Patent Publication Number: US-2010123740-A1

Title: Display adjusting circuit for organic electroluminescence panel, display adjusting circuit, and display device

Description:
TECHNICAL FIELD 
     The present invention relates to a display adjusting circuit for an organic electroluminescence panel, a display adjusting circuit, and a display device. 
     BACKGROUND ART 
     For a display device in the shape of a panel, an organic electroluminescence (OLED) panel is used. This organic electroluminescence panel has a plurality of organic electroluminescence elements arranged in a matrix pattern, and one of the organic electroluminescence elements corresponds to one pixel (a pixel for any of red, green, and blue). 
       FIG. 7  shows, in principle, a driving circuit for one organic electroluminescence element, where a transistor (TFT) Q for driving and an organic electroluminescence element D are connected in series to a power source +VDD and a signal voltage V of a video signal is supplied to the transistor Q. 
     Therefore, because the signal voltage V is converted into a signal current I by the transistor Q and this signal current I flows through the organic electroluminescence element D, light L at the luminance (light intensity) corresponding to the magnitude of the signal current I is output from the organic electroluminescence element D, and as a result, a pixel at the luminance corresponding to the signal voltage V is displayed. 
     Thus, in a display device using a organic electroluminescence panel, an organic electroluminescence element D itself emits light, so that a backlight like a liquid-crystal display device is unnecessary and making thinner is possible. Also, because its light-emitting is caused by excitons within an organic semiconductor, the efficiency of energy conversion is high, and the necessary voltage for light-emitting itself can be lowered to about a few volts. 
     Moreover, the response speed is fast, the viewing angle is wide, and also colour reproducing range is wide. Also, the magnetism will not have any effect, as in a Braun Tube (a receiving tube). Besides, the organic electroluminescence is also called as an organic LED, OLED, etc. 
     Also, prior art documents include the following one, for example. 
     [Patent Document] JP 2005-300929 (A) 
     DISCLOSURE OF THE INVENTION 
     Object to be Achieved by the Invention 
     Now, in a display device using an organic electroluminescence panel, in order to reproduce an image in high definition, various adjustments are necessary for video signals. In the Patent Document 1, there is described a display device, in which a current detecting means is provided for an organic electroluminescence panel, and in which degradation of luminance due to temporal changes and the like is compensated by adjusting a potential difference in accordance with a detected current. 
     However, in a organic electroluminescence panel, various adjustments may be necessary for managing temporal changes in white balance and colour temperature, protecting from an overflowed current, and preventing and reducing sticking, for example, and in such a case, it is demanded to more simply and precisely detect the driving state of the organic electroluminescence panel, and perform adjustments and controls. 
     The present invention enables detecting more simply and precisely the driving state of an organic electroluminescence panel and performing various adjustments and controls in order to keep a better display on a display device using the organic electroluminescence panel. 
     Solution for Achieving the Problems 
     With the present invention, there is provided 
     a display adjusting circuit for performing adjustment for display on a video signal to be supplied to an organic electroluminescence panel, the display adjusting circuit of the organic electroluminescence panel, including 
     a linear gamma circuit where a video signal on which a predetermined gamma adjustment has been performed is supplied to be converted into a video signal with a linear gamma characteristic by cancelling the gamma adjustment of the supplied video signal and to be output, 
     an adjusting circuit to which the video signal output from the linear gamma circuit is supplied, and 
     a panel gamma circuit where the video signal output from the adjusting circuit is supplied to be converted into a video signal with a gamma characteristic corresponding to a gamma characteristic of the organic electroluminescence panel and to be output, 
     the adjusting circuit including 
     a detecting unit for detecting a driving state or a driving history of the organic electroluminescence panel from the supplied video signal, 
     an adjusting unit for performing adjustment on the video signal supplied to the organic electroluminescence panel by a detecting output of the detecting unit. 
     In a display adjusting circuit according the present invention, the gamma characteristic of an input signal is converted into a video signal with a linear input/output characteristic, the driving state of the organic electroluminescence panel is detected based on signal information with the input/output characteristic converted into linear, and a video signal to be output is adjusted by use of the detecting result 
     Therefore, a value of the signal information with the input/output characteristic converted into linear corresponds to a light output of an element of the organic electroluminescence panel, namely the driving state of the element. 
