Patent Publication Number: US-2013249965-A1

Title: Display device

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This is a Continuation application of U.S. patent application Ser. No. 12/923,058 filed Aug. 31, 2010, which in turn claims priority from Japanese Application No.: 2009-217183, filed on Sep. 18, 2009, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE PRESENT INVENTION 
     1. Field of the Present Invention 
     The present invention relates to a display device in which a light emitting element is provided in a display panel. 
     2. Description of the Related Art 
     In recent years, in the field of a display device displaying an image, a display device using, as a light emitting element of a pixel, a current drive type optical element, for example, an organic EL (electro luminescence) element, in which light emission luminance is varied according to the value of a flowing current has been developed, and progressively commercialized. Unlike a liquid crystal element or the like, the organic EL element is a self-luminous element. Thus, in a display device using the organic EL element (organic EL display device), since a light source (backlight) is not necessary, thinning and high luminance are realized in comparison with a liquid crystal display device in which the light source is necessary. In particular, in the case where the active matrix method is used as a driving method, it may be possible to light and hold each pixel, and this enables low power consumption. Therefore, the organic EL display device is expected to become the mainstream of a flat panel display in the next generation. 
     However, in the organic EL element, an element is deteriorated in accordance with the amount of a flowing current, and there is an issue that the luminance is reduced. Thus, in the case where the organic EL element is used as a pixel in the display device, the state of deterioration may be varied for each pixel. For example, in the case where information such as a time and a display channel is displayed with a high luminance in the same place for a long time, deterioration of only the pixels in that section is accelerated. As a result, in the case where a video having a high luminance is displayed in the section including the pixels whose deterioration is accelerated, a phenomenon called “seizure” is generated such that only the section of the pixels whose deterioration is accelerated is darkly displayed. Since the seizure is irreversible, when the seizure is once generated, it is not eliminated. 
     A great number of methods for preventing the seizure have been proposed so far. For example, in Japanese Unexamined Patent Publication No. 2002-351403, the method in which a dummy pixel is provided in a region other than a display region, and the deterioration degree of the dummy pixel is estimated by detecting a terminal voltage when the dummy pixel emits light, thereby correcting a video signal by utilizing that estimation is disclosed. Further, for example, in Japanese Unexamined Patent Publication No. 2008-58446 and International Publication WO 2006/046196, the methods in which an optical sensor is disposed in each display pixel, and a video signal is corrected by utilizing a light reception signal output from the optical sensor are disclosed. 
     SUMMARY OF THE PRESENT INVENTION 
     However, in the method of Japanese Unexamined Patent Publication No. 2002-351403, since the deterioration degree of the pixel is not estimated based on light emission information of a pixel in the display region, and it is difficult to accurately correct the video signal, there is an issue that the seizure is difficult to be prevented. Further, in the methods of Japanese Unexamined Patent Publication No. 2008-58446 and International Publication WO 2006/046196, since the photoelectric conversion efficiency of the optical sensor in each pixel is varied, for example, the intensity of the light reception signal may be varied in two pixels performing a display with the same luminance. As a result, there is an issue that it is difficult to accurately prevent the seizure. 
     In view of the foregoing, it is desirable to provide a display device capable of accurately preventing a seizure. 
     According to an embodiment of the present invention, there is provided a display device including: a display panel including a display region in which a plurality of display pixels are two-dimensionally arranged, and a non-display region in which a plurality of first dummy pixels and a plurality of second dummy pixels are arranged. Also, the display device includes a first drive section allowing each of the first dummy pixels to emit light by applying signal voltages having magnitudes different from each other to each of the first dummy pixels; and a second drive section allowing each of the second dummy pixels to emit light by flowing constant currents having magnitudes different from each other to each of the second dummy pixels. Further, the display device includes a current measurement section outputting current information of each of the first dummy pixels by detecting currents flowing through each of the first dummy pixels; a light reception section outputting luminance information of each of the second dummy pixels by detecting light emitted from each of the second dummy pixels; and a calculation section deriving a current deterioration function by using the current information, and deriving an efficiency deterioration function by using the luminance information. 
     In the display device according to the embodiment of the present invention, the signal voltages having the magnitudes different from each other are applied to each of the first dummy pixels provided in the non-display region of the display panel, each of the first dummy pixels emits the light with the luminance in accordance with the magnitude of the signal voltage, the currents flowing through each of the first dummy pixels are detected by the current measurement section, and the current information of each of the first dummy pixels is output from the current measurement section. Further, constant currents having the magnitudes different from each other are flown to each of the second dummy pixels provided in the non-display region of the display panel, each of the second dummy pixels emits light with luminance in accordance with the magnitude of the constant currents, the light emitted from each of the second dummy pixels is detected by the light reception section, and the luminance information of each of the second dummy pixels is output from the light reception section. Thereafter, the current deterioration function is derived by using the current information, and the efficiency deterioration function is derived by using the luminance information. Thereby, for example, from the current deterioration function, and a history of the video signal of each of the display pixels, the current deterioration ratio of each of the display pixels may be predicted. Further, from the efficiency deterioration function, and the history of the video signal of each of the display pixels, the efficiency deterioration ratio of each of the display pixels may be predicted. 
     Here, in the display device according to the embodiment of the present invention, a cycle in which the current deterioration function is derived is preferably set to be shorter than a cycle in which the efficiency deterioration function is derived. In this case, it may be possible to correct the efficiency deterioration in the state where the current is corrected. 
     Other and further objects, features and advantages of the present invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating an example of the structure of a display device according to an embodiment of the present invention. 
         FIG. 2  is a schematic view illustrating an example of the structure of a pixel circuit of a display region. 
         FIG. 3  is a schematic view illustrating an example of the structure of a pixel circuit of a non-display region. 
         FIG. 4  is a top face view illustrating an example of the structure of a display panel in  FIG. 1 . 
         FIG. 5  is a characteristic view illustrating an example of a temporal change of a current deterioration ratio for each initial current. 
         FIG. 6  is a relationship view illustrating an example of the relationship between the current deterioration ratio and the current deterioration ratio of a dummy pixel of an initial current S s . 
         FIG. 7  is a relationship view illustrating an example of the relationship between a power coefficient n(S i , S s ), and an initial current ratio S i /S s . 
         FIG. 8  is a relationship view illustrating an example of the relationship between a prediction value S s2  of the current deterioration ratio at a time T k , and a measurement value S s1  of the current deterioration ratio at the time T k . 
         FIG. 9  is a relationship view illustrating an example of the relationship between a current deterioration function I s (t) at a time T k−1 , and the current deterioration function I s (t) at the time T k . 
         FIG. 10  is a conceptual view for explaining an example of a calculating method of the power coefficient. 
         FIG. 11  is a relationship view illustrating an example of the relationship between the power coefficient n(S i , S s ) at the time T k−1 , and the power coefficient n(S i , S s ) at the time T k . 
         FIG. 12  is a conceptual view for explaining an example of a calculating method of a current deterioration function I i (t). 
         FIG. 13  is a conceptual view for explaining an example of a deriving method of an light emission accumulation time T xy  in a reference luminance. 
         FIG. 14  is a conceptual view for explaining an example of a deriving method of a current correction amount R I . 
         FIG. 15  is a characteristic view illustrating an example of a temporal change of an efficiency deterioration ratio for each initial luminance. 
         FIG. 16  is a relationship view illustrating an example of the relationship between the efficiency deterioration ratio and the efficiency deterioration ratio of a dummy pixel of an initial luminance Y s . 
         FIG. 17  is a relationship view illustrating an example of the relationship between a power coefficient n(Y i , Y s ), and an initial luminance ratio Y i /Y s . 
