Patent Publication Number: US-8976154-B2

Title: Touch panel system and electronic device

Description:
TECHNICAL FIELD 
     The present invention relates to a touch panel system and an electronic device including the touch panel system. Particularly, the present invention relates to a touch panel system and an electronic device each of which is capable of reliably and effectively removing (canceling) a noise generated by a display device, etc. 
     BACKGROUND ART 
     Recently, introduction of touch panel systems to various kinds of electronic devices has been growing rapidly. For example, the touch panel systems are introduced to portable information devices such as smartphones and automatic vending machines such as automatic ticket machines. 
     The touch panel system is typically configured to include (i) a display device and (ii) a touch panel stacked on an upper side (front surface) of the display device. Therefore, a sensor provided on the touch panel is likely to be affected not only by a noise such as a clock generated in the display device but also by other noises coming from the outside. Such the noises lead to impairment in detection sensitivity for a touch operation. 
     Patent Literature 1 describes a touch panel system (coordinates input device) including a countermeasure against such noises. The touch panel system of Patent Literature 1 includes a noise processing section for removing a noise.  FIG. 19  is a block diagram illustrating a noise processing section  100  included in the touch panel system of Patent Literature 1. As shown in  FIG. 19 , the noise processing section  100  includes a filter section  101 , a logical inversion section  102 , and an adding section  103 . The filter section  101  receives an output signal (analog signal) from a sensor provided in a touch panel (not illustrated). The filter section  101  extracts, as a noise signal, an AC signal component included in the input signal. The logical inversion section  102  inverts by 180° the phase of the noise signal thus extracted. The adding section  103  adds, to the input signal which is supplied to the filter section  101  and which includes the noise signal, the noise signal whose phase has been inverted by 180°. 
     Thus, according to the touch panel system of Patent Literature 1, the noise signal extracted by the filter section  101  is inverted, and the signal thus inverted is added to the input signal (analog signal) supplied from the sensor. Namely, to the noise component included in the input signal supplied from the sensor, such a signal is added which has the same level as the noise component and whose phase has been inverted. This cancels the noise superimposed on the input signal supplied from the sensor. This makes it possible to reduce effects given by the noise included in the input signal supplied from the sensor. 
     Meanwhile, Patent Literature 2 discloses a capacitance value distribution detection circuit that detects a distribution of capacitance values of a plurality of capacitances, which capacitances are each formed at intersections of a plurality of first signal lines with a plurality of second signal lines. As shown in FIG. 1 of Patent Literature 2, a positional relationship of (i) drive lines for driving the touch panel with (ii) sense lines for reading out signals from the touch panel is fixed with respect to the touch panel. 
       FIG. 41  is a block diagram illustrating a configuration of a conventional touch panel system  91 .  FIG. 42  is a schematic view illustrating a configuration of a touch panel  93  provided in the touch panel system  91 . The touch panel system  91  includes the touch panel  93  and a capacitance value distribution detection circuit  92 . The touch panel  93  includes drive lines HL 1  to HLM arranged parallel to each other in a horizontal direction, sense lines VL 1  to VLM arranged parallel to each other in a vertical direction, and capacitances C 11  to CMM each formed at intersections of the drive lines HL 1  to HLM with the sense lines VL 1  to VLM. 
     The capacitance value distribution detection circuit  92  includes a driver  95 . The driver  95  applies a voltage to the drive lines HL 1  to HLM in accordance with a code sequence, to drive the capacitances C 11  to CMM. The capacitance value distribution detection circuit  92  includes a sense amplifier  96 . The sense amplifier  96  reads out, via the sense lines VL 1  to VLM, a linear sum of voltages corresponding to the capacitances C 11  to CMM driven by the driver  95 , and supplies this linear sum of voltages to an A/D converter  98 . The A/D converter  98  converts, from analog to digital, the linear sum of voltages corresponding to the capacitances, read out via the sense lines VL 1  to VLM, and supplies the converted linear sum to a capacitance value distribution calculation section  99 . 
     The capacitance value distribution calculation section  99  calculates a capacitance value distribution on the touch panel  93  based on (i) the linear sum of voltages corresponding to the capacitances, supplied from the A/D converter  98 , and (ii) the code sequence, and supplies the calculation result to a touch recognition section  90 . The touch recognition section  90  recognizes a position touched on the touch panel  93  based on the capacitance value distribution supplied from the capacitance value distribution calculation section  99 . 
     The capacitance value distribution detection circuit  92  includes a timing generator  97 . The timing generator  97  generates a signal specifying an operation of the driver  95 , a signal specifying an operation of the sense amplifier  96 , and a signal specifying an operation of the A/D converter  98 , and supplies these signals to the driver  95 , the sense amplifier  96 , and the A/D converter  98 , respectively. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1
     Japanese Patent Application Publication, Tokukai, No. 2001-125744 A (Publication Date: May 11, 2001)   

     Patent Literature 2
     U.S. Pat. No. 7,812,827 (Oct. 12, 2010)   