     ADVANTAGE OF THE INVENTION 
     According to the invention, because a driving state or a driving history of the organic electroluminescence panel can be detected readily from the signal information with the input/output characteristic converted into linear, a proper adjustment on a video signal is performed by relatively small sized circuitry configuration by use of the detection result, and an image display in high definition can be held on the organic electroluminescence panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system diagram according to an embodiment of the present invention. 
         FIG. 2A  is an illustration that shows an example of a schematic configuration of a display device according to an embodiment of the present invention. 
         FIG. 2B  is an illustration that shows an example of a pixel circuit of the display device according to an embodiment of the present invention. 
         FIG. 3  is an illustration that shows an example of the cross-sectional configuration of the main part in the display area of the display device shown in  FIG. 2A . 
         FIG. 4  is a characteristic diagram for explaining the operation of the circuit in  FIG. 1 . 
         FIG. 5  is a characteristic diagram for explaining the operation of the circuit in  FIG. 1 . 
         FIG. 6  is a characteristic diagram for explaining the operation of the circuit in  FIG. 1 . 
         FIG. 7  is a connection diagram for explaining the characteristic of an organic electroluminescence element. 
         FIG. 8  is a characteristic diagram for explaining the operation of the element in  FIG. 7 . 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  signal source 
           10  display adjusting circuit 
           11  orbit circuit 
           12  linear gamma circuit 
           13  panel gamma circuit 
           14  dither circuit 
           15  output converting circuit 
           20  adjusting circuit 
           21  pattern generator 
           22  colour temperature adjusting circuit 
           23  long-term white balance adjusting circuit 
           24  ABL circuit 
           25  partial sticking adjusting circuit 
           26  luminescence unevenness adjusting circuit 
           32  communication circuit 
           33  still image detecting circuit 
           34  white balance detecting circuit 
           35  average luminance detecting circuit 
           36  gate pulse circuit 
           42  organic electroluminescence panel 
           43  current detecting circuit 
           51  micro computer for control 
           52  non volatile memory 
           100  display device 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 2  is an illustration that shows an example of a schematic configuration of a display device  100  according to an embodiment of the present invention, and  FIG. 2B  is an illustration that shows an example of a pixel circuit of the display device  100  according to an embodiment of the present invention. Also,  FIG. 3  is an illustration that shows an example of the cross-sectional configuration of the main part in the display area of the display device  100  shown in  FIG. 2A . Here will be described an embodiment in which the present invention is applied to the display device  100  in active matrix mode using organic electroluminescence elements  11  for luminescence elements. 
     As shown in  FIG. 2A , on a substrate  12  of the display device  100 , there are designed a display area  12   a  and its surrounding area  12   b . The display area  12   a  has a plurality of scan lines  21  and a plurality of signal lines  23  arranged longitudinally and transversely, and configured as a pixel array in which one pixel a is provided in correspondence to each cross. One of organic electroluminescence elements  11 R ( 11 ),  11 G,  11 B shown in  FIG. 3  is provided for each of these pixels a. Also in the surrounding area  12   b , there are arranged a scan line driving circuit b for scan-driving the scan lines  21 , and a signal line driving circuit c for supplying signal lines  23  with video signals (i.e., input signals) according to luminance information. 
     As shown in  FIG. 2B , the pixel circuit provided for each pixel a is configured with one of each of the organic electroluminescence elements  11 R ( 11 ) (red luminescence element),  11 G (green luminescence element), and  11 B (blue luminescence element), a driving transistor Tr 1 , a writing transistor (sampling transistor) Tr 2 , and a hold capacitance Cs. Then by driving by the scan line driving circuit b, a video signal that has been written from a signal line  23  via the writing transistor (sampling transistor) Tr 2  is held at the hold capacitance Cs, a current depending on the held signal amount is supplied to each organic electroluminescence element  11 R ( 11 ),  11 G, or  11 B, and the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B emit light at the luminance depending on this current value. 
     Besides, the above configuration of the pixel circuit is just one example after all, and as necessary, a capacitance element may be provided within the pixel circuit, or a further plurality of transistors may be provided to configure the pixel circuit. Also, in the surrounding area  2   b , a necessary driving circuit is added according to changes in the pixel circuit. 
     &lt;Cross-Sectional Configuration Example of Organic Electroluminescence Panel&gt; 
     Next, with reference to  FIG. 3 , the cross-sectional configuration of the main part in the display area of the display device  100  will be described. 