         FIG. 18  is a relationship view illustrating an example of the relationship between a prediction value Y s2  of the efficiency deterioration ratio at the time T k , and a measurement value Y s1  of the efficiency deterioration ratio at the time T k . 
         FIG. 19  is a relationship view illustrating an example of the relationship between an efficiency deterioration function F s (t) at the time T k−1 , and an efficiency deterioration function F s (t) at the time T k . 
         FIG. 20  is a conceptual view for explaining an example of a calculating method of the power coefficient. 
         FIG. 21  is a relationship view illustrating an example of the relationship between the power coefficient n(Y i , Y s ) at the time T k−1 , and a power coefficient n(Y i , Y s ) at the time T k . 
         FIG. 22  is a conceptual view for explaining an example of a calculating method of an efficiency deterioration function F i (t). 
         FIG. 23  is a conceptual view for explaining an example of a deriving method of the light emission accumulation time T xy  in the reference luminance. 
         FIG. 24  is a conceptual view for explaining an example of a deriving method of an efficiency correction amount R y . 
         FIG. 25  is a perspective view illustrating an appearance of a first application example of the display device of the foregoing embodiment. 
         FIG. 26A  is a perspective view illustrating an appearance of a second application example as viewed from the front side, and  FIG. 26B  is a perspective view illustrating an appearance as viewed from the rear side. 
         FIG. 27  is a perspective view illustrating an appearance of a third application example. 
         FIG. 28  is a perspective view illustrating an appearance of a fourth application example. 
         FIG. 29A  is an elevation view of a fifth application example unclosed,  FIG. 29B  is a side view thereof;  FIG. 29C  is an elevation view of the fifth application example closed,  FIG. 29D  is a left side view thereof,  FIG. 29E  is a right side view thereof,  FIG. 29F  is a top face view thereof, and  FIG. 29G  is a bottom face view thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The description will be made in the following order. 
     1. Embodiment (FIGS. 1 to 24) 
     2. Modifications (no illustrations) 
     Example where each dummy pixel  16  in which an initial current S i  is low is composed of a plurality of dummy pixels 
     Example where each dummy pixel  18  in which an initial luminance Y i  is low is composed of a plurality of dummy pixels 
     Example where another dummy pixel  16  is newly set as a reference pixel, in the case where a failure occurs in a reference pixel 
     Example where another dummy pixel  18  is newly set as the reference pixel, in the case where a failure occurs in the reference pixel 
     Example where a sampling period ΔT 1  is set to be variable 
     Example where a sampling period ΔT 2  is set to be variable 
     Example where a power coefficient n(S i , S s ) is derived only with four arithmetic operations 
     Example where a power coefficient n(Y i , Y s ) is derived only with the four arithmetic operations 
     3. Application examples ( FIGS. 25 to 29 ) 
     1. Embodiment 
     (Schematic Structure of Display Device  1 ) 
       FIG. 1  illustrates the schematic structure of a display device  1  according to an embodiment of the present invention. The display device  1  includes a display panel  10 , and a drive circuit  20  driving the display panel  10 . 
     The display panel  10  includes a display region  12  in which a plurality of organic EL elements  11 R,  11 G, and  11 B are two-dimensionally arranged. In this embodiment, the three organic EL elements  11 R,  11 G, and  11 B adjacent to each other constitute one pixel (display pixel  13 ). Hereinafter, “organic EL element  11 ” is appropriately used as a general term for the organic EL elements  11 R,  11 G, and  11 B. The display panel  10  also includes a non-display region  15  in which a plurality of organic EL elements  14 R,  14 G, and  14 B are two-dimensionally arranged. In this embodiment, the three organic EL elements  14 R,  14 G, and  14 B adjacent to each other constitute one pixel (dummy pixel  16 ). Hereinafter “organic EL element  14 ” is appropriately used as a general term for the organic EL elements  14 R,  14 G, and  14 B. 
     In the non-display region  15 , further, a plurality of organic EL elements  17 R,  17 G, and  17 B are two-dimensionally arranged. In this embodiment, the three organic EL elements  17 R,  17 G, and  17 B adjacent to each other constitute one pixel (dummy pixel  18 ). Hereinafter, “organic EL element  17 ” is appropriately used as a general term for the organic EL elements  17 R,  17 G, and  17 B. In the non-display region  15 , a light receiving element group  19  (light reception section) receiving light which is emitted from the organic EL elements  17 R,  17 G, and  17 B is provided. Although not illustrated in the figure, the light receiving element group  19  is, for example, composed of a plurality of light receiving elements. The plurality of light receiving elements are, for example, two-dimensionally arranged, while being paired with the individual organic EL elements  17 . Each light emitting element detects light (emitted light) emitted from each dummy pixel  18  (each organic EL element  17 ), and outputs a light reception signal  19 A (luminance information) of each dummy pixel  18 . Each light receiving element is, for example, a photodiode. 
     The drive circuit  20  includes a timing generation circuit  21 , a video signal processing circuit  22 , a signal line drive circuit  23 , a scanning line drive circuit  24 , a dummy pixel drive circuit  25 , a current measurement circuit  26 , a measurement signal processing circuit  27 , and a storage circuit  28 . 
     (Pixel Circuit  31 ) 
       FIG. 2  illustrates an example of a circuit structure in the display region  12 . In the display region  12 , a plurality of pixel circuits  31  are two-dimensionally arranged, while being paired with the individual organic EL elements  11 . Each pixel circuit  31  is, for example, composed of a drive transistor Tr 1 , a write transistor Tr 2 , and a retention capacity C s , and has the circuit structure of 2Tr1C. The drive transistor Tr 1  and the write transistor Tr 2  are, for example, formed of an n-channel MOS thin film transistor (TFT). The drive transistor Tr 1  or the write transistor Tr 2  may be a p-channel MOS TFT. 
     In the display region  12 , a plurality of signal lines DTL are arranged in the column direction, and a plurality of scanning lines WSL and a plurality of power source lines Vcc are arranged in the row direction, respectively. In the vicinity of each intersection of each signal line DTL and each scanning line WSL, one of the organic EL elements  11 R,  11 G, and  11 B (sub-pixel) is provided. Each signal line DTL is connected to an output terminal (not illustrated in the figure) of the signal line drive circuit  23 , and a drain electrode (not illustrated in the figure) of the write transistor Tr 2 . Each scanning line WSL is connected to an output terminal (not illustrated in the figure) of the scanning line drive circuit  24 , and a gate electrode (not illustrated in the figure) of the write transistor Tr 2 . Each power source line Vcc is connected to an output terminal (not illustrated in the figure) of a power source, and a drain electrode (not illustrated in the figure) of the drive transistor Tr 1 . A source electrode (not illustrated in the figure) of the write transistor Tr 2  is connected to a gate electrode (not illustrated in the figure) of the drive transistor Tr 1 , and one end of the retention capacity C s . A source electrode (not illustrated in the figure) of the drive transistor Tr 1 , and the other end of the retention capacity C s  are connected to an anode electrode (not illustrate in the figure) of the organic EL element  11 . A cathode electrode (not illustrated in the figure) of the organic EL element  11  is, for example, connected to a ground line GND. 
       FIG. 3  illustrates an example of the circuit structure in the non-display region  15 . In the non-display region  15 , a plurality of pixel circuits  32  having the same structure as the pixel circuits  31  are two-dimensionally arranged, while being paired with the individual organic EL elements  14 . Each pixel circuit  32  is, for example, composed of a drive transistor Tr 1 ′, a write transistor Tr 2 ′, and a retention capacity C s ′, and has the circuit structure of 2Tr1C. The drive transistor Tr 1 ′ and the write transistor Tr 2 ′ are, for example, formed of an n-channel MOS TFT. The drive transistor Tr 1 ′ or the write transistor Tr 2 ′ may be a p-channel MOS TFT. 
     Also in the non-display region  15 , a plurality of signal lines DTL′ are arranged in the column direction, and a plurality of scanning lines WSL′ and a plurality of power source lines Vcc′ are arranged in the row direction, respectively. In the vicinity of each intersection of each signal line DTL′ and each scanning line WSL′, one of the organic EL elements  14 R,  14 G, and  14 B (sub-pixel) is provided. Each signal line DTL′ is connected to an output terminal (not illustrated in the figure) of a dummy pixel drive circuit  25 , and a drain electrode (not illustrated in the figure) of the write transistor Tr 2 ′. Each scanning line WSL′ is connected to an output terminal (not illustrated in the figure) of the dummy pixel drive circuit  25 , and a gate electrode (not illustrated in the figure) of the write transistor Tr 2 ′. Each power source line Vcc′ is connected to an output terminal (not illustrated in the figure) of the power source, and a drain electrode (not illustrated in the figure) of the drive transistor Tr 1 ′. A source electrode (not illustrated in the figure) of the write transistor Tr 2 ′ is connected to a gate electrode (not illustrated in the figure) of the drive transistor Tr 1 ′, and one end of the retention capacity C s ′. A source electrode (not illustrated in the figure) of the drive transistor Tr 1 ′, and the other end of the retention capacity C s ′ are connected to an anode electrode (not illustrate in the figure) of the organic EL element  14 . A cathode electrode (not illustrated in the figure) of the organic EL element  14  is, for example, connected to the ground line GND. 
