Wireless IC device, electronic apparatus, and method for adjusting resonant frequency of wireless IC device

A wireless IC device and an electronic apparatus are obtained, which can achieve miniaturization and improve the gain of a radiator plate (electrode) without providing a dedicated antenna. A wireless IC device is provided, in which a loop electrode is provided in a ground electrode provided on a printed wiring circuit board, and in which a wireless IC chip that processes a transmission/reception signal or an electromagnetic coupling module is coupled to the loop electrode. The ground electrode is coupled to the wireless IC chip or the electromagnetic coupling module via the loop electrode, and transmits or receives a high-frequency signal. The ground electrode is formed with a slit for adjusting a resonant frequency thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless IC device, and, more particularly, to a wireless IC device having a wireless IC chip used in an RFID (Radio Frequency Identification) system, an electronic apparatus including the wireless IC device, and a method for adjusting a resonant frequency of a wireless IC device.

2. Description of the Related Art

In recent years, an RFID system has been developed as an article management system, which includes: a reader/writer that generates an induction field; and an IC chip (also referred to as IC tag or wireless IC chip) that has stored predetermined information therein and is attached to an article, a container, or the like, and noncontact communication is established between the reader/writer and the IC chip to transmit the information therebetween.

Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 11-515094 discloses an RFID tag including an IC chip and an antenna formed within a printed wiring circuit board. In the RFID tag, the antenna within the printed wiring circuit board and the IC chip mounted on the principal surface of the board are connected to each other in an electrically conductive state. Miniaturization of the RFID tag is achieved by disposing the antenna within the printed wiring circuit board.

However, because the RFID tag includes a dedicated antenna, a process of fabricating an antenna is required, leading to an increase in cost. Further, a mounting space for the antenna is also required, resulting in an increase in size. If the IC chip is changed, it is necessary to change the shape of the antenna or the like as well.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide: a wireless IC device that can achieve miniaturization and improve the gain of a radiator plate (electrode) that functions as an antenna, without providing a dedicated antenna; an electronic apparatus including the wireless IC device; and a method for adjusting a resonant frequency of a wireless IC device.

To achieve the above objective, a first aspect of the present invention provides a wireless IC device that includes:

a wireless IC chip that processes a transmission/reception signal;

a circuit board on which the wireless IC chip is mounted;

an electrode formed on the circuit board; and

a loop electrode formed on the circuit board so as to be coupled to the wireless IC chip and the electrode.

The electrode is formed with a slit and/or a cutout for adjusting a resonant frequency thereof.

A second aspect of the present invention provides a wireless IC device that includes:

an electromagnetic coupling module including a wireless IC that processes a transmission/reception signal and a power supply circuit board that includes an inductance element coupled to the wireless IC;

a circuit board on which the electromagnetic coupling module is mounted;

an electrode formed on the circuit board; and

a loop electrode formed on the circuit board so as to be coupled to the power supply circuit board and the electrode.

The electrode is formed with a slit and/or a cutout for adjusting a resonant frequency thereof.

In the wireless IC device, the wireless IC chip or the power supply circuit board is coupled to the electrode, formed on the circuit board, such as a ground electrode, via the loop electrode, and the electrode formed on the circuit board functions as a radiator plate (antenna) of the wireless IC (chip). In other words, the wireless IC (chip) is activated via the loop electrode by a signal received by the electrode, and a response signal from the wireless IC (chip) is radiated from the electrode to the outside via the loop electrode. Therefore, it is unnecessary to fabricate a dedicated antenna, and it is unnecessary to provide a space for mounting the antenna. Further, the loop electrode can provide impedance matching between the wireless IC (chip) and the electrode, and hence it is unnecessary to provide a separate matching part, thereby improving the efficiency of signal transmission between the wireless IC (chip) and the electrode.

Incidentally, the gain of the radiator plate (antenna) becomes great when the radiator plate resonates, and the resonant frequency becomes a specific value with both ends of the radiator plate (electrode) as resonance ends. When the ground electrode is used as an antenna, the size of the electrode is determined mainly by the size of the circuit board. In this case, the resonant frequency of the electrode may be different from the frequency used in the RFID system, and there is the possibility that the gain, when used as the antenna, decreases. In the wireless IC device, a resonant mode can be optionally set by forming, in an electrode that functions as an antenna, a slit and/or a cutout for adjusting the resonant frequency of the electrode, and the electrode has a preferable resonant frequency close to the frequency used in the RFID system. Thus, the gain is improved.

In the wireless IC device according to the second aspect, the power supply circuit board is interposed between the wireless IC, such as a wireless IC chip, and the loop electrode. The power supply circuit board includes a resonant circuit and/or a matching circuit including an inductance element, and the frequency used is substantially set by the resonant circuit and/or the matching circuit. When the wireless IC is changed in accordance with the frequency used in the RFID system, it is only necessary to change the design of the resonant circuit and/or the matching circuit, and there is no need to change the shape, size, or location of the radiator plate (electrode) or the coupling state between the loop electrode and the electrode or the power supply circuit board. Further, the resonant circuit and/or the matching circuit can also have a function of matching the impedance between the wireless IC and the electrode, thereby making it possible to improve the efficiency of signal transmission between the wireless IC and the electrode.

It is noted that in addition to having stored various kinds of information related to an article to which the wireless IC device is to be attached, the wireless IC (chip) may allow rewriting of information, or may have an information processing function other than the RFID system.

A third aspect of the present invention provides an electronic apparatus that includes the wireless IC device according to the first aspect or the second aspect.

