Abstract:
Provided is a touch panel including: a plurality of scanning electrodes formed on a display panel; a plurality of detecting electrodes intersecting with the plurality of scanning electrodes, the plurality of detecting electrodes being formed on the display panel; a first unit for sequentially connecting a constant current source to each of the plurality of scanning electrodes for each one scanning period; and a second unit for detecting a touch position on the display panel based on a variation of a current detected at each of the plurality of detecting electrodes. One of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed on the display panel surface on a viewer side, and another of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed inside the display panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese application JP 2011-164940 filed on Jul. 28, 2011, 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 touch panel and a display device with a built-in touch panel, and more particularly, to a technology effectively applicable to a touch panel including scanning electrodes and detecting electrodes, which are formed on different surfaces. 
         [0004]    2. Description of the Related Art 
         [0005]    A display device which includes a device for inputting information by a touch operation (contact press operation; hereinafter, simply referred to as touch) onto a display screen with the use of a user&#39;s finger or a pen (hereinafter, the device is referred to also as touch sensor or touch panel) is used for mobile electronic devices such as a PDA and a mobile terminal, various home electric appliances, an automated teller machine, and other such devices. As the touch panel, there are known a resistive type touch panel that detects a change in resistance at a touched portion, a capacitance type touch panel that detects a change in capacitance, and an optical sensor type touch panel that detects a change in light intensity (US 2007/0262966). 
         [0006]    In the capacitance type touch panel, vertical detection electrodes (X electrodes) and horizontal detection electrodes (Y electrodes) are vertically and horizontally arranged in matrix in two dimensions, and the capacitance of each electrode is detected by an input processing portion. When a conductor such as a finger contacts with the surface of the touch panel, the capacitance of each electrode increases. The input processing portion detects the increase in capacitance, and calculates input coordinates based on a signal of the capacitance change detected by each electrode. 
         [0007]      FIGS. 1A and 1B  are diagrams illustrating a conventional display device with a touch panel. 
         [0008]      FIG. 1A  is a block diagram illustrating a schematic configuration of the conventional display device with a touch panel, and  FIG. 1B  is a diagram illustrating a structure of the conventional display device with a touch panel. 
         [0009]    As illustrated in  FIG. 1B , a capacitance type touch panel  106  is adhered onto a display device (in this case, liquid crystal display panel)  101  with an adhesive  110 . As described later, the touch panel  106  includes X electrodes and Y electrodes for capacitance detection. 
         [0010]    The touch panel  106  is arranged in front of the display panel  101 . Therefore, in order to enable an image displayed on the display panel  101  to be viewed by a user, the displayed image is required to transmit the touch panel  106 . Therefore, the touch panel  106  is desired to have a high light transmittance. 
         [0011]    The X electrodes and the Y electrodes of the touch panel  106  are connected to a touch panel control portion  108  through wiring  107 . 
         [0012]    The touch panel control portion  108  sets the Y electrodes as scanning electrodes and sequentially applies a drive voltage thereto, and sets the X electrodes as detecting electrodes to measure interelectrode capacitances at respective electrode intersections. The touch panel control portion  108  calculates and determines input coordinates from capacitance detection signals which vary depending on capacitance values of the respective electrode intersections. 
         [0013]    The touch panel control portion  108  uses an I/F signal  109  to transfer the input coordinates to a system control portion  105 . 
         [0014]    When the input coordinates are transferred from the touch panel  106  by a touch operation, the system control portion  105  generates a display image in accordance with the touch operation, and transfers the generated display image to a display control circuit  103  as a display control signal  104 . 
         [0015]    The display control circuit  103  generates a display signal  102  in accordance with the display image transferred by the display control signal  104 , to thereby display an image on the display panel  101 . 
         [0016]    Note that, any display panel can be used as long as the display panel can be used with the touch panel  106 , and the display panel is not limited to a liquid crystal display panel. Alternatively, it is possible to use a display panel which uses an organic light emitting diode element or a surface-conduction electron emitter, or an organic EL display panel. 