     (Top Face Structure of Display Panel  10 ) 
       FIG. 4  illustrates an example of the top face structure of the display panel  10 . The display panel  10  has, for example, the structure in which a drive panel  30  and a sealing panel  40  are bonded through a sealing layer (not illustrated in the figure). 
     Although not illustrated in  FIG. 4 , the drive panel  30  includes the plurality of organic EL elements  11  two-dimensionally arranged, and the plurality of pixel circuits  31  arranged adjacent to each organic EL element  11  in the display region  12 . Further, although not illustrated in  FIG. 4 , the drive panel  30  includes a plurality of organic EL elements  14  and  17  two-dimensionally arranged, and a plurality of light receiving elements arranged adjacent to each organic EL element  17  in the non-display region  15 . 
     On one side (long side) of the drive panel  30 , for example, as illustrated in  FIG. 4 , a plurality of video signal suppliers TAB  51 , a control signal supplier TCP  54 , and a measurement signal output TCP  55  are installed. On the other side (short side) of the drive panel  30 , for example, scanning signal suppliers TAB  52  are installed. Further, on one side (long side) of the drive panel  30  but different from the side of the video signal supplier TAB  51 , for example, power source suppliers TCP  53  are installed. The video signal supplier TAB  51  is formed by aerially wiring an IC in which the signal line drive circuit  23  is integrated, to an aperture of a film-shaped wiring substrate. The scanning signal supplier TAB  52  is formed by aerially wiring an IC in which the scanning line drive circuit  24  is integrated, to an aperture of a film-shaped wiring substrate. The power source supplier TCP  53  is formed by forming a plurality of wirings which electrically connect an external power source, and the power source lines Vcc and Vcc′ each other on a film. The control signal supplier TCP  54  is formed by forming a plurality of wirings which electrically connect the external dummy pixel drive circuit  25 , and the dummy pixels  16  and  18  and the light receiving element group  19  each other on a film. The measurement signal output TCP  55  is formed by forming a plurality of wirings which electrically connect the external measurement signal processing circuit  27  and the light receiving element group  19  each other on a film. In addition, the signal line drive circuit  23  and the scanning line drive circuit  24  may not be formed in the TABs, and may be formed, for example, on the drive panel  30 . 
     The sealing panel  40  includes, for example, a sealing substrate (not illustrated in the figure) which seals the organic EL elements  11 ,  14 , and  17 , and a color filter (not illustrated in the figure). The color filter is, for example, provided in a region where light of the organic EL element  11  transmits on the surface of the sealing substrate. The color filter includes, for example, a filter for red, a filter for green, and a filter for blue (not illustrated in the figure), corresponding to each of the organic EL elements  11 R,  11 G, and  11 B. Further, the sealing panel  40  includes, for example, a light reflecting section (not illustrated in the figure). The light reflecting section is intended to reflect light emitted from the organic EL element  17 , thereby allowing the light to enter the light receiving element group  19 . For example, the light reflecting section is provided in a region where the light of the organic EL element  17  transmits on the surface of the sealing substrate. 
     (Drive Circuit  20 ) 
     Next, each circuit in the drive circuit  20  will be described with reference to  FIG. 1 . The timing generation circuit  21  controls the video signal processing circuit  22 , the signal line drive circuit  23 , the scanning line drive circuit  24 , the dummy pixel drive circuit  25 , the current measurement circuit  26 , and the measurement signal processing circuit  27 , thereby allowing them to operate in conjugation with each other. 
     The timing generation circuit  21  outputs, for example, a control signal  21 A to each of the above-described circuits in response to (in synchronization with) a synchronization signal  20 B input from outside. The timing generation circuit  21  is formed, for example, together with the video signal processing circuit  22 , the dummy pixel drive circuit  25 , the current measurement circuit  26 , the measurement signal processing circuit  27 , the storage circuit  28 , and the like, for example, on a control circuit substrate (not illustrated in the figure) provided separately from the display panel  10 . 
     The video signal processing circuit  22  corrects, for example, a digital video signal  20 A input from outside in response to (in synchronization with) an input of the control signal  21 A, and converts the corrected video signal into an analogue signal to output the analogue signal to the signal line drive circuit  23 . In this embodiment, the video signal processing circuit  22  corrects the video signal  20 A by using a correction information  27 A (will be described later) read from the storage circuit  28 . For example, the video signal processing circuit  22  reads, as the correction information  27 A, a correction amount (a current correction amount R I , and an efficiency correction amount R y ) (will be described later) of each display pixel  13  of one line from the storage circuit  28  for each horizontal period, and corrects the video signal  20 A by using the read correction amount (the current correction amount R I , and the efficiency correction amount R y ) to output a corrected video signal  22 A to the signal line drive circuit  23 . 
     The signal line drive circuit  23  outputs the analogue video signal  22 A input from the video signal processing circuit  22  to each signal line DTL in response to (in synchronization with) the input of the control signal  21 A. As illustrated in  FIG. 4 , for example, the signal line drive circuit  23  is provided in the video signal supplier TAB  51  installed on one side (long side) of the drive panel  30 . The scanning line drive circuit  24  sequentially selects one scanning line WSL from the plurality of scanning lines WSL in response to (in synchronization with) the input of the control signal  21 A. As illustrated in  FIG. 4 , for example, the scanning line drive circuit  24  is provided in the scanning signal supplier TAB  52  installed on the other side (short side) of the drive panel  30 . 
     The measurement signal processing circuit  27  derives the correction information  27 A based on the light reception signal  19 A input from the light receiving element group  19 , and outputs the derived correction information  27 A to the storage circuit  28  in response to (in synchronization with) the input of the control signal  21 A. In addition, the deriving method of the correction information  27 A will be described later. The storage circuit  28  stores the correction information  27 A input from the measurement signal processing circuit  27 , so that the video signal processing circuit  22  may read the correction information  27 A stored in the storage circuit  28 . 
     (Current Correction) 
     The dummy pixel drive circuit  25  applies signal voltages V sigi  (constant value) whose magnitudes are different from each other to the signal lines DTL′ connected to each dummy pixel  16  in response to (in synchronization with) the input of the control signal  21 A, and thereby allowing each dummy pixel  16  to emit light with gray scales different from each other. For example, in the case where the number of the dummy pixels  16  is n, the dummy pixel drive circuit  25  allows a constant current to flow through the first dummy pixel  16  so that an initial current is S 1 , allows a constant current to flow through the second dummy pixel  16  so that an initial current is S 2 (&gt;S 1 ), allows a constant current to flow through the i th  dummy pixel  16  so that an initial current is S i (&gt;S i−1 ), and allows a constant current to flow through the n th  dummy pixel  16  so that an initial current is S n (&gt;S n−1 ). The dummy pixel drive circuit  25  measures, for example, the time during each dummy pixel  16  emitting light. 
     In addition, even in the case where the signal voltages V sigi  having the constant value are continued to be applied to the signal lines DTL′ which are connected to each dummy pixel  16 , the luminance of each dummy pixel  16  is gradually reduced with the passage of time, for example, as illustrated in  FIG. 5 . This is because a semiconductor element such as the drive transistor Tr 1 ′ included in the pixel circuit  32  which is connected to each dummy pixel  16  has a property to deteriorate in accordance with the current application time (current application accumulation time), and the current becomes difficult to flow in accordance with the progress of the deterioration. In addition, “S S ” in  FIG. 5  represents an initial current flowing through the organic EL element  14  in the pixel set as a reference pixel (will be described later) in each dummy pixel  16 . 
     The change of the deterioration ratio (current deterioration ratio) of the current flowing through the organic EL element  14  in each dummy pixel  16  is not uniform. For example, as illustrated in  FIG. 6 , when the current deterioration ratio of the pixel (dummy pixel  16 ) set as the reference pixel is indicated on the abscissa axis, it can be seen that the change of the current deterioration ratio of the dummy pixel  16  having the initial current smaller than the initial current S S  of the reference pixel is more gradual than the change of the current deterioration of the reference pixel at the beginning. On the other hand, it can be seen that the change of the current deterioration ratio of the dummy pixel  16  having the initial current larger than the initial current S S  of the reference pixel is steeper than the change of the current deterioration of the reference pixel at the beginning. The change of the current deterioration ratio of each dummy pixel  16  exemplified in  FIG. 6  is represented by the following equation. 
         D   si   =D   ss   n(Si,Ss)   Equation 1
 
