JP2009153045A - Audio signal communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal communication system which is a small-sized system but being capable of stably playing music, as well as, of decreasing the number of components to reduce cost. <P>SOLUTION: The audio signal communication system comprises a transmitter 1 which modulates an audio signal, converts it into an electromagnetic field signal and transmits it, a receiver 3 which demodulates the audio signal from the electromagnetic field signal and outputs the demodulated audio signal; and a transmission medium 2 for transmitting the audio signal from the transmitter 1 to the receiver via the electromagnetic field signal, wherein the receiver 3 includes a speaker 31, comprising a voice coil 311 for receiving the electromagnetic field signal and passing the demodulated audio signal, and a field communication circuit 32 for detecting the electromagnetic field signal which has passed through the voice coil 311 and demodulating the detected signal to the audio signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an audio signal communication system that transmits and receives audio signals via a transmission medium such as a human body or space and outputs the audio signals.

  In a system for reproducing an audio signal, for example, an audio signal modulated by a method such as AM, FM, ASK, or FSK is transmitted as an electromagnetic wave signal from a transmitter, and is transmitted to a receiver via a transmission medium such as a human body or space. It is transmitted and demodulated into an audio signal by this receiver, and the demodulated audio signal is reproduced as audio from an output means such as a speaker. In this system, a receiver includes a signal detection circuit that detects a modulated audio signal, a demodulation circuit that demodulates the detected audio signal, an amplification circuit that amplifies the demodulated audio signal, and a speaker that outputs audio. And a voice coil that drives the speaker.

Regarding a communication system that transmits and receives via a transmission medium (mainly a human body), a method of communicating using an electric field is disclosed in Patent Document 1 and the like, and in particular, a configuration of a resonance circuit is disclosed in Patent Document 2. In this configuration, a resonance circuit that extracts a predetermined frequency is constituted by a coil and a capacitor, and one end of the coil is joined to the receiving electrode. Moreover, there is a wireless headphone disclosed in Patent Document 3 as an example of transmitting an audio signal by applying communication technology via a human body. In human body communication, a transmission electrode and a reception electrode that transmit and receive signals through the human body are necessary, and it is important that these electrodes are closely capacitively coupled to the human body. For this reason, in the technique of patent document 3, the example which used the ear pad using a conductive material as an electrode is shown.
Japanese National Patent Publication No. 11-509380 Japanese Patent Laid-Open No. 2005-94466 JP 2001-144661 A

  As shown in Patent Document 2, in a circuit in which the receiving electrode is directly connected to the resonance circuit, there is a problem that communication cannot be performed if the human body and the receiving electrode are slightly separated from each other. Stable music playback was difficult when using while moving. As countermeasures, a method of making the receiving electrode very large or using an ear pad as an electrode so as to ensure that the human body and the receiving electrode are in close contact with each other as shown in Patent Document 3 has been proposed. However, when metal is used for the conductive material, it cannot be used by a person who has a hard feel or is allergic to metal, and there is a problem that using a conductive material other than metal is very expensive. It has not been put to practical use.

  The present invention has been made in view of the above points, and provides an audio signal communication system capable of stably reproducing music and reducing the number of parts and costs while being a small system. For the purpose.

  The audio signal communication system according to the present invention includes a transmitter that modulates an audio signal, converts the signal into an electromagnetic field signal, and transmits the signal, and a receiver that demodulates the audio signal from the electromagnetic field signal and outputs the demodulated audio signal. And a transmission medium for transmitting the audio signal from the transmitter to the receiver via the electromagnetic field signal, wherein the receiver receives the electromagnetic field signal and the demodulated audio signal. Output means having a voice coil that passes the voice coil, and an electric field communication circuit that detects the electromagnetic field signal that has passed through the voice coil and demodulates the detected signal into the voice signal.

  According to this configuration, the voice coil of the speaker is also used as a human body communication receiving electrode, and a signal is received by capacitive coupling between the human body and the voice coil. Since the voice coil and the human body are capacitively coupled in a distributed constant manner, stable communication can be realized against fluctuations in the distance between the human body and the receiving electrode. In other words, the method in which the receiving electrode is directly connected to the resonance circuit has a problem that communication is not possible because the human body and the receiving electrode are slightly separated from each other, but the distance between the human body and the receiving electrode varies due to the distributed constant capacitive coupling. However, the resonance frequency is not easily shifted, and stable communication is possible.

