JP3635722B2 - Headphone receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a headphone receiver suitable for application to, for example, a portable audio device.
[0002]
[Prior art]
Conventionally, a headphone is connected to a relatively small portable tape cassette playback device or a compact disc (CD) playback device so that an audio signal reproduced by the playback device can be heard by the headphone. Various products have been made.
[0003]
In this case, if the signal line for audio signal transmission is connected between the playback device and the headphones, this signal line may get in the way, so wirelessly transmit audio signals etc. from the playback device to the headphones. So-called wireless portable playback devices have been developed. In the case of this wireless reproduction device, a transmission circuit for frequency-modulating (FM) an audio signal reproduced on the reproduction device side and wirelessly transmitting the audio signal is provided, and an audio signal (FM signal) wirelessly transmitted to the headphones side. A receiving circuit for receiving the signal is attached. Then, the audio signal received by the receiving circuit is demodulated and reproduced from the headphones.
[0004]
In this way, usability is improved by wireless transmission between the playback device and the headphones. In other words, it is difficult to reduce the size of this type of audio signal playback device to be smaller than the size of a recording medium to be mounted such as a tape cassette or a compact disc, so there is a limit to downsizing for portable use. However, the receiving circuit attached to the headphones can be made smaller than such a reproducing apparatus. Therefore, by putting the playback device in a bag or the like carried by the user, and using the case in which the receiving circuit for mounting on the headphones is configured in a pocket, the user put the playback device to some extent. Audio can be played back with headphones even when away from the back.
[0005]
In the case of a wireless portable playback device used in this manner, the antenna used by the receiving circuit often uses an audio signal transmission line (so-called headphone cord) of the connected headphones. By using the headphone cord as an antenna line in this way, the receiving circuit does not need to have a separate antenna, and the receiving circuit can be made smaller accordingly.
[0006]
FIG. 5 is a diagram showing an example of a configuration of an antenna input unit connected to a conventional reception circuit of this type, and the audio signal reception system 1 performs reception processing based on a signal supplied from an antenna input circuit described later. The left channel and right channel audio signals obtained in this way are amplified by the output amplifier 2 and then sent to the headphone cords 4L, 4R, 4G via the choke coils 3L, 3R, 3G. In this case, the headphone cord 4L is a signal line for the left channel, the headphone cord 4R is a signal line for the right channel, and the headphone cord 4G is a signal line common to each channel. Then, the headphones cords 4L, 4R, 4G are connected to the headphones 5. In this case, the left channel signal line 4L and the common signal line 4G are connected to the left channel unit 5L, and the right channel signal line 4R and the common signal line 4G are connected to the right channel unit 5R.
[0007]
The common signal line 4G in the headphone cord is used as an antenna line. That is, the common signal line 4G between the choke coil 3G and the headphone units 5L and 5R is drawn out and connected to the antenna input circuit 6. The antenna input circuit 6 connects a connection portion with the common signal line 4G to the base of an NPN transistor Q ₁ through a series circuit of capacitors C ₁ , C ₃ , and C ₆ . Then, the middle point of the coil L ₁ is connected between the capacitor C ₁ and the capacitor C ₃ . Then, between the one end and the other end of the coil L _1, connected through a capacitor C _2, grounding the one end of the coil L _1.
[0008]
Further, between the capacitor C ₃ and the capacitor C ₆ , one end of the capacitor C ₄ and one end of the capacitor C ₅ are connected, and the other ends of both the capacitors C ₄ and C ₅ are connected via the coil L _2. . Then, the ground and the other end of the capacitor C _5. The emitter of the transistor Q ₁ is grounded, and the collector of the transistor Q ₁ is connected to the audio signal receiving system 1, and the audio signal receiving system 1 receives and processes the signal obtained through the transistor Q ₁ .
[0009]
According to the antenna input section configured as described above, a signal received using the headphone cord 4G as an antenna line is extracted by the antenna input circuit 6, and an audio signal received by the audio signal receiving system 1 can be received. In this case, the radio signal to be received is selected by selecting the inductance values of the coils L ₁ and L ₂ in the antenna input circuit 6 and the capacitance values of the capacitors C ₂ , C ₄ and C ₅ connected to the coils L ₁ and L _2. Sets the frequency band of the signal. For example, each value is selected so as to receive a 240 MHz band signal, and the antenna input unit is tuned.