     SUMMARY OF INVENTION 
     Technical Problem 
     However, the touch panel system of Patent Literature 1 has a problem of being incapable of removing noises other than an AC signal component. 
     Specifically, as described above, with respect to an input signal supplied from the sensor, the touch panel system of Patent Literature 1 regards as a noise an AC signal component included in the input signal. The filter section  101  extracts the AC signal, and thereafter the logical inversion section  102  inverts the phase of the AC signal by 180°. Further, the adding section  103  adds the inverted signal to the input signal which includes the AC signal component. Thus, for the noise processing according to Patent Literature 1, the process performed by the filter section  101  for extracting the AC signal component is the most important. 
     However, Patent Literature 1 fails to disclose details of the configuration of the filter section  101 . Therefore, it is unknown how much noise the touch panel system of Patent Literature 1 can remove. Furthermore, Patent Literature 1 regards as a noise an AC signal component included in an analog signal. Namely, the touch panel system of Patent Literature 1 basically assumes removal of an impulse noise only, and does not assume, as the subject of removal, noises other than the impulse noise. Therefore, the touch panel system of Patent Literature 1 cannot reliably cancel a wide variety of noises other than the impulse noise. 
     Moreover, the following description considers a case in which entry is received via a touch panel  93  of a touch panel system  91  with an electrically conductive pen.  FIG. 43  is a view describing phantom noise generated in the touch panel system  91 . It is preferable that a tip of the electrically conductive pen is sharp having a diameter of around 1 mm to 4 mm, for preventing deterioration in the sense of use. Moreover, for easy writing, it is preferable that the pen can be used in a state in which a palm of the hand is placed on a large-sized touch panel. 
     In the present specification, a region in which a hand holding the electrically conductive pen for input is placed on the touch panel is called a “hand placing region”. 
     By fabricating the capacitance value distribution detection circuit  92  so that a signal read out from a capacitance disposed in the hand placing region HDR (illustrated in  FIG. 43 ) via a sense line is not received, it should be possible to input an entry with a pen at a pen input position P in a state in which the hand holding the electrically conductive pen for input is placed on the touch panel. 
     In the foregoing setting, a touch signal of a pen tip of the electrically conductive pen for input is extremely weaker than a touch signal of the hand placed on the touch panel, which hand holds the electrically conductive pen for input, and has a difference in SN ratio of around 10-fold to 20-fold. 
     Furthermore, a human body receives electromagnetic noise that exists in space, and this electromagnetic noise received by the human body from the space is inputted into the touch panel through the hand holding the electrically conductive pen for input. The electromagnetic noise inputted into the touch panel is superposed on a signal flowing through a sense line provided on which the hand holding the electrically conductive pen for input is placed. This causes generation of an error signal in a position of a sense line on which no hand is placed, as illustrated in  FIG. 43  as the phantom noise NZ. As a result, a problem arises that it becomes difficult to detect the signal of the pen. 
     Moreover, not only limited to the input with use of a pen, there also is a problem with a smartphone when using a software keyboard (application) that if the electromagnetic noise received by the body of the user is great, the phantom noise generates on the sense line that the finger or the like of the user touches, thereby causing a key of the software keyboard that is not pressed to react. 
     In the present specification, error signals generated as such is called “phantom noise”, where electromagnetic noise received by the human body from space is inputted into the touch panel via hands, fingers, or the like and is superposed on a signal flowing in the sense line that is touched by the hand, fingers, or the like. For example, as illustrated in  FIG. 43 , the phantom noise NZ generates in an area between circumscribing lines L 1  and L 2  which circumscribe the hand placing region HDR along the sense lines SL 1  to SLM and which is outside the hand placing region HDR. 
     The present invention was made in view of the foregoing problem of the conventional technique, and an object of the present invention is to provide a touch panel system and an electronic device each of which is capable of reliably removing a wide variety of noises. 
     Another object of the present invention to provide a touch panel system and an electronic device, each of which enables eliminating an effect caused by phantom noise generated by touching a panel with a hand, finger and the like of the human body that has received electromagnetic noise. 
     Solution to Problem 
     In order to attain the foregoing object, a touch panel system of the present invention includes: a touch panel; 
     a touch panel controller for processing a signal supplied from the touch panel; 
     a capacitance value distribution detection circuit for detecting a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines; and 
     a drive line driving circuit for driving the first signal lines or the second signal lines as drive lines, 
     the touch panel including (i) the plurality of first signal lines, (ii) the plurality of second signal lines, (iii) the plurality of capacitances, (iv) a main sensor section for detecting a touch operation performed with respect to the touch panel and (v) a sub sensor section provided in a surface of the touch panel in which surface the main sensor section is provided, 
     the touch panel controller including a subtracting section for (i) receiving a signal supplied from the main sensor section and a signal supplied from the sub sensor section and (ii) subtracting, from the signal supplied from the main sensor section, the signal supplied from the sub sensor section, 
     the main sensor section being provided with a plurality of sense lines, 
     the sub sensor section being provided with a sub sense line extending along a direction in which the sense lines extend, 
     the capacitance value distribution detection circuit switching a connection state between a first connection state and a second connection state, the first connection state being a state in which the first signal lines are driven to make the first signal lines serve as the drive lines and the second signal lines are made to output electric charges corresponding to the capacitances to make the second signal lines serve as the sense lines and the sub sense line, and the second connection state being a state in which the second signal lines are driven to make the second signal lines serve as the drive lines, and the first signal lines are made to output the electric charges corresponding to the capacitances to make the first signal lines serve as the sense lines and the sub sense line, 
     the subtracting section, during the first connection state and the second connection state, finding a first difference which is expressed by (Sn+1)−Sn, the first difference corresponding to a difference between (i) a signal of a sense line Sn which is selected from the plurality of sense lines and (ii) a signal of a sense line Sn+1, which is one of two sense lines adjacent to the sense line Sn, the two sense lines being the sense line Sn+1 and a sense line Sn−1 each of which is included in the plurality of sense lines, 
     the subtracting section finding a second difference which is expressed by Sn−(Sn−1), the second difference corresponding to a difference between (i) the signal of the sense line Sn and (ii) a signal of the sense line Sn−1, which is the other one of the two sense lines, 
     the subtracting section finding a third difference, the third difference corresponding to a difference between (i) a signal of the sub sense line and (ii) a signal of a sense line adjacent to the sub sense line which sense line is included in the plurality of sense lines, and 
     the touch panel controller including an adding section for adding up the first difference, the second difference, and the third difference. 
     According to the above configuration, the main sensor section and the sub sensor section are provided in (on) the same surface of the touch panel. This allows both of (i) an output signal supplied from the main sensor section and (ii) an output signal supplied from the sub sensor section to include various kinds of noise signals reflected in the touch panel. Furthermore, the subtracting section finds a difference between (i) the output signal supplied from the main sensor section which signal includes a signal derived from the touch operation and the noise signals and (ii) the output signal supplied from the sub sensor section which signal includes the noise signals. This removes the noise components from the output signal supplied from the main sensor section, thereby extracting the signal derived from the touch operation itself. This makes it possible to reliably remove (cancel) a wide variety of noises reflected in the touch panel. 
     Furthermore, the capacitance value distribution detection circuit switches between a first connection state and a second connection, which first connection state has the first signal lines serve as the drive lines and the second signal lines serve as the sense lines and the sub sense line, and which second connection state has the second signal lines serve as the drive lines and the first signal lines serve as the sense lines and the sub sense line. This allows for outputting the electric charges corresponding to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of a sense line. 
     Moreover, according to the configuration, during the first connection state and the second connection state, the subtracting section obtains a difference signal value between adjacent sense lines. Namely, a difference between adjacent sense lines, which have a higher correlation with noise is obtained. Furthermore, signals (noise signals) from the sub sense line is being eliminated from the output signals of the sense lines. Thus, it is possible to more securely eliminate noise. 
     In order to attain the foregoing object, another touch panel system of the present invention includes: a touch panel; 
     a touch panel controller for processing a signal supplied from the touch panel; 
     a capacitance value distribution detection circuit for detecting a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines; and 
     a drive line driving circuit for driving the first signal lines or the second signal lines as drive lines, 
     the touch panel including (i) the plurality of first signal lines, (ii) the plurality of second signal lines, (iii) the plurality of capacitances, and (iv) a sensor section for detecting a touch operation performed with respect to the touch panel, 
     the touch panel controller including a subtracting section for (i) receiving signals from the sensor section and (ii) finding differences in signal between, among the sense lines, respective pairs of sense lines adjacent to each other, 
     the drive line driving circuit driving the drive lines in parallel, 
     the capacitance value distribution detection circuit switching a connection state between a first connection state and a second connection state, the first connection state being a state in which the first signal lines are driven to make the first signal lines serve as the drive lines and the second signal lines are made to output electric charges corresponding to the capacitances to make the second signal lines serve as the sense lines and the sub sense line, and the second connection state being a state in which the second signal lines are driven to make the second signal lines serve as the drive lines, and the first signal lines are made to output the electric charges corresponding to the capacitances to make the first signal lines serve as the sense lines and the sub sense lines, 
     the subtracting section, during the first connection state and the second connection state, receiving output signals from the sense lines, and finding differences between the capacitances on each of the drive lines in a direction in which the each of the drive lines extends, the differences being found as the differences in signal between the respective pairs of the sense lines adjacent to each other, 
     the touch panel system further including: 
     a decoding section for decoding the values of the differences between the capacitances, which differences are found by the subtracting section, the decoding being carried out in such a manner that an inner product of each of code sequences for driving the drive lines in parallel and each of difference output sequences of the sense lines, which difference output sequences correspond to the code sequences, is calculated; and 
     a switch for switching a signal to be supplied to the subtracting section so that the subtracting section finds a first difference which is expressed by (Sn+1)−Sn or a second difference which is expressed by Sn−(Sn−1), 
     the first difference corresponding to a difference between (i) a signal of a sense line Sn which is selected from the plurality of sense lines and (ii) a signal of a sense line Sn+1, which is one of two sense lines adjacent to the sense line Sn, the two sense lines being the sense line Sn+1 and a sense line Sn−1 each of which is included in the plurality of sense lines, the second difference corresponding to a difference between (i) the signal of the sense line Sn and (ii) a signal of the sense line Sn−1, which is the other one of the two sense lines. 
     In order to attain the foregoing object, another touch panel system of the present invention includes: a touch panel; 
     a touch panel controller for processing a signal supplied from the touch panel; 
     a capacitance value distribution detection circuit for detecting a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines; and 
     a drive line driving circuit for driving the first signal lines or the second signal lines as drive lines, 
     the touch panel including (i) the plurality of first signal lines, (ii) the plurality of second signal lines, (iii) the plurality of capacitances, and (iv) a sensor section for detecting a touch operation performed with respect to the touch panel, 
     the touch panel controller including a subtracting section for (i) receiving signals from the sensor section and (ii) finding differences in signal between, among the sense lines, respective pairs of sense lines adjacent to each other, 
     the drive line driving circuit driving the drive lines in parallel, 
     the capacitance value distribution detection circuit switching a connection state between a first connection state and a second connection state, the first connection state being a state in which the first signal lines are driven to make the first signal lines serve as the drive lines and the second signal lines are made to output electric charges corresponding to the capacitances to have the second signal lines serve as the sense lines and the sub sense lines, and the second connection state being a state in which the second signal lines are driven to make the second signal lines serve as the drive lines, and the first signal lines are made to output the electric charges corresponding to the capacitances to make the first signal lines serve as the sense lines and the sub sense lines, 
     the subtracting section, during the first connection state and the second connection state, receiving output signals from the sense lines, and finding differences between the capacitances on each of the drive lines in a direction in which the each of the drive lines extends, the differences being found as the differences in signal between the respective pairs of the sense lines adjacent to each other, 
     the touch panel system further including: 
     a decoding section for decoding the values of the differences between the capacitances, which differences are found by the subtracting section, the decoding being carried out in such a manner that an inner product of each of code sequences for driving the drive lines in parallel and each of difference output sequences of the sense lines, which difference output sequences correspond to the code sequences, is calculated. 
     According to each of the above configurations, the subtracting section obtains difference in signal values between the respective pairs of the sense lines adjacent to each other. Namely, each difference is found between the adjacent sense lines, which have a higher correlation in terms of noise. This removes a noise component from the output signal supplied from the main sensor, thereby extracting a signal derived from the touch operation itself. This makes it possible to reliably remove (cancel) a wide variety of noises reflected in the touch panel. 
     Furthermore, the capacitance value distribution detection circuit switches between a first connection state and a second connection, which first connection state has the first signal lines serve as the drive lines and the second signal lines serve as the sense lines and the sub sense line, and which second connection state has the second signal lines serve as the drive lines and the first signal lines serve as the sense lines and the sub sense line. This allows for outputting the electric charges corresponding to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of a sense line. 
     Moreover, according to each of the foregoing configurations, the touch panel is driven in parallel, and the decoding section decodes a difference value of the capacitance value calculated by the subtracting section. This makes the signal of the capacitance be found multiplied by a code length (multiplied by N), thereby increasing the signal intensity of the capacitance, without depending on the number of drive lines. Moreover, if the signal intensity is sufficient as being similar to the conventional method, it is possible to reduce the number of times the drive line is driven, thereby allowing for low electricity consumption. 
     In order to attain the foregoing object, an electronic device of the present invention includes a touch panel system of the present invention. 
     Accordingly, it is possible to provide an electronic device capable of reliably removing (canceling) a wide variety of noises reflected in a touch panel. Furthermore, this allows for outputting the electric charges that correspond to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to provide an electronic device that is capable of eliminating the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of the sense line. 
     Advantageous Effects of Invention 
     As described above, a touch panel system of the present invention is configured so that the capacitance value distribution detection circuit switches a connection state between a first connection state and a second connection state, the first connection state being a state in which the first signal lines are driven to make the first signal lines serve as the drive lines and the second signal lines are made to output electric charges corresponding to the capacitances to make the second signal lines serve as the sense lines and the sub sense lines, and the second connection state being a state in which the second signal lines are driven to make the second signal lines serve as the drive lines, and the first signal lines are made to output the electric charges corresponding to the capacitances to make the first signal lines serve as the sense lines and the sub sense lines. Accordingly, the present invention provides an effect of reliably removing (canceling) a wide variety of noises reflected in a touch panel. Furthermore, the present invention provides an effect of eliminating the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of the sense line 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view schematically illustrating a basic configuration of a touch panel system according to the present invention. 
         FIG. 2  is a flow chart illustrating a basic process of the touch panel system shown in  FIG. 1 . 
         FIG. 3  is a view illustrating waveforms of respective signals which are to be processed by a subtracting section in the touch panel system shown in  FIG. 1 . 
         FIG. 4  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 5  is a view schematically illustrating a touch panel which is included in another version of the touch panel system shown in  FIG. 4  and does not include a sub sensor group. 
         FIG. 6  is a flow chart illustrating a basic process of the touch panel system shown in  FIG. 4 . 
         FIG. 7  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 8  is a flow chart illustrating a basic process of the touch panel system shown in  FIG. 7 . 
         FIG. 9  is a view illustrating a driving method of a touch panel which driving method is employed in a conventional touch panel system. 
         FIG. 10  is a view illustrating a driving method (orthogonal sequence driving method) of a touch panel which driving method is employed in a touch panel system of the present invention. 
         FIG. 11  is a view illustrating a process which needs to be performed by the touch panel employing the driving method of  FIG. 9  in order to achieve sensitivity equivalent to that of the touch panel employing the driving method of  FIG. 10 . 
         FIG. 12  is a view schematically illustrating another touch panel system according to the present invention, said another touch panel system including a touch panel driven by the orthogonal sequence driving method. 
         FIG. 13  is a view schematically illustrating a basic configuration of a touch panel system according to another embodiment of the present invention. 
         FIG. 14  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 15  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 16  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 17  is a circuit diagram showing one example of a total differential amplifier included in the touch panel system shown in  FIG. 16 . 
         FIG. 18  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 19  is a block diagram illustrating a noise processing section provided in a touch panel system of Patent Literature 1. 
         FIG. 20  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 21  is a flow chart illustrating a basic process of the touch panel system shown in  FIG. 20 . 
         FIG. 22  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 23  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 24  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 25  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 26  is a view schematically illustrating a basic configuration of another touch panel system according to the present invention. 
         FIG. 27  is a flow chart illustrating a basic process of a judging section in the touch panel system shown in  FIG. 22 . 
         FIG. 28  is a view schematically illustrating a method of recognizing touch information in the flow chart shown in  FIG. 27 . 
         FIG. 29  is a functional block diagram illustrating a configuration of a mobile phone including the touch panel system. 
         FIG. 30  is a block diagram illustrating a configuration of a touch panel system according to Embodiment 18. 
         FIG. 31  is a schematic view illustrating a configuration of a touch panel provided in the touch panel system. 
         FIG. 32  is a circuit diagram illustrating a configuration of a connection switching circuit between (a) signal lines connected to the touch panel, and (b) drive lines connected to a driver and sense lines connected to a sense amplifier. 
         FIG. 33  is a circuit diagram illustrating a configuration of a multiplexer provided in a capacitance value distribution detection circuit of the touch panel system. 
         FIG. 34  Illustrated in (a) and (b) of  FIG. 34  are schematic views for describing an operation method of the touch panel system. 
         FIG. 35  Illustrated in (a) and (b) of  FIG. 35  are schematic views for describing another operation method of the touch panel system. 
         FIG. 36  is a block diagram illustrating a configuration of a touch panel system according to Embodiment 19. 
         FIG. 37  is a circuit diagram illustrating a configuration of a connection switching circuit between (a) signal lines connected to the touch panel, and (b) drive lines connected to a driver and sense lines connected to a sense amplifier. 
         FIG. 38  is a circuit diagram illustrating a configuration of a multiplexer provided in a capacitance value distribution detection circuit of the touch panel system. 
         FIG. 39  is a block diagram illustrating a configuration of a touch panel system according to Embodiment 20. 
         FIG. 40  is a block diagram illustrating a configuration of a touch panel system according to Embodiment 21. 
         FIG. 41  is a block diagram illustrating a configuration of a conventional touch panel system. 
         FIG. 42  is a schematic view illustrating a configuration of a touch panel provided in the touch panel system. 
         FIG. 43  is a view for describing phantom noise that generates in the touch panel system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following will describe embodiments of the present invention with reference to drawings. 
     Embodiment 1 
     (1) Configuration of Touch Panel System  1   
       FIG. 1  is a view schematically illustrating a basic configuration of a touch panel system  1  according to one embodiment of the present invention. The touch panel system  1  includes a display device  2 , a touch panel  3 , a touch panel controller  4 , and a drive line driving circuit  5 . Further, the touch panel system  1  has a noise canceling function. In the descriptions below, a side used by a user is referred to as a “front surface” (or an “upper side”). 
     The display device  2  includes a display screen (display section), which is not illustrated in  FIG. 1 . The display screen displays, e.g., various kinds of icons for operation and text information corresponding to operation instructions for the user. The display device  2  is made of, e.g., a liquid crystal display, a plasma display, an organic EL display, or a field emission display (FED). These displays are used in many generally-used electronic devices. Therefore, making the display device  2  of such the display provides a touch panel system  1  having a great versatility. The display device  2  may have any configuration, and is not limited to any particular configuration. 
     The touch panel  3  is configured to allow the user to perform a touch (press) operation on a surface of the touch panel  3  by his/her finger, a stylus, or the like so as to enter various kinds of operation instructions. The touch panel  3  is stacked on a front surface (upper side) of the display device  2  so as to cover the display screen. 
     The touch panel  3  includes two sensors (one main sensor  31  and one sub sensor  32 ) which are provided on (in) the same surface. The main sensor  31  and the sub sensor  32  are provided so as to be adjacent to each other. Each of the main sensor  31  and the sub sensor  32  is a capacitive type sensor. The touch panel  3 , which is provided with the capacitive type sensors, has an advantage of having high transmittance and having durability. 
     The main sensor (main sensor section)  31  is provided in a region (touched region) of the touch panel  3  in which region a touch operation is performed. The main sensor  31  detects a touch operation that the user performs with respect to the touch panel  3 . The touch operation is, for example, double-click, sliding, single-click, or dragging. The main sensor  31  is provided with a sense line  33  which is made of a linear electrode. The sense line  33  has an end which is connected with the touch panel controller  4 . With this, a signal detected by the main sensor  31  is outputted to the touch panel controller  4  via the sense line  33 . Namely, a signal corresponding to a touch operation detected by the main sensor  31  is outputted to the touch panel controller  4 . 
     The sub sensor (sub sensor section)  32  detects a noise component reflected in the touch panel  3 . The sub sensor  32  is provided in a region (non-touched region) of the touch panel  3  in which region no touch operation is performed. Therefore, the sub sensor  32  is not touched by the user in a touch operation, and the sub sensor  32  detects various kinds of noises generated in the touch panel system  1 . Thus, unlike the main sensor  31 , the sub sensor  32  does not detect a signal corresponding to a touch operation. Namely, the sub sensor  32  is configured not to be touched by the user in a touch operation and to detect a noise generated in the touch panel  3 . 
     The sub sensor  32  is provided with a sub sense line  34  which is made of a linear electrode. The sub sense line  34  is provided so as to extend in parallel with the sense line  33  (i.e., to extend along a direction in which the sense line  33  extends). The sub sense line  34  has an end which is connected with the touch panel controller  4 . With this, a signal detected by the sub sensor  32  is outputted to the touch panel controller  4  via the sub sense line  34 . 
     Meanwhile, the touch panel  3  includes a drive line  35  provided so as to intersect the sense line  33  and the sub sense line  34  at right angles. The drive line  35  is made of a linear electrode. A capacitance is formed in an intersection of the sense line  33  or the sub sense line  34  and the drive line  35 . Namely, a capacitance is formed in an intersection of the sense line  33  and the drive line  35 , and another capacitance is formed in an intersection of the sub sense line  34  and the drive line  35 . The drive line  35  is connected with the drive line driving circuit (sensor driving section)  5 . Upon activation of the touch panel system  1 , the drive line  35  is supplied with an electric potential at a certain interval. 
     Each of the sense line  33 , the sub sense line  34 , and the drive line  35  can be made of, e.g., a transparent wire material such as ITO (Indium Tin Oxide). In other words, each of the sense line  33 , the sub sense line  34 , and the drive line  35  is a sensor electrode in the touch panel  3 . 
     Note that the drive line  35  is provided on a transparent substrate or a transparent film (not illustrated). Further, the drive line  35  is covered with an insulative layer (not illustrated). On the insulative layer, the sense line  33  and the sub sense line  34  are provided. Thus, the sense line  33  or the sub sense line  34  and the drive line  35  are isolated from each other via the insulative layer, and the sense line  33  or the sub sense line  34  and the drive line  35  are coupled to each other via the capacitance. The sense line  33  and the sub sense line  34  are covered with a protective layer (not illustrated). Namely, in the touch panel  3 , the protective layer is positioned so as to be the closest to the front surface side (the user&#39;s side). 
     The touch panel controller  4  reads signals (data) supplied from the main sensor  31  and the sub sensor  32  of the touch panel  3 . Since the touch panel system  1  includes the capacitive type sensors, the touch panel controller  4  detects a capacitance generated in the touch panel  3 . Concretely, the touch panel controller  4  detects (i) a change in the capacitance between the sense line  33  and the drive line  35  and (ii) a change in the capacitance between the sub sense line  34  and the drive line  35 . The touch panel controller  4  includes a subtracting section  41 , a coordinates detecting section  42 , and a CPU  43 . 
     The subtracting section  41  includes (i) an input terminal (i.e., an input terminal for a main sensor output) for receiving a signal outputted by the main sensor  31  and (ii) an input terminal (i.e., an input terminal for a sub sensor output) for receiving a signal outputted by the sub sensor  32 . The subtracting section  41  subtracts (i) the signal supplied to the input terminal for the sub sensor output from (ii) the signal supplied to the input terminal for the main sensor output. The signal obtained as a result of the subtracting operation by the subtracting section  41  is outputted to the coordinates detecting section  42 . Note that the signal supplied to the subtracting section  41  may be either of a digital signal and an analog signal. Namely, the input signal supplied to the subtracting section  41  may be any signal, as long as it suits with the configuration of the subtracting section  41 . 
     According to the signal obtained as a result of the subtracting operation by the subtracting section  41 , the coordinates detecting section  42  detects information indicative of the presence or absence of a touch operation. For example, if a value of the output signal supplied from the subtracting section  41  is equal to or greater than a predetermined threshold value, the coordinates detecting section  42  outputs, to the CPU  43 , a signal indicative of the presence of a touch operation. Note that the touch panel system  1  includes a single main sensor  31 ; therefore, the coordinates detecting section  42  detects information indicative of the presence or absence of a touch operation. Meanwhile, if a touch panel system  1  is configured to include a plurality of main sensors  31 , a coordinates detecting section  42  determines, in addition to the presence or absence of a touch operation, coordinates values indicative of a position touched by the user. 
     The CPU  43  obtains, at a certain interval, information outputted by the coordinates detecting section  42 . Further, according to the information thus obtained, the CPU  43  performs an operation such as output of the information to the display device  2 . 
     The drive line driving circuit  5  is connected with the drive line  35 . Upon activation of the touch panel system  1 , the drive line driving circuit  5  applies an electric potential to the drive line  35  at a certain interval. 