  In the audio signal communication system of the present invention, the receiver includes a low-pass filter or a band-pass filter that removes a high-frequency component from the demodulated audio signal, and an electromagnetic field signal is provided between the voice coil and the signal detection circuit. It is preferable to include a high-pass filter or a band-pass filter. According to this configuration, the electromagnetic field signal and the audio signal can be more reliably separated, and good audio reproduction can be performed.

  In the audio signal communication system of the present invention, it is preferable that a magnetic material is disposed inside the voice coil. According to this configuration, there is nothing that hinders the capacitive coupling between the transmission medium and the voice coil, so that good communication quality can be obtained.

  In the audio signal communication system of the present invention, it is preferable that the magnetic body is electrically insulated from the electric field communication circuit. According to this configuration, capacitive coupling between the voice coil as the reception electrode and the substrate of the electric field communication circuit can be reduced, and the capacitance between the voice coil as the reception electrode and the electric field communication circuit can be reduced. Signal loss can be suppressed and communication quality can be improved.

  In the audio signal communication system according to the present invention, it is preferable that a dielectric is disposed in at least a part of a space between the transmission medium and the voice coil. According to this configuration, since the capacitive coupling between the transmission medium and the voice coil is strengthened, good communication quality can be obtained.

  The audio signal communication system according to the present invention includes a transmitter that modulates an audio signal, converts the signal into an electromagnetic field signal, and transmits the signal, and a receiver that demodulates the audio signal from the electromagnetic field signal and outputs the demodulated audio signal. And a transmission medium for transmitting the audio signal from the transmitter to the receiver via the electromagnetic field signal, wherein the receiver receives the electromagnetic field signal and the demodulated audio signal. An output means having a voice coil that passes through the voice coil, and an electric field communication circuit that detects the electromagnetic field signal that has passed through the voice coil and demodulates the detected signal into the voice signal. Nevertheless, stable music playback can be achieved, and the number of parts can be reduced and the cost can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an audio signal communication system according to an embodiment of the present invention. The communication system for audio signals shown in FIG. 1 includes a transmitter 1 that modulates an audio signal, converts it into an electromagnetic field (electromagnetic wave) signal, and transmits it, and a human body or space that transmits the audio signal through the electromagnetic field signal. The transmission medium 2 and the receiver 3 that detects an electromagnetic field signal via the transmission medium 2, demodulates the electromagnetic field signal into an audio signal, and outputs the demodulated audio signal. Here, the transmission medium 2 is a human body, and specifically assumes an ear.

  The receiver 3 includes a speaker 31 (output means) having a voice coil 311 that receives an electromagnetic field signal and passes a demodulated audio signal, and an electric field communication circuit 32 that demodulates the electromagnetic field signal into an audio signal. . The electric field communication circuit 32 includes a signal detection circuit 321 that detects an electromagnetic field signal that has passed through the voice coil 311, a demodulation circuit 322 that demodulates a signal detected by the signal detection circuit 321 into an audio signal, and an audio signal after demodulation And an audio amplifier circuit 323 for amplifying the signal. Note that since the voice coil 311 also serves as a receiving electrode, it needs to be made of a material suitable as an electrode.

  FIG. 2 is a diagram showing a basic configuration of an inner-ear wireless headphone that is the receiver 3 in the audio signal communication system according to the present invention. This headphone is arranged inside a voice coil 311, that is, a magnet 312 which is a magnetic body inserted in a wound linear body, a diaphragm 313 attached to the magnet 312, a voice coil 311, and a battery 33 attached to the electric field communication circuit 32 electrically connected to 311.

  FIG. 3 shows a state in which the wireless headphones having such a configuration is worn on the ear. As shown in FIG. 3, the ear and the voice coil 311 of the wireless headphone that is the receiving electrode are capacitively coupled. Sufficient communication quality can be ensured by such capacitive coupling. Resonance in a resonance circuit (consisting of a voice coil 311 and a capacitor in the signal detection circuit 321) due to a change in capacitance between the ear that is the transmission medium and the voice coil 311 that is the reception electrode facing the ear. Frequency shift can be suppressed.

