Abstract:
Disclosed herein is an indicator position detecting device that reduces unwanted radiation from a sensor section, while being capable of robustly charging a pen-type position indicator with the sensor section, without requiring reduction in area size of a display region and a detecting region of the sensor section even when the overall device size is reduced. The sensor section has an X-axis direction loop coil group and a Y-axis direction loop coil group disposed in intersecting directions. When a transmission signal is supplied to loop coils of at least one of the X-axis direction loop coil group and the Y-axis direction loop coil group, a control circuit controls a selecting circuit so as not to supply the transmission signal to a determined number of loop coils disposed in at least one peripheral region of the sensor section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. 119(a) to Japanese Patent Application No. 2012-163202, filed Jul. 24, 2012, which is incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an indicator position detecting device including an indicated position detecting sensor of an electromagnetic induction system, and particularly to the control of loop coils formed as the indicated position detecting sensor. 
     2. Description of the Related Art 
     A position input device of an electromagnetic induction system has recently been used as an input device for a tablet type PC (personal computer) or the like. The position input device includes a position indicator in the shape of a pen (pen type position indicator) and an indicator position detecting device having an input surface on which pointing operation and the inputting of characters, figures, and the like are performed using the pen type position indicator. The pen type position indicator has a resonance circuit including a coil and a capacitor. On the other hand, the indicator position detecting device has an indicated position detecting sensor (position detecting coils), in which an X-axis direction loop coil group formed by disposing a plurality of loop coils in a horizontal direction (X-axis direction) and a Y-axis direction loop coil group formed by disposing a plurality of loop coils in a vertical direction (Y-axis direction) are laminated. 
     As an example of detecting a position indicated by the pen type position indicator on the indicator position detecting device, one loop coil is selected from the plurality of loop coils forming the indicated position detecting sensor in predetermined order, and a transmission signal is sent out from the selected loop coil to the pen type position indicator. The capacitor of the pen type position indicator is thereby charged. Next, the loop coil used for the transmission is connected to a receiving circuit to receive a signal transmitted from the resonance circuit of the pen type position indicator. Such signal transmission and reception is performed while the loop coils are sequentially selected, whereby the position indicated by the pen type position indicator can be detected on the indicator position detecting device. 
     The detection of the position indicated by the pen type position indicator on the indicator position detecting device is described in more detail as follows. First, (1) in order to detect where the pen type indicator is on the indicated position detecting sensor, a global scan, which sequentially selects all of the loop coils and detects the position indicated by the pen type position indicator, is performed to identify roughly the indicated position on the indicated position detecting sensor. Next, (2) a sector scan, which selects only a predetermined number of loop coils around the roughly identified position in order and performs signal transmission and reception, is performed to identify the position indicated by the pen type position indicator accurately. Thus, the position indicated by the pen type position indicator on the indicated position detecting sensor can be detected. Incidentally, various inventions have been made for the position input device of the electromagnetic induction system, and Japanese Patent Laid-Open No. 2002-244806, for example, describes details of an example of configuration of the position input device and the like. 
     Such a position input device of the electromagnetic induction system is not only used as an external input device of a personal computer or the like but also used as an input device of a tablet type PC as described above or an input device of a high-functionality portable telephone terminal referred to as a smart phone. In this case, the position input device of the electromagnetic induction system is disposed so as to be superposed on a display element such as an LCD or the like. 
     BRIEF SUMMARY 
     European standards (European Norm) include an R&amp;TTE (Radio equipment and Telecommunications Terminal Equipment) directive, which regulates all wireless devices and the like. This R&amp;TTE directive requires that the position input device of the electromagnetic induction system also reduce unwanted radiation emitted from the indicated position detecting sensor to a predetermined signal level or lower. Accordingly, in a conventional position input device, unwanted radiation is reduced by disposing a magnetic path plate having a larger area than the area of the indicated position detecting sensor in an opposing relationship with the indicated position detecting sensor. 
     There has recently been a desire to further reduce the product size of the position input device while maintaining the areas of a display region and a position detecting region. In order to satisfy this desire, the area of the magnetic path plate needs to be substantially the same as the area of the indicated position detecting sensor, thus presenting again the problem of how to reduce unwanted radiation as described above. Accordingly, unwanted radiation may be reduced by lowering the signal level of the transmission signal supplied to each loop coil forming the indicated position detecting sensor, or shortening the time during which the transmission signal is supplied. However, when the signal level of the transmission signal supplied to the loop coils is lowered or the supply time is shortened, sufficient power cannot be supplied to the pen type position indicator, and therefore sensitivity or accuracy of indicated position detection is decreased. 
     In view of the above, according to an aspect of the present invention, an indicator position detecting device is provided that solves the problem of unwanted radiation while ensuring the charging of a pen type position indicator, without reducing the area of a display region or a position detecting region even when the product is miniaturized. 
     Means for Solving the Problems 
     In order to solve the above problems, according to an embodiment of the present invention, there is provided an indicator position detecting device including: a sensor substrate that detects a position indicated by an indicator, the sensor substrate having a plurality of first loop coils disposed in a first direction and a plurality of second loop coils disposed in a second direction intersecting the first direction; a transmission signal generating circuit that generates a transmission signal to be supplied to at least one loop coil of the first loop coils and the second loop coils to perform electromagnetic coupling with the indicator; a received signal processing circuit that receives a signal induced in at least one loop coil of the first loop coils and the second loop coils by electromagnetic coupling with the indicator, and that detects the position indicated by the indicator; a loop coil selecting circuit that selectively supplies the transmission signal generated by the transmission signal generating circuit to at least one loop coil of the first loop coils and the second loop coils; a control circuit that controls loop coil selection by the loop coil selecting circuit; and a magnetic path plate that forms a magnetic path for a magnetic flux generated by the transmission signal supplied to at least one loop coil of the first loop coils and the second loop coils, the magnetic path plate being disposed so as to be superposed on the sensor substrate; wherein when the transmission signal is supplied to loop coil(s) disposed in at least one direction among the first loop coils disposed in the first direction and the second loop coils disposed in the second direction, the control circuit controls the loop coil selecting circuit so as not to supply the transmission signal to a determined number of loop coils that are disposed in the at least one direction and that are in at least one peripheral region of the sensor substrate. 