         [0017]    When a liquid crystal display panel is used as the display panel  101 , the display panel  101  includes a backlight unit (not shown) arranged below a surface of the liquid crystal display panel on a side opposite to the viewer side. The liquid crystal display panel used in this case is, for example, an IPS type, TN type, or VA type liquid crystal display panel. 
         [0018]    As is well known, the liquid crystal display panel is formed by adhering two substrates arranged opposed to each other, and polarizing plates are provided on outer sides of the two substrates, respectively. 
         [0019]      FIGS. 2A and 2B  are diagrams illustrating the touch panel  106 . 
         [0020]      FIG. 2A  is a diagram illustrating an electrode pattern of the touch panel  106 , and  FIG. 2B  is a sectional view illustrating a sectional structure taken along the cut-line IIB-IIB of  FIG. 2A . 
         [0021]    As illustrated in  FIG. 2A , the touch panel  106  includes X electrodes  201  and Y electrodes  202  for capacitance detection. In this case, for example, five X electrodes  201  and six Y electrodes  202  are illustrated, but the number of the electrodes is not limited thereto. 
         [0022]      FIG. 2B  illustrates a touch panel substrate  204  formed of a glass substrate, a PET film, or the like. In the touch panel  106 , the X electrodes  201  and the Y electrodes  202  are formed on the touch panel substrate  204 , and a protective film  203  is formed on the X electrodes  201  and the Y electrodes  202 . Further, in  FIG. 2B , a shielding electrode  205  is formed on a surface of the touch panel substrate  204  on the display panel side. 
         [0023]      FIGS. 3A and 3B  are diagrams illustrating a conventional display device with a built-in touch panel. 
         [0024]      FIG. 3A  is a block diagram illustrating a schematic configuration of the conventional display device with a built-in touch panel, and  FIG. 3B  is a diagram illustrating a sectional structure of the conventional display device with a built-in touch panel. 
         [0025]    As illustrated in  FIG. 3B , a capacitance type touch panel  301  is formed inside a display device (in this case, liquid crystal display panel)  101 . Other configurations are the same as those of  FIG. 1A , and hence repetition of detailed description thereof is omitted.  FIGS. 4A and 4B  are diagrams illustrating the touch panel  301 .  FIG. 4A  is a diagram illustrating an electrode pattern of the touch panel  301 , and  FIG. 4B  is a sectional view illustrating a sectional structure taken along the cut-line IVB-IVB of  FIG. 4A . 
         [0026]    As illustrated in  FIG. 4A , the touch panel  301  includes X electrodes  201  and Y electrodes  202  for capacitance detection. In this case, for example, five X electrodes  201  and six Y electrodes  202  are illustrated, but the number of the electrodes is not limited thereto. 
         [0027]      FIG. 4B  illustrates a first substrate  211 , a second substrate  212 , a lower polarizing plate  213 , an upper polarizing plate  214 , a liquid crystal layer  215 , and a sealing member  216 . As illustrated in  FIG. 4B , the X electrodes  201  and the Y electrodes  202  are formed at different parts of the structural members of the liquid crystal display panel. 
         [0028]    Note that, the first substrate  211  and the second substrate  212  are desired to have a high light transmittance. 
         [0029]    Further, generally, in an IPS type liquid crystal display panel, on a surface of the first substrate  211  on the liquid crystal layer side, there are formed, in the order from the first substrate  211  toward the liquid crystal layer  215 , scanning lines (also referred to as gate lines), an interlayer insulating film, video lines (also referred to as source lines or drain lines), thin film transistors (TFTs), pixel electrodes, an interlayer insulating film, counter electrodes (also referred to as common electrodes), and an alignment film. In  FIG. 4B , however, illustration of those members is omitted. 
