GB2438135A

GB2438135A - Portable apparatus with built-in FM transmitter

Info

Publication number: GB2438135A
Application number: GB0716779A
Authority: GB
Inventors: Hiroshi Miyagi; Takeshi Ikeda; Akira Okamoto
Original assignee: Nigata Semitsu Co Ltd
Current assignee: NSC Co Ltd
Priority date: 2005-03-18
Filing date: 2006-03-08
Publication date: 2007-11-14
Also published as: GB0716779D0; CN101142749A; TW200637177A; WO2006100911A1; JPWO2006100911A1

Abstract

A portable apparatus with a built-in FM transmitter, where an antenna has a high degree of freedom in installation, less likely to break, and has enhanced transmission efficiency. A portable music playback apparatus (100) comprises an audio playback device (10) for generating an audio signal to be transmitted, a stereo modulation circuit (22) and an FM modulation circuit (24) for FM-modulating the audio signal to generate a carrier wave signal receivable by an FM receiver, an external transmission antenna (102) removably provided exposed to the outside of a housing, and a transmission circuit (26) for transmitting the carrier wave signal through the external transmission antenna (102).

Description

PCHTflT APPARATUS WITH BUILT-rn RI TRNSICnsa

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a portable apparatus with a built-in FM transmitter for transmitting an FM modulated signal.

Description of the Related Art

A portable apparatus, such as a portable phone with a built-in FM transmitter, has been known (for example, refer to Patent Document 1). Use of the built-In FM transmitter enables sound generated in the portable apparatus to be output from an external FM receiver.

This enables the sound generated in a portable apparatus with no speaker to be output from an external speaker, or sound quality and sound volume to be improved or ensured as compared to a case where a built-in small speaker is used. Moreover, an externally attached rod-like antenna has been known as an antenna to be connected to the FM transmitter built in a portable apparatus (refer to, for example, Patent Document 2).

(Patent Document 1]: Japanese Patent Application Laid Open No. 2001-197168 (pp 3 to 6, FIGS. 1 to 5) (Patent Document 2]: Japanese Patent Application Laid Open No. 1110-207972 (pp 4 to 7, FIGS. 1 to 9)

SUMMARY OF THE INVENTION

Incidentally, as disclosed in above-mentioned Patent Document 2, when a rod-shaped antenna is always externally attached to the FM transmitter, it ray be damaged when it is kept in a bag and the like, or carried.

Although a case where such a rod-shaped antenna is built in the portable apparatus, can be considered, since miniaturization of the entire device becomes difficult, and it becomes difficult to ensure a reception space for the antenna in a housing, thereby, the degree of freedom of antenna installat on decreases, moreover, a small antenna must be used, resulting in a problem of degradation of transmission efficiency.

The present invention is invented in view of such points, and the object of the present invention is to provide a portable apparatus with a built-in FM transmitter where an antenna has a high degree of freedom in installation, whose antenna is less likely to break, and has enhanced transmission efficiency.

In order to solve the above-mentioned problems, the portable apparatus with a built-in FM transmitter of the present invention includes an audio signal generation circuit for generating an audio signal to be transmitted, a modulation circuit for FM modulating the audio signal and generating a carrier signal that can be received by an FM receiver, an external transmission antenna exposed outside a housing and removably provided to it, and a transmission circuit for transmitting the carrier signal through the external transmission antenna. Since, by using the removable external transmission antenna, the antenna may be attached only when it is required tonly in transmission operation), the degree of freedom of antenna installation is high, and damage of the antenna when it is carried or kept in bags or the like, can be prevented.

Moreover, since a longer antenna can be used as compared to a case where the antenna is built in, transmission efficiency can be improved.

Moreover, it is desirable that a loading coil is inserted in a part of the above-mentioned external transmission antenna. Otherwise, it is desirable that the external transmission antenna further includes an external antenna terminal provided in the above-mentioned housing and connected to the output terminal of the transmission circuit, and that the loading coil is inserted between the output terminal of the transmission circuit and the external antenna terminal. This enables the antenna length to be adjusted according to the frequency of the carrier signal to be transmitted.

