Communication device and method, and program

The present invention relates to a device and a method for communication, and a program that makes it possible to provide a communication environment not limited by a use environment. An electrode controlling unit 261 in a transmitting device 260 checks a state of capacitive coupling of each of an electrode 271 and an electrode 272 in an electrode unit 262 with surroundings, controls connection of each electrode to a transmitting unit 263 according to a result of the check, and makes the electrode 271 and the electrode 272 function as a transmission signal electrode or a transmission reference electrode, the transmission signal electrode and the transmission reference electrode being different from each other. The transmitting unit 263 connects the electrode 271 and the electrode 272 to an amplifying unit under control of the electrode controlling unit 261, and transmits a signal to a communication medium 280 via one of the electrodes. The present invention is applicable to communication systems.

TECHNICAL FIELD

The present invention relates to a device and a method for communication, and a program, and particularly to a device and a method for communication, and a program that make communication possible in the communication device having at least two electrodes irrespective of physical positional relation between a user of the communication device and the communication device.

BACKGROUND ART

Conventionally, in a communication system including a transmitting device, a communication medium, and a receiving device, a physical communication signal transmitting path for transmitting a communication signal and a physical reference point path different from the communication signal transmitting path, the reference point path being to share a reference point for determining a difference in level of the communication signal between the transmitting device and the receiving device, are provided to perform communication (see for example Patent Document 1 or Patent Document 2).

For example, Patent Document 1 and Patent Document 2 describe communication techniques using a human body as a communication medium. In both methods, a human body is used as a first communication path, and direct capacitive coupling between electrodes in a ground or a space is provided as a second communication path, so that an entire communication path formed by the first communication path and the second communication path forms a closed circuit.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in such a communication system, two communication paths, that is, the communication signal transmitting path and the reference point path (the first communication path and the second communication path) need to be provided as a closed circuit between the transmitting device and the receiving device. Since the two paths are different paths, making the two paths stably coexist with each other may limit a use environment for communication.

For example, the strength of capacitive coupling between the transmitting device and the receiving device in the reference point path depends on a distance between the devices, and therefore the stability of the path differs depending on the distance. That is, in this case, there is a fear of the stability of communication depending on the distance of the reference point path between the transmitting device and the receiving device. In addition, there is a fear of the stability of communication being changed by the presence of a shielding object or the like between the transmitting device and the receiving device. Further, for example, when a ground is set as a reference point, and the transmitting device and the receiving device are capacitively coupled with each other via the ground (when the reference point path includes the ground), the reference point path is changed according to positional relation between the ground, the transmitting device, the receiving device, and the communication medium (for example a human body), and thus there is a fear of the stability of communication being varied.

As described above, in the communication methods that form the two paths, that is, the communication signal transmitting path and the reference point path as a closed circuit, the use environment greatly affects the stability of communication, and it is therefore difficult to perform stable communication.

Further, for example, when such a transmitting device and such a receiving device are applied to mobile devices, and the mobile devices perform communication via a human body, a manner of for example holding or wearing the casing of the transmitting device or the receiving device may differ depending on the user. That is, it is desirable to enable communication in any state as long as the transmitting device and the receiving device are in proximity to the human body; however, in the communication methods that form the two paths, that is, the communication signal transmitting path and the reference point path as a closed circuit as described above, it is difficult to secure each of the two paths unless positional relation between the communicating devices (the transmitting device and the receiving device) and the communication medium is defined.

Conventionally, there is a technique in which the function of each of two electrodes included in a communicating device is fixed in order to secure the two paths. For example, there is a contact type human body communicating device including a wristwatch type ID retaining unit and a reading unit for reading the ID retaining unit. In the human body communicating device, wearing positional relation between the two electrodes attached to the wristwatch type ID retaining unit and a human body is fixed.

However, such a communicating device requires positional relation between a user and the device to be in accordance with a specific rule, thus limiting the use environment.

The present invention has been made in view of such a situation, and it is an object of the present invention to impose no limitations on positional relation between a user and a communicating device, stabilize communication, and provide a high degree of convenience by dynamically controlling the functions of electrodes.

Means for Solving the Problems

A communicating device according to the present invention includes: communication processing means for performing communication processing; connecting means for connecting the communication processing means to a plurality of electrodes; and connection controlling means for controlling the connecting means to connect a first electrode of the plurality of electrodes, the first electrode being capacitively coupled with a communication medium, to a first terminal of the communication processing means, and connect a second electrode capacitively coupled with a space more strongly than the first electrode to a second terminal of the communication processing means.

The connection controlling means can include: signal level detecting means for detecting a signal level of a signal for checking a state of capacitive coupling of each of the plurality of electrodes with surroundings when the signal is supplied to each electrode; and controlling means for controlling connection of the plurality of electrodes to the communication processing means on a basis of the signal level detected by the signal level detecting means.

The connection controlling means further includes electrode selecting means for selecting an electrode to which to supply the signal, and the signal level detecting means can detect the signal level of the signal when the signal is supplied to the electrode selected by the electrode selecting means.

The connection controlling means further includes retaining means for retaining the signal level detected by the signal level detecting means for each electrode, and the controlling means can control the connection of the plurality of electrodes to the communication processing means on the basis of the signal level of each electrode, the signal level being retained by the retaining means.

The connection controlling means can simultaneously supply the signal to all the electrodes, and the signal level detecting means can simultaneously detect the signal level corresponding to each of all the electrodes.

The connection controlling means further includes a plurality of loads connected to each of the plurality of electrodes and connected in series with each other, and the signal level detecting means can detect signal levels occurring at the plurality of loads connected in series with each other.

The connection controlling means can control the connecting means after stopping the communication processing by the communication processing means.

The connection controlling means can control the connecting means in a free time of the communication processing by the communication processing means.

The connection controlling means can control the connecting means in a manner continuous with the communication processing by the communication processing means.

The connection controlling means can control the connecting means simultaneously with a transmission process by the communication processing means, using a transmission signal in the transmission process.

The communication processing means has a transmitting output terminal and a receiving input terminal, and the connection controlling means can control the connecting means to connect the first electrode to the transmitting output terminal or the receiving input terminal of the communication processing means.

A communicating method according to the present invention includes: a communication controlling step of controlling a communication processing unit for performing communication processing; and a connection controlling step of controlling a connecting unit for connecting the communication processing unit for performing the communication processing under control of the communication controlling step to a plurality of electrodes to connect a first electrode of the plurality of electrodes, the first electrode being capacitively coupled with a communication medium, to a first terminal of the communication processing unit, and connect a second electrode capacitively coupled with a space more strongly than the first electrode to a second terminal of the communication processing unit.

A program according to the present invention includes: a communication controlling step of controlling a communication processing unit for performing communication processing; and a connection controlling step of controlling a connecting unit for connecting the communication processing unit for performing the communication processing under control of the communication controlling step to a plurality of electrodes to connect a first electrode of the plurality of electrodes, the first electrode being capacitively coupled with a communication medium, to a first terminal of the communication processing unit, and connect a second electrode capacitively coupled with a space more strongly than the first electrode to a second terminal of the communication processing unit.

The communicating device and method and the program according to the present invention control a communication processing unit to perform communication processing, and control a connecting unit for connecting the communication processing unit to a plurality of electrodes to connect a first electrode of the plurality of electrodes, the first electrode being capacitively coupled with a communication medium, to a first terminal of the communication processing unit, and connect a second electrode capacitively coupled with a space more strongly than the first electrode to a second terminal of the communication processing unit.

Effect of the Invention

According to the present invention, communication is made possible irrespective of physical positional relation between a user of a communicating device and the communicating device.

DESCRIPTION OF REFERENCE NUMERALS

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described with reference to the drawings. Description will first be made of principles of communication by a communication system.

FIG. 1is a diagram showing an example of a configuration according to an embodiment of a communication system to which the present invention is applied.

The communication system1inFIG. 1includes a transmitting device10, a receiving device20, and a communication medium30. In the communication system1, the transmitting device10and the receiving device20transmit and receive a signal via the communication medium30. That is, in the communication system1, a signal transmitted by the transmitting device10is transmitted via the communication medium30, and then received by the receiving device20.

The transmitting device10has a transmission signal electrode11, a transmission reference electrode12, and a transmitting unit13. The transmission signal electrode11is one electrode of the electrode pair provided to transmit a signal to be transmitted via the communication medium30. The transmission signal electrode11is provided in such a manner as to be capacitively coupled to the communication medium30more strongly than the transmission reference electrode12as another electrode of the electrode pair. The transmitting unit13is provided between the transmission signal electrode11and the transmission reference electrode12. The transmitting unit13gives an electric signal (potential difference) desired to be transmitted to the receiving device20between these electrodes.

The receiving device20has a received signal electrode21, a reception reference electrode22, and a receiving unit23. The received signal electrode21is one electrode of the electrode pair provided to receive the signal transmitted via the communication medium30. The received signal electrode21is provided in such a manner as to be capacitively coupled to the communication medium30more strongly than the reception reference electrode22as another electrode of the electrode pair. The receiving unit23is provided between the received signal electrode21and the reception reference electrode22. The receiving unit23detects an electric signal (potential difference) generated between these electrodes by the signal transmitted via the communication medium30, converts the electric signal into a desired electric signal, and thereby reconstructs the electric signal generated by the transmitting unit13in the transmitting device10.

The communication medium30is formed by a material having a physical characteristic that allows the electric signal to be transmitted, for example, an electric conductor, a dielectric or the like. For example, the communication medium30is formed by a conductor typified by a metal such as copper, iron, aluminum or the like, a dielectric typified by pure water, rubber, glass or the like, or a material having both properties of a conductor and properties of a dielectric, such for example as a living body or the like as a complex of the conductor and the dielectric or an electrolytic solution such as a saline solution or the like. In addition, the communication medium30may have any shape. For example, the communication medium30may be of the shape of a line, of the shape of a plate, of the shape of a sphere, a prism, a circular cylinder or the like, or may further be of any arbitrary shape other than these shapes.

