Abstract:
An earphone antenna has an earphone unit including an earphone, an earphone cable for supplying audio signals to the earphone, and a first pin jack connector portion on one end of the earphone cable, the earphone cable functioning as an antenna wire. The earphone antenna further includes a shielded cable having a coaxial core, an insulation-covered signal wire for audio signals, and a ground wire. The coaxial core has a center conductor for transmitting high frequency signals surrounded by an insulator and further surrounded by a shield wire. A multi-pole connector arranged on one end of the shielded cable is adapted to electrically connect the shielded cable to an electronic apparatus. A connection block connects the other end of the shielded cable to the earphone unit, the connection block including a circuit device for separating audio signals and high frequency signals, and a second pin jack connector portion for removably receiving the first pin jack connector portion to removably connect the earphone unit to the connection block.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Application Nos. 2004-227095 filed Aug. 3, 2004 and 2005-167725 filed Jun. 8, 2005, the disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an earphone antenna for portable wireless equipment worn on the human body during use. 
     Portable wireless equipment worn on the human body during use, such as a pager, a radio receiver or a liquid crystal television receiver, has heretofore used an earphone antenna which uses, as an antenna, signal wires for transmitting audio signals to a rod antenna and earphones (Japanese Patent Application Publication No. 2003-163529). 
     However, the portable wireless equipment using a rod antenna or an earphone antenna has drawbacks that when the equipment is used in the state of being worn on the human body, the performance of the antenna is remarkably degraded due to the wear of the equipment on the human body, so that it is difficult to obtain satisfactory reception sensitivity in the case of television broadcasting which handles signals containing a large amount of information such as video images. 
     In particular, the earphone antenna which uses, as an antenna, signal wires for transmitting audio signals to earphones has a drawback that since the earphones or the signal wires come in direct contact with the human body, the human body greatly influences the wireless equipment through the antenna and greatly impairs stability of reception. 
     Television broadcasting in Japan, for example, uses the VHF band of 90–108 MHz (1–3 ch) and 170–222 MHz (4–12 ch) and the UHF band of 470–770 MHz (13–62 ch). Accordingly, liquid crystal television receivers for receiving television broadcasting need to receive high frequency signals over an extremely wide band of 90–770 MHz, but the existing rod antenna and earphone antennas are inferior in performance to fixed types of antennas and have extreme difficulty in obtaining satisfactory sensitivity in the necessary frequency range. 
     In addition, the existing earphone antennas are remarkably low in sensitivity because they make use of ordinary earphones, or have a special structure in which a separate antenna wire is inserted between signal wires of earphones, or have an unremovable structure because of integral molding. 
     The present invention has been made in view of the above-mentioned drawbacks, and intends to provide an earphone antenna able to alleviate the influence of the human body and ensure stability of reception as well as to use replaceable earphone units. 
     SUMMARY OF THE INVENTION 
     To solve the above-mentioned problems, according to one embodiment of the present invention, there is provided an earphone antenna. The earphone antenna includes an earphone unit including an earphone, an earphone cable for supplying audio signals to the earphone, and a first pin jack connector portion on one end of the earphone cable, the earphone cable functioning as an antenna wire; a shielded cable including a coaxial core, an insulation-coated signal wire for audio signals, and a ground wire, the coaxial core having a center conductor for transmitting high frequency signals surrounded by an insulator and further surrounded by a shield wire; a multiple-pole connector arranged on one end of the shielded cable and adapted to electrically connect the shielded cable to an electronic apparatus; and a connection block for connecting the other end of the shielded cable to the earphone unit, the connection block including a circuit device for separating audio signals and high frequency signals, and a second pin jack connector portion for removably receiving the first pin jack connector portion to removably connect the earphone unit to the connection block. 
     In the earphone antenna according to the embodiment of the present invention, an antenna device may be provided in the connection block so that the earphone antenna functions as an antenna even when the earphone unit is disconnected from the connection block. 
     In the earphone antenna according to the embodiment of the present invention, instead of the earphone unit, a speaker may be connected to the connection block via the pin jack connector portions. 
     In the earphone antenna according to the embodiment of the present invention, instead of the earphone unit, a rod antenna may be connected to the connection block via the pin jack connector portions. 
     In the earphone antenna according to the embodiment of the present invention, the first and second pin jack connector portions together define a pin jack connector, the pin jack connector including a switch for opening a circuit in conjunction with an action of connecting the first pin jack connector portion to the second pin jack connector portion, and for closing the circuit in conjunction with an action of disconnecting the first pin jack connector portion from the second pin jack connector portion. 