     In the Equation 1, D si  represents the current deterioration ratio of the i th  dummy pixel  16 . D ss  represents the current deterioration ratio of the reference pixel. n(S i , S s ) represents a power coefficient of the current of the i th  dummy pixel  16  to the current of the reference pixel. The power coefficient n(S i , S s ) is, for example, derived by dividing (Log (S i (T k ))−Log (S i (T k−1 )) by (Log (S s (T k ))−Log (S s (T k−1 )), for example, as indicated in the following equation. 
     
       
         
           
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           S 
                           i 
                         
                         , 
                         
                           S 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               S 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               S 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               S 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               S 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
     In the Equation 2, Log (S s (T k )) represents a logarithm of S s (T k ), Log (S s (T k−1 )) represents a logarithm of S s (T k−1 ), Log (S i (T k )) represents a logarithm of S i (T k ), and Log (S i (T k−1 )) represents a logarithm of S i (T k−1 ). 
     In the Equation 2, S s (T k ) represents a current signal  26 A (current information) of the reference pixel at the time T k , and corresponds to the latest current information in the current information of the reference pixel. S s (T k−1 ) represents the current signal  26 A (current information) of the reference pixel at the time T k−1 (&lt;time T k ), and corresponds to the non-latest current information in the current information of the reference pixel. S i (T k ) represents the current signal  26 A (current information) of the i th  dummy pixel  16  at the time T k , and corresponds to the latest current information in the current information of the dummy pixel  16  (non-reference pixel). S i (T k−1 ) represents the current signal  26 A (current information) of the i th  dummy pixel  16  at the time T k−1 , and corresponds to the non-latest current information in the current information of the i th  dummy pixel  16  (non-reference pixel). The relationship between the time T k−1  and the time T k  is, for example, represented by the following equation. 
         T   k   =T   k1   +ΔT   1   Equation 3
 
     In the Equation 3, ΔT 1  represents a sampling period. Here, the sampling period ΔT 1  indicates, for example, a cycle in which the measurement signal processing circuit  27  derives the value of the denominator and the value of the numerator on the right side of the Equation 2. The sampling period ΔT 1  is preferably set to be shorter than a sampling period ΔT 2  which will be described later. The measurement signal processing circuit  27  sets the sampling period ΔT 1  to be constant at any time. 
     For example, as illustrated in  FIG. 7 , when the abscissa axis indicates the ratio (S i /S s ) of the initial current S i  of each dummy pixel  16  to the initial current S s  of the reference pixel, the power coefficient n(S i , S s ) derived in the manner described above draws a rightward rising curve which increases with an increase of the initial current S i , at the time T k . In addition, as can be obviously seen from the Equation 2, the power coefficient n(S i , S s ) is 1 in S s /S s . 
     Next, with reference to  FIGS. 8 to 14 , the deriving method of the current correction amount R I  used for correcting the video signal  20 A will be described. 
     (Initial Setting) 
     First, the initial setting will be described. The measurement signal processing circuit  27  sets one pixel in the plurality of dummy pixels  16  as the reference pixel. In this embodiment, the reference pixel is not changed to another dummy pixel  16  (non-reference pixel), and the same dummy pixel  16  is always set as the reference pixel. 
     Next, from the current measurement circuit  26 , the measurement signal processing circuit  27  obtains the current signal  26 A at the times T 1  and T 2 . Specifically, from the current measurement circuit  26 , the measurement signal processing circuit  27  obtains the current signal  26 A of the reference pixel as being one pixel in the plurality of dummy pixels  16 , at the times T 1  and T 2 . Further, from the current measurement circuit  26 , the measurement signal processing circuit  27  obtains the current signal  26 A of the plurality of non-reference pixels as being all the pixels except the reference pixel in the plurality of dummy pixels  16 , at the times T 1  and T 2 . Next, the measurement signal processing circuit  27  derives, from the current information of the reference pixel, the current deterioration information (Log (S s (T 2 ))−Log (S s (T 1 ))) of the reference pixel, and derives, from the current information of each non-reference pixel, the current deterioration information (Log (S i (T 2 ))−Log (S i (T 1 ))) of each non-reference pixel. 
     Next, from the current deterioration information of the reference pixel, and the current deterioration information of each non-reference pixel, the measurement signal processing circuit  27  derives the power coefficient n(S i , S s ) of the current information of each non-reference pixel to the current information of the reference pixel at the time T 2 . Next, from the current information of the reference pixel, the measurement signal processing circuit  27  derives a current deterioration function I s (t) representing the temporal change of the current of the reference pixel at the time T 2 . Further, from the current deterioration function I s (t) and the power coefficient n(S i , S s ), the measurement signal processing circuit  27  derives a current deterioration function I i (t) representing the temporal change of the current of each non-reference pixel at the time T 2 . In this manner, the measurement signal processing circuit  27  derives the current deterioration functions I s (t), and I i (t) at the time T 2  by using the initial current information. 
     (Data Update) 
     Next, the data update will be described. From the current measurement circuit  26 , the measurement signal processing circuit  27  obtains the current signal  26 A of the reference pixel, and the current signal  26 A of the plurality of non-reference pixels at the times T k−1  and T k . The value (measurement value) of the current signal  26 A of the reference pixel at this time is regarded as S s1  (refer to  FIG. 8 ). Next, from the current deterioration function I s (t) at the time T k−1 , the measurement signal processing circuit  27  predicts the current information of the reference pixel at the time T k . The prediction value at this time is regarded as S s2  (refer to  FIG. 8 ). Next, from the comparison between the measurement value S s1  and the prediction value S s2 , the measurement signal processing circuit  27  determines whether or not the measurement value S s1  and the prediction value S s2  are coincident with each other. As a result, for example, in the case where the measurement value S s1  and the prediction value Ss 2  are coincident with each other, the measurement signal processing circuit  27  regards the current deterioration function I s (t) at the time T k−1  as the current deterioration function I s (t) at the time T k . On the other hand, for example, in the case where the measurement signal processing circuit  27  determines that the measurement value S s1  is different from the prediction value S s2  based on the comparison between the measurement value S s1  and the prediction value S s2 , the measurement signal processing circuit  27  derives the current deterioration function I s (t) at the time T k , from the current information of the reference pixel. 
     Next, from the current information of the reference pixel, the measurement signal processing circuit  27  derives the current deterioration information (Log (Ss(T k ))−Log (S s (T k−1 ))) of the reference pixel. Further, from the current information of the plurality of non-reference pixels, the measurement signal processing circuit  27  derives the current deterioration information (Log (S i (T k ))−Log (S i (T k−1 ))) of each non-reference pixel. Next, from the current deterioration information of the reference pixel, and the current deterioration information of each non-reference pixel, the measurement signal processing circuit  27  derives the power coefficient n(S i , S s ) at the time T k . 
     Next, the measurement signal processing circuit  27  updates parameters (for example, p 1 , p 2 , . . . , pm) of the current deterioration function I s (t) at the time T k−1  to parameters (for example, p 1 ′, p 2 ′, . . . , pm′) of the current deterioration function I s (t) at the time T k  (refer to  FIG. 9 ). In other words, the measurement signal processing circuit  27  updates the parameters of the current deterioration function I s (t) in accordance with the latest current information (S s (T k )) in the current information of the reference pixel, and the non-latest current information (S s (T k−1 )) in the current information of the reference pixel. The measurement signal processing circuit  27  stores, for example, the parameters of the newly-obtained current deterioration function I s (t) in the storage circuit  28 . 
     Next, from the current deterioration function I s (t) at the time T k  (refer to  FIG. 10 ), and the power coefficient n(S i , S s ) (refer to  FIG. 11 ), the measurement signal processing circuit  27  derives the current deterioration function I i (t) at the time T k  (refer to  FIG. 12 ). Specifically, the measurement signal processing circuit  27  derives the current deterioration function I s (t) at the time T k  by using the following equation. 
         I   i ( t )= I   s ( t ) n(Si,Sa)   Equation 4
 
