Patent Publication Number: US-2023162671-A1

Title: Semiconductor device and electronic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Application JP2021-188892, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device and an electronic apparatus that include a light measuring instrument disposed on the backside of a display panel for measuring the ambient-light illuminance of the display panel. 
     2. Description of the Related Art 
     An illuminance sensor that measures ambient-light illuminance is used for regulating the brightness of a smartphone&#39;s display. Although such an illuminance sensor has been conventionally disposed above the display to measure the ambient-light illuminance, it has been eventually disposed on the backside (back surface or under display) of the smartphone&#39;s display because of upsizing of the smartphone&#39;s display and changing into entire-surface display. 
     The illuminance sensor, when disposed on the display&#39;s backside, is irradiated with ambient light as well as light emitted from the display. Thus, ambient light needs to be determined by subtracting display&#39;s light from a result output from the illuminance sensor. 
     A known electronic apparatus (United States Patent Application Publication No. 2021/0056896) includes a display, and a light sensor disposed on the display&#39;s backside to receive ambient light that has passed through the display. The electronic apparatus calculates the ambient-light illuminance on the basis of a first-subframe count value and a second-subframe count value, obtained by integrating a first sub-frame modulated by at least one modulation parameter and a second sub-frame modulated by at least one modulation parameter with respect to incident light in the light sensor between vertical synchronizing signals of the display. 
     SUMMARY OF THE INVENTION 
     Such a conventional technique as described above unfortunately does not reflect the ON/OFF timing of the light emission in the display. 
     Display&#39;s light cannot be hence subtracted accurately, making it difficult to calculate more accurate ambient-light illuminance. 
     One aspect of the present invention aims to achieve a semiconductor device and an electronic apparatus that can calculate more accurate ambient-light illuminance. 
     To solve the above problem, a semiconductor device according to one aspect of the present invention includes the following: a light measuring instrument disposed opposite the display surface of a display panel provided with a self-emission element, and disposed for measuring the ambient-light illuminance of the display panel; a storage device configured to store a plurality of first measurements measured by the light measuring instrument in synchronization with a synchronizing signal of the display panel during a plurality of first measurement periods that are shorter than an ON/OFF period of the self-emission element; and a calculation unit configured to calculate the light emission illuminance of the self-emission element in accordance with the plurality of first measurements stored in the storage device, and configured to calculate the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument during a second measurement period that is longer than the plurality of first measurement periods. 
     To solve the above problem, a semiconductor device according to one aspect of the present invention includes the following: a light measuring instrument disposed opposite the display surface of a display panel provided with a self-emission element, and disposed for measuring the ambient-light illuminance of the display panel; a storage device configured to store a plurality of first measurements measured by the light measuring instrument in synchronization with a synchronizing signal of the display panel during a first measurement period that is shorter than an ON/OFF period of the self-emission element, and a communication interface configured to calculate the light emission illuminance of the self-emission element in accordance with the plurality of first measurements, and configured to send the plurality of first measurements and a second measurement for subtracting a value based on the light emission illuminance from the second measurement measured by the light measuring instrument during a second measurement period that is longer than the first measurement period. 
     To solve the above problem, an electronic apparatus according to one aspect of the present invention includes the following: a display panel provided with a self-emission element; and a semiconductor device disposed opposite the display surface of the display panel, wherein the semiconductor device includes the following: a light measuring instrument for measuring the ambient-light illuminance of the display panel; a storage device configured to store a plurality of first measurements measured by the light measuring instrument in synchronization with a synchronizing signal of the display panel during a first measurement period that is shorter than an ON/OFF period of the self-emission element; and a calculation unit configured to calculate the light emission illuminance of the self-emission element in accordance with the plurality of first measurements stored in the storage device, and configured to calculate the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument during a second measurement period that is longer than the first measurement period. 
     To solve the above problem, a method for measuring ambient-light illuminance according to one aspect of the present invention is for measuring the ambient-light illuminance of a display panel provided with a self-emission element. The method includes the following process steps: storing, in a storage device, a plurality of first measurements measured by a light measuring instrument disposed opposite the display surface of the display panel in synchronization with a synchronizing signal of the display panel during a first measurement period that is shorter than an ON/OFF period of the self-emission element; and calculating the light emission illuminance of the self-emission element in accordance with the plurality of first measurements stored in the storage device, and calculating the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument during a second measurement period that is longer than the first measurement period. 
     To solve the above problem, a non-transitory computer-readable medium according to one aspect of the present invention stores a program based on the method for measuring the ambient-light illuminance according to one aspect of the present invention. 
