Abstract:
A sensor device which detects a positional relationship between an first member and second member, includes a signal source generating an electrical signal, a first electrode receiving the electrical signal and storing an electrical charge at a first part on the first member, a second electrode inducing an electrical charge at the second part on the second member, a third electrode inducing an electrical charge at the third part on the second member, a fourth electrode inducing an electrical charge at the fourth part on the first member, a reference electrode disposed at a fifth part on the second member to be connected to a reference voltage point, a fifth electrode inducing an electrical charge at the sixth part on the first member, and a differential amplifier amplifying a voltage difference between the fourth electrode and the fifth electrode and outputting a difference signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-249506, filed Sep. 26, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a sensor device, and a sensor system and an electronic device using the sensor device. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, a proximity sensor of this kind detecting electrostatic capacitance has been proposed as a sensor detecting proximity of an object (e.g., refer to International Publication WO2004/059343). Such a proximity sensor includes a first member to detect proximity and a second member to be a detection object, and can detect the proximity of the second member in a non-contact manner. 
         [0006]    However, the proximity sensor disclosed in International Publication WO2004/059343 given above basically detects all objects approaching the first member. Therefore, it is hard to detect only the second member. For instance, if the second member is a tab or a door, the proximity sensor should detect the proximity only of the tab or the door, but the proximity sensor actually detects the proximity of an object other than the tab or the door. 
         [0007]    As mentioned above, it is hard for a conventional proximity sensor to accurately detect the proximity only of an object to be detected. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    According to one embodiment of the present invention, there is provided a sensor device which detects a positional relationship between an insulating first member and second member of which the surfaces face each other in coming close to each other, comprising: a first signal source generating an electrical signal; a first electrode disposed at a first part on a surface of the first member to receive the electrical signal and store an electrical charge at the first part; a second electrode disposed at a second part on a surface of the second member and inducing an electrical charge, corresponding to the electrical charge stored in the first part, at the second part when the first electrode approaches; a third electrode disposed at a third part on a surface of the second member, connected to the second electrode, and inducing an electrical charge, corresponding to the electrical charge induced at the second part, at the third part; a fourth electrode disposed at a fourth part on a surface of the first member and inducing an electrical charge, corresponding to the electrical charge induced at the third part, at the fourth part when the third electrode approaches; a reference electrode disposed at a fifth part on a surface of the second member to be connected to a reference voltage point; a fifth electrode disposed at a sixth part on a surface of the first member, and inducing an electrical charge, corresponding to the electrical charge to be stored in the fifth part, at the sixth part when the reference electrode approaches; and a differential amplifier amplifying a voltage difference between the fourth electrode and the fifth electrode and outputting a difference signal corresponding to the positional relationship. 
         [0009]    According to one embodiment of the present invention, there is provided an electronic device, comprising a first member, a second member and a sensor device which detects a positional relationship between the first and the second members, wherein the sensor device comprises: a first signal source generating an electrical signal; a first electrode disposed at a first part on a surface of the first member to receive the electrical signal and store an electrical charge at the first part; a second electrode disposed at a second part on a surface of the second member and inducing an electrical charge, corresponding to the electrical charge stored in the first part, at the second part when the first electrode approaches; a third electrode disposed at a third part on a surface of the second member, connected to the second electrode, and inducing an electrical charge, corresponding to the electrical charge induced at the second part, at the third part; a fourth electrode disposed at a fourth part on a surface of the first member and inducing an electrical charge, corresponding to the electrical charge induced at the third part, at the fourth part when the third electrode approaches; a reference electrode disposed at a fifth part on a surface of the second member to be connected to a reference voltage point; a fifth electrode disposed at a sixth part on a surface of the first member, and inducing an electrical charge, corresponding to the electrical charge to be stored in the fifth part, at the sixth part when the reference electrode approaches; and a differential amplifier amplifying a voltage difference between the fourth electrode and the fifth electrode and outputting a difference signal corresponding to the positional relationship. 