     The indicator position detecting device according to the embodiment of the present invention includes the sensor substrate, the transmission signal generating circuit, the received signal processing circuit, the loop coil selecting circuit, and the control circuit that controls the loop coil selecting circuit. The plurality of first loop coils and the plurality of second loop coils are disposed in the intersecting directions on the sensor substrate having substantially the same area as the area of the magnetic path plate. When the transmission signal is supplied to at least one loop coil disposed in at least one direction out of the first loop coils and the second loop coils, the control circuit controls the loop coil selecting circuit so as not to supply the transmission signal to a determined number of loop coils that are disposed in the at least one direction and that are in at least one peripheral region of the sensor substrate. 
     Thereby, the transmission signal is not supplied to the determined number of loop coils disposed in the at least one direction and in the at least one peripheral region of the sensor substrate, while the magnetic path plate forms an excellent magnetic path for the magnetic fluxes generated by the other loop coils supplied with the transmission signal. Thus unwanted radiation can be reduced. 
     Effect of the Invention 
     According to the present invention, an indicator position detecting device is provided that solves the problem of unwanted radiation while ensuring the charging of a pen type position indicator without reducing the area of a display region or a position detecting region even when the product is miniaturized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of assistance in explaining an example of configuration of a position input device according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of assistance in explaining a general configuration of a device, which is provided with a display function and which includes an indicator position detecting device according to the embodiment of the present invention; 
         FIGS. 3A and 3B  are diagrams of assistance in explaining the sizes of a magnetic path plate and a position detecting area; 
         FIG. 4  is a diagram of assistance in explaining an indicator position detecting device according to a first embodiment of the present invention; 
         FIG. 5  is a diagram of assistance in explaining an indicator position detecting device according to a second embodiment of the present invention; 
         FIG. 6  is a diagram of assistance in explaining a process of selecting loop coils in the indicator position detecting device according to the first or second embodiment of the present invention; 
         FIG. 7  is a diagram of assistance in explaining an indicator position detecting device according to a third embodiment of the present invention; and 
         FIG. 8  is a diagram of assistance in explaining a process of selecting loop coils in the indicator position detecting device according to the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments of an indicator position detecting device according to the present invention will hereinafter be described with reference to the drawings. 
     Description of Position (Coordinate) Input Device of Electromagnetic Induction System 
     Description will first be made of a general configuration of a position (coordinate) input device of an electromagnetic induction system (which device will hereinafter be described simply as a position input device) including an indicator position detecting device according to the present invention.  FIG. 1  is a diagram of assistance in explaining an example of configuration of the position input device of the electromagnetic induction system according to this embodiment. As shown in  FIG. 1 , the position input device according to the present embodiment includes a pen type position indicator  100  and an indicator position detecting device  200 . 
     Example of Configuration of Pen Type Position Indicator  100   
     A circuit configuration of the pen type position indicator  100  is shown enclosed by a dotted line in  FIG. 1 . Specifically, a coil  111  as an inductance element and a capacitor  306  form a resonance circuit  321 . A switch  307  is connected in parallel with the resonance circuit  321 . The switch  307  is formed so as to be subjected to on-off control by an IC  305 . Incidentally, the coil  111  is wound around a rod-shaped member formed of a magnetic material such as ferrite, for example. 
     The resonance circuit  321  formed by the coil  111  and the capacitor  306  receives an electromagnetic induction signal sent out from the indicator position detecting device  200 . The received electromagnetic induction signal is rectified by a rectifier circuit (power supply circuit)  322  including a diode  308  and a capacitor  309 , whereby power Vcc to be supplied to the IC  305  is generated. The IC  305  is connected to the resonance circuit  321  via a capacitor  310 . The IC  305  controls the operation of the resonance circuit  321  on the basis of a signal supplied to the IC  305  via the capacitor  310 . 
     The IC  305  is connected with a variable capacitance capacitor  311  for sensing pressure, so that the IC  305  can detect a change in capacitance Cv corresponding to pen pressure. That is, the IC  305  detects the pen pressure applied to the pen tip of the pen type position indicator  100  from the value of the capacitance Cv. The IC  305  then converts the detected pen pressure into an eight-bit digital signal. The digital signal is used for on-off control of the switch  307  by the IC  305 , and is thereby detected by the indicator position detecting device  200 . 
     Example of Configuration of Indicator Position Detecting Device  200   
     On the other hand, in a sensor section  20  of the indicator position detecting device  200 , as shown in  FIG. 1 , an X-axis direction loop coil group  21  and a Y-axis direction loop coil group  22  are respectively disposed on the top surface and the undersurface of a sensor substrate  23 . Incidentally, in the embodiments to be described in the following, as shown in  FIG. 1 , the horizontal direction of the sensor substrate  23  is set as an X-axis direction, and the vertical direction of the sensor substrate  23  is set as a Y-axis direction. 
     As shown in  FIG. 1 , the X-axis direction loop coil group  21  includes n (n is an integer of two or more) rectangular loop coils  21 X 0  to  21 X n  arranged in the X-axis direction. The Y-axis direction loop coil group  22  includes m (m is an integer of two or more) rectangular loop coils  22 Y 0  to  22 Y m  arranged in the Y-axis direction. The loop parts of the X-axis direction loop coil group  21  and the loop parts of the Y-axis direction loop coil group  22  in the sensor section  20  form a position detecting area  25 . 
     The sensor section  20  is connected to a position detecting circuit  26  via a connector section not shown in the figures. The position detecting circuit  26  includes a selecting circuit  261 , an oscillator  262 , a current driver  263 , a transmission and reception switching circuit  264 , a receiving amplifier  265 , a detecting circuit  266 , a low-pass filter  267 , a sample and hold circuit  268 , an ND (Analog to Digital) converter circuit  269 , and a processing control section  260 . The X-axis direction loop coil group  21  and the Y-axis direction loop coil group  22  are connected to the selecting circuit  261 . The selecting circuit  261  sequentially selects one loop coil of the two loop coil groups  21  and  22  according to a control signal CT from the processing control section  260 . 
     The oscillator  262  generates an alternating-current signal of a frequency f 0 . This alternating-current signal is supplied to the current driver  263  to be converted into a current, and the current is then sent out to the transmission and reception switching circuit  264 . Incidentally, the oscillator  262  and the current driver  263  form a transmission signal generating circuit. In addition, the processing control section  260  processes a signal output from the ND converter circuit  269 , and thereby determines whether the pen type position indicator  100  is detected by the sensor section  20 , that is, whether the pen type position indicator  100  is in a use state or a non-use state. 