     The aspects of the present invention can offer a semiconductor device and an electronic apparatus that can calculate more accurate ambient-light illuminance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view of an electronic apparatus according to a first preferred embodiment; 
         FIG.  2    is a sectional view taken along line A-A′ shown in  FIG.  1   ; 
         FIG.  3    is a block diagram of a semiconductor device provided in the electronic apparatus; 
         FIG.  4    is a block diagram of a modification of the semiconductor device; 
         FIG.  5    illustrates, in a sectional view, the relationship between ambient light of the display panel provided in the electronic apparatus and light emitted from a self-emission element; 
         FIG.  6    is a graph for describing a measurement period in a light measuring instrument provided in the semiconductor device; 
         FIG.  7    schematically illustrates an aspect where measured data measured during the measurement period is stored in a storage device provided in the semiconductor device; 
         FIG.  8    is a flowchart showing the operation of the electronic apparatus; 
         FIG.  9    is a block diagram of another modification of the semiconductor device; 
         FIG.  10    is a block diagram of further another modification of the semiconductor device; 
         FIG.  11    is a flowchart showing the operation of an electronic apparatus according to a second preferred embodiment; 
         FIG.  12    is a graph for describing the operation of an electronic apparatus according to a third preferred embodiment; and 
         FIG.  13    is a flowchart showing the operation of the electronic apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Preferred Embodiment 
     The following details one embodiment of the present invention. 
       FIG.  1    is a plan view of an electronic apparatus  1  according to the first preferred embodiment.  FIG.  2    is a sectional view taken along line A-A′ shown in  FIG.  1   . 
     The electronic apparatus  1  includes a display panel  2 , and a semiconductor device  3  disposed opposite a display surface  18  of the display panel  2 . The electronic apparatus  1  can be, but not limited to, a portable electronic apparatus, such as a smartphone, a game machine or a watch, or can be, but not limited to, an image display device, such as a TV set, a personal computer or a monitor. The display panel  2  has the following: a substrate  9 ; a thin-film transistor (TFT) layer  10  formed on the substrate  9 ; an organic electroluminescence (EL) layer  11  formed on the TFT layer  10 ; and cover glass  12  formed on the organic EL layer  11 . 
     The organic EL layer  11  has a plurality of pixels  19  disposed in rows and columns in X- and Y-directions. Each pixel  19  includes a red light-emitting element  17 R (self-emission element), a green light-emitting element  17 G (self-emission element) and a blue light-emitting element  17 B (self-emission element) arranged in the X-direction. 
     The display panel  2  further has the following: a gate driver  15  for controlling the operation timing of the individual light-emitting elements  17 R,  17 G and  17 B; a source diver  16  for supplying display data to each of the light-emitting elements  17 R,  17 G and  17 B; and a display circuit  13  that supplies, to the gate driver  15  and semiconductor device  3 , a vertical synchronizing signal (VSYNC) S 1  (synchronizing signal) for controlling the operation timing, a signal that is indicative of a light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B, and other things, and that supplies a display signal for each of the light-emitting elements  17 R,  17 G and  17 B to the source driver  16 . The light emitters  17 R,  17 G and  17 B each can be an organic light-emitting diode (OLED) for instance. 
       FIG.  3    is a block diagram of the semiconductor device  3  provided in the electronic apparatus  1 . 
     The semiconductor device  3  has the following: a light measuring instrument  4  for measuring the ambient-light illuminance of the display panel  2 ; a storage device  5  for storing measurements measured by the light measuring instrument  4 ; an AD-conversion circuit  20  that AD-converts the measurements measured by the light measuring instrument  4 ; a control unit  21  that writes the measurements undergone AD-conversion by the AD-conversion circuit  20  into the storage device  5 ; and a communication interface  22  that reads the measurements stored in the storage device  5  to send them to the display circuit  13 , which controls the display panel  2 . The display circuit  13  sends a control signal for controlling the luminance of each of the light-emitting elements  17 R,  17 G and  17 B to the source driver  16 . The communication interface  22  is in conformance with an inter-integrated circuit (I2C) or a serial peripheral interface (SPI) for instance. 
     It is noted that although the foregoing has described an instance where the communication interface  22  reads the measurements stored in the storage device  5 , the present invention is not limited to this instance. The control unit  21  may read the measurements.  FIG.  4    is a block diagram of a semiconductor device  3 A according to a modification. Components similar to those previously described will be denoted by similar reference signs. The detailed description of these components will not be repeated. 
     The semiconductor device  3 A includes a control unit  21 A. The control unit  21 A, when reading the measurements stored in the storage device  5 , can write and read the measurements into and from the storage device  5  and can send, to the communication interface  22 , the measurements read from the storage device  5 , as illustrated in  FIG.  4   . 
     The light measuring instrument  4  may or may not be provided for each of the plurality of pixels  19 . 
     The storage device  5  includes the following: a first storage unit  6  that stores a first measurement measured by the light measuring instrument  4  in synchronization with the vertical synchronizing signal S 1  of the display panel  2  during a first measurement period T 1  ( FIG.  6   ) that is shorter than an ON/OFF period of each of the light-emitting elements  17 R,  17 G and  17 B; and a second storage unit  7  that stores a second measurement measured by the light measuring instrument  4  during a second measurement period T 2  ( FIG.  6   ) that is longer than the first measurement period T 1 . The first storage unit  6  includes a memory array. 
