Abstract:
A display device includes a display panel and a touch panel built in the display panel. The touch panel includes a sensitivity correcting unit configured to correct the sensitivity of the touch panel. The sensitivity correcting unit includes a difference acquiring unit configured to acquire a signal difference (S1−S2) between a detection signal S1 acquired by detection electrodes when a driving signal V1 is input to scanning electrodes from a driving-signal supplying unit and a detection signal S2 (S1&gt;S2) acquired by the detection electrodes when a driving signal V2 (V1&gt;V2) different from the driving signal V1 is input to the scanning electrodes from the driving-signal supplying unit and a parameter changing unit configured to change parameters of at least one of the driving-signal supplying unit and a detecting unit when the signal difference (S1−S2) is equal to or smaller than a predetermined threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese application JP2012-094777 filed on Apr. 18, 2012, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a display device and, more particularly, to a technique effectively applied to a touch panel-integrated display device in which a touch panel function is incorporated in a liquid crystal display panel. 
         [0004]    2. Description of the Related Art 
         [0005]    A display device including a device referred to as a touch sensor or a touch panel for applying touch operation (contact and pressing operation, hereinafter simply referred to as touch) to a display screen using a finger of a user, a pen, or the like to input information is used for mobile electronic devices such as a PDA and a portable terminal, various household electric appliances, an automated teller machine, and the like. As such a touch panel, a resistance film type for detecting a resistance value change in a touched portion, a capacitance type for detecting a capacitance change, an optical sensor type for detecting alight amount change, and the like are known. 
         [0006]    In the touch panel of the capacitance type, scanning electrodes (Y electrodes) for driving signal application arranged in a two-dimensional matrix shape lengthwise and crosswise and detection electrodes (X electrodes) for signal detection orthogonal to the scanning electrodes are provided. An input processing unit detects capacitances of the electrodes. When a conductor such as a finger comes into contact with the surface of the touch panel, the capacitances of the electrodes increase. Therefore, the input processing unit detects the increase in the capacitances and calculates an input coordinate on the basis of signals of capacitance changes detected by the electrodes. 
       SUMMARY OF THE INVENTION 
       [0007]    For example, in a touch panel-integrated display device in which a touch panel is built in a display panel, detection sensitivity is deteriorated according to aged deterioration of detection electrodes. 
         [0008]    The invention has been devised in order to solve the problem of the related art and it is an object of the invention to provide a technique for making it possible to suppress the deterioration in the detection sensitivity involved in the aged deterioration of the detection electrodes in the touch panel-integrated display device. 
         [0009]    The abovementioned object and other objects and new characteristics of the invention are made apparent by the description of this specification and the accompanying drawings. 
         [0010]    Overviews of representative inventions among inventions disclosed in this application are briefly explained below. 
         [0011]    (1) A display device including a display panel and a touch panel built in the display panel, wherein the touch panel includes a plurality of scanning electrodes formed on the display panel, a plurality of detection electrodes formed on the display panel and crossing the plurality of scanning electrodes, a driving-signal supplying unit configured to input a driving signal to the scanning electrodes when a touch position detection is performed, a detecting unit configured to acquire detection signals from the detection electrodes when the driving signal is input to the scanning electrodes from the driving-signal supplying unit, and a sensitivity correcting unit configured to correct the sensitivity of the touch panel, and the sensitivity correcting unit includes a difference acquiring unit configured to acquire a signal difference (S1−S2) between a detection signal S1 acquired by the detection electrodes when a driving signal V1 is input to the scanning electrodes from the driving-signal supplying unit and a detection signal S2 (S1&gt;S2) acquired by the detection electrodes when a driving signal V2 (V1&gt;V2) different from the driving signal V1 is input to the scanning electrodes from the driving-signal supplying unit and a parameter changing unit configured to change parameters of at least one of the driving-signal supplying unit and the detecting unit when the signal difference (S1−S2) is equal to or smaller than a predetermined threshold D. 