     When the pen type position indicator  100  is recognized to be in a non-use state, the gain of the current driver  263  is set low, whereby a low voltage mode is set in which mode a low voltage transmission signal is generated. When the pen type position indicator  100  is recognized to be in a use state, the gain of the current driver  263  is set high, whereby a high voltage mode is set in which mode a high voltage transmission signal is generated. 
     The transmission and reception switching circuit  264  selects a connection destination (a transmitting side terminal T or a receiving side terminal R) to which the loop coil selected by the selecting circuit  261  is connected, in each predetermined time under control of the processing control section  260 . The transmitting side terminal T is connected with the current driver  263 , and the receiving side terminal R is connected with the receiving amplifier  265 . 
     Therefore, at a time of transmission, the alternating-current signal from the current driver  263  is supplied to the loop coil selected by the selecting circuit  261  via the transmitting side terminal T of the transmission and reception switching circuit  264 . At a time of reception, an electromagnetic induction signal generated in the loop coil selected by the selecting circuit  261  is supplied to the receiving amplifier  265  via the selecting circuit  261  and the receiving side terminal R of the transmission and reception switching circuit  264 , amplified by the receiving amplifier  265 , and then sent out to the detecting circuit  266 . 
     The signal detected by the detecting circuit  266  is supplied to the ND converter circuit  269  via the low-pass filter  267  and the sample and hold circuit  268 . The A/D converter circuit  269  converts the analog signal into a digital signal, and supplies the digital signal to the processing control section  260 . The processing control section  260  performs control for position detection. Specifically, the processing control section  260  controls the selection of a loop coil by the selecting circuit  261 , signal switching by the transmission and reception switching circuit  264 , the timing of the sample and hold circuit  268 , and the like. Incidentally, the receiving amplifier  265 , the detecting circuit  266 , the low-pass filter  267 , the sample and hold circuit  268 , and the A/D converter circuit  269  form a received signal processing circuit. 
     The processing control section  260  forms a control circuit. The processing control section  260  controls operation so as to send out an electromagnetic induction signal from a selected loop coil of the X-axis direction loop coil group  21  or the Y-axis direction loop coil group  22 , by switching the transmission and reception switching circuit  264  so as to be connected to the transmitting side terminal T and controlling the selecting circuit  261 . As described above, the resonance circuit  321  of the pen type position indicator  100  receives the electromagnetic induction signal sent out from the selected loop coil, and the rectifier circuit  322  generates power V CC  to be supplied to the IC  305 . 
     Next, the processing control section  260  switches the transmission and reception switching circuit  264  so as to be connected to the receiving side terminal R. Then, each loop coil of the X-axis direction loop coil group  21  and the Y-axis direction loop coil group  22  receives an electromagnetic induction signal transmitted from the pen type position indicator  100 . The processing control section  260  calculates a position indicated by the pen type position indicator  100  as respective coordinate values in the X-axis direction and the Y-axis direction in the position detecting area  25  of the sensor section  20  on the basis of the level of the voltage value of induced voltage generated in each loop coil. The processing control section  260  then supplies the information of the calculated coordinate values to an external personal computer, for example. 
     In addition, the processing control section  260  can also detect pen pressure information converted into an eight-bit digital signal, for example, by performing control for detecting the on-and-off state of the signal supplied from the pen type position indicator  100  in addition to performing control for detecting the position indicated by the pen type position indicator  100 . 
     General Configuration of Device which is Provided with Display Function and which Includes Indicator Position Detecting Device  200   
       FIG. 2  is an exploded perspective view of assistance in explaining a general configuration of a device provided with a display function, which device is configured using the indicator position detecting device  200  according to the present embodiment. As shown in  FIG. 2 , a protective plate (not shown) such as glass or the like is disposed in one surface (top surface) of a bezel  10 , and operation by the pen type position indicator  100  is performed on the protective plate. An LCD  40  as a display device is disposed on the side of another surface (undersurface) of the bezel  10 . The sensor section  20  and a motherboard  50  opposed to each other with a magnetic path plate  30  interposed between the sensor section  20  and the motherboard  50  form the indicator position detecting device  200  on the lower side of the LCD  40 , that is, on the side of a surface of the LCD  40  opposite from a display surface of the LCD  40 . The indicator position detecting device  200  is disposed so as to be opposed to the bezel  10  with the LCD  40  interposed between the indicator position detecting device  200  and the bezel  10 . The LCD  40 , the sensor section  20 , the magnetic path plate  30 , and the motherboard  50  are housed in a casing  60 , and the bezel  10  is disposed so as to seal the casing  60 , whereby the device provided with a display function is formed. Incidentally, the motherboard  50  is provided with various circuits including a communicating circuit, a control circuit for the LCD  40 , and the like as well as the position detecting circuit  26  of the indicator position detecting device  200  as shown in  FIG. 1 . 
     The magnetic path plate  30  forms a magnetic path for an electromagnetic induction signal (alternating-current magnetic field) generated by each loop coil of the loop coil groups  21  and  22  provided on the sensor section  20 . This prevents the divergence of a magnetic flux generated by each loop coil, thereby improving sensitivity of detection of the position indicated by the pen type position indicator  100 . In a similar manner, the magnetic path plate  30  functions to prevent the radiation of the electromagnetic induction signal to the outside of the indicator position detecting device  200 . 
     Therefore, the magnetic path plate  30  functions effectively when the magnetic path plate  30  has a predetermined area equal to or more than that of the sensor section  20 , more specifically a region formed by the loop coils. 
       FIGS. 3A and 3B  are diagrams of assistance in explaining the size of the position detecting area  25  formed by the loop coils of the X-axis direction loop coil group  21  and the loop coils of the Y-axis direction loop coil group  22  and the sizes of a conventional magnetic path plate  30 X and the magnetic path plate  30  according to the embodiment of the present invention. In order for the magnetic path plate  30  to function effectively, as indicated by the conventional magnetic path plate  30 X in  FIG. 3A , the size of the magnetic path plate  30 X needs to be sufficiently larger than the size of the position detecting area  25  formed by the loop coils of the X-axis direction loop coil group  21  and the loop coils of the Y-axis direction loop coil group  22 . It is known that unwanted radiation is reduced when the magnetic path plate  30 X has a larger region than the region of the position detecting area  25  of the sensor section  20 , as shown in  FIG. 3A . 