[0010]
[Problems to be solved by the invention]
By the way, the cord connected to the headphones used in such a wireless portable playback device has a relatively short length (about several tens of centimeters), and depending on the positional relationship between the playback device and the cord, an antenna may be used. And the reception level of the signal transmitted from the playback device may not be received. In such a case, audio playback from the headphones is interrupted. For example, when an audio signal frequency-modulated in the 240 MHz band is wirelessly transmitted and received by the circuit shown in FIG. 5, even if there is no change in the distance from the playback device that transmits the audio signal, The reception sensitivity may change by about 20 to 30 dB.
[0011]
In order to solve this problem, for example, a separate antenna is provided in addition to the headphone cord, and the reception sensitivity of the two antennas of the headphone cord antenna and the separate antenna is low. It is conceivable to perform so-called diversity reception by receiving and processing the better signal. However, when an antenna separated as described above is provided, a separate part is attached to the receiving unit, and the receiving device connected to the headphones is increased in size. Further, the circuit configuration of the receiving device connected to the headphones also requires a circuit for selecting a signal from a good antenna, resulting in a complicated circuit configuration.
[0012]
SUMMARY OF THE INVENTION The present invention has been made in view of this point, and an object of the present invention is to provide this type of receiving apparatus capable of good reception with a simple configuration.
[0013]
[Means for Solving the Problems]
In order to solve this problem, the present invention provides a receiving device for headphones that uses a common signal line connected to a headphone unit as an antenna line, a resonance circuit connected to the antenna line, and an antenna line and a resonance circuit. And a receiving circuit for receiving a received signal obtained via the resonant circuit.
[0014]
According to the present invention, when the loop circuit functions as an auxiliary antenna and the reception level on the antenna line is low, it is possible to compensate for the signal received by the loop circuit.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS. 1 to 4, the same reference numerals are given to the portions corresponding to FIG. 5 described in the conventional example, and the detailed description thereof is omitted.
[0016]
In this example, an audio signal (for example, FM-modulated analog audio signal) wirelessly transmitted from a portable playback device (tape cassette playback device, disk playback device, etc.) is received, and the audio received by the connected headphones is received. The receiver is configured to supply a signal, and is configured as shown in FIG. That is, the audio signal received and processed by the audio signal receiving system 1 is amplified by the output amplifier 2 and supplied to the headphone cords 4L, 4R and 4G connected via the choke coils 3L, 3R and 3G. Audio signals are supplied to the headphone units 5L and 5R of the headphones 5 connected to the cords 4L, 4R and 4G, and the audio signals are emitted from the speaker units in the headphone units 5L and 5R.
[0017]
Then, the choke coil 3L from the output amplifier 2, 3R, code headphone connected via a 3G 4L, 4R, the common signal line 4G of the 4G, connected to one end of the capacitor C ₁ of the antenna input circuit 10 . The other end of this capacitor C ₁ is connected to the base of an NPN transistor Q ₁ via capacitors C ₃ and C ₆ .
[0018]
The loop unit 11 is connected between the capacitor C ₁ and the capacitor C ₃ . The loop portion 11 is configured by connecting one end and the other end of the capacitor C ₂ with a signal line arranged in a circular shape, and a predetermined portion (here, the capacitor C) of the signal line arranged in the circular shape. ₂ ) and a connection point between the capacitors C ₁ and C ₃ and a predetermined portion of the circular signal line (here, near one end of the capacitor C ₂ ) Is connected to the ground potential section.
[0019]
Then, one end of the capacitor C ₄ and one end of the capacitor C ₅ are connected between the capacitor C ₃ and the capacitor C _6, and the other ends of both the capacitors C ₄ and C ₅ are connected via the coil L _2. . Then, the ground and the other end of the capacitor C _5. The emitter of the transistor Q ₁ is grounded, and the collector of the transistor Q ₁ is connected to the audio signal receiving system 1, and the audio signal receiving system 1 receives and processes the signal obtained through the transistor Q ₁ .