         [0030]    Further, on a surface of the second substrate  212  on the liquid crystal layer side, there are formed, in the order from the second substrate  212  toward the liquid crystal layer  215 , alight shielding film, color filters of red, green, and blue, a planarization film, and an alignment film. In  FIG. 4B , however, illustration of those members is omitted. 
         [0031]    In the structure of  FIG. 4B , a back electrode formed on a surface of the second substrate on a side opposite to the liquid crystal layer doubles as the X electrode  201 , and the counter electrode doubles as the Y electrode  202 . 
         [0032]      FIGS. 5A to 5C  are diagrams illustrating a conventional detection method for the touch panel  106 .  FIG. 5A  is a diagram illustrating a state in which a touch operation is not performed,  FIG. 5B  is a diagram illustrating a state in which a finger  502  has approached the touch panel  106 , and  FIG. 5C  is a graph showing variations of detected signals. 
         [0033]    One of the X electrode  201  and the Y electrode  202  (in this case, the Y electrode  202 ) is connected to a voltage source  504  so that a pulse is input thereto from the voltage source  504 . A transient current associated with the pulse input from the voltage source  504  is detected by a detection circuit ( 505 ,  506 ) via the other electrode at which capacitive coupling occurs (in this case, the X electrode  201 ). As illustrated in  FIG. 5A , the capacitive coupling forms lines  501  of electric force between the X electrode and the Y electrode. 
         [0034]    As illustrated in  FIG. 5B , when the finger  502  approaches the touch panel  106 , the lines  501  of electric force are blocked. With this, the transient current is reduced. 
         [0035]    As shown in  FIG. 5C , when a change occurs from the state of  FIG. 5A  to the state of  FIG. 5B , a signal  507  corresponding to a part closest to the finger  502  is significantly lowered. A reduction amount  503  indicates signal intensity. At a part far from the finger, a variation  508  is minute. 
         [0036]      FIGS. 6A to 6C  are diagrams illustrating a conventional detection method for the touch panel  301 .  FIG. 6A  is a diagram illustrating a state in which a touch operation is not performed,  FIG. 6B  is a diagram illustrating a state in which a finger  502  has approached the touch panel  106 , and  FIG. 6C  is a graph showing variations of detected signals. 
         [0037]    As illustrated in  FIG. 6A , one of the X electrode  201  and the Y electrode  202  (in this case, the Y electrode  202 ) is connected to a voltage source  504  so that a pulse is input thereto from the voltage source  504 . A transient current associated with the pulse input from the voltage source  504  is detected by a detection circuit ( 505 ,  506 ) via the other electrode at which capacitive coupling occurs (in this case, the X electrode  201 ). As illustrated in FIG.  6 A, the capacitive coupling forms lines  601  of electric force between the X electrode and the Y electrode. However, compared to the case where the X electrodes  201  and the Y electrodes  202  are present on the same surface as illustrated in  FIG. 5B , an amount of the lines  601  of electric force generated outside the display panel is smaller. 
         [0038]    As illustrated in  FIG. 6B , when the finger  502  approaches the touch panel  301 , the lines  601  of electric force are blocked. With this, the transient current is reduced. 
         [0039]    However, compared to the case where the X electrodes  201  and the Y electrodes  202  are present on the same surface as illustrated in  FIG. 5B , the amount of the lines  601  of electric force generated outside the display panel is smaller, and hence the reduction rate is smaller. 
         [0040]    As shown in  FIG. 6C , when a change occurs from the state of  FIG. 6A  to the state of  FIG. 6B , a signal  603  corresponding to a part closest to the finger  502  is slightly lowered, but signal intensity is minute. This causes a reduction in detection sensitivity. 
         [0041]      FIGS. 7A and 7B  are diagrams illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the touch panel  106  and the touch panel  301 . 
         [0042]      FIG. 7A  is a diagram illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the electrode structure of the touch panel  106 , and  FIG. 7B  is a diagram illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the electrode structure of the touch panel  301 . 