     However, as shown in  FIG. 3B , the device provided with a display function according to the embodiment of the present invention is miniaturized without the position detecting area  25  of the sensor section  20  being reduced in size. Therefore, the area of a region other than the position detecting area  25  in the sensor substrate  23 , that is, a peripheral region of the sensor substrate  23  is reduced. The magnetic path plate  30  used in the device provided with a display function according to the embodiment of the present invention thus has a slightly larger area than the position detecting area  25  of the sensor section  20 , as shown in  FIG. 3B . Incidentally, the magnetic path plate  30  according to the embodiment of the present invention has substantially the same area as the sensor substrate  23 , and is housed in the casing  60  in a state of being disposed so as to be superposed on the sensor substrate  23 . 
     Therefore, with decrease in difference between the area of the position detecting area  25  and the area of the magnetic path plate  30 , it becomes difficult for the magnetic path plate  30  to reduce unwanted radiation caused by electromagnetic induction signals sent out from a predetermined number of loop coils of the X-axis direction loop coil group  21  that are disposed in one peripheral (end) region or both peripheral (end) regions of the sensor substrate  23  along the X-axis direction or a predetermined number of loop coils of the Y-axis direction loop coil group  22  that are disposed in one peripheral region or both peripheral regions of the sensor substrate  23  along the Y-axis direction. 
     A user can view information displayed on the LCD  40  from the side of the bezel (front panel)  10  of the device provided with a display function, on which side operation is performed by the pen type position indicator  100 , through the protective plate (not shown) such as glass, for example. The protective plate is fitted in the bezel and has transparency. The sensor section  20  disposed under the LCD  40  can receive various instruction inputs from the pen type position indicator  100 . 
     Incidentally, though not shown in  FIG. 2 , the LCD  40  and the sensor section  20  are each connected to a corresponding circuit section on the motherboard  50 . In addition, the device provided with a display function as shown in  FIG. 2  is realized as a tablet type terminal or a high-functionality portable telephone terminal referred to as a smart phone, for example. 
     Description of First to Third Embodiments of Indicator Position Detecting Device  200   
     First to third embodiments of the indicator position detecting device  200  according to the present invention will be described in the following. The general configuration shown in  FIG. 1  can be applied to each of indicator position detecting devices  200 A,  200 B, and  200 C according to the first to third embodiments to be described in the following, and the indicator position detecting devices  200 A,  200 B, and  200 C are each used in, for example, a device provided with a display function as shown in  FIG. 2 . Therefore, in the indicator position detecting devices  200 A,  200 B, and  200 C according to the first to third embodiments to be described in the following, parts formed in a similar manner to those of the indicator position detecting device  200  described with reference to  FIG. 1  and  FIG. 2  are identified by the same reference symbols, and detailed description of the parts will be omitted. 
     However, the first to third embodiments to be described in the following each have a different configuration in the peripheral circuit of the sensor section  20  and the selecting circuit  261  and also have a different configuration for loop coil selection control by the processing control section  260 . In the following, the first to third embodiments will be described in detail. 
     First Embodiment 
       FIG. 4  is a diagram of assistance in explaining a configuration of principal parts of the indicator position detecting device  200 A according to the first embodiment of the present invention.  FIG. 4  shows a part including a sensor section  20 A and a selecting circuit  261  within the indicator position detecting device  200 A. The sensor section  20 A is a part corresponding to the sensor section  20  of the indicator position detecting device  200  shown in  FIG. 1 . 
     In addition,  FIG. 4  shows only a transmission and reception switching circuit  264 , a current driver  263 , and a receiving amplifier  265  forming a position detecting circuit  26  in order to show relation to the selecting circuit  261 . In addition,  FIG. 4  shows three loop coil parts each located in both peripheral regions in the X-axis direction in an X-axis direction loop coil group  21  forming the sensor section  20 A, and does not show the other loop coils in the X-axis direction nor a Y-axis direction loop coil group  22 , in order to simplify description. 
     As shown in  FIG. 4 , the selecting circuit  261  has switches SX 0 , SX 1 , SX 2 , . . . , SX n-2 , SX n-1 , and SX n  so as to correspond to loop coils  21 X 0 ,  21 X 1 ,  21 X 2 , . . . ,  21 X n-2 ,  21 X n-1 , and  21 X n  in the X-axis direction. The switches SX 0 , SX 1 , SX 2 , . . . , SX n-2 , SX n-1 , and SX n  have one terminal thereof connected to the corresponding loop coils  21 X 0 ,  21 X 1 ,  21 X 2 , . . . ,  21 X n-2 ,  21 X n-1 , and  21 X n , respectively, and have another terminal connected to the transmission and reception switching circuit  264 . In addition, capacitors CX 0  to CX n  are disposed between the loop coils  21 X 0  to  21 X n  in the X-axis direction and the switches SX 0  to SX n , respectively. 
     Incidentally, though not shown, the selecting circuit  261  also has switches for loop coils forming the Y-axis direction loop coil group  22  as in the case of the loop coils in the X-axis direction. In addition, capacitors are respectively disposed between the loop coils in the Y-axis direction and the switches corresponding to the loop coils in the Y-axis direction as in the case of the loop coils in the X-axis direction. 
     Thus, the selecting circuit  261  has the switches SX 0 , SX 1 , SX 2 , . . . , SX n-2 , SX n-1 , and SX n  provided so as to correspond to the plurality of loop coils, respectively, arranged in the X-axis direction. Each of the plurality of switches SX 0 , SX 1 , SX 2 , . . . , SX n-2 , SX n-1 , and SX n  forming the selecting circuit  261  is switched by a control signal CT from the processing control section  260  of the position detecting circuit  26 . 
     Similarly, the selecting circuit  261  also has switches corresponding to the plurality of loop coils, respectively, arranged in the Y-axis direction, and each of the switches is switched by the control signal CT from the processing control section  260  of the position detecting circuit  26 . Incidentally, control of the plurality of loop coils arranged in the Y-axis direction is performed in a similar manner to control of the plurality of loop coils arranged in the X-axis direction. Thus, the following description will be made of the control of the plurality of loop coils arranged in the X-axis direction, and description of the control of the plurality of loop coils arranged in the Y-axis direction will be omitted. 