A fourth aspect of the present invention provides a method for adjusting a resonant frequency of a wireless IC device that includes: a wireless IC chip that processes a transmission/reception signal; a circuit board on which the wireless IC chip is mounted; an electrode formed on the circuit board; and a loop electrode formed on the circuit board so as to be coupled to the wireless IC chip and the electrode. The method includes the step of adjusting the resonant frequency by forming a slit and/or a cutout in the electrode.

A fifth aspect of the present invention provides a method for adjusting a resonant frequency of a wireless IC device that includes: an electromagnetic coupling module including a wireless IC that processes a transmission/reception signal, and a power supply circuit board that includes an inductance element coupled to the wireless IC; a circuit board on which the electromagnetic coupling module is mounted; an electrode formed on the circuit board; and a loop electrode formed on the circuit board so as to be coupled to the power supply circuit board and the electrode. The method includes the step of adjusting the resonant frequency by forming a slit and/or a cutout in the electrode.

According to the present invention, an existing electrode on the circuit board can be used as an antenna, and thus it is unnecessary to dispose an antenna as a separate component, thereby achieving miniaturization of the wireless IC device or the apparatus provided with the wireless IC device. Further, by forming a slit and/or a cutout, the resonant frequency of the electrode that functions as an antenna can be adjusted, thereby improving gain.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a wireless IC device, an electronic apparatus, and a method for adjusting a resonant frequency of a wireless IC device, according to the present invention, will be described with reference to the accompanying drawings. It is noted that in the drawings, common elements and portions are denoted by the same reference numerals, and the overlap description is omitted.

First Basic Preferred Embodiment

See FIGS.1and2

FIG. 1shows a wireless IC device according to a first basic preferred embodiment of the present invention. In the first basic preferred embodiment, a loop electrode22and a ground electrode21are separately provided on a printed wiring circuit board20, and a wireless IC chip5that processes a transmission/reception signal of a predetermined frequency is coupled to the loop electrode22. The ground electrode21and the loop electrode22are provided on the principal surface of the printed wiring circuit board20through application of a conductive paste, etching of a metal foil provided on the circuit board20, or the like.

The wireless IC chip5includes a clock circuit, a logic circuit, a memory circuit, and the like, and has stored necessary information therein. As shown inFIG. 2, input/output terminal electrodes6and mounting terminal electrodes7are provided on the back surface of the wireless IC chip5. The input/output terminal electrodes6are electrically connected via metal bumps8to connecting electrodes22aand22bprovided at opposite ends of the loop electrode22. A pair of connecting electrodes22cand22dis provided on the circuit board20. The terminal electrodes7of the wireless IC chip5are electrically connected to the connecting electrodes22cand22dvia metal bumps8.

The loop electrode22is provided parallel to and in proximity to an edge portion21aof the ground electrode21. The two electrodes are coupled together by an electric field. In other words, by placing the loop electrode22in proximity to the edge portion21aof the ground electrode21, a loop magnetic field H (see dotted lines inFIG. 1(A)) is generated in an orthogonal direction from the loop electrode22, and the magnetic field H is orthogonal to the ground electrode21, whereby a loop electric field E (see an alternate long and short dash line inFIG. 1(A)) is excited at the edge portion21aof the ground electrode21. Further, another loop magnetic field H is induced by this loop electric field E. In this manner, the loop electric fields E and the loop magnetic fields H spread out over the entire surface of the ground electrode21, radiating high-frequency signals into the air. By arranging the ground electrode21and the loop electrode22in proximity to each other and in an insulated state as described above, the two electrodes can be electromagnetically coupled to each other in an assured manner, thereby improving a radiation characteristic.

Because the loop electrode22is electromagnetically coupled to the ground electrode21as described above, a high-frequency signal radiated from the reader/writer and received by the ground electrode21is supplied to the wireless IC chip5via the loop electrode22, thereby activating the wireless IC chip5. On the other hand, a response signal from the wireless IC chip5is transmitted to the ground electrode21via the loop electrode22, and radiated to the reader/writer from the ground electrode21.

The ground electrode21may be an existing electrode provided on the printed wiring circuit board20of an electronic apparatus in which this wireless IC device is accommodated. Alternatively, the ground electrode21may be one used as the ground electrode of another electronic component mounted in the electronic apparatus. Therefore, this wireless IC device does not require fabrication of a dedicated antenna, and does not require a space for its mounting. Moreover, the ground electrode21is formed in a large size, thereby improving radiation gain.

Further, proper impedance matching can be achieved between the wireless IC chip5and the ground electrode21by adjusting the length and the width of the loop electrode22, the distance from the ground electrode21to the loop electrode22, and the like. In addition, the circuit board20may be a multilayer board in which multiple dielectric layers or magnetic layers are laminated. When the circuit board20is such a multilayer board, the loop electrode22and the ground electrode21may be disposed in multiple layers of the multilayer circuit board20, so as to be in an electrically conductive state using known via-hole conductors. Moreover, the loop electrode22and the ground electrode21may be disposed on the back surface of the circuit board20, and the wireless IC chip5disposed on the circuit board20may be coupled to the loop electrode22via a via-hole conductor.

Second Basic Preferred Embodiment

See FIG.3

FIG. 3shows a wireless IC device according to a second basic preferred embodiment of the present invention. In the second basic preferred embodiment, by forming an opening21bat one side of the ground electrode21provided on the printed wiring circuit board20, the loop electrode31is provided around the opening21b, and connecting electrodes31aand31bare electrically connected to the input/output terminal electrodes6(seeFIG. 2) of the wireless IC chip5via the metal bumps8. Further, connecting electrodes31cand31dare formed on the front surface of the circuit board20and electrically connected to the mounting terminal electrodes7of the wireless IC chip5via the metal bumps8.

