Abstract:
A communication system is provided comprising a living body-side electrode which primarily capacitively couples with a living body, an environment-side electrode which primarily capacitively couples with an external environment, and a circuit board on which a circuit which processes a signal which is output from at least one of the living body-side electrode and the environment-side electrode is mounted, wherein the circuit board is not placed between the living body-side electrode and the environment-side electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The entire disclosure of Japanese Patent Application No. 2008-155013 including specification, claims, drawings, and abstract is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a communication system for enabling communication through a human body or the like and a receiver used in the communication system. 
     2. Description of the Related Art 
     A communication device which communicates through tissue of a living body such as a human body is known. For example, a technique is known in which data can be exchanged by a user merely holding a hand over a receiver while a portable electronic device such as a portable phone on which a transmitter is mounted is placed in a pocket of clothing of the user, or while the portable electronic device is hung from the neck. 
     For example, as shown in  FIGS. 10A and 10B , a transmitter  100  comprises an encoder  10 , a transmission amplifier  12 , an environment-side electrode  14 , and a living body-side electrode  16 , and a receiver  102  comprises a decoder  18 , a reception amplifier  20 , an environment-side electrode  22 , and a living body-side electrode  24 . The transmitter  100  is mounted on a portable electronic device or the like which is carried by the user. The receiver  102  is placed on a ticket barrier of a station, a vending machine, a shop, etc. 
       FIG. 11  shows a relationship between the transmitter  100 , the receiver  102 , and the human body or the like during the communication.  FIG. 12  shows an equivalent circuit of the relationship. 
     The transmitter  100  capacitively couples with the receiver  102  through tissue of a living body such as human body or the like (hereinafter simply referred to as “human body or the like”). The environment-side electrode  14  of the transmitter  100  forms a capacitive coupling A with an external environmental ground potential, a capacitive coupling B with the human body or the like, and a capacitive coupling D with an external environment. Similarly, the environment-side electrode  22  of the receiver  102  forms a capacitive coupling H with the external environmental ground potential and a capacitive coupling G with the external environment. As described, the environment-side electrodes  14  and  22  are electrodes which form capacitive couplings with the external environment during the communication. 
     The living body-side electrode  16  of the transmitter  100  forms a capacitive coupling C with the human body or the like. The living body-side electrode  24  of the receiver  102  forms a capacitive coupling F with the human body or the like. Moreover, a capacitive coupling E is formed between the human body or the like and the external environment. As described, the living body-side electrodes  16  and  24  are electrodes which form capacitive couplings with the human body or the like during the communication. 
     The transmission amplifier  12  of the transmitter  100  receives information encoded by the encoder  10  and outputs as a potential difference between the environment-side electrode  14  and the living body-side electrode  16 . When the transmitter  100  and the receiver  102  are electrically coupled through the human body or the like as described above, the potential difference between the environment-side electrode  14  and the living body-side electrode  16  of the transmitter  100  causes a change in a potential difference between the environment-side electrode  22  and the living-body side electrode  24  of the receiver  102 . The reception amplifier  20  of the receiver  102  amplifies the potential difference between the environment-side electrode  22  and the living body-side electrode  24  and outputs the amplified signal. The output of the reception amplifier  20  is decoded by the decoder  18 . In this manner, the communication is established. 
     For example, communication is enabled by a user who carries the transmitter  100  holding a hand over (or contacting with a hand) the living body-side electrode  24  of the receiver  102  placed on a ticket barrier of a station. 
     In a portable terminal such as a portable phone and a PDA in the related art, as shown by a cross sectional diagram of  FIG. 13 , the environment-side electrode  14  and the living body-side electrode  16  are placed attached to an internal surface of a housing of the portable terminal and a circuit board  26  on which the reception amplifier  20 , the decoder  18 , etc. which process the signals from the environment-side electrode  14  and the living body-side electrode  16  are mounted is placed in the housing. In this process, in order to prevent influences of electromagnetic waves emitted from the circuit board  26  on the signals received on the environment-side electrode  14  and the living body-side electrode  16 , a structure is employed in which the circuit board  26  is stored in a shield case  28  made of a conductor. 
