Abstract:
Provided is a display device equipped with a touch panel, including a front panel arranged above a capacitive touch panel at a predetermined distance away therefrom, in which the touch panel includes a plurality of X electrodes and a plurality of Y electrodes, and the X electrodes are sequentially applied with pulse signals and the Y electrodes receive the pulse signals. When an arbitrary point on the front panel is touched, the touch panel computes a touched point on the touch panel by using both the received pulse signals obtained from the Y electrodes in a case where the front panel is not deformed and the received pulse signals obtained from the Y electrodes in a case where the front panel is deformed. With this, an erroneous operation in which a measurement value is lowered to finally disappear is prevented.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP 2010-221384 filed on Sep. 30, 2010, 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 display device equipped with a touch panel, which includes a capacitive touch panel, in particular, to a technology effective for preventing an erroneous operation in which a measurement value is lowered to finally disappear occurring in a capacitive touch panel including an air layer provided between a front panel and the touch panel. 
     2. Description of the Related Art 
     A display device including a device (hereinafter, also referred to as “touch sensor” or “touch panel”) for inputting information to a display screen by a touch operation (contact and press operation, hereinafter, simply referred to as “touch”) by using a user&#39;s finger, a pen, or the like is used for mobile electronic devices such as a PDA and a mobile terminal, various consumer electric appliances, an automated teller machine, and the like. As this kind of touch panel, there are known resistance film type of detecting a change in resistance value of a touched portion, capacitive type of detecting a change in capacitance thereof, optical sensor type of detecting a change in amount of light, and the like. 
     An exemplary capacitive touch panel is disclosed in Japanese Patent Application Publication No. 2003-511799. In the capacitive touch panel disclosed therein, a vertical detection electrode (X electrode) and a horizontal detection electrode (Y electrode) are arranged in vertical and horizontal two-dimensional matrix, and a capacitance of each electrode is detected by an input processing part. When a conductor such as a finger touches a surface of the touch panel, the capacitance of each electrode increases. Thus, the input processing part detects the increase to calculate input coordinates based on a signal of a capacitance change detected by each electrode. 
     SUMMARY OF THE INVENTION 
     Conventionally, a capacitive touch panel generally has a structure in which a front panel is bonded to an entire front surface of the capacitive touch panel with an adhesive. Since the front panel is exposed on an outermost surface of the touch panel, the front panel is sometimes damaged or gets dirty, and hence is required to be replaced. 
     With the conventional structure, however, it is inevitable to replace the entire touch panel for replacing the front panel. In this regard, there is a request of replacing only the front panel. 
     In order to respond to the request, a method of providing an air layer between the touch panel and the front panel without bonding the touch panel and the front panel to each other has been proposed. According to the structure, for the repair of capacitive touch panel products, the improvement of workability and a reduction in cost can be realized. 
     When the air layer is provided between the touch panel and the front panel, however, it is supposed that an object to be sensed (for example, a finger or a conductor) may deform the front panel under load. In this case, an erroneous operation in which a measurement value is lowered to finally disappear occurs with an increase in the amount of deformation under load. 
     The present invention has been made to solve the problem of the conventional technology described above, and therefore has an object to provide a technology which enables the prevention of an erroneous operation in which a measurement value is lowered to finally disappear in a display device equipped with a touch panel, which includes a front panel provided above a capacitive touch panel at a predetermined distance away therefrom. 
     The above-mentioned and other objects and novel characteristics of the present invention become apparent from the description of this specification and the accompanying drawings. 
     Among aspects of the present invention disclosed in this application, the summary of the representative one is briefly described as follows. 
     In a display device equipped with a touch panel, which includes a capacitive touch panel provided on a display panel, a front panel provided above the capacitive touch panel, and an air layer provided between the touch panel and the front panel, when an object to be sensed (for example, a finger or a conductor) causes a deformation of the front panel under load, a phenomenon in which a measurement value is lowered to finally disappear occurs with an increase in the amount of deformation under load. The above-mentioned phenomenon is described as follows. 
     In the capacitive touch panel which detects a change in electrostatic capacitance at an intersection of an X electrode and a Y electrode, the object to be sensed (finger or conductor) acts as an electrostatic shield for blocking lines of electric force between the intersections of the X electrodes and the Y electrodes so as to detect a change in electrostatic capacitance, that is, a reduction in electrostatic capacitance at the intersection of the X electrode and the Y electrode. 
     On the other hand, if a larger amount of the front panel generally made of a material having a larger relative permittivity than that of air moves into a path of the lines of electric force at the intersection of the X electrode and the Y electrode due to the deformation under load described above, the electrostatic capacitance at the intersection of the X electrode and the Y electrode is increased to act so as to erase the measurement value of the object to be sensed (finger or conductor). 
     In the present invention, for detecting the proximity or contact of the object to be sensed (finger or conductor) to/with the touch panel, a reference value is set for sequentially tracking a state in which there is no proximity or contact of the object to be sensed (finger or conductor) to/with the touch panel. Based on the reference value, two threshold values, that is, a first threshold value and a second threshold value, each for determining the proximity or contact of the object to be sensed (finger or conductor), are respectively provided on the side where the intensity of a received signal increases and on the side where the intensity of the received signal decreases. When the intensity of the received signal becomes equal to or higher than the first threshold value or becomes equal to or lower than the second threshold value, it is determined that “a touch event occurs”. 