         [0010]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0011]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
           [0012]      FIG. 1  is a schematic view depicting a configuration of the first embodiment of a sensor device regarding the present invention; 
           [0013]      FIG. 2  is a schematic view in a case in which the sensor device of  FIG. 1  is mounted on various switching devices; 
           [0014]      FIG. 3  is a schematic view depicting a modified example of an electrode arrangement of the sensor device  1  of  FIG. 1 ; 
           [0015]      FIG. 4  is a block diagram depicting a configuration example of a circuit to be applied to the sensor device of  FIG. 3 ; 
           [0016]      FIG. 5  is a schematic view depicting a modified example of the electrode arrangement of the sensor device of  FIG. 1 ; 
           [0017]      FIG. 6  is a block diagram depicting a configuration example of a circuit to be applied to the sensor device of  FIG. 5 ; 
           [0018]      FIG. 7  is a schematic view depicting a modified example of the electrode arrangement of the sensor device of  FIG. 1 ; 
           [0019]      FIG. 8  is a block diagram depicting a configuration example of a circuit to be applied to the sensor device of  FIG. 7 ; 
           [0020]      FIG. 9  is a schematic view depicting a modified example of a configuration of the sensor device of  FIG. 1 ; 
           [0021]      FIG. 10  is a schematic view depicting an arrangement example of electrodes of the sensor device of  FIG. 9 ; 
           [0022]      FIG. 11  is a block diagram depicting a configuration example of a circuit to be applied to the sensor device of  FIG. 10 ; 
           [0023]      FIG. 12  is a schematic view depicting a concrete configuration example of the sensor device of the first embodiment; 
           [0024]      FIG. 13  is a schematic view depicting a concrete configuration example of the sensor device of the first embodiment; 
           [0025]      FIG. 14  is a schematic view depicting a concrete configuration example of the sensor device of the first embodiment; 
           [0026]      FIG. 15  is a schematic view depicting a concrete configuration example of the sensor device of the first embodiment; 
           [0027]      FIG. 16  is a cross-sectional view depicting an example in a case in which the sensor device of the first embodiment is used as an angle detection sensor; 
           [0028]      FIG. 17  is a plane view of the angle detection sensor of  FIG. 16 ; 
           [0029]      FIG. 18  is a plane view of the angle detection sensor of  FIG. 16 ; 
           [0030]      FIG. 19  is a schematic view depicting a configuration example when the sensor device of the first embodiment is applied to a mobile communication terminal; 
           [0031]      FIG. 20  is a schematic view depicting a configuration example when the sensor device of the first embodiment is applied to a mobile communication terminal; 
           [0032]      FIG. 21  is a schematic view depicting a configuration example when the sensor device of the first embodiment is applied to a mobile communication terminal; 
           [0033]      FIG. 22  is a schematic view depicting a configuration example when the sensor device of the first embodiment is applied to a mobile communication terminal; 
           [0034]      FIG. 23  is a schematic view depicting a configuration of the second embodiment of the sensor device regarding the present invention; and 
           [0035]      FIG. 24  is a schematic view depicting a configuration of the third embodiment of the sensor device regarding the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       [0036]    Hereinafter, the first embodiment of the present invention will be described with reference to the drawings. 
         [0037]      FIG. 1  shows a schematic view illustrating a configuration of a sensor device regarding the first embodiment of the invention. The sensor device shown in  FIG. 1  detects a positional relationship between insulating first member  10  and a second member  20 , that is, detects whether the members  10 ,  20  are in proximity to each other or apart from each other. 
         [0038]    In the first member  10 , a first electrode  11  to transmit a signal, a first electrode  12  to detect a signal and a second electrode  13  to detect a signal are arranged adjacently to each other. An alternating-current power source  30  is connected to the electrode  11 , and an electrical charge is supplied to the electrode  11  from the power source  30 . Here, although the alternating-current power source  30  is utilized, a fixed electrical charge or a direct-current power source may be used in response to use or detection precision. 
         [0039]    On the second member  20 , a second electrode  21  to transmit a signal, a third electrode to transmit a signal, and an electrode  23  to store a reference electrical charge are arranged adjacently to each other. The electrodes  21 ,  22  are short-circuited. The electrode  23  is grounded. 
         [0040]    When the members  10 ,  20  are close to each other, the electrodes  11 ,  21 , the electrodes  12 ,  22  and the electrodes  13 ,  23  face each other, respectively. That is, if the members  10 ,  20  are brought into a state where they are close to each other from a state where they are apart from each other, the electrodes  11 ,  21  come close to each other, the electrodes  12 ,  22  come close to each other, and the electrodes  12 ,  23  come close to each other. 