     When a structure of storing the circuit board  26  in the shield case  28  is employed, the manufacturing cost is increased by the shield case  28 , and in addition, as shown in an equivalent circuit of  FIG. 14 , the intensity of the signal which can be detected from the environment-side electrode  14  and the living body-side electrode  16  is reduced due to influences of parasitic capacitances C 1  and C 2  between the environment-side and living body-side electrodes  14  and  16  and the shield case  28 . 
     In consideration of this, another configuration is employed in which, as shown in a cross sectional diagram of  FIG. 15 , the circuit board  26  is not stored in the shield case  28 , but is placed between the environment-side electrode  14  and the living body-side electrode  16 . 
     For example, when a reception signal as shown in  FIG. 16A  is obtained in the structure of  FIG. 13 , in a structure having a similar system but with the shield case  28  removed as shown in  FIG. 15 , the reception signal of  FIG. 16B  is obtained. 
     Thus, the shield case  28  becomes unnecessary and the parasitic capacitance between the environment-side and living body-side electrodes  14  and  16  and the circuit board  26  becomes smaller compared to the case where the shield case  28  is provided, so that the absolute intensity of the reception signal can be increased, but the electromagnetic waves transmitted from the circuit board  26  are superposed as noise on the signal received at the environment-side electrode  14  and the living body-side electrode  16 , and the S/N ratio is degraded. 
     In particular, as the size of the portable terminal is reduced and the distance between the environment-side and living body-side electrodes  14  and  16  and the circuit board  26  is reduced, the influence of the electromagnetic noise transmitted from the circuit board  26  becomes more significant, and the problem of reduction in the S/N of the reception signal becomes more significant. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a communication system for enabling communication between a transmitter which is portable and a receiver which is fixed, using a capacitive coupling through a living body, wherein the receiver comprises a living body-side electrode which primarily capacitively couples with a living body, an environment-side electrode which primarily capacitively couples with an external environment, and a circuit board on which a circuit which processes a signal which is output from at least one of the living body-side electrode and the environment-side electrode is mounted, and the circuit board is not placed between the living body-side electrode and the environment-side electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will be described in detail based on the following drawings, wherein: 
         FIG. 1  is a diagram showing a structure of a transceiver in a communication system in a preferred embodiment of the present invention; 
         FIG. 2  is a diagram for explaining a communication session using a transceiver of a preferred embodiment of the present invention; 
         FIG. 3  is a diagram showing a structure of another configuration of a transceiver in a communication system of a preferred embodiment of the present invention; 
         FIG. 4  is a diagram showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention; 
         FIG. 5  is a diagram showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention; 
         FIG. 6  is a diagram showing an equivalent circuit of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention; 
         FIG. 7  is a diagram showing an example of a reception signal of a transceiver of a preferred embodiment of the present invention; 
         FIG. 8  is a diagram showing a structure of a receiver of a communication system in a preferred embodiment of the present invention; 
         FIG. 9  is a diagram showing a structure of another example configuration of a receiver of a communication system of a preferred embodiment of the present invention; 
         FIG. 10A  is a diagram showing a structure of a transmitter in a communication system of related art; 
         FIG. 10B  is a diagram showing a structure of a receiver in a communication system of related art; 
         FIG. 11  is a diagram showing an example of formation of an electric field when a communication system is used; 
         FIG. 12  is a diagram showing an equivalent circuit of a capacitive coupling formed in a communication system; 
         FIG. 13  is a diagram showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board in a transceiver of related art; 
         FIG. 14  is a diagram showing an equivalent circuit of an environment-side electrode, a living body-side electrode, and a circuit board in a transceiver of related art; 
         FIG. 15  is a diagram showing another example placement of an environment-side electrode, a living body-side electrode, and a circuit board in a transceiver of related art; 
         FIG. 16A  is a diagram showing an example of a reception signal of a communication system of related art; 
         FIG. 16B  is a diagram showing an example of a reception signal of a communication system of related art; 
         FIGS. 17A-17E  are diagrams showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention; 
         FIGS. 18A and 18B  are diagrams showing a usage form of a transceiver of a preferred embodiment of the present invention; 
         FIG. 19  is a diagram showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention; and 
         FIG. 20  is a diagram showing a placement of an environment-side electrode, a living body-side electrode, and a circuit board of a transceiver of a preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in a circuit diagram of  FIG. 1 , a transceiver  200  of a communication system of a preferred embodiment of the present invention comprises an encoder  30 , a transmission amplifier  32 , an environment-side electrode  34 , a living body-side electrode  36 , a decoder  40 , a reception amplifier  42 , a changeover switch  44 , and a controller  46 . 