     As described above, in the present invention, even if the measurement value is greatly changed to the negative side as a result of the deformation of the front panel under load, which is caused by the object to be sensed (finger or conductor), the measurement value is treated as an effective signal. As a result, the above-mentioned erroneous operation in which the measurement value disappears can be prevented. 
     The effects obtained by the representative one of the aspects of the present invention disclosed in this application are briefly described as follows. 
     According to the present invention, in the display device equipped with the touch panel, which includes the capacitive touch panel and the air layer provided between the front panel and the touch panel, the erroneous operation in which the measurement value is lowered to finally disappear can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram illustrating a schematic configuration of a display device equipped with a touch panel according to an embodiment of the present invention; 
         FIG. 2  is a sectional view of a principal part, for illustrating the display device equipped with the touch panel according to the embodiment of the present invention; 
         FIG. 3A  is a conceptual diagram illustrating a multi-layered structure of a conventional display device equipped with a touch panel, and  FIG. 3B  is a conceptual diagram illustrating a multi-layered structure of the display device equipped with the touch panel according to the embodiment of the present invention; 
         FIGS. 4A and 4B  are conceptual diagrams respectively illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3A , when a finger is in contact with a front panel with a small load thereon and when the finger is in contact with the front panel with a large load thereon; 
         FIGS. 5A and 5B  are conceptual diagrams respectively illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3B , when the finger is in contact with the front panel with a small load thereon and when the finger is in contact with the front panel with a large load thereon; 
         FIGS. 6A and 6B  are conceptual diagram each illustrating a state of lines of electric force between an X electrode and a Y electrode in the structure illustrated in  FIG. 3A ; 
         FIG. 7A  is a graph showing a time-series change in measurement value obtained when the finger is not in contact with the front panel and when the finger is in contact with the front panel in the structure illustrated in  FIG. 3A , and  FIGS. 7B and 7C  are conceptual diagrams illustrating states of lines of electric force obtained in the time periods respectively denoted by the symbols A and B in  FIG. 7A ; 
         FIGS. 8A and 8B  are conceptual diagrams each illustrating a state of the lines of electric force between the X electrode and the Y electrode in the structure illustrated in  FIG. 3B ; 
         FIG. 9A  is a graph showing a time-series change in measurement value obtained when the finger is not in contact with the front panel and when the finger is in contact with the front panel in the structure illustrated in  FIG. 3B , and  FIGS. 9B to 9D  are conceptual diagrams each illustrating a state of the lines of electric force obtained in the time periods respectively denoted by the symbols B to D in  FIG. 9A ; 
         FIG. 10A  is a graph for illustrating signal processing of the touch panel of the display device equipped with the touch panel according to the embodiment of the present invention, and  FIGS. 10B to 10D  are conceptual diagrams each illustrating a state of the lines of electric force obtained in the time periods respectively denoted by the symbols B to D in  FIG. 10A ; 
         FIG. 11  is a flowchart illustrating a processing procedure of the signal processing of the touch panel of the display device equipped with the touch panel according to the embodiment of the present invention; 
         FIG. 12  is a plan view illustrating an electrode pattern of a capacitive touch panel in the display device equipped with the touch panel according the embodiment of the present invention; 
         FIG. 13  is a sectional view illustrating a sectional structure taken along the line A-A′ of  FIG. 12 ; 
         FIG. 14  is a sectional view illustrating a sectional structure taken along the line B-B′ of  FIG. 12 ; 
         FIG. 15  is a sectional view illustrating another example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 , taken along the line A-A′ of  FIG. 12 ; 
         FIG. 16  is a sectional view illustrating the example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 , taken along the line B-B′ of  FIG. 12 ; 
         FIG. 17  is a sectional view illustrating a further example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 , taken along the line A-A′ of  FIG. 12 ; and 
         FIG. 18  is a sectional view illustrating the further example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 , taken along the line B-B′ of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, an embodiment of the present invention is described in detail with reference to the drawings. 
     Throughout the drawings illustrating the embodiment of the present invention, components that have the same function are denoted by the same reference symbol in order to avoid repetitive description. Further, the following embodiment is not intended to limit the interpretation of the scope of the claims of the present invention in any way. 
       FIG. 1  is a diagram illustrating a schematic configuration of a display device equipped with a touch panel according to the embodiment of the present invention. 
       FIG. 1  illustrates a capacitive touch panel  400 . The touch panel  400  includes X electrodes for capacitance detection and Y electrodes for capacitance detection.  FIG. 1  illustrates as an exemplary case where four X electrodes (X 1  to X 4 ) and four Y electrodes (Y 1  to Y 4 ) are provided. However, each of the numbers of the X electrodes and the Y electrodes is not limited to four. 
     The touch panel  400  is disposed on a front surface of a display device  600 . Accordingly, when an image displayed on the display device  600  is viewed by a user, the displayed image needs to pass through the touch panel  400 , and hence the touch panel  400  is desired to have a high transmittance. 