     In the display area of the substrate  12 , where the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B are provided, the driving transistors, the writing transistors, the scan lines, and the signal lines are provided to configure the above-mentioned pixel circuit (see  FIG. 2 ), and a dielectric film is provided to cover these, though their depictions are omitted here. 
     On the substrate  12  covered with this dielectric film, the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B are arrayed. Each of the organic luminescence elements  11 R ( 11 ),  11 G, and  11 B is configured as a top surface luminescence type element by which light is obtained from the opposite side of the substrate  12 . 
     An anode  13  of each of the electroluminescence elements  11 R ( 11 ),  11 G, and  11 B is patterned for each element. Each anode  13  is connected to the driving transistor of the pixel circuit via a connecting through-hole formed in the dielectric film which covers the surface of the substrate  12 . 
     Each anode  13  has its peripheral part covered with the dielectric film  31 , and the centre parts of the anodes  13  are exposed by the opening parts provided in the dielectric film  31 . Then, in the configuration, organic layers  14  are patterned, covering the exposed parts of the anodes  13 , and a cathode  15  is provided as a shared layer covering each of the organic layers  14 . 
     As for the red luminescence element  11 R of these organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B, the organic layer  14  provided on the anode  13  has, for example, a hole inject layer  14   a , a hole transport layer  14   b , a red luminescence layer  14   c -R ( 14   c ) using a naphthacene derivative for a host material, and an electron transport layer  14   d , which are laminated in this order from the anode  13  side. 
     Also, the organic layer in the green luminescence element  11 G has, for example, in the order from the anode  13  side, a hole inject layer  14   a , a hole transport layer  14   b , a green luminescence layer  14   c -G, and an electron transport layer  14   d , which are laminated in such an order. Similarly, the organic layer in the blue luminescence element  11 B has, for example, in the order from the anode  13  side, a hole inject layer  14   a , a hole transport layer  14   b , a blue luminescence layer  14   c -B, and an electron transport layer  14   d , which are laminated in such an order. 
     Then, a plurality of the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B provided in the above manner is assumed to be covered with a protection film. Besides, this protection film is assumed to be provided to cover the whole display area for which the organic electroluminescence elements  11 R,  11  and  11 B are provided. 
     Here, each of the layers from the anodes  13  to the cathode  15  which configure the red luminescence element  11 R ( 11 ), the green luminescence element  11 G, and the blue luminescence element  11 B can be formed by a dry process, such as vacuum evaporation, ion beam (EB), molecular beam epitaxy (MBE), spattering, organic vapour phase deposition (OVPD), and the like. 
     Also, the organic layers can be formed by, in addition to the above processes, a wet process, for example, coating processes, such as laser transferring, spin coating, dipping, doctor blade process, eject coating, and spray coating, and printing processes, such as ink jet, offset printing, anastatic printing, gravure printing, screen printing, and micro-gravure coating. The dry process and the wet process may be combined, depending on the properties of each organic layer and each member. 
     Then, the organic layer  14  patterned for each of the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B in the above manner, is formed by evaporating and transferring with masks, for example. 
     The so formed display devices can be preferably used for a flat panel display of a wall hanging TV and for a flat illuminator, and can be applied to a light source of a copier, printer, and the like, and to a light source of a liquid-crystal display, meters, and the like, and to a display board, a sign illumination, and the like. 
     Also, in the above example, the explanation has been done with an active matrix type display in mind, but a display device according to an embodiment of the present invention can be, of course, applied to a passive matrix type display device. 
     Besides, in each of the organic electroluminescence elements  11 R ( 11 ),  11 G, and  11 B, the layers can be shared, except for the luminescence layers  14   c . Also, in the green luminescence elements  11 G and the blue luminescence elements  11 B, electron transport layers  14   d  made up of different materials may be provided to adapt to respective luminescence layers  14   c -G and  14   c -B. 
     (1) Example of Whole Configuration 
     When an image in high definition is reproduced by a display device using an organic electroluminescence panel, various adjustments are necessary for video signals. For the adjustments on video signals, there can be given examples, such as adjustment on variation in organic electroluminescence panels, adjustment on luminescence unevenness (uniformity of luminance) on the whole panel, adjustment on local luminescence unevenness, management on temporal changes of white balance and colour temperature, protection from an overflowed current, prevention and reduction of sticking, and the like. 
