Patent Application
20110086595
This application claims benefit of Japanese Patent Application No. 2009-237205 filed on Oct. 14, 2009, the entire contents of which is hereby incorporated by reference.
1. Field of the Invention
Embodiments of the present invention relate to a transceiver that performs both transmission and reception through a transmission medium, such as a human body, and a communication system including the transceiver.
2. Description of the Related Art
PCT Publication No. WO 2008/114729 discloses a communication method using an electric field induced by, for example, a human body. According to such a communication method, a transmitter applies an electric field corresponding to a modulated signal, obtained by modulating an information signal, to a human body which serves as a transmission medium, a receiver detects the electric field transmitted through the human body, and the information signal corresponding to the electric field is demodulated.
The transceiver disclosed in PCT Publication No. WO 2008/114729 includes a transmitting and receiving (hereinafter, “transmitting/receiving”) electrode capacitively coupled to a human body, a transmitting mechanism which applies an electric field, serving as an information signal, to the human body upon signal transmission, and a receiving mechanism which receives a signal from the electric field applied to the human body upon signal reception such that these mechanisms are connected to the transmitting/receiving electrode. The receiving mechanism constituting the transmitting and receiving circuitry includes an LC resonant circuit that extracts a predetermined frequency component from the information signal received through the transmitting/receiving electrode.
A human body typically has a high impedance. Accordingly, the impedance that the human body has can be regarded as a series impedance for the transceiver. In this case, impedance matching between the human body and the transceiver is not achieved only using the impedance of the LC resonant circuit or the like upon signal reception in the transceiver disclosed in PCT Publication No. WO 2008/114729. Disadvantageously, the efficiency of information signal reception is degraded.
Since the human body has a high impedance, the signal level of an information signal output from the transmitting mechanism is set to high (high voltage). At this time, since the transmitting mechanism and the receiving mechanism of the transceiver share the transmitting/receiving electrode, the receiving mechanism may be damaged due to the information signal which enters the receiving mechanism from the transmitting mechanism. Disadvantageously, the transmission level is restricted.
These and other drawbacks exist.
Various embodiment provide a transceiver capable of, when performing transmission and reception through a transmission medium, such as a human body, having a high impedance, increasing the reception efficiency upon reception of an information signal and increasing the transmission level of an information signal upon transmission, and a communication system including the transceiver.
According to an embodiment, a transceiver transmits and receives information signals through a transmission medium having a particular impedance. The transceiver includes a transmitting/receiving electrode that comes into contact with or is capacitively coupled to the transmission medium, a receiving mechanism connected to the transmitting/receiving electrode, and a transmitting mechanism connected to the transmitting/receiving electrode. Upon signal transmission, the receiving mechanism is open-circuited as viewed from the transmitting/receiving electrode to allow the impedance on the transmitting mechanism side as viewed from the transmitting/receiving electrode to match the particular impedance. Upon signal reception, the transmitting mechanism is open-circuited as viewed from the transmitting/receiving electrode to allow the impedance on the receiving mechanism side as viewed from the transmitting/receiving electrode to match the particular impedance.
With this structure, since impedance matching between the transmission medium and the transceiver is achieved upon both signal transmission and signal reception, the efficiency of transmission and reception of information signals can be increased. In addition, since the receiving mechanism of the transceiver is open-circuited upon transmission of an information signal, the signal can be prevented from entering the receiving mechanism from the transmitting mechanism. Even if the transmission level of the information signal is increased, there is no fear of damage of the receiving mechanism due to the information signal. Advantageously, an information signal can be transmitted to a transmission medium having a high impedance without restricting the transmission level of the information signal.
In the above-described transceiver according to this embodiment, the receiving mechanism includes a switching element and the transmitting mechanism includes an amplifying element. Upon signal transmission, the switching element is turned off and the amplifying element is turned on. Upon signal reception, the switching element is turned on and the amplifying element is turned off.
According to this structure, the impedance on the receiving mechanism side can be open-circuited from the transmitting/receiving electrode and the impedance on the transmitting mechanism side can be open-circuited therefrom with the simple structure.
In the above-described transceiver, the switching element may include a gallium arsenide device.
With this structure, since the switching element including the gallium arsenide device has high voltage withstanding characteristics, the transmission level of an information signal can be increased upon transmission of the signal.
Also, the receiving mechanism may further include a matching resistor such that the resistor is connected between the transmitting/receiving electrode and ground.
According to this structure, impedance matching between the transmission medium and the receiving mechanism can be achieved upon signal reception with the simple structure.
The receiving mechanism may also include a parallel resonant circuit including a capacitor and an inductor such that the circuit is connected between the transmitting/receiving electrode and ground.