         [0012]    (2) In (1), the parameter changing unit increases a voltage value of the driving signal input to the scanning electrodes from the driving-signal supplying unit when the touch position detection is performed. 
         [0013]    (3) In (1), the parameter changing unit increases a detection time in which the detecting unit acquires the detection signals from the detection electrodes when the touch position detection is performed. 
         [0014]    (4) In (1), when the touch position detection is performed, the driving-signal supplying unit inputs the driving signals to the scanning electrodes a plurality of times, and the parameter changing unit increases the number of times of input of the driving signals input to the scanning electrodes from the driving-signal supplying unit. 
         [0015]    (5) In (1), when the touch position detection is performed, the detecting unit accumulates a detection signal based on respective driving signals input to the scanning electrodes a plurality of times, and the parameter changing unit increases the number of times of the integration by the detecting unit according to the number of times of the driving signals input to the scanning electrodes. 
         [0016]    (6) In (1), the correction of the sensitivity of the touch panel by the sensitivity correcting unit is periodically executed. 
         [0017]    An effect obtained by the representative inventions among the inventions disclosed in this application is briefly explained below. 
         [0018]    According to the invention, it is possible to suppress the deterioration in the detection sensitivity involved in the aged deterioration of the detection electrodes in the touch panel-integrated display device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIGS. 1A and 1B  are diagrams for explaining a conventional touch panel-equipped display device; 
           [0020]      FIGS. 2A and 2B  are diagrams for explaining a touch panel shown in  FIGS. 1A and 1B ; 
           [0021]      FIG. 2C  is a diagram for explaining a detection procedure of the touch panel shown in  FIGS. 1A and 1B ; 
           [0022]      FIGS. 3A and 3B  are diagrams for explaining a conventional touch panel-integrated display device; 
           [0023]      FIGS. 4A and 4B  are diagrams for explaining a touch panel shown in  FIGS. 3A and 3B ; 
           [0024]      FIGS. 5A ,  5 B, and  5 C are diagrams for explaining a detection principle of a touch panel-integrated liquid crystal display device having a structure shown in  FIGS. 4A and 4B ; 
           [0025]      FIG. 6  is a diagram for explaining a relation between a resistance value of sensor electrodes and detection sensitivity in a touch panel of a capacitance type; 
           [0026]      FIG. 7  is a diagram for explaining a reason why the detection sensitivity falls when the resistance value of the sensor electrodes increases in the touch panel of the capacitance type; 
           [0027]      FIGS. 8A ,  8 B, and  8 C are diagrams for explaining a level difference of a detection signal due to the amplitude of a driving signal in the touch panel of the capacitance type; 
           [0028]      FIGS. 9A and 9B  are diagrams for explaining a relation between a signal difference shown in  FIG. 8C  and the detection sensitivity and the resistance value of the sensor electrodes; 
           [0029]      FIG. 10  is a diagram for explaining a sensitivity correcting method in an embodiment of the invention; 
           [0030]      FIG. 11  is a diagram for explaining a relation between the resistance value of the sensor electrodes and the detection sensitivity in the case in which the sensitivity correcting method in the embodiment of the invention is applied and the case in which the sensitivity correcting method in the embodiment of the invention is not applied; 
           [0031]      FIG. 12  is a perspective view of a more specific configuration of a touch panel-integrated liquid crystal display device in the embodiment of the invention; 
           [0032]      FIG. 13  is a diagram for explaining counter electrodes and detection electrodes in the touch panel-integrated liquid crystal display device shown in  FIG. 12 ; and 
           [0033]      FIG. 14  is an enlarged schematic sectional view of a part of a cross section of a display unit of the touch panel-integrated liquid crystal display device shown in  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    An embodiment of the invention is explained in detail below with reference to the drawings. 
         [0035]    In all the figures for explaining the embodiment, components having the same functions are denoted by the same reference numerals and signs and repeated explanation of the components is omitted. The embodiment explained below is not intended to limit the interpretation of the scope of the claims of the invention. Overview of a conventional touch panel 
         [0036]      FIGS. 1A and 1B  are diagrams for explaining a conventional touch panel-equipped display device. 