     In accordance with the earphone antenna according to the embodiment of the present invention described above, the influence of the human body can be alleviated to ensure the stability of reception. In addition, the pin jack connector portion to which the earphone cable is removably connected is provided in the connection block so that the earphone unit may be removed therefrom. Accordingly, the earphone unit is replaceable, so that ordinary earphones can be used. In addition, in the earphone antenna according to the embodiment of the present invention, instead of the earphone unit, a speaker or a rod antenna can be connected to the connection block via the pin jack connector portions. 
     Accordingly, in accordance with the embodiment of the present invention, it is possible to provide an earphone antenna able to alleviate the influence of the human body and ensure the stability of reception as well as to use replaceable earphone units. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more readily appreciated and understood from the following detailed description of a embodiment of the present invention when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view showing a configuration of a liquid crystal television receiver to which an embodiment of the present invention is applied; 
         FIG. 2  is a schematic view showing a configuration of a pin jack connector which connects an earphone unit to an earphone antenna of the liquid crystal television receiver; 
         FIG. 3  is a schematic view showing a configuration of a pin jack connector which connects a receiver body and the earphone antenna in the liquid crystal television receiver; 
         FIG. 4  is a block diagram showing a configuration of the receiver body; 
         FIG. 5  is a schematic view showing a structure of a shielded cable constituting part of the earphone antenna; 
         FIG. 6  is a schematic view showing a configuration of a connection block constituting part of the earphone antenna; 
         FIG. 7  is a circuit configuration diagram showing an electrical configuration of the earphone antenna; 
         FIG. 8  is a schematic view showing another configuration example of the pin jack connector which connects the earphone unit to the earphone antenna of the liquid crystal television receiver; and 
         FIGS. 9A and 9B  are schematic views showing a state ( 9 A) in which an external speaker, instead of the earphone unit, is connected to the connection block via the pin jack connector, and a state ( 9 B) in which a rod antenna, instead of the earphone unit, is connected to the connection block via the pin jack connector. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. It goes without saying, however, that the present invention is not limited to the following embodiment and can be arbitrarily modified without departing from the scope and spirit of the present invention. 
     The present invention is applied to a liquid crystal television receiver  100  having the configuration shown in  FIG. 1  by way of example. 
     In the liquid crystal television receiver  100  shown in  FIG. 1 , an earphone antenna  10  according to the embodiment of the present invention is connected to a receiver body  120  via a pin jack connector  110 . 
     The earphone antenna  10  includes a shielded cable  20  connected at one end to the receiver body  120  via the 5-pole pin jack connector  110 , a connection block  30  connected to the other end of the shielded cable  20 , and an earphone unit  40  equipped with stereo earphones  40 R and  40 L each provided at one end of a respective one of two earphone cables  41  and  42  connected to the connection block  30  via a pin jack connector  130 . 
     The pin jack connector  130  includes, as shown in  FIG. 2 , a pin  130 A and a jack  130 B each having three poles to which three kinds of lines, i.e., an audio L channel (L), an audio R channel (R) and ground (Gnd), are to be connected, respectively. 
     The pin jack connector  110  includes, as shown in  FIG. 3 , a pin  110 A and a jack  110 B each having five poles to which five kinds of lines, i.e., an antenna (Ant), a headphone detection line (detection), the audio L channel (L), the audio R channel (R) and the ground (Gnd), are to be connected, respectively. 
     The receiver body  120  includes, as shown in  FIG. 4 , a tuner unit  121 , an intermediate frequency signal processing unit  122  connected to the tuner unit  121 , a video signal processing unit  123  and an audio signal processing unit  125  both of which are connected to the intermediate frequency signal processing unit  122 , a liquid crystal display unit  124  connected to the video signal processing unit  123 , and the jack  110 B constituting the pin jack connector  110 . 
     In the liquid crystal television receiver  100 , the jack  110 B is, as shown in  FIG. 3 , equipped with five movable terminals  1 ,  2 ,  5 ,  6  and  7  and two fixing terminals  3  and  4 , and as shown in  FIG. 4 , the movable terminal  7  is connected to the tuner unit  121  as an antenna terminal (Ant), while the movable terminals  2  and  5  are connected to the audio signal processing unit  125  as the audio L channel terminal (L) and the audio R channel terminal (R), respectively. The movable terminal  6  is connected to a headphone detection unit  126  as a headphone detection terminal. The movable terminal  1  is connected to GND of a circuit board of the wireless equipment body as a common ground terminal (Gnd) of the wireless equipment. The fixing terminals  3  and  4  are terminals for fixing the pin  110 A in position. 