     The display panel  2  has a calculation unit  8  that calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B in accordance with the first measurement, and that calculates the ambient-light illuminance by subtracting a value based on the light emission illuminance from the second measurement measured by the light measuring instrument  4  during the second measurement period T 2 . 
     It is noted that the calculation unit  8  may be incorporated in the semiconductor device  3 , as described later on in  FIG.  9    and  FIG.  10   . 
       FIG.  5    illustrates, in a sectional view, the relationship between ambient light  23  of the display panel  2  provided in the electronic apparatus  1  and reflected light  24  of the display panel  2 . 
     The light measuring instrument  4  of the semiconductor device  3  receives the ambient light  23  of the display panel  2  passed through the display panel  2 , and the reflected light  24  emitted from each of the light-emitting elements  17 R,  17 G and  17 B of the display panel  2  and reflected on the cover glass  12 . This unfortunately causes the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B to overlap the ambient-light illuminance that is to be originally measured by the light measuring instrument  4 . 
       FIG.  6    is a graph for describing the first measurement periods T 1  and second measurement period T 2  in the light measuring instrument  4  provided in the semiconductor device  3 .  FIG.  7    schematically illustrates an aspect where measured data measured during the first measurement periods T 1  is stored in the storage device  5  provided in the semiconductor device  3 .  FIG.  8    is a flowchart showing the operation of the electronic apparatus  1 . 
     The light measuring instrument  4  measures first measurements in synchronization with the vertical synchronizing signal S 1  (synchronizing signal) of the display panel  2  during the first measurement periods T 1  that are shorter than an ON/OFF period TO of each of the light-emitting elements  17 R,  17 G and  17 B. 
     The ON/OFF period TO includes an OFF period  25  during which the light emission of each of the light-emitting elements  17 R,  17 G and  17 B remains off, and an ON period  26  during which the light emission remains on. During the OFF period  25 , only the ambient light  23  from outside the display panel  2  enters the light measuring instrument  4 . During the ON period  26 , the reflected light  24  based on light emitted from each of the light-emitting elements  17 R,  17 G and  17 B is added to the ambient light  23  and then enters the light measuring instrument  4 .  FIG.  6    illustrates an instance where the light emission in each of the light-emitting elements  17 R,  17 G and  17 B during the OFF period  25  remains off completely. 
     As such, only the ambient light  23  enters the light measuring instrument  4  when the first measurement periods T 1  are included in the OFF period  25 . The reflected light  24  is added to the ambient light  23  and then enters the light measuring instrument  4  when the first measurement periods T 1  are included in the ON period  26 . Whether each of the plurality of first measurement periods T 1  is included in the OFF period  25  or the ON period  26  can be identified on the basis of the ON/OFF period TO and the light emission duty that is indicative of the ratio between the OFF period  25  and the ON period  26 . 
     The luminance of the display panel  2  is controlled by the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B. Further, the control unit  21  of the semiconductor device  3  can identify, based on a signal supplied from the display circuit  13  and indicative of the light emission duty, which address in the first storage unit  6  each first measurement with each of the light-emitting elements  17 R,  17 G and  17 B remaining on is stored in, as well as which address in the first storage unit  6  each first measurement with each of the light-emitting elements  17 R,  17 G and  17 B remaining off is stored in. 
     It is noted that the horizontal broken line relating to the ambient light  23  in  FIG.  6    indicates the level of complete darkness where the illuminance of the ambient light  23  stands at zero lux. 
     The AD-conversion circuit  20  then AD-converts the first measurements measured by the light measuring instrument  4  and then supplies the first measurements to the control unit  21 . The control unit  21  next stores the first measurements supplied from the AD-conversion circuit  20  in the first storage unit  6  of the storage device  5  in order from the start address. 
     Each address of the first storage unit  6  does not correspond to the pixel  19  of the light-emitting elements  17 R,  17 G and  17 B. It is common to provide the light measuring instrument  4  that is larger than the pixel  19  of the light-emitting elements  17 R,  17 G and  17 B. The first storage unit  6  stores the first measurements corresponding to the amount of light entered the light measuring instrument  4 , irrespective of the number of pixels  19 . 
     As describes above, the first storage unit  6  stores the first measurements in order from the start address, which is an address of 0, in synchronization with the vertical synchronizing signal S 1  during the first measurement periods T 1 . Upon occurrence of the next vertical synchronizing signal S 1 , the first measurements are overwritten again from the start address. 