     As described with reference to  FIGS. 3A and 3B , unwanted radiation of the sensor section  20 A depends on arrangement relation between the position detecting area  25 , which is defined mainly by the loop coils arranged in the peripheral regions in the X-axis direction/Y-axis direction of the sensor section  20 A, and the magnetic path plate  30 . The unwanted radiation is known to occur in large amounts when a transmission signal is sent out from a predetermined number of loop coils located in the peripheral regions of the position detecting area  25  of the sensor section  20 A to the pen type position indicator  100 . Accordingly, the indicator position detecting device  200 A according to the first embodiment suppresses the occurrence of the unwanted radiation by not transmitting the transmission signal to the predetermined number of loop coils located in the peripheral regions of the position detecting area  25  at a time of a global scan in which each loop coil is selected and the position of the pen type position indicator  100  is roughly detected, for example. 
     In the first embodiment, specifically, the processing control section  260  performs switching control so as not to use the two loop coils  21 X 0  and  21 X 1  located in the left peripheral region in the X-axis direction and the two loop coils  21 X n  and  21 X n-1  located in the right peripheral region in the X-axis direction in  FIG. 4  for sending out the transmission signal. However, the processing control section  260  performs switching control so that the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  can be used as usual for receiving a signal from the pen type position indicator  100 . 
     The processing control section  260  performs switching control so as to send out the transmission signal from the loop coil  21 X 2  adjacent to the loop coil  21 X 1  in timing in which the transmission signal would normally be sent out from each of the two loop coils  21 X 0  and  21 X 1  located in the left peripheral region in the X-axis direction. Similarly, the processing control section  260  performs switching control so as to sent out the transmission signal from the loop coil  21 X n-2  adjacent to the loop coil  21 X n-1  in timing in which the transmission signal would normally be sent out from each of the two loop coils  21 X n-1  and  21 X n  located in the right peripheral region in the X-axis direction. 
     Thereby, even when the area of the magnetic path plate  30  is made smaller than conventional, and is substantially the same area as the size of the sensor substrate  23 , for example, because the loop coils located in both peripheral regions in the X-axis direction of the sensor section  20 A are not used, excellent magnetic paths are formed between the loop coils that are disposed in the peripheral regions and driven and the magnetic path plate  30 . Therefore the unwanted radiation can be reduced greatly. As shown in  FIG. 4 , the switches SX o  and SX 1  corresponding to the loop coils  21 X 0  and  21 X 1  are turned off in the normal timing of transmission of the transmission signal. 
     In actuality, however, there is an output impedance (off resistance) of a few MΩ (megohms) to a few tens of MΩ when the switches are off. Alternatively, switches having a desired off resistance are intentionally arranged. Thereby, the output impedance (R) of the switch SX 0 , the loop coil  21 X 0  (L), and the capacitor CX 0  (C) form an RLC resonance circuit. The output impedance (R) of the switch SX 1 , the loop coil  21 X 1  (L), and the capacitor CX 1  (C) similarly form an RLC resonance circuit. 
     When the transmission signal is sent out from the loop coil  21 X 2 , the transmission signal is induced also in the loop coils  21 X 0  and  21 X 1  by tuned resonance, and the transmission signal at such a level as not to constitute unwanted radiation is sent out also from the loop coils  21 X 0  and  21 X 1 . Thus, the resonance circuit formed by the switch SX 0 , the loop coil  21 X 0 , and the capacitor CX 0  and the resonance circuit formed by the switch SX 1 , the loop coil  21 X 1 , and the capacitor CX 1  are configured so as to produce tuned resonance tuned to the transmission signal sent out from the loop coil  21 X 2 . 
     However, the transmission signal used at the time of the global scan is usually a burst wave whose transmission time is 42 μsec (microseconds), so that the transmission signal may not be expected to be induced sufficiently by tuned resonance. Accordingly, when the transmission signal is supplied to the loop coil  21 X 2 , the time of supply of the transmission signal is lengthened through control of the processing control section  260  to raise the transmission level of the transmission signal from the loop coils  21 X 0  and  21 X 1 , which transmission signal is induced by the tuned resonance of the loop coils  21 X 0  and  21 X 1 , in such a range as not to cause unwanted radiation. 
     Incidentally, it suffices to determine a degree to which the time of supply of the transmission signal to the loop coil  21 X 2  is lengthened according to the power supply voltage generated in the pen type position indicator  100  and a frame rate at the time of the global scan for the device provided with a display function in which device the magnetic path plate  30  is disposed. The above description has been made by taking as an example a case where consideration is given to the loop coils  21 X 0 ,  21 X 1 , and  21 X 2  on the side of the left peripheral region in the X-axis direction. However, a similar description applies to a case where consideration is given to the loop coils  21 X n-2 ,  21 X n-1 , and  21 X n  on the side of the right peripheral region in the X-axis direction. 
     Incidentally,  FIG. 4  shows a case in which a global scan is performed in a direction from the left end side to the right end side in the X-axis direction, the switch SX 2  is in an on state, and the other switches are in an off state. 
     Second Embodiment 
       FIG. 5  is a diagram of assistance in explaining a configuration of principal parts of the indicator position detecting device  200 B according to the second embodiment of the present invention. As in the first embodiment described with reference to  FIG. 4 ,  FIG. 5  shows a part including a sensor section  20 B and a selecting circuit  261  within the indicator position detecting device  200 B. The sensor section  20 B is a part corresponding to the sensor section  20  of the indicator position detecting device  200  shown in  FIG. 1 . As in the first embodiment described with reference to  FIG. 4 , parts of an X-axis direction loop coil group  21  on both end sides of the X-axis direction loop coil group  21  are shown, and a Y-axis direction loop coil group  22  is not shown. 
     As is shown by comparison of  FIG. 5  with  FIG. 4 , the indicator position detecting device  200 B according to the second embodiment shown in  FIG. 5  is provided with switches FX 0 , FX 1 , FX n-1 , and FX n  formed by an FET (Field Effect Transistor), for example. Except for this, the indicator position detecting device  200 B according to the second embodiment is configured in a similar manner to the indicator position detecting device  200 A according to the first embodiment shown in  FIG. 4 . 