         [0041]    As a result, an electrical charge corresponding to an electrical charge stored in an installation part of the electrode  11  on the member  10  is induced at an installation part of the electrode  21  on the member  20 . When the electrical charge is induced at an installation part of the electrode  21 , since the electrode  21  is short-circuited to the electrode  22 , an electrical charge corresponding to the electrical charge to be stored at the installation part of the electrode  21  is induced at an installation part of the electrode  22  on the member  20 . When the electrical charge is induced at the installation part of the electrode  22 , at an installation part of the electrode  12  on the member  10 , an electrical charge corresponding to the electrical charge to be stored at the installation part of the electrode  22  is induced. An installation part of the electrode  13  on the member  10  is grounded by the approach to the grounded electrode  23 . Therefore, electrical charges which are different from each other are induced at the installation parts of the electrodes  12 ,  13  on the member  10 . 
         [0042]    A differential amplifier  40  is connected to the electrodes  12 ,  13 . In a case of a state in which the members  10 ,  20  are in proximity to each other, since a electrical potential difference between the electrodes  12 ,  13 , namely an electrical potential difference between two input terminals of the amplifier  40 , is amplified, a large difference signal is output from the amplifier  40 . Meanwhile, if the members  10 ,  20  are in a state in which they are apart from each other, since the electrical potential difference between the electrodes  12 ,  13  is equivalent to zero (or almost zero), the difference signal output from the amplifier  40  is equivalent to zero (or almost zero). 
         [0043]    In a state in which the members  10 ,  20  are in proximity to each other, distances between the electrodes  11 ,  21 , the electrodes  12 ,  22 , and the electrodes  13 ,  23  are vary, respectively, in response to devices to which the sensor devices are applied. The electrical charges to be induced at the installation parts of the electrodes  12 ,  21  vary in response to the distance between the electrodes  11 ,  21  and the distance between the electrodes  12 ,  22 . Therefore, it is preferable for the electrical charge to be stored in the installation part of the electrode  11  to be made variable so as to enable optimum detection corresponding to the device to which the sensor device is applied. More specifically, it is preferable to make the alternating-current power source  30  be a variable voltage power source. Making the electrical charge to be stored at the installation part of the electrode  11  variable enables performing accurate sense adjustment and improving detection precision. 
         [0044]    From a point of view of performing accurate sense adjustment, it is also preferable to make the gain of the amplifier  40  variable. 
         [0045]    From a point of view enhancing detection sensitivity, it is also preferable to dispose an amplification circuit between the electrode  12  and the amplifier  40 . 
         [0046]    It is also able to utilize the difference signal output from the amplifier  40  as a binary logical signal. That is, as the difference signal output from the amplifier  40  is equivalent to zero (or almost zero) in a case where the members  10 ,  20  are apart from each other, the sensor device utilizes the difference signal as a state of logical value ‘0’. Conversely, as the large difference signal is output from the amplifier  40  in a case where the members  10 ,  20  are in proximity to each other, the sensor device utilizes the difference signal as the logical value ‘1’. 
         [0047]      FIG. 2  shows a schematic view illustrating a mounting of an electrode arrangement in a case in which the sensor device of the first embodiment regarding the invention is mounted on various switching devices. The electrodes  11 ,  12 ,  13  are disposed adjacently to each other on the surface of the first member  10 . The electrodes  21 ,  22 ,  23  are disposed adjacently to each other on the surface of the second member  20 . 
         [0048]    When the first member  10  and the second member  20  are in a closed state, the electrodes  11 ,  21 , the electrodes  12 ,  22  and the electrodes  13 ,  23  face each other, respectively. In other words, if the members  10 ,  20  shift from an open state to a closed state, the electrodes  11 ,  21 , the electrodes  12 ,  22  and the electrodes  13 ,  23  come close to each other, respectively. 
         [0049]    The sensor devices in the examples shown in  FIGS. 1 and 2  include one electrode to transmit a signal and two electrodes to detect signals, and further include two electrodes to transmit a signal to the member  20  and one electrode to store a reference electrical charge. However, the sensor device can include two or more electrodes to transmit signals to the member  10  and three or more electrodes to detect signals, and three or more electrodes to transmit signals to the member  20  and two or more electrodes to detect signals. Hereinafter, a concrete example will be described. 