     For instance, when a first measurement period T 1  that synchronizes with the vertical synchronizing signal S 1  is repeated 32 times from the zeroth first measurement period T 1  to the thirty-first first measurement period T 1 , as illustrated in  FIG.  7   , the zeroth to second first measurement periods T 1  are OFF measurement periods T 4  during which the light emission in each of the light-emitting elements  17 R,  17 G and  17 B remains off. Moreover, the fifth to seventh first measurement periods T 1  are ON measurement periods T 3  during which the light emission remains on. The ninth to eleventh first measurement periods T 1  are OFF measurement periods T 4 , during which the light emission remains off. The thirteenth to fifteenth first measurement periods T 1  are ON measurement periods T 3 , during which the light emission remains on. The seventeenth to nineteenth first measurement periods T 1  are OFF measurement periods T 4 , during which the light emission remains off. The twenty-first to twenty-third first measurement periods T 1  are ON measurement periods T 3 , during which the light emission remains on. The twenty-fifth to twenty-seventh first measurement periods T 1  are OFF measurement periods T 4 , during which the light emission remains off. The twenty-ninth to thirty-first first measurement periods T 1  are ON measurement periods T 3 , during which the light emission remains on. 
     It is noted that the remaining third, fourth, eighth, twelfth, sixteenth, twentieth, twenty-fourth and twenty-eighth first measurement periods T 1  indicate transient measurement periods T 5  during which the light emission possibly switches from the ON state to the OFF state, or from the OFF state to the ON state. Thus, the measurements during these transient periods cannot be used in calculation. 
     Further, the light measuring instrument  4  measures the second measurement during the second measurement period T 2 , which is longer than the first measurement periods T 1 . Moreover, the AD-conversion circuit  20  AD-converts the second measurement measured by the light measuring instrument  4  and then supplies the second measurement to the control unit  21 . The control unit  21  next stores the second measurement supplied from the AD-conversion circuit  20  in the second storage unit  7  of the storage device  5 . 
     The second storage unit  7  stores the second measurement measured during the second measurement period T 2 . The second measurement is overwritten in the second storage unit  7  every time the second measurement is measured. 
     Moreover, the communication interface  22  sends the first measurements stored in the first storage unit  6  and the second measurement stored in the second storage unit  7  to the calculation unit  8 . 
     The calculation unit  8  next calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B on the basis of the first measurements sent from the communication interface  22  and calculates the ambient-light illuminance by subtracting a value based on the light emission illuminance from the second measurement sent from the communication interface  22 . 
     The calculation unit  8  calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B by subtracting, based on the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B, the first measurements with each light-emitting element remaining off from the first measurements with each light-emitting element reaming on. 
     The first storage unit  6  stores a measurement where the reflected light  24  based on each of the light-emitting elements  17 R,  17 G and  17 B during the first measurement periods T 1  and the ambient light  23  during the first measurement periods T 1  are added. The second storage unit  7  stores a measurement where the reflected light  24  based on each of the light-emitting elements  17 R,  17 G and  17 B during the second measurement period T 2  and the ambient light  23  during the second measurement period T 2  are added. However, a measurement of the ambient light  23  is stored during the zeroth to second first measurement periods T 1 , the ninth to eleventh first measurement periods T 1 , the seventeenth to nineteenth first measurement periods T 1  and the twenty-fifth to twenty-seventh first measurement periods T 1 , in all of which each of the light-emitting elements  17 R,  17 G and  17 B does not emit light. 
     The control unit  21  determines address information for reading first measurement information from the first storage unit  6  by reflecting ON/OFF information based on the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B. For instance, the control unit  21  determines address information for identifying which address each first measurement with each light-emitting element remaining off are stored in, and which address each first measurement with each light-emitting element remaining on are stored in. 
     The control unit  21  reads the first measurements from the first storage unit  6  by using the determined address information. 
     The control unit  21  defines a first measurement (e.g., the first measurement in an address of 6 of the first storage unit  6 ) with each of the light-emitting elements  17 R,  17 G and  17 B remaining on as OLED_ON and identifies its address with the light-emitting element remaining on. The control unit  21  also defines a first measurement (e.g., the first measurement in an address of 1 of the first storage unit  6 ) with each of the light-emitting elements  17 R,  17 G and  17 B remaining off as OLED_OFF and identifies its address with the light-emitting element remaining off. 
     The calculation unit  8  preferably calculates an average value of the first measurements read from the respective addresses of OLED_ON in the first storage unit  6 . The calculation unit  8  also preferably calculates an average value of the first measurements read from the respective addresses of OLED_OFF in the first storage unit  6 . Accordingly, a more stable OLED_ON value and a more stable OLED_OFF value can be determined. 
     The calculation unit  8  determines OLED_mag, which indicates the light emission intensity of each of the light-emitting elements  17 R,  17 G and  17 B, through Expression 1 below by using the first measurements with each light-emitting element remaining on, and the first measurements with each light-emitting element remaining off. 
       OLED_mag=OLED_on−OLED_off  Expression 1
 
     The calculation unit  8  also determines the ambient-light illuminance through Expression 2 below. 
       Ambient-light illuminance=measurement in second storage unit−OLDE_mag×(second measurement period  T 2/(first measurement period  T 1×2))  Expression 2
 
     The calculation unit  8  calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B by subtracting, based on the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B, the first measurements with each of the light-emitting elements  17 R,  17 G and  17 B remaining off from the first measurements with each of the light-emitting elements  17 R,  17 G and  17 B remaining on. 