[0020]
The frequency band of the received radio signal is set by selecting the inductance value of the coil L ₂ in the antenna input circuit 10 and the capacitance values of the capacitors C ₄ and C ₅ connected to the coil L ₂ . Here, each value is selected so as to receive a 240 MHz band signal, and the antenna input unit is tuned.
[0021]
Other portions are configured in the same manner as the circuit shown in FIG. 5 as a conventional example.
[0022]
Here, FIG. 2 shows an actual configuration example of a receiving apparatus and headphones in which the antenna input circuit 10 having such a circuit configuration is incorporated. The receiving apparatus 20 configured in a relatively small housing has an audio signal. Is connected to a headphone plug 22 so that an audio signal received and processed by an internal circuit is connected to a headphone cord 4 (three cords within the cord 4). The signal lines 4L, 4R, and 4G are housed) and are supplied to the left and right headphone units 5L and 5R. In this case, the length of the headphone cord 4 is about 40 cm, for example.
[0023]
FIG. 2 shows an example in which a headphone without a headband is used. In this case, the left and right headphone units 5L and 5R themselves are headphone bodies. The receiving device 20 is provided with a switch 23 for turning on / off the reception, a volume (not shown) for adjusting the volume, and the like.
[0024]
A circuit board 24 for assembling the circuit shown in FIG. 1 is arranged inside the receiving apparatus 20, and the tip of the portion protruding from the circuit board 24 is circular, and a circuit as the loop part 11 is formed in this circular part. Make up. In this case, the portion of the loop portion 11 protruding from the circuit board 24 is bent with respect to the circuit board 24 and arranged at a position slightly away from the circuit board 24 so as to be accommodated in the receiving device 20.
[0025]
Note that the receiving device 20 is configured to accommodate a battery (not shown) for operating each circuit.
[0026]
Next, the receiving operation of the receiving apparatus of this example will be described. The antenna input circuit 10 is connected to the cord (signal line) 4G of the headphone 5, and the antenna input circuit 10 extracts a received signal in a predetermined band. Processing is performed. That is, a circuit composed of capacitors C ₄ and C ₅ and a coil L ₂ connected in the middle of the signal path from the signal line 4G to the transistor Q ₁ becomes a resonance circuit, and a frequency band determined by the capacitance value and the inductance value is extracted. Functions as a tuning circuit.
[0027]
Similarly, the loop portion 11 connected to the middle of the signal path from the signal line 4G until the transistor Q _1, and functions as a tuning circuit. That is, when the equivalent circuit of the loop portion 11 is shown in FIG. 3, the signal line connecting the one end and the other end of the capacitor C _{2 in} a circular shape functions as a coil L ₀ having a predetermined inductance value. A loop circuit is formed by L ₀ and the capacitor C _2, and a terminal 11a drawn from the middle of the coil L ₀ is connected between the capacitors C ₁ and C ₃ of the circuit shown in FIG. ₀ and the terminal 11b led out from the connection point between the capacitor C ₂ is connected to the ground potential portion.
[0028]
Since the loop portion 11 is shown in the equivalent circuit shown in FIG. 3, the loop portion 11 includes a resonance circuit including a coil L ₁ and a capacitor C ₂ in the antenna input circuit 6 shown in FIG. It can be seen that it functions as a similar circuit. Therefore, the capacitance value of the capacitor C _2, the length of the signal line connecting between the one end and the other end of the capacitor C ₂ in a circular shape (i.e. an inductance value of the coil L ₀ shown in the equivalent circuit), such as a good By selecting, it functions as a tuning circuit that extracts this predetermined frequency band.
[0029]
FIG. 4 is a diagram showing the reception characteristics of the antenna input circuit 10 of this example. Only the reception level in the vicinity of a predetermined frequency f ₁ (about 240 MHz in this example) is increased, and the received signal in this band is shown. Is extracted.
[0030]
In this example, since there is a loop portion 11 that functions as a part of the tuning circuit of the antenna input circuit 10, the loop portion 11 also functions as an auxiliary antenna. That is, when the circuit constituting the loop unit 11 functions as an antenna for picking up a radio signal and the reception sensitivity at the headphone cord 4G as the main antenna is not so high, the received signal at the loop unit 11 is the antenna. It is supplied from the input circuit 10 to the audio signal receiving system 1 and can continuously ensure a good reception state.