         [0037]      FIG. 1A  is a block diagram showing a schematic configuration of the conventional touch panel-equipped display device.  FIG. 1B  is a diagram showing the structure of the conventional touch panel-equipped display device. 
         [0038]    In the touch panel-equipped display device shown in  FIGS. 1A and 1B , as shown in  FIG. 1B , a touch panel  106  of a capacitance type is bonded on a display panel (a liquid crystal display panel)  101  by an adhesive  110 . As explained below, the touch panel  106  includes Y electrodes (scanning electrodes) for driving signal application and X electrodes (detection electrodes) for signal detection orthogonal to the Y electrodes. 
         [0039]    The touch panel  106  is set on the front surface of the display panel  101 . Therefore, when a user views an image displayed on the display panel  101 , a display image needs to be transmitted through the touch panel  106 . Therefore, the touch panel  106  desirably has high light transmittance. 
         [0040]    The X electrodes and the Y electrodes of the touch panel  106  are connected to a touch-panel control unit  108  by a wire  107 . 
         [0041]    The touch-panel control unit  108  sequentially applies a driving signal using the Y electrodes as scanning electrodes and uses the X electrodes as detection electrodes to measure inter-electrode capacitances at electrode intersections and calculates an input coordinate from capacitance detection signals that change according to capacitance values at the intersections among the electrodes. 
         [0042]    The touch-panel control unit  108  transfers the input coordinate to a system control unit  105  using an I/F signal  109 . 
         [0043]    When the input coordinate is transferred from the touch panel  106  by touch operation, the system control unit  105  generates a display image corresponding to the touch operation and transfers the display image to a display control circuit  103  as a display control signal  104 . 
         [0044]    The display control circuit  103  generates a display signal  102  according to the display image transferred by the display control signal  104  and displays an image on the display panel  101 . 
         [0045]    The display panel  101  only has to be a display panel in which the touch panel  106  can be used. The display panel  101  is not limited to a liquid crystal display panel. A display panel including an organic light-emitting diode device or a surface conduction electron-emitting device, an organic EL display panel, and the like can also be used. 
         [0046]      FIGS. 2A and 2B  are diagrams for explaining the touch panel  106  shown in  FIGS. 1A and 1B . 
         [0047]      FIG. 2A  is a diagram showing an electrode pattern of the touch panel  106  shown in  FIGS. 1A and 1B .  FIG. 2B  is a sectional view showing a sectional structure taken along cut line A-B shown in  FIG. 2A . 
         [0048]    As shown in  FIG. 2A , the touch panel  106  shown in  FIGS. 1A and 1B  includes X electrodes  201  for capacitance detection and Y electrodes  202 . In the figure, for example, five X electrodes  201  and six Y electrodes  202  are shown. However, the numbers of the electrodes are not limited to these numbers. 
         [0049]    In  FIG. 2B , reference numeral  204  denotes a touch panel substrate configured by a glass substrate, a PET film, and the like. In the touch panel  106  shown in  FIGS. 1A and 1B , the X electrodes  201  and the Y electrodes  202  are formed on the touch panel substrate  204 . A protective film  203  is formed on the X electrodes  201  and the Y electrodes  202 . In  FIG. 2B , a shield electrode  205  is formed on a surface of the touch panel substrate  204  on the display panel side. 
         [0050]      FIG. 2C  is a diagram for explaining a detection procedure of the touch panel  106  shown in  FIGS. 1A and 1B  and is a diagram for explaining a detection procedure performed when there is no input to the touch panel  106 .  FIG. 2C  is a waveform chart. In the waveform chart of  FIG. 2C , the abscissa indicates time and the ordinate indicates amplitude. 