     Next, the measurement signal processing circuit  27  updates the parameter of the current deterioration function I i (t) of each non-reference pixel at the time T k−1  to the parameters of the current deterioration function I i (t) of each non-reference pixel at the time T k . The measurement signal processing circuit  27  stores, for example, the parameters of the newly-obtained current deterioration function I i (t) in the storage circuit  28 . 
     (Prediction of Current Deterioration Ratio) 
     Next, the measurement signal processing circuit  27  predicts the current deterioration ratio of each display pixel  13  during the time until the next sampling period comes. Specifically, from the current deterioration function I s (t), the current deterioration function I i (t), and a history of the video signal  20 A of each display pixel  13 , the measurement signal processing circuit  27  derives a light emission accumulation time T xy  of each display pixel  13  at the reference current. The measurement signal processing circuit  27  obtains, for example, the light emission accumulation time T xy  of each display pixel  13  at the reference current as will be described below. 
       FIG. 13  schematically illustrates the deriving process of the light emission accumulation time T xy  of each display pixel  13  at the reference luminance. For example, as illustrated in  FIG. 13 , it is assumed that the luminance of a certain display pixel  13  is changed as the certain display pixel  13  emits light with the initial current S 1  (initial luminance Y 1 ) during the time T=0 to t 1 , emits light with the initial current S 2  (initial luminance Y 2 ) during the time T=t 1  to t 2 , and emits light with the initial current S n  (initial luminance Y n ) during the time T=t 2  to t 3 . At this time, in a narrow sense, the luminance of this display pixel  13  is deteriorated along the deterioration curve of the initial current S 1  during the time T=0 to t 1 , deteriorated along the deterioration curve of the initial current S 2  during the time T=t 1  to t 2 , and deteriorated along the deterioration curve of the initial current S n  during the time T=t 2  to t 3 . As a result, it is assumed that the luminance of this display pixel  13  is deteriorated to 48%, for example, as illustrated in  FIG. 13 . Therefore, by obtaining the time when the deterioration ratio in the current deterioration curve (I s (t)) of the reference pixel becomes 48%, it may be possible to obtain the light emission accumulation time T xy  of each display pixel  13  at the reference luminance. In this manner, by tracking the current deterioration curve in each gray scale in accordance with the intensity (gray scale) of the input signal, it may be possible to obtain the light emission accumulation time T xy  of each display pixel  13  at the reference luminance, and the current deterioration ratio of each display pixel  13 . 
     (Derivation of Correction Amount) 
     Next, from the obtained light emission accumulation time T xy  (or the predicted current deterioration ratio of each display pixel  13 ), and the gamma characteristic of the display panel  10 , the measurement signal processing circuit  27  derives the correction amount to the video signal. The measurement signal processing circuit  27  obtains the correction amount to the video signal, for example, as will be described below. 
       FIG. 14  illustrates an example of the relationship between the gray scale (value of the video signal  20 A) and the luminance at T=0, and T xy . The gray scale-luminance characteristic at T=0 is a so-called gamma characteristic. The gray scale-luminance characteristic at T=T xy  is obtained by attenuating the luminance for all the gray scales to 48% with respect to the gamma characteristic. Here, in a certain display pixel  13 , when the value of the video signal  20 A is S xy , it can be seen that the luminance of this display pixel  13  has a value corresponding to a white circle in the figure in the initial state. In other words, when the light emission accumulation time T xy  is passed from the initial state, it is predictable that the luminance of this display pixel  13  has a value obtained by attenuating the luminance in the initial state to 48%. 
     Thus, the measurement signal processing circuit  27  derives the current correction amount R I  to be subjected to the video signal  20 A so that the luminance when the light emission accumulation time T xy  is passed from the initial state is identical to the luminance in the initial state. Specifically, the measurement signal processing circuit  27  derives the current correction amount R I  by using the following equation. 
     
       
         
           
             
               
                 
                   
                     R 
                     I 
                   
                   - 
                   
                     G 
                     I 
                     
                       1 
                       r 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   5 
                 
               
             
           
         
       
     
     In the Equation 5, G I  represents a current correction gain, and it is 1/0.48 in the example above. “r” represents an index number (gamma value) of the gamma characteristic. 
     Finally, the measurement signal processing circuit  27  stores the current correction amount R I  as the correction information  27 A in the storage circuit  28 . In this manner, the measurement signal processing circuit  27  corrects the efficiency deterioration caused by deterioration of the semiconductor element such as the drive transistor Tr 1 ′ included in the pixel circuit  32 . 
     (Efficiency Correction) 
     Further, the dummy pixel drive circuit  25  allows the constant currents having magnitudes different each other to flow through each dummy pixel  18  in response to (in synchronization with) the input of the control signal  21 A, thereby allowing each dummy pixel  18  to emit light. For example, in the case where the number of the dummy pixels  18  is n, the dummy pixel drive circuit  25  allows a constant current to flow through the first dummy pixel  18  so that the initial luminance is Y 1 , allows a constant current to flow through the second dummy pixel  18  so that the initial luminance is Y 2 (&gt;Y 1 ), allows a constant current to flow through the i th  dummy pixel  18  so that the initial luminance is Y i (&gt;Y i−1 ), and allows a constant current to flow through the n th  dummy pixel  18  so that the initial luminance is Y n (&gt;Y n−1 ). The dummy pixel drive circuit  25  measures, for example, the time during the current is passed through each dummy pixel  18 . 
     In addition, even in the case where the constant current is continued to be flown through each dummy pixel  18 , the luminance of each dummy pixel  18  is gradually reduced with the passage of the time, for example, as illustrated in  FIG. 15 . This is because the organic EL element  17  included in each dummy pixel  18  has a property to deteriorate in accordance with the current application time (light emission accumulation time), and the light emission efficiency is deteriorated in accordance with the progress of the deterioration. In addition, Y s  in  FIG. 15  represents the initial luminance of the pixel set as the reference pixel (will be described later) in each dummy pixel  18 . 
     The change of the efficiency deterioration ratio of each dummy pixel  18  is not uniform. For example, as illustrated in  FIG. 16 , when the efficiency deterioration ratio of the pixel (dummy pixel  18 ) set as the reference pixel is indicated on the abscissa axis, it can be seen that the change of the efficiency deterioration ratio of the dummy pixel  18  having the initial luminance smaller than the initial luminance Y S  of the reference pixel is more gradual than the change of the efficiency deterioration of the reference pixel at the beginning. On the other hand, it can be seen that the change of the efficiency deterioration ratio of the dummy pixel  18  having the initial luminance larger than the initial luminance Y S  of the reference pixel is steeper than the change of the efficiency deterioration of the reference pixel at the beginning. The change of the efficiency deterioration ratio of each dummy pixel  18  exemplified in  FIG. 16  is represented by the following equation. 
         D   i   =D   s   n(Yi/Ys)   Equation 6
 
     In the Equation 6, D i  represents the efficiency deterioration ratio of the i th  dummy pixel  18 . D s  represents the efficiency deterioration ratio of the reference pixel. n(Y i , Y s ) represents a power coefficient of the luminance of the i th  dummy pixel  18  to the luminance of the reference pixel. The power coefficient n(Y i , Y s ) is, for example, derived by dividing (Log (Y i (T k ))−Log (Y i (T k−1 )) by (Log (Y s (T k ))−Log (Y s (T k−1 )), for example, as indicated in the following equation. 
     
       
         
           
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           Y 
                           i 
                         
                         , 
                         
                           Y 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               Y 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               Y 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               Y 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         Log 
                          
                         
                           ( 
                           
                             
                               Y 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   7 
                 
               
             
           
         
       
     
     In the Equation 7, Log (Y s (T k )) represents a logarithm of Y s (T k ), Log (Y s (T k−1 )) represents a logarithm of Y s (T k−1 ), Log (Y i (T k )) represents a logarithm of Y i (T k ), and Log (Y i (T k−1 )) represents a logarithm of Y i (T k−1 ). 
     In the Equation 7, Y s (T k ) represents the light reception signal  19 A (luminance information) of the reference pixel at the time T k , and corresponds to the latest luminance information in the luminance information of the reference pixel. Y s (T k−1 ) represents the light reception signal  19 A (luminance information) of the reference pixel at the time T k−1 (&lt;time T k ), and corresponds to the non-latest luminance information in the luminance information of the reference pixel. Y i (T k ) represents the light reception signal  19 A (luminance information) of the i th  dummy pixel  18  at the time T k , and corresponds to the latest luminance information in the luminance information of the i th  dummy pixel  18  (non-reference pixel). Y i (T k−1 ) represents the light reception signal  19 A (luminance information) of the i th  dummy pixel  18  at the time T k−1 , and corresponds to the non-latest luminance information in the luminance information of the i th  dummy pixel  18  (non-reference pixel). The relationship between the time T k−1  and the time T k  is, for example, represented by the following equation. 
         T   k   =T   k−1   +ΔT   2   Equation 8
 