         [0043]    As illustrated in  FIG. 7A , in the electrode structure of the touch panel  106 , an electrode interval  701  is fine and cannot be easily observed visibly. 
         [0044]    As illustrated in  FIG. 7B , in the electrode structure of the touch panel  301 , an electrode interval  702  is enlarged and can be easily observed visibly. 
         [0045]    In the conventional touch panels, for example, when the X electrodes and the Y electrodes are formed on different surfaces and the electrode interval is increased, as in the case of a display device with a built-in touch panel in which a touch panel is built into a display panel, there have been problems in that the detection sensitivity reduces and that the X electrodes and the Y electrodes may be easily observed visibly from the viewer. 
         [0046]    When the X electrodes and the Y electrodes are formed on different surfaces and the X electrodes as well as the Y electrodes are densely arranged, the intervals between the X electrodes and between the Y electrodes become fine, and thus the X electrodes and the Y electrodes may not be easily observed visibly from the viewer. In this manner, it is possible to solve the problem in that the X electrodes and the Y electrodes may be easily observed visibly from the viewer. 
         [0047]    However, when the X electrodes and the Y electrodes are formed on different surfaces and the X electrodes as well as the Y electrodes are densely arranged, there has been a problem in that it becomes impossible to apply a conventional mutual capacitance detection method (that is, a method of detecting an influence of blocking an electric field between the X electrode and the Y electrode by the finger). 
         [0048]    The present invention has been made to solve the above-mentioned problems of the conventional technology, and it is an object of the present invention to provide a touch panel and a display device with a built-in touch panel, which adopt a novel detection method different from a conventional mutual capacitance detection method. 
       SUMMARY OF THE INVENTION 
       [0049]    The above-mentioned and other objects and novel features of the present invention are made clear from the following description of the subject specification and the accompanying drawings. 
         [0050]    Exemplary embodiments of the invention disclosed herein are briefly outlined as follows. 
         [0051]    (1) A touch panel, including: a plurality of scanning electrodes; a plurality of detecting electrodes intersecting with the plurality of scanning electrodes; first means for sequentially connecting a constant current source to each of the plurality of scanning electrodes for each one scanning period; and second means for detecting a touch position on the touch panel based on a variation of a current detected at each of the plurality of detecting electrodes. 
         [0052]    (2) In the touch panel according to the above-mentioned item (1), the plurality of scanning electrodes and the plurality of detecting electrodes are formed on different surfaces. 
         [0053]    (3) In the touch panel according to the above-mentioned item (1), in which the plurality of scanning electrodes and the plurality of detecting electrodes are formed on different surfaces across an insulating member. 
         [0054]    (4) In the touch panel according to any one of the above-mentioned items (1) to (3), the plurality of scanning electrodes and the plurality of detecting electrodes are each a stripe-type electrode. 
         [0055]    (5) In the touch panel according to the above-mentioned item (4), an electrode interval between the plurality of scanning electrodes and an electrode interval between the plurality of detecting electrodes are each 20 μm or more and 30 μm or less. 
         [0056]    (6) The touch panel according to anyone of the above-mentioned items (1) to (5) further includes third means for adjusting a frequency of the constant current source. 
         [0057]    (7) A display device with a built-in touch panel, including: a display panel; and a touch panel built into the display panel, in which the touch panel includes: a plurality of scanning electrodes formed on the display panel; a plurality of detecting electrodes intersecting with the plurality of scanning electrodes, the plurality of detecting electrodes being formed on the display panel; first means for sequentially connecting a constant current source to each of the plurality of scanning electrodes for each one scanning period; and second means for detecting a touch position on the display panel based on a variation of a current detected at each of the plurality of detecting electrodes. 
         [0058]    (8) In the display device with a built-in touch panel according to the above-mentioned item (7), the plurality of scanning electrodes and the plurality of detecting electrodes are formed on different surfaces. 