In the second basic preferred embodiment, the loop electrode31is coupled to the ground electrode21in an electrically conductive state, and the wireless IC chip5and the ground electrode21are coupled to each other due to the intermediation of the loop electrode31. The operation of the second basic preferred embodiment is basically the same as that of the above-mentioned first basic preferred embodiment. Also, the effects and advantages of the second basic preferred embodiment are as described in the above-mentioned first basic preferred embodiment.

It is noted that the loop electrode31can have various structures as described in detail below. Further, it should be understood that the ground electrode21and the loop electrode31may be disposed within the circuit board20or on the back surface of the circuit board20.

Third Basic Preferred Embodiment

See FIG.4

FIG. 4shows a wireless IC device according to a third basic preferred embodiment of the present invention. In the third basic preferred embodiment, the wireless IC chip5is mounted on a power supply circuit board10to form an electromagnetic coupling module1, and the electromagnetic coupling module1is electrically connected to a loop electrode35provided on the printed wiring circuit board20. Like the loop electrode22(seeFIG. 1) described in the above-mentioned first basic preferred embodiment, the loop electrode35is disposed in proximity to the ground electrode21provided on the front surface of the circuit board20, and is magnetically coupled to the ground electrode21.

In the wireless IC chip5, the input/output terminal electrodes6shown inFIG. 2are electrically connected via the metal bumps8to electrodes12aand12b(seeFIGS. 6 and 7) provided on the front surface of the power supply circuit board10, and the mounting terminal electrodes7are electrically connected to electrodes12cand12d. Further, a protective film is provided between the front surface of the power supply circuit board10and the back surface of the wireless IC chip5. The protective film9also provides an effect of enhancing the bonding strength between the power supply circuit board10and the wireless IC chip5.

The power supply circuit board10incorporates a resonant circuit (not shown inFIG. 4) having an inductance element. External electrodes19aand19b(seeFIGS. 6 and 7) are provided on the back surface of the power supply circuit board10. The connecting electrodes12ato12d(seeFIGS. 6 and 7) are provided on the front surface of the power supply circuit board10. The external electrodes19aand19bare electromagnetically coupled to the resonant circuit incorporated in the board10, and are connected to connecting electrodes35aand35bof the loop electrode35in an electrically conductive state via a conductive adhesive (not shown). Alternatively, solder or the like may be used for this electrical connection.

In other words, a resonant circuit having a predetermined resonant frequency is incorporated in the power supply circuit board10, and a transmission signal originated from the wireless IC chip5and having a predetermined frequency is transmitted to the ground electrode21via the external electrodes19aand19band the loop electrode35, and a reception signal having a predetermined frequency is selected from signals received by the ground electrode21and is supplied to the wireless IC chip5. Thus, in this wireless IC device, the wireless IC chip5is activated by a signal received by the ground electrode21, and a response signal from the wireless IC chip5is radiated to the outside from the ground electrode21.

In the electromagnetic coupling module1, the external electrodes19aand19bprovided on the back surface of the power supply circuit board10are electromagnetically coupled to the resonant circuit incorporated in the board10, and are also electrically conducted to the loop electrode35that is electrically coupled to the ground electrode21that functions as an antenna. Because the electromagnetic coupling module1does not need to be provided with an antenna element that is relatively large in size as a separate part, the electromagnetic coupling module1can be reduced in size. Because the power supply circuit board10is also reduced in size, the wireless IC chip5may simply be mounted on the power supply circuit board10thus reduced in size, which allows use of an IC mounter or the like widely used in the related art, leading to a reduction in mounting cost. Further, a frequency band used can be changed by simply changing the design of the resonant circuit.

Only an inductance element may be formed as an element formed within the power supply circuit board10. The inductance element has a function of matching the impedance between the wireless IC chip5and the radiator plate (ground electrode21).

Fourth Basic Preferred Embodiment

See FIG.5

FIG. 5shows a wireless IC device according to a fourth basic preferred embodiment of the present invention. In the fourth basic preferred embodiment, by forming the opening21bat one side of the ground electrode21provided on the printed wiring circuit board20, a loop electrode36is provided around the opening21b, and the electromagnetic coupling module having the wireless IC chip5mounted on the power supply circuit board10is electrically connected to the loop electrode36. The loop electrode36has connecting electrodes36aand36bthat are connected to the external electrodes19aand19b, which are provided on the back surface of the power supply circuit board10, in an electrically conductive state via a conductive adhesive (not shown). It is noted that the configuration and the operation of the power supply circuit board10in the fourth basic preferred embodiment are the same as those in the above-mentioned third basic preferred embodiment, and the effects and advantages of the loop electrode36are the same as those of the loop electrode31described in the above-mentioned second basic preferred embodiment.

First Example of Resonant Circuit

See FIG.6

A first example of a resonant circuit incorporated in the power supply circuit board10is shown inFIG. 6. The power supply circuit board10is formed by laminating, pressure-bonding, and firing ceramic sheets11A to11H each made of a dielectric material. The connecting electrodes12aand12b, the electrodes12cand12d, and via-hole conductors13a,13bare formed in the sheet11A; a capacitor electrode18a, conductor patterns15aand15b, and via-hole conductors13cto13eare formed in the sheet11B; and a capacitor electrode18band via-hole conductors13dto13fare formed in the sheet11C. Further, conductor patterns16aand16band via-hole conductors13e,13f,14a,14b, and14dare formed in the sheet11D; conductor patterns16aand16band via-hole conductors13e,13f,14a,14c, and14eare formed in the sheet11E; a capacitor electrode17, conductor patterns16aand16b, and via-hole conductors13e,13f,14f, and14gare formed in the sheet11F; conductor patterns16aand16band via-hole conductors13e,13f,14f, and14gare formed in the sheet11G; and conductor patterns16aand16band a via-hole conductor13fare formed in the sheet11H.