Description will first be made of relation between each electrode and the communication medium or a space surrounding the devices in such a communication system1. Incidentally, suppose in the following that the communication medium30is a perfect conductor for convenience of description. In addition, suppose that there is a space between the transmission signal electrode11and the communication medium30and there is a space between the received signal electrode21and the communication medium30, and that there is no electric coupling between the transmission signal electrode11and the communication medium30and there is no electric coupling between the received signal electrode21and the communication medium30. That is, a capacitance is formed between the transmission signal electrode11or the received signal electrode21and the communication medium30.

The transmission reference electrode12is disposed so as to face a space around the transmitting device10. The reception reference electrode22is disposed so as to face a space around the receiving device20. Generally, when a conductor sphere is present in a space, a capacitance is formed between the conductor sphere and the space. For example, when the shape of the conductor is a sphere with a radius r [m], the capacitance C is obtained by the following Equation (1).

In Equation (1), π denotes a ratio of the circumference of a circle to its diameter, and ∈ denotes a dielectric constant, which is obtained by the following Equation (2).

In Equation (2), ∈0denotes a dielectric constant in a vacuum and is 8.854×10−12[F/m], and ∈rdenotes a relative dielectric constant, which represents a ratio to the dielectric constant ∈0in the vacuum.

As shown in the above Equation (1), the larger the radius r, the larger the capacitance C. Incidentally, the magnitude of the capacitance C of a conductor having a complex shape other than a sphere cannot be expressed simply as in the above Equation (1). It is obvious, however, that the magnitude of the capacitance C of the conductor changes according to the magnitude of the surface area of the conductor.

As described above, the transmission reference electrode12forms a capacitance with the space surrounding the transmitting device10, and the reception reference electrode22forms a capacitance with the space surrounding the receiving device20. That is, it is shown that as viewed from a virtual point at infinity outside the transmitting device10and the receiving device20, the potentials of the transmission reference electrode12and the reception reference electrode22increase resistance thereof to variation as the capacitances are increased.

Incidentally, though for convenience of description or in a context or the like, a capacitor may herein be expressed simply as a capacitance, the capacitor and the capacitance have the same meaning. In addition, suppose that the transmitting device10and the receiving device20inFIG. 1are arranged such that a sufficient distance is maintained between the devices, and that therefore effects of the transmitting device10and the receiving device20on each other can be ignored. Further, suppose that the transmission signal electrode11in the transmitting device10is capacitively coupled with only the communication medium30, and that the transmission reference electrode12is located at a sufficient distance from the transmission signal electrode11, so that effects of the transmission reference electrode12and the transmission signal electrode11on each other can be ignored (the transmission reference electrode12and the transmission signal electrode11are not capacitively coupled with each other). Similarly, suppose that the received signal electrode21in the receiving device20is capacitively coupled with only the communication medium30, and that the reception reference electrode22is located at a sufficient distance from the received signal electrode21, so that effects of the reception reference electrode22and the received signal electrode21on each other can be ignored (the reception reference electrode22and the received signal electrode21are not capacitively coupled with each other). Further, in practice, the transmission signal electrode11, the received signal electrode21, and the communication medium30are disposed within a space, and therefore the transmission signal electrode11, the received signal electrode21, and the communication medium30each have a capacitance in relation to the space. For convenience of description, however, suppose that these capacitances can be ignored.

FIG. 2is a diagram in which the communication system1ofFIG. 1is represented by an equivalent circuit. That is, a communication system50shown inFIG. 2is equivalent in effect to the communication system1.

Specifically, the communication system50has a transmitting device60, a receiving device70, and a connection line80. The transmitting device60corresponds to the transmitting device10in the communication system1shown inFIG. 1. The receiving device70corresponds to the receiving device20in the communication system1shown inFIG. 1. The connection line80corresponds to the communication medium30in the communication system1shown inFIG. 1.

In the transmitting device60inFIG. 2, a signal source63-1and a reference point63-2within the transmitting device correspond to the transmitting unit13inFIG. 1. The signal source63-1generates, as a signal for transmission, a sine wave having a specific period ω×t [rad], where t [s] denotes time, and ω [rad/s] denotes an angular frequency, which can be expressed by the following Equation (3).

In Equation (3), π denotes a ratio of the circumference of a circle to its diameter, and f [Hz] denotes the frequency of the signal generated by the signal source63-1. The reference point63-2within the transmitting device is a point connected to a ground of a circuit within the transmitting device60. That is, one of terminals of the signal source63-1is set to a predetermined reference potential of the circuit within the transmitting device60.

Cte64is a capacitor, and represents a capacitance between the transmission signal electrode11and the communication medium30inFIG. 1. That is, Cte64is provided between the connection line80and the terminal of the signal source63-1which terminal is on an opposite side from the reference point63-2within the transmitting device. Ctg65is a capacitor, and represents a capacitance of the transmission reference electrode12inFIG. 1in relation to the space. Ctg65is disposed between the terminal of the signal source63-1which terminal is on the side of the reference point63-2within the transmitting device and a reference point representing a point at infinity (virtual point) on the space with the transmitting device60as a reference.

In the receiving device70inFIG. 2, Rr73-1, a detector73-2, and a reference point73-3within the receiving device correspond to the receiving unit23inFIG. 1. Rr73-1is a load resistance (reception load) for extracting a received signal. The detector73-2formed by an amplifier detects a potential difference across Rr73-1, and amplifies the potential difference. The reference point73-3within the receiving device is a point connected to a ground of a circuit within the receiving device70. That is, one of terminals of Rr73-1(one of input terminals of the detector73-2) is set to a predetermined reference potential of the circuit within the receiving device70.

Incidentally, the detector73-2may have other functions of for example demodulating a detected modulated signal and decoding encoded information included in the detected signal.

Cre74is a capacitor, and represents a capacitance between the received signal electrode21and the communication medium30inFIG. 1. That is, Cre74is provided between the connection line80and the terminal of Rr73-1which terminal is on an opposite side from the reference point73-3within the receiving device. Crg75is a capacitor, and represents a capacitance of the reception reference electrode22inFIG. 1in relation to the space. Crg75is disposed between the terminal of Rr73-1which terminal is on the side of the reference point73-3within the receiving device and a reference point76representing a point at infinity (virtual point) on the space with the receiving device20as a reference.

The connection line80represents the communication medium30as a perfect conductor. Incidentally, in the communication system50inFIG. 2, Ctg65and Crg75are expressed as electrically connected to each other via the reference point66and the reference point76on the equivalent circuit. In practice, however, these capacitors do not need to be electrically connected to each other, and it suffices for each of the capacitors to form a capacitance in relation to the space surrounding the transmitting device60or the receiving device70. It is important to know that when there is a conductor, a capacitance proportional to the magnitude of the surface area of the conductor is always formed between the conductor and a surrounding space. Incidentally, the reference point66and the reference point76do not need to be electrically connected to each other, and may have potentials independent of each other.

When the communication medium30inFIG. 1is a perfect conductor, for example, the conductivity of the connection line80is infinite. Therefore the length of the connection line80inFIG. 2does not affect communication. Incidentally, when the communication medium30is a conductor having a sufficient conductivity, a distance between the transmitting device and the receiving device does not affect the stability of communication practically. Thus, in such a case, the distance between the transmitting device60and the receiving device70may be any length.

In the communication system50, a circuit formed of the signal source63-1, Rr73-1, Cte64, Ctg65, Cre74, and Crg75is formed. A combined capacitance Cxof the four capacitors (Cte64, Ctg65, the Cre capacitor74, and Crg75) connected in series with each other can be expressed by the following Equation (4).

A sine wave Vt(t) generated by the signal source63-1is expressed by the following Equation (5).

Where Vm [V] denotes a maximum amplitude of a signal source voltage, and θ [rad] denotes an initial phase angle. An effective value Vtrms [V] of the voltage generated by the signal source63-1can be obtained by the following Equation (6).

A combined impedance Z of the whole circuit can be obtained by the following Equation (7).

Thus, an effective value Vrrms[V] of a voltage across Rr73-1can be obtained by the following Equation (8).

Hence, as shown in Equation (8), as the resistance value of Rr73-1is increased, and as the term 1/((2×π×f×Cx)2) is reduced with increase in the capacitance Cxand increase in frequency f [Hz] of the signal source63-1, a signal having a greater magnitude can be generated across Rr73-1.

For example, results of calculation of the effective value Vrrms[V] of the voltage across Rr73-1when the effective value Vtrms[V] of the voltage generated by the signal source63-1in the transmitting device60is fixed at 2 [V], the frequency f of the signal generated by the signal source63-1is set at 1 [MHz], 10 [MHz], or 100 [MHz], the resistance value of Rr73-1is set at 10 [KΩ],100[KΩ], or1[MΩ], and the capacitance Cxof the whole circuit is set at 0.1 [pF],1[pF], or10[pF] show that other conditions being equal, the effective value Vrrmsis higher when the frequency f is 10 [MHz] than when the frequency f is 1 [MHz], is higher when the resistance value of Rr73-1as reception load is 1 [MΩ] than when the resistance value of Rr73-1is 10 [KΩ], and is higher when the capacitance Cxis 10 [pF] than when the capacitance Cxis 0.1 [pF]. That is, as the value of the frequency f, the resistance value of Rr73-1, and the capacitance Cxare increased, the effective value Vrrmsof higher voltage is obtained.

Incidentally, when a transmitted signal has a very low signal level, communication is made possible by for example amplifying the signal detected by the detector73-2in the receiving device70.

Description will next be made of a case where the present communication system is physically formed in practice.FIG. 3is a diagram showing an example of a model for computing parameters occurring on the system when the above-described communication system is physically formed in practice.

That is, a communication system100has a transmitting device110, a receiving device120, and a communication medium130. The communication system100corresponds to the above-described communication system1(communication system50). Only parameters to be evaluated are different, and the communication system100has basically the same configuration as the communication system1and the communication system50.

That is, making description by comparison with the communication system1ofFIG. 1, the transmitting device110corresponds to the transmitting device10, the receiving device120corresponds to the receiving device20, and the communication medium130corresponds to the communication medium30.