     The X electrodes and the Y electrodes of the touch panel  400  are connected to a capacitance detecting unit  102  by wirings  21 . The capacitance detecting unit  102  is controlled by a detection control signal  22  output from a control unit  103  so as to sequentially apply pulses by using the X electrodes X 1  to X 4  as transmitting electrodes (drive electrodes) and the Y electrodes Y 1  to Y 4  as receiving electrodes. In this manner, the intensity of a received signal at each of intersections of the X electrodes X 1  to X 4  and the Y electrodes Y 1  to Y 4  is measured. The measurement value is output as a capacitance measurement value  23  to the control unit  103 . 
     A storage unit  4  stores a reference value  41 , a measurement value  42 , and a signal value  43  for each of the intersections of the electrodes (X electrodes and Y electrodes) as working data required for the control unit  103  to perform touch-detection processing. The storage unit  4  also stores a touch-state management table  44 . 
     Each of the reference value  41 , the measurement value  42 , and the signal value  43  is two-dimensional array data with the number of X electrodes as the number of lateral elements and the number of Y electrodes as the number of longitudinal elements. The reference value  41  is data of the measurement value  42  obtained in a state in which no touch event occurs. The signal value  43  is data calculated based on the measurement value  42  in the touch-detection processing. The touch-state management table  44  is a table for storing touch coordinates and the like as the results of detection of a touch event. 
     The control unit  103  obtains input coordinates from the capacitance measurement value  23  of each electrode by a computation. The control unit  103  then transfers the input coordinates to a system control unit  104  by using an I/F signal  24 . 
     When the input coordinates are transferred from the touch panel  400  in response to a touch operation, the system control unit  104  generates a display image according to the touch operation and then transfers the generated display image to a display control circuit  105  as a display control signal  25 . 
     The display control circuit  105  generates a display signal  26  according to the display image transferred as the display control signal  25  and then displays an image on the display device  600 . 
       FIG. 2  is a sectional view of a principal part, for illustrating the display device equipped with the touch panel according to the embodiment of the present invention, which illustrates a multi-layered structure in which the touch panel and a front panel are laminated on a display panel. 
     As the display panel, any display panel can be used as long as the touch panel can be used therewith. Therefore, the display panel is not limited to a liquid crystal display panel, and a display panel using organic light-emitting diode elements or surface-conduction electron emitters or an organic EL display panel can also be used. 
     The display device  600  of this embodiment includes, as illustrated in  FIG. 2 , a liquid crystal display panel  100 , the capacitive touch panel  400 , which is placed on an observer side of the liquid crystal display panel  100 , and a backlight  700 , which is placed under the opposite side of the liquid crystal display panel  100  from the observer side. The liquid crystal display panel  100  may be, for example, an IPS liquid crystal display panel, a TN liquid crystal display panel, or a VA liquid crystal display panel. 
     The liquid crystal display panel  100  includes two substrates  620  and  630  bonded to each other, which are provided so as to be opposed to each other. A polarizer  601  is provided on an outer surface of the substrate  630 , whereas a polarizer  602  is provided on an outer surface of the substrate  620 . 
     The liquid crystal display panel  100  and the touch panel  400  are bonded to each other by an adhesive  501  made of a resin or made from an adhesive film. Further, a front panel (also referred to as “front-surface protective plate”)  12  made of an acrylic resin is provided on an outer surface of the touch panel  400  via spacers  502  arranged in an peripheral portion of the front panel  12 . 
     A flexible printed board  70  is connected to the touch panel  400 . A drive circuit  150  is mounted on the flexible printed board  70 . A signal output from the drive circuit  150  is fed to the touch panel  400  via the flexible printed board  70 . The storage unit  4 , the capacitance detecting unit  102 , and the control unit  103 , which are described above and illustrated in  FIG. 1 , are provided in the drive circuit  150  so as to control the detection of a position of input or the like. 
     In  FIG. 2 , a protective sheet  510  is provided on a front surface of the front panel  12  so as to prevent the front panel  12  from being scratched or damaged by a pen or the like. An electrode pattern of the touch panel  400  is described below. 
     In  FIG. 2 , a region of the substrate  620 , on which a liquid crystal driving circuit  50  is mounted, projects from the other substrate  630  to form a single-plate shape. A problem of damaging the substrate  620  sometimes occurs in the region of the substrate  620 , on which the liquid crystal driving circuit  50  is mounted. For preventing the problem, a spacer  30  is provided between the substrate  620  and the touch panel  400  so as to improve strength. 
     A liquid crystal display device includes the liquid crystal display panel  100 , the liquid crystal driving circuit  50 , a flexible printed board  72 , and a backlight  700 . On one side of the liquid crystal display panel  100 , the liquid crystal driving circuit  50  is provided. Various signals are fed to the liquid crystal display panel  100  by the liquid crystal driving circuit  50 . The flexible printed board  72  is electrically connected to the liquid crystal driving circuit  50  so as to feed a signal from the exterior thereto. 