         [0050]      FIGS. 3 and 4  show examples in which more than one detection unit (electrodes  11 ,  12 ,  13  provided for member  10 , electrodes  21 ,  22 ,  23  provided for member  20  and a differential amplifier  40 ) shown in  FIG. 1  is included.  FIG. 3  shows an electrode arrangement, and  FIG. 4  shows a circuit configuration. 
         [0051]    As shown in  FIGS. 3 and 4 , a first detection unit is composed of electrodes  11   a ,  12   a ,  13   a , electrodes  21   a ,  22   a ,  23   a  and a differential amplifier  40   a . A second detection unit is composed of electrodes  11   b ,  12   b ,  13   b , electrodes  21   b ,  22   b ,  23   b  and a differential amplifier  40   b . The differential amplifiers  40   a ,  40   b  are connected to a generation unit  50  generating an output signal. An example of the generation unit  50  will be described hereinafter. 
         [0052]    In a first example, the generation unit  50  generates an output signal when all the differential amplifiers generate difference signals. That is, the generation unit  50  functions as an AND circuit. In the example shown in  FIGS. 3 and 4 , when all the differential amplifiers  40   a ,  40   b  generate the difference signals, the generation unit  50  generates the output signal. With such a configuration adopted, an incorrect operation can be prevented. Therefore, it becomes possible for the sensor device to accurately detect the approach of a detection object. 
         [0053]    In a second example, the generation unit  50  generates an output signal when at least one differential amplifier generates a difference signal. That is, the generation unit  50  functions as an OR circuit. In the examples shown in  FIGS. 3 and 4 , when at least any one of the differential amplifiers  40   a ,  40   b  generates the difference signal, the generation unit  50  generates the output signal. By adopting such a configuration, even in a case in which one detection unit can perform a normal detection operation while the other detection unit cannot perform a normal detection operation, the whole sensor device can retain the normal detection operation. Therefore the sensor device can become able to accurately detect the proximity of the detection object. 
         [0054]      FIGS. 5 and 6  also show examples in which more than one detection unit (electrodes  11 ,  12 ,  13  provided for member  10 , electrodes  21 ,  22 ,  23  provided for member  20  and differential amplifier  40 ) shown in  FIG. 1  is included. 
         [0055]    As shown in  FIGS. 5 and 6 , electrodes  11 ,  12 ,  13   a , electrodes  21 ,  22 ,  23   a  and a differential amplifier  40   a  compose one detection unit, and electrodes  11 ,  12 ,  13   b , electrodes  21 ,  22 ,  23   b  and a differential amplifier  40   b  compose another detection unit. The differential amplifiers  40   a ,  40   b  are connected to the generation unit  50 . The generation unit  50  operates in the same manner as the examples described for  FIGS. 3 and 4 . That is, the generation unit  50  can function as an AND circuit or an OR circuit. Thus the sensor device can obtain the same effects as those of the examples described for  FIGS. 3 and 4  may be produced. 
         [0056]    Further,  FIGS. 7 and 8  also show examples in which more than one detection unit (electrodes  11 ,  12 ,  13  provided for member  10 , electrodes  21 ,  22 ,  23  provided for member  20  and differential amplifier  40 ) shown in  FIG. 1  is included.  FIG. 7  shows an electrode arrangement, and  FIG. 8  shows a circuit configuration. 
         [0057]    As shown in  FIGS. 7 and 8 , electrodes  11   a ,  12   a ,  13 , electrodes  21   a ,  22   a ,  23  and a differential amplifier  40   a  compose one detection unit, and electrodes  11   b ,  12   b ,  13 , electrodes  21   b ,  22   b    23  and a differential amplifier  40   b  compose another detection unit. The differential amplifiers  40   a ,  40   b  are connected to the generation unit  50 . The generation unit  50  operates in the same manner as those of examples described for  FIGS. 3 and 4 . That is, the generation unit  50  can function as an AND circuit and an OR circuit. Thus the sensor device can obtain the same effects as those of the examples described for  FIGS. 3 and 4 . 
         [0058]    The detection unit shown in  FIG. 1  can be operated similarly by the same configuration as that of  FIG. 9 . On the first member  10 , the electrodes  11 ,  12 ,  13  and the third electrode  14  to detect the signal are arranged adjacently to each other. An alternating-current power source  30  is connected to the electrode  11 , and the power source  30  supplies an electrical charge to the electrode  11 . A differential amplifier  40  is connected to the electrodes  12 ,  13 . A second differential amplifier  41  is connected to the electrodes  13 ,  14 . 