     (2) Noise Processing Performed by Touch Panel System  1   
     The touch panel system  1  determines, according to a change in the capacitance which change is detected by the touch panel controller  4 , the presence or absence of a touch operation. However, since the touch panel  3  is bonded to the front surface (the user&#39;s side) of the display device  2 , the touch panel system  1  is likely to be affected not only by a noise such as a clock generated in the display device  2  but also by other noises coming from the outside. This leads to impairment in detection sensitivity for a touch operation (i.e., detection sensitivity of the coordinates detecting section  42 ). 
     In order to address this, as a measure for removing such the noises, the touch panel system  1  includes the sub sensor  32  and the subtracting section  41 . With reference to  FIG. 2 , a noise canceling process of the touch panel system  1  will be described.  FIG. 2  is a flow chart illustrating a noise canceling process, which is a basic process of the touch panel system  1 . 
     Upon activation of the touch panel system  1 , the drive line driving circuit  5  applies an electric potential to the drive line  35  at a certain interval. When the user performs a touch operation on the touch panel  3 , both of the main sensor  31  and the sub sensor  32  output signals to the subtracting section  41 . 
     Here, (i) a noise such as a clock generated in the display device  2  and (ii) other noises coming from the outside are reflected in the touch panel  3 . Therefore, various kinds of noise components are detected by the main sensor  31  and the sub sensor  32 . Namely, the output signal supplied from the main sensor  31  includes not only a signal derived from the touch operation itself but also a noise signal (noise component). Meanwhile, since the sub sensor  32  is configured not to detect any touch operation, the output signal supplied from the sub sensor  32  includes a noise signal (noise component), but does not include a signal derived from the touch operation (F 201 ). 
     In the touch panel system  1 , the main sensor  31  and the sub sensor  32  are provided in the same surface so as to be adjacent to each other. Therefore, (i) a value of the noise signal included in the output signal supplied from the main sensor  31  and (ii) a value of the noise signal included in the output signal supplied from the sub sensor  32  can be regarded as being basically the same. In view of this, the subtracting section  41  included in the touch panel controller  4  executes an operation for subtracting (i) the input signal (signal value) supplied from the sub sensor  32  from (ii) the input signal (signal value) supplied from the main sensor  31  (F 202 ). Namely, the subtracting section  41  finds a difference between the sense line  33  and the sub sense line  34 . This removes the noise signal from the output signal supplied from the main sensor  31 . This provides the signal value derived from the touch operation itself, which signal value is generated in response to the touch operation. 
     The signal thus obtained by the subtracting operation (the signal derived from the touch operation itself) is outputted to the coordinates detecting section  42  included in the touch panel controller  4  (F 203 ). Namely, the signal derived from the touch operation itself is outputted to the coordinates detecting section  42 . According to the signal derived from the touch operation itself, the coordinates detecting section  42  determines the presence or absence of a touch operation. With this configuration, it is possible to prevent impairment in detection sensitivity of the coordinates detecting section  42  (e.g., detection sensitivity as to the presence or absence of a touch operation). 
     Thus, according to the touch panel system  1 , the subtracting section  41  finds a difference between the sense line  33  and the sub sense line  34 , so as to cancel, from an input signal which is supplied from the sense line  33  and includes a wide variety of noise components, the noise components. Namely, the subtracting section  41  cancels a noise signal from an input signal supplied from the sense line  33 , so as to extract a signal derived from a touch operation itself. Thus, it is possible to provide the touch panel system  1  capable of reliably canceling a wide variety of noises. 
     The noise canceling process of the touch panel system  1  is visually illustrated in  FIG. 3 .  FIG. 3  is a view illustrating waveforms of respective signals which are to be processed by the subtracting section  41  in the touch panel system  1 . (a) of  FIG. 3  shows an output signal supplied from the main sensor  31 , (b) of  FIG. 3  shows an output signal supplied from the sub sensor  32 , and (c) of  FIG. 3  is a signal processed by the subtracting section  41 . Each signal shown in  FIG. 3  is a signal generated in response to a touch operation performed by the user. 
     The touch panel system  1  is configured such that the user&#39;s performing a touch operation increases the capacitance of the main sensor  31  which detects a touch operation ((a) of  FIG. 3 ). Namely, the user&#39;s performing a touch operation increases a value of an output signal supplied from the main sensor  31  (the sense line  33 ). However, the output signal supplied from the main sensor  31  in response to the touch operation includes not only (i) a signal derived from the touch operation itself but also (ii) various kinds of noise signals (e.g., a noise such as a clock generated in the display device  2  and/or a noise coming from the outside). 
     Meanwhile, since the sub sensor  32  does not detect a touch operation, the capacitance of the sub sensor  32  (the sub sense line) is not increased by the touch operation. Namely, an output signal supplied from the sub sensor  32  does not include a signal derived from the touch operation, but includes a noise component reflected in the touch panel  3  ((b) of  FIG. 3 ). 
     The subtracting section  41  subtracts (i) the output signal supplied from the sub sensor  32  from (ii) the output signal supplied from the main sensor  31  (i.e., the signal value of (a) of FIG.  3 —the signal value of (b) of  FIG. 3 ). As shown in (c) of  FIG. 3 , this subtracting operation removes (i) the noise component outputted by the sub sensor  32  from (ii) the output signal supplied from the main sensor  31 . This provides the signal derived from the touch operation itself, which signal is generated in response to the touch operation. Furthermore, since the coordinates detecting section  42  is supplied with the signal derived from the touch operation itself, detection accuracy for a touch operation is not impaired. 
     As described above, according to the touch panel system  1  of the present embodiment, the main sensor  31  and the sub sensor  32  are provided in (on) the same surface of the touch panel  3 . Consequently, each of (i) an output signal supplied from the main sensor  31  and (ii) an output signal supplied from the sub sensor  32  includes various kinds of noise signals reflected in the touch panel  3 . Furthermore, the subtracting section  41  finds a difference between (i) the output signal supplied from the main sensor  31  which signal includes a signal derived from a touch operation and a noise signal and (ii) the output signal supplied from the sub sensor  32  which signal includes a noise signal. This removes the noise component from the output signal supplied from the main sensor  31 , thereby extracting the signal derived from the touch operation itself. Therefore, it is possible to reliably remove (cancel) a wide variety of noises reflected in the touch panel  3 . 
     Note that, according to the touch panel system of Patent Literature 1, a noise component which is the subject of removal is an AC signal component included in a signal which includes noise components. On the other hand, according to the touch panel system  1 , each of (i) an output signal supplied from the main sensor  31  and (ii) an output signal supplied from the sub sensor  32  includes various kinds of noise components. Therefore, according to the touch panel system  1 , a noise component which is the subject of removal is not limited to an AC signal component. Thus, the touch panel system  1  can cancel all noises reflected in the touch panel  3 . 
     In the touch panel system  1 , the sub sensor  32  only needs to be provided in a surface of the touch panel  3  in which surface the main sensor  31  is also provided. With this configuration, both of the main sensor  31  and the sub sensor  32  can detect a noise component (noise signal) reflected in the touch panel  3 . Note that the sub sensor  32  is preferably configured not to detect a touch operation performed on the touch panel  3 . With this configuration, the sub sensor  32  does not detect a signal derived from a touch operation; therefore, an output signal supplied from the sub sensor  32  does not include the signal derived from the touch operation. This prevents a case where the signal value derived from the touch operation is reduced by the subtracting operation performed by the subtracting section  41 . Namely, the noise component is removed without reducing the signal derived from the touch operation which signal is detected by the main sensor  31 . Therefore, it is possible to further enhance detection sensitivity for a touch operation. 
     The touch panel system  1  is configured such that the sub sensor  32  is provided in the region (non-touched region) of the touch panel  3  in which region no touch operation is performed by the user. In such a configuration, a signal derived from a touch operation is not detected by the sub sensor  32 . Therefore, on the sub sensor  32 , the user would not perform a touch operation. Accordingly, although the sub sensor  32  detects a noise reflected in the touch panel, the sub sensor  32  does not detect the signal derived from the touch operation. Thus, it is possible to reliably prevent the sub sensor  32  from detecting a touch operation. 
     In order that the sub sensor  32  detects a noise component, the sub sensor  32  is preferably provided as close to the main sensor  31  as possible. More preferably, the sub sensor  32  and the main sensor  31  are arranged side by side so as to be in contact with each other. With this configuration, the main sensor  31  and the sub sensor  32  are provided under almost the same condition. Particularly in a configuration in which the sub sensor  32  and the main sensor  31  are arranged side by side so as to be in contact with each other, the main sensor  31  and the sub sensor  32  are arranged so that a distance therebetween is shortest. Therefore, a value of a noise signal included in an output signal supplied from the sub sensor  32  can be regarded as being the same as that of a noise signal included in an output signal supplied from the main sensor  31 . Therefore, by the subtracting operation performed by the subtracting section  41 , it is possible to more reliably remove a noise component reflected in the touch panel  3 . This makes it possible to further enhance detection sensitivity for a touch operation. 
     The present embodiment has dealt with the touch panel system  1  including the touch panel  3  of capacitive type. However, the principle of operation of the touch panel  3  (i.e., the method of operating the sensor) is not limited to the capacitive type. For example, the noise canceling function can be achieved similarly by a touch panel system including a touch panel of resistance film type, infrared type, ultrasonic wave type, or electromagnetic induction coupling type. Further, regardless of the type of the display device  2 , the touch panel system  1  of the present embodiment provides the noise canceling function. 
     The touch panel system  1  of the present embodiment is applicable to various kinds of electronic devices provided with touch panels. Examples of such the electronic device encompass televisions, personal computers, mobile phones, digital cameras, portable game devices, electronic photo frames, personal digital assistants (PDAs), electronic books, home electronic appliances (e.g., microwave ovens, washing machines), ticket vending machines, automatic teller machines (ATM), and car navigation systems. Thus, it is possible to provide an electronic device which is capable of effectively preventing impairment in detection sensitivity for a touch operation. 
     Embodiment 2 
     (1) Configuration of Touch Panel System  1   a    
       FIG. 4  is a view schematically illustrating a basic configuration of a touch panel system  1   a  according to another embodiment of the present invention. A basic configuration of the touch panel system  1   a  is substantially the same as that of the touch panel system  1  of Embodiment 1. The following will describe the touch panel system  1   a , focusing on differences between the touch panel system  1   a  and the touch panel system  1 . For convenience of explanation, members having the same functions as those explained in the drawings described in Embodiment 1 are given the same reference signs, and explanations thereof are omitted here. 
     The touch panel system  1   a  differs from the touch panel system  1  in terms of configurations of sensors provided in a touch panel  3   a . Specifically, the touch panel  3   a  includes (i) a main sensor group  31   a  made of a plurality of main sensors  31  and (ii) a sub sensor group  32   a  made of a plurality of sub sensors  32 . The touch panel system  1   a  detects not only (i) the presence or absence of a touch operation performed by the user but also (ii) positional information (coordinates) indicative of a position where the user performs the touch operation. 
     Specifically, according to the touch panel system  1   a , the touch panel  3   a  includes the main sensor group  31   a  and the sub sensor group  32   a  which are provided on (in) the same surface of the touch panel  3   a . The main sensor group  31   a  and the sub sensor group  32   a  are provided so as to be adjacent to each other. Each of the main sensor group  31   a  and the sub sensor group  32   a  is made of capacitive type sensors. 
     The main sensor group (main sensor section)  31   a  is provided in a region (touched region) of the touch panel  3   a  in which region a touch operation is performed. The main sensor group  31   a  detects a touch operation that the user performs with respect to the touch panel  3   a . The main sensor group  31   a  is made of the plurality of main sensors  31  which are arranged in a matrix. The main sensor group  31   a  is provided with L sense lines  33  (L is an integer of 2 or greater). The sense lines  33  are provided so as to be parallel with each other and evenly spaced. On each of the sense lines  33 , M main sensors  31  are provided (M is an integer of 2 or greater). 
     Each of the sense lines  33  has an end which is connected with a subtracting section  41  of a touch panel controller  4 . With this, a signal detected by each main sensor is outputted to the subtracting section  41  via its corresponding sense line  33 . Namely, a signal corresponding to a touch operation detected by the main sensor  31  is outputted to the subtracting section  41 . 
     The sub sensor group (sub sensor section)  32   a  detects a noise component reflected in the touch panel  3   a . The sub sensor group  32   a  is provided in a region (non-touched region) of the touch panel  3   a  in which region no touch operation is performed. Therefore, the sub sensor group  32   a  is not touched by the user in a touch operation, and the sub sensor group  32   a  detects various kinds of noises generated in the touch panel system  1   a . Thus, unlike the main sensor group  31   a , the sub sensor group  32   a  does not detect a signal corresponding to a touch operation. Namely, the sub sensor group  32   a  is configured not to be touched by the user in a touch operation but to detect a noise generated in the sensor. The sub sensor group  32   a  is provided with one sub sense line  34 . The sub sense line  34  is provided so as to extend in parallel with the sense lines  33  (i.e., to extend along a direction in which the sense lines  33  extend). On the sub sense line  34 , M sub sensors  32  are provided (M is an integer of 2 or greater). Namely, the number of main sensors  31  provided on each sense line  33  is equal to the number of sub sensors  32  provided on the sub sense line  34 . 
     The sub sense line  34  has an end which is connected with the subtracting section  41  of the touch panel controller  4 . With this, a signal detected by the sub sensor group  32   a  is outputted to the subtracting section  41  via the sub sense line  34 . 
     Meanwhile, the touch panel  3   a  includes M drive lines  35  provided so as to intersect the sense lines  33  and the sub sense line  34  at right angles (M is an integer of 2 or greater). The drive lines  35  are provided so as to extend in parallel with each other and to be evenly spaced. On each of the drive lines  35 , L main sensors  31  and one sub sensor  32  are provided (L is an integer of 2 or greater). Further, a capacitance is formed in an intersection of each of the sense lines  33  or the sub sense line  34  and a corresponding one of the drive lines  35 . Namely, capacitances are formed in intersections of the sense lines  33  and the drive lines  35 , and capacitances are formed in intersections of the sub sense line  34  and the drive lines  35 . The drive lines  35  are connected with a drive line driving circuit (not illustrated). Upon activation of the touch panel system  1   a , the drive lines  35  are supplied with electric potentials at a certain interval. 
     Thus, in the touch panel  3   a , (i) the sense lines  33  and the sub sense line  34 , which are provided in a horizontal direction, and (ii) the drive lines  35 , which are provided in a vertical direction, are arranged in a two-dimensional matrix. For the sense line  33 , the sub sense lines  34 , and the drive line  35 , the number thereof, a length thereof, a width thereof, a space therebetween, and/or the like can be arbitrarily set according to the intended purpose of the touch panel system  1   a , the size of the touch panel  3   a , and/or the like. 
     (2) Noise Processing Performed by Touch Panel System  1   a    
     The touch panel system  1   a  determines, according to a change in the capacitance which change is detected by the touch panel controller  4 , (i) the presence or absence of a touch operation and (ii) a touched position. However, similarly to the touch panel system  1 , the touch panel system  1   a  is likely to be affected by various kinds of noises. This leads to impairment in detection sensitivity for a touch operation (i.e., detection sensitivity of the coordinates detecting section). Specifically,  FIG. 5  is a view schematically illustrating a touch panel  3   b , which is made by modifying the touch panel of the touch panel system  1   a  shown in  FIG. 4  so that it does not include the sub sensor group  32   a . As shown in  FIG. 5 , the touch panel  3   b  includes only a main sensor group  31   a  but does not include a sub sensor group  32   a . Namely, the touch panel  3   b  shown in  FIG. 5  has a configuration which is not provided with a countermeasure against noises yet. According to this configuration, the touch panel  3   b  is affected by various kinds of noises. Accordingly, a signal outputted by each sense line  33  includes various kinds of noises, and thus detection sensitivity for a touch operation is impaired. 
     In order to avoid this, the touch panel system  1   a  includes, as a measure for removing such the noises, the sub sensor group  32   a  and the subtracting section  41 . With reference to  FIG. 6 , the following will describe a noise canceling process performed by the touch panel system  1   a .  FIG. 6  is a flow chart illustrating a noise canceling process, which is a basic process of the touch panel system  1   a.    
     Upon activation of the touch panel system  1   a , the drive line  35  is supplied with an electric potential at a certain interval. When the user performs a touch operation on the touch panel  3   a , both of the main sensor group  31   a  and the sub sensor group  32   a  output signals to the subtracting section  41 . Specifically, the user&#39;s performing the touch operation increases a capacitance of a specific main sensor  31  corresponding to the touched position. Namely, the user&#39;s performing the touch operation increases a value of an output signal supplied from that main sensor  31  (sense line  33 ). The touch panel system  1   a  outputs, to the subtracting section  41 , output signals supplied from the sense line  33  and the sub sense line  34 , while driving the drive lines  35 . 
     To be more specific, a noise such as a clock generated in the display device  2  and other noises coming from the outside are reflected in the touch panel  3   a . Therefore, the main sensor group  31   a  and the sub sensor group  32   a  detect various kinds of noise components. Specifically, the output signal supplied from the main sensor group  31   a  includes not only a signal derived from the touch operation itself but also a noise signal (noise component). Meanwhile, the sub sensor group  32   a  is configured not to detect a touch operation. Therefore, the output signal supplied from the sub sensor group  32   a  includes a noise signal (noise component), but does not include a signal derived from the touch operation (F 501 ). 
     In the touch panel system  1   a , the main sensor group  31   a  and the sub sensor group  32   a  are provided in the same surface so as to be adjacent to each other. Therefore, (i) a value of a noise signal included in the output signal supplied from the main sensor group  31   a  and (ii) a value of a noise signal included in the output signal supplied from the sub sensor group  32   a  can be regarded as being basically the same. In view of this, the subtracting section  41  in the touch panel controller  4  executes an operation for subtracting (i) the input signal (signal value) supplied from the sub sensor group  32   a  from (ii) the input signal (signal value) supplied from the main sensor group  31   a  (F 502 ). Namely, the subtracting section  41  finds a difference between each sense line  33  and the sub sense line  34 . This removes the noise signal from the output signal supplied from the main sensor group  31   a . This provides the signal value derived from the touch operation itself, which signal is generated in response to the touch operation. 
     The signal thus obtained by the subtracting operation is outputted to the coordinates detecting section  42  included in the touch panel controller  4  (F 503 ). Thus, the signal derived from the touch operation itself is outputted to the coordinates detecting section  42 . According to the signal derived from the touch operation itself, the coordinates detecting section  42  detects (i) the presence or absence of a touch operation and (ii) a touched position (coordinates). With this configuration, it is possible to prevent impairment in detection sensitivity of the coordinates detecting section  42  (e.g., detection accuracy as to the presence or absence of a touch operation, detection sensitivity as to a touched position). 
     Note that, according to the touch panel system  1   a , an output signal of the sense line  33  provided with the specific main sensor  31  corresponding to the touched position has a waveform as shown in (a) of  FIG. 3 , whereas an output signal of the sub sensor group  32   a  (sub sense line  34 ) has a waveform as shown in (b) of  FIG. 3 . The subtracting section  41  subtracts, from the output signal supplied from the main sensor group  31   a , the output signal supplied from the sub sensor group  32   a . As shown in (c) of  FIG. 3 , this subtracting operation removes, from the output signal supplied from the main sensor group  31   a , the noise component outputted by the sub sensor group  32   a . This provides the signal derived from the touch operation itself, which signal is generated in response to the touch operation. Furthermore, since the coordinates detecting section  42  is supplied with the signal derived from the touch operation itself, detection accuracy for a touch operation is not impaired. Therefore, it is possible to reduce a difference between (i) the actual touched position and (ii) the detected position which is detected by the coordinates detecting section  42 . 
     As described above, while driving the drive lines  35 , the touch panel system  1   a  reads, from the sense line  33 , a change in a capacitance value of the main sensor group  31   a  which change is caused by the touch operation performed by the user. Furthermore, the touch panel system  1   a  reads a noise component from the sub sense line  34 . Moreover, the touch panel system  1   a  allows the subtracting section  41  to find a difference between the sense line  33  and the sub sense line  34 , so as to remove (cancel) the noise component. 
     The touch panel system  1   a  includes the main sensor group  31   a  made of the plurality of main sensors  31  arranged vertically and horizontally in the form of a matrix. Thanks to this configuration, in addition to the same effects as those given by the touch panel system  1 , the touch panel system  1   a  can detect, by the coordinates detecting section  42 , coordinates indicative of a touched position. Namely, the touch panel system  1   a  can detect a touched position (coordinates value) in addition to the presence or absence of a touch operation. 
     As with the case of the touch panel system  1 , for the touch panel system  1   a , a noise component which is the subject of removal is not limited to an AC signal component. Accordingly, the touch panel system  1   a  also can cancel all noises reflected in the touch panel  3   a.    
     Embodiment 3 
     (1) Configuration of Touch Panel System  1   b    
       FIG. 7  is a view schematically illustrating a basic configuration of a touch panel system  1   b  according to another embodiment of the present invention. A basic configuration of the touch panel system  1   b  is substantially the same as that of the touch panel system  1   a  of Embodiment 2. The following will describe the touch panel system  1   b , focusing on differences between the touch panel system  1   a  and the touch panel system  1   b . For convenience of explanation, members having the same functions as those explained in the drawings described in Embodiments 1 and 2 are given the same reference signs, and explanations thereof are omitted here. 
     A touch panel  3   b  has the same configuration of that of the touch panel  3   a  in the touch panel system  1   a  of Embodiment 2. Namely, the touch panel  3   b  includes (i) a plurality of drive lines  35  (in  FIG. 7 , five drive lines  35 ), (ii) a plurality of sense lines  33  (in  FIG. 7 , seven sense lines  33 ) intersecting the drive lines  35 , and (iii) one sub sense line  34  which intersects the drive lines  35  at right angles and extends in parallel with the sense lines  33 . The sense lines  33  and the drive lines  35  are isolated from each other, and are coupled to each other via capacitances. The sub sense line  34  and the drive lines  35  are isolated from each other, and are coupled to each other via capacitances. 
     In the following description, eight sense/sub sense arrays, including the one sub sense line  34  and the seven sense lines  33 , are referred to as Arrays (1) through (8), respectively. 
     A touch panel controller  4  includes switches SW, a subtracting section  41 , storage sections  45   a  through  45   d , and an adding section  46 , which are arranged in this order from an input-receiving side of the touch panel controller  4 . Note that the touch panel controller  4  also includes a coordinates detecting section  42  (not illustrated) and a CPU  43  (not illustrated) ( FIG. 1 ). Thus, the touch panel system  1   b  differs from the touch panel systems  1  and  1   a  in terms of the configuration of the touch panel controller  4 . 
     The switches SW select, from signals supplied from the sense lines  33  and the sub sense line  34 , signals to be supplied to the subtracting section  41 . More specifically, each of the switches SW includes two terminals (upper and lower terminals), and selects one of the upper and lower terminals.  FIG. 7  shows a state where the switches SW select the lower terminals. 
     The subtracting section  41  performs difference signal operations on, out of signals supplied from Arrays (1) through (8), signals selected by the switches SW. Specifically, the subtracting section  41  performs difference signal operations between sense lines  33  which are adjacent to each other, and between a sense line  33  and the sub sense line  34  which are adjacent to each other. For example, in a case where the switches SW select the lower terminals as shown in  FIG. 7 , the subtracting section  41  performs the following difference signal operations: Array (8)−Array (7); Array (6)−Array (5); Array (4)−Array (3); and Array (2)−Array (1). On the other hand, in a case where the switches SW select the upper terminals (not illustrated), the subtracting section  41  performs the following difference signal operations: Array (7)−Array (6); Array (5)−Array (4); and Array (3)−Array (2). 
     In a case where each of the switches SW selects one of the upper and lower terminals, the storage sections  45   a  through  45   d  store signals (difference operation signals) obtained by the difference operations performed by the subtracting section  41 . The difference operation signals stored in the storage sections  45   a  through  45   d  are outputted to the adding section  46 . On the other hand, in a case where each of the switches SW selects the other one of the upper and lower terminals, difference operation signals are directly outputted to the adding section  46 , not via the storage sections  45   a  through  45   d.    
     The adding section  46  adds up the difference operation signals each of which is obtained from the sense lines  33  adjacent to each other and which are supplied from the subtracting section  41  and the storage sections  45   a  through  45   d . Thereafter, the adding section  46  outputs a result of the adding operation. Further, the adding section  46  outputs the difference operation signal (Array (2)−Array (1)) which is obtained from the sub sense line  34  and the sense line  33  adjacent to the sub sense line  34  and which is stored in the storage section  45   a . Ultimately, the adding section  46  outputs signals obtained by the following operations: Array (2)−Array (1); Array (3)−Array (1); Array (4)−Array (1); Array (5)−Array (1); Array (6)−Array (1); Array (7)−Array (1); and Array (8)−Array (1). Namely, each signal outputted by the adding section  46  is such a signal from which the noise signal (corresponding to the signal of Array (1)) included in the sense lines  33  has been removed. Furthermore, the subtracting section  41  has performed the difference signal operation between the sense lines  33  adjacent to each other. This allows the adding section  46  to output the signals from which the noise signals have been more reliably removed. 
     (2) Noise Processing Performed by Touch Panel System  1   b    
     With reference to  FIGS. 7 and 8 , the following will describe noise processing performed by the touch panel system  1   b .  FIG. 8  is a flow chart illustrating a noise canceling process, which is a basic process of the touch panel system  1   b.    
     Upon activation of the touch panel system  1   b , the drive line  35  is supplied with an electric potential at a certain interval. The user&#39;s performing a touch operation on the touch panel  3   b  increases a capacitance of a specific sense line  33  corresponding to the touched position. Namely, the user&#39;s performing the touch operation on the touch panel  3   b  increases a value of an output signal supplied from that sense line  33 . The touch panel system  1   b  outputs, to the touch panel controller  4 , output signals supplied from the sense lines  33  and the sub sense line  34 , while driving the drive lines  35 . Thus, while driving the drive lines  35 , the touch panel system  1   b  detects changes in the capacitances of the sense lines  33  and a change in the capacitance of the sub sense line  34 , so as to determine the presence or absence of a touch operation and a touched position. 
     To be more specific, a noise such as a clock generated in the display device  2  and other noises coming from the outside are reflected in the touch panel  3   b . Therefore, each of the main sensor group  31   a  and the sub sensor group  32   a  detects various kinds of noise components. Specifically, the output signal supplied from the sense line  33  includes not only a signal derived from the touch operation itself but also a noise signal (noise component). Meanwhile, the sub sense line  34  is configured not to detect a touch operation. Therefore, the output signal supplied from the sub sense line  34  includes a noise signal (noise component), but does not include a signal derived from the touch operation (F 601 ). 
     Next, the switches SW select the lower terminals (F 602 ). Then, the subtracting section  41  finds a difference (sense line (Sn+1)−sense line Sn: a first difference) between a sense line  33  (sense line Sn) and a sense line (sense line Sn+1) which is one of two sense lines  33  adjacent to the certain sense line  33  and is closer to the sub sense line  34  than the other is. In this step, a difference (third difference) between the sub sense line  34  and a sense line  33  which is closer to the sub sense line  34  than any other sense lines  33  is found (F 603 ). 
     For Arrays (1) through (8) shown in  FIG. 7 , the subtracting section  41  performs the following four difference signal operations:
         Array (2)−Array (1) (The resulting difference value is referred to as “A”.)   Array (4)−Array (3) (The resulting difference value is referred to as “C”.)   Array (6)−Array (5) (The resulting difference value is referred to as “E”.)   Array (8)−Array (7) (The resulting difference value is referred to as “G”.)
 