  This capacitive coupling is coupled in a distributed constant manner in parallel with the voice coil 311. That is, the voice coil 311 is coupled in a state in which the distance between each line and the ear changes. In the human body communication, the inventors of the present invention have a change in capacitance between the human body and the receiving electrode (corresponding to a distance between the transmission medium and the receiving electrode) that affects the output change (resonance frequency shift). Furthermore, the present inventors have found that this resonance frequency shift suppresses the resonance frequency shift if the resonance inductor is divided even if the distance between the human body and the receiving electrode varies. Has found that can. This finding is described in detail in Japanese Patent Application No. 2007-69265 of the present applicant. Therefore, according to such knowledge, in the configuration shown in FIG. 3, even if the distance between the ear and the voice coil 311 that is the reception electrode varies, the resonance frequency (the voice coil 311 and the capacitor in the signal detection circuit 321) The resonance frequency of the configured resonance circuit is not easily shifted, and stable communication can be maintained. In the above knowledge, it has been found that the greater the number of divisions of the resonance inductor, the more effectively the resonance frequency shift can be suppressed. Therefore, the more stable communication can be achieved by increasing the number of turns of the voice coil 311. Can be realized.

  When the voice coil 311 is also used as a receiving electrode for human body communication due to capacitive coupling between the voice coil 311 and the human body (ear) as in the audio signal communication system according to the present invention, the magnet 312 is disposed outside the voice coil 311 Since the magnet 312 is interposed between the human body and the voice coil 311, capacitive coupling between the voice coil (reception electrode) and the human body is hindered, and problems such as easy noise picking up by the magnet 312 occur. Therefore, the magnet 312 in the speaker 31 is preferably arranged inside the voice coil 311.

  When the capacitive coupling between the electric field communication circuit board 32 and the voice coil (reception electrode) 311 is large, the electromagnetic field signal received by the voice coil 311 passes through the capacity between the circuit board 32 and the circuit board 32. It is conceivable that the reception sensitivity is lowered because of escaping to the ground. In the configuration shown in FIG. 2, it is conceivable that the voice coil 311 and the circuit board 32 are capacitively coupled via the magnet 312. To prevent this, the magnet 312 is electrically insulated from the electric field communication circuit. It is desirable that For example, the magnet 312 is preferably made of an insulator.

  Thus, in the audio signal communication system of the present invention, the voice coil 311 of the receiver 3 also serves as a human body communication reception electrode, so there is no need to newly add a reception electrode, and the number of parts can be reduced. In addition, the size can be reduced. In addition, since the voice coil 311 and the human body are coupled in a distributed constant manner in parallel, the communication stability is high and stable music reproduction is possible. In addition, an expensive material is not used for the receiving electrode, and the cost can be reduced.

  An operation in the case of performing communication in the audio signal communication system having the above configuration will be described. Here, a case where the communication system is a wireless headphone system will be described.

  First, in the transmitter 1 which is an audio signal source, for example, an audio signal (20 kHz or less) is modulated with a carrier wave having a frequency (several hundred kHz to several tens of MHz) at which the human body exhibits conductivity to obtain a modulated signal. This modulated signal is amplified and converted into a voltage change, thereby becoming an electromagnetic field signal corresponding to the modulated signal. This electromagnetic field signal is applied to the human body that is the transmission medium 2. There is no particular limitation on the modulation method in the transmitter 1.

  The electromagnetic field signal applied to the human body is received by the voice coil 311 of the receiver 3. The electromagnetic field signal (high frequency signal) applied to the voice coil 311 is sent to the signal detection circuit 321. At this time, the signal flowing through the voice coil 311 is an audio signal amplified by the audio amplifier circuit 323 and a received high-frequency signal, as shown in FIG. Here, for the audio signal, a current of several mA or more flows through the voice coil 311, and for the high frequency signal, a minute current of about several μA flows. In this way, the current that flows due to the passage of the high-frequency signal is much smaller than the current that flows due to the passage of the audio signal, so the high-frequency signal has little influence on the driving of the speaker 31 by the voice coil 311. In FIG. 4, the signal intensity on the vertical axis is normalized with the peak of each signal as 100.

  Only a high-frequency signal is detected from the current flowing through the voice coil 311 by the LC resonance circuit including the voice coil 311 and the inductor and capacitor in the signal detection circuit 321. The high frequency signal is amplified by an amplifier circuit in the signal detection circuit 321 and sent to the demodulation circuit 322. The demodulation circuit 322 demodulates using the carrier wave used in the transmitter 1, and an audio signal as shown in FIG. Is output only. The audio signal is amplified by the audio amplifying circuit 323, and then sent to the voice coil 311 of the speaker 31, whereby the speaker 31 is driven and output as audio.