     In the Equation 8, ΔT 2  represents a sampling period. Here, the sampling period ΔT 2  indicates, for example, a cycle in which the measurement signal processing circuit  27  derives the value of the denominator and the value of the numerator on the right side of the Equation 7. The measurement signal processing circuit  27  sets the sampling period ΔT 2  to be constant at any time. 
     For example, as illustrated in  FIG. 17 , when the abscissa axis indicates the ratio (Y i /Y s ) of the initial luminance Y i  of each dummy pixel  16  to the initial current Y s  of the reference pixel, the power coefficient n(Y i , Y s ) derived in the manner described above draws a rightward rising curve which increases with an increase of the initial luminance Y i , at the time T k . In addition, as can be obviously seen from the Equation 7, the power coefficient n(Y i , Y s ) is 1 in Y s /Y s . 
     Next, with reference to  FIGS. 18 to 24 , the deriving method of the efficiency correction amount R y  used for correcting the video signal  20 A will be described. 
     (Initial Setting) 
     First, the initial setting will be described. The measurement signal processing circuit  27  sets one pixel in the plurality of dummy pixels  18  as the reference pixel. In this embodiment, the reference pixel is not change to another dummy pixel  18  (non-reference pixel), and the same dummy pixel  18  is always set as the reference pixel. 
     Next, from the light receiving element group  19 , the measurement signal processing circuit  27  obtains the light reception signal  19 A at the times T 1  and T 2 . Specifically, from the light receiving element group  19 , the measurement signal processing circuit  27  obtains the light reception signal  19 A of the reference pixel as being one pixel in the plurality of dummy pixels  18 , at the times T 1  and T 2 . Further, from the light receiving element group  19 , the measurement signal processing circuit  27  obtains the light reception signal  19 A of the plurality of non-reference pixels as being all the pixels except the reference pixel in the plurality of dummy pixels  18 , at the times T 1  and T 2 . Next, the measurement signal processing circuit  27  derives, from the luminance information of the reference pixel, the efficiency deterioration information (Log (Y s (T 2 ))−Log (Y s (T 1 ))) of the reference pixel, and derives, from the luminance information of each non-reference pixel, the efficiency deterioration information (Log (Y i (T 2 ))−Log (Y i (T 1 ))) of each non-reference pixel. 
     Next, from the efficiency deterioration information of the reference pixel, and the efficiency deterioration information of each non-reference pixel, the measurement signal processing circuit  27  derives the power coefficient n(Y i , Y s ) of the luminance information of each non-reference pixel to the luminance information of the reference pixel at the time T 2 . Next, from the luminance information of the reference pixel, the measurement signal processing circuit  27  derives an efficiency deterioration function F s (t) representing the temporal change of the luminance of the reference pixel at the time T 2 . Further, from the efficiency deterioration function F s (t) and the power coefficient n(Y 1 , Y s ), the measurement signal processing circuit  27  derives an efficiency deterioration function F, (t) representing the temporal change of the luminance of each non-reference pixel, at the time T 2 . In this manner, the measurement signal processing circuit  27  derives the efficiency deterioration functions F s (t), and F i (t) at the time T 2  by using the initial luminance information. 
     (Data Update) 
     Next, the data update will be described. From the light receiving element group  19 , the measurement signal processing circuit  27  obtains the light reception signal  19 A of the reference pixel, and the light reception signal  19 A of the plurality of non-reference pixels at the times T k−1  and T k . The value (measurement value) of the light reception signal  19 A of the reference pixel at this time is regarded as Y s1  (refer to  FIG. 18 ). Next, from the efficiency deterioration function F s (t) at the time T k−1 , the measurement signal processing circuit  27  predicts the luminance information of the reference pixel at the time T k . The prediction value at this time is regarded as Y s2  (refer to  FIG. 18 ). Next, from the comparison between the measurement value Y s1  and the prediction value Y s2 , the measurement signal processing circuit  27  determines whether or not the measurement value Y s1  and the prediction value Y s2  are coincident with each other. As a result, for example, in the case where the measurement value Y s1  and the prediction value Y s2  are coincident with each other, the measurement signal processing circuit  27  regards the efficiency deterioration function F s (t) at the time T k−1  as the efficiency deterioration function F s (t) at the time T k . On the other hand, for example, in the case where the measurement signal processing circuit  27  determines that the measurement value Y s1  is different from the prediction value Y s2  based on the comparison between the measurement value Y s1  and the prediction value Y s2 , the measurement signal processing circuit  27  derives the efficiency deterioration function F s (t) at the time T k  from the luminance information of the reference pixel. 
     Next, from the luminance information of the reference pixel, the measurement signal processing circuit  27  derives the efficiency deterioration information (Log (Y i (T k ))−Log (Y i (T k−1 ))) of the reference pixel. Further, from the luminance information of the plurality of non-reference pixels, the measurement signal processing circuit  27  derives the efficiency deterioration information (Log (Y i (T k ))−Log (Y i (T k−1 ))) of each non-reference pixel. Next, from the efficiency deterioration information of the reference pixel, and the efficiency deterioration information of each non-reference pixel, the measurement signal processing circuit  27  derives the power coefficient n(Y i , Y s ) at the time T k . 
     Next, the measurement signal processing circuit  27  updates the parameters (for example, p 1 , p 2 , . . . , pm) of the efficiency deterioration function F s (t) at the time T k−1  to parameters (for example, p 1 ′, p 2 ′, . . . , pm′) of the efficiency deterioration function F s (t) at the time T k  (refer to  FIG. 19 ). In other words, the measurement signal processing circuit  27  updates the parameters of the efficiency deterioration function F s (t) in accordance with the latest luminance information (Y s (T k )) in the luminance information of the reference pixel, and the non-latest luminance information (Y s (T k−1 )) in the luminance information of the reference pixel. The measurement signal processing circuit  27  stores, for example, the parameters of the newly-obtained efficiency deterioration function F s (t) in the storage circuit  28 . 
     Next, from the efficiency deterioration function F s (t) at the time T k  (refer to  FIG. 20 ), and the power coefficient n(Y i , Y s ) (refer to  FIG. 21 ), the measurement signal processing circuit  27  derives the efficiency deterioration function F i (t) at the time T k  (refer to  FIG. 22 ). Specifically, the measurement signal processing circuit  27  derives the efficiency deterioration function F i (t) at the time T k  by using the following equation. 
         F   i ( t )= F   s ( t ) n(Yi,Ys)   Equation 9
 
     Next, the measurement signal processing circuit  27  updates the parameters of the efficiency deterioration function F i (t) of each non-reference pixel at the time T k−1  to the parameters of the efficiency deterioration function F i (t) of each non-reference pixel at the time T k . The measurement signal processing circuit  27  stores, for example, the parameters of the newly-obtained efficiency deterioration function F i (t) in the storage circuit  28 . 
     (Prediction of Efficiency Deterioration Ratio) 
     Next, the measurement signal processing circuit  27  predicts the efficiency deterioration ratio of each display pixel  13  during the time until the next sampling period comes. Specifically, from the efficiency deterioration function F s (t), the efficiency deterioration function F i (t), and the history of the video signal  20 A of each display pixel  13 , the measurement signal processing circuit  27  derives the light emission accumulation time T xy  of each display pixel  13  at the reference luminance. The measurement signal processing circuit  27  obtains, for example, the light emission accumulation time T xy  of each display pixel  13  at the reference luminance as will be described below. 
       FIG. 23  schematically illustrates the deriving process of the light emission accumulation time T xy  of each display pixel  13  at the reference luminance. For example, as illustrated in  FIG. 23 , it is assumed that the luminance of a certain display pixel  13  is changed as the certain display pixel  13  emits light with the initial luminance Y 1  during the time T=0 to t 1 , emits light with the initial luminance Y 2  during the time T=t 1  to t 2 , and emits light with the initial luminance Y n  during the time T=t 2  to t 3 . At this time, in a narrow sense, the luminance of this display pixel  13  is deteriorated along the deterioration curve of the initial luminance Y 1  during the time T=0 to t 1 , deteriorated along the deterioration curve of the initial luminance Y 2  during the time T=t 1  to t 2 , and deteriorated along the deterioration curve of the initial luminance Y n  during the time T=t 2  to t 3 . As a result, it is assumed that the luminance of this display pixel  13  is deteriorated to 48%, for example, as illustrated in  FIG. 23 . Therefore, by obtaining the time when the deterioration ratio in the efficiency deterioration curve (F s (t)) of the reference pixel becomes 48%, it may be possible to obtain the light emission accumulation time T xy  of each display pixel  13  at the reference luminance. In this manner, by tracking the efficiency deterioration curve in each gray scale in accordance with the intensity (gray scale) of the input signal, it may be possible to obtain the light emission accumulation time T xy  of each display pixel  13  at the reference luminance, and the efficiency deterioration ratio of each display pixel  13 . 
     (Derivation of Correction Amount) 
     Next, from the obtained light emission accumulation time T xy  (or the predicted efficiency deterioration ratio of each display pixel  13 ), and the gamma characteristic of the display panel  10 , the measurement signal processing circuit  27  derives the correction amount to the video signal. The measurement signal processing circuit  27  obtains the correction amount to the video signal, for example, as will be described below. 
       FIG. 24  illustrates an example of the relationship between the gray scale (value of the video signal  20 A), and the luminance at T=0, and T xy . The gray scale-luminance characteristic at T=0 is a so-called gamma characteristic. The gray scale-luminance characteristic at T=T xy  is obtained by attenuating the luminance to 48% for all the gray scales with respect to the gamma characteristic. Here, in a certain display pixel  13 , when the value of the video signal  20 A is S xy , it can be seen that the luminance of this display pixel  13  has a value corresponding to a white circle in the figure in the initial state. In other words, when the light emission accumulation time T xy  is passed from the initial state, it is predictable that the luminance of this display pixel  13  has a value obtained by attenuating the luminance in the initial state to 48%. 
     Thus, the measurement signal processing circuit  27  derives the efficiency correction amount R y  to be subjected to the video signal  20 A so that the luminance when the light emission accumulation time T xy  is passed from the initial state is identical to the luminance in the initial state. Specifically, the measurement signal processing circuit  27  derives the efficiency correction amount R y  by using the following equation. 
     