         [0051]    As shown in  FIG. 2C , a driving voltage (a driving pulse)  401  is sequentially input to the Y electrodes  202  of TX1 to TX6 in every one scanning period. On the other hand, a waveform of a detection signal  402  detected by the X electrodes  201  of RX1 to RX5 changes in synchronization with the input of the driving voltage  401 . In  FIG. 2C , since there is no input to the touch panel  106 , a large change does not occur in the amplitude of the detection signal  402  detected by the X electrodes  201  of RX1 to RX5. 
         [0052]    As shown in A in  FIG. 2C , the driving signal (the input pulse)  401  sequentially input to the Y electrodes  202  of TX1 to TX6 in every one detection period is a plurality of pulse trains. Similarly, as shown in B in  FIG. 2C , the detection signal  402  detected by the X electrodes  201  of RX1 to RX5 is also a plurality of pulse trains. 
         [0053]      FIGS. 3A and 3B  are diagrams for explaining a conventional touch panel-integrated display device. 
         [0054]      FIG. 3A  is a block diagram showing a schematic configuration of the conventional touch panel-integrated display device.  FIG. 3B  is a diagram showing a sectional structure of the conventional touch panel-integrated display device. 
         [0055]    In the touch panel-integrated display device shown in  FIGS. 3A and 3B , as shown in  FIG. 3B , a touch panel  301  of a capacitance type is formed on the inside of the display device (here, the liquid crystal display panel)  101 . Otherwise, the configuration of the touch panel  301  is the same as the configuration of the touch panel  106  shown in  FIG. 1A . Therefore, redundant detailed explanation of the configuration is omitted. 
         [0056]      FIGS. 4A and 4B  are diagrams for explaining the touch panel  301  shown in  FIGS. 3A and 3B .  FIG. 4A  is a diagram showing an electrode pattern of the touch panel  301  shown in  FIG. 3A and 3B .  FIG. 4B  is a sectional view showing a sectional structure taken along cut line A-B shown in  FIG. 4A . 
         [0057]    As shown in  FIG. 4A , the touch panel  301  shown in  FIGS. 3A and 3B  includes the X electrodes  201  for capacitance detection and the Y electrodes  202 . In the figure, for example, five X electrodes  201  and seven Y electrodes  202  are shown. However, the numbers of the electrodes are not limited to these numbers. 
         [0058]    In  FIG. 4B , reference numeral  211  denotes a first substrate,  212  denotes a second substrate,  213  denotes a lower sheet polarizer,  214  denotes an upper sheet polarizer,  215  denotes a liquid crystal layer, and  216  denotes a seal material. As shown in  FIG. 4B , the X electrodes  201  and the Y electrodes  202  are formed in different regions of a structure member of the liquid crystal display panel  101 . The first substrate  211  and the second substrate  212  desirably have high light transmittance. 
         [0059]    In general, in a liquid crystal display panel of an IPS type, on a surface of the first substrate  211  on the liquid crystal layer side, scanning lines (referred to as gate lines as well), an interlayer insulating film, video lines (referred to as source lines or drain lines as well) and thin film transistors (TFTs), pixel electrodes, an interlayer insulating film, counter electrodes (referred to as common electrodes as well), and an oriented film are formed in order from the first substrate  211  toward the liquid crystal layer  215 . However, in  FIG. 4B , these components are not shown. 
         [0060]    On the liquid crystal layer side of the second substrate  212 , a light blocking film, red, green, and blue color filters, a planarizing film, and an oriented film are formed in order from the second substrate  212  toward the liquid crystal layer  215 . However, in  FIG. 4B , these components are not shown. 
         [0061]    In the structure shown in  FIG. 4B , rear surface electrodes formed on a surface of the second substrate  212  on the opposite side of the liquid crystal layer  215  function as the X electrodes  201  as well and the counter electrodes function as the Y electrodes  202  as well. 
         [0062]      FIGS. 5A ,  5 B, and  5 C are diagrams for explaining a detection principle of the touch panel-integrated liquid crystal display device having the structure shown in  FIGS. 4A and 4B . 