         [0059]    (9) In the display device with a built-in touch panel according to the above-mentioned item (7), one of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed on a surface of the display panel on a viewer side, and another of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed inside the display panel. 
         [0060]    (10) In the display device with a built-in touch panel according to the above-mentioned item (7), the display panel is a liquid crystal display panel including: a first substrate; a second substrate; and a liquid crystal layer sandwiched between the first substrate and the second substrate, the second substrate is arranged on a viewer side, one of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed on a surface of the second substrate on a side opposite to the liquid crystal layer, and another of the each of the plurality of scanning electrodes and the each of the plurality of detecting electrodes is formed on a surface of the first substrate on the liquid crystal layer side. 
         [0061]    (11) In the display device with a built-in touch panel according to any one of the above-mentioned items (7) to (10), the plurality of scanning electrodes and the plurality of detecting electrodes are each a stripe-type electrode. 
         [0062]    (12) In the display device with a built-in touch panel according to the above-mentioned item (11), an electrode interval between the plurality of scanning electrodes and an electrode interval between the plurality of detecting electrodes are each 20 μm or more and 30 μm or less. 
         [0063]    (13) The display device with a built-in touch panel according to anyone of the above-mentioned items (7) to (12) further includes third means for adjusting a frequency of the constant current source. 
         [0064]    An effect obtained by the exemplary embodiments of the invention disclosed herein is briefly described as follows. 
         [0065]    According to the exemplary embodiments of the present invention, it is possible to provide the touch panel and the display device with a built-in touch panel, which adopt a novel detection method different from the conventional mutual capacitance detection method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0066]    In the accompanying drawings: 
           [0067]      FIGS. 1A and 1B  are diagrams illustrating a conventional display device with a touch panel; 
           [0068]      FIGS. 2A and 2B  are diagrams illustrating the touch panel illustrated in  FIGS. 1A and 1B ; 
           [0069]      FIGS. 3A and 3B  are diagrams illustrating a conventional display device with a built-in touch panel; 
           [0070]      FIGS. 4A and 4B  are diagrams illustrating the touch panel illustrated in  FIGS. 3A and 3B ; 
           [0071]      FIGS. 5A to 5C  are diagrams illustrating a conventional detection method for the touch panel illustrated in  FIGS. 1A and 1B ; 
           [0072]      FIGS. 6A to 6C  are diagrams illustrating a conventional detection method for the touch panel illustrated in  FIGS. 3A and 3B ; 
           [0073]      FIGS. 7A and 7B  are diagrams illustrating visibility of an X electrode and a Y electrode in the touch panel illustrated in  FIGS. 1A and 1B  and the touch panel illustrated in  FIGS. 3A and 3B ; 
           [0074]      FIGS. 8A and 8B  are diagrams illustrating an electrode structure of a touch panel in a display device with a built-in touch panel according to an embodiment of the present invention; 
           [0075]      FIGS. 9A to 9C  are diagrams illustrating a problem which occurs when the touch panel of the embodiment of the present invention is combined with the conventional detection method; 
           [0076]      FIGS. 10A and 10B  are diagrams illustrating an electrode structure of the touch panel of the display device with a built-in touch panel according to the embodiment of the present invention; 
           [0077]      FIGS. 11A to 11C  are diagrams illustrating a detection method for the touch panel of the embodiment of the present invention; 
           [0078]      FIGS. 12A and 12B  are diagrams illustrating a detection principal of the touch panel of the embodiment of the present invention; 
           [0079]      FIGS. 13A and 13B  are diagrams illustrating the detection principal of the touch panel of the embodiment of the present invention; 
           [0080]      FIGS. 14A to 14C  are diagrams illustrating the detection principal of the touch panel of the embodiment of the present invention; 
           [0081]      FIGS. 15A to 15C  are diagrams illustrating the detection principal of the touch panel of the embodiment of the present invention; 
           [0082]      FIGS. 16A and 16B  are diagrams illustrating an example of detection results obtained from the touch panel of the embodiment of the present invention; and 
           [0083]      FIGS. 17A and 17B  are diagrams illustrating another example of the detection results obtained from the touch panel of the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0084]    Hereinafter, an embodiment of the present invention is described in detail with reference to the accompanying drawings. 