The transmitting device110has a transmission signal electrode111corresponding to the transmission signal electrode11, a transmission reference electrode112corresponding to the transmission reference electrode12, and a signal source113corresponding to the transmitting unit13. That is, the transmission signal electrode111is connected to one of terminals on both sides of the signal source113, and the transmission reference electrode112is connected to the other terminal. The transmission signal electrode111is disposed in proximity to the communication medium130. The transmission reference electrode112is formed in such a manner as to have a capacitance in relation to a space external to the transmitting device110. Incidentally, while the signal source63-1and the reference point63-2within the transmitting device inFIG. 2correspond to the transmitting unit13, the reference point within the transmitting device is omitted inFIG. 3for convenience of description.

As with the transmitting device110, the receiving device120has a received signal electrode121corresponding to the received signal electrode21, a reception reference electrode122corresponding to the reception reference electrode22, and Rr123-1and a detector123-2corresponding to the receiving unit23. That is, the received signal electrode121is connected to one of terminals on both sides of Rr123-1, and the reception reference electrode122is connected to the other terminal. The received signal electrode121is disposed in proximity to the communication medium130. The reception reference electrode122is formed in such a manner as to have a capacitance in relation to a space external to the receiving device120. Incidentally, while Rr73-1, the detector73-2, and the reference point73-3within the receiving device inFIG. 2correspond to the receiving unit23, the reference point within the receiving device is omitted inFIG. 3for convenience of description.

Incidentally, suppose that the communication medium130is a perfect conductor as in the cases ofFIG. 1andFIG. 2. Suppose that the transmitting device110and the receiving device120are arranged at a sufficient distance from each other, and that effects of the transmitting device110and the receiving device120on each other can be ignored.

Description will be made of the parameters. A capacitance Cte114between the transmission signal electrode111and the communication medium130corresponds to Cte64inFIG. 2. A capacitance of the transmission reference electrode112in relation to the space (a capacitance between the transmission reference electrode112and a reference point116-1representing a virtual point at infinity from the transmission reference electrode112on the space) Ctg115corresponds to Ctg65inFIG. 2. The reference point116-1and a reference point116-2representing a virtual point at infinity from the transmitting device110on the space correspond to the reference point66inFIG. 2. The transmission signal electrode111is a disk-shaped electrode having an area Step [m2], and is located at a minute distance dte [m] from the communication medium130. The transmission reference electrode112is also a disk-shaped electrode, and has a radius rtg [m].

On the receiving device120side, a capacitance Cre124between the received signal electrode121and the communication medium130corresponds to Cre74inFIG. 2. A capacitance of the reception reference electrode122in relation to the space (a capacitance between the reception reference electrode122and a reference point representing a virtual point at infinity from the reception reference electrode122on the space) Crg125corresponds to Crg75inFIG. 2. The reference point126-1and a reference point126-2representing a virtual point at infinity from the receiving device120on the space correspond to the reference point76inFIG. 2. The received signal electrode121is a disk-shaped electrode having an area Sre [m2], and is located at a minute distance dre [m] from the communication medium130. The reception reference electrode122is also a disk-shaped electrode, and has a radius rrg [m].

Further, new parameters are added to the communication system100ofFIG. 3as follows.

For example, added to the transmitting device110as new parameters are a capacitance Ctb117-1formed between the transmission signal electrode111and the transmission reference electrode112, a capacitance Cth117-2formed between the transmission signal electrode111and the space (a capacitance between the transmission signal electrode111and a reference point116-2representing a virtual point at infinity from the transmission signal electrode111on the space), and a capacitance Cti117-3formed between the transmission reference electrode112and the communication medium130.

Added to the receiving device120as new parameters are a capacitance Crb127-1formed between the received signal electrode121and the reception reference electrode122, a capacitance Crh127-2formed between the received signal electrode121and the space (a capacitance between the received signal electrode121and a reference point126-2representing a virtual point at infinity from the received signal electrode121on the space), and a capacitance Cri127-3formed between the reception reference electrode122and the communication medium130.

Further, a capacitance Cm132formed between the communication medium130and the space (a capacitance between the communication medium130and a reference point136representing a virtual point at infinity from the communication medium130on the space) is added to the communication medium130as a new parameter. In addition, since the communication medium130in practice has an electric resistance depending on the size, material and the like of the communication medium130, resistance values Rm131and Rm133as resistance components of the communication medium130are added as new parameters.

Incidentally, though omitted in the communication system100ofFIG. 3, when the communication medium has not only conductivity but also dielectric properties, a capacitance according to the dielectric properties is also formed. When the communication medium does not have conductivity but has dielectric properties, coupling between the transmission signal electrode111and the received signal electrode121is provided by a capacitance determined by the dielectric constant, distance, size, and disposition of the dielectric.

In this case, it is assumed that the transmitting device110and the receiving device120are separated from each other at a distance such that an element of capacitive coupling can be ignored (effects of capacitive coupling between the transmitting device110and the receiving device120can be ignored). If the distance is short, depending on positional relation between each electrode within the transmitting device110and each electrode within the receiving device120, capacitances between the electrodes may need to be considered according to the above-described way of thinking.

The communication system100having such parameters has characteristics as follows.

For example, the higher the value of Cte114(the higher the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130. In addition, the higher the value of Ctg115(the higher the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130. Further, the lower the value of Ctb117-1(the lower the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130. In addition, the lower the value of Cth117-2(the lower the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130. Further, the lower the value of Cti117-3(the lower the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130.

The higher the value of Cre124(the higher the capacitance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120. In addition, the higher the value of Crg125(the higher the capacitance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120. Further, the lower the value of Crb127-1(the lower the capacitance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120. In addition, the lower the value of Crh127-2(the lower the capacitance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120. Further, the lower the value of Cri127-3(the lower the capacitance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120. In addition, the lower the value of Rr123-1(the higher the resistance), the greater the magnitude of the signal extracted from the communication medium130by the receiving device120.

The lower the values of Rm131and Rm133as resistance components of the communication medium130(the lower the resistances), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130. In addition, the lower the value of Cm132as the capacitance of the communication medium130in relation to the space (the lower the capacitance), the greater the magnitude of the signal applied by the transmitting device110to the communication medium130.

The magnitude of capacitance of a capacitor is substantially proportional to the magnitude of the surface area of the electrode. Therefore it is generally desirable to increase the size of each electrode as much as possible. However, simply increasing the size of electrodes may also increase capacitances between the electrodes. In addition, an extreme ratio between the sizes of electrodes may decrease efficiency. It is thus necessary to determine the size, arrangement position and the like of each electrode in consideration of a total balance.

Incidentally, with the characteristics of the above-described communication system100, efficient communication is made possible by viewing the present equivalent circuit from a viewpoint of impedance matching and determining each parameter in a frequency band of high frequencies of the signal source113. By raising the frequency, it is possible to secure a reactance even with a low capacitance, so that each device can be miniaturized easily.

The reactance of a capacitor is generally increased with decrease in frequency. On the other hand, the communication system100operates based on capacitance coupling, and therefore this determines a lower limit of the frequency of the signal generated by the signal source113. In addition, an arrangement of Rm131, Cm132, and Rm133forms a low-pass filter, and therefore characteristics thereof determine an upper limit of the frequency.

A specific numerical value of each parameter will next be considered. Incidentally, suppose in the following that the communication system100is placed in the air for convenience of description. In addition, suppose that the transmission signal electrode111, the transmission reference electrode112, the received signal electrode121, and the reception reference electrode122of the communication system100are each a conductor disk having a diameter of 5 cm.

Supposing that the interval dte between the transmission signal electrode111and the communication medium130is 5 mm, the value of the capacitance Cte114formed by the transmission signal electrode111and the communication medium130is obtained by the following Equation (9).

Assume that Equation (9) can be adapted to Ctb117-1as the capacitance between the electrodes. While the equation essentially holds when the area of the electrodes is sufficiently large as compared with the interval as described above, an approximation may be made by this equation in this case. Supposing that the interval between the electrodes is 5 cm, Ctb117-1is expressed by the following Equation (10).

An assumption is made in this case that when the interval between the transmission signal electrode111and the communication medium130is short, the transmission signal electrode111is weakly coupled with the space. Therefore suppose that the value of Cth117-2is sufficiently lower than the value of Cte114, and that the value of Cth117-2can be set to one tenth of the value of Cte114as expressed by Equation (11).

Ctg115indicating the capacitance formed by the transmission reference electrode112and the space can be obtained by the following Equation (12).

Since the transmission signal electrode111and the communication medium130are situated at substantially the same position, the value of Cti117-3is considered to be equal to Ctb117-1as follows.
Cti=Ctb=0.35 [pF]

When the formation (size, placement position and the like) of each electrode in the receiving device120is the same as in the transmitting device110, the parameters of the receiving device120are set in the same manner as the parameters of the transmitting device110as follows.
Cre=Cte=3.5 [pF]
Crb=Ctb=0.35 [pF]
Crh=Cth=0.35 [pF]
Crg=Ctg=1.8 [pF]
Cri=Cti=0.35 [pF]

For convenience of description, suppose in the following that the communication medium130is an object having characteristics close to those of a living body of about a size of a human body. Suppose that an electric resistance of the communication medium130from the position of the transmission signal electrode111to the position of the received signal electrode121is 1 [MΩ], and that the values of Rm131and Rm133are each 500 [KΩ]. Suppose that the value of the capacitance Cm132formed between the communication medium130and the space is 100 [pF]. Further, suppose that the signal source113generates a sine wave having a maximum value of 1 [V] and a frequency of 10 [MHz].

When a simulation is performed using the above parameters, a difference between a maximum value and a minimum value (a difference between peak values) of the waveform of a received signal is observed to be about 10 [μV]. Thus, by amplifying this by an amplifier (detector123-2) having a sufficient gain, it is possible to reconstruct the signal of the transmitting side (signal generated in the signal source113) on the receiving side.

Thus, the above-described communication system to which the present invention is applied eliminates a need for a physical reference point path, and can achieve communication by only a communication signal transmitting path. Therefore a communication environment not limited by a use environment can be readily provided.

A concrete example of application of a communication system as described above will next be described. For example, a communication system as described above can use a living body as a communication medium.FIG. 4is a schematic diagram showing an example of a communication system when communication is performed via a human body. The communication system150inFIG. 4is a system in which music data is transmitted from a transmitting device160attached to an arm part of a human body, and a receiving device170attached to a head part of the human body receives the music data, converts the music data into audio, and outputs the audio to allow the user to listen to the audio. The communication system150corresponds to the above-described communication systems (for example the communication system1). The transmitting device160and the receiving device170correspond to the transmitting device10and the receiving device20, respectively. The human body180in the communication system150is a communication medium, and corresponds to the communication medium30inFIG. 1.