         [0063]      FIG. 5A  is a diagram showing a state in which touch operation is not performed.  FIG. 5B  is a diagram showing a state in which a finger  502  is brought close to the touch panel  106 .  FIG. 5C  is a graph showing a change in a detected signal. 
         [0064]    As shown in  FIGS. 5A ,  5 B, and  5 C, a voltage source  504  is connected to one of the X electrodes  201  and the Y electrodes  202  (in the figures, connected to the Y electrodes  202 ). A pulse (a driving signal) is input to one of the X electrodes  201  and the Y electrodes  202  from the voltage source  504 . A transient current involved in the input pulse from the voltage source  504  is detected by detecting circuits ( 505  and  506 ) through the other electrodes (in the figures, the X electrodes  201 ) capacitively coupled to the one electrodes. As shown in  FIG. 5A , the capacitive coupling forms lines of electric force  601  between the X electrodes  201  and the Y electrodes  202 . 
         [0065]    As shown in  FIG. 5B , when the finger  502  is brought close to the touch panel  106 , the lines of electric force  601  are blocked. Consequently, the transient current decreases. 
         [0066]    As shown in  FIG. 5C , when the finger  502  or the like closely contacts with the touch panel  106 , a detection signal level detected by the detecting circuits ( 505  and  506 ) changes from a detection signal level  507  before the contact shown in  FIG. 5A  to a detection signal level  508  after the contact shown in  FIG. 5B . A difference between the detection signal level  507  and the detection signal level  508  is detection sensitivity. 
         [0067]    As shown in B in  FIG. 2C , the detection signal detected by the X electrodes  201  is a plurality of pulse trains. Therefore, the detecting circuits ( 505  and  506 ) accumulate the detection signal of the plurality of pulse trains, specifically, integrate the detection signal using integrating circuits, and detect signals of the detection signal level  507  and the detection signal level  508 . 
         [0068]      FIG. 6  is a diagram explaining a relation between a resistance value of sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) and detection sensitivity in a touch panel of a capacitance type. 
         [0069]    As shown in  FIG. 6 , the detection sensitivity falls when the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) increases. 
         [0070]      FIGS. 7A to 7C  are diagrams for explaining a reason why the detection sensitivity falls when the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) increases in the touch panel of the capacitance type. 
         [0071]    An input pulse voltage a shown in  FIG. 7A  indicates a waveform of a driving signal input to scanning electrodes (the Y electrodes  202  shown in  FIGS. 4A and 4B ). As shown in  FIG. 7A , a predetermined period from a rising edge of the driving signal is an effective detection time. 
         [0072]    Detected currents b and c shown in  FIGS. 7B and 7C  indicate waveforms of electric currents flowing to the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) according to the input of the input pulse voltage a to the scanning electrodes (the Y electrodes  202  shown in  FIGS. 4A and 4B ). 
         [0073]    As shown in  FIG. 7B , when the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) are in a state of low resistance, an electric current having a steep characteristic flows at the rising edge of the input pulse voltage a. The electric current finishes flowing within the effective detection time. 
         [0074]    On the other hand, as shown in  FIG. 7C , when the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) are in a high-resistance state, an electric current flowing to the sensor electrodes has a gently rising characteristic. The electric current does not finish flowing within the effective detection time. Therefore, a difference occurs between total amounts of electric currents detected when the resistance value of the sensor electrode is low resistance and when the resistance value is high resistance. The difference is a sensitivity fall. 
         [0075]      FIGS. 8A ,  8 B, and  8 C are diagrams for explaining a level difference of a detection signal due to the amplitude of a driving signal in the touch panel of the capacitance type. 
         [0076]      FIG. 8A  is a diagram showing a state in which a driving signal having amplitude of 5 V is input to the Y electrodes  202  from the voltage source  504  in the touch panel shown in  FIGS. 4A and 4B . 
         [0077]    The lines of electric force  601  are formed between the Y electrodes  202  and the X electrodes  201 . An electric current transiently flows along the lines of electric force  601 . The electric current is measured by the detecting circuits ( 505  and  506 ) respectively provided in the X electrodes  201 . 
