory device, such as, for example, a random access memory (RAM). The computer program instructions may also be stored in other non-transitory computer readable media such as, for example, a CD-ROM, flash drive, or the like. Also, a person of skill in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the spirit and scope of the exemplary embodiments of the present invention. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification, and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
       FIG. 1  is a block diagram illustrating a display device according to some example embodiments of the present invention. 
     Referring to  FIG. 1 , the display device  100  may include a display panel  110 , a scan driver  120 , a data driver  130 , a power supplier (or power supply)  140 , a current sensor  150 , and a timing controller  160 . The display device  100  may display an image based on image data provided from an outside (or, an external) component or source. For example, the display device  100  may be an organic light emitting display device. 
     The display panel  110  may include scan lines S 1  through Sn, data lines D 1  through Dm, and pixels  111  disposed in pixel regions. Here, the pixel regions may be cross-regions of the scan lines S 1  through Sn and the data lines D 1  through Dm, where each of m and n is an integer greater than or equal to 2. 
     Each of the pixels  111  may store a data signal in response to a scan signal and may emit light based on a stored data signal. Here, the scan signal may be provided from the scan driver  120  to the pixels  111  through the scan lines S 1  through Sn, and the data signal may be provided from the data driver  130  to the pixels through the data lines D 1  through Dm. 
     The scan driver  120  may generate the scan signal based on the scan driving control signal. The scan driving control signal may be provided from the timing controller  130  to the scan driver  120 . Here, the scan driving control signal may include a start pulse and clock signals, and the scan driver  120  may include a shift register sequentially generating the scan signal based on the start pulse and the clock signals. 
     The data driver  130  may generate the data signal based on the image data. The data driver  130  may provide a generated data signal to the display panel  110  in response to a data driving control signal. Here, the data driving control signal may be provided from the timing controller  160  to the data driver  130 . 
     The power supplier  140  may generate a driving voltage to drive the display device  100 . The driving voltage may include a first power voltage ELVDD and a second power voltage ELVSS. The first power voltage ELVDD may be greater than the second power voltage ELVSS. The power supplier  140  may supply the first and second power voltages ELVDD and ELVSS to the display panel  110  through first and second power supplying (or first and second power supply) lines. 
     The current sensor  150  may measure (or, sense, detect) a driving current (or, a total driving current) supplied to the display panel  110 . The current sensor  150  may measure a returned current (or, a feedback current) that is returned from the display panel  110  to the power supplier  140  through the second power supplying line. A configuration of the current sensor  150  will be described in more detail with reference to  FIG. 2 . 
     The timing controller  160  may calculate a reference driving current (or, an ideal driving current) and a degradation ratio of each of the pixels  111  based on the image data, and may compensate the image data based on the driving current (e.g., the driving current measured by the current sensor  150 ), the reference driving current, and the degradation ratio of each of the pixels  111 . In some example embodiments, the timing controller  160  may calculate the reference driving current based on the image data and may calculate a degradation current (or, a total degradation current of the pixels  111 ) based on the measured driving current (measured by the current sensor  150 ) and the reference driving current. 
     Here, the degradation current may be a difference between the measured driving current and the reference driving current due to degradation of the pixels  111 . In some example embodiments, the timing controller  160  may calculate the degradation ratio of each of the pixels  111  based on the image data, may calculate a pixel degradation current of each of the pixels  111  based on the degradation current and the degradation ratio, and may calculate an offset grayscale of each of the pixels  111  based on the pixel degradation current. Here, the degradation ratio may represent a relative degradation degree between the pixels  111 . For example, the degradation ratio of a certain pixel may be a ratio of an amount of degradation of the certain pixel to an amount of degradation of all the pixels  111  (or, the display panel  110 ). The timing controller  160  may compensate the image data based on the offset grayscale, where the offset grayscale may be added to a grayscale for a pixel to offset (or, compensate for) a luminance reduction due to the pixel degradation. 
     In some example embodiments, the timing controller  160  may calculate an average grayscale based on grayscales included in the image data and may calculate the reference driving current based on the average grayscale and a look-up table, where the look-up table may include a real driving current that is measured for each of grayscales of the image data. The timing controller  160  may obtain the reference driving current corresponding to the average grayscale from the look-up table. 
     In some example embodiments, the timing controller  160  may calculate the degradation current based on the reference driving current and the measured driving current. For example, the timing controller  160  may calculate the degradation current by calculating a difference between the reference driving current and the measured driving current. 
     In some example embodiments, the timing controller  160  may calculate the degradation ratio of each of the pixels  111  based on sum of grayscales included in the image data (e.g., a total grayscale) and a grayscale for each of the pixels  111  among the grayscales. For example, when a first grayscale of a first pixel is 50 and a second grayscale of a second pixel is 150, the timing controller  160  may calculate the total grayscale as 200 and may calculate a first degradation ratio of the first pixel as 0.25 (i.e., 50/200=0.25) and a second degradation ratio of the second pixel as 0.75 (e.g., 150/200=0.75). 