According to an embodiment, a communication system includes the above-described transceiver and a communication device applying an information signal as an electric field to the transmission medium.
With this configuration, the efficiency of transmission and reception of information signals can be increased, so that appropriate communication can be performed through a transmission medium having a high impedance.
The following description is intended to convey a thorough understanding of the embodiments described by providing a number of specific embodiments and details involving transceiver and communication systems. It should be appreciated, however, that the present invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of the invention for its intended purposes and benefits in any number of alternative embodiments, depending on specific design and other needs.
A transceiver according to various embodiments achieves impedance matching with a transmission medium, such as a human body, having a high impedance to increase the efficiency of transmission and reception of information signals through the transmission medium. In the following description, the transceiver transmitting and receiving information signals through a human body, serving as a transmission medium, will be described as an example.
A communication system including a transceiver according to the various embodiments will be described with reference to
Referring to
In this communication system 1, the communication device 3 may be electrically capacitively coupled to the human body 2 and the transceiver 4 may be electrically capacitively coupled thereto so that an information signal may be transmitted by an electric field obtained by modulating the information signal. In this case, displacement current flows through the human body 2 but steady-state current does not flow through the human body 2. Accordingly, the communication device 3 may not have to be in electrical conduction with the human body 2. Therefore, since an electrode of the communication device 3 is capacitively coupled to the human body 2 through, for example, a thin cloth, an information signal can be transmitted through clothes.
The human body 2 is a transmission medium through which displacement current flows and has a high impedance of, for example, several hundreds of ohms [Ω]. In the communication system 1, therefore, in order to transmit information signals through the human body 2, the transmission level of an information signal output from each of the communication device 3 and the transceiver 4 may be set to high (high voltage). A transmitting mechanism of each of the communication device 3 and the transceiver 4 may be designed to withstand such a high transmission level. On the other hand, a receiving mechanism of each of the communication device 3 and the transceiver 4 may not withstand a high signal level because the mechanism may receive an information signal having a signal level reduced through the human body 2.
The transceiver 4 may include a transmitting and receiving electrode (hereinafter, referred to as “transmitting/receiving electrode”) 11 that may come into contact with or may be electrically capacitively coupled to the human body 2. The transmitting/receiving electrode 11 may be connected to a receiving mechanism 12 which may receive an information signal through the transmitting/receiving electrode 11 from the communication device 3 and a transmitting mechanism 13 which may transmit an information signal through the transmitting/receiving electrode 11 to the communication device 3. The transmitting/receiving electrode 11, including a flat plate electrode, may come into contact with or may be capacitively coupled to the human body 2, thus providing communication with the communication device 3 through an electric field applied to the human body 2.
The receiving mechanism 12 may include an LC resonant circuit 22 which may be connected to the transmitting/receiving electrode 11 through a coupling capacitor 21. The LC resonant circuit 22 may include an inductor 23 and a capacitor 24 which may be connected in parallel between the coupling capacitor 21 and ground. A resonant frequency (for example, about 10.7 [MHz]) corresponding to a frequency component for communication may be set in the LC resonant circuit 22. A matching resistor 25 for impedance matching may be provided in parallel with the LC resonant circuit 22 between the coupling capacitor 21 and the ground.
The LC resonant circuit 22 may be connected through a coupling capacitor 26 to a receiving unit 27 provided for an electric field communication IC 14 such that the receiving unit 27 is positioned downstream of the LC resonant circuit 22. The receiving unit 27 may include a demodulating circuit (not illustrated) and may demodulate a modulated signal received from the communication device 3 through the transmitting/receiving electrode 11 using, for example, a carrier used by the communication device 3 to acquire an information signal. A switching element 28 may be provided between the coupling capacitor 21 and the transmitting/receiving electrode 11.
The switching element 28 may be, for example, a GaAs switch including a gallium arsenide device and has high voltage withstanding characteristics. Consequently, even when an information signal entering from the transmitting mechanism 13 upon signal transmission by the transceiver 4 is at a high voltage level, the switching element 28 can perform an appropriate switching operation. The switching element 28 may be connected to a control unit 15 provided for the electric field communication IC 14 and may be switched between on and off states under the control of the control unit 15.
In this case, the switching element 28 may be turned on upon signal reception by the transceiver 4 to bring the transmitting/receiving electrode 11 and the receiving mechanism 12 into conduction and may be turned off upon signal transmission by the transceiver 4 to bring the transmitting/receiving electrode 11 and the receiving mechanism 12 out of conduction. As described above, upon signal transmission by the transceiver 4, the switching element 28 may disconnect the transmitting/receiving electrode 11 from the receiving mechanism 12, so that the impedance on the receiving mechanism 12 side as viewed from the transmitting/receiving electrode 11 may be open-circuited.