       
         
           
             
               
                 
                   
                     R 
                     Y 
                   
                   - 
                   
                     G 
                     Y 
                     
                       1 
                       r 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   10 
                 
               
             
           
         
       
     
     In the Equation 10, G y  represents a luminance correction gain, and it is 1/0.48 in the example above. 
     Finally, the measurement signal processing circuit  27  stores the efficiency correction amount R y  as the correction information  27 A in the storage circuit  28 . In this manner, the measurement signal processing circuit  27  corrects the deterioration of the light emission efficiency caused by the deterioration of the organic EL element  17  included in each dummy pixel  18 . 
     (Operations and Effects) 
     Next, operations and effects of the display device  1  of this embodiment will be described. The video signal  20 A and the synchronization signal  20 B are input to the display device  1 . Then, each display pixel  13  is driven by the signal line drive circuit  23  and the scanning line drive circuit  24 , and a video in response to the video signal  20 A of each display pixel  13  is displayed on the display region  12 . Meanwhile, signal voltages V sigi  (constant value) having magnitudes different from each other are applied to the signal lines DTL′ connected to each dummy pixel  16  by the dummy pixel drive circuit  25 , and each dummy pixel  16  emits light with gray scales different from each other. As a result, the current signal  26 A corresponding to the current value flowing through the organic EL element  14  of each dummy pixel  16  is output from the current measurement circuit  26 . Further, when each dummy pixel  18  is driven by the dummy pixel drive circuit  25 , the light receiving element group  19  is also driven at the same time. Therefore, the constant currents having magnitudes different from each other are allowed to flow through each dummy pixel  18 , each dummy pixel  18  emits light with the luminance according to the magnitude of the constant current, and the light emitted from each dummy pixel  18  is detected in the light receiving element group  19 . As a result, the light reception signal  19 A corresponding to the light emitted from each dummy pixel  18  is output from the light receiving element group  19 . Next, the following process is performed by the measurement signal processing circuit  27 . 
     In other words, the power coefficient n(S i , S s ) of the current signal  26 A (current information) of the non-reference pixel to the current signal  26 A (current information) of the reference pixel is derived from the current signal  26 A. Next, the current deterioration function I s (t) of the reference pixel is derived from the current information of the reference pixel, and the current deterioration function I i (t) of the non-reference pixel is derived from the current deterioration function I s (t) and the power coefficient n(S i , S s ). Next, by utilizing the current deterioration function I s (t), the current deterioration function I i (t), and the history of the video signal  20 A of each display pixel  13 , the light emission accumulation time T xy  of each display pixel  13  at the reference current, and the current deterioration ratio of each display pixel  13  are predicted. Next, the current correction amount R I  is applied to the video signal  20 A of each display pixel  13  so that the luminance when the light emission accumulation time T xy  is passed from the initial state is identical to the luminance in the initial state. 
     Further, the power coefficient n(Y i , Y s ) of the light reception signal  19 A (luminance information) of the non-reference pixel to the light reception signal  19 A (luminance information) of the reference pixel is derived from the light reception signal  19 A. Next, the efficiency deterioration function F s (t) of the reference pixel is derived from the luminance information of the reference pixel, and the efficiency deterioration function F j  (t) of the non-reference pixel is derived from the efficiency deterioration function F s (t) and the power coefficient n(Y i , Y s ). Next, by utilizing the efficiency deterioration function F s (t), the efficiency deterioration function F i (t), and the history of the video signal  20 A of each display pixel  13 , the light emission accumulation time T xy  of each display pixel  13  at the reference current, and the efficiency deterioration ratio of each display pixel  13  are predicted. Next, the efficiency correction amount R y  is applied to the video signal  20 A of each display pixel  13  so that the luminance when the light emission accumulation time T xy  is passed from the initial state is identical to the luminance in the initial state. 
     In this manner, in this embodiment, by utilizing the current deterioration function I s (t), the current deterioration function I i (t) obtained from the current deterioration function I s (t) and the power coefficient n(S i , S s ), and the history of the video signal  20 A of each display pixel  13 , the current deterioration ratio of each display pixel  13  is predicted. Further, by utilizing the efficiency deterioration function F s (t), the efficiency deterioration function F i (t) obtained from the efficiency deterioration function F s (t) and the power coefficient n(Y i , Y s ), and the history of the video signal  20 A of each display pixel  13 , the efficiency deterioration ratio of each display pixel  13  is predicted. Thereby, it may be possible to predict the efficiency deterioration of each display pixel  13  with a high accuracy, and thus it may be possible to apply the appropriate correction amount (the current correction amount R I  and the efficiency correction amount R y ) to the video signal  20 A of each display pixel  13  so that the luminance of each display pixel  13  is identical to the luminance in the initial state. As a result, it may be possible to accurately prevent seizure. 
     Further, in this embodiment, it may be possible to predict the current deterioration ratio and the efficiency deterioration ratio of each display pixel  13  by using the data (S s (T k ), S s (T k−1 ), Y s (T k ), and Y s (T k−1 )) at the time of observation. Therefore, it may be possible to predict the efficiency deterioration of each display pixel with a high accuracy without an observation for a long time. Therefore, the predicting method of this embodiment is extremely practical. Further, in this embodiment, since it may be possible to predict the efficiency deterioration ratio of each display pixel  13  by using the data at the time of observation, it may be possible to suppress and reduce the memory amount and the calculation amount which are necessary for the update. 
     2. Modification 
     In the foregoing embodiment, although the correction by using both the current correction amount R I  and the efficiency correction amount R y  is performed on the video signal  20 A of each display pixel  13 , the correction by using only one of the current correction amount R I  and the efficiency correction amount R y  may be performed. 
     Further, in the foregoing embodiment, although all the dummy pixels  16  of the initial currents S 1  to S n  are composed of a single pixel of a set of organic EL elements  14 R,  14 G, and  14 B, each dummy pixel  16  (low-current pixel) in which the initial current S i  is low may be composed of a plurality of dummy pixels (second dummy pixels) (not illustrated in the figure). In this case, from the average value of the currents flowing through the organic EL elements  14  which are connected to the plurality of second dummy pixels, the measurement signal processing circuit  27  may derive the denominator or the numerator on the right side of the Equation 2. Therefore, it may be possible to make a measurement error small in the dummy pixel  16  having the low luminance. Thus, it may be possible to predict the efficiency deterioration of the display pixel  13  having the low luminance with a high accuracy. As a result, it may be possible to more accurately prevent the seizure. 
     Further, in the foregoing embodiment, although all the dummy pixels  18  of the initial luminances Y 1  to Y n  are composed of a single pixel of a set of organic EL elements  17 R,  17 G, and  17 B, each dummy pixel  18  (low-luminance pixel) in which the initial luminance Y i  is low may be composed of a plurality of dummy pixels (third dummy pixels) (not illustrated in the figure). In this case, from the average value of the luminance of the plurality of third dummy pixels, the measurement signal processing circuit  27  may derive the denominator or the numerator on the right side of the Equation 7. Therefore, it may be possible to make a measurement error small in the dummy pixel  18  having the low luminance. Thus, it may be possible to predict the efficiency deterioration of the display pixel  13  having the low luminance with a high accuracy. As a result, it may be possible to more accurately prevent the seizure. 
     In the foregoing embodiment, although the specific dummy pixel  16  is set as the reference pixel at any time, the dummy pixel  16  which has been set as the non-reference pixel may be set as the reference pixel, if necessary. For example, when the measurement signal processing circuit  27  detects that the current flowing through the organic EL element  14  which is connected to the reference pixel has a value equal to or lower than a predetermined value, the measurement signal processing circuit  27  excludes the dummy pixel  16  which has been set as the reference pixel so far, and sets one pixel in the plurality of non-reference pixels as the new reference pixel. Thereafter, the measurement signal processing circuit  27  derives the denominator and the numerator on the right side of the Equation 2 in the same manner as heretofore. In this case, even in the case where a failure is generated in the reference pixel, it may be possible to continue to predict the efficiency deterioration. Therefore, it may be possible to improve the reliability of the prediction of the efficiency deterioration. 
     Further, in the foregoing embodiment, although the specific dummy pixel  18  is set as the reference pixel at any time, the dummy pixel  18  which has been set as the non-reference pixel may be set as the reference pixel, if necessary. For example, when the measurement signal processing circuit  27  detects that the luminance of the reference pixel has a value equal to or lower than a predetermined value, the measurement signal processing circuit  27  excludes the dummy pixel  18  which has been set as the reference pixel so far, and sets one pixel in the plurality of non-reference pixels as the new reference pixel. Thereafter, the measurement signal processing circuit  27  derives the denominator and the numerator on the right side of the Equation 7 in the same manner as heretofore. In this case, even in the case where a failure is generated in the reference pixel, it may be possible to continue to predict the efficiency deterioration. Therefore, it may be possible to improve the reliability of the prediction of the efficiency deterioration. 
     In the foregoing embodiment, although the sampling period ΔT 1  is constant at any time, it may be variable. For example, the measurement signal processing circuit  27  may change the sampling period ΔT 1  according to the light emission accumulation time of the plurality of dummy pixels  16 . In that case, for example, when the light emission accumulation time T xy  is a long time, and the efficiency deterioration is hardly generated, it may be possible to extend the sampling period ΔT 1 . Therefore, it may be possible to suppress and reduce the calculation amount which is necessary for the update. 
     In the foregoing embodiment, although the sampling period ΔT 2  is constant at any time, it may be variable. For example, the measurement signal processing circuit  27  may change the sampling period ΔT 2  according to the light emission accumulation time of the plurality of dummy pixels  18 . In that case, for example, when the light emission accumulation time T xy  is a long time, and the efficiency deterioration is hardly generated, it may be possible to extend the sampling period ΔT 2 . Therefore, it may be possible to suppress and reduce the calculation amount which is necessary for the update. 
     In the foregoing embodiment, although the power coefficient n(S i , S s ) is derived by using the Equation 2, for example, the power coefficient n(S i , S s ) may be derived by using the following equation. 
     