Namely, in the step F 603 , the subtracting section  41  performs the difference signal operations on Arrays (1) through (8), which includes the sub sense line  34 .
       

     The difference values A, C, E, and G found by the subtracting section  41  are stored in the storage sections  45   a  through  45   d , respectively. Namely, the storage section  45   a  stores the difference value A, the storage section  45   b  stores the difference value C, the storage section  45   c  stores the difference value E, and the storage section  45   d  stores the difference value G (F 604 ). 
     Next, the switches SW selecting the lower terminals are turned to select (close) the upper terminals (F 605 ). Then, the subtracting section  41  performs an operation similar to that of F 603 . Specifically, the subtracting section  41  performs a difference signal operation (sense line Sn−sense line (Sn−1): a second difference) between the sense line  33  (sense line Sn) and a sense line (sense line Sn−1) which is one of the two sense lines  33  adjacent to the certain sense line  33  and is further away from the sub sense line  34  than the other is (F 606 ). 
     For Arrays (1) through (8) shown in  FIG. 7 , the subtracting section  41  performs the following three difference signal operations:
         Array (3)−Array (2) (The resulting difference value is referred to as “B”.)   Array (5)−Array (4) (The resulting difference value is referred to as “D”.)   Array (7)−Array (6) (The resulting difference value is referred to as “F”.)
 