     The ON/OFF period T 0  includes the ON period  26 , during which each of the light-emitting elements  17 R,  17 G and  17 B remains on, and the OFF period  25 , during which each of the light-emitting elements  17 R,  17 G and  17 B remains off. 
     Some of the plurality of first measurement periods T 1  are ON measurement periods T 3  for measurement during the ON period  26 . Some of the plurality of first measurement periods T 1  are OFF measurement periods T 4  for measurement during the OFF period  25 . The remaining first measurement periods T 1  are transient measurement periods T 5 , during which the ON period  26  possibly switches to the OFF period  25 , or the OFF period  25  possibly switches to the ON period  26 . 
     The first storage unit  6  stores the plurality of first measurements in order from the start address. 
     Moreover, the calculation unit  8  calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B by subtracting the first measurements measured during the OFF measurement periods T 4  from the first measurements measured during the ON measurement periods T 3 . 
     The calculation unit  8  calculates the ambient-light illuminance by subtracting a value based on the light emission illuminance, first measurement periods T 1  and second measurement period T 2  from the second measurement. 
       FIG.  8    is a flowchart showing the operation of the electronic apparatus  1 . 
     Firstly, the first measurements are measured by the light measuring instrument  4  during the first measurement periods T 1  in synchronization with the vertical synchronizing signal S 1  of the display panel  2 . The control unit  21  then stores the first measurements in the first storage unit  6  in order from the start address. 
     Next, the second measurement is measured by the light measuring instrument  4  during the second measurement period T 2  in synchronization with the vertical synchronizing signal S 1 . The control unit  21  stores the second measurement in the second storage unit  7 . The second measurement period T 2  may last for equal to or shorter than the interval between the vertical synchronizing signals S 1  or may last for longer than the interval between the vertical synchronizing signals S 1 . Indoor light typically undergoes superimposition of oscillations of 100 Hz or 120 Hz, which is double the commercial power supply frequency, i.e., 50 Hz or 60 Hz; accordingly, the influence of the oscillations of this frequency can be eliminated when the second measurement period T 2  is set at 100 ms. 
     Next (Step S 11 ), the control unit  21  determines addresses for read in the first storage unit  6  by using the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B. 
     Then (Step S 12 ), the control unit  21  reads the first measurements OLED_ON and the first measurements OLED_OFF from the first storage unit  6  and reads the second measurement from the second storage unit  7 . 
     The communication interface  22  then sends the first measurements OLED_ON, first measurements OLED_OFF and second measurement read by the control unit  21  to the calculation unit  8 . 
     Next (Step S 13 ), the calculation unit  8  determines the light emission intensity OLED_mag of each of the light-emitting elements  17 R,  17 G and  17 B on the basis of the first measurements OLED_ON and the first measurements OLED_OFF sent from the communication interface  22 . 
     Then (Step S 14 ), the calculation unit  8  calculates the ambient-light illuminance through foregoing Expression 2 by using the second measurement sent from the communication interface  22 , and the light emission intensity OLED_mag of each of the light-emitting elements  17 R,  17 G and  17 B. 
       FIG.  9    is a block diagram of a semiconductor device  3 B according to another modification. Components similar to those previously described will be denoted by similar reference signs. The detailed description of these components will not be repeated. 
     The semiconductor device  3 B includes the calculation unit  8 . The calculation unit  8  calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B in accordance with first measurements stored in the first storage unit  6  and calculates the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement stored in the second storage unit  7 . The communication interface  22  sends the ambient-light illuminance calculated by the calculation unit  8  to the display circuit  13 , which controls the display panel  2 . 
     As described above, the calculation unit  8  may be provided in the semiconductor device  3 A instead of the display panel  2 . 
       FIG.  10    is a block diagram of a semiconductor device  3 C according to further another modification. Components similar to those previously described will be denoted by similar reference signs. The detailed description of these components will not be repeated. 
     The semiconductor device  3 C includes a control unit  21 C. The control unit  21 C writes and reads measurements into and from the storage device  5  and supplies the measurements read from the storage device  5  to the calculation unit  8 . The control unit  21 C also supplies the ambient-light illuminance calculated by the calculation unit  8  to the communication interface  22 . The communication interface  22  also sends the ambient-light illuminance calculated by the calculation unit  8  to the display circuit  13 , which controls the display panel  2 . 
     Second Preferred Embodiment 
     The following describes another preferred embodiment of the present invention. It is noted that for convenience in description, components having the same functions as components described in the foregoing preferred embodiment will be denoted by the same signs, and their description will not be repeated. 
       FIG.  11    is a flowchart showing the operation of an electronic apparatus according to the second preferred embodiment. 
     In the second preferred embodiment, no address information synchronizing with the vertical synchronizing signal S 1  is provided; the ambient-light illuminance is calculated by reading measurements during all the first measurement periods T 1  between the vertical synchronizing signals S 1 . 