     Also, as shown in  FIG. 8A , an organic electroluminescence element D has the luminance (light intensity) L in proportion to a signal current I. However, when a signal voltage V is supplied to a transistor Q, the relation between the signal voltage V and the signal current I gets an exponential characteristic due to the characteristic of the transistor Q, as shown in  FIG. 8B . As a result, the relation between the signal voltage V and the luminance L of the organic electroluminescence element D gets an exponential characteristic, as shown in  FIG. 8C . 
     Therefore, for the display device using an organic electroluminescence panel, it is necessary to provide a circuit whose input/output characteristic is an exponential characteristic that is complementary to the characteristic of  FIG. 8C , as shown in  FIG. 8D , and to adjust the level of the signal voltage V of a video signal by this adjusting circuit so that the relation between the signal voltage V (before adjustment) and the luminance L gets linear; namely, for the display device using an organic electroluminescence panel, inverse gamma adjustment is necessary. 
     Then, it is preferable to set an adjustment value depending on an individual organic electroluminescence panel, because this inverse gamma adjustment varies depending on the variation of the characteristics of the transistors Q. Also, the inverse gamma adjustment may be realised by, for example, adaptively adjusting by the displayed location and the signal level in correspondence to the transistor Q for each pixel, and further, another functional block may be provided for adjusting by the displayed location and the signal level. 
     On the other hand, when a video signal for TV broadcasting or the like is supplied to a Braun tube, for example, it has been gamma-adjusted so that relation between its signal voltage and luminance gets linear. However, the characteristic of this gamma adjustment for a Braun tube is different from the characteristic ( FIG. 8D ) of the gamma adjustment that is necessary for an organic electroluminescence element. Therefore, for the display device using an organic electroluminescence panel, it is necessary to consider the difference between the characteristic of the gamma adjustment for a Braun tube and the characteristic of the gamma adjustment for an organic electroluminescence element. 
       FIG. 1  shows an example of a display adjusting circuit that execute the above-mentioned various adjustments, and its usage example; namely, in  FIG. 1 , the section  10  enclosed by the dashed line indicates the display adjusting circuit for definition, and this is configured to be, for example, an LSI, or an IC as one-chip IC by FPGA. Then, this IC (display adjusting circuit)  10  has terminal pins T 11 -T 15  for external connection. 
     Also, the reference numeral  1  indicates a signal source, such as a tuner circuit or a DVD player, and from this signal source  1 , a video signal (a signal of three primary colours: red; green; and blue) S 1  is taken. This video signal S 1  is a digital signal, and also a signal in a format similar to that of video signals for TV broadcasting. Therefore, as shown in  FIG. 4A , the video signal S 1  can be approximated to the characteristic as shown by Equation 1 below, for example, by being performed the gamma adjustment for a Braun tube, where, “L” in Equation 1 denotes the luminance of an object, and “V” denotes the signal voltage of the signal S 1 . Also, “γ1” in Equation 1 denotes a gamma value (e.g., γ1=approximately 2.2), “k1” denotes a constant, and “̂” denotes an operation sign representing an exponential. 
         L=k 1· V ̂(1/γ1)  (Equation 1) 
     Moreover, the reference numeral  42  indicates an organic electroluminescence panel for image display. The organic electroluminescence panel  42  has a transistor for driving for each organic electroluminescence element, as described with reference to  FIG. 7 , and also, as shown in  FIG. 8C , the luminescence characteristic can be approximated by Equation 2 below, where, “L” in Equation 2 denotes the luminance of the luminance of an organic electroluminescence element, and “V” denotes an input signal voltage. Also, “γ2” in Equation 2 denotes a gamma value, “k2” denotes a constant, and “̂” denotes an operation sign representing an exponential. Besides, the aspect ratio of the organic electroluminescence panel  42  is, for example, 16:9. 
         L=k 2· V̂γ 2  (Equation 2) 
     Also, the reference numeral  51  is a micro computer for control that controls adjustments by this display adjusting circuit  10  automatically or according to instructions from the outside. 
     Then, the video signal S 1  from the signal source  1  is supplied to an orbit circuit  11  through the terminal pin T 11  of the IC  10 . This orbit circuit  11  is a circuit for periodically deviating up/down and to the right/left the whole image displayed on the organic electroluminescence panel  42  in a slow speed so that viewers will not notice; namely, because of such a configuration, even if a still image or a image in the standard format (4:3) has been displayed to result in sticking, the outline of the sticking will be vague and indistinctive. Thus, from the orbit circuit  11 , a video signal S 11  is taken out with sticking reduced. 