  In this audio signal communication system, a voice coil of a speaker is also used as a reception electrode for human body communication, and a signal is received by capacitive coupling between the human body and the voice coil. Since the voice coil and the human body are capacitively coupled in a distributed constant manner, stable communication can be realized against fluctuations in the distance between the human body and the receiving electrode. In other words, the method in which the receiving electrode is directly connected to the resonance circuit has a problem that communication is not possible because the human body and the receiving electrode are slightly separated from each other, but the distance between the human body and the receiving electrode varies due to the distributed constant capacitive coupling. However, the resonance frequency is not easily shifted, and stable communication is possible.

  Here, if there is a possibility that the voice amplification circuit 323 may be affected by the addition of an electromagnetic field signal (high frequency signal) before demodulation to the voice coil 311, as shown in FIG. It is preferable to provide a low-pass filter (LPF) 34 or a band-pass filter that passes a voice band (usually 20 kHz or less) between the coils 311. Thereby, an extra high frequency component can be removed from the audio signal before demodulation, and good audio reproduction can be performed. In this case, the inductance of the voice coil 311 can be used as a part of the low-pass filter. Thereby, the inductor at the time of comprising a filter can be reduced in size or eliminated, and the performance can be improved without increasing the size of the apparatus.

  Further, since the audio signal supplied to the voice coil 311 is extremely larger than the electromagnetic field signal, the audio signal may adversely affect the signal detection circuit 321. In this case, as shown in FIG. 6, a high-pass filter (HPF) 35 or a band-pass filter that passes the frequency of the modulated signal (several hundred kHz or more) is provided between the voice coil 311 and the signal detection circuit 321. preferable. Even in this case, good audio reproduction can be performed. Even in this case, the inductance of the voice coil 311 can be a part of the filter. Thereby, the inductor at the time of comprising a filter can be reduced in size or eliminated, and the performance can be improved without increasing the size of the apparatus.

  In order to improve the reception sensitivity of the receiver 3, it is effective to strengthen the capacitive coupling between the human body and the reception electrode. For this reason, as shown in FIG. 7, it is preferable that the housing shape of the wireless headphones be as close to the ear as possible, and the gap between the housing 37 and the voice coil 311 be filled with a dielectric 36. With such a configuration, the coupling capacitance between the human body and the receiving electrode can be increased. The dielectric 36 may be made of the same material as that of the housing 37 and may be molded integrally with the housing 37.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, the circuit configuration, the number of parts, numerical values, and the like in the above embodiment are merely examples, and the present invention is not limited thereto and can be implemented with appropriate modifications. Other modifications can be made without departing from the scope of the present invention.

It is a schematic block diagram which shows the communication system for audio | voice signals which concerns on embodiment of this invention. It is a figure which shows the basic composition of the inner ear type | mold wireless headphone which is a receiver in the communication system for audio | voice signals which concerns on this invention. FIG. 3 is a diagram showing a state in which the inner-ear wireless headphones shown in FIG. 2 are worn on the ear. It is a figure which shows the relationship between a frequency and signal strength. It is a figure which shows the relationship between a frequency and output intensity. It is a figure which shows the other example of the receiver of the communication system for audio | voice signals shown in FIG. It is a figure which shows the other example of the receiver of the communication system for audio | voice signals shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmitter 2 Transmission medium 3 Receiver 31 Speaker 32 Electric field communication circuit 33 Battery 34 Low pass filter 35 High pass filter 36 Dielectric body 37 Housing 321 Signal detection circuit 322 Demodulation circuit 323 Audio amplification circuit

Claims (5)

  A transmitter that modulates and converts an audio signal into an electromagnetic field signal, transmits a demodulator of the audio signal from the electromagnetic field signal, and outputs a demodulated audio signal; A transmission medium for transmitting an audio signal from the transmitter to the receiver, the receiver receiving the electromagnetic field signal and having a voice coil for passing the demodulated audio signal; An audio signal communication system comprising: an electric field communication circuit that detects the electromagnetic field signal received by the voice coil and demodulates the detected signal into the audio signal.   2. The receiver according to claim 1, wherein the receiver includes a low-pass filter or a band-pass filter that removes a high-frequency component from the demodulated audio signal, and includes a high-pass filter or a band-pass filter connected to the voice coil. Audio signal communication system.   3. The voice signal communication system according to claim 1, wherein a magnetic body is disposed inside the voice coil.   The audio signal communication system according to any one of claims 1 to 3, wherein the magnetic body is electrically insulated from the electric field communication circuit.   The audio signal communication system according to any one of claims 1 to 4, wherein a dielectric is disposed in at least a part of a space between the transmission medium and the voice coil.

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