         [0078]      FIG. 8B  is a diagram showing a state in which a driving signal having amplitude of 4.5 V is input to the Y electrodes  202  from the voltage source  504  in the touch panel shown in  FIGS. 4A and 4B . 
         [0079]    As in  FIG. 8A , the lines of electric force  601  are formed between the Y electrodes  202  and the X electrodes  201 . However, since the amplitude of the driving signal is small, the density of the formed lines of electric force  601  is low. As a result, when the amplitude of the driving signal is changed, a detection signal level changes from a detection signal level  517  in the case of the amplitude 5 V of the driving signal to a detection signal level  518  in the case of the amplitude 4.5 V of the driving signal. A difference between the levels is defined as a signal difference. 
         [0080]      FIGS. 9A and 9B  are diagrams for explaining a relation between the signal difference shown in  FIGS. 8A ,  8 B, and  8 C and the detection sensitivity and the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ). 
         [0081]    As shown in  FIG. 9A , like the detection sensitivity, the signal difference shown in  FIGS. 8A ,  8 B, and  8 C has dependency on the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ). 
         [0082]    As shown in  FIG. 9B , there is a high correlation between the signal difference shown in  FIGS. 8A ,  8 B, and  8 C and the detection sensitivity. The detection sensitivity can be estimated from the signal difference shown in  FIGS. 8A ,  8 B, and  8 C. 
         [0083]    Characteristics of the Touch Panel in this Embodiment 
         [0084]      FIG. 10  is a diagram for explaining a sensitivity correcting method in the embodiment of the invention. 
         [0085]    As shown in  FIG. 10 , a sensitivity correcting process in this embodiment (a thick broken line portion in  FIG. 10 ) includes a sensitivity inspecting step in step S 1 , a result determining step in step S 2 , a sensitivity adjustment necessity determining step in step S 3 , a sensitivity adjusting step in step S 4 , and a sensitivity check necessity determining step in step S 5 . 
         [0086]    The sensitivity inspecting step in step S 1  shown in  FIG. 10  roughly includes three steps explained below. 
         [0087]    In Step 1, the amplitude of a driving signal is set to V1 to perform detection. As a result, a detection value A is obtained. 
         [0088]    In Step 2, the amplitude of the driving signal is set to V2 to perform detection. As a result, a detection value B is obtained. Different values are set for the amplitude V1 and the amplitude V2 so that the voltage difference (V1−V2) might be constant. 
         [0089]    In Step 3, a signal difference, which is a difference between the detection value A and the detection value B, is calculated. 
         [0090]    The signal difference is the signal difference explained with reference to  FIGS. 8A ,  8 B, and  8 C. Detection sensitivity can be estimated from the signal difference. As a result, a value C is obtained as an amount of change in the detection sensitivity at the present point with respect to sensitivity in an initial state. 
         [0091]    In the result determining step in step S 2 , the value C is evaluated. 
         [0092]    In  FIG. 10 , a determination threshold D is provided for the sensitivity change amount. Comparison between the value C and the determination threshold D is evaluated. 
         [0093]    In the sensitivity adjustment necessity determining step in step S 3 , a sensitivity-adjustment-necessity determining unit determines from a result of the result determining step in step S 2  whether sensitivity adjustment is necessary. 
         [0094]    When it is determined that the sensitivity adjustment is unnecessary, the sensitivity correcting process ends and shifts to the next operation. When the sensitivity adjustment is necessary, the sensitivity correcting process shifts to the sensitivity adjusting step in step S 4  and sensitivity adjustment is carried out. 
         [0095]    In  FIG. 10 , the sensitivity adjusting step in step S 4  includes three steps explained below. 
         [0096]    In Step 1, a parameter to be changed when the sensitivity adjustment is carried out is selected. The parameter is different for each configuration of the detecting circuits ( 505  and  506 ). However, in view of the object of the invention, it is evident that the parameter is not limited to a peculiar parameter. 