         [0085]    Note that, throughout the drawings illustrating the embodiment, the same reference symbol is given to components having the same function, and repeated description thereof is omitted. Also note that, the following embodiment is not intended to limit the interpretation of the scope of claims of the present invention. 
         [0086]    (Feature of Touch Panel of Embodiment of the Present Invention) 
         [0087]      FIGS. 8A and 8B  are diagrams illustrating a touch panel  301  in a display device with a built-in touch panel according to the embodiment of the present invention. 
         [0088]      FIG. 8A  is a diagram illustrating an electrode pattern of the touch panel  301  of this embodiment, and  FIG. 8B  is a sectional view illustrating a sectional structure taken along the cut-line VIIIB-VIIIB of  FIG. 8A . 
         [0089]    In the touch panel  301  of this embodiment, an X electrode  201  and a Y electrode  202  are each formed into a stripe shape, and a plurality of the Y electrodes  202  are arranged so as to intersect with a plurality of the X electrodes  201 . 
         [0090]    Also in this embodiment, aback electrode formed on a surface of a second substrate on a side opposite to a liquid crystal layer doubles as the X electrode  201 , and a counter electrode doubles as the Y electrode  202 . 
         [0091]    As illustrated in  FIG. 8A , in the electrode structure of the touch panel  301  of this embodiment, an electrode interval  701  is set fine and the electrodes are densely arranged. Therefore, in the electrode structure of the touch panel  301  of this embodiment, the electrode interval  701  cannot be easily observed visibly because the electrode interval  701  is fine similarly to the case of the touch panel  106  of the conventional technology. 
         [0092]    Here, when the electrode interval  701  is 30 μm, the interval can be slightly observed, and the interval becomes nearly invisible when the electrode interval  701  is about 20 μm. 
         [0093]      FIGS. 9A to 9C  are diagrams illustrating a problem which occurs when the touch panel  301  of the embodiment of the present invention is combined with a conventional detection method. 
         [0094]      FIG. 9A  is a diagram illustrating a state in which a touch operation is not performed,  FIG. 9B  is a diagram illustrating a state in which a finger  502  has approached the touch panel  301 , and  FIG. 9C  is a graph showing a variation of a detected signal. 
         [0095]    As illustrated in  FIG. 9A , a voltage source  504  is connected to the Y electrode  202 , and a detection circuit  505  is connected to the X electrode  201 . A pulse input from the voltage source  504  forms an electric field between the X electrode  201  and the Y electrode  202 . However, the X electrodes  201  are densely arranged, and hence lines  901  of electric force do not leak outside. 
         [0096]    As illustrated in  FIG. 9B , even when the finger  502  approaches the touch panel  301  of this embodiment, there is almost no interactions between the finger  502  and the lines  901  of electric force. 
         [0097]    Therefore, as shown in  FIG. 9C , even when the change occurs from the state of  FIG. 9A  to the state of  FIG. 9B , a signal  603  detected by the detection circuit  505  does not vary, and the touch operation cannot be detected. 
         [0098]      FIGS. 10A and 10B  are diagrams illustrating an electrode structure of the touch panel  301  of the display device with a built-in touch panel according to the embodiment of the present invention. 
         [0099]      FIG. 10A  is a diagram illustrating an electrode pattern of the touch panel  301  of this embodiment, and  FIG. 10B  is a sectional view illustrating a sectional structure taken along the cut-line XB-XB of  FIG. 10A . 