     Subsequently, this video signal S 11  is supplied to a linear gamma circuit  12  to become a video signal S 12 . This linear gamma circuit  12  is configured to cancel the gamma characteristic of the video signal S 11 , so that, as shown in  FIG. 2B , it has a complemented input/output characteristic with the gamma characteristic given to the video signal S 11 . The complemented input/output characteristic is expressed by Equation 3 below, for example, where “k3” in Equation 3 denotes a constant. 
         S 12= k 3· S 11̂γ1  (Equation 3) 
     Therefore, from the linear gamma circuit  12 , as shown in  FIG. 4C , the video signal S 12  with characteristic in which the signal voltage V varies linearly to the luminance L of the object is output. Besides, at this point, the video signal S 12  is configured to be 14 bits for one sample, for example. 
     Then, this video signal S 12  is supplied to an adjusting circuit  20 . This adjusting circuit  20  has circuits  21 - 26  and executes the above-mentioned various adjustments, controlled by the micro computer  51 ; the details of this adjusting circuit  20  will be described in (2). Then, the adjusting circuit  20  outputs an adjusted video signal S 26 . Besides this video signal S 26  will be a signal that changes in linear to the luminance L as also shown in  FIG. 4C . 
     Then, this video signal S 26  is supplied to a panel gamma circuit  13  to become a video signal S 13 . This panel gamma circuit  13  is configured to cancel the gamma characteristic of the organic electroluminescence panel  42  by attaching a predetermined gamma characteristic to the video signal S 13 . Thus, the panel gamma circuit  13  has, as shown in  FIG. 4D , a complemented input/output characteristic (equal to the input/output characteristic in  FIG. 8D ) with the characteristic in  FIG. 8C . The complemented input/output characteristic is expressed by Equation 4 below, for example, where “k4” in Equation 4 denotes a constant. 
         S 13= k 4· S 26̂(1/γ2)  (Equation 4) 
     Therefore, from the panel gamma circuit  13 , as shown in  FIG. 4E , the video signal  13  with a gamma characteristic in which the relation of the luminance L of the organic electroluminescence panel  42  and the signal voltage becomes a linear relation is output. Besides, at this point, the video signal S 13  is configured to be 12 bits for one sample, for example. 
     This video signal S 13  is supplied to a dither circuit  14  to become a video signal S 14  on which a dither process is performed by 10 bits for one sample, for example. Also, this video signal S 14  is supplied to an output converting circuit  15  to format-converted into a video signal S 15  in the RSDS (registered trademark) format from the signal of the three primary colours. Then, this video signal S 15  is taken out to the terminal pin for output T 13 . 
     The video signal S 15  taken out to this terminal pin T 13  is supplied to a driving circuit  41  to be D/A-converted from a digital signal to an analogue signal, and then, supplied to the organic electroluminescence panel  42 . Therefore, the video signal S 1  supplied from the signal source  1  is displayed on the organic electroluminescence panel  42  as a coloured image. 
     (2) Configuration Example of Adjusting Circuit  20   
     The adjusting circuit  20  is configured with detecting units including circuits  33 - 35  and adjusting units including circuits  21 - 26 , and an adjustment is executed by these adjusting units  21 - 26  as follows. 
     Now, the video signal S 12  output from the linear gamma circuit  12  is supplied to a pattern generator circuit  21 . This pattern generator circuit  21  outputs the supplied video signal S 12  directly as a video signal S 21  in the case of normal viewing. However, When adjustments, tests, and the like are performed on this organic electroluminescence display device using the display adjusting circuit  10  and the organic electroluminescence panel  42 , a video signal for various adjustments or tests which is displayed as a test pattern or a colour bar is formed, and this signal is output as the video signal S 21  instead of the video signal S 12 . 
     Then, the video signal S 21  output from the pattern generator circuit  21  is supplied to a colour temperature adjusting circuit  22  to be converted into a video signal S 22  of a colour temperature set by a viewer, and then this video signal S 22  is supplied to a long-term white balance adjusting circuit  23 . This long-term white balance adjusting circuit  23  is configured to adjust temporal changes in white balance which occur at a long-term use of the organic electroluminescence panel  42 , and to output the video signal S 23  with its white balance adjusted. 