     The transceiver  200  can be incorporated into a portable electronic device such as a portable phone and a PDA, and used as a portable communication terminal. In addition, the transceiver  200  may be placed in infrastructures such as a ticket barrier in a station, a vending machine, a shop, etc., and used as a communication terminal. 
     For example, users carrying portable communication terminals on each of which the transceiver  200  is mounted may contact or closely place a part of the body, to exchange information between the transceivers  200 . In addition, a user carrying the portable communication terminal on which the transceiver  200  is mounted may contact or closely place a part of the body to the living body-side electrode  36  of the transceiver  200  placed in an infrastructure such as a ticket barrier, to exchange data between the transceivers  200 . 
     The encoder  30  encodes data which is input from the outside using a predetermined encoding method and outputs the encoded data to the transmission amplifier  32 . The data which is input from the outside is input in a superposed state on a base wave of a high frequency. The frequency of the base wave is preferably set, for example, to 5 MHz or higher or 15 MHz or lower. 
     The transmission amplifier  32  comprises a differential amplifier circuit. An inverted input terminal (−) and a non-inverted input terminal (+) of the differential amplifier circuit are connected to an output terminal of the encoder  30 . An inverted output terminal and a non-inverted output terminal of the transmission amplifier  32  are connected to the environment-side electrode  34  and the living body-side electrode  36  through the changeover switch  44 . In the state where the inverted output terminal and the non-inverted output terminal of the transmission amplifier  32  are connected to the environment-side electrode  34  and the living body-side electrode  36  by the changeover switch  44 , the transmission amplifier  32  amplifies a signal which is input from the encoder  30  and differentially outputs to the environment-side electrode  34  and the living body-side electrode  36 . A potential difference between the environment-side electrode  34  and the living body-side electrode  36  changes according to the output of the transmission amplifier  32 . 
     The environment-side electrode  34  and the living body-side electrode  36  are each formed with a conductor. For example, these electrodes are formed in a sheet shape or a plate shape with a conductor such as aluminum, stainless steel, copper foil, copper sheet, etc. The environment-side electrode  34  and the living body-side electrode  36  are preferably placed in a state electrically insulated from each other, sandwiching a dielectric layer  38 . 
     The reception amplifier  42  comprises a differential amplifier circuit. An inverted input terminal (−) and a non-inverted input terminal (+) of the differential amplifier circuit are connected to the environment-side electrode  34  and the living body-side electrode  36  through the changeover switch  44 . An inverted output terminal and a non-inverted output of the differential amplifier circuit are connected to an input terminal of the decoder  40 . In the state where the inverted input terminal (−) and the non-inverted input terminal (+) of the reception amplifier  42  are connected to the environment-side electrode  34  and the living body-side electrode  36  by the changeover switch  44 , the reception amplifier  42  amplifies a potential difference between the environment-side electrode  34  and the living body-side electrode  36  and outputs as a potential difference between the inverted output terminal and the non-inverted output terminal. The decoder  40  receives an output signal from the reception amplifier  42 , decodes the signal using a decoding method corresponding to the encoding method used in the encoder  30 , and outputs the decoded signal. 
     In the transceiver  200 , the environment-side electrode  34  and the living body-side electrode  36  are shared between transmission and reception. The controller  46  switches the changeover switch  44  to the transmission amplifier  32  when data is to be transmitted and switches the changeover switch  44  to the reception amplifier  42  when data is to be received. The timing of the switching of the changeover switch  44  may be at a predetermined time period or may be achieved by the user. 
     For example, as shown in  FIG. 2 , a communication session can be executed by executing a polling process. In the following description, the transceivers  200  provided in the fixed device and the portable device periodically switch between the transmission state and the reception state at a predetermined period. 