Specifically, the transmitting device160has a transmission signal electrode161, a transmission reference electrode162, and a transmitting unit163. The transmission signal electrode161, the transmission reference electrode162, and the transmitting unit163correspond to the transmission signal electrode11, the transmission reference electrode12, and the transmitting unit13, respectively, inFIG. 1. The receiving device has a received signal electrode171, a reception reference electrode172, and a receiving unit173. The received signal electrode171, the reception reference electrode172, and the receiving unit173correspond to the received signal electrode21, the reception reference electrode22, and the receiving unit23, respectively, inFIG. 1.

Thus, the transmitting device160and the receiving device170are placed such that the transmission signal electrode161and the received signal electrode171are in contact with or in proximity to the human body180as a communication medium. Since it suffices for the transmission reference electrode162and the reception reference electrode172to be in contact with a space, coupling with a ground in the vicinity or coupling between the transmitting device and the receiving device (or electrodes) is not required.

FIG. 5is a diagram of assistance in explaining another example of realizing the communication system150. InFIG. 5, the receiving device170is in contact with (or in proximity to) a sole part of the human body180, and communicates with the transmitting device160attached to an arm part of the human body180. Also in this case, the transmission signal electrode161and the received signal electrode171are disposed so as to be in contact with (or in proximity to) the human body180as a communication medium, and the transmission reference electrode162and the reception reference electrode172are disposed so as to face the space. This application example cannot be realized by the conventional techniques using a ground as one communication path, in particular.

That is, the communication system150as described above eliminates the need for a physical reference point path, and can achieve communication by only a communication signal transmitting path. Therefore a communication environment not limited by a use environment can be readily provided.

In the communication system as described above, a method of modulation of a signal to be passed through the communication medium is not particularly limited as long as both the transmitting device and the receiving device can deal with the modulation method. An optimum method can be selected in consideration of characteristics of the communication system as a whole. Specifically, the modulation method may provide one of a baseband, an amplitude-modulated, and a frequency-modulated analog signal and a baseband, an amplitude-modulated, a frequency-modulated, and a phase-modulated digital signal, or a mixture of a plurality of signals.

Further, in the communication system as described above, a plurality of communications may be established using one communication medium, so that full-duplex communication, communication between a plurality of devices by a single communication medium, or the like can be performed.

Methods for realizing such multiplex communication include for example a spread spectrum system, a frequency band division system, a time division system and the like. By communicating using each such system, the communication system can perform simultaneous communication with a plurality of devices using the same communication medium, such for example as communication between a plurality of devices and a single device, communication between a plurality of devices and a plurality of devices, and the like. Further, two or more of the above-described methods may be combined with each other, of course.

It is particularly important in a specific application that the transmitting device and the receiving device can simultaneously communicate with a plurality of other devices. Assuming application to a ticket for a transportation, for example, when a user carrying both a device A having information on a commuter pass and a device B having an electronic money function uses an automatic ticket gate, a system as described above is used, and thereby simultaneous communication with the device A and the device B is performed. When a used section includes a section not covered by the commuter pass, the system can be used conveniently to deduct an amount of money that is lacking from the electronic money of the device B.

As described above, the transmitting device10and the receiving device20do not need to construct a closed circuit using a reference electrode, and can easily perform a stable communication process unaffected by an environment only by transmitting and receiving a signal via signal electrodes. Incidentally, since a structure for the communication process is simplified, the communication system1can easily use various communication systems such as modulation, encoding, encryption, multiplexing and the like in combination with each other.

When such a communication system is used to perform communication via the human body180as shown inFIG. 4, for example, it is preferable that the transmitting device and the receiving device be miniaturized as mobile devices. While a method of use is conceivable in which the transmitting device and the receiving device are for example fixed to an arm, a leg or the like using a belt or the like so that positional relation between the devices and the human body is stabilized, a method of use in which a user freely holds or places the transmitting device and the receiving device as in a case of a portable type telephone, for example, is also assumed. Therefore a higher degree of freedom of a wearing method (positional relation between the devices and the human body) is desirable, and widens a range of applications.

For example, as shown inFIG. 6, a casing of the transmitting device10inFIG. 1is formed as a casing200. Electrodes211to216to be used as the transmission signal electrode11and the transmission reference electrode12are provided in external surfaces of the casing200. When a user holds such a transmitting device by a hand220, the transmitting device10can perform communication via the human body as shown inFIG. 4orFIG. 5.

Incidentally, each of the electrodes211to216can be used as the transmission signal electrode11or the transmission reference electrode12. That is, by controlling (changing) connections of the electrodes211to216to an internal circuit, the transmitting device10can use arbitrary electrodes as the transmission signal electrode11, and use other arbitrary electrodes as the transmission reference electrode12.

In such a case, however, it is not possible to predict how the user (the hand220of the user) holds the casing200. Therefore, when the electrodes211to216are fixedly assigned the role of one of the transmission signal electrode11and the transmission reference electrode12, both the transmission signal electrode11and the transmission reference electrode12may be close to the hand220as a communication medium in similar manners to each other depending on a holding state. In this case, a desirable communication environment may not be obtained.

Accordingly, the communication device10inFIG. 6controls the connection of the electrodes211to216to the internal circuit according to the position of the hand220to thereby optimize the positional relation between the transmission signal electrode (electrodes used as the transmission signal electrode) and the transmission reference electrode (electrodes used as the transmission reference electrode) and the communication medium (hand220). For example, inFIG. 6, the transmitting device10connects the electrode212, the electrode213, the electrode215, and the electrode216covered by the hand220to the internal circuit so that the electrode212, the electrode213, the electrode215, and the electrode216are used as the transmission signal electrode11, and connects the other electrodes211and214to the internal circuit so that the electrodes211and214are used as the transmission reference electrode12. In other words, the communication device10performs control so as to optimize the positional relation between the communication medium and the electrode pair (electrode pair formed by the transmission signal electrode11and the transmission reference electrode12).

Incidentally, the transmitting device10can control the connection so as to use a plurality of electrodes as the transmission signal electrode11or the transmission reference electrode12. In addition, the transmitting device10does not need to make connection so as to use all the electrodes as the transmission signal electrode11or the reception reference electrode12, and there may be unconnected electrodes. In the case ofFIG. 6, for example, electrodes only partly covered by the hand220, such as the electrode212, the electrode213, and the electrode215, may be disconnected. By thus controlling the connection, the transmitting device10is for example able to use only electrodes that can be clearly distinguished as electrodes capacitively coupled with the communication medium strongly or weakly among a group of electrodes as the transmission signal electrode11or the transmission reference electrode12, and not to use electrodes capacitively coupled with the communication medium to a medium degree (electrodes that cannot be clearly distinguished as electrodes to be used as the transmission signal electrode11or to be used as the transmission reference electrode12). The transmitting device10can thereby set the transmission signal electrode11and the transmission reference electrode having an optimum positional relation to the communication medium.

FIG. 7is a block diagram showing an example of configuration of an embodiment of the transmitting device in this case.

The transmitting device260inFIG. 7has an electrode controlling unit261, an electrode unit262, and a transmitting unit263. The electrode unit262has an electrode271and an electrode272as a pair of electrodes having the shape of a disk, for example, and capacitively coupled with an outside. The electrode controlling unit261controls connection of each electrode of the electrode unit262to the transmitting unit263. The transmitting unit263performs a process of transmitting a signal via the electrode unit262.

The transmitting device260corresponds to the transmitting device10inFIG. 1. The transmitting device260outputs a signal to a communication medium280corresponding to the communication medium30, using electrostatic induction, and thereby transmits the signal to a receiving device via the communication medium280, which is a conductor or a dielectric. The electrode pair of the electrode271and the electrode272of the electrode unit262corresponds to the electrode pair of the transmission signal electrode11and the transmission reference electrode12inFIG. 1. The transmitting unit263corresponds to the transmitting unit13inFIG. 1.

That is, one of the electrode271and the electrode272is connected as the transmission signal electrode11to the transmitting unit263, and the other is connected as the transmission reference electrode12to the transmitting unit263. The electrode controlling unit261checks a state of capacitive coupling (magnitude of capacitance) of the electrode271and the electrode272with the external part, and controls the connection of the electrode271and the electrode272to the transmitting unit263to be optimized according to the state.

For example, suppose that as shown inFIG. 7, the communication medium280serving as a communication path and having conductivity or dielectric properties approaches the electrode271. At this time, the electrode272is facing a free space, and forms a capacitance Ctg295with the free space. On the other hand, as the communication medium280approaches the electrode271, capacitive coupling of the electrode271with the free space is weakened, and capacitive coupling of the electrode271with the communication medium280becomes dominant. When the communication medium280is a conductor or an object having a higher dielectric constant than air, a capacitance Cte294viewed from the electrode271is larger than the capacitance Ctg295. Hence, when some signal is supplied to the electrodes, the magnitude of a load attached to the paths is known on the basis of the magnitude of signal level of the load. In the case of the free space, the capacitance is low, and thus the signal level of the load is low. In the case of a conductor or a dielectric, the capacitance is high, and thus the signal level of the load is higher.

The capacitance as viewed from the electrode is thus changed, and thereby the signal level (magnitude of amplitude) detected when a signal is applied to the electrode is changed. Thus, by detecting the signal level, the electrode controlling unit261can grasp a state of the electrode (whether the communication medium280is in the vicinity or not). The electrode controlling unit261controls the connection between the transmitting unit263and the electrode unit262according to the state of each electrode which state is thus grasped.

The transmitting unit263connects each of the electrode271and the electrode272of the electrode unit262as the transmission signal electrode or the transmission reference electrode under control of the electrode controlling unit261.

FIG. 8is a block diagram showing an example of detailed configuration of the electrode controlling unit261inFIG. 7. The electrode controlling unit261inFIG. 8has a main control unit301, a signal input controlling unit302, a retaining unit303, a connection controlling unit304, a switching controlling unit305, a signal source311, a switch312, a detecting unit313, and a connecting unit314.