         [0100]    The electrode pattern of the touch panel  301  of this embodiment illustrated in  FIG. 10A  is the same as the electrode pattern illustrated in  FIG. 8A . However, the segment for obtaining the sectional structure illustrated in  FIG. 10B  is set parallel to the X electrode  201 . 
         [0101]      FIGS. 11A to 11C  are diagrams illustrating a detection method for the touch panel  301  of the embodiment of the present invention. 
         [0102]      FIG. 11A  is a diagram illustrating a state in which a touch operation is not performed,  FIG. 11B  is a diagram illustrating a state in which the finger  502  has approached the touch panel  301 , and  FIG. 11C  is a graph showing variations of detected signals. 
         [0103]    As illustrated in  FIG. 11A , in the detection method of this embodiment, one of the X electrode  201  and the Y electrode  202  (in this case, the X electrode  201 ) is connected to a constant current source  1106 . On the other hand, another of the X electrode  201  and the Y electrode  202  (in this case, the Y electrode  202 ) is each connected to a detection circuit ( 1101  to  1105 ). 
         [0104]    In the touch panel  301  of this embodiment, the constant current source  1106  is used as a detection signal source. With use of the constant current source  1106 , regardless of the state of the touch panel  301 , a constant current flows through each X electrode  201 . 
         [0105]    As illustrated in  FIG. 11B , when the finger  502  approaches the touch panel  301 , a current passage is added to the touch panel  301 , but the current is constant, and hence the current in other passages reduce by an amount of current flowing through the added current passage. This phenomenon becomes remarkable in a passage connected to a position close to the finger  502 . 
         [0106]    Therefore, as shown in  FIG. 11C , of detection signals  1107  to  1109 , the detection signal  1107  of the detection circuit  1103  reduces in a greatest amount, and thus the contact position of the finger  502  can be determined. 
         [0107]      FIG. 12A  to  FIG. 14C  are diagrams illustrating a detection principal of the touch panel  301  of the embodiment of the present invention. 
         [0108]      FIG. 12A  and  FIG. 13A  are diagrams illustrating an electrode structure of the touch panel  301  of the embodiment of the present invention, and a connection relationship of the constant current source  1106  and the detection circuits ( 1101  to  1105 ). 
         [0109]      FIG. 12B  is a circuit diagram illustrating an equivalent circuit of the touch panel  301  of the embodiment of the present invention in a state in which a touch operation is not performed. 
         [0110]      FIG. 13B  is a circuit diagram illustrating an equivalent circuit of the touch panel  301  of the embodiment of the present invention in a state in which the finger  502  has approached the touch panel  301 . 
         [0111]      FIG. 14A  is a circuit diagram illustrating the equivalent circuit of the touch panel  301  of the embodiment of the present invention in the state in which a touch operation is not performed, and is the same diagram as that of  FIG. 12B . 
         [0112]      FIG. 14B  is a circuit diagram illustrating the equivalent circuit of the touch panel  301  of the embodiment of the present invention in the state in which the finger  502  has approached the touch panel  301 , and is the same diagram as that of  FIG. 13B . 
         [0113]      FIG. 14C  is a graph showing a variation of a current which occurs along with a change from the state of  FIG. 14A  to the state of  FIG. 14B . 
         [0114]    A total current amount ( 10 ) to be generated by the constant current source  1106  is constant regardless of the state of the touch panel  301 . Therefore, as illustrated in  FIG. 12B , in the state in which a touch operation is not performed to the touch panel  301 , the total current amount ( 10 ) to be generated by the constant current source  1106  becomes a sum of the currents (I 1  to I 5 ) flowing through the detection circuits  101  to  1105  (I 0 =I 1 +I 2 +I 3 +I 4 +I 5 ). 
         [0115]    Further, as illustrated in  FIG. 13B , in the equivalent circuit in the state in which the finger  502  has approached the touch panel  301 , the finger  502  that has approached the touch panel  301  is represented by a capacitance  512 . This becomes a new current passage (current amount I 3 ″) with respect to the constant current source  1106 . 