         [0097]    For example, as the parameter, there are (1) a method of increasing a voltage value of a driving signal input to the scanning electrodes (the Y electrodes  202  shown in  FIGS. 4A and 4B ) when a touch position detection is performed, (2) a method of increasing the effective detection time shown in  FIGS. 7A to 7C , and (3) a method of increasing the number of times of input of a driving signal to the scanning electrodes (the Y electrodes  202  shown in  FIGS. 4A and 4B ) when the touch position detection is performed. 
         [0098]    In Step 2, a change amount of the parameter is calculated. 
         [0099]    In Step 3, the parameter is changed. 
         [0100]    Thereafter, sensitivity check necessity determination in step S 5  is performed. When a sensitivity check is necessary, the sensitivity check is carried out and sensitivity is checked. When the sensitivity check is unnecessary, the sensitivity correcting process ends and shifts to the next operation. 
         [0101]    In  FIG. 11 , a relation between the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) and the detection sensitivity is shown in the case in which the sensitivity correcting method in the embodiment of the invention is applied and the case in which the sensitivity correcting method in the embodiment of the invention is not applied. 
         [0102]    As it is seen from  FIG. 11 , when the sensitivity correcting method in this embodiment is applied, it is possible to suppress deterioration in the detection sensitivity involved in aged deterioration of the resistance value of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ). 
         [0103]    The signal difference shown in  FIG. 8C  is detected for each of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ). Therefore, the sensitivity adjustment executed in step S 4  shown in  FIG. 10  may be set for each of the sensor electrodes. Alternatively, when the sensitivity adjustment for one sensor electrode among a plurality of sensor electrodes is necessary or when the sensitivity adjustment for the majority of the sensor electrodes among the plurality of sensor electrodes is necessary, the sensitivity adjustment may be executed for all the sensor electrodes. 
         [0104]    As explained above, according to this embodiment, it is possible to estimate a resistance value change of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ) using the signal difference obtained in the predetermined step as an index. Consequently, it is possible to suppress a change in the detection sensitivity due to the resistance value change of the sensor electrodes by calculating a correction value of sensitivity. The sensitivity correcting method in this embodiment is desirably executed periodically, for example, at an interval of several month or one year. However, the sensitivity correction method may be executed when a power supply is turned on. 
         [0105]    A more specific configuration of the touch panel-integrated liquid crystal display device in the embodiment of the invention is explained below. 
         [0106]      FIG. 12  is a perspective view showing the more specific configuration of the touch panel-integrated liquid crystal display device in the embodiment of the invention. A liquid crystal display device  100  shown in  FIG. 12  includes a liquid crystal display panel  1 , a driving circuit  5 , a flexible board  70 , a front panel  40 , a storage case (not shown in the figure), and a backlight (not shown in the figure). 
         [0107]    The liquid crystal display panel  1  includes a TFT substrate  2  and a color filter substrate  3 . The TFT substrate  2  and the color filter substrate  3  are superimposed one on top of the other a predetermined space apart from each other. Both the substrates are bonded together by a seal material (not shown in the figure) provided in a frame shape in the vicinity of the peripheral edge portion between the substrates. A liquid crystal composition is encapsulated and sealed on the inner side of the seal material. A sheet polarizer is bonded to the outer side of both the substrates. 
         [0108]    On the TFT substrate  2 , counter electrodes  21  and a counter electrode signal line  22  connected from the driving circuit  5  to the counter electrodes  21  are provided. A counter electrode signal is transmitted from the driving circuit  5  to the counter electrodes  21  via the counter electrode signal line  22 . Detection electrodes  31  (the X electrodes  201  shown in  FIGS. 4A and 4B ) are provided on the color filter substrate  3 . The detection electrodes  31  are connected to a flexible board  75  by a connecting section  77 . The flexible board  75  is connected to the flexible board  70  by a connector  80 . A detection signal from the detection electrode  31  is transmitted to the driving circuit  5  via the flexible board  75 , the connector  80 , and the flexible board  70 . 