Since the receiving mechanism 12 may include the matching resistor 25 in addition to the LC resonant circuit 22 and the receiving unit 27, an input impedance may be set to a value equal to the impedance of the human body 2. The matching resistor 25 may be a fixed resistor or a variable resistor. When the matching resistor 25 is a fixed resistor, the impedance of the matching resistor 25 may be set in accordance with the magnitude of the impedance of an average human body. When the matching resistor 25 is a variable resistor, the impedance of the matching resistor 25 may be individually adjusted so as to match the impedance of the human body 2.
The transmitting mechanism 13 may be connected through a coupling capacitor 31 to the transmitting/receiving electrode 11 and may include a transmitting unit 32 provided for the electric field communication IC 14. The transmitting unit 32 may include a modulating circuit (not illustrated) and may modulate a carrier with an information signal to generate a modulated signal. In this case, the modulated signal may have a frequency (ranging from, for example, several hundreds of kilohertz to several tens of megahertz) exhibiting the conductivity of the human body 2. This modulated signal may be amplified and may be applied as a change in voltage to the transmitting/receiving electrode 11, so that an electric field signal corresponding to the information signal is generated in the vicinity of the transmitting/receiving electrode 11. This electric field signal may be given to the human body 2 and may be then applied to the electrode of the communication device 3, so that the information signal is transmitted from the transceiver 4 to the communication device 3.
The transmitting mechanism 13 may further include an amplifier 33 that may amplify a modulated signal. The amplifier 33 may include a transistor (not illustrated) which may serve as an amplifying element. The transistor may function as the amplifying element and also may function as a switching element. The transistor may be connected to the control unit 15 provided for the electric field communication IC 14 and may be switched between on and off states under the control of the control unit 15.
In this case, the transistor may be turned on upon signal transmission by the transceiver 4 to bring the transmitting unit 32 and the transmitting/receiving electrode 11 into conduction and may be turned off upon signal reception by the transceiver 4 to bring the transmitting unit 32 and the transmitting/receiving electrode 11 out of conduction. As described above, upon signal reception by the transceiver 4, the transistor may disconnect the transmitting/receiving electrode 11 from the transmitting mechanism 13, so that the impedance on the transmitting mechanism 13 side as viewed from the transmitting/receiving electrode 11 is open-circuited. In the transmitting mechanism 13, the transmitting unit 32 may set an output impedance to a value approximately equal to the impedance of the human body 2.
As described above, in the transceiver 4, the impedance of the receiving mechanism 12 and that of the transmitting mechanism 13 may be set to a value approximately equal to the impedance of the human body 2 and each of the switching element 28 and the transistor may be switched between the on and off states in accordance with signal transmission or reception. This configuration allows each of the input and output impedances of the transceiver 4 to match the impedance of the human body 2.
As described above, the communication device 3 may have substantially the same structure as that of the transceiver 4. Specifically, the communication device 3 may be configured to transmit a modulated signal corresponding to an information signal to the transceiver 4 through an electric field applied to the human body 2 upon signal transmission and extract an information signal from a modulated signal received from the transceiver 4 upon signal reception. The communication device 3 is also may be configured so that each of the input and output impedances of the communication device 3 matches the impedance of the human body 2.
Referring to
In this state, a modulated signal corresponding to an information signal may be transmitted from the communication device 3 through an electric field applied to the human body 2 to the transmitting/receiving electrode 11 of the transceiver 4. The LC resonant circuit 22 may extract a frequency component for communication from the modulated signal received by the transmitting/receiving electrode 11, the demodulating circuit in the receiving unit 27 may demodulate the component, thus obtaining the information signal. At this time, since the input impedance of the receiving mechanism 12 is allowed to match the impedance of the human body 2, the efficiency of reception of the information signal may be increased.
The operation of the transceiver 4 upon signal transmission will be subsequently described with reference to
In this state, an information signal may be modulated in the transmitting unit 32 and the modulated signal may be amplified through the amplifier 33. The modulated signal may be amplified to a high transmission level so that the signal can be transmitted through the human body 2 having a high impedance. At this time, since the impedance on the receiving mechanism 12 side as viewed from the transmitting/receiving electrode 11 is open-circuited, output from the transmitting mechanism 13 can be prevented from being distorted due to the effect of the receiving mechanism 12 and the receiving mechanism 12 which does not withstand a high voltage can be prevented from being damaged due to the entry of the information signal from the transmitting mechanism 13 into the receiving mechanism 12.