         [0059]    Electrodes  21 ,  22 ,  23  and a fourth electrode  24  to transfer a signal are disposed adjacently to each other on a second member  20 . The electrodes  21 ,  22 ,  23  are short-circuited. The electrode  23  is grounded. 
         [0060]    In a case in which the members  10 ,  20  are in proximity to each other, the electrodes  11 ,  21 , the electrodes  12 ,  22 , the electrodes  14 ,  24  and the electrodes  13 ,  24  face each other, respectively. That is, when the members  10 ,  20  shift from a separation state to a proximity state, the electrodes  11 ,  21  come close to each other, the electrodes  12 ,  22  come close to each other, the electrodes  14 ,  24  come close to each other, and the electrodes  13 ,  23  come close to each other. 
         [0061]      FIGS. 10 and 11  show examples in which more than one detection unit (electrodes  11 ,  12 ,  13 ,  14  provided for member  10 , electrodes  21 ,  22 ,  23 ,  24  provided for member  20 , differential amplifier  40  and second differential amplifier  41 ) shown in  FIG. 9  is included.  FIG. 10  shows an electrode arrangement, and  FIG. 11  shows a circuit configuration. 
         [0062]    As shown in  FIGS. 10 and 11 , electrodes  11   a - 14   a , electrodes  21   a - 24   a  and differential amplifiers  40   a ,  41   a  compose one detection unit, and electrodes  11   b - 14   b , electrodes  21   b - 24   b  and differential amplifiers  40   b ,  41   b  compose another detection unit. The differential amplifiers  40   a ,  41   a  and differential amplifiers  40   b ,  41   b  are connected to a generation unit  50 . The generation unit  50  operates in the same manner as that of examples described for  FIGS. 3 and 4 . That is, the generation unit  50  can function as an AND circuit or an OR circuit. Thus the sensor device can obtain the same effects as those of the example described for  FIGS. 3 and 4 . 
         [0063]    Next, concrete examples of the sensor devices of  FIGS. 1 and 2  of the first embodiment regarding the invention will be described. 
         [0064]      FIG. 12  shows a plan view schematically illustrating a first configuration example of the sensor device. The left view in  FIG. 12  shows a configuration example of electrodes  21 ,  22 ,  23 , and the right view thereof shows configuration example of electrodes  21 ,  22 ,  23 . 
         [0065]    In the left view of  FIG. 12 , the electrodes  11 ,  12 ,  13  and a circuit unit  62  composed of an integrated circuit (IC) are arranged on the same substrate  61 . That is, the electrodes  11 ,  12 ,  13  and the circuit unit  62  are disposed on the same plane. The circuit unit  62  includes various circuits, such as a differential amplifier  40  (refer to  FIGS. 1 and 2 ). The electrodes  11 ,  12 ,  13  and the circuit unit  62  are connected with one another by wires  63 . Arranging the electrodes  11 ,  12 ,  13  and the circuit unit  62  on the same substrate  61  (disposing on the same plane) enables realizing a compact mounting. The circuit  62  may be disposed on another substrate if necessary. 
         [0066]    In the right view of  FIG. 12 , the electrodes  21 ,  22 ,  23  are arranged on the same substrate  64 . That is, the electrodes  21 ,  22 ,  23  are disposed on the same plane. 
         [0067]    The substrates  61 ,  64  are mounted on the foregoing members  10 ,  20 , respectively. Thus, the electrodes  11 ,  12 ,  13  are disposed on the surface of the member  10 . The electrodes  21 ,  22 ,  23  are disposed on the surface of the member  20 . 
         [0068]      FIG. 13  shows a cross-sectional view schematically illustrating a second configuration example. In the second configuration example, the electrodes  11 ,  12 ,  13  are arranged so as to cover at least a part of a circuit unit  71  composed of an IC. The circuit unit  71  includes various circuits, such as a differential amplifier  40  (refer to  FIGS. 1 and 2 ). The electrodes  11 ,  12 ,  13  and the circuit unit  71  are connected with one another through wires  72 . The circuit units  71  and the wires  72  are covered with a molded resin  73 . Since the electrodes  11 ,  12 ,  13  are arranged so as to cover at least a part of the circuit unit  71 , a mounting area may be reduced, and compact mounting may be achieved. 