By laminating the above sheets11A to11H, an inductance element L1is formed of the conductor patterns16aconnected spirally via the via-hole conductors14c,14d, and14g; an inductance element L2is formed of the conductor patterns16bconnected spirally via the via-hole conductors14b,14e, and14f; a capacitance element C1is formed of the capacitor electrodes18aand18b; and a capacitance element C2is formed of the capacitor electrodes18aand17.

One end of the inductance element L1is connected to the capacitor electrode18bvia the via-hole13d, the conductor pattern15a, and the via-hole conductor13c. One end of the inductance element L2is connected to the capacitor electrode17via the via-hole conductor14a. In addition, the other ends of the inductance elements L1and L2are combined together on the sheet11H, and connected to the connecting electrode12avia the via-hole conductor13e, the conductor pattern15b, and the via-hole conductor13a. Further, the capacitor electrode18ais electrically connected to the connecting electrode12bvia the via-hole conductor13b.

The connecting electrodes12aand12bare electrically connected to the terminal electrodes6of the wireless IC chip5via the metal bumps8. The electrodes12c,12dare connected to the terminal electrodes7of the wireless IC chip5.

Further, the external electrodes19aand19bare provided on the back surface of the power supply circuit board by application of a conductive paste or the like. The external electrode19ais magnetically coupled to the inductance elements L (L1and L2), and the external electrode19bis electrically connected to the capacitor electrode18bvia the via-hole conductor13f. As described above, the external electrodes19aand19bare electrically connected to the connecting electrodes35aand35bor36aand36bof the loop electrode35or36.

It is noted that in the resonant circuit, the inductance elements L1and L2are structured such that the two conductor patterns16aand16bare arranged in parallel with each other. The two conductor patterns16aand16bhave different line lengths, so different resonant frequencies can be set for the two conductor patterns16aand16b. Thus, the wireless IC device can have a wide band.

It is noted that the ceramic sheets11A to11H may be made of a magnetic ceramic material, and the power supply circuit board10can be easily obtained by a process of fabricating a multilayer board, such as sheet lamination or thick film printing used in the related art.

Further, the sheets11A to11H may be formed as flexible sheets made of a dielectric material such as polyimide or liquid crystal polymer, electrodes and conductors may be formed on the sheets by thick film formation or the like, these sheets may be laminated and thermally bonded to form a laminated body, and the inductance elements L1and L2and the capacitance elements C1and C2may be incorporated in the laminated body.

In the power supply circuit board10, the inductance elements L1and L2and the capacitance elements C1and C2are provided at different positions in plan view. The power supply circuit board10is magnetically coupled to the external electrode19aby the inductance elements L1and L2, and the external electrode19bis one electrode constituting the capacitance element C1.

Therefore, in the electromagnetic coupling module1having the wireless IC chip5mounted on the power supply circuit board10, a high-frequency signal (in a UHF frequency band, for example) radiated from the reader/writer (not shown) is received by the ground electrode21, the resonant circuit that is magnetically and electrically coupled to the external electrodes19aand19bvia the loop electrode35or36is resonated, and only a reception signal in a predetermined frequency band is supplied to the wireless IC chip5. On the other hand, predetermined energy is extracted from this reception signal, and information stored in the wireless IC chip is matched with a predetermined frequency in the resonant circuit using this energy as a driving source. After that, the information is transmitted to the ground electrode21via the external electrodes19aand19band the loop electrode35or36, and then transmitted and transferred from the ground electrode21to the reader/writer.

In the power supply circuit board10, a resonant frequency characteristic is determined by the resonant circuit formed of the inductance elements L1and L2and the capacitance elements C1and C2. The resonant frequency of a signal radiated from the ground electrode21is substantially determined by the self resonant frequency of the resonant circuit.

Incidentally, the resonant circuit also serves as a matching circuit for matching the impedance of the wireless IC chip5with the impedance of the ground electrode21. The power supply circuit board10may include a matching circuit provided separately from the resonant circuit formed of the inductance elements and the capacitance elements (in this sense, the resonant circuit is also referred to as matching circuit). If the function of a matching circuit is added to the resonant circuit, the design of the resonant circuit tends to be complex. When a matching circuit is provided separately from the resonant circuit, the resonant circuit and the matching circuit can be designed separately. It is noted that the loop electrodes35and36may have an impedance matching function or a function as a resonant circuit. In this case, the radiation characteristic can be improved by designing the resonant circuit (matching circuit) within the power supply circuit board10while taking into consideration the shape of the loop electrode, the size of the ground electrode serving as a radiator plate, and the like.

Second Example of Resonant Circuit

See FIG.7

A second example of a resonant circuit incorporated in a power supply circuit board70is shown inFIG. 7. The power supply circuit board70is made of a flexible PET film or the like. Spiral conductor patterns72constituting an inductance element L and a capacitor electrode73constituting a capacitance element C are formed on the board70. The electrodes12aand12b, led out from the conductor patterns72, and the capacitor electrode73are electrically connected to the terminal electrodes6of the wireless IC chip5. The electrodes12cand12dformed on the board70are electrically connected to the terminal electrodes7of the wireless IC chip5.