     The liquid crystal display panel  100  includes the substrate  620 , the substrate  630 , the polarizers  601  and  602 , and the flexible printed board  72 . Although the illustration thereof is omitted, a thin-film transistor, a pixel electrode, and a counter electrode (common electrode) are formed on the substrate  620  (hereinafter, also referred to as “TFT substrate”). Color filters and the like are formed on the substrate  630  (hereinafter, also referred to as “filter substrate”). The substrates  620  and  630  are overlapped with a predetermined gap therebetween. The substrates  620  and  630  are bonded to each other by a frame-like sealing member (not shown) provided in the vicinity of a peripheral portion between the substrates  620  and  630 . A liquid-crystal composition is injected and sealed inside the sealing member. Further, the polarizers  601  and  602  are respectively bonded to the outer surfaces of the substrates  630  and  620 . Then, the flexible printed board  72  is connected to the TFT substrate  620 . 
     This embodiment can be applied in the similar manner even to a so-called in-plane switching type liquid crystal display panel in which the counter electrode is provided on the TFT substrate  620  and to a so-called vertical electric field type liquid crystal display panel in which the counter electrode is provided on the filter substrate  630 . 
       FIGS. 3A and 3B  are conceptual diagrams respectively illustrating multi-layered structures of a conventional display device equipped with a touch panel and the display device equipped with the touch panel according to the embodiment of the present invention. 
       FIG. 3A  is a conceptual diagram for illustrating the multi-layered structure of the conventional display device equipped with the touch panel. The touch panel  400  is bonded onto the liquid crystal display panel  100  with an adhesive  33 . Then, the front panel  12  is bonded onto the touch panel  400  with an adhesive  32 . 
       FIG. 3B  is a conceptual diagram for illustrating the multi-layered structure of the display device equipped with the touch panel according to this embodiment. The touch panel  400  is bonded onto the liquid crystal display panel  100  with the adhesive  33 . In contrast to the conventional display device, an air layer  34  is provided without bonding the front panel  12  onto the touch panel  400 . 
       FIGS. 4A and 4B  are conceptual diagrams illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3A , when a finger is in contact with the front panel  12  with a small load thereon and when the finger is in contact with the front panel  12  with a large load thereon, respectively. 
       FIG. 4A  is a diagram illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3A , when a finger  10  is in contact with the front panel  12  with a small load (indicated by an arrow F 1  of  FIG. 4A ).  FIG. 4B  is a diagram illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3A , when the finger  10  is in contact with the front panel  12  with a large load (indicated by an arrow F 2  of  FIG. 4B ). 
     As can be seen from  FIGS. 4A and 4B , in each of the case where the finger  10  is brought into contact with the front panel with the small load (indicated by the arrow F 1  of  FIG. 4A ) and the case where the finger  10  is brought into contact with the front panel with the large load (indicated by the arrow F 2  of  FIG. 4B ), the front panel  12  is not deformed in the conventional display device equipped with the touch panel because the liquid crystal display panel  100 , the touch panel  400 , and the front panel  12  are bonded to each other with the adhesives  32  and  33 . 
       FIGS. 5A and 5B  are conceptual diagrams illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3B , when the finger is in contact with the front panel  12  with a small load thereon and when the finger is in contact with the front panel  12  with a large load thereon, respectively. 
       FIG. 5A  is a diagram illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3B , when the finger  10  is in contact with the front panel  12  with a small load (indicated by an arrow F 1  of  FIG. 5A ).  FIG. 5B  is a diagram illustrating a structural deformation occurring, in the structure illustrated in  FIG. 3B , when the finger  10  is in contact with the front panel  12  with a large load (indicated by an arrow F 2  of  FIG. 5B ). 
     As can be seen from  FIG. 5A , when the finger  10  is brought into contact with the front panel  12  with the small load thereon in the structure illustrated in  FIG. 3B , the front panel  12  is not deformed. However, as illustrated in  FIG. 5B , when the finger  10  is brought into contact with the front panel  12  with the large load thereon in the structure illustrated in  FIG. 3B , the air layer  34  is compressed to deflect the front panel  12 . 
       FIGS. 6A and 6B  are conceptual diagrams, each illustrating a state of lines of electric force between the X electrode and the Y electrode in the structure illustrated in  FIG. 3A . 
       FIG. 6A  is a conceptual diagram illustrating a state of lines of electric force between an X electrode  311  and a Y electrode  312  which is obtained when the finger  10  is not in contact with the front panel  12  in the structure illustrated in  FIG. 3A .  FIG. 6B  is a conceptual diagram illustrating a state of lines of electric force between the X electrode  311  and the Y electrode  312  which is obtained when the finger  10  is in contact with the front panel  12  in the structure illustrated in  FIG. 3A . 
     As illustrated in  FIG. 6B , a change in potential of a finger surface is small. Therefore, lines  61  of electric force are blocked by the finger surface. As a result, an electrostatic capacitance between the X electrode  311  and the Y electrode  312  is reduced. The touch panel  400  included in each of the conventional display device equipped with the touch panel and the display device equipped with the touch panel according to this embodiment uses a method of detecting a change in capacitance. 
     In  FIGS. 6A and 6B  and  FIGS. 7A to 9  referred to below, the plurality of X electrodes are representatively illustrated as the X electrode  311  and the plurality of Y electrodes are representatively illustrated as the Y electrode  312 . 
       FIG. 7A  is a graph showing a time-series change in measurement value obtained when the finger  10  is not in contact with the front panel  12  and the finger  10  is in contact with the front panel  12  in the structure illustrated in  FIG. 3A . 