     In some example embodiments, the timing controller  160  may calculate the pixel degradation current of each of the pixels  111  based on the degradation ratio of each of the pixels  111 . For example, the timing controller  160  may calculate the pixel degradation current by multiplying the degradation ratio of each of the pixels  111  with the degradation current. 
     In some example embodiments, the timing controller  160  may calculate the offset grayscale of each of the pixels  111  based on the pixel degradation current and a grayscale-current characteristic of a pixel (e.g., variation characteristic of the driving current according to a variation of a grayscale). 
     In some example embodiments, the timing controller  160  may include a degradation predicting profile and may compensate the degradation predicting profile based on the degradation current. Here, the degradation predicting profile may include a change of the degradation current in time (or, with time) and the change of the degradation current may be pre-determined. That is, the degradation prediction profile may include luminance degradation rate of the display panel with time. 
     The timing controller  160  may predict the pixel degradation (or, an amount of degradation of the pixel) based on the degradation predicting profile and may generate compensated image data that is compensated based on a predicted pixel degradation. Because a characteristic of the pixel degradation may be changed according to a change of a driving condition (e.g., a temperature) of the display device  100 , the timing controller  160  may compensate the degradation predicting profile to correctly predict the pixel degradation based on a calculated degradation current (e.g., a real degradation current). In an example embodiment, the timing controller  160  may calculate a degradation time constant, which represents a change of the degradation current with time, based on the degradation current and may compensate the degradation predicting profile based on the degradation time constant. 
     The timing controller  160  may compensate the image data based on a compensated degradation predicting profile. 
     As described above, the display device  100  according to example embodiments may measure the total driving current that is supplied to the display panel  110 , may calculate the degradation ratio of each of the pixels  111  and the reference driving current (or, ideal driving current) based on the image data, and may calculate the offset grayscale of each of the pixels  111  based on the total driving current, the reference driving current, and the degradation ratio of each of the pixels  111 . Therefore, the display device  100  may respectively compensate for degradation of pixels  111  using a relatively simple configuration (or, a relatively simple current sensing configuration). 
     In addition, the display device  100  may compensate the degradation predicting profile based on a measured total driving current. Therefore, the display device  100  may correctly compensate for the pixel degradation considering (e.g., based on or according to) a change of the driving condition of the display device  100 . 
       FIG. 2  is a diagram illustrating an example of a current sensor included in the display device of  FIG. 1 . 
     Referring to  FIG. 2 , the current sensor  150  may include a resistor Rs and a current sensing unit  152  (or, a sensing integrated circuit). The resistor Rs may be electrically connected in parallel to a second power supplying line  141 . The current sensing unit  152  may measure a driving current based on a voltage (or, a voltage drop) across the resistor Rs. Here, the driving current may be a returned current that is returned from the display panel  110  to the power supplier  140 . For example, the current sensing unit  152  may amplify the voltage across the resistor Rs and may output an amplified voltage. 
     As described above, the current sensor  150  may include one-channel current sensing configuration. The one-channel current sensing configuration is simpler than a two-channel current sensing configuration (e.g., a configuration that has a voltage supplying configuration and a current measuring configuration). 
       FIG. 3  is a diagram illustrating an example of a timing controller included in the display device of  FIG. 1 . 
     Referring to  FIG. 3 , the timing controller may include a reference current calculating unit  310 , a degradation ratio calculating unit  320 , and a compensating unit  330 . 
     The reference current calculating unit  310  may calculate a reference driving current IREF based on grayscales included in first image data IMAGE 1 . Here, the first image data IMAGE 1  may be image data supplied from an outside (or, an external) component at a certain time (e.g., a predetermined time) or during a certain period (e.g., a predetermined period). For example, the first image data IMAGE 1  may include a frame image corresponding to the certain time or frame images supplied during the certain period. In some example embodiments, the reference current calculating unit  310  may include a look-up table, where the look-up table may include a real driving current that is pre-measured for grayscales of the first input data IMAGE 1 . 
       FIG. 4A  is a diagram illustrating an example of a first look-up table included in the timing controller of  FIG. 3 . Here, the first look-up table  410  may be used to calculate a driving current of each grayscale. 
     Referring to  FIG. 4A , the first look-up table  410  may include a total driving current Wmc corresponding to a grayscale Gray of image data. The total driving current Wmc may be calculated by summing a first current Rsc, a second current Gsc, and a third current Bsc, where the first through third currents Rsc, Gsc, and Bsc may be total driving currents that is respectively measured for sub pixels included in the pixels  111 . 