Namely, in the step F 606 , the subtracting section  41  performs the difference signal operations on Arrays (2) through (7), which does not include the sub sense line  34 .
       

     Next, the adding section  46  performs an adding operation for adding up (i) the difference values B, D, and F found in the step F 606  and (ii) the difference values A, C, E, and G stored in the respective storage sections  45   a  through  45   d . Namely, the adding section  46  adds up (i) the difference values (the difference values A, C, E, and G) found when the lower terminals are selected by the switches SW and (ii) the difference values (the difference values B, D, and F) found when the upper terminals are selected by the switches SW (F 607 ). 
     In the case of Arrays (1) through (8) shown in  FIG. 7 , the adding section  46  adds up (i) the difference value A (Array (2)−Array (1) signal) stored in the storage section  45   a  and (ii) the difference value B (Array (3)−Array (2) signal) outputted by the subtracting section  41 . This adding operation is expressed as below: 
                 Difference   ⁢           ⁢   value   ⁢           ⁢   A     +     Difference   ⁢           ⁢   value   ⁢           ⁢   B       =         {       Array   ⁡     (   2   )       -     Array   ⁡     (   1   )         }     +     {       Array   ⁡     (   3   )       -     Array   ⁡     (   2   )         }       =       Array   ⁡     (   3   )       -     Array   ⁡     (   1   )       ⁢     (     The   ⁢           ⁢   resulting   ⁢           ⁢   difference   ⁢           ⁢   value   ⁢           ⁢   is   ⁢           ⁢   referred   ⁢           ⁢   to   ⁢           ⁢   as   ⁢           ⁢       “     difference   ⁢           ⁢   value   ⁢           ⁢   H     ”     .       )               
This provides an Array (3)−Array (1) signal. The adding section  46  performs such operations sequentially.
 
     Specifically, the adding section  46  adds, to the difference value H (Array (3)−Array (1) signal), the difference value C (Array (4)−Array (3) signal) stored in the storage section  45   b . This provides an Array (4)−Array (1) signal (difference value I). 
     Next, the adding section  46  adds, to the difference value I (Array (4)−Array (1) signal), the difference value D (Array (5)−Array (4) signal) outputted by the subtracting section  41 . This provides an Array (5)−Array (1) signal (difference value J). 
     Next, the adding section  46  adds, to the difference value J (Array (5)−Array (1) signal), the difference value E (Array (6)−Array (5) signal) stored in the storage section  45   c . This provides an Array (6)−Array (1) signal (difference value K). 
     Next, the adding section  46  adds, to the difference value K (Array (6)−Array (1) signal), the difference value F (Array (7)−Array (6) signal) outputted by the subtracting section  41 . This provides an Array (7)−Array (1) signal (difference value L). 
     Next, the adding section  46  adds, to the difference value L (Array (7)−Array (1) signal), the difference value G (Array (8)−Array (7) signal) stored in the storage section  45   d . This provides an Array (8)−Array (1) signal (difference value M). 
     Note that the difference value A (i.e., Array (2)−Array (1) signal) stored in the storage section  45   a  is outputted without being subjected to any adding operation by the adding section  46 . 
     Thus, the adding section  46  outputs the following signals:
         Array (2)−Array (1) signal=Difference value A   Array (3)−Array (1) signal=Difference value H   Array (4)−Array (1) signal=Difference value I   Array (5)−Array (1) signal=Difference value J   Array (6)−Array (1) signal=Difference value K   Array (7)−Array (1) signal=Difference value L   Array (8)−Array (1) signal=Difference value M       

     In the configuration shown in  FIG. 7 , Arrays (2) through (8) are the sense lines  33 , and Array (1) is the sub sense line  34 . As a result of the adding operations performed by the adding section  46 , the signal of Array (1) (noise signal) is removed from each of the signals of Arrays (2) through (8). Accordingly, each output signal supplied from the adding section  46  is such a signal from which a noise signal included in the sense line  33  has been removed. Thus, it is possible to provide a signal value derived from a touch operation itself, which signal value is generated in response to the touch operation. Each output signal of the adding section  46 , from which the noise signal has been removed, is outputted to the coordinates detecting section  42  in the touch panel controller  4 . Namely, the signals derived from the touch operation itself are outputted to the coordinates detecting section  42  (F 608 ). 
     As described above, the touch panel system  1   b  obtains a difference signal value between sense lines  33  adjacent to each other. Namely, a difference is found between the adjacent sense lines  33 , which have a higher correlation in terms of noise. Furthermore, from an output signal supplied from each sense line  33 , a signal (noise signal) of the sub sense line  34  is removed. Therefore, as compared with the touch panel systems  1  and  1   a  of Embodiments 1 and 2, the touch panel system  1   b  can remove a noise more reliably. 
     In addition, according to the touch panel system  1   b , the adding section  46  sequentially performs adding operations from the sub sense line  34  side (i.e., in the order of increasing distance between a sense line involved in a certain adding operation and the sub-sense line). Therefore, it is possible to remove a noise by performing the adding operations in such a manner that a result of an adding operation is used in a next adding operation. 
     Embodiment 4 
     A driving method of a touch panel system of the present invention is not particularly limited. Preferably, the driving method is an orthogonal sequence driving method. In other words, drive lines  35  are preferably parallel driven.  FIG. 9  is a view illustrating a driving method of a touch panel which driving method is employed in a conventional touch panel system.  FIG. 10  is a view illustrating a driving method (orthogonal sequence driving method) of a touch panel which driving method is employed in a touch panel system of the present invention. 
       FIG. 9  shows one sense line extracted from the touch panel and provided with four sensors. As shown in  FIG. 9 , the conventional touch panel system drives drive lines in the following manner: +V volt is applied to a drive line which is to be driven, so that the drive lines are driven sequentially. 
     Specifically, in the first drive line driving, +V volt is applied to the leftmost sensor. This gives the first Vout measurement result (X1) expressed by:
 
 X 1= C 1× V/C int
 
     Similarly, in the second drive line driving, +V volt is applied to the second sensor from the left. This gives the second Vout measurement result (X2) expressed by:
 
 X 2= C 2× V/C int
 
     In the third drive line driving, +V volt is applied to the third sensor from the left. This gives the third Vout measurement result (X3) expressed by:
 
 X 3= C 3× V/C int
 
     In the fourth drive line driving, +V volt is applied to the rightmost sensor. This gives the fourth Vout measurement result (X4) expressed by:
 
 X 4= C 4× V/C int
 
       FIG. 10  shows, as well as  FIG. 9 , one sense line extracted from the touch panel and provided with four sensors. As shown in  FIG. 10 , according to the orthogonal sequence driving method, drive lines are driven in such a manner that +V volt or −V volt is applied to all the drive lines. Namely, according to the orthogonal sequence driving method, the drive lines are parallel driven. 
     Specifically, in the first drive line driving, +V volt is applied to all the sensors. This gives the first Vout measurement result (Y1) expressed by:
 
 Y 1=( C 1+ C 2+ C 3+ C 4)× V/C int
 
     In the second drive line driving, +V volt is applied to the leftmost sensor, −V volt is applied to the second sensor from the left, +V volt is applied to the third sensor from the left, and −V volt is applied to the rightmost sensor. This gives the second Vout measurement result (Y2) expressed by:
 
 Y 2=( C 1− C 2+ C 3− C 4)× V/C int
 
     In the third drive line driving, +V volt is applied to the leftmost sensor, +V volt is applied to the second sensor from the left, −V volt is applied to the third sensor from the left, and −V volt is applied to the rightmost sensor. This gives the third Vout measurement result (Y3) expressed by:
 
 Y 3=( C 1+ C 2− C 3− C 4)× V/C int
 
     In the fourth drive line driving, +V volt is applied to the leftmost sensor, −V volt is applied to the second sensor from the left, −V volt is applied to the third sensor from the left, and +V volt is applied to the rightmost sensor. This gives the fourth Vout measurement result (Y4) expressed by:
 
 Y 4=( C 1− C 2− C 3+ C 4)× V/C int
 
     According to the configuration shown in  FIG. 10 , capacitance values (C1, C2, C3, C4) can be obtained by an inner product calculation of (i) output sequences (Y1, Y2, Y3, Y4) and (ii) orthogonal codes di. Such the formula is established due to orthogonality of the orthogonal code di. Here, the code di indicates codes of positive and/or negative voltages applied to a respective drive line. Specifically, the code d1 indicates codes of voltages applied to the leftmost sensor, and is expressed as “+1, +1, +1, +1”. The code d2 indicates codes of voltages applied to the second sensor from the left, and is expressed as “+1, −1, +1, −1”. The code d3 indicates codes of voltages applied to the third sensor from the left, and is expressed as “+1, +1, −1, −1”. The code d4 indicates codes of voltages applied to the rightmost sensor, and is expressed as “+1, −1, −1, +1”. 
     The values of C1, C2, C3, C4 are found by inner product calculations of (i) the output sequences Y1, Y2, Y3, Y4 and (ii) the codes d1, d2, d3, d4 as follows: 
     
       
         
           
             
               C 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             = 
             
               
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 + 
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 + 
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 + 
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
               = 
               
                 4 
                 ⁢ 
                 C 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
                 × 
                 
                   V 
                   / 
                   Cint 
                 
               
             
           
         
       
       
         
           
             
               C 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             = 
             
               
                 
                   1 
                   × 
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                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 + 
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
               = 
               
                 4 
                 ⁢ 
                 C 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 2 
                 × 
                 
                   V 
                   / 
                   Cint 
                 
               
             
           
         
       
       
         
           
             
               C 
               ⁢ 
               
                   
               
               ⁢ 
               3 
             
             = 
             
               
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 + 
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
               = 
               
                 4 
                 ⁢ 
                 C 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 3 
                 × 
                 
                   V 
                   / 
                   Cint 
                 
               
             
           
         
       
       
         
           
             
               C 
               ⁢ 
               
                   
               
               ⁢ 
               4 
             
             = 
             
               
                 
                   1 
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 + 
                 
                   
                     ( 
                     
                       - 
                       1 
                     
                     ) 
                   
                   × 
                   Y 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
               = 
               
                 4 
                 ⁢ 
                 C 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 3 
                 × 
                 
                   V 
                   / 
                   Cint 
                 
               
             
           
         
       
     
     Thus, due to the orthogonality of the codes di, Ci are obtained by inner product calculation of the codes di and the output sequences Yi. Now, the result thus obtained is compared with the result obtained by the conventional driving method shown in  FIG. 9 . In a case where the orthogonal sequence driving method and the conventional driving method perform the same number of driving operations, the orthogonal sequence driving method allows detection of values four times greater than those of the conventional driving method.  FIG. 11  is a view illustrating a process which needs to be performed by the touch panel of the driving method of  FIG. 9  in order that it achieves sensitivity equivalent to that of the touch panel of the driving method of  FIG. 10 . As shown in  FIG. 11 , in order that the driving method of  FIG. 9  achieves the sensitivity equivalent to that given by the driving method of  FIG. 10 , the driving method of  FIG. 9  needs to drive a certain drive line four times and to sum the results. Namely, according to the driving method of  FIG. 9 , a driving period for the drive lines is four times longer than that of the driving method of  FIG. 10 . Conversely, with a driving period for the drive lines which driving period is reduced to one-quarter of that of the driving method shown in  FIG. 9 , the driving method shown in  FIG. 10  achieves sensitivity equivalent to that given by the conventional driving method shown in  FIG. 9 . Thus, according to the driving method shown in  FIG. 10 , it is possible to reduce electric power consumption of the touch panel system. 
       FIG. 12  is a view schematically illustrating a touch panel system  1   c  including a touch panel  3  driven by such the orthogonal sequence driving method. Specifically, the touch panel system  1   c  of  FIG. 12  is shown with drive lines and sense lines, which correspond to the generalized four drive lines and one sense line of  FIG. 10 . 
     Specifically, the touch panel system  1   c  includes M drive lines  35 , L sense lines  33  (each of M and L is a natural number), and capacitances which are formed between the drive lines  35  and the sense lines  33  so as to be arranged in a matrix. The touch panel system  1   c  performs the following operation: With respect to a matrix Cij (i=1, . . . , M, j=1, . . . , L) of these capacitances, the code di=(di1, . . . , diN) (i=1, . . . , M) is used, which is constituted by “+1” and “−1” being orthogonal to each other and each having a code length N. Consequently, all the M drive lines  35  are driven concurrently in parallel, while applying +V volt in a case of “+1” and applying −V volt in a case of “−1”. Further, capacitance values Cij are estimated by inner product calculation “di·sj=Σ(k=1, . . . , N)dik·sjk”, i.e., inner product calculation of (i) output sequences sj=(sj1, . . . , sjN) (j=1, . . . , L) read from respective sense lines  33  and (ii) the codes di. In order to perform such the inner product calculation, the touch panel system  1   c  includes an electric charge integrator (calculation section)  47 . A strength of an output signal (Vout) supplied from the electric charge integrator  47  is found by:
 
 V out= Cf×V drive× N/C int
 
     The output sequence sj is expressed as follows: 
     
       
         
           
             
               
                 
                   sj 
                   = 
                     
                   ⁢ 
                   
                     ( 
                     
                       
                         sj 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
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                       ⁢ 
                       
                           
                       
                       , 
                       sjN 
                     
                     ) 
                   
                 
               
             
             
               
                 
                   = 
                     
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                         ∑ 
                         
                           
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                               , 
                               M 
                             
                             ) 
                           
                           ⁢ 
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                           1 
                         
                       
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                         ⁢ 
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                     ( 
                     
                       Vdrive 
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                           / 
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                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
     The inner product of the code di and the output sequence sj is expressed as follows: 
     
       
         
           
             
               
                 
                   
                     di 
                     · 
                     sj 
                   
                   = 
                     
                   ⁢ 
                   
                     di 
                     · 
                     
                       ( 
                       
                         ∑ 
                         
                           
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                                 = 
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                               M 
                             
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                         ) 
                       
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                         ) 
                       
                       ⁢ 
                       
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                           × 
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                           ⁢ 
                           
                               
                           
                           ⁢ 
                           ik 
                         
                         ) 
                       
                       × 
                     
                   
                 
               
             
             
               
                 
                     
                   ⁢ 
                   
                     
                       ( 
                       
                         Vdrive 
                         / 
                         Cint 
                       
                       ) 
                     
                     ⁡ 
                     
                       [ 
                       
                         
                           
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                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ik 
                           
                           = 
                           
                             
                               1 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               if 
                               ⁢ 
                               
                                   
                               
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                             = 
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                         , 
                         
                           0 
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                           ⁢ 
                           
                               
                           
                           ⁢ 
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                       ] 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
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                     × 
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                     × 
                     