     The following describes the operation of the electronic apparatus according to the second preferred embodiment that includes the semiconductor device  3 C shown in  FIG.  10   . The control unit  21 C reads (Step S 21 ) all first measurements stored in addresses of 0 to 31 of the first storage unit  6  within a period between the vertical synchronizing signals S 1 . Next (Step S 22 ), the calculation unit  8  selects a maximum value and a minimum value from among all the first measurements within the period between the vertical synchronizing signals S 1 . 
     Next (Step S 23 ), the calculation unit  8  sets the maximum value to a first measurement OLED_ON, sets the minimum value to a first measurement OLED_OFF and determines the light emission intensity, OLED_mag, of each of the light-emitting elements  17 R,  17 G and  17 B on the basis of the first measurement OLED_ON and first measurement OLED_OFF. 
     Then (Step S 24 ), the calculation unit  8  calculates the ambient-light illuminance through foregoing Expression 2 by using a second measurement and the light emission intensity OLED_mag of each of the light-emitting elements  17 R,  17 G and  17 B. 
     The communication interface  22  then sends the ambient-light illuminance calculated by the calculation unit  8  to the display circuit  13 , which controls the display panel  2 . 
     When the electronic apparatus according to the second preferred embodiment includes the semiconductor device  3 B shown in  FIG.  9   , the calculation unit  8  reads all the first measurements stored in the first storage unit  6 . When the electronic apparatus includes the semiconductor device  3  shown in  FIG.  3   , the communication interface  22  reads all the first measurements stored in the first storage unit  6 . When the electronic apparatus includes the semiconductor device  3 A shown in  FIG.  4   , the control unit  21 A reads all the first measurements stored in the first storage unit  6 . 
     As described above, the calculation unit  8  selects a maximum value and a minimum value from among the first measurements read from the first storage unit  6  and calculates the light emission illuminance of each of the light-emitting elements  17 R,  17 G and  17 B by subtracting the minimum value from the maximum value. 
     Third Preferred Embodiment 
       FIG.  12    is a graph for describing the operation of an electronic apparatus according to the third preferred embodiment.  FIG.  13    is a flowchart showing the operation of the electronic apparatus. Components similar to those previously described will be denoted by similar reference signs. Their detailed description will not be repeated. 
     The third preferred embodiment describes how to calculate the ambient-light illuminance when the light emission in each of the light-emitting elements  17 R,  17 G and  17 B does not completely turn off. 
       FIG.  12    illustrates a case where the light emission in each of the light-emitting elements  17 R,  17 G and  17 B does not completely turn off during the OFF period  25 . In this case, the reflected light  24  based on light emitted from each of the light-emitting elements  17 R,  17 G and  17 B is added to the ambient light  23  and then enters the light measuring instrument  4  during the OFF period  25 , thus compensating for the ambient-light illuminance with a predetermined compensation coefficient based on light that always enters the light measuring instrument  4 . 
     The following describes an instance where the electronic apparatus according to the third preferred embodiment includes the semiconductor device  3 C shown in  FIG.  10   . 
     Firstly, first measurements are measured by the light measuring instrument  4  during the first measurement periods T 1  in synchronization with the vertical synchronizing signal S 1  of the display panel  2 , and a second measurement is measured by the light measuring instrument  4  during the second measurement period T 2  in synchronization with the vertical synchronizing signal S 1 . Then, the control unit  21 C stores the first measurements in the first storage unit  6  in order from the start address and stores the second measurement in the second storage unit  7 . Then (Step S 31 ), the control unit  21 C determines addresses for read in the first storage unit  6  by using the light emission duty of each of the light-emitting elements  17 R,  17 G and  17 B. 
     Then (Step S 32 ), the control unit  21 C reads the first measurements OLED_ON and the first measurements OLED_OFF from the first storage unit  6  and reads the second measurement from the second storage unit  7 . 
     Next (Step S 33 ), the calculation unit  8  determines the light emission intensity OLED_mag of each of the light-emitting elements  17 R,  17 G and  17 B on the basis of the first measurements OLED_ON and the first measurements OLED_OFF. 
     Then (Step S 34 ), the calculation unit  8  calculates the ambient-light illuminance through Expression 3 below by using the second measurement and the light emission intensity OLED_mag of each of the light-emitting elements  17 R,  17 G and  17 B. 
       Ambient-light illuminance=measurement in second storage unit−OLDE_mag×(second measurement period  T 2/(first measurement period  T 1×2))−compensation coefficient   Expression 3
 
     The above compensation coefficient is a coefficient corresponding to light that always enters the light measuring instrument  4  during the OFF period  25  and the ON period  26 . The compensation coefficient is a value that depends on the size of the light measuring instrument  4  and the luminance of the display panel  2  and is a value that is determined in advance through actual measurement. 