     The transceiver  200  which is at a transmission side sends a call to the transceiver  200  which is at a reception side. When there is no transceiver  200  of the reception side in the reception range of the calling signal from the transceiver  200  of the transmission side, the call is repeated. When, on the other hand, the transceiver  200  of the reception side can receive the calling signal from the transceiver  200  of the transmission side, the transceiver  200  of the reception side receiving the calling signal is activated. The activated transceiver  200  of the reception side transmits a connection request signal to the transceiver  200  of the transmission side. When the transceiver  200  of the transmission side receives the connection request signal, the transceiver  200  of the transmission side returns a connection response signal if connection is possible. When the transceiver  200  of the reception side receives the connection response signal, the transceiver  200  of the reception side returns a connection response signal to the transceiver  200  of the transmission side. When the transceiver  200  of the transmission side receives the connection response signal, a data communication session is started. When the communication of data is completed, a completion signal is transmitted from the transceiver  200  of the transmission side to the transceiver  200  of the reception side, and the transceiver  200  of the reception side enters a sleep mode. 
     Alternatively, the transceiver  200  may have a structure as shown in  FIG. 3 . In this structure, the transmission amplifier  32  comprises a single amplifier circuit. An output terminal of the encoder  30  is connected to an input terminal of the amplifier circuit, and an output terminal of the amplifier circuit is connected to the living body-side electrode  36  through the changeover switch  44 . The environment-side electrode  34  is grounded. In the state where the output terminal of the transmission amplifier  32  is connected to the living body-side electrode  36  by the changeover switch  44 , the transmission amplifier  32  amplifies a signal which is input from the encoder  30  and outputs the amplified signal to the living body-side electrode  36 . A potential difference between the environment-side electrode  34  and the living body-side electrode  36  changes according to an output of the transmission amplifier  32 . The reception amplifier  42  comprises a single amplifier circuit. An input terminal of the amplifier circuit is connected to the living body-side electrode  36  through the changeover switch  44 , and an output terminal of the amplifier is connected to the decoder  40 . The environment-side electrode  34  is grounded. In the state where the input terminal of the reception amplifier  42  is connected to the living body-side electrode  36  by the changeover switch  44 , the reception amplifier  42  amplifies a signal which is input from the living body-side electrode  36  and outputs the amplified signal to the decoder  40 . The decoder  40  decodes the output of the reception amplifier  42  using a decoding method corresponding to the encoding method used in the encoder  30  and outputs the decoded signal. 
     The transceiver  200  of the present embodiment is mounted in a housing  50  as shown in  FIG. 4 . Such a configuration is particularly preferable, for example, when the transceiver  200  is used as a portable communication terminal such as a portable phone and a PDA. 
     In  FIG. 4 , electronic circuits used in the transceiver  200  are mounted on a circuit board  52 . In the present embodiment, at least the reception amplifier  42  is mounted on the circuit board  52 . For example, the encoder  30 , the transmission amplifier  32 , the decoder  40 , the reception amplifier  42 , the changeover switch  44 , and the controller  46  are mounted on the circuit board  52 . 
     Here, the environment-side electrode  34 , the living body-side electrode  36 , and the circuit board  52  are placed in the housing  50 . In the present embodiment, as shown in a perspective view of  FIG. 5 , the circuit board  52  is placed not in a location sandwiched between the environment-side electrode  34  and the living body-side electrode  36 . 
     When the environment-side electrode  34  and the living body-side electrode  36  are plate-shaped electrodes and are placed opposing each other in a manner where at least a part of the electrodes overlap each other, the circuit board  52  is preferably placed at a position where the circuit board  52  is spatially hidden by at least a part of one of the electrodes from at least a part of the other electrode. 
     For example, as shown in  FIG. 17A , preferably, a configuration is employed in which the circuit board  52 , the environment-side electrode  34 , and the living body-side electrode  36  are set to approximately the same size and the circuit board  52  is spatially hidden by one of the electrodes from the other electrode. Alternatively, as shown in  FIG. 17B , preferably, a configuration is employed in which the environment-side electrode  34  and the living body-side electrode  36  are set to approximately the same size, the circuit board  52  is set to a size smaller than the environment-side electrode  34  and the living body-side electrode  36 , and the circuit board  52  is spatially hidden by one of the electrodes from the other electrode. Alternatively, as shown in  FIG. 17C , preferably, a configuration is employed in which one of the environment-side electrode  34  and the living body-side electrode  36  which is placed closer to the circuit board  52  is set to approximately the same size as the circuit board  52 , the other electrode is set to a size smaller than the circuit board  52 , and the circuit board  52  is spatially hidden by the one electrode from the other electrode. Alternatively, as shown in  FIG. 17D , preferably, a configuration is employed in which the environment-side electrode  34  and the living body-side electrode  36  are set to approximately the same size, the circuit board  52  is set to a size larger than the environment-side electrode  34  and the living body-side electrode  36 , and at least a part of the circuit board  52  is spatially hidden by one of the electrodes from the other electrode. 
