Patent Publication Number: US-2006017717-A1

Title: Controlling apparatus and method, recording medium, program, and inputting/outputting apparatus

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to a controlling apparatus and method, a recording medium, a program and an inputting/outputting apparatus, and more particularly to a controlling apparatus and method, a recording medium, a program and an inputting/outputting apparatus which involve detection of light irradiated from the outside.  
      In recent years, various apparatus have been proposed which can input various kinds of information directly to a display apparatus without providing a touch panel or a like apparatus in an overlapping relationship. An apparatus of the type described is disclosed, for example, in Japanese Patent Laid-Open No. Hei 11-53111 (hereinafter referred to as Patent Document 1) or Japanese Patent Laid-Open No. 2004-127272 (hereinafter referred to as Patent Document 2).  
      For example, Patent Document 2 discloses a display apparatus wherein the voltage to be applied to each pixel is controlled to cause the pixel to execute a light emitting action for causing the pixel to emit light so that an image is displayed and a light receiving action of detecting light to the pixel from the outside. In the display apparatus, in the light receiving action, a voltage in a direction opposite to that in the light emitting action is applied to each pixel, and leak current generated in a pixel when light is irradiated upon the pixel while such a voltage in the opposite direction as just mentioned is applied to the pixel is used to detect light from the outside. Consequently, a user can directly input predetermined data to the display apparatus by irradiating light representing such data upon the display apparatus.  
      Also different apparatus have been proposed which perform a predetermined action in response to light from the outside. One of the apparatus of the type described is disclosed in Japanese Patent Laid-Open No. 2003-173876 (hereinafter referred to as Patent Document 3) which is formed as a light emitting display element which uses a film having a light responding property and emits displaying light in response to an input of light to the film. Another apparatus of the type described is disclosed in Japanese Patent Laid-Open No. Hei 9-282078 (hereinafter referred to as Patent Document 4) wherein striped electrodes are disposed perpendicularly to each other and a layer of amorphous silicon is interposed at intersecting points of and between the electrodes to dispose a photocell at each of the intersecting points.  
      Further, an apparatus is disclosed in Japanese Patent Laid-Open No. Hei 7-175420 (hereinafter referred to as Patent Document 5) wherein information inputted in the form of light is detected by an organic EL (electroluminescence) element serving as a light emitting element.  
     SUMMARY OF THE INVENTION  
      Incidentally, in an apparatus of the type wherein leak current generated in a pixel is used to detect whether or not there exits light from the outside like, for example, the display apparatus disclosed in Patent Document 2, the detection sensitivity depends upon the amount (energy) of light irradiated upon pixels included in a unit area.  
      In particular, if a sufficient amount of light is irradiated, then a sufficient amount of leak current is generated in response the light, which provides high detection sensitivity. However, if a small amount of light is irradiated, then a small amount of leak current is generated in response to the light, which provides low detection sensitivity.  
      Since the detection sensitivity depends upon the amount of irradiated light in this manner, although there is no problem where the amount of light is large, conversely where the amount of irradiated light is small, there is the possibility that disadvantageously the input from the outside may not be detected correctly.  
      This commonly applies also to the other elements and apparatus disclosed in the other documents which perform a predetermined action in response to an input of light from the outside.  
      It is an object of the present invention to provide a controlling apparatus and method, a recording medium, a program and an inputting/outputting apparatus wherein high detection sensitivity to light irradiated from the outside can be assured.  
      In order to attain the object described above, according to an embodiment of the present invention, there is provided a controlling apparatus for controlling an inputting/outputting apparatus of the active matrix driving type which includes a pixel including an element whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element, including an accumulation control section for causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and a detection section for detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the accumulation control section.  
      According to another embodiment of the present invention, there is provided a controlling method for a controlling apparatus for controlling an inputting/outputting apparatus of the active matrix driving type which includes a pixel including an element whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element, including the steps of controlling accumulation of causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and a detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the processing of the accumulation control step.  
      According to a further embodiment of the present invention, there is provided a recording medium on which a program for causing a computer to execute a controlling processing for a controlling apparatus for an inputting/outputting apparatus of the active matrix driving type which includes a pixel including an element whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element is recorded, the program including the steps of controlling accumulation of causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the processing of the accumulation control step.  
      According to a still further embodiment of the present invention, there is provided a program for causing a computer to execute a controlling processing for a controlling apparatus for an inputting/outputting apparatus of the active matrix driving type which includes a pixel including an element whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element is recorded, the program including the steps of controlling accumulation of causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the processing of the accumulation control step.  