Moreover, it is desirable that an output circuit for outputting an audio signal generated by the above-mentioned audio signal generation circuit is further included, and an insertable/extractable earphone cord to be connected to the output circuit is used as the external transmission antenna. Since, this enables the earphone for listening to an audio Sound to be used as the external transmission antenna, the external transmission antenna as a separate component can be eliminated, the number of components can be reduced.

Furthery, since it is not necessary to include the external antenna terminal dedicated to the external transmission antenna, the number of components can be reduced as a result, and the configuration thereof can be simplified.

Moreover, It is desirable that a choke coil is inserted between the above-mentioned transmission circuit and output circuit. This enables the transmission signal to be prevented from flowing in the output stage of the output circuit having low output impedance, when the transmission signal is output from the transmission circuit towards the earphone cord.

Moreover, it is desirable that a power supply circuit for receiving electric power from a rechargeable secondary battery and supplying an operation voltage to each component is further included; where the secondary battery is charged when it is connected to a battery charger for stepping down and rectifying an AC voltage supplIed from a commerciaL power supply through a power cable; the power cable is used as the external transmission antenna; and the transmission cIrcuit and the power cable are electrically connected through internal wiring of the battery charger. This enables the power cable drawn from the battery charger to be used as the external transmission antenna, when the portable apparatus is set to the battery charger in order to charge the built-in secondary battery. Furthermore, the external transmission antenna as a separate component becomes unnecessary, the number of components can be reduced, and the configuration of the portable apparatus can be simplified.

Moreover, it is desirable that one end of the above-mentioned power cable is connected to the battery charger and the other end thereof is provided with a plug corresponding to a home-use electric outlet, and a choke coil is inserted in a position nearer to the other end provided with the plug than former end of the power cable.

This enables power-supply noise inunersion from the home-use electric outlet to be removed, when the power cable is used as the external transmission antenna.

Moreover, it is desirable that a power supply circuit for receiving electric power from a rechargeable secondary battery and supplying an operation voltage to each component is further included; where the external transmission antenna is electrically connected to an antenna terminal for an battery charger provided in the housing of the battery charger for charging the secondary battery by stepping down and rectifying an AC voltage supplied from a commercial power supply through a power cable and supplying resultant charging current to the secondary battery; and the transmission circuit and the external transmission antenna are electrically connected through the internal wiring of the battery charger. This enables the external transmission antenna attached to the battery charger to be used, when the portable apparatus is set to the battery charger in order to charge the built-in secondary battery. Therefore, since the portable apparatus itself does not need to have the external antenna terminal, the configuration can be simplified.

Moreover, it is desirable that the above-mentioned external transmission antenna and the transmission circuit are isolated from each other in terms of a DC.

Specifically, the above-mentioned isolation in terms of a DC is performed by capacitance coupling through a capacitor. Otherwise, the above-mentioned isolation in terms of a DC is performed by electromagnetic coupling using a transformer. This enables the transmission circuit to be protected when the external transmission antenna is brought into contact with a fixed potential and a ground potential.

Moreover, it is desirable that an internal transmission antenna built in the housing connected to the above-mentioned transrnissjor. circuit is further included. By this, the external transmission antenna may be used orasy if sufficient signal quality cannot be -7-.

obtained on the receiver side, in case where only the internal transnjssicn antenna is used. Thus, when the external transmission antenna is not used, handling of the portable apparatus becomes easy.

Moreover, it is desirable that the above-mentioned audio signal generation circuit, is an audio playback device for elongating audio data recorded in a compressed form and playing the audio signal. By this, since the audio signal reproduced by a small compressed audio playback device excellent in portability, such as an MP3 (MPEG Audio Layer-3) player can be transmitted as an FM signal, the audio sound can be output from speakers of such as an in-vehicle FM receiver and a home-use FM receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the configuration of the portable music playback apparatus of a first embodiment; FIG. 2 is a perspective view illustrating the appearance of the portable music playback apparatus; FIG. 3 is a view illustrating a modification of the present embodiment; FIG. 4 is a view illustrating another modification of the present embodiment; FIG. 5 is a view illustrating another modification of the present embodiment; FIG. 6 is a view illustrating the configuration of the portable music playback apparatus of a second embodiment; FIG. 7 is a view illustrating the configuration of the portable music playback apparatus of a third embodiment; FIG. 8 is a perspective view of the appearance of a battery charger 300; and FIG. 9 is a view illustrating the configuration of the portable music playback apparatus of a fourth embodiment.