     In the graph of  FIG. 7A , the horizontal axis represents time, whereas the vertical axis represents signal intensity (digital value obtained by AD conversion of the measurement value of the received signal).  FIG. 7A  shows a measurement value  701  of the signal intensity for each of the intersections of the electrodes, a reference value  702  for continuously monitoring a state in which no contact is made, and criterion threshold values  703  and  704  set based on the reference value  702 . 
     In the touch panel  400  of each of the conventional display device equipped with the touch panel and the display device equipped with the touch panel according to this embodiment, the signals (pulses) are sequentially applied from the X electrodes X 1  to X 4 . From the measurement values  701  of the signals received by the Y electrodes Y 1  to Y 4 , the reference value  702  is calculated so as to detect whether or not a touch event occurs. This processing is for preventing an erroneous operation even if the capacitance between the electrodes for each intersection of the X electrode and the Y electrode changes due to a change in temperature or humidity. 
     A method of calculating the reference value  702  is as follows. It is first determined whether the measurement value  701  of the intensity of the received signal for each intersection of the X electrode and the Y electrode is larger or smaller than the current reference value  702  for each scan. When the measurement value  701  of the intensity of the received signal for each intersection of the electrodes is larger than the current reference value  702 , a value of a counter for increasing the reference value is incremented. When the value of the counter reaches a predetermined count value, the reference value  702  is updated to a value larger than the current reference value  702 . 
     On the other hand, when the measurement value  702  of the intensity of the received signal for each intersection of the electrodes is smaller than the current reference value  702 , a value of a counter for reducing the reference value is incremented. When the value of the counter reaches a predetermined count value, the reference value  702  is updated to a value smaller than the current reference value  702 . 
     In the graph of  FIG. 7A , a time period between time  0  and time  75  and a time period between time  110  and time  200  are a time period in which the finger  10  is not in contact with the front panel  12 , as illustrated in  FIG. 7B . The remaining time period (a time period between time  75  and time  110 ) is a time period in which the finger  10  is in contact with the front panel  12 , as illustrated in  FIG. 7C . 
     As shown in the graph of  FIG. 7A , by the contact of the finger  10  with the front panel  12 , the measurement value  701  suddenly changes (the polarity is set so that the measurement value shifts toward the positive side in this case). When the measurement value  701  exceeds the threshold value  703 , it is determined that a contact is made, specifically, it is determined that effective data exists. In this time period, the reference value  702  is not updated. 
     When the finger  10  is released from the front panel  12  and hence the measurement value  701  becomes lower than the threshold value  703  again, it is determined that no contact is made, specifically, it is determined that no effective data exists. At this point, the update of the reference value  702  is restarted. 
       FIGS. 8A and 8B  are conceptual diagrams, each illustrating a state of lines of electric force between the X electrode  311  and the Y electrode  312  in the structure illustrated in  FIG. 3B . 
       FIG. 8A  is a conceptual diagram illustrating a state of lines of electric force between the X electrode  311  and the Y electrode  312  which is obtained, in the structure illustrated in  FIG. 3B , when the finger  10  is not in contact with the front panel  12 .  FIG. 8B  is a conceptual diagram illustrating a state of lines of electric force between the X electrode  311  and the Y electrode  312  which is obtained, in the structure illustrated in  FIG. 3B , when the finger  10  is in contact with the front panel  12  with a large load thereon. 
     As illustrated in  FIGS. 8A and 8B , a change in potential of the finger surface is small. Therefore, the lines  61  of electric force are blocked by the finger surface. As a result, the electrostatic capacitance between the X electrode  311  and the Y electrode  312  is reduced. 
     On the other hand, when the finger  10  comes into contact with the front panel  12  with the large load thereon as illustrated in  FIG. 8B , the front panel  12  comes closer to the X electrode  311  and the Y electrode  312 . By the movement of the front panel  12  closer to the electrodes, a permittivity between the X electrode  311  and the Y electrode  312  increases to increase the capacitance between the X electrode  311  and the Y electrode  312 . In this case, the effects of increasing the electrostatic capacitance by the proximity of the front panel to the electrodes surpass the blocking effects obtained by the finger  10 . As a result, the polarity of the measurement value is reversed as compared to that described referring to  FIGS. 6A and 6B . 
       FIG. 9A  is a graph showing a time-series change in measurement value obtained when the finger  10  is not in contact with the front panel  12  and the finger  10  is in contact with the front panel  12  in the structure illustrated in  FIG. 3B . 
     In the graph of  FIG. 9A , the horizontal axis represents time, whereas the vertical axis represents signal intensity (digital value obtained by AD conversion of the measurement value of the received signal).  FIG. 9A  shows a measurement value  901  of the signal intensity for each of the intersections of the electrodes, a reference value  902  for continuously monitoring a state in which no contact is made, and criterion threshold values  903  and  904  set based on the reference value  902 . 
     A time period between time  0  and time  75  and a time period between time  150  and time  200  are a time period in which the finger  10  is not in contact with the front panel  12  as illustrated in  FIG. 9B . The remaining time period (a time period between time  75  and time  150 ) is a time period in which the finger  10  is in contact with the front panel  12  as illustrated in  FIGS. 9C and 9D . 