     This video signal S 23  as a result of the white balance adjustment is supplied to an ABL circuit  24 , and from the ABL circuit  24 , a video signal S 24  with the peak luminance controlled is output. Also, this video signal S 24  is supplied to a partial sticking adjusting circuit  25 , and the partial sticking circuit  25  detects a partial sticking from a signal level and time. Then, the partial sticking adjusting circuit  25  outputs a video signal S 25  which is adjusted based on a detection result. 
     Then, this video signal S 25  is supplied to an adjusting circuit  26  for luminescence unevenness (uniformity of luminance) on the whole screen of the organic electroluminescence panel  42 , and adjusted to be a video signal S 26  with uniform luminance. Therefore, from the adjusting circuit  20 , the video signal S 26  in which luminescence unevenness is adjusted by the luminescence unevenness adjusting circuit  26  and also in which various adjustments are performed by the circuits  21 - 25  is taken out, and this video signal S 26  is supplied to the panel gamma circuit  13  as described above. 
     (3) Details of Control over Adjusting Circuit  20   
     In order to execute appropriately the above-mentioned adjusting process, a bus line for control  31  is provided for the display adjusting circuit  10 , and this bus line  31  is connected to the terminal pin T 12  through a communication circuit  32 , and also the micro computer for control  51  is connected to this terminal pin T 12 . Also, a non volatile memory  52  for storing various data, histories, and the like is connected to this micro computer  51 . 
     Then, the video signal S 21  (normally a video signal for broadcasting or the like) output from the pattern generator circuit  21  is supplied to a still image detecting circuit  33 , it is detected whether an image to be displayed based on the video signal S 21  is a still image, and its detection signal S 32  is supplied to the micro computer  51  through the communication circuit  32 . 
     Then, in the micro computer  51 , a predetermined control signal is formed based on the detection signal S 32 , and also this control signal is supplied to the orbit circuit  11  through the communication circuit  32 . As a result, when an image displayed based on the video signal S 21  is a still image, its display location is controlled, and sticking on the organic electroluminescence panel  42  is reduced or gets indistinct. Besides, this process can be realised by, for example, shifting the waveform part which is to be displayed as an image with respect to the perpendicular and horizontal synchronous pulses. 
     Moreover, the control signal is supplied from the micro computer  51  to the pattern generator circuit  21  through the communication circuit  32 , and the pattern generator circuit  21  performs a switching control as follows, for example. Besides, this switching control is performed by, for example, instructing the micro computer  51  by a viewer or a testing operator and an adjusting operator at a manufacturer via a main micro computer (not shown). 
     Output directly the video signal S 12  supplied from the linear gamma circuit  12 . 
     Form a video signal to be displayed as a test pattern or a colour bar and output it. 
     Form a video signal at a constant level so that the whole screen has a uniform luminance, and output it. 
     Also, for example, if a viewer or a testing operator and an adjusting operator at a manufacturer instruct the micro computer  51  on adjusting and setting colour temperature via the main micro computer, this is informed to the colour temperature adjusting circuit  22  from the micro computer  51  through the communication circuit  32 , and the colour temperature is adjusted and set to a target characteristic. Besides, this adjustment and setting of colour temperature are performed by, for example, adjusting and setting the slope of the input/output characteristic in  FIG. 5  with respect to each of the three primary colour signals R-B. 
     Moreover, in order to adjust temporal changes in white balance, the video signal S 24  output from the ABL circuit  24  is supplied to a white balance detecting circuit  34 , and a detection signal S 34  that indicates each level for each colour signal of the video signal (three primary colours signal) S 24  is taken out. Then, this detection signal S 34  is supplied to the micro computer  51  through the communication circuit  32 . 
     In this case, the detection signal S 34  indicates the level of each colour signal, and accordingly, it is a signal that indicates the luminance of each colour of the organic electroluminescence panel  42 . Then, in the micro computer  51 , the detection signal S 34  for each of the colours is accumulated, and the accumulated luminescence amount (luminance×time) for each colour of the organic electroluminescence panel  42  is calculated. 