       
         
           
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           S 
                           i 
                         
                         , 
                         
                           S 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           S 
                           s 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                       
                         
                           S 
                           i 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                     
                     × 
                     
                       
                         
                            
                           
                              
                             t 
                           
                         
                          
                         
                           ( 
                           
                             
                               S 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       
                         
                            
                           
                              
                             t 
                           
                         
                          
                         
                           ( 
                           
                             
                               S 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   11 
                 
               
             
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           S 
                           i 
                         
                         , 
                         
                           S 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           S 
                           s 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                       
                         
                           S 
                           i 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                     
                     × 
                     
                       
                         
                           
                             S 
                             i 
                           
                            
                           
                             ( 
                             
                               T 
                               k 
                             
                             ) 
                           
                         
                         - 
                         
                           
                             S 
                             i 
                           
                            
                           
                             ( 
                             
                               T 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             S 
                             s 
                           
                            
                           
                             ( 
                             
                               T 
                               k 
                             
                             ) 
                           
                         
                         - 
                         
                           
                             S 
                             s 
                           
                            
                           
                             ( 
                             
                               T 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   12 
                 
               
             
           
         
       
     
     In the Equation 11, the denominator in the second term on the right side represents the deterioration rate of the reference pixel at the time T k . The numerator in the second term on the right side represents the deterioration rate of the non-reference pixel at the time T k . In the Equation 12, the second term on the right side is obtained by dividing the deterioration rate of the reference pixel at the time T k  by the deterioration rate of the non-reference pixel at the time T k . 
     In the case where the power coefficient n(S i , S s ) is derived by using the Equation 11 or the Equation 12, it may be possible to derive the power coefficient n(S i , S s ) only with the four arithmetic operations, and calculation of a logarithm like when the Equation 2 is used is not necessary. Therefore, it may be possible to suppress and reduce the calculation amount, in comparison with the case where the power coefficient n(S i , S s ) is derived by using the Equation 2. 
     In the foregoing embodiment, although the power coefficient n(Y i , Y s ) is derived by using the Equation 7, for example, the power coefficient n(Y i , Y s ) may be derived by using the following equation. 
     
       
         
           
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           Y 
                           i 
                         
                         , 
                         
                           Y 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           Y 
                           s 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                       
                         
                           Y 
                           i 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                     
                     × 
                     
                       
                         
                            
                           
                              
                             t 
                           
                         
                          
                         
                           ( 
                           
                             
                               Y 
                               i 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                       
                         
                            
                           
                              
                             t 
                           
                         
                          
                         
                           ( 
                           
                             
                               Y 
                               s 
                             
                              
                             
                               ( 
                               
                                 T 
                                 k 
                               
                               ) 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   13 
                 
               
             
             
               
                 
                   
                     n 
                      
                     
                       ( 
                       
                         
                           Y 
                           i 
                         
                         , 
                         
                           Y 
                           s 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           Y 
                           s 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                       
                         
                           Y 
                           i 
                         
                          
                         
                           ( 
                           
                             T 
                             k 
                           
                           ) 
                         
                       
                     
                     × 
                     
                       
                         
                           
                             Y 
                             i 
                           
                            
                           
                             ( 
                             
                               T 
                               k 
                             
                             ) 
                           
                         
                         - 
                         
                           
                             Y 
                             i 
                           
                            
                           
                             ( 
                             
                               T 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             Y 
                             s 
                           
                            
                           
                             ( 
                             
                               T 
                               k 
                             
                             ) 
                           
                         
                         - 
                         
                           
                             Y 
                             s 
                           
                            
                           
                             ( 
                             
                               T 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   14 
                 
               
             
           
         
       
     
     In the Equation 13, the denominator in the second term on the right side represents the deterioration rate of the reference pixel at the time T k . The numerator in the second term on the right side represents the deterioration rate of the non-reference pixel at the time T k . In the Equation 14, the second term on the right side is obtained by dividing the deterioration rate of the reference pixel at the time T k  by the deterioration rate of the non-reference pixel at the time T k . 
     In the case where the power coefficient n(Y i , Y s ) is derived by using the Equation 13 or the Equation 14, it may be possible to derive the power coefficient n(Y i , Y s ) only with the four arithmetic operations, and calculation of a logarithm like when the Equation 7 is used is not necessary. Therefore, it may be possible to suppress and reduce the calculation amount, in comparison with the case where the power coefficient n(Y i , Y s ) is derived by using the Equation 7. 
     3. Application Examples 
     Hereinafter, a description will be made on application examples of the display device  1  described in the foregoing embodiment and its modification. The display device  1  of the foregoing embodiment and the like is applicable to display devices in electronic appliances in various fields, in which a video signal input from outside, or a video signal generated inside the display device is displayed as an image or a video, such as a television device, a digital camera, a notebook personal computer, a mobile terminal device such as a mobile phone, and a video camera. 
     First Application Example 
       FIG. 25  illustrates an appearance of a television device to which the display device  1  of the foregoing embodiment and the like is applied. The television device includes, for example, a video display screen section  300  including a front panel  310  and a filter glass  320 . The video display screen section  300  is composed of the display device  1  of the foregoing embodiment and the like. 
     Second Application Example 
       FIGS. 26A and 26B  illustrate an appearance of a digital camera to which the display device  1  of the foregoing embodiment and the like is applied. The digital camera includes, for example, a light emitting section  410  for a flash, a display section  420 , a menu switch  430 , and a shutter button  440 . The display section  420  is composed of the display device  1  of the foregoing embodiment and the like. 
     Third Application Example 
       FIG. 27  illustrates an appearance of a notebook personal computer to which the display device  1  of the foregoing embodiment and the like is applied. The notebook personal computer includes, for example, a main body  510 , a keyboard  520  for operation of inputting characters and the like, and a display section  530  for displaying an image. The display section  530  is composed of the display device  1  of the foregoing embodiment and the like. 
     Fourth Application Example 
       FIG. 28  illustrates an appearance of a video camera to which the display device  1  of the foregoing embodiment and the like is applied. The video camera includes, for example, a main body  610 , a lens  620  for capturing an object provided on the front side face of the main body  610 , a start/stop switch in capturing  630 , and a display section  640 . The display section  640  is composed of the display device  1  of the foregoing embodiment and the like. 
     Fifth Application Example 
       FIGS. 29A to 29G  illustrate an appearance of a mobile phone to which the display device  1  of the foregoing embodiment and the like is applied. In the mobile phone, for example, an upper package  710  and a lower package  720  are jointed by a joint section (hinge section)  730 . The mobile phone includes a display  740 , a sub-display  750 , a picture light  760 , and a camera  770 . The display  740  or the sub-display  750  is composed of the display device  1  of the foregoing embodiment and the like. 
     The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-217183 filed in the Japanese Patent Office on Sep. 18, 2009, the entire contents of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.