      With the controlling apparatus and method, recording medium and program, charge generated by an element included in a pixel during a light receiving action in response to reception of light from the outside is accumulated for predetermined period of time. Then, an input of the light from the outside to the inputting/outputting apparatus is detected based on the accumulated charge.  
      According to a yet further embodiment of the present invention, there is provided an inputting/outputting apparatus of the active matrix driving type which includes a pixel including an element whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element, the pixel including an accumulation section for accumulating charge generated by the element included in the pixel upon the light receiving action in response to reception of light from the outside for a predetermined period of time under the control of a controlling apparatus, and an outputting section for outputting the charge accumulated in the accumulation section to the controlling apparatus.  
      With the inputting/outputting apparatus, charge generated by the element included in the pixel upon the light receiving action in response to reception of light from the outside is accumulated for a predetermined period of time under the control of the controlling apparatus. The accumulated charge is outputted to the controlling apparatus.  
      With the controlling apparatus and method, recording medium, program and inputting/outputting apparatus, light from the outside can be detected.  
      With the controlling apparatus and method, recording medium, program and inputting/outputting apparatus, high detection sensitivity to light irradiated from the outside can be assured.  
      The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view showing an example of an appearance of an I/O display apparatus to which the present invention is applied;  
       FIG. 2  is a diagrammatic view illustrating an output function of the I/O display apparatus;  
       FIG. 3  is a similar view but illustrating an input function of the I/O display apparatus;  
       FIG. 4  is a diagram illustrating an example of a current characteristic of a pixel shown in  FIGS. 2 and 3 ;  
       FIG. 5  is a diagram showing, in an enlarged scale, a portion of the current characteristic of  FIG. 4  around 0 V;  
       FIGS. 6 and 7  are circuit diagrams illustrating different actions of a circuit provided in a pixel;  
       FIG. 8  is a circuit diagram showing a particular example of the circuit;  
       FIGS. 9 through 12  are circuit diagrams illustrating different actions of the particular circuit;  
       FIG. 13  is a block diagram showing an example of a configuration of a controlling apparatus;  
       FIG. 14  is a block diagram illustrating an example of a functional configuration of the controlling apparatus;  
       FIG. 15  is a flow chart illustrating a controlling processing of the controlling apparatus;  
       FIGS. 16, 17  and  18  are block diagrams showing different particular examples of the circuit; and  
       FIG. 19  is a block diagram showing another different particular example of the circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Before a preferred embodiment of the present invention is described in detail, a corresponding relationship between several features recited in the accompanying claims and particular elements of the preferred embodiment described below is described. The description, however, is merely for the confirmation that the particular elements which support the invention as recited in the claims are disclosed in the description of the embodiment of the present invention. Accordingly, even if some particular element which is recited in description of the embodiment is not recited as one of the features in the following description, this does not signify that the particular element does not correspond to the feature. On the contrary, even if some particular element is recited as an element corresponding to one of the features, this does not signify that the element does not correspond to any other feature than the element.  
      Further, the following description does not signify that the prevent invention corresponding to particular elements described in the embodiment of the present invention is all described in the claims. In other words, the following description does not deny the presence of an invention which corresponds to a particular element described in the description of the embodiment of the present invention but is not recited in the claims, that is, the description does not deny the presence of an invention which may be filed for patent in a divisional patent application or may be additionally included into the present patent application as a result of later amendment to the claims.  
      According to the invention as set forth in claim  1 , a controlling apparatus (for example, a controlling apparatus  2  of  FIG. 1 ) for controlling an inputting/outputting apparatus (for example, an I/O display apparatus  1  of  FIG. 1 ) of the active matrix driving type which includes a pixel including an element (for example, an EL element  12  of  FIG. 1 ) whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element includes an accumulation control section (for example, a light reception control section  124  of  FIG. 14  which causes a processing at step S 5  of  FIG. 15  to be executed) for causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and a detection section (for example, a detection section  124  of  FIG. 18 ) for detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the accumulation control section.  
      According to the invention as set forth in claim  5 , a controlling method for a controlling apparatus (for example, a controlling apparatus  2  of  FIG. 1 ) for controlling an inputting/outputting apparatus (for example, an I/O display apparatus  1  of  FIG. 1 ) of the active matrix driving type which includes a pixel including an element (for example, an EL element  12  of  FIG. 1 ) whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element includes an accumulation control step (for example, a step S 5  of  FIG. 15 ) of causing charge generated by the element included in the pixel during the light receiving action in response to reception of light from the outside to be accumulated for a predetermined period of time, and a detection step (for example, a step S 8  of  FIG. 15 ) of detecting an input of the light from the outside to the inputting/outputting apparatus based on the charge accumulated by the processing of the accumulation control section.  