Description of Symbols

AUDIO PLAYBACK DEVICE

12 OUTPUT CIRCUIT

FM TRANSMITTER

22 STEREO MODULATION CIRCUIT 24 FM MODULATION CIRCUIT 26 TRANSMISSION CIRCUIT

OPERATION SECTION

32 DISPLAY SECTION 34 CONTROL SECTION 36 POWER SUPPLY CIRCUIT 38 SECONDARY BATTERY 401 108, 314, 322 LOADING COILS 42, 46, 320 CAPACITORS 44 COIL 48, 334, 336 CHOKE COILS 100, 100A, 100B PORTABLE MUSIC PLAYBACK APPARATUSES 102 EXTERNAL TRANSMISSION ANTENNA 104, 116A, 1163, 118 EXTERNAL ANTENNA TERMINALS 106 EARPHONE TERMINAL

EARPHONE

11OA EARPHONE CORD 112A, 1123, 114A, 1148 CHARGING TERMINALS 200, 400 HOUSINGS 300, 300A BATTERY CHARGERS 310 STEP-DOWN CIRCUIT 312 RECTIFICATION CIRCUIT 330 POWER CABLE

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a portable music playback apparatus of one embodiment to which the present invention is applied, will be described ifl detail with reference to drawings.

(First Embodiment) FIG. 1 is a view illustrating the configuration of the portable music p.ayback apparatus cf a first embodiment. The portable music playback apparatus 100 of the present embodiment illustrated in FIG. 1 is configured by including an audio playback device 10, an output circuit 12, an FM transmitter 20, an operation section 30, a display section 32, a control section 34, a power supply ci.rcuit 36 and secondary battery 36. Among -10 -these components, most components except for the operation section 30, the display section 32 and the secondary battery 38 are formed on a semiconductor substrate, by means cf a CMCS process or an MOS process, as one chip component (however, driving mechanisms etc. that cannot be formed by these processes, are excluded.).

Use of these processes enables miniaturization and lowering power consumption of one chip component formed on the semiconductor substrate and the portable music playback apparatus 100 as a whole.

The audio playback device 10 is an audio signal generation circuit for elongating audio data recorded in a compressed form, and playing and outputting the audio signal, and it corresponds to, for examples, an MP3 player and an MD (mini disc) player etc. In addition, the audio playback device 10 in the present embodiment requires at least one function of generating an audio signal to be transmitted, thereby, the audio playback device 10 may be configured by a sound playback circuit such as a CD (compact disk) player and a portable phone, which reproduces an audio signal from non-compressed audic data. From the audio playback device 10, an L-signal and a H-signal, which are the separate left audio signal and the right audio signal, respectively, are output. The output circuit 12 cutputs a signai, which is generated by amplifying and tone adjusting an audio signal output from the audio playback device IC, to an -11 -La.

earphone (not illustrated in figures) through an earphone terminal 106.

The FM transmitter 20 transmits signals generated by FM modulating the L-signal and the R-sigr.al output from the audio playback device 10, from the external transmission antenna 102 via an external antenna terminal 104. For this reason, the FM transmitter 20 includes a stereo modulation circuit 22, an Eli modulation circuit 24, and a transmission circuit 26. The stereo modulation circuit 22 performs stereo modulation processing synthesizing input L*signal and R signal, and generates a stereo composite signal (stereophonic composite signal).

The FM modulation circuit 24 performs FM modulation processing to the stereo composite signal, and generates a carrier wave signal which can be received by an external FM receiver (not illustrated in figures) disposed in the vicinity of the portable music playback apparatus 100. The transmission circuit 26 amplifies the carrier wave signal generated by the FM modulation circuit 24, and transmits it from the external transmission antenna 102.