[0031]
In particular, when a headphone cord is used as an antenna as in this example, the impedance of the antenna (that is, the headphone cord) is high, and a phenomenon called a body effect, that is, the antenna (code) is attached to the body of the headphone wearer. When approaching, the phenomenon that the reception sensitivity falls due to the influence of the body occurs, but the loop part 11 functions as a low impedance antenna, and the phenomenon called the body effect hardly occurs. Therefore, even when the reception sensitivity of the headphone cord is lowered due to the body effect, the loop unit 11 is likely to be able to receive with good sensitivity, and it is highly likely that the reception device connected to the headphone is always good. Become.
[0032]
In the above-described embodiment, the receiving device receives an audio signal transmitted in the 240 MHz band. However, the receiving device may receive a signal other than the audio signal, and may be transmitted in another band. The signal may be received. If this transmission band is different, it can be dealt with by setting the value of each element in the antenna input circuit correspondingly. In FIG. 2 described in the above embodiment, the headphone plug 22 is attached to the jack 21 of the receiving device 20 so that the headphone can be attached. However, there is no such jack and the receiving device is connected to the headphone. You may comprise so that it may not remove.
[0033]
In the above-described embodiment, the headphone cord is used as an antenna. However, another appropriate length of conductor may be used as the antenna. Furthermore, in the above-described embodiment, the receiving device is used in combination with a portable playback device, but can be applied to other receiving devices. For example, the present invention can also be applied to a radio receiver that receives FM broadcast waves. In this case, for example, a part of the elements in the antenna input circuit may be variable elements, and the frequency band to be extracted may be changed by changing the capacitance of the capacitor in conjunction with the channel selection operation.
[0034]
【The invention's effect】
According to the present invention, when the loop circuit functions as an auxiliary antenna and the reception level at the antenna line is low, it can be supplemented with a signal received by the loop circuit, and a decrease in the reception level can be suppressed. The good reception state continues.
In this case, a capacitor and a coil are connected as a resonance circuit, and a capacitor is connected in the middle of the loop circuit, so that the resonance circuit and the loop circuit function as a tuning circuit that extracts a signal in a predetermined band. A signal transmitted in the band can be received well.
[0035]
In addition, by using an audio signal transmission line for headphones as an antenna line, it becomes possible to receive well without providing a separate antenna at all, and the reception sensitivity by this audio signal transmission line is improved. If it is not good, the loop circuit effectively functions as an auxiliary antenna, and a good reception state is maintained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram according to an embodiment of the present invention.
FIG. 2 is a perspective view showing an apparatus according to an embodiment.
FIG. 3 is a circuit diagram showing an equivalent circuit of a loop circuit according to one embodiment.
FIG. 4 is a characteristic diagram illustrating reception characteristics according to an embodiment.
FIG. 5 is a configuration diagram illustrating a configuration example of a conventional antenna input unit.
[Explanation of symbols]
1 Audio signal reception system 2 Output amplifier 3L, 3R, 3G Choke coil 4L, 4R, 4G Headphone cord (signal line)
5 Headphones 5L, 5R Headphone unit 10 Antenna input circuit 11 Loop section

Claims (1)

A receiving circuit for receiving an audio signal;
An output amplifier for amplifying the audio signal received by the receiving circuit;
A left signal supply line that supplies a signal to the left headphone unit of the headphone, a right signal supply line that supplies a signal to the right headphone unit of the headphone, and a left and right headphone unit that are connected from the output amplifier via a choke coil, respectively. A receiving device for headphones having a common signal line connected thereto,
The antenna input circuit of the receiving circuit is
First and second capacitors connected in series to the common signal line at the connection point between the left and right headphone units and the choke coil;
Auxiliary antenna wire formed in a loop shape with one end and the other end of the auxiliary capacitor,
A first connection point and a second connection point that are separated from each other by a predetermined distance of each of the loop-shaped auxiliary antennas are set, and the first connection point is connected to a connection midpoint of the first and second capacitors, The second connection point is connected to the ground location of the resonance circuit including the resonance capacitor and the coil, and the signal obtained at the connection point between the second capacitor and the resonance capacitor is supplied to the reception circuit.
Headphone receiver.

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