      Also in a program recorded on a recording medium as set forth in claim  6  and a program as set forth in claim  7 , an embodiment (a mere example) to which each step corresponds is similar to that in the controlling method as set forth in claim  5 .  
      According to the invention as set forth in claim  8 , an inputting/outputting apparatus (for example, an I/O display apparatus  1  of  FIG. 1 ) of the active matrix driving type which includes a pixel including an element (for example, an EL element  12  of  FIG. 1 ) whose action can be changed over between a light emitting action and a light receiving action in response to a voltage applied to the element, the pixel including an accumulation section (for example, a parasitic capacitor  13  of  FIG. 1 ) for accumulating charge generated by the element included in the pixel upon the light receiving action in response to reception of light from the outside for a predetermined period of time under the control of a controlling apparatus, and an outputting section (for example, a circuit group  32  of  FIG. 8 ) for outputting the charge accumulated in the accumulation section to the controlling apparatus.  
      Now, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawings.  
       FIG. 1  shows an example of an appearance of an IN/OUT (I/O) display apparatus  1  to which the present invention is applied.  
      Referring to  FIG. 1 , the I/O display apparatus  1  shown includes pixels by which an input function (detection function) of detecting light irradiated from the outside and an output function (display function) of displaying a predetermined image can be implemented.  
      As shown in an enlarged scale in a circuit in  FIG. 1 , each of the pixels which form the I/O display apparatus  1  is represented by a switch  11  which may be, for example, a thin film transistor (TFT), an organic or inorganic EL element  12  and a parasitic capacitor  13  which is a capacitance parasitic in the EL element  12 . In particular, the I/O display apparatus  1  is a self-luminous EL display apparatus which can be driven by active matrix driving.  
      In the I/O display apparatus  1 , action of each of the pixels is controlled by a controlling apparatus  2  to implement the input function and the output function.  
      Here, the input function and the output function are described.  
       FIGS. 2 and 3  show an example of a circuit corresponding to one pixel of the I/O display apparatus  1 .  
      When a forward voltage (bias) is applied to the gate electrode G of the TFT from a display line selection line (gate line), current flows in a direction from the source electrode S toward the drain electrode D in an active semiconductor layer (channel) made of amorphous silicon or polysilicon in response to a voltage applied to the source electrode S from a display data signal line (source line) as indicated by a solid line arrow mark in  FIG. 2 .  
      The anode electrode of the EL element is connected to the drain electrode D of the TFT, and the EL element emits light as indicated by a void arrow mark in  FIG. 2  in response to a potential difference between the anode and the cathode which is caused by current flowing through the channel of the TFT.  
      The light from the EL element goes out to the outside of the display apparatus. Accordingly, display of an image, that is, the output function, is implemented by such action of the pixels.  
      On the other hand, a voltage near 0 V or a reverse voltage is applied to the gate electrode G of the TFT through the display line selection line, then even when a voltage is applied to the source electrode S through the display data signal line, no current flows in the channel, and no potential difference generates between the anode and cathode electrodes of the EL element. Consequently, no light is emitted from the pixel.  
      If, in this state, light from the outside is irradiated upon the pixel of  FIG. 3  as indicated by void arrow marks, then the gate electrode G is opened (a channel is formed) by the photoconductivity of the channel of the TFT. Consequently, although the amount is very small, leak current (off current) flows in the direction from the drain electrode D toward the source electrode S. Further, leak current is generated in the EL element.  
      From this, if leak current flowing through the pixel (TFT and EL element) to which a voltage near 0 V or a reverse voltage is applied is amplified to detect whether or not such leak current exists, then it is possible to identify whether or not light is irradiated upon the pixel from the outside. Further, the amount of light can be identified depending on the amount of the leak current. Thus, the input function is achieved thereby.  
      For example, by irradiating light representative of predetermined data toward the display apparatus formed from such pixels as described above, the user can cause the display apparatus to detect the incoming light to the display apparatus. Consequently, data can be inputted to the display apparatus through the light.  
      In the following description, action of a pixel (EL element) when a forward voltage is applied as seen in  FIG. 2  is referred to as light emitting action, and action of a pixel of generating leak current in response to light irradiated from the outside when a reverse voltage is applied as seen in  FIG. 3  is referred to as light receiving action.  
       FIG. 4  illustrates a current characteristic of the pixel shown in  FIGS. 2 and 3 . The axis of ordinate represents the value of the current in the pixel, and the axis of abscissa represents the value of the voltage applied to the gate electrode G.  