     In a configuration as shown in  FIG. 17E  where one of the environment-side electrode  34  and the living body-side electrode  36  which is closer to the circuit board  52  is set to a size smaller than the circuit board  52  and the other electrode is set to a size larger than the circuit board  52 , on the other hand, there is a portion where the circuit board  52  is not spatially hidden by one of the electrodes from the other electrode, and thus the obtained advantage is lower. 
     By relatively placing the environment-side electrode  34 , the living body-side electrode  36 , and the circuit board  52  in a manner described above, as shown in  FIG. 6 , it is possible to block the circuit board  52  by one of the environment-side electrode  34  and the living body-side electrode  36 , set a capacitive coupling C 4  between the other electrode and the circuit board  52  to be smaller than the parasitic capacitances C 1  and C 2  in the structure of related art, and reduce the influence of the electromagnetic noise from the circuit board  52  on the other electrode. 
     For example, in a circuit structure which shows reception signals of  FIGS. 16A and 16B , if the structure is changed to a structure as in the present embodiment where the circuit board  52  is not sandwiched between the environment-side electrode  34  and the living body-side electrode  36 , a reception signal as shown in  FIG. 7  is obtained. The reception signal obtained in the structure of the present embodiment has a higher absolute intensity than the reception signal of  FIG. 16A  and an improved S/N ratio over the reception signal of  FIG. 16B . 
     As described, by employing the structure of the transceiver  200  of the present embodiment, it is possible to improve the intensity of the reception signal at the reception and to improve S/N ratio of the reception signal. 
     As shown in  FIG. 18A , the electrode which is placed nearer to the circuit board  52  may be set as the environment-side electrode  34  and the other electrode may be set as the living body-side electrode  36 . Alternatively, as shown in  FIG. 18B , the electrode placed nearer to the circuit board  52  may be set as the living body-side electrode  36  and the other electrode maybe set as the environment-side electrode  34 . In these configurations, the phase of the reception signal during usage would be inverted. However, by applying a modulation method which does not depend on phase inversion such as PSK, FSK, and ASK, it is possible to use in the reverse direction. In other words, the names of the environment-side electrode  34  and the living body-side electrode  36  are only for the purpose of convenience, and the electrodes may be used in the opposite configuration. 
     As shown in  FIG. 19 , the dielectric layer  38  which functions as an antenna and which is sandwiched between the environment-side electrode  34  and the living body-side electrode  36  is not limited to a resin such as epoxy, and an insulating material similar to the circuit board  52  or a foam resin having a low dielectric constant may be used. 
     When the housing of the electronic device such as the portable phone is made of an insulating member, as shown in  FIG. 20 , a structure may be employed in which the housing itself is used as the dielectric layer  38  and sandwiched by the environment-side electrode  34  and the living body-side electrode  36 . In this case, it is also preferable to cover the electrode which is placed outside of the housing with an insulating film  54 . With such a structure, it is possible to improve the degree of freedom of placement of the members in the housing. 
     In the present embodiment, a transceiver  200  having both the transmission system and reception system is exemplified, but the present invention is not limited to such a configuration, and may be applied to a communication system in which a transmitter of a transmission system and a receiver of a reception system are separately formed. 
     Specifically, as shown in  FIG. 8 , in a receiver  202  comprising an environment-side electrode  44 , a living body-side electrode  46 , a decoder  40 , and a reception amplifier  42 , the circuit board may be provided not sandwiched between the environment-side electrode  44  and the living body-side electrode  46 , to obtain similar advantages. Alternatively, as shown in  FIG. 9 , a configuration may be employed in which the reception amplifier  42  is changed from the differential amplifier circuit to a single amplifier circuit.