     Although not shown, a capacitor having a capacitance of approximately 1,000 pF is generally inserted between the movable terminal  7  and the tuner unit  121  in order to prevent electrostatic discharge damage. 
     As shown in  FIG. 5 , the shielded cable  20  includes a coaxial core  24 , insulator-covered signal wires  25 L and  25 R for audio signals, and an insulator-covered headphone-detecting signal wire  25 C. The coaxial core  24  has a center conductor  21  extended to transmit high frequency signals and covered with an insulator  22  and further with a shield wire  23 , and the signal wires  25 L and  25 R and the headphone-detecting signal wire  25 C are wound around the coaxial core  24  and an insulating jacket covers the outside of the wound wires  25 L,  25 R and  25 C. The shielded cable  20  at one end is provided with the pin  110 A having five poles respectively connected to the center conductor  21  and the shield wire  23  of the coaxial core  24 , the signal wires  25 L and  25 R for audio signals, and the headphone-detecting signal wire  25 C. The shielded cable  20  at the other end is provided with the connection block  30  which is connected to the center conductor  21 , the shield wire  23 , the signal wires  25 L and  25 R for audio signals, and the headphone-detecting signal wire  25 C. 
     The connection block  30  is, as shown in  FIG. 6 , equipped with a circuit board  34  on which are formed a ground pattern  31  provided at the central location, stereo-audio-signal transmission line patterns  32 L and  32 R respectively provided on the both sides of the ground pattern  31 , three connection lands  33 L,  33 R and  33 C provided on an extending-end side of the ground pattern  31 , and a connection land  33 D provided on one side of the ground pattern  31 . Mounted on the circuit board  34  are high frequency chokes  35 L and  35 R which respectively connect extending-end portions of the stereo-audio-signal transmission line patterns  32 L and  32 R to the connection lands  33 L and  33 R, a high frequency choke  35 C which connects the connection land  33 C to the connection land  33 C, a chip capacitor  36 L which connects the connection land  33 L and the connection land  33 C, a chip capacitor  36 R which connects the connection land  33 R and the connection land  33 C, and a chip capacitor  36  which connects the connection land  33 C and the connection land  33 D. 
     The stereo-audio-signal transmission line patterns  32 L and  32 R formed on the circuit board  34  are connected to the ground pattern  31  via chip capacitors  37 L and  37 R, respectively, so that the transmission line patterns  32 L and  32 R can be integrated with the ground (Gnd) on a high-frequency basis. 
     The jack  130 B of the pin jack connector  130  is, as shown in  FIG. 2 , equipped with an L terminal  2 ′ to which the audio L channel (L) is to be connected, an R terminal  3 ′ to which the audio R channel (R) is to be connected, and a ground terminal  1 ′ for the ground (Gnd). 
     The connection block  30  is provided with the connector jack  130 B in order to transmit audio signals, and as shown in  FIGS. 6 and 7 , the land  33 L connected to the left transmission line pattern  32 L by the high frequency choke  35 L and an L land  39 L to which the L terminal  2 ′ of the connector jack  130 B is fixed are connected to each other in order to supply left audio signals to the left earphone  40 L. In addition, the land  33 R connected to the right transmission line pattern  32 R by the high frequency choke  35 R and an R land  39 R to which the R terminal  3 ′ of the connector jack  130 B are connected to each other in order to supply right audio signals to the right earphone  40 R. The connection land  33 C which serves as ground for both earphones  40 L and  40 R and a ground land  38  to which the ground terminal  1 ′ of the connector jack  130 B are connected to each other. The connection land  33 C serves as an antenna for high frequencies, and as shown in  FIGS. 6 and 7 , a meander-shaped pattern  60  is formed to extend from the connection land  33 C so that the connection land  33 C functions as an antenna even when the connector pin  130 A of the earphone unit  40  is removed from the connection block  30 . 
     An electrical circuit configuration formed on the connection block  30  is shown in  FIG. 7 . 
     The shielded cable  20  is connected to the connection block  30  in the following manner. 
     The left audio signal wire  25 L and the right audio signal wire  25 R of the shielded cable  20  are respectively connected to the stereo-audio-signal transmission line patterns  32 L and  32 R formed on the circuit board  34 , and the headphone-detecting signal wire  25 C of the shielded cable  20  is connected to the ground pattern  31 . The center conductor  21  and the shield wire  23  of the coaxial core  24  constituting the coaxial structure of the shielded cable  20  are placed on the ground pattern  31  so that the shield wire  23  is connected to the ground pattern  31  and the extending end of the center conductor  21  is connected to the connection land  33 D. 