         [0069]    The electrodes  21 ,  22 ,  23  are, as shown in  FIG. 13 , disposed on the same plane which faces the electrodes  11 ,  12 ,  13 , respectively. A wire  74  which connects between the electrodes  21 ,  22  is covered with the molded resin  73 . 
         [0070]    While the example shown in  FIG. 13  has described the configuration in which the electrodes  11 ,  12 ,  13  are disposed outside a package of the molded resin  73 , they may be disposed inside the package. Adopting such a configuration enables achieving further compact mounting. 
         [0071]      FIG. 14  shows a cross-sectional view schematically illustrating a third configuration example. In the example, an electrode  84  is arranged so as to cover at least a part of the circuit unit  82 , in order to transmit a signal in the member  10 . More specifically, the circuit  82  is arranged on a substrate  81 , and the circuit unit  82  is covered with a molded resin  83 . The electrode  84  is formed on the molded resin  83  using a plating method (actually, the electrodes  12 ,  13  are also formed similarly). A hole is formed in the molded resin  83 , and the electrode  84  and a pad  85  of the circuit unit  82  are electrically connected through the hole. Also in the embodiment, since the electrode  84  is arranged so as to cover at least a part of the circuit unit  82 , a mounting area may be decreased, which enables more compact mounting. 
         [0072]      FIG. 15  shows a cross-sectional view schematically illustrating a fourth configuration example. Also in the example, an electrode  94  to transmit a signal in the member  10  is arranged so as to cover a part of a circuit unit  92 . More specifically, the circuit unit  92  is formed on a semiconductor substrate (e.g., silicon substrate)  91  by means of a usual IC forming technique to cover the circuit  92  with an insulating film  93 . On the insulating film  93 , the electrode  94  is formed (actually, electrodes  12 ,  13  are also formed similarly). A via hole is formed in the insulating film  93 , and a conducting part  95  formed in the via hole electrically connects the electrode  94  to the circuit unit  92 . Also in the example, since the electrode  94  is arranged so as to cover at least a part of the circuit unit  92 , the sensor device can reduce a mounting area and realize compact mounting. 
         [0073]    Each of  FIGS. 16 ,  17  and  18  shows a schematic view illustrating an example of a case in which the sensor device of the first embodiment regarding the invention is used as an angle detection sensor.  FIG. 16  shows a cross-sectional view, and  FIGS. 17 and 18  show plan views. 
         [0074]    As shown in  FIGS. 16 and 17 , a plurality of first electrode groups consisting of electrodes  11 ,  12 ,  13  are arranged from one end to the other end of the first member  10 . Similarly, as shown in  FIGS. 16 and 18 , a plurality of second electrode groups consisting of electrodes  21 ,  22 ,  23  are arranged from one end to the other end of the second member  20 . The one end of the first member  10  and the one end of the second member  20  are connected to each other at a connecting point P. The first and the second members  10 ,  20  are relatively rotatable in an arrow direction around the point P. 
         [0075]    As can be seen in  FIGS. 16 ,  17  and  18 , as the angle θ made by the members  10 ,  20  becomes small, the number of the first electrode groups (electrodes  11 ,  12 ,  13 ) which are brought into on states (proximity detecting states) increases. Therefore, if a relationship between the on/off state of each first electrode group (electrodes  11 ,  12 ,  13 ) and the angle θ is obtained in advance, the on/off state of each first electrode group (electrodes  11 ,  12 ,  13 ) enables measuring the angle θ. Therefore, increasing the number of the second electrode groups (electrodes  21 ,  22 ,  23 ) and the first electrode groups (electrode  11 ,  12 ,  13 ) enables the angle θ to be measured as an analog value, and an angle detection device can be configured with a simple configuration. 
         [0076]      FIGS. 19-22  show configuration examples in which the sensor devices of the first embodiments regarding the inventions are applied to mobile communication terminals. As a mobile communication terminal, a cellular phone is assumed. 