         [0109]    The liquid crystal display panel  1  includes a display unit including a large number of pixels in a matrix shape. The counter electrodes  21  are arranged to be opposed to pixel electrodes in pixels. When a voltage is applied between the electrodes, the orientation of liquid crystal molecules changes. According to the change in the orientation of the liquid crystal molecules, the transmittance of light changes, whereby an image is displayed. 
         [0110]    The counter electrodes  21  and the detection electrodes  31  of the liquid crystal display device  100  shown in  FIG. 12  are explained with reference to  FIG. 13 . 
         [0111]    As explained above, the counter electrodes  21  are provided on the TFT substrate  2 . A plurality of (e.g., about twenty) counter electrodes  21  are connected in common at both ends and connected to the counter electrode signal line  22 . A counter electrode signal is supplied from the driving circuit  5  to the bundle-like counter electrodes  21 . 
         [0112]    In the liquid crystal display device  100  shown in  FIG. 12 , the bundle-like counter electrodes  21  function as the Y electrodes  202  shown in  FIGS. 4A and 4B  as well and configure the scanning electrodes in the invention. The detection electrodes  31  correspond to the X electrodes  201  shown in  FIGS. 4A and 4B  and configure the detection electrode in the invention. 
         [0113]    Therefore, the counter electrode signal includes a counter voltage used for image display and a driving signal (the input pulse voltage shown in  FIG. 7A ) used for detection of a touch position. When the driving signal is applied to the counter electrodes  21 , a detection signal is generated in the detection electrodes  31  arranged at a fixed space from the counter electrodes  21  to form capacitance. The detection signal is extracted to the outside via terminals for detection electrodes  36 . 
         [0114]    Dummy electrodes  33  are formed on both sides of the detection electrodes  31 . The detection electrodes  31  expand toward the dummy electrodes  33  side at one ends and form the terminals for detection electrodes  36  having a T-shape. On the TFT substrate  2 , besides the counter electrode signal line  22 , various wires, terminals, and the like such as an input terminal for driving circuit  25  are formed. 
         [0115]    A partially enlarged schematic sectional view of the cross section of the display unit in the liquid crystal display device  100  shown in  FIG. 12  is shown in  FIG. 14 . 
         [0116]    As shown in  FIG. 14 , a pixel unit  200  is provided on the TFT substrate  2 . The counter electrodes  21  are used for image display as apart of pixels. A liquid crystal composition  4  is held between the TFT substrate  2  and the color filter substrate  3 . The detection electrodes  31  provided on the color filter substrate  3  and the counter electrodes  21  provided on the TFT substrate  2  form capacitance. When a driving signal is applied to the counter electrodes  21 , the voltage of the detection electrodes  31  changes. 
         [0117]    At this point, as shown in  FIG. 14 , when a conductor such as a finger is brought close to or into contact with the front panel  40 , a change occurs in the capacitance and a change occurs in the voltage generated in the detection electrode  31  compared with a voltage generated when the conductor is not brought close to or into contact with the front panel  40 . 
         [0118]    In this way, the change in the capacitance generated between the counter electrodes  21  and the detection electrodes  31  formed on the liquid crystal display panel  1  is detected. Consequently, it is possible to provide a function of a touch panel in the liquid crystal display panel  1 . 
         [0119]    As explained above, according to this embodiment, it is possible to suppress a change in the detection sensitivity due to a resistance value change of the sensor electrodes (the X electrodes  201  shown in  FIGS. 4A and 4B ). Therefore, it is possible to allow resistance value fluctuation in the sensor electrodes. Consequently, since a baking step for ITO films included in the sensor electrodes can be omitted, it is possible to realize a reduction in costs. 
         [0120]    The invention devised by the inventor is specifically explained above on the basis of the embodiment. However, the invention is not limited to the embodiment. It goes without saying that various changes are possible without departing from the spirit of the invention. 
         [0121]    While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claim cover all such modifications as fall within the true spirit and scope of the invention.