The operation sectIon 30 includes various kinds of keys and control dials or the like in order to be operated by a user. For examples, it includes an "UP" key and a "DOWNs key for a volume setup in order to indicate the extent of amplification of the output circuit 12, while including a "play" key and a wstoplt key -12 -in order to give various kinds of instructions to the reproduction operation of the audIo signal by the audio playback device 10. The display section 32 displays the contents of operation by the operation section 30, and the contents of play by the audio playback device 10 for examples, the title (song name) of a song being played, artist name singing the song, and elapsed time of play etc.) and the like. The control section 34 controls whole of the portable music playback apparatus 100. For examples, it sets the playing state by the audio playback* device 10, and the sound volume using the output circuit 12.

The power supply circuit 36 to which a terminal voltage of the secondary battery 38 is applied, generates an operation voltage to be supplied to each section of the portable music playback apparatus 100. In addition, practically, protection circuits for protecting the secondary battery 38 and the power supply circuit 36 from an excessive voltage and a noise etc. externally applied, are provided between the power supply circuit 36 and the secondary battery 38, or between the secondary battery 38 and charging terminals fl2A and ll4A exposed outside, however, in FIG. 1, the protection circuit is omitted.

FIG. 2 is a perspective view l1ustrating the appearance of the portable music playback apparatus 100.

As illustrated in FIG. 2, the housing 200 of the portable music playback apparatus 100 is provided with an external -13 -antenna terminal 104 exposed outside, to which an external transmission antenna 102 is removably attached.

As illustrated in FIG. 2, the external transmission antenna 102 has a rod-like shape, for an example, and can be attached to the housing 200 by inserting one end thereof in the external antenna terminal 104. In addition, the external transmission antenna 102 may be attached to the external antenna terminal 104 by forming a male screw groove in one end of the external transmission antenna 102 and a female screw groove in the external antenna terminal 104, in advance, respectively.

Moreover, the shape of the external transmission antenna 102 is not necessary to be rod-shaped, instead, it may be string-shaped, or a bending shape such as a letter of L. In this manner, since in the portable music playback apparatus 100 of the present embodiment, the removable external transmission antenna 102 is used, the antenna may be attached only when it is necessary (only in transmission operation). Therefore, the degree of freedom of antenna installation is high, and, moreover, the external transmission antenna 102 can be prevented from being damaged when it is carried or kept in a pocket or the bag, and the like. Moreover, since the external transmission antenna whose length is comparatively longer than that of a built-in antenna, can be used, transmIssion efficiency can be improved.

-14 -FIG. 3 is a view illustrating a modification of the present embodiment. In the configuration of the modification illustrated in FIG. 3, a loading coil 40 is inserted between the transmission circuit 26 and the external transmission antenna 102. Use of the loading coil 40 as a part of the external transmission antenna 102 enables to lengthen an effective length of the external transmission antenna 102. In addition, in the configuration illustrated in FIG. 3, the Loading coil 40 is inserted between the transmission circuit 26 and the external antenna terminal 104, however, the loading coil may be inserted in a part of the external transmission antenna 102 externally attached to the external antenna terminal 104. Moreover, in order to use a space effectively, the loading coil 40 may be formed by winding a copper line around the outer circumference of the external antenna terminal 104.

FIGS. 4 and 5 are views illustrating other modifications of the present embodiment. In configurations of the modifications illustrated in these figures, the transmission circuit 26 and the external transmission antenna 102 are isolated from each other in terms of a DC. Specifically, in the example illustrated in FIG. 4, by inserting a capacitor 42 between the transmission circuIt 26 and the external antenna terminal 104, the transmission circuit 26 and the external transmission antenna 102 are connected through the -15 -capacitance thereof (capacitance coupling). Moreover, in the example illustrated in FIG. 5, by inserting two coils 44 electromagnetically coupled with each other between the transmission circuit 26 and the external antenna terminal 204, the transmission circuit 26 and the external transmission antenna 102 are electromagnetically coupled. This enables the transmission circuit 26 to be protected when the external transmission antenna 102 is brought into contact with a fixed potential and a ground potential.