      Referring to  FIG. 4 , a line L 1  representing a result of the measurement represents the value of current detected with the pixel when light is irradiated upon the pixel while a forward voltage is applied to the pixel, that is, the value of the sum of current flowing in the channel of the TFT and current generated by the EL element. Another line L 2  represents the value of current detected with the pixel when no light is irradiated upon the pixel while a forward voltage is applied to the pixel.  
      From the lines L 1  and L 2 , it can be seen that, where a forward voltage is applied, no difference is found between the values of detected current irrespective of whether or not light from the outside exists.  
      On the other hand, a further line L 3  of  FIG. 4  represents the value of current detected with the pixel when light is irradiated upon the pixel while a reverse voltage is applied to the pixel. A still further line L 4  represents the value of current detected with the pixel when no light is irradiated upon the pixel while a reverse voltage is applied to the pixel.  
      Where the line L 3  and the line L 4  are compared with each other, it can be recognized that, when a reverse voltage is applied to the pixel, a difference appears between the value of current detected with the pixel when light is irradiated from the outside and the value of current detected when no light is irradiated from the outside. For example, if a predetermined amount of light is irradiated upon the pixel from the outside while, for example, a voltage of approximately −5 V (reverse voltage) is applied to the pixel, then current (the sum of current flowing in the active semiconductor layer of the TFT and current generated by the EL element) of approximately “1 −8  (A)” is detected.  
      In  FIG. 4 , it is indicated by the line L 4  that, even when no light is irradiated from the outside, current of a very low level of approximately “1 −10  (A)” is generated. However, this originates from noise during the measurement. It is to be noted that measurement results similar to those of  FIG. 4  are obtained irrespective of whichever one of the colors of R, G and B the light emitted from the pixel of the EL element is.  
       FIG. 5  shows a portion of the diagram of  FIG. 4  in the proximity of 0 V.  
      As seen from the line L 3  and the line L 4  shown in  FIG. 5 , also when a voltage near 0 V is applied, a difference appears between the current value when light is irradiated and the current value when no light is irradiated.  
      Accordingly, even when a voltage of near 0 V is applied, the difference, that is, detection of whether or not light is irradiated, can be detected by amplifying the generated current.  
      From this, it is possible to cause a certain pixel to perform a light receiving action by controlling the gate voltage so as to have a value of near 0 V without positively applying a reverse voltage.  
      Where the gate voltage is controlled so as to have a value of near 0 V so that the pixel performs a light receiving action, the power consumption can be reduced by an amount arising from a reverse voltage when compared with the alternative case wherein a reverse voltage is applied to cause the pixel to perform a light receiving action.  
      Further, since the number of voltages to be controlled decreases, the control of the voltages and the system configuration are facilitated. In particular, since to control the voltage so as to have a value of near 0 V is to control so that a forward voltage may not be applied, the control can be implemented only by means of a control line and a power supply circuit for controlling the gate voltage so that a forward voltage may not be applied. In other words, a control line for controlling the gate voltage so that a reverse voltage may be applied need not be provided separately.  
      Consequently, the configuration of the power supply circuit on a driving circuit board or a system circuit board of the display apparatus can be simplified, and reduction in power consumption can be achieved. Also, efficient utilization of the limited space on the circuit board can be achieved.  
      Furthermore, by preventing application of a reverse voltage, otherwise possible breakdown of a TFT or an EL element which may occur when a reverse voltage is applied can be prevented. For example, although the voltage endurance of a TFT can be raised, for example, by increasing the channel length, in this instance, the current upon conduction decreases, and in order to assure sufficient current, it is necessary to increase the channel width (W length).  
      As a result, in order to raise the voltage endurance without changing the value of current flowing through a TFT, it is necessary to increase the size of the TFT. This makes it difficult to dispose such a TFT of an increased size as described above in each of pixels of a display apparatus of a high definition wherein the size of the pixels is small.  
      Accordingly, by eliminating the reverse voltage, design of the voltage endurance for a TFT or an EL element is facilitated and the size of the TFT or the EL element itself can be reduced. Consequently, a high definition display apparatus can be implemented.  
      As described above, according to the I/O display apparatus  1  wherein a TFT and an EL element are provided in each of the pixels, not only it is possible to display an image, but also it is possible to detect light from the outside using the pixels by applying a voltage of near 0 V or a reverse voltage.  
      Incidentally, in a display apparatus which includes pixels which can perform not only a light emitting action but also a light receiving action in this manner, the amount of leak current generated by a photoelectric effect of an EL element differs depending upon the amount (energy) of light irradiated on the pixel which is performing a light receiving action.  