     As described above, when the light emission in each of the light-emitting elements  17 R,  17 G and  17 B does not completely turn off, the calculation unit  8  calculates the ambient-light illuminance in accordance with a compensation coefficient that is for compensating for the influence of light that is always input to the light measuring instrument  4 . 
     Implementation by Software 
     The functions of the calculation unit  8  and control unit  21  (hereinafter referred to as a devise) in the electronic apparatus  1  can be implemented by programs that are for a computer to function as the device and that are for the computer to function as each control block in the device. 
     The device in this case includes a computer that has, as hardware for executing the programs, at least one control device (e.g., a processor) and at least one storage device (e.g., a memory). Executing the programs by using these control device and storage device implements the functions described in the foregoing respective preferred embodiments. 
     The programs may be stored in one or more non-transitory computer-readable storage media. These storage media may or may not be included in the foregoing device. When the storage media are not included in the device, the programs may be supplied to the device via any wired or wireless transmission medium. 
     The function of each control block in part or in whole can be implemented by a logic circuit. For instance, an integrated circuit provided with logic circuits that function as the individual control blocks is also included in the scope of the present invention. Other than the foregoing, the functions of the individual control blocks can be implemented by a quantum computer for instance. 
     SUMMARY 
     A semiconductor device  3 A according to a first aspect of the present invention includes the following: a light measuring instrument  4  disposed opposite a display surface  18  of a display panel  2  provided with a self-emission element (light-emitting element  17 R,  17 G,  17 B), and disposed for measuring the ambient-light illuminance of the display panel  2 ; a storage device  5  configured to store a plurality of first measurements measured by the light measuring instrument  4  in synchronization with a synchronizing signal (vertical synchronizing signal S 1 ) of the display panel  2  during a plurality of first measurement periods T 1  that are shorter than an ON/OFF period T 0  of the self-emission element (light-emitting element  17 R,  17 G,  17 B); and a calculation unit  8  configured to calculate the light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) in accordance with the plurality of first measurements stored in the storage device  5 , and configured to calculate the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument  4  during a second measurement period T 2  that is longer than the plurality of first measurement periods T 1 . 
     In the foregoing configuration, the light measuring instrument, disposed opposite the display surface of the display panel provided with the self-emission element, measures the first measurements in synchronization with the synchronizing signal of the display panel during the first measurement periods, which are shorter than the ON/OFF period of the self-emission element. The first measurements measured by the light measuring instrument are then stored in the storage device. The light emission illuminance of the self-emission element is next calculated in accordance with the first measurements stored in the storage device. The ambient-light illuminance is then calculated by subtracting the value based on the light emission illuminance from the second measurement, measured by the light measuring instrument during the second measurement period, which is longer than the first measurement periods. 
     Accordingly, the light emission illuminance of the self-emission element can be subtracted accurately from the second measurement, measured by the light measuring instrument during the second measurement period, in accordance with the synchronizing signal of the display panel. This can achieve a semiconductor device that can calculate more accurate ambient-light illuminance. 
     The semiconductor device  3 A according to a second aspect of the present invention is preferably configured, in the first aspect, such that the calculation unit  8  calculates the light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) by subtracting, based on a light emission duty of the self-emission element (light-emitting element  17 R,  17 G,  17 B), the plurality of first measurements with the self-emission element (light-emitting element  17 R,  17 G,  17 B) remaining off from the plurality of first measurements with the self-emission element (light-emitting element  17 R,  17 G,  17 B) remaining on. 
     The foregoing configuration enables the light emission illuminance of the self-emission element to be subtracted accurately based on the light emission duty of the self-emission element. 
     The semiconductor device  3 A according to a third aspect of the present invention is preferably configured, in the first aspect, such that the calculation unit reads the plurality of first measurements stored in the storage device, selects a maximum value and a minimum value from among the plurality of first measurements read, and calculates the light emission illuminance of the self-emission element by subtracting the minimum value from the maximum value. 
     The foregoing configuration eliminates the need for address information about the first measurements based on the synchronizing signal of the display panel and on the light emission duty of the self-emission element, thereby enabling the light emission illuminance of the self-emission element to be subtracted with a simple configuration. 
     The semiconductor device  3 A according to a fourth aspect of the present invention is preferably configured, in any one of the first to third aspects, such that when the light emission in the self-emission element (light-emitting element  17 R,  17 G,  17 B) does not completely turn off, the calculation unit  8  calculates the ambient-light illuminance in accordance with a compensation coefficient for compensating for the influence of light that is always input to the light measuring instrument  4 . 
     The foregoing configuration enables calculation of the ambient-light illuminance of a display panel that includes a self-emission element where illuminance does not stand at zero during an OFF period. 