     A time period between time  75  and time  110  is a time period in which the finger  10  is in contact with the front panel  12  with a small load thereon, as illustrated in  FIG. 9C . A time period between time  110  and time  150  is a time period in which the finger  10  is in contact with the front panel  12  with a large load thereon, as illustrated  FIG. 9D . 
     As described above referring to  FIG. 5A , when the finger  10  comes into contact with the front panel  12  with the small load, the structure illustrated in  FIG. 3B  is not deformed. Therefore, in the time period between time  75  and time  110 , the same signal as that generated in the time period between time  75  and time  110  shown in  FIG. 7A  is generated. 
     On the other hand, when the finger  10  comes into contact with the front panel  12  with the large load thereon, the front panel  12  is deformed as illustrated in  FIG. 5B . As a result, the front panel  12  is deflected toward the touch panel. Then, by the phenomenon illustrated in  FIG. 8B , the measurement value  901  is reduced to be finally shifted to the negative side. 
     In the signal processing for the touch panel  400  of the conventional display device equipped with the touch panel, the generation of the negative measurement value  901  is not taken into consideration. The above-mentioned behavior of the measurement value  901  appears as the disappearance of the measurement value  901 . If the above-mentioned phenomenon occurs, the touch panel  400  is placed in a state in which there is no reaction from the touch panel  400  even though the user touches the touch panel  400  with the finger  10 . 
       FIG. 10A  is a graph for illustrating the signal processing for the touch panel  400  according to this embodiment.  FIG. 10A  is a graph for illustrating the result of using the signal processing for the touch panel  400  according to this embodiment in the state described referring to  FIGS. 9A to 9D . The graph shows a time-series change in measurement value obtained when the finger  10  is in contact with the touch panel  12  and when the finger  10  is not in contact with the touch panel  12  in the structure illustrated in  FIG. 3B . 
     In the graph of  FIG. 10A , the horizontal axis represents time, whereas the vertical axis represents signal intensity (digital value obtained by AD conversion of the measurement value of the received signal). 
     A time period between time  0  and time  75  and a time period between time  150  and time  200  are a time period in which the finger  10  is not in contact with the front panel  12  as illustrated in  FIG. 10B . The remaining time period (a time period between time  75  and time  150 ) is a time period in which the finger  10  is in contact with the front panel  12 . 
     A time period between time  75  and time  110  is a time period in which the finger  10  is in contact with the front panel  12  with a small load thereon, as illustrated in  FIG. 10C . A time period between time  110  and time  150  is a time period in which the finger  10  is in contact with the front panel  12  with a large load thereon, as illustrated  FIG. 10D . 
     As described above referring to  FIG. 5A , when the finger  10  comes into contact with the front panel  12  with the small load, the structure illustrated in  FIG. 3B  is not deformed. Therefore, in the time period between time  75  and time  110 , the same signal as that generated in the time period between time  75  and time  110  shown in  FIG. 7A  is generated. 
     On the other hand, when the finger  10  comes into contact with the front panel  12  with the large load thereon, the front panel  12  is deformed as illustrated in  FIG. 5B . As a result, the front panel  12  is deflected toward the touch panel. Then, by the phenomenon illustrated in  FIG. 8B , the measurement value  901  is reduced to be finally shifted to the negative side. 
     In the signal processing for the touch panel  400  of the conventional display device equipped with the touch panel, the generation of the negative measurement value  901  is not taken into consideration. The above-mentioned behavior of the measurement value  901  appears as the disappearance of the measurement value  901 . If the above-mentioned phenomenon occurs, the touch panel  400  is placed in a state in which there is no reaction from the touch panel  400  even though the user touches the touch panel  400  with the finger  10 . 
     In this embodiment, however, even when the measurement value is below the threshold value  904  provided on the negative side of the reference value  902 , a contact is recognized and then the generation of the effective data is recognized. Further, a function of reversing the polarity of the signal component below the threshold value provided on the negative side of the reference value  902  to obtain a signal  1001  in this state is provided. 
     As a result, even when the finger  10  is in contact with the front panel  12  with the large load thereon, the disappearance of the measurement value  901  does not occur. Thus, a state, in which no reaction is obtained from the touch panel  400  even though the finger  10  of the user is in contact with the front panel  12 , can be avoided. 
       FIG. 11  is a flowchart illustrating a processing procedure of the signal processing for the touch panel  400  of the display device equipped with the touch panel according to the embodiment of the present invention. The processing illustrated in  FIG. 11  is executed by the control unit  103  illustrated in  FIG. 1 . 
     First, when the detection is started in Step  201 , one electrodes of the two kinds of electrodes (for example, the X electrodes) is selected (Step  202 ). Signals (pulses) are input from the selected one electrodes (Step  203 ). Then, the signals are received by the other one electrodes (for example, the Y electrodes) so that the intensity of each of the signals is measured (Step  204 ). The measurement value obtained in Step  204  is stored in the storage unit  4  illustrated in  FIG. 1  for each of the intersections of the X electrodes and the Y electrodes. 