         [0077]    In  FIGS. 19-22 , the member  10  corresponds to a lower side member of the cellular phone, and the member  20  corresponds to an upper side member of the cellular phone. The electrodes  11 ,  12 ,  13  are arranged in an area  100  in which electrodes are arranged, and the electrodes  21 ,  22 ,  23  are arranged in an area  200  in which electrodes are arranged. The members  10 ,  20  each include communication function units. 
         [0078]      FIG. 19  shows an open/close type cellular phone. When the members  10 ,  20  move in an arrow direction and the areas  100 ,  200  are in proximity to each other, a closed state of the members  10 ,  20  is detected. 
         [0079]      FIG. 20  shows a slide type cellular phone. When the members  10 ,  20  move in an arrow direction and the areas  100 ,  200  are in proximity to each other, the closed state of the members  10 ,  20  is detected. 
         [0080]      FIG. 21  shows a rotary cellular phone. When the members  10 ,  20  rotate in an arrow direction and the areas  100 ,  200  come close to each other, the closed state of the members  10 ,  20  is detected. 
         [0081]      FIG. 22  shows a rotary cellular phone. When the members  10 ,  20  rotate in an arrow direction and the areas  100 ,  200  come close to each other, the rotated states of the members  10 ,  20  are detected. 
         [0082]    While the case in which the sensor device is applied to the opening/closing detection of the mobile communication terminal of the cellular phone, etc., has been described in detail, the sensor device may be applied to opening/closing detection of an electronic device such as a personal computer, a refrigerator, an oven range, i.e., a door other than that of a mobile communication terminal. 
         [0083]    As mentioned above, in the embodiment, when the members  10 ,  20  are brought into a closed state, an electrical charge is induced at the installation part of the electrode  21  by the stored electrical charge at the installation part of the electrode  11 , and an electrical charge is induced at the installation part of the electrode  22  which has been short-circuited to the electrode  21 . Here, since the electrode  23  is grounded, the electrical charges differing from each other are stored at the installation parts of the electrodes  22 ,  23 , respectively. Thereby, when the members  10 ,  20  are closed, the sensor device may induce electrical charges which are different from each other at the installation part of the electrodes  12 ,  13 . That is, with the fluctuations of a positional relationship between the members  10 ,  20 , when the electrodes  12 ,  22  come close to each other, and the electrodes  13 ,  23  come close to each other, the sensor device can induce electrical charges differing from each other at the installation parts of the electrodes  12 ,  13 . Therefore, the sensor device can accurately detect the closed state of the members  10 ,  20  by means of a difference signal of the induced electrical charges. 
         [0084]    When an object other than the electrodes  22 ,  23  comes close to the electrodes  12 ,  13 , the electrical charges having the equivalent values are induced at the installation parts of the electrodes  12 ,  13 . Thereby, there is no difference between the electrical charges induced at the installation parts of the electrode  12  and the electrical charge induced at the installation part of the electrode  13 . Therefore, the sensor device may accurately detect solely the proximity of the electrodes  22 ,  23  to the electrodes  12 ,  13 . 
         [0085]    When the electrode  13  approaches the electrode  23 , since the electrical charge at the installation part of the electrode  13  becomes almost zero, even if noise is present, the sensor device becomes able to find the difference between the electrical charge at the installation part of the electrode  13  and that of the electrode  12 . Therefore, even if noise is present, the sensor device may accurately detect the open and closed state of the members  10 ,  20 . 
         [0086]    For concretely arranging electrodes, it is possible to arrange the electrodes  11 ,  12 ,  13  on the same plane, and to arrange the electrodes  21 ,  22 ,  23  on the same plane. Thereby, the sensor device may accurately detect the open and closed state without increasing the arrangement area of the electrodes. The member  20  does not need the circuit unit composed of the IC. Thereby, the arrangement area of the sensor device may be further reduced. Thus, according to the embodiment, the sensor device becomes able to accurately detect solely the proximity of the specified detection object with a compact configuration. 
       Second Embodiment 
       [0087]    Referring now to  FIG. 23 , the second embodiment regarding the present invention will be described in detail. Since the sensor device of the embodiment has basically the same configuration as that of the first embodiment, the description will be omitted and components differing from those of the first embodiment will be described hereinafter. 
         [0088]      FIG. 23  shows a schematic view depicting a configuration of the sensor device of the second embodiment regarding the invention. The sensor device shown in  FIG. 23  detects a positional relationship between a first member (e.g., corresponding to the member  10  shown in  FIGS. 1 and 2 ) and a second member (e.g., corresponding to the member  20  shown in  FIGS. 1 and 2 ). 