The power supply circuit board70is the same as that of the above-mentioned first example in that the inductance element L and the capacitance element C constitute a resonant circuit, and in that the electrodes35aand35bor the electrodes36aand36bthat are opposed to each other are electrically and magnetically coupled to each other to thereby transmit/receive a high-frequency signal having a predetermined frequency. In particular, because the power supply circuit board70is made of a flexible film in the second example, the height of the electromagnetic coupling module1is reduced. Further, as for the inductance element L, its inductance value is changed by changing the line width or line interval of the conductor patterns72, thereby enabling fine adjustment of the resonant frequency.

In the second example as well, the inductance element L is formed of the two conductor patterns72arranged spirally, and the two conductor patterns72are connected to each other at the center portion of the spiral. The two conductor patterns72have different inductance values L1and L2, and different resonant frequency values can be set for the two conductor patterns72. Thus, it is possible to widen the frequency band used in the wireless IC device, as in the above-mentioned first example.

Another Example of Electromagnetic Coupling Module

Instead of the electromagnetic coupling module having the wireless IC chip mounted on the power supply circuit board, an electromagnetic coupling module having a power supply circuit board that is provided with the function of a wireless IC may have a wireless IC and a power supply circuit formed thereon. Thus, the size and the height of the wireless IC device can be reduced.

First Preferred Embodiment

See FIGS.8and9

The following will describe wireless IC devices according to first to fourteenth preferred embodiments of the present invention. In these preferred embodiments, a loop electrode is formed by an opening formed in a ground electrode, as described in the above-mentioned second and fourth basic preferred embodiments (seeFIGS. 3 and 5).

In the wireless IC device according to the first preferred embodiment, as shown inFIGS. 8 and 9, by forming the opening21bat one side of the ground electrode21provided on the printed wiring circuit board20, the loop electrode31is provided around the opening21b, and the connecting electrodes31aand31bare coupled to the wireless IC chip5or the electromagnetic coupling module1.

The ground electrode21that functions as an antenna is formed with slits23aand23bfor adjusting the resonant frequency thereof. If the slits23aand23bare not formed, the ground electrode21resonates in a resonant mode in which both ends21cthereof become resonance ends. In general, the size of the ground electrode21is determined in advance by the size of the circuit board20. Thus, the resonant frequency in the resonant mode with the ends21cas the resonance ends may not agree with a frequency used in an RFID system. In this case, the gain decreases. By forming the slits23aand23bat the side at which the wireless IC chip5or the electromagnetic coupling module1is disposed, the resonant mode can be adjusted to be short as shown inFIG. 8, and the resonant frequency is increased so as to be close to the frequency used in the RFID system. Thus, the gain is improved.

Incidentally, with reference toFIG. 1, the loop electrode22is used for causing the ground electrode21to function as an antenna, and the loop electrode22also has a function of impedance conversion. Specifically, the loop electrode22has impedance between its connecting electrodes22aand22bdue to the loop shape. An electric current corresponding to a signal transmitted from the wireless IC chip5or the power supply circuit board10coupled to the electrodes22aand22bflows along the loop shape.

The impedance (Z) between the connecting electrodes22aand22bis expressed by the sum of a real part (R) and an imaginary part (X). Because the length of the electric current path becomes small when the shape of the loop electrode22becomes small, resistance (R) in the loop electrode22becomes small. When the length of the electric current path becomes small, the impedance (X=ωL) also becomes small because of an inductance (L) generated due to the electric. When the space for disposing the loop electrode22becomes small due to size reduction of an apparatus such as a cellular phone, the impedance of the loop electrode22becomes excessively small, and greatly differs from the impedance of the wireless IC chip and the impedance of the feeder (resonant/matching) circuit, causing a problem that sufficient electric power cannot be transferred from the wireless IC chip5or the power supply circuit to the radiator plate.

In order to solve this problem, the impedance (Z) of the loop electrode22needs to be increased, and the real part (R) or the imaginary part (X) needs to be increased. The first preferred embodiment is also intended to solve such a problem. That is, an annular matching electrode32is disposed inside the loop electrode31. The length of the electric current path of the loop electrode31becomes great due to the matching electrode32, the resistance (R) becomes great, and the real part (R) also becomes great, resulting in that the impedance (Z) becomes great. It is noted that the shape of the matching electrode32shown inFIG. 9is one example, and may be changed to a meander shape or the like, in accordance with the shape and the size of the opening21b.

Second Preferred Embodiment

See FIG.10

In a wireless IC device according to a second preferred embodiment, as shown inFIG. 10, the ground electrode provided on the printed wiring circuit board20is formed with slits23cand23dfor adjusting the resonant frequency thereof. By forming the slits23cand23dat the side opposite to the side at which the wireless IC chip5or the electromagnetic coupling module1is disposed, the resonant mode can be long, and even with the small-size ground electrode21, the resonant frequency can be lowered so as to be close to the frequency used in the RFID system. Thus, the gain is improved.

Third Preferred Embodiment

See FIG.11

In a wireless IC device according to a third preferred embodiment, as shown inFIG. 11, the ground electrode21is formed with the slit23a. By the one slit23a, the resonant mode can be short, and the resonant frequency can be increased so as to be close to the frequency used in the RFID system. Thus, the gain is improved.

Fourth Preferred Embodiment

See FIG.12

In a wireless IC device according to a fourth preferred embodiment, as shown inFIG. 12, the ground electrode is formed with the slit23d. By the one slit23d, the resonant mode can be long, and the resonant frequency can be lowered so as to be close to the frequency used in the RFID system. Thus, the gain is improved.