         [0116]    However, the total current amount to be generated by the constant current source  1106  does not vary. Therefore, as shown in the graph of  FIG. 14C , the current flowing through the existing current passage, which is connected to a point to which the capacitance  512  of the finger  502  connects, is reduced by the amount of the new current (I 3 ″) to become I 3 ′. 
         [0117]      FIG. 15A  to  FIG. 15C  are diagrams illustrating the detection principal of the touch panel  301  of the embodiment of the present invention. 
         [0118]      FIG. 15A  is a circuit diagram illustrating the equivalent circuit of the touch panel  301  of the embodiment of the present invention in the state in which a touch operation is not performed, and is the same diagram as that of  FIG. 12B . 
         [0119]      FIG. 15B  is a circuit diagram illustrating the equivalent circuit of the touch panel  301  of the embodiment of the present invention in the state in which the finger  502  has approached the touch panel  301 , and is the same diagram as that of  FIG. 13B . 
         [0120]      FIG. 15C  is a graph showing a relationship between a current generation frequency of the constant current source  1106  and the detection sensitivity. 
         [0121]    The approach of the finger  502  with respect to the touch panel  301  of this embodiment changes transfer characteristics of a measuring system. Therefore, as shown in  FIG. 15C , at a specific frequency, the change is remarkably reflected to the current variation. 
         [0122]    In this embodiment, the constant current source  1106  is set so as to generate a current at such an optimum frequency. 
         [0123]      FIGS. 16A and 16B  are diagrams illustrating an example of detection results obtained from the touch panel  301  of the embodiment of the present invention. 
         [0124]      FIG. 16A  is a diagram illustrating that the contact position of the finger  502  sequentially moves from the Y electrode  202  of RY 1  to the Y electrode  202  of RY 8 . 
         [0125]      FIG. 16B  is a graph showing detection signals detected from the Y electrodes  202  of RY 1  to RY 8  in a state in which the contact position of the finger  502  has sequentially moved from the Y electrode  202  of RY 1  to the Y electrode  202  of RY 8 . 
         [0126]    As shown in  FIG. 16B , it is understood that, in accordance with the movement of the contact position of the finger  502 , the detection signals detected from the Y electrodes  202  of RY 1  to RY 8  vary to a distribution state that is capable of detecting the contact position of the finger  502 . 
         [0127]      FIGS. 17A and 17B  are diagrams illustrating another example of the detection results obtained from the touch panel  301  of the embodiment of the present invention. 
         [0128]      FIG. 17A  is a diagram illustrating that the finger  502  is simultaneously held in contact to the Y electrodes  202  of RY 2  and RY 7 . 
         [0129]      FIG. 17B  is a graph showing detection signals detected from the Y electrodes  202  of RY 1  to RY 8  in the state in which the finger  502  is simultaneously held in contact to the Y electrodes  202  of RY 2  and RY 7 . 
         [0130]    As shown in  FIG. 17B , it is understood that, in the state in which the finger  502  is simultaneously held in contact to the Y electrodes  202  of RY 2  and RY 7 , a signal distribution corresponding to the two simultaneous contact positions is obtained. In this manner, even when contact is made at a plurality of points on the same surface, the coordinates of the respective points can be calculated. 
         [0131]    Note that, in the above-mentioned embodiment, description is made of a case where the present invention is applied to a display device with a built-in touch panel, but the present invention is not limited to the above-mentioned embodiment. It should be understood that the present invention is applicable to a touch panel including a plurality of X electrodes and a plurality of Y electrodes formed on different surfaces, in which the plurality of X electrodes and the plurality of Y electrodes are formed on different surfaces across an insulating member. 
         [0132]    While the invention made by the inventor of the present invention has been concretely described based on the embodiment, it should be understood that the present invention is not limited to the embodiment and various modifications may be made thereto without departing from the gist of the invention.