     For example, when each of the pixels  111  includes a first sub pixel to display a first color, a second sub pixel to display a second color, and a third sub pixel to display a third color, the first current Rsc may be a first total driving current supplied to the first sub pixels included in the display panel  110 , the second current Gsc may be a second total driving current supplied to the second sub pixels included in the display panel  110 , and the third current Bsc may be a third total driving current supplied to the third sub pixels included in the display panel  110 . 
     As illustrated in  FIG. 4A , the total driving current Wmc corresponding to a grayscale of 255 may be 113.4094 mill ampere (mA) that is sum of 23.6698 mill ampere (mA) of the first current Rsc, 31.9698 mill ampere (mA) of the second current Gsc, and 57.7698 mill ampere (mA) of the third current Bsc. 
     For reference, a loading effect may exist between the first through third currents Rsc, Gsc, and Bsc. That is, other currents may be changed according to a change of a certain current. For example, when grayscales of the first through third sub pixels are 255, the total driving current Wmc may be measured as not 113.4074 mill ampere (mA) but 101.3698 mill ampere (mA). 
     However, the first look-up table  410  may include the first through the third currents and the total driving current that do not consider the loading effects between the currents because manufacturing cost of the display device  100  is increased when the first look-up table  410  includes values considering all cases of the loading effects (e.g., 256*256*256 number of cases). 
     The first through third currents Rsc, Gsc, and Bsc may be measured at a manufacturing process of the display panel  110  and may be stored in a storage device (e.g., ROM) included in the timing controller  160 . In an example embodiment, the first look-up table  410  may include the first through third currents Rsc, Gsc, and Bsc that are measured for all grayscales (e.g., grayscales in a range of 0 through 255) of the image data. In an example embodiment, the first look-up table  410  may include the first through third currents Rsc, Gsc, and Bsc that are measured for only some grayscales (e.g., 31, 63, 127, 203, and 255). Here, the first through third currents Rsc, Gsc, and Bsc corresponding to other grayscales may be calculated based on measured currents. For example, the first through third currents Rsc, Gsc, and Bsc may be calculated by a general gamma equation or a linear equation. 
       FIG. 4B  is a diagram illustrating an example of a second look-up table included in the timing controller of  FIG. 3 . Here, the second look-up table  420  may be used to calculate a driving current of each grayscale. 
     Referring to  FIGS. 4A and 4B , the second look-up table  420  may include the first through third currents Rsc, Gsc, and Bsc and total driving currents Wmc_Log for all grayscales. Here, the first through third currents Rsc, Gsc, and Bsc and the total driving currents Wmc_Log for a range of a grayscale  228  through a grayscale  232  may be calculated based on those for a grayscale  203  and those for a grayscale  255 . 
     The second look-up table  420  may include current ratios RofWmc, GofWmc, and BofWmc that represent a correlation between the first through third currents Rsc, Gsc, and Bsc. Here, each of the current ratios RofWmc, GofWmc, and BofWmc may be a proportion of a certain current to the total driving current. 
     For example, when the first current Rsc corresponding to a grayscale  228  is 17.6743 mill ampere (mA), the second current Gsc is 23.6063 mill ampere (mA), the third current Bsc is 44.5042 mill ampere (mA), and the total driving current Wmc_Log is 85.7848 mill ampere (mA), a first current ratio RofWmc of the first current Rsc may be 0.2060 (e.g., the first current Rsc/the total driving current Wmc_Log=17.6743/85.7548=0.2060). The current ratios RofWmc, GofWmc, and BofWmc may be used to calculate the reference driving current IREF. 
     Referring again to  FIG. 3 , the reference current calculating unit  310  may calculate the average grayscale based on grayscales included in the first image data IMAGE 1  and may calculate the reference driving current IREF based on the average grayscale and the look-up table (e.g., the second look-up table  420 ). 
     In some example embodiments, the reference current calculating unit  310  may generate average image data based on frame images and may calculate the average grayscale based on the average image data. That is, when the first image data IMAGE 1  includes frame images, the reference current calculating unit  310  may normalize the frame images into the average image data and may normalize the average image data into one grayscale. 
     For example, the first image data IMAGE 1  may include ten frame image groups, and one frame image group may include ten frame images. That is, the first image data IMAGE 1  may include one hundred frame images. Here, the reference current calculating unit  310  may generate one group data based on ten frame images and may generate the average image data based on ten group images. 
     In some example embodiments, the reference current calculating unit  310  may generate one group image by calculating an arithmetic-mean of the frame images or by calculating a harmonic-mean of the frame images and may generate one average image data by calculating an arithmetic-mean of a group of images. For example, the reference current calculating unit  310  may generate one group image by calculating arithmetic-mean of ten frame images or by calculating harmonic-mean of ten frame images and may generate one average image data by calculating arithmetic-mean of ten group images. 