Fifth Preferred Embodiment

See FIG.13

In a wireless IC device according to a fifth preferred embodiment, as shown inFIG. 13, the ground electrode21is formed with a slit23ein addition to the slit23d. By so forming the slits23dand23e, the resonant mode can be long, and the resonant frequency can be lowered so as to be close to the frequency used in the RFID system. Thus, the gain is improved.

Sixth Preferred Embodiment

See FIG.14

In a wireless IC device according to a sixth preferred embodiment, as shown inFIG. 14, the ground electrode21is formed with the slits23c,23d, and23e. By so forming the slits23c,23d, and23e, two resonant modes can be obtained, and the ground electrode21has two different resonant frequencies. Thus, the gain is improved and the frequency band used is widened.

Seventh Preferred Embodiment

See FIG.15

In a wireless IC device according to a seventh preferred embodiment, as shown inFIG. 15, the ground electrode is formed with a slit23fat another side thereof, in addition to the slits23c,23d, and23e. By so forming the slits23c,23d,23e, and23f, four resonant modes can be obtained, and the ground electrode21has four different resonant frequencies. Thus, the gain is improved and the frequency band used is widened.

Eighth Preferred Embodiment

See FIG.16

In a wireless IC device according to an eighth preferred embodiment, as shown inFIG. 16, the ground electrode21is formed with L-shaped slits23gand23hat the side thereof at which the wireless IC chip5or the electromagnetic coupling module1is disposed. Thus, the resonant mode can be adjusted to be short, and the resonant frequency can be increased so as to be close to the frequency used in the RFID system, thereby improving the gain. In particular, in the eighth preferred embodiment, by forming the slits23gand23hin an L shape, the resonance ends are clearly defined, and a sharp resonant characteristic is obtained. In addition, reciprocal influence with wirings (not shown) disposed around the resonant part can be reduced.

Ninth Preferred Embodiment

See FIG.17

In a wireless IC device according to a ninth preferred embodiment, as shown inFIG. 17, the ground electrode21is formed with L-shaped slits23g′ and23h′, similarly as in the above-mentioned eighth preferred embodiment, and the same effects and advantages as those in the above-mentioned eighth preferred embodiment are provided. Further, the slits23g′ and23h′ have connection parts21dat the side of the electrode21. The impedance at the connection parts21dis low, and thus the effect as the ground electrode is greater than that in the above-mentioned first preferred embodiment.

Tenth Preferred Embodiment

See FIG.18

In a wireless IC device according to a tenth preferred embodiment, as shown inFIG. 18, the printed wiring circuit board20is formed as a multilayer board, the ground electrode21provided on the front surface of the printed wiring circuit board20is formed with the slit23c, and an end of the ground electrode21is electrically connected via a via-hole conductor25to an electrode24formed in an inner layer of the circuit board20. Thus, the resonant mode can be long. In addition, because the resonant mode is set using multiple layers of the circuit board20, flexibility in adjusting the resonant frequency is increased, and it is possible to design a complicated resonant mode.

Eleventh Preferred Embodiment

See FIG.19

In a wireless IC device according to an eleventh preferred embodiment, as shown inFIG. 19, circuit wirings26are disposed in slits23ifor adjusting the resonant frequency. Even with the small-sized ground electrode21, the resonant frequency can be adjusted to be low. In other words, in the eleventh preferred embodiment, a plurality of the slits23iin which the circuit wirings26are disposed are used as slits for adjusting the resonant frequency, and there is no need to form a dedicated slit for adjusting the resonant frequency.

Twelfth Preferred Embodiment

See FIG.20

In a wireless IC device according to a twelfth preferred embodiment, as shown inFIG. 20, the slits23iin which the circuit wirings26are disposed are closed inside the ground electrode21. In the twelfth preferred embodiment, the same effects and advantages as those in the above-mentioned eleventh preferred embodiment are provided. Because all the circuit wirings26are surrounded by the ground electrode21, electric stability of the circuit parts thereof improves.

Thirteenth Preferred Embodiment

See FIG.21

In a wireless IC device according to a thirteenth preferred embodiment, as shown inFIG. 21, the ground electrode is formed with cutouts27aand27bhaving relatively large areas. The cutouts27aand27bare formed at the side at which the wireless IC chip5or the electromagnetic coupling module1is disposed, and the effects and advantages thereof are the same as those in the above-mentioned first preferred embodiment.

It is noted that the outer shape of the printed wiring circuit board20may be the shape corresponding to the cutouts27aand27b. In this case, the resonant frequency is adjusted using the outer shape of the circuit board20. Further, as in the above-mentioned second preferred embodiment (seeFIG. 10), cutouts for adjusting the resonant frequency may be formed at the side opposite to the side at which the wireless IC chip5or the electromagnetic coupling module1is disposed.

Fourteenth Preferred Embodiment

See FIG.22

In a wireless IC device according to a fourteenth preferred embodiment, as shown inFIG. 22, a metal member mounted on the printed wiring circuit board20is in a conductive state with the ground electrode21. Specifically, a metal case28for electronic parts, such as a power amplifier, mounted on the circuit board20is electrically connected to one end of the ground electrode21. Further, the other end of the ground electrode21is electrically connected via the via-hole conductor25to the electrode24formed in the inner layer of the circuit board20, similarly as in the above-mentioned tenth preferred embodiment (seeFIG. 18).

In the fourteenth preferred embodiment, a resonant mode is formed, in which an end of the electrode24and an end of the metal case28are the resonance ends. Thus, the resonant frequency is adjusted to be short.

Various Shapes of Loop Electrode, SeeFIGS. 23 to 28

The loop electrode can have various shapes different from the shape shown inFIG. 9. Such shapes will be described below. Of course, shapes other than the shapes shown here may be used.