     Then, it is determined whether or not the above-mentioned processing has been executed for all the selected type of electrodes (Step S 205 ). When the result of determination is NO in Step  205 , the above-mentioned processing starting from Step  201  is executed again. On the other hand, when the result of determination in Yes in Step  205 , processing starting from subsequent Step  206  is executed. 
     In Step  206 , it is determined whether or not the measurement value ( 901  shown in  FIG. 10A ) is larger than the positive-side threshold value ( 903  shown in  FIG. 10A ) for each of the intersections of the electrodes. When the result of determination in Step  206  is YES, it is determined that “effective data exists” (Step  207 ). 
     On the other hand, when the result of determination in Step  206  is NO, it is then determined whether or not the measurement value is smaller than the negative-side threshold value ( 904  shown in  FIG. 10A ) (Step  208 ). When the result of determination in Step  208  is YES, it is determined that “effective data exists” (Step  209 ). Then, polarity reverse processing (processing for obtaining the signal  1001  shown in  FIG. 10A ) is performed (Step  210 ). 
     When the result of determination is NO in Step  208 , it is determined “no effective data exists” (Step  211 ), and then it is determined whether or not the current reference value ( 902  shown in  FIG. 10A ) is required to be updated. When it is determined that the reference value is required to be updated, the reference value is updated (Step  212 ). 
     Then, it is determined whether or not the above-mentioned processing has been performed for all the intersections of the electrodes (Step  213 ). When the result of determination is NO in Step  213 , the above-mentioned processing starting from Step  206  is executed. When the result of determination is YES in Step  213 , the coordinates are computed by using the data determined as effective data in Step  207  and the data determined as effective data in Step  209  to be performed the polarity reverse processing in Step  210  (Step  214 ). Then, the processing returns to Step  201  to execute a subsequent scan. 
     In the flowchart of  FIG. 11 , processing surrounded by a broken line  1101  corresponds to processing additionally provided in this embodiment. By the added processing, even if the measurement value is below the negative-side threshold value, it is determined that “effective data exists”. The polarity of the measurement value which is below the negative-side threshold value is reversed so that the measurement value can be treated in the same manner as that for the normal signal. 
     In general, it is difficult to regulate the operating force of the user (or an operator) to the touch panel  400  because the usability of the equipment would be restricted. Accordingly, it is required to avoid the erroneous operation within the range of the operating force of the user (or an operator) when the user (or operator) unconsciously performs the operation. 
     In this embodiment, even when the user (or operator) operates the touch panel  400  unconsciously with a strong operating force, the operation can be continued without causing the erroneous operation. As a result, the cost of the equipment equipped with the touch panel can be reduced without impairing the user-friendliness. 
     Hereinafter, the electrode pattern of the capacitive touch panel according to this embodiment is described. 
       FIG. 12  is a plan view illustrating the electrode pattern of the capacitive touch panel according to this embodiment. 
       FIGS. 13 and 14  are sectional views illustrating a sectional structure of the capacitive touch panel illustrated in  FIG. 12 .  FIG. 13  is a sectional view illustrating a sectional structure taken along the line A-A′ of  FIG. 12 , whereas  FIG. 14  is a sectional view illustrating a sectional structure taken along the line B-B′ of  FIG. 12 . 
     In  FIG. 12 , wirings  6  and connection terminals  7  are illustrated. An effective touch region AR is a region in which a touch event can be detected when the touch panel  400  is touched with a finger or a conductive pen. 
     The capacitive touch panel  400  illustrated in  FIG. 12  includes the plurality of X electrodes and the plurality of Y electrodes provided on an observer-side surface of a touch-panel substrate  15 . Each of the X electrodes extends in a second direction (for example, a Y direction). The plurality of X electrodes are arranged side by side at predetermined arrangement intervals in a first direction (for example, an X direction) crossing the second direction. Each of the Y electrodes extends in the first direction. The plurality of Y electrodes are arranged side by side at predetermined arrangement intervals in the second direction so as to cross the plurality of X electrodes. As the touch-panel substrate  15 , a transparent insulating substrate made of, for example, glass or the like is used. 
     The plurality of X electrodes are each formed in an electrode pattern in which thin-line portions  1   a  and pad portions  1   b  are arranged alternately in the second direction. Each of the pad portions  1   b  has a larger width than that of each of the thin-line portions  1   a . The plurality of Y electrodes are each formed in an electrode pattern in which thin-line portions  2   a  and pad portions  2   b  are arranged alternately in the first direction. Each of the pad portions  2   b  has a larger width than that of each of the thin-line portions  2   a.    
     The region in which the plurality of X electrodes and Y electrodes are arranged is the effective touch region AR. Around the effective touch region AR, as illustrated in  FIG. 12 , the plurality of wirings  6  electrically connected respectively to the plurality of Y electrodes and the plurality of X electrodes are provided. 
     The plurality of X electrodes are arranged on the observer-side surface of the touch-panel substrate  15 . The pad portions  2   b  of the plurality of Y electrodes are formed on the observer-side surface of the touch-panel substrate  15  so as to be separated away from the X electrodes. 
     The thin-line portions  2   a  of the plurality of Y electrodes are provided on an insulating film (PAS 1 ) formed on the observer-side surface of the touch-panel substrate  15 . The thin-line portions  2   a  of the plurality of Y electrodes are covered with a protective film (PAS 2 ) formed thereon. 