       FIG. 4C  is a diagram illustrating an example of average image data generated by the timing controller of  FIG. 3 . 
     Referring to  FIG. 4C , each of the frame images IMAGE_T 1 , IMGAE_T 2 , and etc may include one hundred grayscales (e.g., grayscales corresponding to pixels). However, the frame images are not limited thereto. For example, each of the frame images may include 1920*1080 numbers of grayscales. 
     In some example embodiments, the reference current calculating unit  310  may calculate a pixel average grayscale by averaging grayscales for the pixels and may generate average image data based on calculated pixel average grayscales. For example, when grayscales  431  for a first pixel included in the ten frame images IMAGE_T 1 , IMAGE_T 2 , and etc are 0, 200, 200, 200, 200, 200, 200, 200, 100, and 20, the reference current calculating unit  310  may calculate a first group grayscale  432  having 152 by averaging the grayscales. 
     In addition, when each of group grayscales  432  for a first pixel included in ten group images IMAGE_S 1 , IMAGE_S 2 , and etc is 152, the reference current calculating unit  310  may calculate a first pixel average grayscale  433  having 152 by averaging the group grayscales. Furthermore, the reference current calculating unit  310  may generate average image data IMAGE_C by respectively calculating one hundred number of pixel average grayscales. 
     In some example embodiments, the reference current calculating unit  310  may generate a group image by calculating harmonic meaning of a number of frame images (e.g., a predetermined number of frame images) and may generate average image data by calculating arithmetic meaning of a number of group images (e.g., a predetermined number of group images). For example, the reference current calculating unit  310  may generate a group image by sequentially calculating harmonic meaning of frame images that is sequentially provided in time and may generate average image data by calculating arithmetic meaning of group images that are sequentially generated. 
       FIG. 4D  is a diagram illustrating another example of average image data generated by the timing controller of  FIG. 3 . 
     Referring to  FIG. 4D , the reference current calculating unit  310  may generate three sub average image data  441 ,  442 , and  443 . As described with reference to  FIG. 4A , when the pixels  111  include three types of sub pixels, the reference current calculating unit  310  may generate the sub average image data  441 ,  442 , and  443  for each type of the sub pixels. 
     The first sub average image data  441  may be sub image data for the first pixels to display a first color, the second sub average image data  442  may be sub image data for the second pixels to display a second color, and the third sub average image data  441  may be sub image data for the third pixels to display a third color. 
     In some example embodiments, the reference current calculating unit  310  may calculate an average grayscale by averaging grayscales included in average image data  440 . For example, the reference current calculating unit  310  may calculate a first average grayscale AG 1  having 195 based on the first sub average image data  441 , may calculate a second average grayscale AG 2  having 195 based on the second sub average image data  442 , and may calculate a third average grayscale AG 3  having 195 based on the third sub average image data  443 . 
     In some example embodiments, the reference current calculating unit  310  may calculate the reference driving current IREF based on the average grayscale. For example, the reference current calculating unit  310  may calculate the reference driving current IREF based on the first through third average grayscales AG 1 , AG 2 , and AG 3  illustrated in  FIG. 4D  and the second look-up table  420  described with reference to  FIG. 4B . 
     For example, the reference current calculating unit  310  may obtain the first through third currents Rmc, Gmc, and Bmc corresponding to the first through third average grayscales AG 1 , AG 2 , and AG 3 , may obtain first through third current ratios RoWmc, GofWmc, and BofWmc of the first through third currents Rmc, Gmc, and Bmic from the second look-up table  420 , and may calculate the reference driving current IREF based on those (e.g., the first through third current ratios RofWmc, GofWmc, and BofWmc). For example, the first through third current ratio RofWm, GofWmc, and BofWmc are 0.2022, 0.2679, and 0.5300, and the reference driving current IREF corresponding to those (e.g., the first through third current ratio RofWm, GofWmc, and BofWmc) may be 56.0835 mill amperes (mA). 
     Referring again to  FIG. 3 , the degradation ratio calculating unit  320  may calculate a degradation ratio DR of each of the pixels  111  based on the first image data IMAGE 1 . In an example embodiment, the degradation ratio calculating unit  320  may calculate the degradation ratio DR of each of the pixels  111  based on a total sum (or, a total grayscale) of grayscales included in the first image data IMAGE 1  and a grayscale for each of the pixels  111 . 
       FIG. 4E  is a diagram illustrating an example of a degradation ratio table generated by the timing controller of  FIG. 3 . 