The loop electrode31shown inFIG. 23is formed with the relatively-short matching electrodes32. The loop electrodes31shown inFIGS. 24 and 25are formed with the relatively-long matching electrodes32, and the impedance (Z) can be great as described in the above-mentioned first preferred embodiment.

The loop electrode31shown inFIG. 26is formed with the opening21bhaving a relatively large size.

The loop electrode31shown inFIG. 27has the matching electrodes32arranged in a meander shape therein, and the impedance (Z) can be great.

A loop electrode33shown inFIG. 28is formed in an opening21esurrounded by the ground electrode21, and has meander-shaped matching electrodes34. The matching electrodes34have, at their ends, connecting electrodes34aand34bthat are connected to the wireless IC chip5or the electromagnetic coupling module1. The loop electrode33is electrically coupled to the ground electrode21, similarly to the loop electrode22shown in the first basic preferred embodiment (seeFIG. 1).

Fifteenth Preferred Embodiment

See FIGS.29to32

In a wireless IC device according to a fifteenth preferred embodiment, as shown inFIG. 29, a meander-shaped electrode121that functions as a radiator plate is formed on the front surface of a flexible circuit board120, and a loop electrode131mainly for adjusting impedance is also formed thereon. Connecting electrodes131aand131bare provided at ends of the loop electrode131, and are connected to the wireless IC chip5or the electromagnetic coupling module1. Between the connecting electrodes131aand131band the loop electrode131, a matching electrode132is formed.

In the fifteenth preferred embodiment, when the resonant frequency of the electrode121that functions as a radiator plate agrees with the operating frequency of the RFID system, the wireless IC device efficiently operates, and long-distance communication is possible. An equivalent circuit formed in the electrode121is as shown inFIG. 30. Specifically, the electrode121is provided with a plurality of slits so as to generate inductance components L11and capacitance components C11that are connected in parallel with each other, thus forming an inductance component L12that is connected in series with the inductance components L11and the capacitance components C11.

Each constant of the circuit changes according to the dielectric constant of an article to which the wireless IC device is attached. When the dielectric constant of the article is great, the inductance components and the capacitance components become great. When the inductance components L11and the capacitance components C11are appropriately designed, the impedance of the parallel part changes with change of the dielectric constant as shown inFIG. 31. When the impedance (imaginary part) obtained by combining the impedance of the parallel part (L11and C11) and the impedance of the serially-connected inductance component L12is appropriately designed, the impedance becomes substantially the same at a dielectric constant of 1 and at a dielectric constant of 3 to 4, as shown by a curve Ya inFIG. 32. In other words, changes of the impedances of L11and C11with the change of the dielectric constant are cancelled with each other. When an electrode in which L11and C11are not formed is assumed as a comparative preferred embodiment, its impedance (imaginary part) increases with increase of the dielectric constant as shown by a curve Yb inFIG. 32. Thus, the resonant frequency becomes low. On the other hand, in the fifteenth preferred embodiment, even when the dielectric constant of the attachment target article changes, the impedance (imaginary part) almost does not change, and thus the resonant frequency does not change. As described above, by forming a plurality of slits in the electrode, the resonant frequency of the electrode that functions as a radiator plate can be adjusted.

Sixteenth Preferred Embodiment

See FIG.33

In a wireless IC device according to a sixteenth preferred embodiment, as shown inFIG. 33, the electrode121and the loop electrode131are independently formed so as to be adjacent to each other. The electrode121and the loop electrode131are electromagnetically coupled to each other at their adjacent portions. The effects and advantages are the same as those in the above-mentioned fifteenth preferred embodiment.

Seventeenth Preferred Embodiment

See FIG.34

In a wireless IC device according to a seventeenth preferred embodiment, as shown inFIG. 34, portions for forming the capacitance components C11are adjacent to each other. The effects and advantages are the same as those in the above-mentioned fifteenth preferred embodiment, and in particular, the capacitance components C11become great. It is noted thatFIG. 34andFIG. 35described next illustrate a state in which the wireless IC chip5is connected to the loop electrode131.

Eighteenth Preferred Embodiment

See FIG.35

In a wireless IC device according to an eighteenth preferred embodiment, the shape is, as shown inFIG. 35, such that inductance components L11and L12and capacitance components C11are formed. The effects and advantages are the same as those in the above-mentioned fifteenth preferred embodiment.

Nineteenth Preferred Embodiment

See FIGS.36to39

In a wireless IC device according to a nineteenth preferred embodiment, as shown inFIG. 36, the meander-shaped electrode121that functions as a radiator plate is formed on the front surface of the flexible circuit board120, and the loop electrode131mainly for adjusting impedance is also formed thereon. The connecting electrodes131aand131bare provided at the ends of the loop electrode131, and are connected to the wireless IC chip5or the electromagnetic coupling module1. Between the connecting electrodes131aand131band the loop electrode131, the matching electrode132is formed.

In the nineteenth preferred embodiment, the imaginary part of the impedance is determined mainly by the loop electrode131and the matching electrode132. For causing the wireless IC device to efficiently operate, the impedance needs to match with the wireless IC chip5or the electromagnetic coupling module1. An equivalent circuit formed by the loop electrode131and the matching electrode132is as shown inFIG. 37, and includes: inductance components L11and capacitance components C11that are connected in parallel with each other; and an inductance component L12that is connected in series with the inductance components L11and the capacitance components C11.