                       ( 
                       
                         Vdrive 
                         / 
                         Cint 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
     Thus, according to the touch panel system  1   c , the touch panel  3  is driven by the orthogonal sequence driving method. Therefore, the following generalization is possible: By finding an inner product of the code di and the output sequence sj, a signal of the capacitance Cij is multiplied by N (code length). This driving method provides an effect that a signal strength of a capacitance is N-folded, regardless of the number of drive lines  35  (i.e., “M”). Conversely, by employing the orthogonal sequence driving method, sensitivity equivalent to that given by the conventional driving method shown in  FIG. 9  can be achieved with a driving period for the drive lines which period is reduced to one-Nth of that of the driving method shown in  FIG. 9 . Namely, employing the orthogonal sequence driving method can reduce the number of times that the drive lines should be driven. This makes it possible to reduce electric power consumption of the touch panel system  1   c.    
     Embodiment 5 
       FIG. 13  is a view schematically illustrating a basic configuration of a touch panel system  1   d  according to the present embodiment. The touch panel system  1   d  is configured by employing, in the touch panel system  1   b  with the noise canceling function shown in  FIG. 7 , the orthogonal sequence driving method for the drive lines  35  which is shown in  FIGS. 10 and 12  and which is employed in the touch panel system  1   c . Since the touch panel system  1   d  operates in the same manner as the above-described touch panel systems  1   b  and  1   c , explanations thereof are omitted here. 
     According to the touch panel system  1   d , a difference signal value is found between sense lines  33  which are adjacent to each other. Namely, a difference is found between the adjacent sense lines  33 , which have a higher correlation in terms of noise. Furthermore, from an output signal supplied from each sense line  33 , a signal (noise signal) of a sub sense line  34  is removed. Therefore, as compared with the touch panel systems  1  and  1   a  of Embodiments 1 and 2, the touch panel system  1   d  can remove a noise more reliably. Moreover, a signal of a capacitance Cij is multiplied by N (code length). This allows a capacitance to have an N-folded signal strength, regardless of the number of drive lines  35 . In addition, since the orthogonal sequence driving method is employed, sensitivity equivalent to that given by the conventional driving method shown in  FIG. 9  can be achieved with a driving period for the drive lines which period is reduced to one-Nth of that of the driving method shown in  FIG. 9 . Namely, employing the orthogonal sequence driving method can reduce the number of times that the drive lines should be driven. This makes it possible to reduce electric power consumption of the touch panel system  1   d.    
     Embodiment 6 
       FIG. 14  is a view schematically illustrating a basic configuration of a touch panel system  1   e  according to the present embodiment. The touch panel system  1   e  includes a subtracting section  41  having a different configuration. 
     Each of output signals supplied from a sense line  33  and a sub sense line  34  of a touch panel  3   b  is an analog signal. Therefore, the subtracting section  41  includes an analog-to-digital converting section (first analog-to-digital converting section)  48  and a digital subtracter (not illustrated). 
     With this configuration, output signals (analog signals) supplied from the touch panel  3   b  are converted into digital signals by the analog-to-digital converting section  48  of the subtracting section  41 . The digital subtracter performs, by use of the digital signals thus converted, subtracting operations in the same manner as in the touch panel system  1   b  shown in  FIG. 7 . 
     Thus, the touch panel system  1   e  can remove a noise by (i) converting, into digital signals, analog signals outputted by the touch panel  3   b  and thereafter (ii) performing subtracting operations. 
     Embodiment 7 
       FIG. 15  is a view schematically illustrating a basic configuration of a touch panel system  1   f  according to the present embodiment. The touch panel system  1   f  includes a subtracting section  41  having a different configuration. 
     Output signals supplied from a sense line  33  and a sub sense line  34  of a touch panel  3   b  are analog signals. Therefore, the subtracting section  41  includes a differential amplifier  49  and an analog-to-digital converting section  48 . 
     With this configuration, in the same manner as in the touch panel system  1   b  shown in  FIG. 7 , the differential amplifier  49  performs subtracting operations on output signals (analog signals) supplied from the touch panel  3   b , without converting the analog signals into digital signals. The analog-to-digital converting section  48  (second analog-to-digital converting section) converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
     Thus, the touch panel system  1   f  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   b , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. 
     Embodiment 8 
       FIG. 16  is a view schematically illustrating a basic configuration of a touch panel system  1   g  according to the present embodiment. The touch panel system  1   g  includes a subtracting section  41  having a different configuration. The touch panel system  1   g  includes a total differential amplifier  50  instead of the differential amplifier  49  in the touch panel system  1   f  shown in  FIG. 15 . 
     Output signals supplied from sense lines  33  and a sub sense line  34  of a touch panel  3   b  are analog signals. Therefore, the subtracting section  41  includes a total differential amplifier  50  and an analog-to-digital converting section  48 . 
     With this configuration, in the same manner as in the touch panel system  1   b  shown in  FIG. 7 , the total differential amplifier  50  performs subtracting operations on output signals (analog signals) supplied from the touch panel  3   b , without converting the analog signals into digital signals. The analog-to-digital converting section  48  converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
       FIG. 17  is a circuit diagram illustrating one example of the total differential amplifier  50 . The total differential amplifier  50  includes two pairs each including a capacitance and a switch, the two pairs being arranged so as to be symmetric to each other with respect to a differential amplifier. Specifically, a non-inverting input terminal (+) and an inverting input terminal (−) of the differential amplifier are supplied with signals from sense lines  33  which are adjacent to each other. A capacitance (feedback capacitance) is provided between an inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier so that the capacitance is connected with the inverting output terminal (−) and the non-inverting input terminal (+), and another capacitance (feedback capacitance) is provided between a non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier so that said another capacitance is connected with the non-inverting output terminal (+) and the inverting input terminal (−), these capacitances having the same capacitance value. Furthermore, a switch is provided between the inverting output terminal (−) and the non-inverting input terminal (+) so that the switch is connected with the inverting output terminal (−) and the non-inverting input terminal (+), and another switch is provided between the non-inverting output terminal (+) and the inverting input terminal (−) so that said another switch is connected with the non-inverting output terminal (+) and the inverting input terminal (−). 
     Thus, the touch panel system  1   g  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   b , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. 
     Embodiment 9 
       FIG. 18  is a view schematically illustrating a basic configuration of a touch panel system  1   h  according to the present embodiment. The touch panel system  1   h  includes (i) a subtracting section  41  having a different configuration and involves (i) a different driving method of a touch panel  3   b . The touch panel system  1   h  includes a total differential amplifier  50  instead of the differential amplifier  49  in the touch panel system  1   f  shown in  FIG. 15 . 
     Output signals supplied from sense lines  33  and a sub sense line  34  of the touch panel  3   b  are analog signals. Therefore, the subtracting section  41  includes a total differential amplifier  50  and an analog-to-digital converting section  48 . 
     With this configuration, in the same manner as in the touch panel system  1   b  shown in  FIG. 7 , the total differential amplifier  50  performs subtracting operations on output signals (analog signals) supplied from the touch panel  3   b , without converting the analog signals into digital signals. The analog-to-digital converting section  48  converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
     Further, the touch panel system  1   h  employs, as a driving method for the touch panel  3   b , the orthogonal sequence driving method shown in  FIGS. 10 ,  12 , and  13 . According to this configuration, as shown in  FIG. 10 , a voltage for driving four drive lines is applied as follows: In the second driving through the fourth driving, +V is applied twice and −V is also applied twice, i.e., the number of times of application of +V is equal to that of −V. On the other hand, in the first driving, +V is applied four times. Accordingly, an output value of an output sequence Y1 of the first driving is greater than that of each of output sequences Y2 through Y4 of the second driving through the fourth driving. Therefore, applying a dynamic range to the output value of any of the output sequences Y2 through Y4 of the second driving through the fourth driving causes saturation of the output sequence Y1 of the first driving. 
     In order to address this, the subtracting section  41  of the touch panel system  1   h  includes the total differential amplifier  50 . Further, employed as the total differential amplifier  50  is the one whose input common-mode voltage range is rail to rail. Namely, the total differential amplifier  50  has a wide common-mode input range. Consequently, the total differential amplifier  50  can operate in a voltage range from a power source voltage (Vdd) to GND. Furthermore, a difference between input signals supplied to the total differential amplifier  50  is amplified. Therefore, regardless of the type of the orthogonal sequence driving method employed in the touch panel  3   b  which is combined with the touch panel system  1   h , an output signal from the total differential amplifier  50  is free from the problem of output saturation. Note that one example of the total differential amplifier  50  is as previously described with reference to  FIG. 17 . 
     Thus, the touch panel system  1   h  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   b , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. Furthermore, since the touch panel system  1   h  includes the total differential amplifier  50  capable of rail-to-rail operation, an output signal from the total differential amplifier  50  is free from the problem of output saturation. 
     Embodiment 10 
     In Embodiments 1 through 9, a touch panel system provided with a sub sensor  32  (sub sense line  34 ) has been described. However, for a touch panel system of the present invention, the sub sensor  32  is not essential. In the present embodiment, a touch panel system not provided with a sub sensor  32  will be described. 
       FIG. 20  is a view schematically illustrating a basic configuration of a touch panel system  1   i  of the present embodiment. The touch panel system  1   i  includes a subtracting section  41   a  for finding a difference signal of sense lines  33  adjacent to each other. 
     More specifically, a touch panel  3   c  includes a plurality of (in  FIG. 20 , five) drive lines  35  and a plurality of (in  FIG. 20 , eight) sense lines  33  intersecting the drive lines  35 . The sense lines  33  and the drive lines  35  are isolated from each other, and the sense lines  33  and the drive lines  35  are coupled to each other via capacitances. 
     A touch panel controller  4  includes switches SW, the subtracting section  41   a , storage sections  45   a  through  45   d , which are arranged in this order from an input-receiving side of the touch panel controller  4 . Note that the touch panel controller  4  also includes a coordinates detecting section  42  (not illustrated) and a CPU  43  (not illustrated) (see  FIG. 1 ). 
     The subtracting section  41   a  includes input terminals (input terminals for outputs of main sensors) for receiving signals outputted by main sensors  31 . The subtracting section  41   a  receives the signals from the main sensors  31 . Then, the subtracting section  41   a  subtracts one of adjacent sense lines  33  from the other of the adjacent sense lines  33 , so as to find a difference value (difference signal). The signal thus obtained as a result of the subtracting operation by the subtracting section  41   a  is outputted to the coordinates detecting section  42  (see  FIG. 1 ). 
     Thus, the touch panel system  1   i  differs from the touch panel systems of the above-described embodiments in terms of that the touch panel system  1   i  is not provided with a sub sensor  32  (sub sense line  34 ) and the subtracting section  41   a  performs a different operation. 
     The switches SW select, from signals supplied from the sense lines  33 , signals to be supplied to the subtracting section  41   a . More specifically, each of the switches SW includes two terminals (upper and lower terminals), and selects one of the upper and lower terminals.  FIG. 20  shows a state where the switches SW select the lower terminals. 
     The subtracting section  41   a  performs difference signal operations on, out of signals supplied from Arrays (1) through (8), signals selected by the switches SW. Specifically, the subtracting section  41   a  performs a difference signal operation between sense lines  33  which are adjacent to each other. For example, in a case where the switches SW select the lower terminals as shown in  FIG. 20 , the subtracting section  41   a  performs the following signal operations: Array (8)−Array (7); Array (6)−Array (5); Array (4)−Array (3); and Array (2)−Array (1). On the other hand, in a case where the switches SW select the upper terminals (not illustrated), the subtracting section  41   a  performs the following difference signal operations: Array (7)−Array (6); Array (5)−Array (4); and Array (3)−Array (2). 
     In a case where each of the switches SW selects one of the upper and lower terminals, the storage sections  45   a  through  45   d  store signals (difference operation signals) obtained by the difference operations performed by the subtracting section  41   a . On the other hand, in a case where each of the switches SW selects the other one of the upper and lower terminals, difference operation signals are directly outputted, not via the storage sections  45   a  through  45   d.    
     (2) Noise Processing Performed by Touch Panel System  1   i    
     With reference to  FIGS. 20 and 21 , the following will describe noise processing performed by the touch panel system  1   i .  FIG. 21  is a flow chart illustrating a noise canceling process, which is a basic process of the touch panel system  1   i.    
     Upon activation of the touch panel system  1   i , the drive line is supplied with an electric potential at a certain interval. The user&#39;s performing a touch operation on the touch panel  3   c  changes a capacitance of a specific sense line  33  corresponding to the touched position. Namely, the user&#39;s performing the touch operation on the touch panel  3   c  changes a value of an output signal supplied from that sense line  33 . The touch panel system  1   i  outputs, to the touch panel controller  4 , output signals from the sense lines  33 , while driving the drive lines  35 . Thus, while driving the drive lines  35 , the touch panel system  1   i  detects a change in the capacitance of the sense line  33 , so as to determine the presence or absence of a touch operation and a touched position. 
     To be more specific, a noise such as a clock generated in the display device  2  and other noises coming from the outside are reflected in the touch panel  3   c . Therefore, a main sensor group  31   b  detects various kinds of noise components. Specifically, the output signal supplied from the sense line  33  includes not only a signal derived from the touch operation itself but also a noise signal (noise component) (F 701 ). 
     Next, the switches SW select the lower terminals (F 702 ). Then, the subtracting section  41   a  finds a difference (sense line (Sn+1)−sense line Sn: a first difference) between a sense line  33  (sense line Sn) and a sense line (sense line Sn+1) which is one of two sense lines  33  adjacent to the certain sense line  33  (F 703 ). 
     For Arrays (1) through (8) shown in  FIG. 20 , the subtracting section  41   a  performs the following four difference signal operations:
         Array (2)−Array (1) (The resulting difference value is referred to as “A”.)   Array (4)−Array (3) (The resulting difference value is referred to as “C”.)   Array (6)−Array (5) (The resulting difference value is referred to as “E”.)   Array (8)−Array (7) (The resulting difference value is referred to as “G”.)
 
Namely, in the step F 703 , the subtracting section  41   a  performs the difference signal operations on Arrays (1) through (8) of the sense lines  33 .
       

     The difference values A, C, E, and G found by the subtracting section  41   a  are stored in the storage sections  45   a  through  45   d , respectively. Namely, the storage section  45   a  stores the difference value A, the storage section  45   b  stores the difference value C, the storage section  45   c  stores the difference value E, and the storage section  45   d  stores the difference value G (F 704 ). 
     Next, the switches SW selecting the lower terminals are turned to select (close) the upper terminals (F 705 ). Then, the subtracting section  41   a  performs an operation similar to that of F 703 . Specifically, the subtracting section  41   a  performs a difference signal operation (sense line Sn−(Sn−1): a second difference) between the sense line  33  (sense line Sn) and a sense line (sense line Sn−1) which is the other one of the two sense lines  33  adjacent to the certain sense line  33  (F 706 ). 
     For Arrays (1) through (8) shown in  FIG. 20 , the subtracting section  41   a  performs the following three difference signal operations:
         Array (3)−Array (2) (The resulting difference value is referred to as “B”.)   Array (5)−Array (4) (The resulting difference value is referred to as “D”.)   Array (7)−Array (6) (The resulting difference value is referred to as “F”.)
 
Namely, in the step F 706 , the subtracting section  41   a  performs the difference signal operations on Arrays (2) through (7).
       

     As described above, the touch panel system  1   i  obtains a difference signal value between sense lines  33  adjacent to each other. Namely, a difference is found between the adjacent sense lines  33 , which have a higher correlation in terms of noise. This removes the noise component from the output signal supplied from the main sensor group  31   b , thereby extracting the signal derived from the touch operation itself. This makes it possible to reliably remove (cancel) a wide variety of noises reflected in the touch panel  3   c.    
     Embodiment 11 
       FIG. 22  is a view schematically illustrating a basic configuration of a touch panel system  1   j  of the present embodiment. The touch panel system  1   j  is configured by employing, in the above-described touch panel system  1   i  having the noise canceling function shown in  FIG. 20 , a drive line driving circuit (not illustrated) for parallel driving the drive lines  35 . Further, the touch panel system  1   j  includes (i) a decoding section  58  for decoding difference values of capacitances which difference values are found by a subtracting section  41   a , (ii) a non-touch operation information storage section  61  for storing a distribution of differences between the capacitances which differences are decoded by the decoding section  58  when no touch operation is performed, and (iii) a calibration section  62  for calibrating a distribution of differences between the capacitances which differences are decoded by the decoding section  58  when a touch operation is performed. Since the touch panel system  1   j  operates in the same manner as the above-described touch panel system  1   i , explanations thereof are omitted here. The following descriptions focus on processes performed by the subtracting section  41   a , the decoding section  58 , the non-touch operation information storage section  61 , and the calibration section  62 . Further, the following descriptions deal with an example where orthogonal sequences or M sequences are used as code sequences for parallel driving. 
     Concretely, assume that code sequences (a component is 1 or −1) for parallel driving the first drive line through the Mth drive line are as follows:
 
 d   1 =( d   11   ,d   12   , . . . ,d   1N )
 
 d   2 =( d   21   ,d   22   , . . . ,d   2N )
 
. . .
 
 d   M =( d   M1   ,d   M2   , . . . ,d   MN )
 
Hereinafter, the code sequences are assumed as orthogonal sequences or M sequences having a code length N (=2^n−1), having been shifted. Such sequences have a nature of establishing the following formula:
 
     
       
         
           
             
               
                 d 
                 i 
               
               · 
               
                 d 
                 j 
               
             
             = 
             
               
                 
                   ∑ 
                   
                     k 
                     = 
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                 ⁢ 
                 
                   
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                     ik 
                   
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               = 
               
                 N 
                 × 
                 
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                   ij 
                 
               
             
           
         
       
     
     where if d 1  to d M  is an orthogonal sequence, δ ij =1 if i=j, 0 if i≠j, 
     if d 1  to d M  is an M sequence, δ ij =1 if i=j, −1/N if i≠j. 
     Difference output sequences “S j,P  (j=1, . . . , [L/2], P 1,2) (L indicates the number of sense lines  33 , [n]=an integer part of n)” of sense lines  33 , which difference output sequences correspond to the aforementioned sequences, are defined as follows: 
     S j,1 : An output sequence for d 1  through d M  when the switches SW select the lower terminals. 
     S j,2 : An output sequence for d 1  through d M  when the switches SW select the upper terminals. 
     Further, a distribution of differences “(∂sC) kj,P  (k=1, . . . , M; j=1, . . . , [L/2]; P=1, 2)” of capacitance values in a direction in which each of the drive lines  35  extends (in a direction in which the sense lines  33  are arranged) is defined as follows:
 
(∂ sC ) kj,1   =C   k,2j   −C   k,2j−1  
 
(∂ sC ) kj,2   =C   k,2j+1   −C   k,2j  
 
     In this case, a difference output of capacitances in the direction in which each of the drive lines  35  extends obtained by parallel driving is as follows: 
     
       
         
           
             
               
                 
                   
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     The decoding section  58  decodes the difference values of the capacitances which differences value are found by the subtracting section  41   a  (i.e., the distribution of differences between the capacitance values in the direction in which each of the drive lines  35  extend). Specifically, the decoding section  58  finds inner products of (i) the code sequences for parallel driving the drive lines  35  and (ii) difference output sequences of the sense lines  33 , which difference output sequences correspond to the aforementioned sequences. Therefore, an inner product value decoded by the decoding section  58  is expressed as follows: 
     
       
         
           
             
               
                 
                   
                     
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     where 
                   d   i     ·     d   j       =         ∑     k   =   1     N     ⁢       d   ik     ×     d   jk         =     N   ×     δ   ij           ,         
and
 