     Referring to  FIGS. 4D, 4F, and 4E , the degradation ratio calculating unit  320  may calculate the degradation ratio DR by calculating a ratio of a pixel average grayscale of each of the pixels  111  to the total grayscale of the average image data  440 . Here, the degradation ratio DR may represent a relative degradation degree of a certain pixel, and sum of degradation ratios DR may be constant. For example, the degradation ratio calculating unit  320  may calculate a first degradation ratio  451   a  having 0.0097 by dividing the first pixel average grayscale  433  having 194 illustrated in  FIG. 4D  with a total sum of pixel average grayscales illustrated in  FIG. 4D . 
     In an example embodiment, the degradation ratio calculating unit  320  may calculate the degradation ratio DR of each of the pixels  111  by diving pixel average grayscales with the average grayscale, respectively. For example, the degradation ratio calculating unit  320  may calculate the first degradation ratio  451   a  having 0.0097 by dividing the first pixel average grayscale  433  having 194 with the first average grayscale AG 1  (or, a value multiplied the first average grayscale AG 1  with a number of pixels  111 ) having 195. 
     In some example embodiments, the degradation ratio calculating unit  320  may generate first through third degradation ratio tables  451 ,  452 , and  453  for the first through the third sub pixels. The first through third degradation ratio tables  451 ,  452 , and  453  may be used to calculate a pixel degradation current. 
     Referring again to  FIG. 3 , the compensating unit  330  may calculate the degradation current based on the reference driving current IREF and the measured driving current ISEN and may calculate a pixel degradation current of each of the pixels  111  based on the degradation current and the degradation ratio DR. 
       FIG. 4F  is a diagram illustrating an operation of compensating unit included in the timing controller of  FIG. 3 .  FIG. 4G  is a diagram illustrating an example of a pixel degradation current generated by the timing controller of  FIG. 3 . 
     Referring to  FIGS. 4F and 4G , as described with reference to  FIG. 4D , the reference driving current IREF may be 56.0835 mill ampere (mA), and the measured driving current ISEN may be 50.1241 mill ampere (mA). Here, the measured driving current ISEN may be an average current that is measured at a time (or, during a period) in which the first image data IMAGE 1  is provided. For example, the measured driving current ISEN may have an average value of driving currents that are measured during one hundred number of frame images are provided. 
     The compensating unit  330  may generate the degradation current by calculating a difference between the reference driving current IREF and the measured driving current ISEN. For example, when the reference driving current IREF is 56.0835 mill ampere (mA) and the measured driving current ISEN is 50.1241 mill ampere (mA), the degradation current may be 5.9595 mill ampere (mA) (e.g., 56.0835 mA-50.1241 mA). 
     The compensating unit  330  may calculate first through third degradation currents based on the degradation current and grayscale ratios of the first through third average grayscales. Here, the first through third degradation currents may be degradation currents for the first through third sub pixels. As illustrated in  FIG. 4F , the compensating unit  330  may calculate the grayscale ratios (e.g., 0.0335, 0.3333, and 0.3334) of the first through third average grayscales and may calculate the first through third degradation currents (ΔI_RGB) (e.g., 1.9875, 1.9863, and 1.9869) based on the degradation current and the grayscale ratios. 
     The compensating unit  330  may calculate pixel degradation currents  470  of the pixels  111  based on the degradation currents ΔI_RGB illustrated in  FIG. 4F  and the degradation ratio table  450 . For example, the compensating unit  330  may calculate the pixel degradation currents  470  illustrated in  FIG. 4G  based on the first through third degradation currents R_BURNDELTA, G_BURNDELTA, and B_BURNDELTA and the degradation ratio tables  451 ,  452 , and  453  illustrated in  FIG. 4E . Because the degradation ratio DR represents a relative degradation degree of a certain pixel, the compensating unit  330  may divide the degradation current to the pixels based on the degradation ratio DR. For example, a first pixel degradation current  471  of a first pixel may be 0.019300 mill ampere (mA) (e.g., 1.9875 mA*0.0097). 
     The compensating unit  330  may calculate an offset grayscale of each of the pixels  111  based on the pixel degradation currents  470 . Here, the offset grayscale may be a grayscale, which is added to each of grayscales included in the image data, for compensating the luminance reduction due to a pixel degradation. The compensating unit  330  may calculate the offset grayscale corresponding to the pixel degradation currents  470  based on a grayscale-current characteristic (a variation characteristic of a driving current according to a change of a grayscale) of a pixel. The compensating unit  330  may generate a compensating grayscale table based on calculated offset grayscales. 
       FIG. 4H  is a diagram illustrating an example of a compensation grayscale table generated by the timing controller of  FIG. 3 . 
     Referring to  FIG. 4H , a first offset grayscale  481   a  of the first pixel, which corresponds to the first degradation current  471  having 0.019300, is 10, and a second offset grayscale of a second pixel, which corresponds to a second degradation current having 0.023700, is 12. 