     As shown in  FIG. 5 , the switches FX 0 , FX 1 , FX n-1 , and FX n  are provided respectively for loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  located in peripheral regions in the X-axis direction, so that the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  are connected to or disconnected from a ground by switching control of a processing control section  260 . 
     Also in the indicator position detecting device  200 B according to the second embodiment, the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  located in the peripheral regions in the X-axis direction are not used for sending out a transmission signal. In timing in which the transmission signal would normally be sent out from the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  located in the peripheral regions in the X-axis direction, the transmission signal is sent out from respective adjacent loop coils  21 X 2  and  21 X n-2 . Switches SX 0 , SX 1 , SX 2 , . . . , SX n-2 , SX n-1 , and SX n  forming the selecting circuit  261  are thus controlled by the processing control section  260  as in the case of the indicator position detecting device  200 A according to the first embodiment shown in  FIG. 4 . 
     In the indicator position detecting device  200 B according to the second embodiment, the switches FX 0 , FX 1 , FX n-1 , and FX n  are each turned on simultaneously in timing in which the transmission signal would normally be supplied to the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n . In other words, the switches FX 0 , FX 1 , FX n-1 , and FX n  are each turned on simultaneously in timing in which the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2  adjacent to the loop coils ( 21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n ) to which the transmission signal is not supplied. The loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  are thereby connected to the ground in timing in which the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2 . 
     When the switch FX 0  is turned on, an RLC resonance circuit is formed by an output impedance (R) when the switch FX 0  is on, the loop coil  21 X 0  (L), and a capacitor CX 0  (C), and a Q (Quality factor) value is increased. Similarly, when the switch FX 1  is turned on, an RLC resonance circuit is formed by an output impedance (R) when the switch FX 1  is on, the loop coil  21 X 1  (L), and a capacitor CX 1  (C), and a Q-value is increased. 
     That is, in the case of the RLC resonance circuits including the loop coil  21 X 0  and the loop coil  21 X 1 , respectively, as shown in  FIG. 4 , tuned resonance is produced with the off resistances of the switches SX 0  and SX 1 , so that a high Q-value cannot be expected to be obtained. However, as shown in  FIG. 5 , the switches FX 0  and FX 1  for connecting the respective loop coils  21 X 0  and  21 X 1  connected to the switches SX 0  and SX 1  to the ground are provided, and the switches FX 0  and FX 1  having a low on resistance are turned on in timing in which the transmission signal is supplied to the loop coil  21 X 2 . Thereby, the RLC resonance circuits including the loop coil  21 X 0  and the loop coil  21 X 1 , respectively, can be driven with a low resistance. Thus, tuned resonance can be produced efficiently with the high Q-value for a frequency being used. 
     Incidentally, the Q-value indicates the sharpness of a peak of resonance in the resonance circuit. In the RLC resonance circuit, the smaller the value of the series resistance (R), the larger the Q-value, which means that tuned resonance can be produced efficiently between the resonance circuits. Thus, the transmission signal supplied to the loop coils  21 X 2  and  21 X n-2  effects tuned resonance of the resonance circuits including the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  and increased in the Q-value, so that the transmission signal having a predetermined signal level can be sent out also from the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n . 
     It is therefore possible to sent out the transmission signal having a predetermined signal level also from the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  to which the transmission signal is not supplied. The pen type position indicator  100  is thereby supplied with power properly even in the peripheral regions in the X-axis direction. In this case, the transmission signal is not supplied to the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n . Consequently, the magnetic path plate  30  is in a state of extending out with respect to the loop coils  21 X 2  and  21 X n-2  driven as loop coils for sending out the transmission signal. This means that the magnetic path plate  30  having a greater distance between ends thereof than a distance between the loop coil  21 X 2  and the loop coil  21 X n-2  driven as loop coils for sending out the transmission signal is disposed, and the magnetic path plate  30  functions effectively against unwanted radiation. The same is true for the Y-axis direction loop coil group. When the Y-axis direction loop coil group is used for sending out the transmission signal, the magnetic path plate  30  is in a state of extending out with respect to the loop coils  22 Y 2  and  22 Y n-2 . This means that the magnetic path plate  30  having a greater distance between ends thereof than a distance between the loop coil  22 Y 2  and the loop coil  22 Y n-2  driven as loop coils for sending out the transmission signal is disposed, and the magnetic path plate  30  functions effectively against unwanted radiation. 
     Incidentally, when the switches FX 0 , FX 1 , FX n-1 , and FX n  remain turned on, the Q-values are kept high, and phase variations are increased, which may cause jitter and a coordinate shift. Accordingly, when the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  are used as receiving conductors for receiving a signal from the pen type position indicator  100 , the switches FX 0 , FX 1 , FX n-1 , and FX n  are switched off by the processing control section  260 . 
     All Scan Operation in X-Direction in First and Second Embodiments 
       FIG. 6  is a diagram of assistance in explaining all scan operation performed on the X-axis direction loop coil group  21  of the indicator position detecting device  200 A or  200 B according to the first or second embodiment described with reference to  FIG. 4  or  FIG. 5 . In  FIG. 6 , a column of phases indicates whether a loop coil selected in the selecting circuit  261  is used for sending out a transmission signal or used for receiving a signal from the pen type position indicator  100 . Specifically, a transmission phase (T) is a state in which the transmission and reception switching circuit  264  is switched to the transmitting side terminal T, and a reception phase (R) is a state in which the transmission and reception switching circuit  264  is switched to the receiving side terminal R. 
     A column of selected coils indicates a coil selected in the selecting circuit  261  as a transmitting coil for sending out the transmission signal or as a receiving coil for receiving the signal from the pen type position indicator  100 . A column of switches for resonance indicates the on/off state of the switches FX 0 , FX 1 , FX n-1 , and FX n  provided for the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  not used as transmitting coils. Incidentally, the indicator position detecting device  200 A according to the first embodiment does not have the switches FX 0 , FX 1 , FX n-1 , and FX n , and thus the item is referred to only in the case of the second embodiment. 
     Description in the following will be made of operation when a global scan is performed from the left end side to the right end side in the X-axis direction in the sensor section  20 A or  20 B shown in  FIG. 4  or  FIG. 5 . The transmission and reception switching circuit  264  of the position detecting circuit  26  is switched so as to select the transmitting side terminal T and the receiving side terminal R in order by switching control of the processing control section  260 . Thereby, as shown on the left end side of  FIG. 6 , the indicator position detecting device  200 A or  200 B is sequentially switched to the transmission phase and the reception phase. 