Each constant of the circuit changes according to the dielectric constant of the article to which the wireless IC device is attached. When the dielectric constant of the article is great, the inductance components and the capacitance components become great. When the inductance components L11and the capacitance components C11are appropriately designed, the impedance of the parallel part changes with change of the dielectric constant as shown inFIG. 38. When the impedance (imaginary part) that is obtained by combining the impedance of the parallel part (L11and C11) and the impedance of the serially-connected inductance component L12and that is observed from the terminal of the wireless IC chip5or the electromagnetic coupling module1is appropriately designed, the impedance becomes substantially the same at a dielectric constant of 1 and a dielectric constant of 3 to 4, as shown by a curve Ya inFIG. 39. In other words, changes of the impedances of L11and C11with the change of the dielectric constant are cancelled with each other. When an electrode in which L11and C11are not formed is assumed as a comparative preferred embodiment, the impedance (imaginary part) increases with increase of the dielectric constant as shown by a curve Yb inFIG. 39. On the other hand, in the nineteenth preferred embodiment, even when the dielectric constant of the attachment target article changes, the impedance (imaginary part) almost does not change. Thus, impedance matching is not needed in the wireless IC chip5or the electromagnetic coupling module1, and a process for impedance adjustment is not needed in the wireless IC chip5or the electromagnetic coupling module1.

It is noted that the loop electrode131can be used solely as shown inFIG. 40. Further, in the present preferred embodiment, the electrode is provided with a plurality of slits so as to be meander-shaped, but the electrode may have a shape of another example.

Twentieth Preferred Embodiment

See FIG.41

In a wireless IC device according to a twentieth preferred embodiment, as shown inFIG. 41, the electrode121and the loop electrode131are independently formed so as to be adjacent to each other. The electrode121and the loop electrode131are electromagnetically coupled to each other at their adjacent portions. The effects and advantages are the same as those in the above-mentioned nineteenth preferred embodiment.

See FIG.42

In a wireless IC device according to a twenty-first preferred embodiment, as shown inFIG. 42, the loop electrode131and the electrode121, shown in the above-mentioned twentieth preferred embodiment, are disposed so as to partially overlap each other. The electrode121and the loop electrode131are electromagnetically coupled to each other at their overlapping portions. The effects and advantages are the same as those in the above-mentioned nineteenth preferred embodiment.

See FIG.43

In a wireless IC device according to a twenty-second preferred embodiment, as shown inFIG. 43, the inductance components L11and capacitance components C11that are connected in parallel with each other are formed between the loop electrode131and the matching electrode132. The effects and advantages are the same as those in the above-mentioned nineteenth preferred embodiment.

See FIG.44

In a wireless IC device according to a twenty-third preferred embodiment, as shown inFIG. 44, the capacitance component C11is disposed at a central portion of the loop electrode131, and cooperates with the inductance component L11to form a parallel resonant circuit. The inductance component L12connected in series with the parallel resonant circuit is formed at two locations. The effects and advantages are the same as those in the above-mentioned nineteenth preferred embodiment.

See FIG.45

In a wireless IC device according to a twenty-fourth preferred embodiment, as shown inFIG. 45, the capacitance component C11is disposed outside the loop electrode131, and cooperates with the inductance component L11disposed at the central portion of the loop electrode131, to form a parallel resonant circuit. The inductance component L12connected in series with the parallel resonant circuit is formed at two locations. The effects and advantages are the same as those in the above-mentioned nineteenth preferred embodiment.

The following will describe a cellular phone that is one preferred embodiment of an electronic apparatus according to the present invention. A cellular phone80shown inFIG. 46is able to handle a plurality of frequencies, and receives a terrestrial digital signal, a GPS signal, a WiFi signal, and a communication signal such as CDMA and GSM.

As shown inFIG. 47, the printed wiring circuit board is installed within a casing81. A wireless communication circuit90and the electromagnetic coupling module1are disposed on the printed wiring circuit board20. The wireless communication circuit90includes an IC91, a balun92incorporated in the circuit board20, a BPF93, and a capacitor94. The power supply circuit board10equipped with the wireless IC chip5is mounted on the loop electrode coupled to the ground electrode21provided on the printed wiring circuit board20, thereby forming the wireless IC device.

Alternative Preferred Embodiments

It is noted that the wireless IC device, the electronic apparatus, and the method for adjusting the resonant frequency of the wireless IC device, according to the present invention, are not limited to the above-mentioned preferred embodiments, and can be modified in a variety of ways within the scope of the present invention.

For example, as an electrode for transmitting or receiving a high-frequency signal, not only the ground electrode but also various electrodes provided on the circuit board can be used. Further, resonant circuits of various configurations can be adopted as the resonant circuit. Further, the materials of the external electrode and the power supply circuit board described in the above-mentioned preferred embodiments are only examples, and any materials with necessary properties can be used.

Further, a process other than using a metal bump may be used for mounting the wireless IC chip on the power supply circuit board. Between the electrode of the wireless IC chip and the connecting electrode of the power supply circuit board, a dielectric member may be disposed such that these electrodes are capacitively coupled to each other. Further, the wireless IC chip and the loop electrode, or the power supply circuit board and the loop electrode, may be capacitively coupled to each other.

Further, the apparatus on which the wireless IC device is mounted is not limited to a wireless communication apparatus such as a cellular phone, but may be various apparatuses including a circuit board having a ground electrode (for example, household electric products such as televisions and refrigerators).

INDUSTRIAL APPLICABILITY

The present invention is useful for a wireless IC device, an electronic apparatus, and a method for adjusting a resonant frequency of a wireless IC device, and in particular, is advantageous in that miniaturization is achieved and the gain of a radiator plate (electrode) that functions as an antenna is improved without providing a dedicated antenna.