      Accordingly, since, as the amount of irradiated light increases, the amount of generated leak current increases, the light receiving sensitivity rises. On the other hand, since as the mount of irradiated light decreases, the amount of generated leak current decreases, the light receiving sensitivity decreases.  
      Therefore, the I/O display apparatus  1  of  FIG. 1  is configured such that, charge generated upon reception of light from the outside by a pixel which is performing a light receiving action is accumulated into a predetermined capacitor for a predetermined period of time, and the amount of the accumulated charge (amount of current) is detected collectively to raise the light receiving sensitivity.  
      In particular, not the amount of current generated upon reception of light is detected immediately after the current is generated to detect whether or not there is an input of light from the outside, but whether or not there is an input of light from the outside is detected based on the amount of the entire current generated within the predetermined period of time.  
      For the capacitor for accumulating the charge, for example, the parasitic capacitor  13  connected in parallel to the EL element  12  is used.  
      Here, operation of the circuit is described with reference to  FIGS. 6 and 7 .  
      It is assumed that, in the example shown, detection of light from the outside is performed based on leak current generated by the EL element  12 . Also it is assumed that a light receiving action is performed not by positively applying a reverse bias but controlling the voltage to be applied to the switch  11  (TFT) to a value of near 0 V (to switch off the switch  11 ).  
       FIG. 6  shows an example of the circuit when it performs a light emitting action (display of an image).  
      If the switch  11  is switched on to apply a forward bias as seen in  FIG. 6 , then light emitting current I_el 1  in a forward direction flows through the EL element  12 , whereupon the EL element  12  emits light. At this time, positive charge is accumulated into the parasitic capacitor  13  on the anode electrode side of the EL element  12  and negative charge is accumulated into the parasitic capacitor  13  on the cathode electrode side of the EL element  12  both by an amount corresponding to the amount of the light emitting current I_el 1 . For example, where the amount of the light emitting current I_el 1  increases and the level of light emission increases (as the luminance increases), the potential difference applied between the electrodes of the EL element  12  increases and also the amount of charge accumulated in the parasitic capacitor  13  increases.  
       FIG. 7  shows an example of the circuit when it performs a light receiving action.  
      As seen in  FIG. 7 , when light is irradiated upon the node from the outside while a bias near 0 V is applied (while the switch  11  is off), light receiving current I_el 2  flows in the opposite direction to that of the light emitting current I_el 1 .  
      At this time, the EL element  12  does not emit light. Further, since the directions of the light emitting current I_el 1  and the light receiving current I_el 2  are opposite to each other, charge of the opposite polarities to those in the light emitting action is accumulated in the parasitic capacitor  13 .  
      This state is held for a predetermined period of time. Accordingly, charge generated by the EL element  12  within the predetermined period is all accumulated into the parasitic capacitor  13 .  
      After the predetermined period of time elapses, the input of light from the outside is detected based on the overall amount of the charge accumulated in the parasitic capacitor  13 . In particular, the overall accumulated charge is extracted from a bus (not shown) connected to the parasitic capacitor  13  to detect the input.  
      Since an input from the outside is detected based on the entire charge generated within the predetermined period of time in this manner, the amplitude of the signal representative of the amount of the charge (that is, a signal representative of the value of current, or a signal representative of the value of a voltage obtained by converting the current value into a voltage value) can be set to an increased value, and this facilitates detection of the input performed based on the signal.  
      Now, a series of actions from light emission to light reception are described in connection of an example of a more particular circuit with reference to FIGS.  8  to  12 .  
       FIG. 8  shows an example of a circuit in each of the pixels which form the I/O display apparatus  1 .  
      Switches SW 1  to SW 3  are switching elements made of amorphous silicon, polysilicon or the like.  
      Among them, the switch SW 1  (which corresponds to the switch  11  of  FIG. 6 ) is controlled between on and off states by a display line selection line  22 , and outputs, when it is in an on state, a signal supplied thereto from a display data signal line  21  and representative of display data to a circuit group  31 . The signal representative of the display data is supplied, for example, from the controlling apparatus  2 .  
      The switch SW 2  is controlled between on and off states by EL element light emission control by the controlling apparatus  2  and supplies, when it is in the on state, an output of the circuit group  31  to the EL element  12 .  
      The switch SW 3  is controlled between on and off states by reading line selection line  23  and supplies, when it is in the on state, leak current (charge accumulated in the parasitic capacitor  13 ) generated by the EL element  12  upon reception of irradiation of light for the predetermined period of time to a circuit group  32 . Thus, the switch SW 3  is placed into the on state after the predetermined period of time elapses after the light receiving action is started.  