(Second nbodiinent) FIG. 6 is a view illustrating the configuration of the portable music playback apparatus of a second embodiment. The configuration of the portable music playback apparatus 100A of the present embodiment illustrated in FIG. 6 is almost the same as that of the portable music playback apparatus 100 illustrated in FIG. 1, but differs from it in that an insertable/extractable earphone cord connected to the output circuit 12 is used as the external transmission antenna. In the configuration illustrated in FIG. 6, the output terminal of the transmission circuit 26 in the FM transmitter 20 is connected to the wiring between the output circuit 22 and the earphone terminal 106 through the capacitor 46 for isolation in terms of a DC. Moreover, between the output circuit 12 and the earphone terminal 206, a choke t coil 48 is inserted at the output circuit 12 side, and -16 -the loading coil 108 is inserted at the earphone terminal 106 side, respectively. The signal output from the transmission circuit 26 is input into the connection point between the choke coil 48 and the loading coil 108 through the capacitor 46, and transmitted through the loading coil 108 and the earphone terminal 106 by using the earphone cord 11OA of an earphone 110 as the external transmission antenna.

In this manner, since the earphone cord 11OA of the earphone 110 for listening to audio sound can be used as the external transmission antenna, the external transmission antenna 102 as a separate component can be eliminated, resulting In reduction of the number of components. Furthermore, since the external transmission antenna terminal 104 dedicated to the external transmission antenna is not necessary to be provided, the number of components can be reduced as a result, and the configuration can be simplified.

Moreover, since the output impedance of the output stage of the output circuit 12 is low in general, if the output terminal of the transmission circuit 26 is directly connected to the output stage of the output circuit 12, a transmitted signal wili flow into the transmission circuit 26, however, by insertIng a choke coil 48 at the output side of the output circuit 12, such inflow of a transmitted signal to the output circuit 12 car; be prevented.

-17 - (Third Embodiment) FIG. 7 is a view illustrating the configuration of the portable music playback apparatus of a third embodiment, the entire configuration of a system cf the portable music playback apparatus including the battery charger is illustrated. The configuration of the portable music playback apparatus 1008 of the present embodiment illustrated in FIG. 7 is almost the same as that of the portable music playback apparatus 100 illustrated in FIG. 1, where the external antenna terminal 104 is replaced by the external antenna terminal 11GA provided in the vicinity of the charging terminals 1].2A and 114A.

Moreover, a battery charger 300 used for charging the built-in secondary battery 38 is externally attached to the portable music playback apparatus 100B of the present embodiment. The battery charger 300 includes a step-down circuit 310 for stepping down an AC voltage supplied from a commercial power supply through a power cable 330, and a rectification circuit 312 for rectifying the stepped down AC voltage to generate a DC charging current. For an example, ft the simplest manner, the step-down circuit 310 is configured by a transformer, and the rectification circuit 312 is configured by a bridge circuit by using a rect!fier cell such as a diode. The positive/negative output terminals of the rectification circuit 312 are connected to the charging terminals 1123 -18 -and 1143 exposed outside, respectively. The charging terminals 1123 and 1143 are provided at positions where, when a portable music playback apparatus 100B is set to a predetermined position of the battery charger 300, they are electrically connected to the charging terminals ll2A and 114A, respectively, at the side of the portable music playback apparatus 2003. This causes the charged current generated by the battery charger 300 to be supplied to the secondary battery 38 through the charging terminals 112A and 1128 and the charging terminals 114A and 1143.

FIG. 8 is a perspective view of the appearance of the battery charger 300, and a state where the housing 2003 for the portable music playback apparatus 1003 is set, is illustrated. The battery charger 300 of the present embodIment includes an external antenna terminal 1168 provided in the vicinity of the charging terminals 1123 and 1143, an external antenna terminal 118 provided at a position which is a part of the housing of the battery charger 300 and being exposed outside, and a loading coil 314 inserted between the external antenna terminals 1168 and 118. The external antenna terminal 1168 is provided at a position where, when the portable music playback apparatus 1008 is set to a predetermined position of the battery charger 300, !t is electrically connected to the external antenna terminal 116A at the side of the portable music p.ayback apparatus 1003.