The main control unit301performs a process of controlling the connection between the electrode unit262and the transmitting unit263by controlling various parts within the electrode controlling unit261, for example the signal input controlling unit302, the retaining unit303, the connection controlling unit304, and the switching controlling unit305. The signal input controlling unit302is controlled by the main control unit301to turn on or off the switch312. The signal input controlling unit302thereby controls input of a signal generated in the signal source311to each electrode of the electrode unit262.

The retaining unit303is controlled by the main control unit301to retain a signal level detected in the detecting unit313and supply the value to the main control unit301as required. The connection controlling unit304is controlled by the main control unit301to control the switching of connection by the connecting unit314. The switching controlling unit305is controlled by the main control unit301to supply information for controlling the connection between the electrode unit262and the transmitting unit263to the transmitting unit263. The switching controlling unit305thereby controls the connection between the electrode unit262and the transmitting unit263.

The signal source311supplies a signal of a predetermined frequency to the switch312. The switch312is controlled by the signal input controlling unit302to supply the signal from the signal source311to the detecting unit313, or to stop the supply. The detecting unit313has a load resistance321having a predetermined resistance value within the detecting unit313. The detecting unit313can detect a potential across the load resistance321. That is, information on the potential across the load resistance321is supplied to the retaining unit303. The retaining unit303obtains a signal level applied to an electrode on the basis of the information on the potential across the load resistance321, and retains the value.

The connecting unit314has a kind of multi-contact switch. The multi-contact switch changes connection between a terminal322connected to the detecting unit313and a plurality of terminals provided for each electrode. In the case ofFIG. 8, for example, the terminal323is connected to the electrode271, and the terminal324is connected to the electrode272. That is, the connecting unit314is controlled by the connection controlling unit304to perform switching so as to connect the terminal322to the terminal323or the terminal324or not to connect the terminal322to the terminal323or the terminal324. The connecting unit314thereby performs switching so as to supply the signal from the signal source311to the electrode271or the electrode272, or not to supply the signal from the signal source311to the electrode271or the electrode272.

In a mode of checking capacitive coupling of each electrode, the main control unit301controls the connection controlling unit304to sequentially connect the terminal322in the connecting unit314to each of the terminal323and the terminal324, and finally release the connection and set an open state. In addition, the main control unit301controls the signal input controlling unit302in each of these states (the state of the terminal322being connected to the terminal323, the state of the terminal322being connected to the terminal324, and the state of the terminal322being unconnected), so that the switch is turned on for a predetermined time to apply the signal. The detecting unit313detects the signal level of each signal thus applied, and then supplies the signal level to the retaining unit303to make the signal level retained by the retaining unit303. When obtaining the result of detection of the signal level from the retaining unit303, the main control unit301supplies the result of detection of the signal level as control information to the transmitting unit263via the switching controlling unit305.

FIG. 9is a block diagram showing an example of detailed configuration of the transmitting unit263inFIG. 7.

The transmitting unit263inFIG. 9has a transmission controlling unit351, a transmission signal generating unit352, an amplifying unit353, a connecting unit354, and a connection controlling unit355.

The transmission controlling unit351controls each part within the transmitting unit263to thereby perform a control process for signal transmission, such as controlling connection to the electrode unit262and outputting a transmission signal, on the basis of the control information supplied from the electrode controlling unit261(the switching controlling unit305in the electrode controlling unit261).

The transmission signal generating unit352can generate a plurality of kinds of transmission signals, for example. The transmission signal generating unit352generates a transmission signal corresponding to transmission information indicated by the transmission controlling unit351, and then supplies the transmission signal to the amplifying unit353. The amplifying unit353is formed by an operational amplifier or the like. Under control of the transmission controlling unit351, the amplifying unit353amplifies the transmission signal supplied from the transmission signal generating unit352, and then supplies the transmission signal to the connecting unit354to supply the transmission signal to the transmission signal electrode and the transmission reference electrode. The connecting unit354has a multi-contact switch for switching connection between output terminals of the amplifying unit353and electrodes. That is, under control of the connection controlling unit355, the connecting unit354connects each of the output terminal361and the output terminal362of the amplifying unit353to one of a terminal363and a terminal364(terminals different from each other), or disconnect (open) both the output terminal361and the output terminal362. In the example ofFIG. 9, the connecting unit354connects the output terminal361of the amplifying unit353for the transmission signal electrode to the terminal364(electrode272), and connects the output terminal362for the transmission reference electrode to the terminal363(electrode271). That is, in this case, the electrode271acts as the transmission reference electrode, and the electrode272acts as the transmission signal electrode.

For example, in a mode of transmitting a signal, on the basis of the control information generated and supplied by the electrode controlling unit261in the mode of checking the capacitive coupling of each electrode, the transmission controlling unit351controls the connection controlling unit355to connect each terminal of the connecting unit354and thereby determine the transmission signal electrode and the transmission reference electrode. When the connection to the electrode unit262is established, the transmission controlling unit351controls the transmission signal generating unit352to generate a transmission signal, controls the amplifying unit353to amplify the transmission signal, and then makes the transmission signal output from the electrode unit262to the communication medium280via the connecting unit354.

As described above, the transmitting device260performs optimization by switching the transmission signal electrode and the transmission reference electrode according to a state of capacitive coupling of each electrode, and then transmits a signal. Therefore the signal can be transmitted to the receiving device stably irrespective of positional relation to the human body of a user as communication medium.

A flow of a process for such control of the electrodes will next be described. First, a flow of an electrode controlling process in a transmission process performed by the transmitting device260will be described with reference to a flowchart ofFIG. 10.

While the transmission process is performed, the main control unit301in step S1controls the transmission controlling unit351in the transmitting unit263via the switching controlling unit305to stop transmitting a signal, with predetermined timing or a predetermined process as a cue. According to an instruction from the main control unit301, the transmission controlling unit351controls the transmission signal generating unit352to stop generating the signal.

When the generation of the signal is stopped, the main control unit301advances the process to step S2, where the main control unit301performs the electrode controlling process for controlling the connection between the electrode unit262and the transmitting unit263. Details of the electrode controlling process will be described later. When the electrode controlling process is ended, the main control unit301advances the process to step S3, where the main control unit301controls the transmission controlling unit351in the transmitting unit263via the switching controlling unit305to start transmitting a signal. According to an instruction from the main control unit301, the transmission controlling unit351controls the transmission signal generating unit352to start generating the signal.

When the transmission of the signal is ended, the main control unit301ends the transmission process.

As described above, the signal is transmitted, and optimization is performed by switching the transmission signal electrode and the transmission reference electrode according to a state of capacitive coupling of each electrode. Therefore the main control unit301can transmit the signal to the receiving device stably irrespective of positional relation between the transmitting device260and the communication medium280.

Details of the electrode controlling process performed in step S2inFIG. 10will next be described with reference to a flowchart ofFIG. 11.

When the electrode controlling process is started, the main control unit301in step S21controls the transmitting unit263via the switching controlling unit305to disconnect the electrodes and the transmitting unit from each other. Under the control, the transmission controlling unit351in the transmitting unit263makes each terminal of the connecting unit354opened, thereby disconnecting the electrode unit262and the transmitting unit263from each other.

After each electrode and the transmitting unit263are disconnected from each other, the main control unit301in step S22controls the connecting unit314via the connection controlling unit304to set the connection between the electrode unit262and the electrode controlling unit261to an initial value. That is, the main control unit301controls the connecting unit314to connect the electrode to be checked first to the detecting unit313. Then, the main control unit301in step S23controls the signal input controlling unit302to set the switch312in an on state, whereby a signal generated in the signal source311is input to the detecting unit313. The signal is supplied to an electrode of the electrode unit262via the detecting unit313and the connecting unit314. The detecting unit313in step S24detects a potential difference across the load resistance321as a signal level, and supplies information on the potential difference to the retaining unit303. The retaining unit303in step S25retains the information on the potential difference as signal level.

In step S26, the main control unit301determines whether the signal level is detected in all patterns. When the main control unit301determines that the detection is completed, the main control unit301advances the process to step S27, where the main control unit301obtains the detected signal level from the retaining unit303, and selects each of the electrodes of the electrode unit262as an electrode to be used as the transmission signal electrode or as an electrode to be used as the transmission reference electrode on the basis of the obtained signal level. For example, when the signal level is a predetermined threshold value or higher, the capacitance formed between the electrode and the surroundings is large, and therefore the main control unit301determines that the communication medium280is in proximity, and selects the electrode as the transmission signal electrode. Conversely, for example, when the signal level is lower than the predetermined threshold value, the capacitance formed between the electrode and the surroundings is small, and therefore the main control unit301determines that the electrode is capacitively coupled with the space, and selects the electrode as the transmission reference electrode.

The main control unit301in step S28controls the connecting unit314via the connection controlling unit304to open all the terminals and thereby disconnect the electrode unit262and the electrode controlling unit261from each other. Then, the main control unit301supplies identifying information for the transmission signal electrode and the transmission reference electrode which information indicates which electrode is to be used as the transmission signal electrode or the transmission reference electrode to the transmission controlling unit351in the transmitting unit263via the switching controlling unit305. The transmission controlling unit351in step S29controls the connecting unit354to connect the electrodes of the electrode unit262to the transmitting unit263on the basis of the supplied identifying information. That is, the electrode unit262is thereby connected to the transmitting unit263by a method optimized on the basis of checks by the electrode controlling unit261. When the process of step S29is ended, the main control unit301ends the electrode controlling process.

Incidentally, when the main control unit301determines in step S26that the signal level is not detected in all the patterns (signal levels for all the electrodes are not detected), the main control unit301in step S30controls the connecting unit314via the connection controlling unit304to reset a pattern of connection between the electrode unit262and the electrode controlling unit261. That is, the connecting unit314connects the terminal322connected to the detecting unit313to the terminal for the electrode to be checked next. After the process of step S30is ended, the main control unit301returns the process to step S23to perform the process for the new electrode.

That is, each part of the electrode controlling unit261repeatedly performs the processes of steps S23to S26and step S30to check a state of capacitive coupling of each electrode. When the checking of all the electrodes is thereafter ended, the main control unit301performs the process from step S27on down to optimize the connection between the electrode unit262and the transmitting unit263.