      The circuit group  31  includes, for example, a display data writing circuit, a threshold value dispersion correction circuit and so forth. The display data writing circuit temporarily accumulates a signal supplied thereto from the switch SW 1  and performs I/V (current/voltage) conversion for causing the EL element  12  to emit light. The threshold value dispersion correction circuit is a circuit (threshold value correction circuit for the TFT) for correcting the dispersion of a signal, for example, appearing at the output of the switch SW 1 .  
      The circuit group  32  includes, for example, a reading circuit, a current-voltage amplification circuit, an A/D (Analog/Digital) conversion circuit, and so forth. The reading circuit reads out a light reception signal generated by the EL element  12  through the switch SW 3 . The current-voltage amplification circuit amplifies light reception current or a voltage corresponding to the light reception current. The A/D conversion circuit converts the current value or the voltage value amplified by the current-voltage amplification circuit into digital data (light reception data) and outputs the light reception data to a light reception data signal line  24 . The light reception data outputted to the light reception data signal line  24  is supplied to the controlling apparatus  2  so that the input of light from the outside is detected by the controlling apparatus  2 .  
      In  FIG. 8 , all of the switches SW 1  to SW 3  are in the off state. In this state, none of the light emitting action and the light receiving action is performed.  
      In order to cause the pixel in such a state as described above to perform a light emitting action, the switch SW 1  is placed into the on state first by the display line selection line  22  as seen in  FIG. 9 . At this time, a signal supplied from the display data signal line  21  and representative of display data is inputted to the circuit group  31  through the switch SW 1 . Consequently, I/V conversion and correction of the dispersion of the signal are performed by the circuit group  31 .  
      Then, after the switch SW 1  is placed into the off state as seen in  FIG. 10 , EL element light emission control is performed by the controlling apparatus  2 . Thus, since the switch SW 2  is placed into the on state, light emitting current I_el 1  corresponding to the display data flows from the circuit group  31  to the EL element  12 . Consequently, the EL element  12  emits light with a luminance level corresponding to the display data.  
      At this time, a potential difference corresponding to the level of light emission, that is, a potential difference corresponding to the display data, is applied between the anode and cathode electrodes of the EL element  12 , and charge corresponding to the potential difference is accumulated in the parasitic capacitor  13 . The state of  FIG. 10  corresponds to the state of  FIG. 6 .  
      Then, in order to change over the action of the pixel from the light emitting action to the light receiving action, the switch SW 2  is placed into the off state as seen in  FIG. 11  and this state is kept for the predetermined period of time. Charge (light receiving current I_el 2 ) generated by the EL element  12  upon reception of the light from the outside is accumulated into the parasitic capacitor  13 . In the example of  FIG. 11 , since the impedance of the cathode electrode side of the EL element  12  is lower than that of the anode electrode side of the EL element  12 , the charge on the cathode electrode side of the parasitic capacitor  13  escapes. However, since a path for discharging the charge is not provided for the anode electrode side, negative charge remains accumulated. The state of  FIG. 11  corresponds to the state of  FIG. 7 .  
      After the state of  FIG. 11  is kept for the predetermined period of time, the switch SW 3  is placed into the on state by the reading line selection line  23  as seen in  FIG. 12 . Consequently, current corresponding to the amount of charge accumulated in the parasitic capacitor  13  is supplied to the circuit group  32  through the switch SW 3 . Also light receiving current I_el 2  generated by the EL element  12  while the switch SW 3  keeps the on state is supplied to the circuit group  32 .  
      The circuit group  32  performs predetermined processing such as amplification for the signal supplied thereto and outputs resulting light reception data to the controlling apparatus  2  through the light reception data signal line  24 .  
      By the series of actions described above, detection of an input from the outside is performed based on the overall amount of charge accumulated in the parasitic capacitor  13 . The processing of the controlling apparatus  2  which controls the actions of the pixels in this manner is hereinafter described.  
       FIG. 13  shows an example of a configuration of the controlling apparatus  2 .  
      Referring to  FIG. 13 , a central processing unit (CPU)  101  executes various processing based on a program stored in a ROM (Read Only Memory)  102  or a program loaded into a RAM (Random Access Memory)  103  from a storage section  106 . Also data and so forth necessary for the CPU  101  to execute the various processing are suitably stored into the RAM  103 .  
      The CPU  101 , ROM  102  and RAM  103  are connected to each other by a bus  104 . Also an input/output interface  105  is connected to the bus  104 .  