Moreover, the external antenna terminal 118 has a -19 -function being the same as that of the external antenna terminal 104 illustrated in FIGS. 1 and 2, and, the external transmission antenna 102 is detachably attached to it. In addition, in the present embodiment, since the external antenna terminal 118 to which the external transmissicn antenna 102 Is attached, is provided in the housing 400 of the battery charger 300 there is no need to use, the transmission antenna 102 which Is attached eternally and removable, instead, a transmission antenna 102 may be attached to the external antenna terminal 118 of the battery charger300 in a state where the transmission antenna 102 cannot be detached. In addition, since the function of the loading coil 314 is to adjust the antenna length, the loading coil 314 may be omitted.

In this manner, when the portable music playback apparatus 100B is set to the battery charger 300 in order to charge the built-in secondary battery 38, the external transmission antenna 102 attached to the battery charger 300 can be used. Therefore, since the portable music playback apparatus 100B itself does not require the external antenna terminal, the configuration thereof can be simplified.

(Fourth Embodiment) FIG. 9 is a view illustrating the configuration of the portable music playback apparatus of a fourth embodiment, and the entire configuration of a system of the portable music playback apparatus including the -20 -battery charger. The portable music playback apparatus 1008 of the present embodiment illustrated in FIG. 9, is the same one as that illustrated in FIG. 7, and includes an external antenna terminal I1GA.

Moreover, the battery charger 300A differs from the battery charger 300 illustrated in FIG. 7 in that the external antenna terminal 118 and the loading coil 314 connected thereto are removed, instead, a capacitor 320 for isolating in tertns of a DC, connected to an external antenna terminal 116B, a loading coil 322 inserted in the power cable 330, and two choke coils 334 and 336 are added. The two choke coils 334 and 336 have a function for removing the power supply noIse penetrating from a home-use electric outlet, and are inserted in the power cable 330 at positions nearer to the end of attachment plug 332 side rather than to the end of the step-down circuit 310 side. In addition, since the function of the loading coil 322 is to adjust the antenna length, the loading coil 322 may be omitted.

Use of such a battery charger 300A enables the power cable 330 drawn from the battery charger 300A to be used as the external transmission antenna, when the portable music playback apparatus 10GB is set to the battery charger 300A in order to charge the built-in secondary battery 38. Furthermore, since this causes the external transmission antenna as a separate component to be unnecessary, the number of components can be reduced and -21 -the configuration of the portable music playback apparatus 100B can be simplified.

In addition, the present invention is not limited to the above-mentIoned embodiments, and, within the gist of the present invention, various kinds of modifications can be performed. For an example, in the above-mentIoned embodiments, only the detachable external transmission antenna is paid attention to and described, however, other than the detachable external transmission antenna, an internal transmission antenna may be built in the portable music playback apparatus 100 etc. In this case, when the internal transmission antenna and the external transmission antenna are used at the same time, it is desirable to connect them through a balun so that mismatching of impedance does not occur. Ir. this manner, in a case where both of the internal transmission antenna and the external transmission antenna are provided, only when suffIcient quality of signal cannot be obtained at the FM receiver side byusing only the internal transmission antenna, the external transmission antenna may be used. Therefore, since the external transmission antenna protruding outside the housing 200 of the portable music playback apparatus 100 etc. can be removed when the external transmission antenna is not used, handling of the portable music playback apparatus 1OC etc. when it is carried or kept in a pocket or a bag, and the like, can be easy.

-22 -According to the present invention, since, by using the detachable external transmission antenna, the antenna may be attached only when it is required (only in transmission operation), the degree of freedom of antenna installation is high, and the antenna can be prevented from being damaged when it is carried or kept in a pocket or in a bag, and the like. Moreover, since an antenna whose length is longer than that when it is built in can be used, transmission efficiency can be improved.