Because the electrode controlling process is performed as described above, the main control unit301can determine for each of the electrodes whether to use the electrode as the transmission reference electrode or whether to use the electrode as the transmission signal electrode, and a signal can be transmitted to the receiving device stably irrespective of the positional relation between the transmitting device260and the communication medium280.

Incidentally, there may be three or more electrodes in the electrode unit262. In this case, the transmitting device260can control selection of an electrode pair by switching the connecting unit354. That is, in this case, the transmitting device260does not need to determine an electrode to be used as the transmission signal electrode and an electrode to be used as the transmission reference electrode in such a manner as to distinguish the electrodes from each other; it suffices to determine which plurality of electrodes among the group of electrodes of the electrode unit262are to be used as a pair of the transmission signal electrode and the transmission reference electrode. That is, in this case, of the electrodes connected to the output terminal361and the output terminal362, the electrode nearer to the communication medium280acts as the transmission signal electrode as a consequence, and the electrode more distant from the communication medium280acts as the transmission reference electrode as a consequence. Therefore the output terminal for the transmission reference electrode and the output terminal for the transmission signal electrode do not need to be differentiated from each other.

In addition, the transmitting device260may specify and use a plurality of electrodes as the transmission signal electrode, and specify and use a plurality of electrodes as the transmission reference electrode. In addition, the transmitting device260may specify electrodes to be used as the transmission signal electrode and electrodes to be used as the transmission reference electrode such that the electrodes to be used as the transmission signal electrode and the electrodes to be used as the transmission reference electrode are different from each other in number.

While the transmitting device has been described above, the present invention can be similarly adapted to the receiving device corresponding to the transmitting device. That is, the receiving device can also change (control) connection between electrodes and an internal circuit such that positional relation between the received signal electrode and the reception reference electrode and the communication medium is optimized according to positional relation between the receiving device and the communication medium. Hence, the description of the electrode connection control in the transmitting device described above with reference toFIG. 6can be applied to the receiving device. In addition, arrangement relation of the electrodes is arbitrary. Further, the magnitudes of surface areas and shapes of the electrodes are arbitrary, and may be different from each other, of course.

FIG. 12is a block diagram showing an example of internal configuration of an embodiment of such a receiving device.

A receiving device370inFIG. 12corresponds to the transmitting device260, and receives a signal supplied by the transmitting device260via the communication medium280. The receiving device370mainly has an electrode controlling unit371, an electrode unit372, and a receiving unit373.

The electrode controlling unit371is a processing unit corresponding to the electrode controlling unit261in the transmitting device260shown inFIG. 7. The electrode controlling unit371controls connection between the receiving unit373and the electrode unit372. Specifically, the electrode controlling unit371checks a state of capacitive coupling of each electrode in the electrode unit372, identifies the electrode to be used as received signal electrode and the electrode to be used as reception reference electrode, and then supplies identifying information identifying the electrodes as control information to the receiving unit373. The electrode controlling unit371has basically the same configuration and operation as the electrode controlling unit261. The description above made with reference toFIG. 7and the block diagram and the description of the electrode controlling unit261shown inFIG. 8can be applied to the electrode controlling unit371, and therefore description thereof will be omitted.

The electrode unit372corresponds to the electrode unit262in the transmitting device260shown inFIG. 7. As with the electrode unit262, the electrode unit372has an electrode381and an electrode382as a pair of electrodes having the shape of a disk, for example, and capacitively coupled with an outside. The receiving unit373corresponds to the transmitting unit263in the transmitting device260shown inFIG. 7. The receiving unit373performs a process of receiving a signal via the electrode unit372instead of the transmission process.

For example, suppose that as shown inFIG. 12, the communication medium280serving as a communication path and having conductivity or dielectric properties approaches the electrode381. At this time, the electrode382is facing a free space, and forms a capacitance Crg395with the free space. On the other hand, as the communication medium280approaches the electrode381, capacitive coupling of the electrode381with the free space is weakened, and capacitive coupling of the electrode381with the communication medium280becomes dominant. When the communication medium280is a conductor or an object having a higher dielectric constant than air, a capacitance Cre394viewed from the electrode381is larger than the capacitance Crg395. Hence, when some signal is supplied to the electrodes, the magnitude of a load attached to the paths is known on the basis of the magnitude of signal level of the load. In the case of the free space, the capacitance is low, and thus the signal level of the load is low. In the case of a conductor or a dielectric, the capacitance is high, and thus the signal level of the load is higher.

The capacitance as viewed from the electrode is thus changed, and thereby the signal level (magnitude of amplitude) detected when a signal is applied to the electrode is changed. Thus, as with electrode controlling unit261, by detecting the signal level, the electrode controlling unit371can grasp a state of the electrode (whether the communication medium280is in the vicinity or not). The electrode controlling unit371controls the connection between the receiving unit373and the electrode unit372according to the state of each electrode which state is thus grasped.

Incidentally, the pattern of connection of the terminals in the connecting unit354shown inFIG. 9is an example of connection. In practice, the connecting unit354is controlled by the connection controlling unit355as described above to change the connection of each terminal in a plurality of connection patterns including a connection pattern shown inFIG. 13.

FIG. 13is a block diagram showing an example of detailed configuration of the receiving unit373. The receiving unit373inFIG. 13has a reception controlling unit401, a connection controlling unit402, a connecting unit403, an amplifying unit404, and a received signal obtaining unit405.

On the basis of the control information supplied from the electrode controlling unit371(identifying information identifying the electrode to be used as the received signal electrode and the electrode to be used as the reception reference electrode in the electrode group of the electrode unit372), the reception controlling unit401controls the connecting unit403via the connection controlling unit402to connect a terminal413connected to a terminal of the amplifying unit404for the received signal electrode to the received signal electrode, and connect a terminal414connected to a terminal of the amplifying unit404for the reception reference electrode to the reception reference electrode. In the case ofFIG. 13, the connecting unit403connects the terminal413to a terminal412connected to the electrode382, and connects the terminal414to a terminal411connected to the electrode381. That is, in this case, the electrode381is connected so as to act as the reception reference electrode, and the electrode382is connected so as to act as the reception reference electrode.

In addition, the reception controlling unit401controls the amplifying unit404as required to amplify a received signal and then supply the received signal to the received signal obtaining unit405, and controls the received signal obtaining unit405as required to obtain the amplified received signal.

As described above, the receiving device370controls the electrodes in the same manner as the transmitting device260. That is, the receiving device370performs a reception process in a similar manner to the transmission process shown in the flowchart ofFIG. 10. The receiving device370stops signal reception, and then performs the electrode controlling process. After the electrode controlling process is ended, the receiving device370resumes signal reception. The receiving device370performs an electrode controlling process as in the case of the electrode controlling process represented in the flowchart ofFIG. 11. The receiving device370inputs a signal to each electrode, grasps a state of capacitive coupling of each electrode on the basis of a signal level obtained, and then determines the received signal electrode and the reception reference electrode.

As described above, the signal is received, and optimization is performed by switching the received signal electrode and the reception reference electrode according to the state of the capacitive coupling of each electrode. Therefore the reception controlling unit401enables a signal transmitted from the transmitting device to be received stably irrespective of positional relation between the receiving device370and the communication medium280.

Incidentally, the electrode controlling process may be performed while the transmitting device260and the receiving device370performing communication are synchronized with each other. A flow of the process in this case will be described with reference to a flowchart ofFIG. 14.

The transmitting device260that has been performing the transmission process first transmits a transmission stop notifying signal to the receiving device370in step S41to notify the receiving device370that the transmission process will be stopped. When the notification is completed, the transmitting device260advances the process to step S42, where the transmitting device260stops signal transmission. The transmitting device260performs the electrode controlling process described with reference to the flowchart ofFIG. 11in step S43.

When the receiving device370in step S61receives the transmission stop notifying signal transmitted in step S41by the transmitting device260, the receiving device370advances the process to step S62, whereby the receiving device370stops signal reception. The receiving device370thereafter performs the electrode controlling process described with reference to the flowchart ofFIG. 11in step S63.

After the electrode controlling process in step S43is ended, and thus the connection between the electrode unit262and the transmitting unit263is optimized, the transmitting device260advances the process to step S44, where the transmitting device260starts signal transmission. Then the process is ended.

After the receiving device370ends the electrode controlling process, and thus optimizes the connection between the electrode unit372and the receiving unit373, the receiving device370advances the process to step S64, where the receiving device370starts signal reception. Then the process is ended.

As described above, the transmitting device260and the receiving device370synchronize timing of performing the electrode controlling process with each other. Thereby, the transmitting device260and the receiving device370reduce problems in communication such for example as a case where the transmitting device260transmits a signal while the receiving device370is performing the electrode controlling process. Therefore the communication process can be performed more efficiently and more accurately.

Incidentally, while in the above description, the electrode unit372has two electrodes (the electrode381and the electrode382), the present invention is not limited to this, and the number of such electrodes may be three or more. In this case, the receiving device370can control selection of an electrode pair by switching the connecting unit403. That is, in this case, the receiving device370does not need to determine an electrode to be used as the received signal electrode and an electrode to be used as the reception reference electrode in such a manner as to distinguish the electrodes from each other; it suffices to determine which plurality of electrodes among the group of electrodes of the electrode unit372are to be used as a pair of the received signal electrode and the reception reference electrode. That is, in this case, of the electrodes connected to the input terminal413and the input terminal414, the electrode nearer to the communication medium280acts as the received signal electrode as a consequence, and the electrode more distant from the communication medium280acts as the reception reference electrode as a consequence. Therefore the output terminal for the reception reference electrode and the output terminal for the received signal electrode do not need to be differentiated from each other. In addition, arrangement relation of the electrodes is arbitrary. Further, the magnitudes of surface areas and shapes of the electrodes are arbitrary, and may be different from each other, of course.

In addition, the receiving device370may specify and use a plurality of electrodes as the received signal electrode, and specify and use a plurality of electrodes as the reception reference electrode. In addition, the receiving device370may specify electrodes to be used as the received signal electrode and electrodes to be used as the reception reference electrode such that the electrodes to be used as the received signal electrode and the electrodes to be used as the reception reference electrode are different from each other in number.

Incidentally, one device may of course have both the functions of the above-described transmitting device260and the functions of the receiving device370.