     In the case of the indicator position detecting device  200 A or  200 B according to the first or second embodiment shown in  FIG. 4  or  FIG. 5 , the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  in both peripheral regions in the X-axis direction are not used as transmitting coils. Therefore, as shown in  FIG. 6 , in a zeroth and a first transmission phase in which the loop coil  21 X 0  and the loop coil  21 X 1  should normally be selected as a transmitting coil, the loop coil  21 X 2  adjacent to these loop coils is selected as a transmitting coil. That is, in the zeroth and first transmission phases, as shown in  FIG. 4  and  FIG. 5 , the switches SX 0  and SX R  are set in an off state, and the switch SX 2  is set in an on state. 
     Thereafter, from a second transmission phase to an (n−2)th transmission phase, the loop coils from the loop coil  21 X 2  to the loop coil  21 X n-2  are selected as a transmitting coil in order. Then, in an (n−1)th and an nth transmission phase in which the loop coil  21 X n-1  and the loop coil  21 X n  should normally be selected as a transmitting coil, the loop coil  21 X n-2  adjacent to these loop coils is selected as a transmitting coil. That is, in the (n−1)th and nth transmission phases, as shown in  FIG. 4  and  FIG. 5 , the switches SX n-1  and SX n  are set in an off state, and the switch SX n-2  is set in an on state. 
     Thereby, the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  in both peripheral regions in the X-axis direction are not supplied with the transmission signal. Thus, in the transmission phases for sending out the transmission signal, the magnetic path plate has a size such that end parts of the magnetic path plate respectively extend out further outward than the loop coils  21 X 2  and  21 X n-2  disposed in both peripheral regions in the X-axis direction, and exerts a function as a magnetic path plate, so that unwanted radiation can be reduced greatly. When the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2 , the transmission signal is sent out also from the adjacent loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  due to tuned resonance. Therefore, power can be supplied to the pen type position indicator  100  also through these loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  to such a degree as not to cause unwanted radiation. However, the transmission signal is not supplied to a desired number of loop coils disposed in each peripheral region of the sensor section  20 A or  20 B, or the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  in the present example. Thus, the magnetic path plate  30  having a large size is disposed for the loop coils located at extreme ends of the sensor section  20 A or  20 B, which loop coils are driven to send out the transmission signal. Therefore unwanted radiation can be reduced effectively by the magnetic path plate  30 . 
     Incidentally, in the reception phases, the loop coils  21 X 0  to  21 X n  are selected in order as in a conventional manner, and therefore a position indicated by the pen type position indicator  100  is detected as in a conventional manner. In the case of the indicator position detecting device  200 B according to the second embodiment, when the transmission signal is supplied to the loop coil  21 X 2  or  21 X n-2 , the switches FX 0  and FX 1  or the switches FX n-1  and FX n  are turned on, as indicated in the column of the switches for resonance in  FIG. 6 . In this case, the Q-values of the resonance circuits including the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  are increased by tuned resonance. Thus, the transmission signal supplied to the loop coils  21 X 2  and  21 X n-2  can be induced in the resonance circuits including the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  more efficiently, and the transmission signal can be sent out efficiently with the signal level thereof within such a range as not to cause unwanted radiation. 
     Third Embodiment 
       FIG. 7  is a diagram of assistance in explaining a configuration of principal parts of the indicator position detecting device  200 C according to the third embodiment of the present invention. As in the first embodiment described with reference to  FIG. 4 ,  FIG. 7  shows a part including a sensor section  20 C and a selecting circuit  261  within the indicator position detecting device  200 C. The sensor section  20 C is a part corresponding to the sensor section  20  of the indicator position detecting device  200  shown in  FIG. 1 . As in the first embodiment described with reference to  FIG. 4 , parts of an X-axis direction loop coil group  21  on both end sides of the X-axis direction loop coil group  21  are shown, and a Y-axis direction loop coil group  22  is not shown. 
     As is shown by comparison of  FIG. 7  with  FIG. 5 , the indicator position detecting device  200 C according to the present third embodiment has a similar configuration to that of the indicator position detecting device  200 B according to the second embodiment. However, switching control of each switch forming the selecting circuit  261  in the indicator position detecting device  200 C according to the present third embodiment is different from that of the indicator position detecting device  200 B according to the foregoing second embodiment. Specifically, as shown in  FIG. 7 , when a transmission signal is supplied to the loop coil  21 X 2 , the transmission signal is also supplied to the loop coil  21 X n-2  simultaneously. Conversely, when the transmission signal is supplied to the loop coil  21 X n-2 , the transmission signal is also supplied to the loop coil  21 X 2  simultaneously. 
     In addition, when the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2 , the transmission time of the transmission signal is lengthened so as to correspond to the times that the transmission signal should normally be supplied to each of the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n , as in the foregoing first and second embodiments. Thereby, at a time of a global scan, the time during which the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2  is lengthened, and a pen type position indicator  100  can secure power supply voltage for driving an IC  305  favorably even when one or a plurality of loop coils disposed in each of both peripheral regions in the X-axis direction are not used for sending out the transmission signal. 
     All Scan Operation in X-Direction in Third Embodiment 
       FIG. 8  is a diagram of assistance in explaining all scan operation performed on the X-axis direction loop coil group  21  of the indicator position detecting device  200 C according to the third embodiment described with reference to  FIG. 7 . In  FIG. 8 , respective columns of phases, selected coils, and switches for resonance have similar meanings to those of  FIG. 6  described above. Also in the present third embodiment, description will be made of operation when a global scan is performed from the left end side to the right end side in the X-axis direction in the sensor section  20 C shown in  FIG. 7 . 
     Also in the case of the indicator position detecting device  200 C according to the present third embodiment, the transmission and reception switching circuit  264  of a position detecting circuit  26  is switched so as to select a transmitting side terminal T and a receiving side terminal R in order by switching control of a processing control section  260 . Thereby, as shown on the left end side of  FIG. 8 , the indicator position detecting device  200 C is sequentially switched to a transmission phase and a reception phase. 