     The semiconductor device  3 A according to a fifth aspect of the present invention is preferably configured, in the second aspect, such that the ON/OFF TO period includes an ON period  26  during which the self-emission element (light-emitting element  17 R,  17 G,  17 B) remains on, and an OFF period  25  during which the self-emission element (light-emitting element  17 R,  17 G,  17 B) remains off, such that some of the plurality of first measurement periods T 1  are ON measurement periods T 3  for measurement during the ON period  26 , some of the plurality of first measurement periods T 1  are OFF measurement periods T 4  for measurement during the OFF period  25 , and the plurality of remaining first measurement periods T 1  are transient measurement periods  25  during which the ON period  26  possibly switches to the OFF period  25 , or the OFF period  25  possibly switches to the ON period  26 , such that the storage device  5  stores the plurality of first measurements in order from a start address, and such that the calculation unit  8  calculates the light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) by subtracting the plurality of first measurements measured during the OFF measurement periods T 4  from the plurality of first measurements measured during the ON measurement periods T 3 . 
     The foregoing configuration enables the first measurements with the self-emission element remaining off to be subtracted from the first measurements with the self-emission element remaining on. 
     The semiconductor device  3 A according to a sixth aspect of the present invention is configured, in the second aspect, such that the calculation unit  8  calculates the ambient-light illuminance by subtracting, from the second measurement, a value based on the light emission illuminance, the plurality of first measurement periods T 1  and the second measurement period T 2 . 
     The foregoing configuration enables calculation of more accurate ambient-light illuminance. 
     The semiconductor device  3 A according to a seventh aspect of the present invention is preferably configured, in any one of the first to sixth aspects, such that the storage device  5  includes a first storage unit  6  configured to store the plurality of first measurements, and a second storage unit  7  configured to store the second measurement. 
     The foregoing configuration enables the ambient-light illuminance to be calculated based on the first measurements stored in the first storage unit and the second measurement stored in the second storage unit. 
     A semiconductor device  3  according to an eighth aspect of the present invention includes the following: a light measuring instrument  4  disposed opposite a display surface  18  of a display panel  2  provided with a self-emission element (light-emitting element  17 R,  17 G,  17 B), and disposed for measuring the ambient-light illuminance of the display panel  2 ; a storage device  5  configured to store a plurality of first measurements measured by the light measuring instrument  4  in synchronization with a synchronizing signal (vertical synchronizing signal S 1 ) of the display panel  2  during a first measurement period T 1  that is shorter than an ON/OFF period T 0  of the self-emission element (light-emitting element  17 R,  17 G,  17 B); and a communication interface  22  configured to calculate the light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) in accordance with the plurality of first measurements, and configured to send the plurality of first measurements and a second measurement for subtracting a value based on the light emission illuminance from the second measurement measured by the light measuring instrument  4  during a second measurement period T 2  that is longer than the first measurement period T 1 . 
     An electronic apparatus  1  according to a ninth aspect of the present invention includes the following: a display panel  2  provided with a self-emission element (light-emitting element  17 R,  17 G,  17 B); and a semiconductor device  3  disposed opposite a display surface  18  of the display panel  2 , wherein the semiconductor device  3  includes the following: a light measuring instrument  4  for measuring the ambient-light illuminance of the display panel  2 ; a storage device configured to store a plurality of first measurements measured by the light measuring instrument  4  in synchronization with a synchronizing signal (vertical synchronizing signal S 1 ) of the display panel  2  during a first measurement period T 1  that is shorter than an ON/OFF TO period of the self-emission element (light-emitting element  17 R,  17 G,  17 B); and a calculation unit  8  configured to calculate light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) in accordance with the plurality of first measurements stored in the storage device  5 , and configured to calculate the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument  4  during a second measurement period T 2  that is longer than the first measurement period T 1 . 
     A method for measuring ambient-light illuminance according to a tenth aspect of the present invention is for measuring the ambient-light illuminance of a display panel  2  provided with a self-emission element (light-emitting element  17 R,  17 G,  17 B). The method includes the following process steps: storing, in a storage device  5 , a plurality of first measurements measured by a light measuring instrument  4  disposed opposite a display surface  18  of the display panel  2  in synchronization with a synchronizing signal (vertical synchronizing signal S 1 ) of the display panel  2  during a first measurement period that is shorter than an ON/OFF period TO of the self-emission element (light-emitting element  17 R,  17 G,  17 B); and calculating the light emission illuminance of the self-emission element (light-emitting element  17 R,  17 G,  17 B) in accordance with the plurality of first measurements stored in the storage device  5 , and calculating the ambient-light illuminance by subtracting a value based on the light emission illuminance from a second measurement measured by the light measuring instrument  4  during a second measurement period T 2  that is longer than the first measurement period T 1 . 
     A non-transitory computer-readable medium according to an eleventh aspect of the present invention stores a program based on the method for measuring the ambient-light illuminance according to the tenth aspect of the present invention. 
     The present invention is not limited to the foregoing preferred embodiments. Various modifications can be devised with the scope of the claims. A preferred embodiment that is obtained in combination, as appropriate, with the technical means disclosed in the respective preferred embodiments is also included in the technical scope of the present invention. Furthermore, combining the technical means disclosed in the respective preferred embodiments can form a new technical feature. 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.