     Here, if the accumulated luminescence amount is large, it means that the luminance of the organic electroluminescence  42  is lowered correspondingly; namely, the accumulated luminescence amount will also correspond to the degradation amount of the luminance for each colour of the organic electroluminescence panel  42 . Hence, the micro computer  51  can derive an adjustment value for each colour, based on a calculated value for the accumulated luminescence amount, by, for example, referring to a table which is prepared in advance in the memory  52  to show luminance degradation of each colour with respect to the accumulated luminescence amount. Then, this adjustment value is supplied to the long-term white balance adjusting circuit  23  through the communication circuit  32 , the slope of the input/output characteristic in  FIG. 5  is altered, and a temporal change in white balance is adjusted, for example. 
     Thus, information corresponding to the driving state of the organic electroluminescence panel  42  is detected by converting the gamma characteristic of an input signal into a video signal with a linear input/output characteristic, and based on the signal information with the input/output characteristic converted into linear, deriving an accumulated value of luminescence amount via a simple adding process. Then, the table prepared in the memory  52  is read out by use of the detection result, so that a video signal to be output is adjusted via a simple operation for altering the slope of the input/output characteristic. 
     And then, an adjustment on the video signal is configured to be performed according to the gamma characteristic of the organic electroluminescence panel  42 , and light L at the luminance (light intensity) which is in proportion to the size of a driving current I is output (light output for the driving current has a linear characteristic). Therefore, a value for signal information with the input/output characteristic converted into linear corresponds to light output of an element of the organic electroluminescence panel  42 , namely to the driving state of the element. 
     Thus, the driving state of the organic electroluminescence panel is detected readily from the signal information with the input/output characteristic converted into linear, and because the driving history can be further detected based on the driving state, a proper adjustment on a video signal can be performed by relatively small sized circuitry configuration by use of the detection result. Therefore, an image display in high definition is held on the organic electroluminescence panel  42 . 
     Also, the video signal S 24  output from the ABL circuit  24  is supplied to an average luminance detecting circuit  35 , and from a rate of voltage of each colour signal in the video signal S 24 , an average luminance for one frame period, for example. Then, this detection signal S 35  is supplied as a control signal to a gate pulse circuit  36 . This gate pulse circuit  36  is configured to control a duty ratio of the luminescence period of the organic electroluminescence panel  42 , namely a rate of the luminescence period of the organic electroluminescence panel  42  for one frame period. 
     Thus, from the gate pulse circuit  36 , a control signal S 36  is output for controlling a duty ratio of the luminescence period in the frame next to the frame for which a duty ratio of the luminescence period of the organic electroluminescence panel  42  is calculated. Then, this control signal S 36  is supplied as a control signal for the duty ratio of the luminescence period to the organic electroluminescence panel  42  through the terminal pin T 14 , and the organic electroluminescence panel  42  is protected. 
     Also, at this point, the magnitude of the signal current I flowing to the organic electroluminescence panel  42  is detected by a current detecting circuit  43 , and a detection signal S 43  of this is supplied to the gate pulse circuit  36  through the terminal pin T 15 . Then, the control signal S 36  is controlled based on a result of detecting the signal current I flowing to the organic electroluminescence panel  42 , and if the magnitude of the signal current changes sharply by the frame next to the frame for which the signal current I flowing to the organic electroluminescence panel  42  is detected, the current amount to be supplied to the organic electroluminescence panel  42  is controlled. Therefore, the organic electroluminescence panel  42  is protected from an overflowed signal current I. 
     Even in this case, between the linear gamma circuit  12  and the panel gamma circuit  13 , an average luminance can be detected by deriving the sum of values of image data for one frame by use of signal information with the input/output characteristic converted into linear. Here, because the above average luminance corresponds to the total current amount to be supplied to the whole organic electroluminescence panel  42 , control for protecting the organic electroluminescence panel  42  is realised via a simple signal process by four arithmetic operations. 
     Moreover, in the luminescence unevenness adjusting circuit  26 , adjustment on luminescence unevenness on the whole screen of the organic electroluminescence panel  42  is performed. This adjustment is performed at the time of alignment, testing, and the like. Now, the video signal S 12  at a uniform level is output from the pattern generator  21 , and therefore, the whole screen of the panel  42  emits light at a uniform luminance if there is no luminescence unevenness on the organic electroluminescence panel  42 . 
     Then, the whole screen of this organic electroluminescence panel  42  is captured by an imaging element, such as a video camera, and luminescence unevenness of the panel  42  is detected. Besides, this detection is performed for each luminescence colour of red, blue, and green, for example. Then, this detection result is supplied to the micro computer  51 , an adjustment value is calculated by referring to the table with reference to the level of the video signal S 25  and the coordinate location (scanning location) on the organic electroluminescence panel  42 , and this adjustment value is supplied to the luminescence unevenness adjusting circuit  26  through the communication circuit  32 , so that luminescence unevenness is adjusted. 