     if d 1  to d M  is an orthogonal sequence, δ ij =1 if i=j, 0 if i≠j 
     if d 1  to d M  is an M sequence, δ ij =1 if i=j, −1/N if i≠j. 
     Thus, the decoding section  58  finds, as a main component of the decoded inner product value d i ·s j,P , an N-folded distribution of differences (∂sC) kj,P  between the capacitance values in the direction in which each of the drive lines  35  extends. Accordingly, by regarding an estimate value of the distribution of differences (∂sC) ij,P  between the capacitance values in the direction in which each of the drive lines  35  extends as the inner product value d i ·s j,P , it is possible to read signal strengths of the capacitance values which signal strengths have been multiplied by N (i.e., multiplied by a code length). 
     Meanwhile, as described above, by defining the difference output sequences S j,P  (P=1, 2) of the sense lines  33 , a common mode noise superimposed in common on sense lines  33  adjacent to each other is canceled. This makes it possible to read a difference capacitance with a high SNR. 
     As described above, according to the touch panel system  1   j , the touch panel  3   c  is parallel driven, and the decoding section  58  decodes the values of the differences between the capacitances which values are found by the subtracting section  41   a . Consequently, signals of the capacitances are multiplied by a code length (i.e., multiplied by N). Therefore, signal strengths of the capacitances are increased, regardless of the number of drive lines  35 . Further, provided that necessary signal strengths are merely equal to those of the conventional driving method shown in  FIG. 9 , it is possible to reduce a driving period for the drive lines  35  to one-Nth of that of the driving method shown in  FIG. 9 . Namely, it is possible to reduce the number of times that the drive lines  35  should be driven. This makes it possible to reduce electric power consumption of the touch panel system  1   j.    
     Preferably, the touch panel system  1   j  is configured such that the calibration section  62  subtracts (i) differences between respective pairs of the sense lines  33  adjacent to each other (=a distribution of difference values in the entire touch panel) which differences are found when no touch operation is performed from (ii) differences between the respective pairs of the sense lines  33  adjacent to each other (i.e., a distribution of difference values in the entire touch panel  3   c ) which differences are found when a touch operation is performed. Namely, it is preferable that (i) such the difference signal operation is performed before and after a touch operation and (ii) subtraction is performed between difference value signals obtained before and after the touch operation. For example, the non-touch operation information storage section  61  stores an estimated value of a distribution of differences (∂sC) kj,P  found in an initial state where no touch operation is performed (when no touch operation is performed). Then, the calibration section  62  subtracts (i) the estimated value of the distribution of the differences (∂sC) kj,P  found when no touch operation is performed, which estimated value is stored in the non-touch operation information storage section  61 , from (ii) an estimated value of a distribution of differences (∂sC) kj  found when a touch operation is performed. Thus, the calibration section  62  subtracts (i) the distribution of the differences between capacitances found when no touch operation is performed which distribution is stored in the non-touch operation information storage section from (ii) the distribution of differences between the capacitances found when a touch operation is performed (i.e., the difference value signal found when a touch operation is performed−the difference value signal found when no touch operation is performed). This makes it possible to cancel an offset inherent in the touch panel  3   c.    
     Thus, the touch panel system  1   j  is free from a difference component resulting from a variation in capacitances which variation is inherent in the touch panel  3   c . Consequently, only a difference component resulting from the touch operation is detected. In the case of the M sequence, an error component (δ ij =−1/N if else i≠j) mixes therein, which does not occur in the case of the orthogonal sequence. However, this error component results only from the touch operation. Therefore, if N is increased (e.g., N=63 or 127), a degree of deterioration of SNR becomes smaller. 
     Embodiment 12 
       FIG. 23  is a view schematically illustrating a basic configuration of a touch panel system  1   k  of the present embodiment. The touch panel system  1   k  includes a subtracting section  41   a  having a different configuration. 
     Output signals supplied from sense lines  33  of a touch panel  3   c  are analog signals. Therefore, the subtracting section  41   a  includes an analog-to-digital converting section (third analog-to-digital converting section)  48   a  and a digital subtracter (not illustrated). 
     With this configuration, output signals (analog signals) supplied from the touch panel  3   c  are converted into digital signals by the analog-to-digital converting section  48   a  of the subtracting section  41   a . The digital subtracter performs, by use of the digital signals thus converted, subtracting operations in the same manner as in the touch panel systems  1   i  and  1   j  shown in  FIG. 20 . 
     Thus, the touch panel system  1   k  can remove a noise by (i) converting, into digital signals, analog signals outputted by the touch panel  3   c  and thereafter (ii) performing subtracting operations. 
     Embodiment 13 
       FIG. 24  is a view schematically illustrating a basic configuration of a touch panel system  1   m  of the present embodiment. The touch panel system  1   m  includes a subtracting section  41   a  having a different configuration. 
     Output signals supplied from sense lines  33  of a touch panel  3   c  are analog signals. Therefore, the subtracting section  41   a  includes a differential amplifier  49  and an analog-to-digital converting section  48   a  (fourth analog-to-digital converting section). 
     With this configuration, in the same manner as in the touch panel system  1   i  shown in  FIG. 20 , the differential amplifier  49  performs subtracting operations on output signals (analog signals) supplied from the touch panel  3   c , without converting the analog signals into digital signals. The analog-to-digital converting section  48   a  converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
     Thus, the touch panel system  1   m  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   c , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. 
     Embodiment 14 
       FIG. 25  is a view schematically illustrating a basic configuration of a touch panel system  1   n  of the present embodiment. The touch panel system  1   n  includes a subtracting section  41   a  having a different configuration. The touch panel system  1   n  includes a total differential amplifier  50  instead of the differential amplifier  49  in the touch panel system  1   m  shown in  FIG. 24 . 
     Output signals supplied from sense lines  33  of a touch panel  3   c  are analog signals. Therefore, the subtracting section  41   a  includes the total differential amplifier  50  and an analog-to-digital converting section  48   a.    
     With this configuration, in the same manner as in the touch panel system  1   i  shown in  FIG. 20 , the total differential amplifier  50  performs subtracting operations on output signals (analog signals) from the touch panel  3   c , without converting the analog signals into digital signals. The analog-to-digital converting section  48   a  converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
     Thus, the touch panel system  1   n  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   c , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. 
     Embodiment 15 
       FIG. 26  is a view schematically illustrating a basic configuration of a touch panel system  1   o  of the present embodiment. The touch panel system  1   o  includes a subtracting section  41   a  having a different configuration. The touch panel system  1   o  includes a total differential amplifier  50  instead of the differential amplifier  49  in the touch panel system  1   m  shown in  FIG. 26 . 
     Output signals supplied from sense lines  33  of a touch panel  3   c  are analog signals. Therefore, the subtracting section  41   a  includes the total differential amplifier  50  and an analog-to-digital converting section  48   a.    
     With this configuration, in the same manner as in the touch panel system  1   i  shown in  FIG. 20 , the total differential amplifier  50  performs subtracting operations on output signals (analog signals) from the touch panel  3   c , without converting the analog signals into digital signals. The analog-to-digital converting section  48   a  converts, into a digital signal, an analog signal thus obtained by the subtracting operations. 
     Further, the touch panel system  1   o  employs, as a driving method for the touch panel  3   c , the orthogonal sequence driving method shown in  FIGS. 10 ,  12 , and  22 . According to this configuration, as shown in  FIG. 10 , a voltage for driving four drive lines is applied as follows: In the second driving through the fourth driving, +V is applied twice and −V is also applied twice, i.e., the number of times of application of +V is equal to that of −V. On the other hand, in the first driving, +V is applied four times. Accordingly, an output value of an output sequence Y1 of the first driving is greater than that of each of output sequences Y2 through Y4 of the second driving through the fourth driving. Therefore, adding a dynamic range to the output values of the output sequences Y2 through Y4 of the second driving through the fourth driving causes saturation of the output sequence Y1 of the first driving. 
     In order to address this, the subtracting section  41   a  of the touch panel system  1   o  includes the total differential amplifier  50 . 
     Further, employed as the total differential amplifier  50  is the one whose input common-mode voltage range is rail to rail. Namely, the total differential amplifier  50  has a wide common-mode input range. Consequently, the total differential amplifier  50  can operate in a voltage range from a power source voltage (Vdd) to GND. Furthermore, a difference between input signals supplied to the total differential amplifier  50  is amplified. Therefore, regardless of the type of the orthogonal sequence driving method employed in the touch panel  3   c  which is combined with the touch panel system  1   o , an output signal from the total differential amplifier  50  is free from the problem of output saturation. Note that one example of the total differential amplifier  50  is as previously described with reference to  FIG. 17 . 
     Thus, the touch panel system  1   o  can remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel  3   c , without converting the analog signals into digital signals, and thereafter (ii) converting the resulting signal into a digital signal. Furthermore, since the touch panel system  1   o  includes the total differential amplifier  50  capable of rail-to-rail operation, an output signal from the total differential amplifier  50  is free from the problem of output saturation. 
     Embodiment 16 
     Next, the following will describe a method for detecting a touch operation, which method is employed in the touch panel systems of the above-described embodiments. The following descriptions deal with, as an example, the touch panel system  1   j  of  FIG. 22 . However, the touch panel systems of other embodiments perform the same operation. The touch panel system  1   j  includes a judging section  59  for determining the presence or absence of a touch operation based on a comparison of (i) a difference between signals of sense lines  33  adjacent to each other which difference is found by the subtracting section  41   a  and the decoding section  58 , and (ii) positive and negative threshold values. Note that the judging section  59  is supplied with (i) a signal (a distribution of differences between capacitances) having been subjected to a calibration process by the calibration section  62  or (ii) a signal (a distribution of differences between capacitances) having not been subjected to a calibration process by the calibration section  62 . In the case where the signal having not been subjected to the calibration process by the calibration section  62  is inputted to the judging section  59 , a distribution of differences between the capacitances which distribution has been decoded by the decoding section  58  is directly inputted to the judging section  59 . The following will describe the case where the signal having not been subjected to the calibration process by the calibration section  62  is inputted to the judging section  59 . However, the same operation is performed also in the case where the signal having been subjected to the calibration process is inputted to the judging section  59 . 
       FIG. 27  is a flow chart illustrating a basic process of the judging section  59  in the touch panel system  1   j  shown in  FIG. 22 .  FIG. 28  is a view schematically illustrating a method of recognizing touch information in the flow chart shown in  FIG. 27 . 
     As shown in  FIG. 27 , the judging section  59  first obtains values of differences in signal between respective pairs of sense lines adjacent to each other (difference information) “(∂sC) ij,P ” which values are found by the subtracting section  41   a  and the decoding section  59  (F 801 ). Next, the judging section  59  compares the values of the differences with a positive threshold value THp and a negative threshold value THm, each of which is stored in the judging section  59 , so as to create an increase and decrease table (F 802 ). This increase and decrease table is, for example, a ternary increase and decrease table as shown in (a) of  FIG. 28 . 
     Next, the ternary increase and decrease table is converted into a binary image (i.e., binarized) (F 803 ). For example, in a case where the increase and decrease table shown in (a) of  FIG. 28  is scanned in the order from a sense line S 1  to a sense line S 7  (in a direction toward the right in  FIG. 28 ), the following operation is carried out: In the increase and decrease table, if the value “+” is scanned, the value therein and subsequent value(s) are all converted into “1” until the value “−” is scanned next. Meanwhile, if the value “−” is scanned, the scanning is performed in a direction opposite to the scanning direction (in a direction toward the left in  FIG. 28 ) and the value therein is surely converted into “1”. In this manner, binarized data as shown in (b) of  FIG. 28  is obtained. 
     Next, in order to extract touch information from the binarized data, a connected component is extracted (F 804 ). For example, in (b) of  FIG. 28 , if the values “1” are arranged side by side on drive lines adjacent to each other and on a single sense line, (i) a connected component including one of such the values “1” and (ii) a connected component including the other one of such the values “1” are regarded as a single connected component, which is set as a candidate of a touched position. Namely, each of the boxed parts including the values “1” in (c) of  FIG. 28  is regarded as a single connected component, and is extracted as a candidate of a touched position. 
     Lastly, based on the extracted candidates of the touched position, touch information (the size, position, etc. of the touch) is recognized (F 805 ). 
     Thus, based on a difference between signals of sense lines  33  adjacent to each other from which difference a noise signal has been removed, the judging section  59  determines the presence or absence of a touch operation. This makes it possible to accurately determine the presence or absence of the touch operation. 
     Furthermore, in the above-described example, based on a comparison of (i) the differences in signals between the respective pairs of sense lines  33  adjacent to each other which differences are found by the subtracting section  41   a  and (ii) the positive and negative threshold values (THp, THm), the judging section  59  creates the increase and decrease table indicating, in ternary, the distribution of the differences in signal between the sense lines  33 , and converts the increase and decrease table into the binary image. Namely, the differences in signals between the respective pairs of sense lines  33  adjacent to each other from which differences the noise signal has been removed are inputted to the judging section  59 . The judging section  59  compares (i) the differences in signals between the respective pairs of sense lines  33  adjacent to each other and (ii) the positive and negative threshold values (THp, THm) stored in the judging section  59 , so as to create the increase and decrease table indicating, in ternary, the distribution of the differences in signal between the sense lines  33 . Further, the judging section  59  binarizes the increase and decrease table, so that the increase and decrease table is converted into the binary image. Consequently, from the binary image thus converted, the candidates of the touched position are extracted. Thus, by recognizing the touch information (the size, position, etc. of the touch) based on the binary image, it is possible not only to determine the presence or absence of the touch operation but also to recognize the touch information more accurately. 
     Embodiment 17 
       FIG. 29  is a functional block diagram illustrating a configuration of a mobile phone  10  including a touch panel system  1 . The mobile phone (electronic device)  10  includes a CPU  51 , a RAM  53 , a ROM  52 , a camera  54 , a microphone  55 , a speaker  56 , an operation key  57 , and the touch panel system  1 . These elements are connected with each other via data bus. 
     The CPU  51  controls operation of the mobile phone  10 . The CPU  51  executes, for example, a program stored in the ROM  52 . The operation key  57  receives an instruction entered by a user of the mobile phone  10 . The RAM  53  stores, in a volatile manner, data generated as a result of the CPU  51 &#39;s executing the program or data inputted via the operation key  57 . The ROM  52  stores data in an involatile manner. 
     Further, the ROM  52  is a ROM into which data can be written and from which data can be deleted, for example, an EPROM (Erasable Programmable Read-Only Memory) or a flash memory. The mobile phone  10  may be configured to include an interface (IF) (not illustrated in  FIG. 29 ) which allows the mobile phone  10  to be connected with another electronic device via a wire. 
     The camera  54  takes an image of a subject in response to the user&#39;s operation on the operation key  57 . The obtained image data of the subject is stored in the RAM  53  or an external memory (e.g., a memory card). The microphone accepts an inputted voice of the user. The mobile phone  10  binarizes the inputted voice (analog data). Then, the mobile phone  10  transmits the binarized voice to a receiver (e.g., to another mobile phone). The speaker  56  outputs, for example, sounds based on music data stored in the RAM  53 . 
     The touch panel system  1  includes a touch panel  3 , a touch panel controller  4 , a drive line driving circuit  5 , and a display device  2 . The CPU  51  controls operation of the touch panel system  1 . The CPU  51  executes, for example, a program stored in the ROM  52 . The RAM  53  stores, in a volatile manner, data generated as a result of the CPU  51 &#39;s executing the program. The ROM  52  stores data in an involatile manner. 
     The display device  2  displays an image stored in the ROM  52  or the RAM  53 . The display device  2  is stacked on the touch panel  3  or includes the touch panel  3 . 
     Embodiment 18 
     The touch panel system described in the foregoing embodiments may further include configurations as described below. 
     Described below is an embodiment related to a touch panel system of the present invention, with respect to  FIG. 30  to  FIG. 40 . 
     (Configuration of Touch Panel System  71   a ) 
       FIG. 30  is a block diagram illustrating a configuration of a touch panel system  71   a  according to Embodiment 18.  FIG. 31  is a schematic view illustrating a configuration of a touch panel  73  provided in the touch panel system  71   a.    
     The touch panel system  71   a  includes a touch panel  73  and a capacitance value distribution detection circuit  72 . The touch panel  73  includes signal lines HL 1  to HLM (first signal lines) arranged parallel to each other in a horizontal direction, signal lines VL 1  to VLM (second signal lines) arranged parallel to each other in a vertical direction, and capacitances C 11  to each provided at intersections of the signal lines HL 1  to HLM with the signal lines VL 1  to VLM. It is preferable that the touch panel  73  is of a size in which a hand holding the input pen can be placed on the touch panel  73 . However, the touch panel  73  may be of a size that is usable for smartphones. 
     The capacitance distribution detection circuit  72  includes a driver  75 . The driver  75  applies a voltage to drive lines DL 1  to DLM in accordance with a code sequence. The capacitance value distribution detection circuit  72  includes a sense amplifier  76 . The sense amplifier  76  reads out, via the sense lines SL 1  to SLM, a linear sum of electric charges that correspond to the capacitances, and supplies the linear sum to an A/D converter  78 . 
     The capacitance value distribution detection circuit  72  illustrating a configuration of a connection switching circuit between (a) signal lines HL 1  to HLM and VL 1  to VLM connected to the touch panel  73 , and (b) drive lines DL 1  to DLM connected to the driver  75  and sense lines SL 1  to SLM connected to the sense amplifier  76 . 
     The multiplexer  74  causes a switchover between (a) a first connection state in which the signal lines HL 1  to HLM are connected to the drive lines DL 1  to DLM of the driver  75  and the signal lines VL 1  to VLM are connected to the sense lines SL 1  to SLM of the sense amplifier  76  and (b) a second connection state in which the signal lines HL 1  to HLM are connected to the sense lines SL 1  to SLM of the sense amplifier  76  and the signal lines VL 1  to VLM are connected to the drive lines DL 1  to DLM of the driver  75 . 
       FIG. 33  is a circuit diagram illustrating a configuration of the multiplexer  74  provided in the capacitance value distribution detection circuit  72  of the touch panel system  71   a . The multiplexer  74  includes four CMOS switches SW 1  to SW 4 , which are connected in series. A signal from a timing generator  77  via the control line CL is supplied from (i) one end of the CMOS switch SW 1  opposite of the CMOS switch SW 2 , (ii) between the CMOS switch SW 2  and the CMOS switch SW 3 , (iii) one end of the CMOS switch SW 4  opposite of the CMOS switch SW 3 , and (iv) a terminal input of a reverser inv. The reverser inv has its output be supplied between the CMOS switch SW 1  and the CMOS switch SW 2 , and between the CMOS switch SW 3  and the CMOS switch SW 4 . The signal lines HL 1  to HLM are connected to the CMOS switches SW 1  and SW 2 . The signal lines VL 1  to VLM are connected to the CMOS switches SW 3  and SW 4 . The drive lines DL 1  to DLM are connected to the CMOS switches SW 1  and SW 4 . The sense lines SL 1  to SLM are connected to the CMOS switches SW 2  and SW 3 . 
     When the signal of the control line CL is made Low, the signal lines HL 1  to HLM become connected to the drive lines DL 1  to DLM and the signal lines VL 1  to VLM become connected to the sense lines SL 1  to SLM. When the signal of the control line CL is made High, the signal lines HL 1  to HLM become connected to the sense lines SL 1  to SLM and the signal lines VL 1  to VLM become connected to the drive lines DL 1  to DLM. 
     The A/D converter  78  converts from analog to digital a linear sum of electric charges read out via the sense lines SL 1  to SLM, which electric charges correspond to the capacitances, and supplies the converted linear sum to the capacitance value distribution calculation section  79 . 
     The capacitance value distribution calculation section  79 , based on the code sequence and the linear sum of the electric charges supplied from the A/D converter  78 , which electric charges correspond to the capacitances, calculates a capacitance value distribution on the touch panel  73  and supplies the calculated capacitance value distribution to a touch recognition section  80 . The touch recognition section  80  recognizes a touched position on the touch panel  73  based on the capacitance value distribution supplied from the capacitance value distribution calculation section  79 . 
     The capacitance value distribution detection circuit  72  includes the timing generator  77 . The timing generator  77  generates (i) a signal for specifying an operation of the driver  75 , (ii) a signal for specifying an operation of the sense amplifier  76 , and (iii) a signal for specifying an operation of the A/D converter  78 , and supplies these signals to the driver  75 , the sense amplifier  76 , and the A/D converter  78 , respectively. 
     (Operation of Touch Panel System  71   a ) 
     Illustrated in (a) and (b) of  FIG. 34  is a schematic view for describing an operation method of the touch panel system  71   a . As described above with reference to  FIG. 43 , there is the problem that the phantom noise NZ generates in an area between the circumscribing lines L 1  and L 2  that circumscribe the hand placing region HDR along the sense lines SL 1  to SLM and which is outside the hand placing region HDR. However, when a pen signal is inputted on a sense line that does not overlap the hand placing region HDR, i.e., on a pen input position P outside the circumscribing lines L 1  and L 2  as illustrated in (a) of  FIG. 34 , this pen signal is detectable since no phantom noise NZ is generated on the sense line that the pen input position P passes, thereby having no deterioration in SNR caused by the phantom noise NZ. 
     Hence, in a case in which the hand placing region HDR and the pen input position P are in a positional relationship as illustrated in  FIG. 43 , the drive lines DL 1  to DLM and the sense lines SL 1  to SLM are switched over therebetween, to have the signal lines HL 1  to HLM in the horizontal direction function as the drive lines DL 1  to DLM and the signal lines VL 1  to VLM in the vertical direction function as the sense lines SL 1  to SLM, as illustrated in (b) of  FIG. 34 , so that the signal is detected outside the area between the circumscribing lines L 3  and L 4 . Consequently, it is possible to detect the pen signal of the pen input position P. 
     Accordingly, for example, by alternately switching over with the multiplexer  4  between a first connection state ((b) of  FIG. 34 ) and a second connection state ( FIG. 43 ) every one frame, which first connection state is a state in which the signal lines HL 1  to HLM are connected to the drive lines DL 1  to DLM of the driver  75  and the signal lines VL 1  to VLM are connected to the sense lines SL 1  to SLM of the sense amplifier  76  and the second connection state is a state in which the signal lines HL 1  to HLM are connected to the sense lines SL 1  to SLM of the sense amplifier  76  and the signal lines VL 1  to VLM are connected the drive lines DL 1  to DLM of the driver  75 , it is possible to detect the pen signal at one of timings of the first connection state and the second connection state, even if the phantom noise NZ generates due to the hand placing region HDR. Since the phantom noise NZ is generated in the other timing, the SNR of the pen signal is reduced to half. However, by alternately switching over between the first connection state and the second connection state, it is possible to detect the pen signal even if the phantom noise NZ is generated caused by the hand placing region HDR. 
     Therefore, for example, the touch panel system  71   a  (i) drives, in a first timing, the signal lines HL 1  to HLM so that the signal lines VL 1  to VLM output electric charges that correspond to the capacitances (first signal line driving step), (ii) controls, with use of the multiplexer  74 , in a second timing subsequent to the first timing, a switching of connection of the signal lines HL 1  to HLM and the signal lines VL 1  to VLM (switching step), and (iii) drives, in a third timing subsequent to the second timing, the signal lines VL 1  to VLM so that the signal lines HL 1  to HLM output the electric charges that correspond to the capacitances (second signal line driving step). 
     The capacitance value distribution calculation section  79  is configured so that a signal read out through a sense line from a capacitance disposed in a rectangle circumscribing with the hand placing region HDR, is not received. The hand placing region HDR is a region in which a hand holding the electrically conductive pen for input is placed on the touch panel; the capacitance value distribution calculation section can be configured to recognize this region by image recognition means not illustrated. Moreover, the configuration may be provided so that a user of the touch panel system  71   a  specifies the hand placing region HDR. 
     Moreover, when the switching between the drive lines and the sense lines similarly to the above is carried out in a smartphone with which no hand placing region HDR by pen input occurs, although a signal to be detected generated by touching with a finger is generated in either of the driving states, an error signal caused by the phantom noise is removable since a position in which the phantom noise is generated differs by the switching of the drive lines and the sense lines. 
     Illustrated in (a) and (b) of  FIG. 35  are schematic views for describing another operation method of the touch panel system  71   a . As illustrated in (a) of  FIG. 35 , after the vertical signal lines VL 1  to VLM are connected to the drive lines DL 1  to DLM and vertical signal lines VL 1  to VLM are driven, and the horizontal signal lines HL 1  to HLM are connected to the sense lines SL 1  to SLM, the phantom noise NZ that generates in an area between circumscribing lines L 5  and L 6  (circumscribing along a horizontal direction of a finger-touched region FR where the finger is touched) and which is outside the finger-touched region FR, is read out via the sense line together with a signal corresponding to the finger-touched region FR. Thereafter, as illustrated in (b) of  FIG. 35 , after the horizontal signal lines HL 1  to HLM are connected to the drive lines DL 1  to DLM and the horizontal signal lines HL 1  to HLM are driven, and the vertical signal lines VL 1  to VLM are connected to the sense lines SL 1  to SLM, the phantom noise NZ generated between the circumscribing lines L 7  and L 8  that circumscribe the finger-touched region FR along the vertical direction, is read out via a sense line together with a signal corresponding to the finger-touched region FR. 
     The phantom noise NZ generated between the circumscribing lines L 5  and L 6  as illustrated in (a) of  FIG. 35  and the phantom noise generated between the circumscribing lines L 7  and L 8  as illustrated in (b) of  FIG. 35  are generated randomly, unrelated to each other. Accordingly, when an AND operation is carried out with use of (i) the signal corresponding to the phantom noise NZ generated between the circumscribing lines L 5  and L 6  as in (a) of  FIG. 35 , read out via the sense line, and corresponding to the finger-touched area FR, and (ii) the signal read out via the sense line, corresponding to the phantom noise NZ generated between the circumscribing lines L 7  and L 8  as in (b) of  FIG. 35 , read out via the sense line, and corresponding to the finger-touched area FR, it is possible to cancel the phantom noise NZ generated between the circumscribing lines L 5  and L 6  with the phantom noise NZ generated between the circumscribing lines L 7  and L 8 . 
     Embodiment 19 
     Configuration of Touch Panel System  71   b    
       FIG. 36  is a block diagram illustrating a configuration of a touch panel system  71   b  according to Embodiment 19.  FIG. 37  is a circuit diagram illustrating a configuration of a connection switching circuit (multiplexers  74   a  and  74   b ) between (a) signal lines HL 1  to HLM and VL 1  to VLM connected to a touch panel  73 , and (b) drive lines DL 1  to DLM connected to drivers  75   a  and  75   b  and sense lines SL 1  to SLM connected to sense amplifiers  76   a  and  76   b . Components identical to those described above are provided with identical reference signs, and detailed descriptions thereof are not repetitively provided. 
     The touch panel system  71   b  includes a capacitance value distribution detection circuit  72   a . The capacitance value distribution detection circuit  72   a  includes two multiplexers,  74   a  and  74   b . The multiplexer  74   a  is connected to the touch panel  73  in a fixed manner, via the signal lines HL 1  to HLM. The capacitance value distribution detection circuit  72   a  includes the driver  75   a  and the sense amplifier  76   a . The driver  75   a  is connected to the multiplexer  74   a  via the drive lines DL 1  to DLM, and the sense amplifier  76   a  is connected to the multiplexer  74   a  via the sense lines SL 1  to SLM. 
     The capacitance value distribution detection circuit  72   a  includes an A/D converter  78   a  and a timing generator  77   a . The A/D converter  78   a  converts an output from the sense amplifier  76   a  from analog to digital, and supplies this converted output to a capacitance value distribution calculation section  79 . The timing generator  77   a  generates (i) a signal specifying an operation of the driver  75   a , (ii) a signal specifying an operation of the sense amplifier  76   a , and (iii) a signal specifying an operation of the A/D converter  78   a , and supplies these signals to the driver  75   a , the sense amplifier  76   a , and the A/D converter  78   a , respectively. The timing generator  77   a  supplies a signal for controlling the multiplexer  74   a , via a control line CLa. 
     The multiplexer  74   b  is connected to the touch panel  73  in a fixed manner via the signal lines VL 1  to VLM. The capacitance value distribution detection circuit  72   a  includes the driver  75   b  and the sense amplifier  76   b . The driver  75   b  is connected to the multiplexer  74   b  via the drive lines DL 1  to DLM and the sense amplifier  76   b  is connected to the multiplexer  74   b  via the sense lines SL 1  to SLM. 
     The capacitance value distribution detection circuit  72   a  includes an A/D converter  78   b  and a timing generator  77   b . The A/D converter  78   b  converts an output from the sense amplifier  76   b  from analog to digital, and supplies this converted output to the capacitance value distribution calculation section  79 . The timing generator  77   b  generates (i) a signal specifying an operation of the driver  75   b , (ii) a signal specifying an operation of the sense amplifier  76   b , and (iii) a signal specifying an operation of the A/D converter  78   b , and supplies these signals to the driver  75   b , the sense amplifier  76   b , and the A/D converter  78   b , respectively. The timing generator  77   b  supplies a signal for controlling the multiplexer  74   b , via the control line CLb. 
     The capacitance distribution detection circuit  72   a  includes a sync signal generation section  81 . The sync signal generation section  81  generates a sync signal for the timing generators  77   a  and  77   b  to control the multiplexers  74   a  and  74   b  to cause the switching over between (a) a first connection state in which the signal lines HL 1  to HLM are connected to the driver  75   a  and the signal lines VL 1  to VLM are connected to the sense amplifier  76   b  and (b) a second connection state in which the signal lines HL 1  to HLM are connected to the sense amplifier  76   a  and the signal lines VL 1  to VLM are connected to the driver  75   b , and supplies the generated sync signal to the timing generators  77   a  and  77   b.    
       FIG. 38  is a circuit diagram illustrating a configuration of the multiplexers  74   a  and  74   b  provided in the capacitance value distribution detection circuit  72   a  of the touch panel system  71   b . The multiplexer  74   a  includes two CMOS switches SW 5  and SW 6  that are connected in series. A signal from the timing generator  77   a  via the control line CLa is inputted from (i) one end of the CMOS switch SW 5  opposite of the CMOS switch SW 6 , (ii) one end of the CMOS switch SW 6  opposite of the CMOS switch SW 5 , and (iii) a terminal input of a reverser inv. The reverser inv has its output be inputted between the CMOS switch SW 5  and CMOS switch SW 6 . The signal lines HL 1  to HLM are connected to the CMOS switches SW 5  and SW 6 . The drive lines DL 1  to DLM are connected to the CMOS switch SW 5 . The sense lines SL 1  to SLM are connected to the CMOS switch SW 6 . 
     (Operation of Touch Panel System  71   b ) 
     When a signal of the control line CLa is made Low, the signal lines HL 1  to HLM become connected to the drive lines DL 1  to DLM. When the signal of the control line CLa is made High, the signal lines HL 1  to HLM become connected to the sense lines SL 1  to SLM. The multiplexer  74   b  is also configured similarly to this. 
     As such, the touch panel system  71   b  includes the multiplexers  74   a  and  74   b  having similar configurations; the multiplexer  74   a  is connected to the signal lines HL 1  to HLM of the touch panel  73  in a fixed manner, and the multiplexer  74   b  is connected to the signal lines VL 1  to VLM of the touch panel  73  in a fixed manner. Furthermore, the multiplexers  74   a  and  74   b  are operated in sync, based on a sync signal generated by the sync signal generation section  81 . When the multiplexer  74   a  is connected to the driver  75   a , the multiplexer  74   b  is connected to the sense amplifier  76   b , and when the multiplexer  74   a  is connected to the sense amplifier  76   a , the multiplexer  74   b  is connected to the driver  75   b.    
     Embodiment 20 
       FIG. 39  is a block diagram illustrating a configuration of a touch panel system  71   c  according to Embodiment 20. Components identical to those described above are provided with identical reference signs, and detailed descriptions thereof are not repetitively provided. 
     The touch panel system  71   c  includes a capacitance value distribution detection circuit  72   c . The capacitance value distribution detection circuit  72   c  includes controllers  82   a  and  82   b . The controller  82   a  includes multiplexers  74   a   1  to  74   a   4 . The multiplexers  74   a   1  to  74   a   4  have configurations similar to that of the multiplexer  74   a  described above with reference to  FIG. 36  through  FIG. 38 , however is connected to a fewer number of signal lines; the multiplexer  74   a   1  is connected to signal lines HL 1  to HL(m1), the multiplexer  74   a   2  is connected to signal lines HL(m1+1) to HL(m2), the multiplexer  74   a   3  is connected to signal lines HL(m2+1) to HL(m3), and the multiplexer  74   a   4  is connected to signal lines HL(m3+1) to HLM, where 1&lt;m1&lt;m2&lt;m3&lt;M. 
     The controller  82   b  includes multiplexers  74   b   1  to  74   b   4 . The multiplexers  74   b   1  to  74   b   4  have configurations similar to that of the multiplexer  74   b  described above with reference to  FIG. 36  through  FIG. 38 , however is connected to a fewer number of signal lines; the multiplexer  74   b   1  is connected to signal lines VL 1  to VL(k1), the multiplexer  74   b   2  is connected to signal lines VL(k1+1) to VL(k2), the multiplexer  74   b   3  is connected to signal lines VL(k2+1) to VL(k3), and the multiplexer  74   b   4  is connected to signal lines VL(k3+1) to VLM, where 1&lt;k1&lt;k2&lt;k3&lt;M. 
     The multiplexers  74   a   1  to  74   a   4  and the multiplexers  74   b   1  to  74   b   4  each include respective drivers, sense amplifiers, timing generators, and ADC, and operate in sync based on a sync signal generated by a sync signal generation section. The controllers  82   a  and  82   b  may be fabricated as an integrated circuit (IC). 
     In the touch panel system  71   c , control is carried out to switch between (a) a first connection state in which the signal lines HL 1  to HL(m1), the signal lines HL(m1+1) to HL(m2), the signal lines HL(m2+1) to HL(m3), and the signal lines HL(m3+1) to HLM are connected to a driver and the signal lines VL 1  to VL(k1), the signal lines VL(k1+1) to VL(k2), the signal lines VL(k2+1) to VL(k3), and the signal lines VL(k3+1) to VLM are connected to a sense amplifier, and (b) a second connection state in which the signal lines HL 1  to HL(m1), the signal lines HL(m1+1) to HL(m2), the signal lines HL(m2+1) to HL(m3), and the signal lines HL(m3+1) to HLM are connected to a sense amplifier and the signal lines VL 1  to VL(k1), the signal lines VL(k1+1) to VL(k2), the signal lines VL(k2+1) to VL(k3), and the signal lines VL(k3+1) to VLM are connected to a driver. 