     The compensating unit  330  may generate first through third compensating grayscale tables  481 ,  482 , and  483 . Here, the first through third compensating grayscale tables  481 ,  482 , and  483  may be compensating grayscale tables for the first through third sub pixels. The first through third compensating grayscale tables  481 ,  482 , and  483  may include offset grayscales for each of the sub pixels. 
     The compensating unit  330  may generate a compensating grayscale curve of each of the pixels  111  based on the offset grayscale. Here, the compensating grayscale curve may represent a relation between a predetermined grayscale and a compensation grayscale (or, a compensated grayscale), where the compensation grayscale may have a grayscale value that is compensated based on the offset grayscale. 
       FIG. 5  is a diagram illustrating an example of a compensation grayscale curve generated by the timing controller of  FIG. 3 . 
     Referring to  FIG. 5 , the compensating unit  330  may convert a certain grayscale included in the image data into a compensation grayscale based on the offset grayscale. 
     For example, the compensating unit  330  may convert a grayscale  433  of a first pixel having 194 illustrated in  FIG. 4D  into a compensation grayscale of 204 (i.e., a first grayscale of a first pixel+an offset grayscale of the first pixel=194+10=204). For example, the compensating unit  330  may convert a grayscale of a second pixel having 200 illustrated in  FIG. 4D  into a compensation grayscale of 200. 
     The compensating unit  330  may compensate second image data IMAGE 3  based on the compensation grayscale curve  500 . Here, the second image data IMAGE 3  may be image data that is provided after the compensation grayscale curve is generated (or, after the offset grayscale is calculated). For example, the compensating unit  330  may compensate a grayscale of 194 included in the second image data IMAGE 3  as a compensation grayscale of 204. For example, the compensating unit  330  may compensate a grayscale of 97 included in the second image data IMAGE 3  as a compensation grayscale of 102 according to the compensation grayscale curve  500 . 
     Because a maximum grayscale used in the display device  100  may be predetermined, the compensating unit  330  may generate the compensation grayscale curve  500  with respect to an average grayscale and may compensate image data based on the compensation grayscale curve  500 . 
     In an example embodiment, the display device  100  may repeatedly generate the compensation grayscale curve  500  with a certain period. That is, the display device  100  may update the compensation grayscale curve  500  with a certain period. 
     As described above, the timing controller  160  may calculate the reference driving current IREF and the degradation ratio DR of each of the pixels  111  based on image date and may calculate the offset grayscale for each of the pixels  111  based on the measured driving current ISEN, the reference driving current IREF, and the degradation ratio DR. Therefore, the display device  100  may compensate degradation of a pixel (or, degradation of each of the pixels  111 ). 
       FIG. 6  is a flowchart illustrating a method of compensating degradation of a display panel according to example embodiments. 
     Referring to  FIGS. 1, 3, and 6 , the method of  FIG. 6  may be performed by the display device  100 . The method of  FIG. 6  may measure a driving current provided to the display panel  110  (S 610 ). The method of  FIG. 6  may measure the driving current (or, a returned current) that is returned from the display panel  110  to the power supplier  140  through a second power supplying lines. 
     The method of  FIG. 6  may calculate a degradation current based on first image data IMAGE 2  and the driving current ISEN that is measured (S 620 ). The first image data may be image data provided from an outside (or, from an external component) at a certain time or during a certain period. When the display device  100  performs compensating a degradation with a certain period, the first image data IMAGE 1  may be image data provided to the display device  100  during a first period, and second image data IMAGE 2  may be image data provided during a second period (e.g., a next period of the first period). For example, the method of  FIG. 6  may calculate a reference driving current IREF based on image data (or, the first image data IMAGE 1 ) and may calculate the degradation current based on driving current ISEN and the reference driving current IREF. 
     The method of  FIG. 6  may calculate a pixel degradation current of each of the pixels  111  based on the first image data IMAGE 1  and the degradation current (S 630 ). For example, the method of  FIG. 6  may calculate a degradation ratio DR of each of the pixels  111  based on grayscales (or, grayscale values) included in the image data IMAGE 1  and may calculate the pixel degradation current of each of the pixels  111  based on the degradation current and the degradation ratio DR. 
     The method of  FIG. 6  may compensate the second image data IMAGE 2  based on the pixel degradation current. For example, the method of  FIG. 6  may calculate an offset grayscale of each of the pixels  111  based on the degradation current and a grayscale-current characteristic (e.g., a variation characteristic of the driving current according to a change of a grayscale) of a pixel, may generate a degradation compensation curve  500  of each of the pixels  111  based on the offset grayscale, and may compensate grayscales (or, grayscale include in the second image data IMAGE 2 ) for the pixels  111  based on the degradation compensation curve  500 . 
       FIG. 7  is a flowchart illustrating an example in which a degradation current is calculated by the method of  FIG. 6 . 
     Referring to  FIGS. 1, 3, and 7 , the method of  FIG. 7  may calculate the reference driving current IREF based on the first image data IMAGE 1 . 