Claims

-23 -What is claimed is: 1. A portable apparatus with a built-in FM

transmitter comprising: an audio signal generation circuit for generating an audio signal to be transmitted; a modulation circuit for FM modulating the audio sIgnal and generating a carrier wave signal that can be received by an FM receiver; an external transmission antenna exposed outside a housing and removably provided; and a transmission circuit for transmitting the carrier wave signal through the external transmission antenna.

2. The portable apparatus with a built-in FM transmitter according to claim 1, wherein a loading coil is inserted in a part of the external transmission antenna.

3. The portable apparatus with a built-in FM transmitter according to claIm 2, further comprising an externaa antenna terminal provIded in the housing and connected to an output terminal of the transmission circuit, wherein -24 -a loading COi is inserted between the output terminal of the transmission circuit and the external antenna terminal.

4. The portable apparatus with a built-in FM transmitter according to claim 1, further comprising an output circuit for outputting an audio signal generated by the audio signal generation circuit, an insertable/extractable earphone cord connected to the output circuit is used as the external transmission antenna.

5. The portable apparatus with a built-in FM transmitter according to claim 4, wherein a choke coil is inserted between the transmission circuit and the output circuit.

6. The portable apparatus with a built-in FM transmitter according to claim i, further comprising a power supply circuit for receiving electric power supply from a rechargeable secondary battery to supply an operat ion voltage to each compcnent, wherein the secondary battery is charged when it is connected to a battery charger for stepping down and rectifying an AC voltage supplied from a coimnercial power supply through a power cable; and -25 -the power cable is used as the external transmission antenna, and the transmission circuit and the power cable are electrically connected with each other through internal wiring of the battery charger.

7. The portable apparatus with a built-in FM transxr.tter according to claim 6, wherein one end of the power cable is connected to the battery charger, and the other end is provided with a plug corresponding to a home-use electric outlet; and a choke coil is inserted in a position nearer to the other end provided with the plug rather than the former end of the power cable.

8. The portable apparatus wIth a built-in FM transmitter according to claim 1, further comprising a power supply circuit for receiving electric power supply from a rechargeable secondary battery to supply an operation voltage to each component, wherein the external transmission antenna is electrically connected to an antenna terminal for a battery charger provided in a housing of the battery charger for charging the secondary battery by stepping down and rectifying an AC voLtage supplied from a commercial power supply through a power cable and supplying resultant charging current to the secondary battery; and -26 -the transmission circuit and the external transmission antenna are electrically connected with each other through an internal wiring of the battery charger.

9. The portable apparatus with a built-in FM transmitter according to claim 1, wherein the external trnsmission antenna and the transmission circuit are isolated from each other in terms of a DC.

10. The portable apparatus with a built-in FM transmitter according to claim 9, wherein the external transmission antenna and the transmission circuit are isolated from each other by means of capacitance coupling through a capacitor.

11. The portable apparatus with a built-in FM transmitter according to claim 9, wherein the external transmission antenna and the transmission circuit are isolated from each other by means of electromagnetic coupling using a transformer.

12. The portable apparatus with a built-in FM transmitter according to claim 1, further comprising an internal transmission antenna built in the housing connected to the transmission circuit.

-27 - 13. The portable apparatus with a built-in FM transmitter according to claim 1, wherein the audio signal generation circuit is an audio playback device for elongating audic data recorded in a compressed form to reproduce the audio signal.

14. The portable apparatus with a built-in FM transmitter according to claim 1, wherein components corresponding to the audio signal generation circuit, the modulation circuit, and the transmission circuit are formed on a semiconductor substrate by using a CMOS process or an MOS process.

15. The portable apparatus with a built-in FM *transmitter according to claim 1, wherein the audio signal generation circuit is an MP3 player.

16. The portable apparatus with a built-in FM transmitter according to claim 1, wherein the audio signal generation circuit is an MD player.

17. The portable apparatus with a built-in FM transmttter acccrding to claim 1, wherein the audio signal generation circuit is a CD player.

18. The portable apparatus with a built-in FM transmitter according to claim 1, wherein -28 -the audio signal generation circuit is a portable phone.