FIG. 15is a block diagram showing an example of configuration of an embodiment of a communicating device to which the present invention is applied, the communicating device corresponding to the transmitting device260inFIG. 7and the receiving device370inFIG. 13.

The communicating device450inFIG. 15performs the same communications as the communications performed by the transmitting device260and the receiving device370bidirectionally with another communicating device450via a communication medium280. The communicating device450has an electrode controlling unit451, an electrode unit452, and a communicating unit453.

The electrode controlling unit451is a processing unit corresponding to the electrode controlling unit261(FIG. 7) and the electrode controlling unit371(FIG. 12). The electrode controlling unit451controls connection between the electrode unit452and the communicating unit453. Specifically, the electrode controlling unit451checks a state of capacitive coupling of each electrode in the electrode unit452, identifies an electrode to be used as transmission signal electrode, an electrode to be used as received signal electrode, an electrode to be used as transmission reference electrode, and an electrode to be used as reception reference electrode, and then supplies identifying information identifying the electrodes as control information to the communicating unit453. The electrode controlling unit451has basically the same configuration and operation as the electrode controlling unit261and the electrode controlling unit371. The block diagram and the description of the electrode controlling unit261shown inFIG. 8can be applied to the electrode controlling unit451, and therefore description thereof will be omitted. However, since the electrode unit452has four electrodes, the electrode controlling unit451checks states of capacitive coupling of all the four electrodes. More specifically, while the connecting unit314inFIG. 8has been described as a switch having two contacts on one side which switch selectively connects the terminal322to the terminal323or the terminal324, because the number of terminals selected to be connected to the terminal322corresponds to the number of electrodes in the electrode unit, the connecting unit in the communicating device450is formed by a switch having four contacts on one side.

The electrode unit452corresponds to the electrode unit262in the transmitting device260shown inFIG. 7. As with the electrode unit262, the electrode unit452has pairs of electrodes having the shape of a disk, for example, and capacitively coupled with an outside. However, the electrode unit452has four electrodes461to464. The communicating unit453corresponds to the transmitting unit263in the transmitting device260shown inFIG. 7. The communicating unit453performs not only a transmission process but also a process of receiving a signal via the electrode unit452. That is, the electrode unit452performs a communication process for achieving a two-way communication with another communicating device450.

For example, suppose that as shown inFIG. 15, the communication medium280serving as a communication path and having conductivity or dielectric properties approaches the electrode461and the electrode462. At this time, the electrode463is facing a free space, and forms a capacitance Ccg473with the free space (a capacitance between the electrode463and a reference point496-1representing a virtual point at infinity from the electrode463). Similarly, the electrode464is also facing the free space, and forms a capacitance Ccg474with the free space (a capacitance between the electrode464and a reference point496-2representing a virtual point at infinity from the electrode464). On the other hand, as the communication medium280approaches the electrode461and the electrode462, capacitive coupling of the electrode461and the electrode462with the free space is weakened, and capacitive coupling of the electrode461and the electrode462with the communication medium280becomes dominant. When the communication medium280is a conductor or an object having a higher dielectric constant than air, a capacitance Cce471viewed from the electrode461and a capacitance Cce472viewed from the electrode462are larger than the capacitance Ccg473or Ccg474. Hence, when some signal is supplied to the electrodes, the magnitude of a load attached to the paths is known on the basis of the magnitude of signal level of the load. In the case of the free space, the capacitance is low, and thus the signal level of the load is low. In the case of a conductor or a dielectric, the capacitance is high, and thus the signal level of the load is higher.

The capacitance as viewed from the electrode is thus changed, and thereby the signal level (magnitude of amplitude) detected when a signal is applied to the electrode is changed. Thus, by detecting the signal level, the electrode controlling unit451can grasp a state of the electrode (whether the communication medium280is in the vicinity or not). The electrode controlling unit451controls the connection between the communicating unit453and the electrode unit452according to the state of each electrode which state is thus grasped.

Under control of the electrode controlling unit451, the communicating unit453connects each of the electrodes461to464of the electrode unit452as the transmission signal electrode, the transmission reference electrode, the received signal electrode, or the reception reference electrode, or does not connect each of the electrodes461to464.

Incidentally, the pattern of connection of the terminals in the connecting unit403shown inFIG. 13is an example of connection. In practice, the connecting unit403is controlled by the connection controlling unit as described above to change the connection of each terminal in a plurality of connection patterns including the connection pattern shown inFIG. 13.

FIG. 16is a block diagram showing an example of detailed configuration of the communicating unit453inFIG. 15. As shown inFIG. 16, the communicating unit453has a communication controlling unit501, a transmission signal generating unit502, an amplifying unit503, a connection controlling unit504, a connecting unit505, an amplifying unit506, and a received signal obtaining unit507.

That is, for two-way communication, the communicating unit453has both a configuration corresponding to the transmitting unit263inFIG. 9and a configuration corresponding to the receiving unit373shown inFIG. 13. Specifically, the communication controlling unit501corresponds to the transmission controlling unit351inFIG. 9and the reception controlling unit401inFIG. 13. The communication controlling unit501performs a control process involved in a transmission process and a reception process on the basis of control information supplied from the electrode controlling unit451. The transmission signal generating unit502corresponds to the transmission signal generating unit352inFIG. 9. The transmission signal generating unit502is controlled by the communication controlling unit501to generate a transmission signal corresponding to transmission information, and supply the transmission signal to the amplifying unit503. The amplifying unit503corresponds to the amplifying unit353inFIG. 9. The amplifying unit503is controlled by the communication controlling unit501to amplify the transmission signal supplied from the transmission signal generating unit502, and supply the amplified transmission signal to the connecting unit505.

The connection controlling unit504corresponds to the connection controlling unit355inFIG. 9and the connection controlling unit402inFIG. 13. The connection controlling unit504is controlled by the communication controlling unit501to control connections in the connecting unit505. The connecting unit505corresponds to the connecting unit354inFIG. 9and the connection controlling unit402inFIG. 13. The connecting unit505controls connections between the amplifying unit503and the amplifying unit506and the electrodes461to464. The connecting unit505has a terminal511connected to a terminal of the amplifying unit503for the transmission signal electrode, a terminal512connected to a terminal of the amplifying unit503for the transmission reference electrode, a terminal531connected to a terminal of the amplifying unit506for the received signal electrode, and a terminal532connected to a terminal of the amplifying unit506for the reception reference electrode. The connecting unit505connects each of these terminals to one of a terminal521connected to the electrode461, a terminal522connected to the electrode462, a terminal523connected to the electrode463, and a terminal524connected to the electrode464(terminals different from each other). That is, the connecting unit505performs a process of assigning the electrodes461to464as one of the transmission signal electrode, the transmission reference electrode, the received signal electrode, and the reception reference electrode.

The amplifying unit506corresponds to the amplifying unit404inFIG. 13. The amplifying unit506is controlled by the communication controlling unit501to amplify a received signal supplied via the connecting unit505and supply the received signal to the received signal obtaining unit507. The received signal obtaining unit507corresponds to the received signal obtaining unit405inFIG. 13. The received signal obtaining unit507is controlled by the communication controlling unit501to obtain the received signal supplied from the amplifying unit506.

Since the electrode controlling process is performed as described above, the communicating device450can determine for each of the electrodes whether to use the electrode as the transmission reference electrode, whether to use the electrode as the transmission signal electrode, whether to use the electrode as the reception reference electrode, whether to use the electrode as the received signal electrode, or whether to disconnect the electrode. The communicating device450can therefore perform signal transmission and reception stably irrespective of positional relation between the communicating device450and the communication medium280.

Incidentally, there may be five or more electrodes in the electrode unit452. In this case, the communicating device450can control selection of an electrode pair by switching the connecting unit505. That is, in this case, the communicating device450does not need to determine an electrode to be used as the transmission signal electrode and an electrode to be used as the transmission reference electrode in such a manner as to distinguish the electrodes from each other, and does not need to determine an electrode to be used as the received signal electrode and an electrode to be used as the reception reference electrode in such a manner as to distinguish the electrodes from each other. It suffices for the communicating device450to determine which plurality of electrodes or which electrode among the group of electrodes of the electrode unit452are to be used as an electrode pair for signal transmission, and determine which plurality of electrodes or which electrode among the group of electrodes of the electrode unit452are to be used as an electrode pair for signal reception.

In addition, the communicating device450may allow an electrode to be shared between the electrode pair for signal transmission and the electrode pair for signal reception. Further, the communicating device450may identify a plurality of electrodes as electrodes to be used as the transmission signal electrode, identify a plurality of electrodes as electrodes to be used as the transmission reference electrode, identify a plurality of electrodes as electrodes to be used as the received signal electrode, and identify a plurality of electrodes as electrodes to be used as the reception reference electrode.

In addition, the communicating device450may identify electrodes to be used as the transmission signal electrode, electrodes to be used as the transmission reference electrode, electrodes to be used as the received signal electrode, and electrodes to be used as the reception reference electrode such that the electrodes to be used as the transmission signal electrode, the electrodes to be used as the transmission reference electrode, the electrodes to be used as the received signal electrode, and the electrodes to be used as the reception reference electrode are different from each other in number. In addition, arrangement relation of the electrodes is arbitrary. Further, the magnitudes of surface areas and shapes of the electrodes are arbitrary, and may be different from each other, of course.

Incidentally, the pattern of connection of the terminals in the connecting unit505shown inFIG. 16is an example of connection. In practice, the connecting unit505is controlled by the connection controlling unit504as described above to change the connection of each terminal in a plurality of connection patterns including a connection pattern shown inFIG. 16.

Incidentally, the communicating device450performs a transmission process and a reception process in the same manner as the transmitting device260and the receiving device370described above. Hence, the communicating device450performs the electrode controlling process of checking a state of capacitive coupling of each electrode and assigning each electrode as one of the transmission signal electrode, the transmission reference electrode, the received signal electrode, and the reception reference electrode according to the state in the same manner as described with reference to the flowchart ofFIG. 11. Therefore description thereof will be omitted.

Incidentally, a plurality of communicating devices performing communication may synchronize timing of performing the electrode controlling process as in the case of the transmitting device260and the receiving device370described above. A flow of the process in this case will be described with reference to a flowchart ofFIG. 17.