     In the case of the indicator position detecting device  200 C according to the third embodiment shown in  FIG. 7 , the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  in both peripheral regions in the X-axis direction are not used as loop coils for sending out the transmission signal. Therefore, as shown in  FIG. 8 , in a zeroth and a first transmission phase in which the loop coil  21 X 0  and the loop coil  21 X 1  should normally be a loop coil for sending out the transmission signal, the adjacent loop coil  21 X 2  and the loop coil  21 X n-2  located on an opposite side in the sensor section  20 C are loop coils for sending out the transmission signal. Also in a second transmission phase, in addition to the loop coil  21 X 2  that should normally be a loop coil for sending out the transmission signal, the loop coil  21 X n-2  located on the opposite side in the sensor section  20 C is also a transmitting coil. That is, in the zeroth, first, and second transmission phases, the switches SX 0  and SX 1  are set in an off state, and the switches SX 2  and SX n-2  are set in an on state. 
     Thereafter, from a third transmission phase to an (n−3)th transmission phase, the loop coils from the loop coil  21 X 3  to the loop coil  21 X n-3  are selected as a loop coil for sending out the transmission signal in order. Then, in an (n−2)th transmission phase, the loop coil  21 X n-2  and the loop coil  21 X 2  located on the opposite side in the sensor section  20 C are selected as loop coils for sending out the transmission signal. Similarly, also in an (n−1)th and an nth transmission phase in which the loop coil  21 X n-1  and the loop coil  21 X n  should normally be a loop coil for sending out the transmission signal, the loop coil  21 X n-2  adjacent to these loop coils and the loop coil  21 X 2  located on the opposite side in the sensor section  20 C are selected as transmitting coils. That is, in the (n−2)th, (n−1)th, and nth transmission phases, the switches SX n-1  and SX n  are set in an off state, and the switches SX n-2  and SX 2  are set in an on state. 
     Thereby, the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  located respectively in both peripheral regions in the X-axis direction are not supplied with the transmission signal. Thus, unwanted radiation caused by the transmission signal supplied to the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  located in both peripheral regions in the X-axis direction can be reduced greatly. When the transmission signal is supplied to the loop coils  21 X 2  and  21 X n-2 , the transmission signal is also induced in the adjacent loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  due to tuned resonance, and the transmission signal is sent out. Thereby, power can be supplied to the pen type position indicator  100  also through these loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  at a desired transmission signal level. In addition, because the transmission signal is not supplied to the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n , the transmission signal can be sent out efficiently at such a signal level as not to cause unwanted radiation. 
     Incidentally, in the reception phases, the loop coils  21 X 0  to  21 X n  are selected in order as in a conventional manner, and therefore a position indicated by the pen type position indicator  100  is detected as in a conventional manner. In the case of the indicator position detecting device  200 C according to the third embodiment, when the transmission signal is supplied to each of the loop coils  21 X 2  and  21 X n-2 , the switches FX 0 , FX 1 , FX n-1 , and FX n  are turned on simultaneously, as indicated in the column of the switches for resonance in  FIG. 8 . In this case, the Q-values of the resonance circuits including the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  are increased by tuned resonance. Thus, the transmission signal supplied to the loop coils  21 X 2  and  21 X n-2  can be induced in the resonance circuits including the loop coils  21 X 0 ,  21 X 1 ,  21 X n-1 , and  21 X n  more efficiently, and the transmission signal can be sent out efficiently as a transmission signal having a desired signal level within such a range as not to cause unwanted radiation. 
     Effects of Embodiments 
     An indicator position detecting device that solves the problem of unwanted radiation caused by the electromagnetic induction system while excellently maintaining electromagnetic coupling relation to a position indicator can be realized without the area of a position detecting region being reduced even when the product is miniaturized. That is, when loop coils are driven to transmit an electromagnetic induction signal to the position indicator, unwanted radiation can be reduced by not supplying the transmission signal to a determined number of loop coils disposed in a peripheral region of the sensor section  20 . In addition, the electromagnetic coupling relation to the position indicator in the peripheral region can be maintained excellently by lengthening the transmission time of the signal transmitted from a loop coil adjacent to the determined number of loop coils disposed in the peripheral region of the sensor section  20 . Further, the transmission signal at a predetermined signal level is also sent out from the determined number of loop coils disposed in the peripheral region of the sensor section  20 , which loop coils are controlled not to be supplied with the transmission signal, by making the determined number of loop coils produce tuned resonance with the adjacent loop coil. It is thereby possible to secure excellent electromagnetic coupling relation to the position indicator while dealing with unwanted radiation. 
     Modifications 
     It is to be noted that while the foregoing embodiments have been described by taking as an example a case where a scan for locating a position indicated by the position indicator is performed on the loop coils forming the X-axis direction loop coil group  21 , the present invention is not limited to this. A scan for locating a position indicated by the position indicator can also be performed on the loop coils forming the Y-axis direction loop coil group  22  in place of the loop coils forming the X-axis direction loop coil group  21 . 
     In addition, a scan for locating a position indicated by the position indicator can also be performed while selecting the loop coils forming the X-axis direction loop coil group  21  and the loop coils forming the Y-axis direction loop coil group  22  as appropriate. In addition, while description has been made of loop coils disposed in the X-axis direction as loop coils from which the transmission signal is not sent out, it is needless to say that loop coils disposed in the Y-axis direction can also be loop coils from which the transmission signal is not sent out. 
     Further, while description has been made of a case where the same loop coils are selectively used for signal transmission and signal reception, it is obvious that the present invention is also applicable to a case where a loop coil group disposed in a first direction (for example the X-axis direction) is used for signal transmission, and a loop coil group disposed in a second direction (for example the Y-axis direction) different from the first direction is used for signal reception. 
     In addition, the number of loop coils subjected to transmission signal sending-out control, which loop coils are disposed in one peripheral region or both peripheral regions of the sensor section  20 , depends on positional relation between the determined number of loop coils disposed in the peripheral region or the peripheral regions of the sensor section  20  and the magnetic path plate disposed so as to be superposed on the sensor section, that is, relation between the area occupied by the loop coil group and the area of the magnetic path plate. In addition, while description has been made of one or a plurality of loop coils from an extreme end of the sensor section  20  as an object of transmission signal sending-out control, it is not necessarily required that consecutive loop coils be set as the object. It suffices to perform the transmission signal sending-out control on a determined number of loop coils disposed in a peripheral region of the sensor section  20  so as to reduce unwanted radiation with relation to the performance of the magnetic path plate.