The amplified modulated signal may be transmitted to the communication device 3 through an electric field applied to the human body 2. In the communication device 3, the signal may be demodulated, so that the information signal may be acquired. At this time, since the output impedance of the transmitting mechanism 13 is allowed to match the impedance of the human body 2, the efficiency of transmission of the information signal may be increased.
As described above, in the transceiver 4 according to the present embodiment, since the input impedance of the receiving mechanism 12 or the output impedance of the transmitting mechanism 13 may be allowed to match the impedance of the human body 2 upon signal reception or transmission, the efficiency of transmission and reception of information signals can be increased. In addition, since the receiving mechanism 12 of the transceiver 4 is open-circuited upon signal transmission, an information signal can be prevented from entering the receiving mechanism 12 from the transmitting mechanism 13. Even if the transmission level of the information signal is increased, there is no fear of damage of the receiving mechanism 12 due to the information signal. Accordingly, the information signal can be transmitted to the human body 2 having a high impedance without restricting the transmission level of the information signal.
In the above-described embodiment, the communication device may be attached to the human body and the transceiver may be placed apart from the human body. The configuration is not limited to this one. Any configuration is permissible so long as the communication device can communicate with the transceiver through a human body. For example, such a configuration that the communication device is placed apart from a human body and the transceiver is attached to the human body may be used.
In the above-described embodiment, the communication device and the transceiver may have substantially the same structure. The structure may not be limited to this one. The communication device may have any structure so long as the communication device can communicate with the transceiver through an electric field applied to a human body.
In the above-described embodiment, the transistor included in the amplifier in the transmitting mechanism may be turned on or off, thus switching the impedance of the transmitting mechanism as viewed from the transmitting/receiving electrode between the open-circuited mode and the non-open-circuited mode. The structure may not be so limited. The transmitting mechanism may have a structure in which the impedance of the transmitting mechanism as viewed from the transmitting/receiving electrode is switched between the open-circuited mode and the non-open-circuited mode. For example, the transmitting mechanism may include a component for controlling power supply to the transmitting unit, instead of the transistor.
In the above-described embodiment, the switching element in the receiving mechanism may be turned on or off, thereby switching the impedance of the receiving mechanism as viewed from the transmitting/receiving electrode between the open-circuited mode and the non-open-circuited mode. The structure may not be so limited. The receiving mechanism may have any structure so long as the impedance of the receiving mechanism as viewed from the transmitting/receiving electrode is switched between the open-circuited mode and the non-open-circuited mode. In such an embodiment, the receiving mechanism may withstand a high-voltage information signal entering from the transmitting mechanism upon signal transmission by the transceiver.
In the above-described embodiment, the transmitting/receiving electrode has been described as a flat plate electrode. The structure may not be so limited. The transmitting/receiving electrode may have any structure so long as the electrode can be come into contact or capacitively coupled to a human body. For example, the transmitting/receiving electrode may comprise a thin conductive material, such as a flexible conductive film.
In the above-described embodiment, the human body has been described as a transmission medium. The transmission medium may not be so limited. Any transmission medium may be used so long as the medium can perform electric field communication. For example, the living body of a plant or animal, or anything other than the living body may be used.
In the above-described embodiment, the matching resistor may allow the input impedance of the receiving mechanism to be equal to the impedance of a human body. The structure may not be limited to using the matching resistor. If the input impedance of the receiving mechanism is equal to the impedance of a human body, a structure without the matching resistor may be used.
In the structure according to the above-described embodiment, the input impedance of the receiving mechanism may be equal to the impedance of the human body upon signal reception. The structure may be not limited to the case where the input impedance of the receiving mechanism is exactly equal to the impedance of the human body. The input impedance of the receiving mechanism may match the impedance of the human body to such an extent that matching therebetween is achieved.
In the structure according to the above-described embodiment, the output impedance of the transmitting mechanism may be equal to the impedance of the human body upon signal transmission. The structure may not be limited to the case where the output impedance of the transmitting mechanism is exactly equal to the impedance of the human body. The output impedance of the transmitting mechanism may match the impedance of the human body to such an extent that matching therebetween is achieved.
The embodiments disclosed herein are exemplary at all points and the present invention is not limited to the embodiments. The scope of the present invention is defined not by the description of only the above-described embodiments but by the scope of the appended claims. It should be understood that all variations may be included within the scope of the appended claims and the equivalent thereof.
As described above, the present invention has advantages in that the reception efficiency can be increased upon reception of an information signal and the transmission level of an information signal can be increased upon transmission of the signal. The present invention is useful to a transceiver and a communication system which perform both of transmission and reception through a transmission medium, such as a human body.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-237205 | Oct 2009 | JP | national |