With predetermined timing or a predetermined event as a cue, one of two communicating devices450communicating with each other (a communicating device450-1) transmits a transmission and reception stop notifying signal notifying a stoppage of a transmission and reception process to the other communicating device in step S81. The other communicating device450-2as the other device communicating with the communicating device450-1receives the transmission and reception stop notifying signal in step S101. The communicating device450-2transmits an acknowledgment signal in response to the received transmission and reception stop notifying signal in step S102.

The communicating device450-1receives the acknowledgment signal in step S82. Receiving the acknowledgment signal, the communicating device450-1stops signal transmission and reception in step S83, and performs the electrode controlling process in step S84. Details of the electrode controlling process are the same as described with reference to the flowchart ofFIG. 11, and therefore description thereof will be omitted. After the electrode controlling process is ended, the communicating device450-1starts signal transmission and reception in step S85, and then ends the process.

The communicating device450-2that has transmitted the acknowledgment signal stops signal transmission and reception in step S103, and performs the electrode controlling process in step S104. Details of the electrode controlling process are the same as described with reference to the flowchart ofFIG. 11, and therefore description thereof will be omitted. After the electrode controlling process is ended, the communicating device450-2starts signal transmission and reception in step S105, and then ends the process.

As described above, the communicating device450-1and the communicating device450-2performing communication synchronize the timing of performing the electrode controlling process with each other. Thereby, the communicating devices450reduce problems in communication such for example as a case where while one of the communicating devices450is performing the electrode controlling process, the other device transmits a signal. Therefore the communication process can be performed more efficiently and more accurately.

For the determination of the detecting unit in each device described above, a method can be considered in which method a comparison signal level is determined in advance, and determination is made on the basis of whether a signal level is higher or lower than the comparison signal level. The electrode whose level is close to the comparison signal level may be in a subtle position relation to the communication medium30(for example the hand220inFIG. 6), and therefore is not connected to any electrode by the connecting unit of the transmitting device, the receiving device, and the communicating device, whereby adverse effects on other electrodes can be avoided.

Incidentally, the timing of performing the electrode controlling process described above (that is, updating the function assigned to each electrode) may be any timing. For example, however, when the communicating device450is formed as a mobile device or the like, and communication is performed with a human body (user) as a communication medium, positional relation between the user (communication medium) and the communicating device450(electrodes) may be changed during the communication as a result of for example the user changing a manner of holding the communicating device450. It is therefore desirable not only to perform the electrode controlling process in an initial state at a time of a start or the like but also to repeatedly perform the electrode controlling process at a predetermined frequency during communication.

For example, as shown inFIG. 18A, the communicating device450may perform the electrode controlling process (control551or control554) using a free time during which the transmission process (transmission552) or the reception process (reception553or reception555) is not performed (when the transmission process or the reception process is not performed for a predetermined time, for example), and thereby update the assignment of electrodes as the transmission signal electrode, the transmission reference electrode, the received signal electrode, or the reception reference electrode. Thus, the communicating device450can perform communication while using time effectively, and thereby improve communication efficiency.

In addition, for example, as shown inFIG. 18B, the communicating device450may continuously perform the electrode controlling process, the transmission process, and the reception process such as control561, transmission562, reception563, control564, transmission565, and reception566, and repeatedly perform the processes as one cycle. For example, in the example shown inFIG. 18B, the communicating device450continuously performs the electrode controlling process, the transmission process, and the reception process in respective T/3 times with a periodic T time as a repetition period, and further repeatedly performs the series of processes as one cycle. Thus, timing of performing each process is fixed. Therefore the communicating device450can easily synchronize the timing of the performance with another communicating device450.

Further, as shown inFIG. 18C, for example, the communicating device450may perform the electrode controlling process using a transmission signal. In this case, the transmission process (transmission571or transmission574) and the electrode controlling process (control572or control575) are performed simultaneously. The reception process (reception573or reception576) is performed in other times. In this case, the communicating device450measures a signal level when supplying a transmission signal to an electrode (that is, when transmitting a signal), and grasps a state of capacitive coupling of each electrode on the basis of the signal level. Thus, the communicating device450can simplify process steps, reduce a load, and also shorten a process performing time and thereby shorten the repetition period.

Incidentally, in the above description, the electrode controlling unit261, the electrode controlling unit371, and the electrode controlling unit451each check states of capacitive coupling of respective electrodes one by one. However, the present invention is not limited to this; for example, states of capacitive coupling of all electrodes may be checked simultaneously.

FIG. 19is a block diagram showing an example of internal configuration of the electrode controlling unit in the communicating device450in this case. The electrode controlling unit451shown inFIG. 19has a detecting unit613and a connecting unit614different from the detecting unit and the connecting unit of the electrode controlling unit261shown inFIG. 8.

The detecting unit613has a plurality of load resistances621to625connected in series with each other between the switch312and a reference point626. Terminals631A to634A of the connecting unit614are connected between the respective resistances (four points). Potentials of these connection points are each supplied to the retaining unit303.

The resistance values of the load resistances621to625are each known. The terminals631A to634A of the connecting unit614are respectively one terminal of switches631to634. When the switches631to634are brought into an on state, the terminals631A to634A are respectively connected to other terminals631B to634B. The terminals631B to634B are respectively connected to the electrodes461to464of the electrode unit452.

Hence, for example, respective capacitances when the electrodes461to464are each capacitively coupled with a space surrounding the communicating device450(when the communication medium is not in the vicinity) are known, and thus potentials between the load resistances621to625when each switch of the connecting unit614is turned on are also known.

When the communication medium is placed in proximity to an electrode, on the other hand, the capacitance between the electrode and the surroundings is changed. Thus, the detecting unit613detects resulting changes in the potentials between the load resistances621to625(changes in signal level), and makes the retaining unit303retain a result of the detection. On the basis of the changes in the levels of the signals input to the respective electrodes which changes are retained in the retaining unit303, the main control unit301controls the assignment of a function (the transmission signal electrode, the transmission reference electrode, the received signal electrode, or the reception reference electrode) to each electrode.

Thus, since the states of capacitive coupling of the plurality of electrodes can be checked in one process, the communicating device450can control the assignment of a function to each electrode more easily and more quickly. Incidentally, any number of electrodes may be checked simultaneously at this time. All the electrodes possessed by the communicating device450may be checked simultaneously, or a part of the electrodes possessed by the communicating device450may be checked simultaneously.

In addition, while in the above description, all the electrodes are checked using one detecting unit, a plurality of detecting units may be provided. For example, detecting units equal in number to that of electrodes may be provided, and the detecting units may be connected to the electrodes different from each other. In this case, the detecting units respectively detect signals input to the electrodes different from each other (each detecting unit detects a signal input to the corresponding electrode).

As described above, the communicating device450to which the present invention is applied not only achieves a communication environment not limited by a use environment by eliminating a need for a physical reference point path and achieving communication by only a communication signal transmitting path, but also can perform stable communication irrespective of positional relation between the communicating device450and the communication medium in proximity to the communicating device450by controlling the assignment of a function to each electrode.

Incidentally, in the above description, each device (the transmitting device, the receiving device, and the communicating device) in the communication system to which the present invention is applied transmits or receives a signal with a predetermined potential as a reference. However, the present invention is not limited to this, and for example two signals whose phases are reversed with respect to each other may be transmitted via two transmission lines, so that a differential signal transmitting information represented by difference between the signals is transmitted and received. In this case, the two transmission lines are provided as communication medium between the devices communicating with each other. Also, in this case, the transmitting unit in the transmitting device, the receiving unit in the receiving device, and the communicating unit in the communicating device are each formed by a differential circuit.

Incidentally, the series of processes described above (for example the electrode controlling process and the like) can be carried out not only by hardware but also by software. In this case, for example, the above-described main control unit301may be formed as a personal computer as shown inFIG. 20.

InFIG. 20, a CPU701of the personal computer700performs various processes according to a program stored in a ROM702or a program loaded from a storage unit713into a RAM703. The RAM703also stores data and the like necessary for the CPU701to perform the various processes as required.

The CPU701, the ROM702, and the RAM703are interconnected via a bus704. The bus704is also connected with an input/output interface710.

The input/output interface710is connected with an input unit711formed by a keyboard, a mouse and the like, an output unit712including a display formed by a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display) or the like, a speaker, and the like, the storage unit713formed by a hard disk or the like, and a communication unit714formed by a modem or the like. The communication unit714performs a process of communication via a network including the Internet. In addition, the output unit712is connected with the signal input controlling unit302, the retaining unit303, the connection controlling unit304, the switching controlling unit305and the like. The output unit712outputs control information to each of the units. Further, the input unit711is connected with the retaining unit303, so that information retained in the retaining unit303is input from the retaining unit303. This information is supplied to the CPU701.

The input/output interface710is also connected with a drive715as required. A removable medium721such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory or the like is loaded into the drive715as required. A computer program read from the medium is installed in the storage unit713as required.

When the above-described series of processes is to be carried out by software, a program constituting the software is installed from a network or a recording medium.

As shown inFIG. 20, for example, the recording medium is not only formed by the removable medium721distributed to users to provide the program separately from the device proper and having the program recorded thereon, the removable medium721including a magnetic disk (including flexible disks), an optical disk (including CD-ROM (Compact Disk-Read Only Memory) and DVD (Digital Versatile Disk)), a magneto-optical disk (including MD (Mini-Disk) (registered trademark)), a semiconductor memory or the like, but also formed by the ROM702, the hard disk included in the storage unit713, or the like that has the program recorded thereon and which is distributed to the user in a state of being preincorporated in the device proper.

It is to be noted that in the present specification, the steps describing the program recorded on the recording medium include not only processes carried out in time series in the described order but also processes carried out in parallel or individually and not necessarily in time series.

In addition, in the present specification, a system refers to an apparatus as a whole formed by a plurality of devices. Incidentally, a constitution described above as one device may be divided and formed as a plurality of devices. Conversely, constitutions described above as a plurality of devices may be combined with each other and formed as one device. In addition, a constitution other than the above-described constitutions may be added to the constitution of each device, of course. Further, a part of the constitution of a device may be included in the constitution of another device as long as the constitution and operation of the system as a whole are the same in effect.