     In addition, the above-mentioned capacitor (not shown) for prevention of electrostatic discharge damage inserted between the movable terminal  7  and the tuner unit  121  can be substituted for the chip capacitor  36  which connects the connection land  33 C and the connection land  33 D. In this case, the extending end of the center conductor  21  constituting the coaxial structure of the shielded cable  20  is directly connected to the connection land  33 C. 
     In the present embodiment, ferrite beads, for example, BLM18HD102SN1 (1608 size) manufactured by Murata Manufacturing Co., Ltd., are used as the high frequency chokes  35 L,  35 R and  35 C. The high frequency chokes  35 L,  35 R and  35 C using such beads provide low impedance for audio signals in the frequency band of not higher than 20 kHz, and provide high impedance for high frequency signals so as to prevent passage of the high frequency signals. Each of the chip capacitors  36 L,  36 R,  37 L and  37 R uses a type having a capacitance of 1,000 pF, and provides high impedance for audio signals in the frequency band of not higher than 20 kHz to prevent passage of the audio signals, and provide low impedance for high frequency signals. The high frequency chokes  35 L,  35 R and  35 C and the chip capacitors  36 L,  36 R,  37 L and  37 R function as circuit devices for separating audio signals and high frequency signals. 
     When the earphone unit  40  is attached to the connection block  30 , the earphone antenna  10  functions as a sleeve antenna which resonates at 100 MHz in the VHF band, because the two earphone cables  41  and  42 , the meander-shaped pattern  60  on the connection block  30 , the shield wire  23  of the coaxial core  24 , and the signal wires  25 L,  25 R and  25 C constitute such sleeve antenna. In addition, the earphone antenna  10  functions as a sleeve antenna of 1λ at 200 MHz, and can also make use of harmonic excitations of 100 MHz and 200 MHz (the third harmonic, the fifth harmonic and the seventh harmonic) in the UHF band. 
     In addition, in the earphone antenna  10 , the earphone unit  40  can be removably attached to the connection block  30 , and even when the earphone unit  40  is removed from the connection block  30 , the meander-shaped pattern  60  on the connection block  30 , the shield wire  23  of the coaxial core  24 , and the signal wires  25 L,  25 R and  25 C function as the sleeve antenna. In addition, receivable frequencies can be varied by adjusting the length of the meander-shaped pattern  60  formed to extend from the connection land  33 C on the circuit board  34 . In addition, it is possible to connect a coil to the connection land  33 C instead of forming the meander-shaped pattern  60  on the circuit board  34 , and in this case as well, it is possible to obtain a similar advantage. 
     The present invention can be applied to antennas other than the above-mentioned example, and can also be applied to a case where audio signals and high frequency signals are multiplexed in the earphone unit  40  and the shielded cable  20  is used to construct a dipole antenna. 
     Since the earphone unit  40  can be separated from the earphone antenna  10  at the pin jack connector  130  provided in the connection block  30 , users can freely select desired earphone units as the earphone unit  40 , so that it is possible to improve convenience of users who have found it inconvenient that the earphone unit  40  does not fit their ears. 
     In addition, since the earphone antenna  10  functions as an antenna even when the earphone unit  40  is removed, a jack having a mute terminal  4 ′ may also be adopted as the connector jack  130 B, as shown in  FIG. 8 , so that the headphone-detecting signal wire  25 C can be connected to the mute terminal  4 ′ of the connector jack  130 B by a method similar to that used for each of the audio signal wires  25 L and  25 R. The mute terminal  4 ′ contacts the ground terminal  1 ′ when the earphone unit  40  is removed from the connection block  30 . If this configuration is applied to a portable terminal having a mute function, the portable terminal can be configured to detect the presence or absence of earphones and reproduce sound from its built-in speaker during reception of television broadcasting. 
     In addition, during the state shown in  FIG. 9A , instead of the earphone unit  40 , an external speaker  140  can be connected to the connection block  30  via the pin jack connector  130 , so that the functions of both a speaker and an antenna can be satisfied even in the case of a portable terminal having no internal speakers. 
     In addition, the earphone antenna  10  functions as a sleeve antenna irrespective of the presence or absence of the earphone unit  40 , but during the state shown in  FIG. 9B , instead of the earphone unit  40 , a rod antenna  150  can be connected to the connection block  30  via the pin jack connector  130  so that the rod antenna  150 , the meander-shaped pattern  60  on the connection block  30 , the shield wire  23  of the coaxial core  24 , and the signal wires  25 L,  25 R and  25 C function as a sleeve antenna. In this case, sensitivity can be improved compared to the case where the earphone unit  40  is absent. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.