         [0089]    The first member  10  is provided with electrodes  11 ,  12 ,  13 . At this time, the electrode  13  is arranged so as to surround the electrodes  11 ,  12 . An alternating-current power source  30  is connected to the electrode  11  and the power source  30  supplies an electrical charge to the electrode  11 . 
         [0090]    The second member  20  is provided with electrodes  21 ,  22 ,  23 . At this time, the electrode  23  is arranged so as to surround the electrodes  21 ,  22 . The electrodes  21 ,  22  are short-circuited. The electrode  23  is grounded. 
         [0091]    As mentioned above, in the second embodiment, the grounded electrode  23  is arranged so as to surround the electrodes  21 ,  22 . Thereby, it becomes possible to prevent an electric field of the electrode  11  from leaking to the electrode  12 . 
         [0092]    Therefore, since it is able to decrease adverse effects from the electric field of the electrode  11  on the electrode  12 , the sensor device may accurately detect the approaching of the member  10  to the member  20 . 
       Third Embodiment 
       [0093]    The following will describe the details of the third embodiment regarding the present invention by referring to  FIG. 24 . Since the sensor device of the embodiment has basically the same configuration as that of the first embodiment, the description will be omitted and only different components will be described. 
         [0094]      FIG. 24  shows a schematic view illustrating a configuration of a sensor device of the third embodiment regarding the invention. The sensor device shown in  FIG. 24  detects a positional relationship between a first member (e.g., corresponding to the member  10  shown in  FIGS. 1 and 2 ) and a second member (e.g., corresponding to the member  20  shown in  FIGS. 1 and 2 ). 
         [0095]    Electrodes  11 ,  12 ,  13  are disposed adjacently to each other on the first member  10 . An alternating-current power source  31  supplying an alternating signal with a first frequency f 1  is connected to the electrode  11 . An alternating-current power source  32  supplying an alternating signal with a second frequency f 2  is connected to the electrode  12 . Here, it is assumed that a difference between the first frequency f 1  and the second frequency f 2  is sufficiently smaller than frequencies f 1 , f 2 . A symbol R 1  designates an input resistor. 
         [0096]    When the first member  10  and the second member  20  becomes into a proximity state, the electrodes  12 ,  22  come close to each other. As a result, at an installation part of the electrode  12 , a beat corresponding to the difference between the first frequency f 1  and the second frequency f 2  occurs. 
         [0097]    A differential amplifier  40  is connected to the electrodes  12 ,  13 . In a case of a proximity state of the members  10 ,  20 , since a difference between a beat to be input to the amplifier  40  and the ground becomes larger than a fixed value, the amplifier  40  outputs a large difference signal. A beat detection unit  42  detects a beat frequency component of the difference signal output from the amplifier  40 . The detection unit  42  consists of a low-pass filter (LPF)  421  and a comparator  422 . The LPF  421  extracts the beat frequency component. If the value of the beat frequency component extracted by the LPF  421  is larger than a reference voltage value, the comparator  422  outputs a beat detection signal. 
         [0098]    As mentioned above, in the third embodiment, when the electrodes  12 ,  22  come close to each other with fluctuations of the positional relationship between the members  10 ,  20 , a difference signal having the beat frequency component occurs. Therefore, when the beat detection unit  42  detects the beat frequency component, the sensor device can accurately detect the positional relationship (open and closed state, etc.) between the first and the second members. 
         [0099]    Since the sensor device detects the beat frequency component corresponding to the difference between the first and the second frequencies f 1 , f 2 , the sensor device becomes able to accurately detect solely the proximity of the electrode  21  to the electrode  22 . Therefore, the sensor device can accurately detect solely the proximity of the specified detection object with a compact configuration. 
         [0100]    A mechanism which applies amplitude modification to a carrier signal of a fixed frequency by a variable capacitance sensor, applies detection of an envelope of a signal, and detects an accelerated velocity is disclosed in Jpn. Pat. Appln. KOKAI publication No. 2003-43078. The mechanism requires a function that adjusts phases of the two signals. However, the configuration of the third embodiment regarding the invention detects the frequency difference as a beat which thus omits the need for a phase adjustment function. 
         [0101]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.