     The method of  FIG. 7  may generate a look-up table for a total driving current (S 710 ). The method of  FIG. 7  may calculate the total driving current for each of grayscales based on currents, which are pre-measured, for sub pixels included in the pixels  111  and may generate the look-up table based on the total driving current for each of grayscales. The method of  FIG. 7  may calculate first through third currents by removing a loading effect between the currents from pre-measured currents for each of the sub pixels. 
     As described with reference to  FIG. 4A , the method of  FIG. 7  may calculate the total driving current Wmc for each of grayscales by summing the first through third currents Rsc, Gsc, and Bsc. As described with reference to  FIG. 4B , the method of  FIG. 7  may calculate current ratios RofWmc, GofWmc, and BofWmc of the first through third currents Rsc, Gsc, and Bsc. The method of  FIG. 7  may generate a second look-up table  420  that includes the total driving current Wmc and the current ratios RofWmc, GofWmc, and BofWmc of the first through third currents Rsc, Gsc, and Bsc. 
     The method of  FIG. 7  may generate average image data based on frame images (S 720 ), and may calculate an average grayscale based on the average image data (S 730 ). For example, the method of  FIG. 7  may generate one group image based on ten (or, ten number of) frame images and may generate one average image data based on ten (or, ten number of) group images. The method of  FIG. 7  may generate the group image and the average image data by using arithmetic meaning and/or harmonic meaning. 
     In an example embodiment, the method of  FIG. 7  may calculate the average grayscale for each of images. For example, when the first image data IMAGE 1  includes RGB data, the method of  FIG. 7  may calculate the average grayscale for each of images (e.g., a red image, a green image, and a blue image). 
     The method of  FIG. 7  may calculate a reference driving current based on the average grayscale (S 740 ). The method of  FIG. 7  may obtain the total driving current corresponding to the average grayscale from a look-up table that is predetermined (or, pre-generated). 
     In an example embodiment, the method of  FIG. 7  may calculate a current ratio for each of images for the average grayscale and may calculate the reference driving current based on the current ratio for the average grayscale. For example, when the first image IMAGE 1  has RGB data, the method of  FIG. 7  may calculate the current ratio for each of the images (e.g., a red image, a green image, and a blue image) based on the average grayscale of each of the images and may obtain the total driving current (or, the reference driving current) corresponding to the current ratio from a look-up table that is predetermined (or, pre-generated). 
     The method of  FIG. 7  may calculate a degradation current based on a difference between the driving current (or, a measured driving current) and the reference driving current (S 750 ). For example, the method of  FIG. 7  may determine the degradation current with the difference between the driving current and the reference driving current. 
       FIG. 8  is a flowchart illustrating an example in which a pixel degradation current is calculated by the method of  FIG. 6 . 
     Referring to  FIGS. 1, 3, and 8 , the method of  FIG. 8  may calculate a degradation ratio DR of each of the pixels  111  based on the first image data IMAGE 1 . When the first image data IMAGE 1  includes frame images, the method of  FIG. 8  may generate an average image data based on the frame images and may calculate the degradation ratio DR of each of the pixels  111  based on the average image data. 
     As described with reference to  FIG. 4E , the method of  FIG. 8  may calculate a ratio of the average grayscale of each of the pixels  111  to a total grayscale (or, sum of grayscales) of the average image data and may determine the degradation ratio DR as the ratio. 
     The method of  FIG. 8  may calculate a pixel degradation current of each of the pixels  111  based on the degradation ratio DR and the degradation current. As described with reference to  FIG. 4G , the method of  FIG. 8  may divide the degradation current for the pixels  111  based on the degradation ratio. 
     As described with reference to  FIGS. 6 through 8 , the method of compensating a degradation according to example embodiments may measure a driving current (or, a total driving current) that is provided to the display panel  110  and may calculate the reference driving current and the degradation ratio of each of the pixels  111  based on image data (or, the first image data IMAGE 1 ). In addition, the method may calculate the offset grayscale of each of the pixels based on the driving current (or, the total driving current), the reference driving current, and the degradation ratio. Therefore, the method may respectively compensate a degradation of each of the pixels  111  even though the display device  100  has a one-channel current sensing configuration. 
       FIG. 9  is a diagram illustrating another example of the timing controller included in the display device of  FIG. 1 . 
     Referring to  FIGS. 1 and 9 , the timing controller  160  may calculate a reference driving current Iref based on image data, may calculate a degradation current based on a driving current measured by the current sensor  150  and the reference driving current Iref, and may compensate a degradation prediction profile based on the degradation current. 
     As illustrated in  FIG. 9 , the timing controller  160  may include a reference current calculating unit  910  and a compensating unit  920 . 