      The storage section  106 , which is formed from a hard disk, a communication section  107  which performs a communication processing through a network and so forth are connected to the input/output interface  105  in addition to the I/O display apparatus  1 .  
      When necessary, a drive  108  is connected to the input/output interface  105 , and a removable medium  109  which may be a magnetic disk, an optical disk, a magneto-optical disk or a semiconductor memory is loaded suitably into the drive  108  such that a computer program read out from the removable medium  109  is installed into the storage section  106  as occasion demands.  
       FIG. 14  shows an example of a functional configuration of the controlling apparatus  2 .  
      At least part of the configuration shown in  FIG. 14  is implemented by a predetermined program executed by the CPU  101  of  FIG. 13 .  
      A control section  121  outputs, for example, acquired display data to a display control section  122  so that the display data is displayed using the pixels of the I/O display apparatus  1  which perform the light emitting action (to cause each of the pixels to emit light with a level corresponding to the display data).  
      Further, the control section  121  controls a light reception control section  123  to cause predetermined ones of the pixels of the I/O display apparatus  1  to perform the light receiving action. The control section  121  performs, when light reception data is supplied thereto from a detection section  124 , a predetermined processing based on the received light reception data.  
      The display control section  122  selects a line of those pixels which are to perform the light emitting action from among the display line selection lines  22  based on the display data supplied thereto from the control section  121  and supplies signals representative of the display data to the selected lines from the display data signal lines  21  to cause the pixels of the selected line to perform the light emitting action. Further, the display control section  122  performs EL element light emission control at a predetermined time to place the switch SW 2  into the on state.  
      The light reception control section  123  selects, under the control of the control section  121 , a line of those pixels which are to perform the light receiving action through the reading line selection line  23  and places the switches SW 3  into the on state after the predetermined period of time elapses after the light receiving action is started.  
      The detection section  124  detects data inputted from the outside using light based on the light reception data supplied thereto through the light reception data signal line  24  and outputs the detected light reception data to the control section  121 .  
      Now, a controlling processing of the I/O display apparatus  1  performed by the controlling apparatus  2  having the configuration described above is described with reference to the flow chart of  FIG. 15 . This processing is started when display data are supplied from the control section  121  to the display control section  122  when the I/O display apparatus  1  is in such a state as seen in  FIG. 8 .  
      At step S 1 , the display control section  122  selects a line of those pixels which are to perform the light emitting action through the display line selection line  22  based on the display data supplied thereto from the control section  121  and places the switches SW 1  of the pixels of the selected line into the on state ( FIG. 9 ).  
      Further, the display control section  122  supplies signals representative of the display data to the pixels which are to perform the light emitting action through the respective display data signal lines  21  at step S 2 . Then at step S 3 , the display control section  122  performs EL element light emission control. Consequently, each of the switches SW 2  is placed into the on state, and light emitting current I_el 1  obtained by the predetermined processing performed by the circuit group  31  flows through the EL element  12  to cause the EL element  12  to emit light ( FIG. 10 ).  
      It is to be noted that the display control section  122  performs further control to place the switch SW 1  into the off state before the EL element light emission control is performed and to place the switch SW 2  into the off state after the EL element  12  emits light.  
      The display control section  122  decides, at step S 4 , whether or not the action of the pixel having performed the light emitting action should be changed over to the light receiving action. If it is decided that the action of the pixel should not be changed over, then the processing returns to step S 1  to repeat the series of processing described above.  
      If it is decided at step S 4  by the display control section  122  that the action of the pixel having performed the light emitting action should be changed over to the light receiving action, then the processing advances to step S 5 .  
      At step S 5 , the off state of the switch SW 2  is maintained so that charge generated by the EL element  12  in response to reception of light remains accumulated into the parasitic capacitor  13  ( FIG. 11 ).  
      At step S 6 , the light reception control section  123  decides whether or not the predetermined period of time elapses after the switch SW 2  of the pixel which is performing the light receiving action is placed into the off state. Thus, the light reception control section  123  stands by until after it is decided that the predetermined period of time elapses.  
      If the light reception control section  123  decides at step S 6  that the predetermined period of time elapses after the switch SW 2  is placed into the off state, then the processing advances to step S 7 . At step S 87 , the light reception control section  123  places the switch SW 3  of the pixel having performed the light receiving action into the on state so that a signal corresponding to the charge generated by the EL element  12  and accumulated in the parasitic capacitor  13  is supplied to the circuit group  32 .  