     Embodiment 21 
       FIG. 40  is a block diagram illustrating a configuration of a touch panel system  71   d  according to Embodiment 21. Components identical to those described above are provided with identical reference signs, and detailed descriptions thereof are not repetitively provided. 
     A sense amplifier of the touch panel system  71   d  includes a configuration to read out a signal from adjacent sense lines upon subtraction, allowing for canceling noise from a liquid crystal panel and the like and improve SNR. 
     The touch panel system  71   d  includes a capacitance value distribution detection circuit  72   d . The capacitance value distribution detection circuit  72   d  includes controllers  83   a  and  83   b . The controller  83   a  includes multiplexers  84   a   1  to  84   a   4 . The multiplexers  84   a   1  to  84   a   4  have configurations similar to that of the multiplexer  74   a  described above with reference to  FIG. 36  to  FIG. 38 , however is connected to a fewer number of signal lines, and adjacent multiplexers share a signal line that is disposed on their common boundary. 
     The multiplexer  84   a   1  is connected to signal lines HL 1  to HL(m1), the multiplexer  84   a   2  is connected to signal lines HL(m1) to HL(m2), the multiplexer  84   a   3  is connected to signal lines HL(m2) to HL(m3), and the multiplexer  84   a   4  is connected to signal lines HL(m3) to HLM, where 1&lt;m1&lt;m2&lt;m3&lt;M. As such, adjacent multiplexers  84   a   1  and  84   a   2  share the signal line HL(m1) disposed on their common boundary, adjacent multiplexers  84   a   2  and  84   a   3  share the signal line HL(m2) disposed on their common boundary, and adjacent multiplexers  84   a   3  and  84   a   4  share the signal line HL(m3) disposed on their common boundary. 
     The controller  83   b  includes multiplexers  84   b   1  to  84   b   4 . The multiplexers  84   b   1  to  84   b   4  have configurations similar to that of the multiplexer  74   b  described above with reference to  FIG. 36  to  FIG. 38 , however is connected to a fewer number of signal lines, and adjacent multiplexers share a signal line disposed on their common boundary. 
     The multiplexer  84   b   1  is connected to signal lines VL 1  to VL(k1), the multiplexer  84   b   2  is connected to signal lines VL(k1) to VL(k2), the multiplexer  84   b   3  is connected to signal lines VL(k2) to VL(k3), and the multiplexer  84   b   4  is connected to signal lines VL(k3) to VLM, where 1&lt;k1&lt;k2&lt;k3&lt;M. As such, adjacent multiplexers  84   b   1  and  84   b   2  share the signal line VL(k1) disposed on their common boundary, adjacent multiplexers  84   b   2  and  84   b   3  share the signal line VL(k2) disposed on their common boundary, and adjacent multiplexers  84   b   3  and  84   b   4  share the signal line VL(k3) disposed on their common boundary. 
     The multiplexers  84   a   1  to  84   a   4  and the multiplexers  84   b   1  to  84   b   4  each include respective drivers, sense amplifiers, timing generators, and ADC, and operate in sync based on a sync signal generated by a sync signal generation section. The controllers  83   a  and  83   b  may be fabricated as an integral circuit (IC). 
     As such, in a case in which the sense amplifier is configured so as to read out a signal from adjacent sense lines upon subtraction, to allow for canceling noise from the liquid crystal panel and the like and improve SNR, by sharing a signal line disposed on a common boundary of adjacent multiplexers, it is possible to continuously carry out differential read-out of sense lines disposed on the boundary of the sense lines corresponding to the adjacent multiplexers in a manner exceeding that boundary. 
     The touch panel systems according to Embodiments 18 to 21 may be constituted in a media blackboard (information input/output device) capable of receiving input by being handwritten thereon while a plurality of persons touch the blackboard, by superposing the touch panel system with a liquid crystal display panel or by building the touch panel system inside a liquid crystal display panel. 
     The present invention can also be expressed as below: 
     [1] A touch panel system including: a touch panel including a plurality of sensors; and a touch panel controller for receiving signals from the sensors so as to read data, the plurality of sensors including (i) a main sensor for inputting a signal in response to a touch operation performed by a user and (ii) a sub sensor provided on a surface of the touch panel on which surface the main sensor is provided, and the touch panel controller including subtracting means for (i) receiving a signal supplied from the main sensor and a signal supplied from the sub sensor and (ii) subtracting, from the signal supplied from the main sensor, the signal supplied from the sub sensor. 
     [2] The touch panel system described in [1], wherein the sub sensor is not touched by the user in the touch operation, and detects a noise generated in the sensor. 
     [3] The touch panel system described in [1] or [2], wherein the main sensor and the sub sensor are provided so as to be adjacent to each other. 
     [4] A touch panel system including: a display device; a touch panel which is provided on an upper section or the like of a display screen of the display device and which includes a plurality of sensor groups including sensors arranged in a matrix; and a touch panel controller for receiving signals from the sensor groups so as to read data, the sensor groups including (i) a main sensor group for inputting a signal in response to a touch operation performed by a user and (ii) a sub sensor group provided on a surface of the touch panel on which surface the main sensor group is provided, and the touch panel controller including subtracting means for (i) receiving a signal supplied from the main sensor group and a signal supplied from the sub sensor group and (ii) subtracting, from the signal supplied from the main sensor group, the signal supplied from the sub sensor group. 
     [5] The touch panel system described in [4], wherein the sub sensor group is not touched by the user in the touch operation, and detects a noise generated in the sensor group. 
     [6] The touch panel system described in [4] or [5], wherein the main sensor group and the sub sensor group are provided so as to be adjacent to each other. 
     [7] The touch panel system described in any of [1] through [6], wherein the display device is a liquid crystal display, a plasma display, an organic electroluminescence display, or a field emission display. 
     [8] An electronic device including a touch panel system described in any of [1] through [7]. 
     According to each of the above configurations, the touch panel includes the main sensor section for detecting a touch operation and the sub sensor section for detecting a noise, and a difference between a signal of the main sensor section and a signal of the sub sensor section is found by the subtracting section. This removes a noise signal from the output signal which is supplied from the main sensor section, thereby extracting a signal derived from the touch operation itself, which signal is generated in response to the touch operation. Therefore, it is possible to reliably remove (cancel) a wide variety of noises reflected in the touch panel. Thus, a noise component which is the subject of removal is not limited to an AC signal component in a signal including noises, but is all noise components reflected in the touch panel. Namely, it is possible to provide a touch panel system and an electronic device each of which is capable of canceling basically all noise components. 
     Also, the present invention can be described as below: 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the main sensor section is provided with a plurality of sense lines; the sub sensor section is provided with a sub sense line extending along a direction in which the sense lines extend; the subtracting section finds a first difference which is expressed by (Sn+1)−Sn, the first difference corresponding to a difference between (i) a signal of a sense line Sn which is selected from the plurality of sense lines and (ii) a signal of a sense line Sn+1, which is one of two sense lines adjacent to the sense line Sn, the two sense lines being the sense line Sn+1 and a sense line Sn−1 each of which is included in the plurality of sense lines; the subtracting section finds a second difference which is expressed by Sn−(Sn−1), the second difference corresponding to a difference between (i) the signal of the sense line Sn and (ii) a signal of the sense line Sn−1, which is the other one of the two sense lines; the subtracting section finds a third difference, the third difference corresponding to a difference between (i) a signal of the sub sense line and (ii) a signal of a sense line adjacent to the sub sense line which sense line is included in the plurality of sense lines; and the touch panel controller includes an adding section for adding up the first difference, the second difference, and the third difference. 
     According to the above configuration, the subtracting section obtains a difference signal value between sense lines adjacent to each other. Namely, a difference is found between the adjacent sense lines, which have a higher correlation in terms of noise. Furthermore, from an output signal supplied from each sense line, a signal (noise signal) of the sub sense line is removed. This makes it possible to remove a noise more reliably. 
     The touch panel system of any of the embodiments of the present invention may be configured to include: drive lines provided so as to intersect the sense lines and the sub sense line; a drive line driving circuit for driving the drive lines by use of orthogonal sequences or M sequences; capacitances being formed (i) between the sense lines and the drive lines and (ii) between the sub sense line and the drive lines; and a calculation section for finding capacitance values of the respective capacitances by (i) reading output signals from the sense lines and the sub sense line and by (ii) finding inner products of the output signals and the code sequences for driving the drive lines in parallel. 
     According to the above configuration, the touch panel is driven by the orthogonal sequence driving method. Consequently, a signal of the capacitance is multiplied by a code length (i.e., multiplied by N). Therefore, a signal strength of the capacitance is increased, regardless of the number of drive lines. Further, provided that a necessary signal strength is merely equal to that of the conventional method, it is possible to reduce the number of times that the drive lines should be driven, thereby enabling to reduce electric power consumption. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the subtracting section includes a first analog-to-digital converting section for converting, into digital signals, analog signals supplied from the sense lines and the sub sense line to the subtracting section; and the subtracting section uses, in order to find the first difference, the second difference, and the third difference, the digital signals obtained by the first analog-to-digital converting section. 
     According to the above configuration, it is possible to remove a noise by (ii) converting, into digital signals, analog signals outputted by the touch panel, and thereafter by (ii) performing subtracting operations. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the subtracting section includes a second analog-to-digital converting section for converting, into digital signals, analog signals supplied from the sense lines and the sub sense line to the subtracting section; and the second analog-to-digital converting section converts, into a digital signal, each of the first difference, the second difference, and the third difference that are found by the subtracting section with use of the analog signals. 
     According to the above configuration, it is possible to remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel, without converting the analog signals into digital signals, and thereafter by (ii) converting the resulting signal into a digital signal. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the subtracting section includes a total differential amplifier for finding the first difference, the second difference, and the third difference with use of the analog signals. 
     According to the above configuration, it is possible to remove a noise by (i) causing the total differential amplifier to perform subtracting operations on analog signals without converting the analog signals into digital signals which analog signals are outputted by the touch panel, and thereafter by (ii) converting the resulting signal into a digital signal. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the total differential amplifier has an input common-mode voltage range which is rail to rail. 
     The above configuration includes the total differential amplifier capable of rail-to-rail operation. Therefore, the total differential amplifier is operable in a voltage range from a power source voltage (Vdd) to GND. Accordingly, an output signal from the total differential amplifier is free from a problem of output saturation. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the adding section adds the first difference, the second difference, and the third difference in such a manner that individual adding operations are carried out in the order of increasing distance between a sense line involved in a certain adding operation and the sub-sense line, and the adding section uses a result of one adding operation in a next adding operation. 
     According to the above configuration, the adding section sequentially performs adding operations in the order of increasing distance between a sense line involved in a certain adding operation and the sub-sense line, while utilizing the results of the adding operations. This makes it possible to increase a speed at which an adding operation is performed. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the sub sensor section is configured not to detect a touch operation performed with respect to the touch panel. 
     According to the above configuration, since a signal generated by a touch operation is not detected by the sub sensor section, an output signal from the sub sensor section does not include the signal generated by the touch operation. This prevents a case where the signal value derived from the touch operation is reduced by the subtracting operation performed by the subtracting section. Namely, a noise component is removed without reducing the signal detected by the main sensor section, which signal is generated in response to the touch operation. This makes it possible to further enhance detection sensitivity for a touch operation. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the sub sensor section is provided in a region of the touch panel in which region no touch operation is performed. 
     According to the above configuration, the sub sensor section is provided so as not to be positioned in a region (touched region) where a user performs a touch operation. Therefore, on the sub sensor section, the user would not perform a touch operation. Accordingly, although the sub sensor section detects a noise reflected in the touch panel, the sub sensor section does not detect a signal generated by a touch operation. This can reliably prevent the sub sensor section from detecting a touch operation. 
     Namely, since the above configuration does not allow the sub sensor section to detect a signal generated by a touch operation, an output signal supplied from the sub sensor section does not include the signal generated by the touch operation. This prevents a case where the signal value derived from the touch operation is reduced by the subtracting operation performed by the subtracting section. Namely, a noise component is removed without reducing the signal generated by the touch operation and detected by the main sensor section. This makes it possible to further enhance detection sensitivity for a touch operation. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the main sensor section and the sub sensor section are provided so as to be adjacent to each other. 
     According to the above configuration, the main sensor section and the sub sensor section are arranged so that a distance therebetween is shortest. Namely, the main sensor section and the sub sensor section are provided under substantially the same condition. Therefore, a value of a noise signal included in an output signal from the sub sensor section can be regarded as being the same as that of a noise signal included in an output signal from the main sensor section. This can more reliably remove, by the subtracting operation performed by the subtracting section, a noise component reflected in the touch panel. This makes it possible to further enhance detection sensitivity for a touch operation. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the main sensor section is made of one main sensor. 
     According to the above configuration, the main sensor section is made of a single main sensor. This can provide a touch panel system capable of determining the presence or absence of a touch operation. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the main sensor section is made of a plurality of main sensors arranged in a matrix. 
     According to the above configuration, the main sensor section is made of a plurality of main sensors arranged in a matrix. This can provide a touch panel system capable of determining (i) the presence or absence of a touch operation and (ii) a touched position. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured so as to include: drive lines provided so as to intersect the sense lines; a drive line driving circuit for driving the drive lines in parallel; capacitances being formed between the sense lines and the drive lines; and a decoding section for decoding values of differences between the capacitances in the direction in which the drive lines extend which differences are found by the subtracting section as the differences in signal between the respective pairs of the sense lines adjacent to each other, based on output signals that the subtracting section receives from the sense lines. 
     According to the above configuration, the touch panel is parallel driven, and the decoding section decodes the difference values of the capacitances which difference values are found by the subtracting section. Consequently, signals of the capacitances are multiplied by a code length (i.e., multiplied by N). Therefore, signal strengths of the capacitances are increased, regardless of the number of drive lines. Further, provided that necessary signal strengths are merely equal to those of a conventional method, it is possible to reduce the number of times that the drive lines should be driven. This makes it possible to reduce electric power consumption. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the subtracting section includes a third analog-to-digital converting section for converting, into digital signals, analog signals supplied from the sense lines to the subtracting section; and the subtracting section uses, in order to find the differences in signal between the respective pairs of the sense lines adjacent to each other, the digital signals obtained by the third analog-to-digital converting section. 
     According to the above configuration, it is possible to remove a noise by (ii) converting, into digital signals, analog signals outputted by the touch panel, and thereafter by (ii) performing subtracting operations. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the subtracting section includes a fourth analog-to-digital converting section for converting, into digital signals, analog signals supplied from the sense lines to the subtracting section; and the fourth analog-to-digital converting section converts, into digital signals, the differences in signal between the respective pairs of the sense lines adjacent to each other, the differences being found by the subtracting section with use of the analog signals. 
     According to the above configuration, it is possible to remove a noise by (i) performing subtracting operations on analog signals outputted by the touch panel, without converting the analog signals into digital signals, and thereafter by (ii) converting the resulting signal into a digital signal. 
     The touch panel system of any of the embodiments of the present invention may be configured such that: the subtracting section includes a total differential amplifier for finding, with use of the analog signals, the differences in signal between the respective pairs of the sense lines adjacent to each other. 
     According to the above configuration, it is possible to remove a noise by (i) causing the total differential amplifier to perform subtracting operations on analog signals without converting the analog signals into digital signals which analog signals are outputted by the touch panel, and thereafter by (ii) converting the resulting signal into a digital signal. 
     The touch panel system of any of the embodiments of the present invention may be configured so as to include: a non-touch operation information storage section for storing a first distribution of differences between the capacitances which differences are decoded by the decoding section when no touch operation is performed; and a calibration section for subtracting (i) the first distribution stored in the non-touch operation information storage section from (ii) a second distribution of differences between the capacitances which differences are decoded by the decoding section when a touch operation is performed, so as to calibrate the second distribution. 
     According to the above configuration, the non-touch operation information storage section stores the first distribution of the differences between the capacitances which differences are decoded by the decoding section when no touch operation is performed. Further, the calibration section subtracts (i) the first distribution stored in the non-touch operation information storage section from (ii) the second distribution of the differences between the capacitances which differences are found when a touch operation is performed. Namely, the calibration section performs the following calculation: (the second distribution of the differences between the capacitances which differences are found when the touch operation is performed)−(the first distribution of the differences between the capacitances which differences are found when no touch operation is performed). This can cancel an offset inherent in the touch panel. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured so as to include: a judging section for determining the presence or absence of a touch operation based on a comparison of (i) the differences in signal between the respective pairs of the sense lines adjacent to each other which differences are found by the subtracting section and (ii) positive and negative threshold values. 
     According to the above configuration, the judging section determines the presence or absence of a touch operation based on the differences in signal between the respective pairs the sense lines adjacent to each other from which differences a noise signal has been removed. This makes it possible to accurately determine the presence or absence of the touch operation. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the judging section creates, based on the comparison of (i) the differences in signal between the respective pairs of the sense lines adjacent to each other which differences are found by the subtracting section and (ii) the positive and negative threshold values, an increase and decrease table which indicates, in ternary, a distribution of differences between signals of the sense lines, and the judging section converts the increase and decrease table into a binary image, so as to extract touch information therefrom. 
     According to the above configuration, the differences in signal between the respective pairs of the sense lines adjacent to each other from which differences a noise signal has been removed are inputted to the judging section. Based on the comparison of (i) the differences in signal between the respective pairs of the sense lines adjacent to each other and (ii) the positive and negative threshold values stored in the judging section, the judging section creates the increase and decrease table indicating, in ternary, the distribution of the differences in signal between the respective pairs of the sense lines adjacent to each other. Further, the judging section binarizes the increase and decrease table, so that the increase and decrease table is converted into the binary image. Consequently, from the binary image thus converted, candidates of a touched position are extracted. Thus, by recognizing the touch information (the size, position, etc. of the touch) based on the binary image, it is possible not only to determine the presence or absence of the touch operation but also to recognize the touch information more accurately. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured to further include a display device, the touch panel being provided to a front surface of the display device. 
     According to the above configuration, since the touch panel is provided on the front surface of the display device, it is possible to reliably remove a noise generated in the display device. 
     Preferably, the touch panel system of any of the embodiments of the present invention is configured such that: the display device is a liquid crystal display, a plasma display, an organic electroluminescence display, or a field emission display. 
     According to the above configuration, the display device is made of any of various kinds of displays used in generally-used electronic devices. Therefore, it is possible to provide a touch panel system having a great versatility. 
     A capacitance value distribution detection method according to the present invention is a method of detecting capacitance value distribution, to detect a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines, the method including: driving the first signal lines in a first timing, to output from the second signal lines electric charges that correspond to the capacitances; controlling, in a second timing subsequent to the first timing, a switching of connections of the first signal lines with that of the second signal lines; and driving the second signal lines in a third timing subsequent to the second timing, to output from the first signal lines the electric charges that correspond to the capacitances. 
     According to this feature, in a first timing, first signal lines are driven to output from second signal lines electric charges that correspond to the capacitances, in a second timing subsequent to the first timing, switching of connection of the first and second signal lines are controlled, and in a third timing subsequent to the second timing, the second signal lines are driven to output from the first signal lines the electric charges that correspond to the capacitances. Hence, it is possible to output the electric charges corresponding to the capacitances from both of the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hand, fingers or the like and is superposed on a signal of a sense line. 
     A capacitance value distribution detection circuit according to the present invention is a capacitance value distribution detection circuit that detects a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines, the capacitance value distribution detection circuit including: a multiplexer connected to the plurality of first signal lines and the plurality of second signal lines; a driver connected to the multiplexer; and a sense amplifier connected to the multiplexer; the multiplexer switching a connection state between a first connection state in which the first signal lines are connected to the driver and the second signal lines are connected to the sense amplifier and a second connection state in which the first signal lines are connected to the sense amplifier and the second signal lines are connected to the driver. 
     With this feature, it is possible to switch between a first connection state which connects the first signal lines with the driver and connects the second signal lines with the sense amplifier and a second connection state which connects the first signal lines with the sense amplifier and connects the second signal lines with the driver. This allows for outputting the electric charges corresponding to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of a sense line. 
     Another capacitance value distribution detection circuit according to the present invention is a capacitance value distribution detection circuit that detects a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines, the capacitance value distribution detection circuit including: a first multiplexer connected to the first signal lines; a first driver connected to the first multiplexer; a first sense amplifier connected to the first multiplexer; a second multiplexer connected to the second signal lines; a second driver connected to the second multiplexer; a second sense amplifier connected to the second multiplexer; and a control circuit that controls the first multiplexer and the second multiplexer so that a connection state is switchable between a first connection state in which the first signal lines are connected to the first driver and the second signal lines are connected to the second sense amplifier, and a second connection state in which the first signal lines are connected to the first sense amplifier and the second signal lines are connected to the second driver. 
     With this feature, it is possible to switch over between a first connection state which connects the first signal lines with the first driver and connects the second signal lines with the second sense amplifier, and a second connection state which connects the first signal lines with the first sense amplifier and connects the second signal lines with the second driver. This allows for outputting the electric charges corresponding to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of the sense line. 
     Yet another capacitance value distribution detection circuit according to the present invention is a capacitance value distribution detection circuit that detects a distribution of capacitance values of a plurality of capacitances that are each formed on intersections of a plurality of first signal lines with a plurality of second signal lines; the capacitance value distribution detection circuit including: a first multiplexer connected to a portion of the plurality of first signal lines; a first driver connected to the first multiplexer; a first sense amplifier connected to the first multiplexer; a second multiplexer connected to another portion of the plurality of first signal lines; a second driver connected to the second multiplexer; a second sense amplifier connected to the second multiplexer; a third multiplexer connected to a portion of the plurality of second signal lines; a third driver connected to the third multiplexer; a third sense amplifier connected to the third multiplexer; a fourth multiplexer connected to another portion of the plurality of second signal lines; a fourth driver connected to the fourth multiplexer; a fourth sense amplifier connected to the fourth multiplexer; and a control circuit that controls the first to fourth multiplexers so that a connection state is switchable between (a) a first connection state in which the portion of the first signal lines is connected to the first driver, the another portion of the first signal lines is connected to the second driver, the portion of the second signal lines is connected to the third sense amplifier, and the another portion of the second signal lines is connected to the fourth sense amplifier, and (b) a second connection state in which the portion of the first signal lines is connected to the first sense amplifier, the another portion of the first signal lines is connected to the second sense amplifier, the portion of the second signal lines is connected to the third driver, and the another portion of the second signal lines is connected to the fourth driver. 
     With this feature, it is possible to switch between (a) a first connection state in which a portion of the first signal lines is connected to the first driver, another portion of the first signal lines is connected to the second driver, a portion of the second signal lines is connected to the third sense amplifier, and another portion of the second signal lines is connected to the fourth sense amplifier, and (b) a second connection state in which a portion of the first signal lines is connected to the first sense amplifier, another portion of the first signal lines is connected to the second sense amplifier, a portion of the second signal lines is connected to the third driver, and another portion of the second signal lines is connected to the fourth driver. 
     This allows for outputting the electric charges corresponding to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of the sense line. 
     A touch panel system according to the present invention includes: the capacitance value distribution detection circuit according to the present invention; and a touch panel including the plurality of first signal lines, the plurality of second signal lines, and the plurality of capacitances. 
     An information input/output device according to the present invention includes: the touch panel system according to the present invention; and a display panel (i) being superposed on a touch panel provided in the touch panel system or (ii) having the touch panel be built therein. 
     A method according to the present invention of detecting a capacitance value distribution drives first signal lines in a first timing to output from second signal lines electric charges that correspond to the capacitances, controls, in a second timing subsequent to the first timing, switching of connection of the first and second signal lines, and drives the second signal lines in a third timing subsequent to the second timing, to output from the first signal lines the electric charges that correspond to the capacitances. This allows for outputting the electric charges that correspond to the capacitances from both the first signal lines and the second signal lines. As a result, it is possible to eliminate the effect caused by electromagnetic noise that is inputted into the touch panel via the hands, fingers and the like and is superposed on the signal of the sense line. 
     With the capacitance value distribution detection method according to the present embodiment, it is preferable that the plurality of first signal lines, the plurality of second signal lines, and the plurality of capacitances constitute a touch panel, the touch panel being of a size allowing for a hand that holds a pen for input to be placed thereon. 
     According to the configuration, it is possible to eliminate an effect caused by electromagnetic noise inputted into a touch panel via a hand touched on the touch panel while holding a pen for input, and which electromagnetic noise is superposed on a signal of a sense line. 
     With the capacitance value distribution detection circuit according to the present embodiment, it is preferable that the plurality of first signal lines, the plurality of second signal lines, and the plurality of capacitances constitute a touch panel, the touch panel being of a size allowing for a hand that holds a pen for input to be placed thereon. 
     According to the configuration, it is possible to eliminate an effect caused by electromagnetic noise inputted into a touch panel via a hand touched on the touch panel while holding a pen for input, and which electromagnetic noise is superposed on a signal of a sense line. 
     With yet another capacitance value distribution detection circuit according to the present embodiment, it is preferable that the portion of the plurality of first signal lines and the another portion of the plurality of first signal lines share a signal line disposed on their common boundary, and the portion of the plurality of second signal lines and the another portion of the plurality of second signal lines share a signal line disposed on their common boundary. 
     With the foregoing configuration, it is possible to continuously carry out differential read-out of a sense line disposed on a common boundary of portions of adjacent multiplexers, exceeding the common boundary. 
     With a touch panel system according to the present embodiment, it is preferable that the capacitance value distribution detection circuit detects a distribution of capacitance values in accordance with an input with use of a pen. 
     With an information input/output device according to the present embodiment, it is preferable that the capacitance value distribution detection circuit detects a distribution of capacitance values in accordance with an input with use of a pen. 
     The present invention is not limited to the description of the embodiments above, but may be altered by a skilled person within the scope of the claims. An embodiment based on a proper combination of technical means disclosed in different embodiments is encompassed in the technical scope of the present invention. Namely, the embodiments above are just examples in all respects, and provide no limitations. The scope of the present invention is indicated by the claims, rather than by the descriptions of the embodiments. Any meanings equivalent to the claims and all modifications made in the scope of the claims are included within the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to various kinds of electronic devices including touch panels, for example, to televisions, personal computers, mobile phones, digital cameras, portable game devices, electronic photo frames, personal digital assistants, electronic books, home electronic appliances, ticket vending machines, automatic teller machines, and car navigation systems. 
     The present invention is applicable to a capacitance value distribution detection method, a capacitance value distribution detection circuit, a touch panel system, and an information input/output device, each of which detects a distribution of capacitance values of a plurality of capacitances each formed on intersections of a plurality of first signal lines with a plurality of second signal lines. 
     Moreover, the present invention can be used in a touch panel system including a large-sized touch panel in which a hand placing region would occur when entering with use of a pen, for example, a media blackboard, a tablet terminal, and the like, which is capable of receiving entry via handwriting on the blackboard by a plurality of persons. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Touch panel system 
               1   a  Touch panel system 
               1   b  Touch panel system 
               1   c  Touch panel system 
               1   d  Touch panel system 
               1   e  Touch panel system 
               1   f  Touch panel system 
               1   g  Touch panel system 
               1   h  Touch panel system 
               1   i  Touch panel system 
               1   j  Touch panel system 
               1   k  Touch panel system 
               1   m  Touch panel system 
               1   n  Touch panel system 
               1   o  Touch panel system 
               2  Display device 
               3  Touch panel 
               3   a  Touch panel 
               3   b  Touch panel 
               3   c  Touch panel 
               4  Touch panel controller 
               31  Main sensor (main sensor section) 
               31   a  Main sensor group (main sensor section) 
               31   b  Main sensor group (sensor section) 
               32  Sub sensor (sub sensor section) 
               32   a  Sub sensor group (sub sensor section) 
               33  Sense line 
               34  Sub sense line 
               35  Drive line 
               41  Subtracting section 
               41   a  Subtracting section 
               46  Adding section 
               47  Electric charge integrator (calculation section) 
               48  Analog-to-digital converting section (first analog-to-digital converting section, second analog-to-digital converting section) 
               48   a  Analog-to-digital converting section (third analog-to-digital converting section, fourth analog-to-digital converting section) 
               49  Differential amplifier 
               50  Total differential amplifier 
               58  Decoding section 
               59  Judging section 
               61  Non-touch operation information storage section 
               62  Calibration section 
               71   a  Touch panel system 
               71   b  Touch panel system 
               71   c  Touch panel system 
               72  Capacitance value distribution detection circuit 
               73  Touch panel 
             HL 1 -HLM Signal line (first signal line) 
             VL 1 -VLM Signal line (second signal line) 
             C 11 -CMM Capacitance 
             DL 1 -DLM Drive line 
             SL 1 -SLM Sense line