     The reference current calculating unit  910  may be substantially the same as or similar to the reference current calculating unit  310  described with reference to  FIG. 3 . Therefore, some duplicated description will not be repeated. 
     The compensating unit  920  may calculate the degradation current based on the driving current Isen and the reference driving current Iref. For example, the compensating unit  920  may determine the degradation current by calculate a difference between the reference driving current Iref and the driving current Isen. A configuration of calculating the degradation current may be substantially the same as or similar to a configuration of calculating the degradation current by the compensating unit  330  described with reference to  FIG. 3 . Therefore, some duplicated description will not be repeated. 
     The compensating unit  920  may compensate the degradation prediction profile based on the degradation current. Here, the degradation prediction profile may include luminance degradation of a pixel (or, the display panel  110 ) in time. The degradation prediction profile may be predetermined in a manufacturing process of the display device  100 . In some example embodiments, the compensating unit  920  may calculate a degradation time constant based on the degradation current and may compensate the degradation prediction profile based on the degradation time constant. Here, the degradation time constant may represent a change (or, a variation) of the degradation current in time. 
     The compensating unit  920  may compensate the second image data IMAGE 2  based on the degradation prediction profile that is compensated. 
       FIG. 10  is a diagram illustrating an example of a degradation predicting profile generated by the timing controller of  FIG. 9 . 
     Referring to  FIGS. 1, 9 and 10 , luminance of a pixel may be reduced in time. That is, a pixel that receives a constant grayscale (or, a constant data signal) may emit light with a reduced luminance in time according to the pixel is used, instead of a constant luminance. A ratio of luminance reduction may be substantially the same as or similar to a ratio of a degradation current to a reference driving current. 
     The compensating unit  920  may calculate a degradation time constant based on a change of the degradation current in time and may compensate the degradation prediction profile to have a slope (of a degradation prediction curve) of which value is substantially the same as a value of the degradation time constant. For example, a first degradation prediction profile may have a first slope at a first time point. Here, the compensating unit  920  may calculate a second slope at the first time point, where the second slope is different from the first slope. As illustrated in  FIG. 10 , a first degradation curve  1010 , which is generated by the first degradation prediction profile, having the first slope may be different from a second degradation curve  1020 , which is measured, having the second slope. Therefore, the compensating unit  920  may compensate the degradation prediction profile (or, the first degradation prediction profile) to have the second slope. 
     The compensating unit  920  may compensate image data based on a compensated degradation prediction profile. That is, the compensating unit  920  may predict that degradation having a certain vale occurs when a certain time elapses, based on the compensated degradation prediction profile, and may compensate the image data to compensate the degradation (or, a predicted degradation). 
     As described above, the display device  100  according to example embodiments may compensate the degradation prediction profiled based on a measured total driving current. Therefore, the display device  100  may exactly (or accurately, or relatively accurately) compensate degradation considering (or based on) a change of a driving condition of the display device  100 . 
       FIG. 11  is a flowchart illustrating a method of compensating degradation of a display panel according to example embodiments. 
     Referring to  FIGS. 1, 9 and 11 , the method of  FIG. 11  may measure a driving current provided to the display panel  110  (S 1110 ). 
     The method of  FIG. 11  may calculate a reference driving current based on image data (S 1120 ). 
     The method of  FIG. 11  may calculate a degradation current based on the driving current (or, a measure driving current) and the reference driving current (S 1130 ). 
     For example, the method of  FIG. 11  may determine the degradation current by calculating a difference between the reference driving current and the driving current. 
     The method of  FIG. 11  may compensate a degradation prediction profile based on the degradation current (S 1140 ). In some example embodiments, the method of  FIG. 11  may calculate a degradation time constant based on the degradation current and may compensate the degradation prediction profile based on the degradation time constant. 
     The method of  FIG. 11  may compensate the image data based on a compensated degradation prediction profile. 
     As described above, the method of compensating a degradation according to example embodiments may compensate the degradation prediction profile based on a measured total driving current and may compensate the image data based on the compensated degradation prediction profile. Therefore, the method may exactly (or accurately, or relatively accurately) compensate for degradation considering (or based on) a change of a driving condition of the display device  100 . 
     Aspects of embodiments of the present invention may be applied to any display device (e.g., an organic light emitting display device, a liquid crystal display device, etc). For example, embodiments of the present invention may be applied to a television, a computer monitor, a laptop, a digital camera, a cellular phone, a smart phone, a personal digital assistant (PDA), a portable multimedia player (PMP), an MP3 player, a navigation system, a video phone, etc. 
     The foregoing is illustrative of example embodiments, and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and aspects of example embodiments. Accordingly, all such modifications are intended to be included within the scope of example embodiments as defined in the claims, and their equivalents. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of example embodiments and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims, and their equivalents. The present invention is defined by the following claims, with equivalents of the claims to be included therein.