     Thus, in the adjusting circuit  20 , various adjustments are performed, such as adjustment on colour temperature, adjustment on temporal changes in white balance, adjustment on sticking and luminescence unevenness of the organic electroluminescence panel  42 , and control over the maximum luminance, etc., so that an image as a result of executing them is displayed on the organic electroluminescence panel  42 . 
     (4) Conclusion 
     According to the above-mentioned display adjusting circuit  10 , various adjustments for the organic electroluminescence panel  42  are configured to be performed by the adjusting circuit  20  configured with the detecting units including the circuit  33 - 35  and the adjusting units including the circuit  21 - 26 , so that an image in high definition can be achieved. Then, if the adjusting circuit  20  performs adjustment, the adjustment can be performed certainly by simple configuration, because the video signal S 1  with the gamma characteristic for a Braun tube is made to be the video signal S 13  with a linear gamma characteristic as shown in  FIG. 4E  by the linear circuit  12  and various adjustments and level detections which are necessary for the adjustments are performed on this video signal S 13 . 
     Now, because the input video signal S 1  has a gamma characteristic as shown in  FIG. 6 , when adjustment is performed on this video signal S 1  (or the video signal S 11 ), even if the voltage variation range ΔV in the case where its voltage level is low and the voltage variation range ΔV in the case of high are equal, the luminance variation range ΔLL 1  for the variation range ΔV in the case where voltage level is low and the luminance variation range ΔLH 1  for the variation range ΔV in the case of high get different. 
     In other words, adjustment sensitivities (ΔLL 1 /ΔV, ΔLH 1 /ΔV) get different depending on the voltage level of the video signal S 1 . Therefore, if various adjustments are done as described above, corresponding to the level of the video signal S 1 , the control range (ΔV) of its adjustment is necessarily changed, the configuration of the adjusting circuit  10  may become complicated, and also the adjustments may be not put into an optimal value. 
     However, in the described display adjusting circuit  10 , the input video signal S 1  is made to be the video signal S 12  with a linear characteristic as shown in  FIG. 4C  by the linear gamma circuit  12 , and adjustment is configured to be performed on this video signal S 12  (or signal S 21 -S 25 ). Therefore, for the display adjustment circuit  10 , as shown in  FIG. 6 , the luminance variation range ΔLL 12  for the variation range ΔV in the case where the voltage level of the video signal S 12  is low and the luminance variation range ΔLH 12  for the variation range ΔV in the case of high get equal. 
     In other words, adjustment sensitivities (ΔLL 12 /ΔV, ΔLH 12 /ΔV) get equal, regardless of the voltage level of the video signal S 12 . Therefore, in the adjusting circuit  20 , if various adjustments are done as described above, the video signal S 12  can be appropriately adjusted, and also the configuration for that gets simple. 
     Furthermore, on the video signal S 12  (S 21 -S 25 ) which is made to have a linear gamma characteristic as shown in  FIG. 4C  by the linear gamma circuit  12 , gamma adjustment for the organic electroluminescence panel  42  is now done by the panel gamma circuit  13 , so that gamma adjustment can be performed properly on the organic electroluminescence panel with a different gamma characteristic, and an image in high definition can be achieved. 
     Also, when the detecting circuit  33 - 35  perform various detections, because a video signal has a linear characteristic, the detection sensitivities for the video signal get equal, regardless of the level of the video signal, therefore, detection in high precision can be done, and as a result, high definition can be achieved. 
     (5) Notes 
     In the above, if the same gamma characteristic as those of the video signal S 1  are given to a test video signal to be output from the pattern generator  21 , then the pattern generator  21  can come before the linear gamma circuit  12 . 
     LIST OF ABBREVIATIONS 
     ABL: Automatic Brightness Limiter 
     EL: ElectroLuminescence 
     FPGA: Field Programble Gate Array 
     IC: Integrated Circuit 
     LED: Light Emitting Diode 
     LSI: Large Scale Integration 
     OLED: Organic Light Emitting Diode 
     RSDS: Reduced Swing Differential Signalling (registered trademark) 
     TFT: Thin Film Transistor