     The thin-line portions  2   a  of the Y electrodes planarly cross the thin-line portions  1   a  of the X electrodes. Each of the thin-line portions  2   a  is connected to the two pad portions  2   b , which are adjacent to each other with the thin-line portion  2   a  therebetween, through a contact hole  12   a  formed through the insulating film (PAS 1 ) corresponding to an interlayer insulating film between the thin-line portions  2   a  of the Y electrodes and the thin-line portions  1   a  of the X electrodes. 
     As viewed planarly, the pad portion  2   b  of the Y electrode is arranged between the thin-line portions  1   a  of the adjacent two X electrodes. The pad portion  1   b  of the X electrode is arranged between the thin-line portions  2   a  of the adjacent two Y electrodes. 
     The plurality of X electrodes and the plurality of Y electrodes are made of a material having a high transmissivity, for example, a transparent conductive material such as indium tin oxide (ITO). Each of the wirings  6  includes a transparent conducive layer made of a transparent conductive material, for example, indium tin oxide (ITO), corresponding to a lower layer, and a metal layer made of, for example, a silver alloy material, corresponding to an upper layer. 
       FIGS. 15 and 16  are sectional views illustrating another example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 .  FIG. 15  is a sectional view illustrating the sectional structure taken along the line A-A′ of  FIG. 12 , and  FIG. 16  is a sectional view illustrating the sectional structure taken along the line B-B′ of  FIG. 12 . 
     In the capacitive touch panel illustrated in  FIGS. 15 and 16 , the thin-line portions  2   a  of the plurality of Y electrodes are formed on the observer-side surface of the touch-panel substrate  15 . The thin-line portions  1   a  and the pad portions  1   b  of the plurality of X electrodes and the pad portions  2   b  of the plurality of Y electrodes are formed on the insulating film (PAS 1 ). The thin-line portions  1   a  and the pad portions  1   b  of the plurality of X electrodes and the pad portions  2   b  of the plurality of Y electrodes are covered with the protective film (PAS 2 ) formed thereon. 
     The thin-line portions  2   a  of the Y electrodes planarly cross the thin-line portions  1   a  of the X electrodes. Each of the thin-line portions  2   a  is connected to the two pad portions  2   b , which are adjacent to each other with the thin-line portion  2   a  therebetween, through the contact hole  12   a  formed through the insulating film (PAS 1 ) corresponding to the interlayer insulating film between the thin-line portions  2   a  of the Y electrodes and the thin-line portions  1   a  of the X electrodes. 
     As viewed planarly, the pad portion  2   b  of the Y electrode is arranged between the thin-line portions  1   a  of the adjacent two X electrodes. The pad portion  1   b  of the X electrode is arranged between the thin-line portions  2   a  of the adjacent two Y electrodes. 
     The plurality of X electrodes and the plurality of Y electrodes are made of a material having a high transmissivity, for example, a transparent conductive material such as indium tin oxide (ITO). Each of the wirings  6  includes a transparent conducive layer made of a transparent conductive material, for example, indium tin oxide (ITO), corresponding to a lower layer, and a metal layer made of, for example, a silver alloy material, corresponding to an upper layer. 
       FIGS. 17 and 18  are sectional views illustrating another example of the sectional structure of the capacitive touch panel illustrated in  FIG. 12 .  FIG. 17  is a sectional view illustrating the sectional structure taken along the line A-A′ of  FIG. 12 , and  FIG. 18  is a sectional view illustrating the sectional structure taken along the line B-B′ of  FIG. 12 . 
     In the capacitive touch panel illustrated in  FIGS. 17 and 18 , the thin-line portions  1   a  and the pad portions  1   b  of the plurality of X electrodes are formed on the observer-side surface of the touch-panel substrate  15 . The thin-line portions  2   a  and the pad portions  2   b  of the plurality of Y electrodes are formed on the insulating film (PAS 1 ). The thin-line portions  2   a  and the pad portions  2   b  of the plurality of Y electrodes are covered with the protective film (PAS 2 ) formed thereon. 
     In the capacitive touch panel illustrated in  FIGS. 17 and 18 , the X electrodes and the Y electrodes are formed in different layers. The thin-line portions  2   a  of the Y electrodes planarly cross the thin-line portions  1   a  of the X electrodes. 
     As viewed planarly, the pad portion  2   b  of the Y electrode is arranged between the thin-line portions  1   a  of the adjacent two X electrodes. The pad portion  1   b  of the X electrode is arranged between the thin-line portions  2   a  of the adjacent two Y electrodes. 
     The plurality of X electrodes and the plurality of Y electrodes are made of a material having a high transmissivity, for example, a transparent conductive material such as indium tin oxide (ITO). Each of the wirings  6  includes a transparent conducive layer made of a transparent conductive material, for example, indium tin oxide (ITO), corresponding to a lower layer, and a metal layer made of, for example, a silver alloy material, corresponding to an upper layer. 
     The invention made by the present inventor is described above specifically based on the embodiment, but the present invention is not limited to the embodiment described above, and it is to be understood that various modifications can be made thereto without departing from the gist thereof.