      The predetermined processing such as amplification are performed for the light receiving current I_el 2  supplied to the circuit group  32 , and resulting light reception data is supplied to the detection section  124  of the controlling apparatus  2  through the light reception data signal line  24 .  
      At step S 8 , the detection section  124  detects the light reception data supplied thereto through the light reception data signal line  24  and outputs the detected light reception data to the control section  121 .  
      At step S 9 , the light reception control section  123  decides whether or not the light receiving action should be ended. If it is decided that the light receiving action should not be ended, then the light reception control section  123  places the switch SW 3  into the off state. Thereafter, the processing returns to step S 5  so that the processing at the steps beginning with step s 5  are repeated. If the light reception control section  123  decides at step S 9  that the light receiving action should be ended, then it ends the processing.  
      Each of the pixels can perform display of an image and detection of light by causing the pixel to repetitively execute the series of processing described above.  
      In the description above, it is described that the parasitic capacitor  13  is used as an element for accumulating charge generated by the EL element  12 , a capacitor  131  different from the capacitance parasitic to the EL element  12  may be provided in parallel to the EL element  12  as seen in  FIG. 16 .  
      In this instance, charge generated by the EL element  12  can be accumulated into the capacitor  131  by an arbitrary amount which does not rely upon the parasitic capacitor  13 .  
      Further, a switch SW 4  may be interposed between the anode electrode of the EL element  12  and the capacitor  131  as seen in  FIG. 17  such that it can be changed over between a state wherein the capacitor  131  is connected in parallel to the EL element  12  and another state wherein the capacitor  131  is not connected in parallel to the EL element  12 .  
      The switch SW 4  is placed into the on state when the EL element  12  is to perform the light receiving action, but is placed into the off state when the I/O display apparatus  1  is to perform the light emitting action (when the light emitting action is started). The capacitor  131  connected in parallel to the EL element  12  acts as an element for increasing the time constant in the light emitting action, and where the capacitor  131  is normally connected to the EL element  12 , it acts to deteriorate the responsibility of light emission. Therefore, the capacitor  131  can be disconnected from the EL element  12  in the light emitting action in this manner so that deterioration of the responsiveness in light emission can be prevented.  
      In this manner, the capacitor  131  which is a capacitor for accumulating charge generated by the EL element  12  is not limited to that which is provided in each pixel but may be provided outside the pixels such that it is connected to the reading line selection line  23 . In the example of  FIG. 18 , the switches SW 1 , SW 2  and SW 3 , EL element  12 , parasitic capacitor  13  and circuit group  31  are provided in the inside of each pixel, and a capacitor  141  is provided outside the pixel (outside the range surrounded by the gate line (display line selection line  22 ) and the source line (display data signal line  21 )).  
       FIG. 19  shows an example wherein a capacitor  141  which is a capacitor for accumulating charge generated by the EL element  12  is provided outside a display unit. Here, the display unit signifies a display surface formed from a plurality of pixels disposed thereon and each including the switches SW 1 , SW 2  and SW 3 , EL element  12 , parasitic capacitor  13  and circuit group  31 , and in the example of  FIG. 19 , the capacitor  141  and the circuit group  32  are provided outside the display surface.  
      In particular, the capacitor  141  can be provided at any various positions outside the pixels or outside the display unit as seen in  FIG. 18  or  19  only if charge generated by the EL element  12  can be accumulated at the position.  
      While it is described in the foregoing description that the controlling apparatus  2  is built in the I/O display apparatus  1  as seen in  FIG. 1 , naturally it may otherwise be provided outside the I/O display apparatus  1 .  
      While the series of processing described above can be executed by hardware, it may otherwise be executed by software.  
      Where the series of processing is executed by software, a program which constructs the software is installed from a network or a recording medium into a computer incorporated in hardware for exclusive use or, for example, a personal computer for universal use which can execute various functions by installing various programs.  
      The recording medium may be formed as the removable medium  109  such as, as shown in  FIG. 13 , a magnetic disk (including a floppy disk), an optical disk (including a CD-ROM (Compact Disc-Read Only Memory) and a DVD (Digital Versatile Disk)), a magneto-optical disk (including an MD (trademark) (Mini-Disc)), or a semiconductor memory which has the program recorded thereon or therein and is distributed in order to provide the program to a user separately from an apparatus body, or as the ROM  102  having the program recorded therein or thereon or a hard disk included in the storage section  106  which is provided to a user in a form wherein it is incorporated in an apparatus body in advance.  
      It is to be noted that, in the present specification, the steps may be but need not necessarily be processed in a time series in the order as described, and include processing which are executed parallelly or individually without being processed in a time series.  
      While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.