JP5218369B2 - RFID and wireless communication device - Google Patents

Description

  The present invention relates to an RFID and a wireless communication device.

  FIG. 10A is a diagram showing a configuration of an RFID according to the background art of the present invention. As shown in the figure, the RFID 100 according to the background art includes a transmission / reception circuit 101 and an external antenna 102. The transmission / reception circuit 101 includes an IC chip 103 and a filter 104.

  The IC chip 103 has a transmission terminal Tx, a reception terminal Rx, and a ground terminal G. The transmission terminal Tx and the reception terminal Rx are on one input terminal IN1 of the external antenna 102, and the ground terminal G is the other side of the external antenna 102. To the input terminal IN2. The filter 104 is for EMC countermeasures and is inserted on the transmission side as shown in FIG.

JP 2008-306869 A

By the way, when connecting the external antenna 102 to the transmission / reception circuit 101, it is necessary to match the impedance between them. That is, since it is necessary to equalize the impedance _{Z A} and _{Z B} shown in FIG. 10 (a), usually a completely different value than the impedance _{Z A} and _{Z B,} the actual RFID 100, FIG. 10 (b ), A matching circuit 105 is required between the transmission / reception circuit 101 and the external antenna 102. This will be described in detail below.

First, determine the specific value of the impedance Z _A. To determine the impedance _{Z A,} replacing the transmission and reception circuit 101 in the equivalent circuit shown in FIG. 11. The resistor R10 is an internal resistance of the IC chip 103 and is generally 50Ω or less. Since the RFID operating frequency is generally 13.56 MHz, the inductance of the inductor L10 and the capacitance of the capacitor C10 are 0.33 μH and 390 pF, respectively, so that the resonance frequency of the filter 104 is about 14 MHz. Set.

Figure 12 (a) (b) is a graph showing the results of calculating the impedance Z _A by using the equivalent circuit shown in FIG. 11. As an example, FIG. 12A shows a case where R10 = 5Ω, and FIG. 12B shows a case where R10 = 30Ω. As is clear from these figures, the impedance Z _A at the operating frequency of 13.56 MHz is Z _A = 156.6 + j31.9Ω when R10 = 5Ω, and Z _A = 30.1 when R10 = 30Ω. −j28.1Ω.

Next, the impedance Z _B, the standard RFID, that the real part of the impedance Z _B is very small and approximately 10Ω or less are known. The imaginary part of the impedance Z _B, but it is difficult to show a specific example greatly differs depending on the implementation, it is most often a value which differs greatly from the imaginary part of the impedance Z _A.

Thus, the impedance Z _A and the impedance Z _B are completely different values. Therefore, in order to match the impedance between the transmission / reception circuit 101 and the external antenna 102, the matching circuit 105 shown in FIG.

  However, the insertion of the matching circuit increases the number of parts, which increases the manufacturing cost. Therefore, there is a need for an RFID that does not require a matching circuit for connecting an external antenna.

  Accordingly, one of the objects of the present invention is to provide an RFID that does not require a matching circuit for connecting an external antenna.

  To achieve the above object, an RFID according to the present invention is an RFID magnetically coupled to an RFID reader, and includes an integrated circuit having a transmission terminal and a ground terminal, and a filter having a resonance frequency substantially equal to an operating frequency, The filter includes an inductor and a capacitor connected in series between the transmission terminal and the ground terminal, and the inductor is magnetically coupled to the RFID reader.

  According to the present invention, the inductor that functions as a filter for EMC countermeasures is also made to function as an antenna. That is, since the RFID is composed of only the transmission / reception circuit and there is no external antenna, a matching circuit for connecting the external antenna is also unnecessary.

  The RFID may further include a resin body formed on a magnetic substrate, and the inductor may be constituted by a planar spiral coil embedded in the resin body. The filter may be a low pass filter.

  The RFID may further include a booster coil, and the inductor may be magnetically coupled to the RFID reader via the booster coil. In this way, a long communication distance can be obtained.

  In the RFID, the filter may further include a resistance element connected in series with the capacitor. According to this, even when an integrated circuit having a relatively large internal resistance is used, impedance can be matched between the integrated circuit and the filter by appropriately adjusting the resistance value of the resistance element.

  In the RFID, the transmission terminal includes first and second transmission terminals, the inductor includes first and second inductors, and the first inductor includes the first transmission terminal and the first transmission terminal. The second inductor connected between the ground terminals is connected between the second transmission terminal and the ground terminal, and the first and second inductors are magnetically coupled to the RFID reader. Also good. According to this, a matching circuit for connecting an external antenna can also be omitted for an RFID that handles a differential signal.

  In addition, a wireless communication device according to the present invention is equipped with any one of the above RFIDs.

  According to the present invention, an inductor that functions as a filter for EMC countermeasures also functions as an antenna, and there is no external antenna. Therefore, a matching circuit for connecting the external antenna becomes unnecessary.

1 is a diagram showing a system configuration of an RFID system according to a first embodiment of the present invention. This figure shows a case where the internal resistance of the IC chip is 5Ω. (A) is a top view of the coil component according to the first embodiment of the present invention. (B) is the sectional view on the A-A 'line of (a). (A) is an equivalent circuit of the filter shown in FIG. (B) is a graph showing the results of calculating the impedance Z ₂ with reference to the equivalent circuit shown in (a). It is a figure which shows the system configuration | structure of an RFID system in case the internal resistance of an IC chip is 30 (ohm). (A) is an equivalent circuit of the filter shown in FIG. (B) is a graph showing the results of calculating the impedance Z ₄ with reference to the equivalent circuit shown in (a). It is a figure which shows the system configuration | structure of the RFID system by the 2nd Embodiment of this invention. (A) is a top view of the booster by the 2nd Embodiment of this invention. (B) is the figure which extracted and showed only the lower layer conductor pattern from (a). (A) is sectional drawing of the booster corresponding to the B-B 'line of Fig.7 (a), (b) is sectional drawing of the booster corresponding to the C-C'line of Fig.7 (a). It is a figure which shows the system configuration | structure of the RFID system by the 3rd Embodiment of this invention. It is a figure which shows the structure of RFID by the background art of this invention. 3 is an equivalent circuit of an RFID transceiver circuit according to the background art of the present invention. It is a diagram illustrating the results of calculating the impedance Z _A by using the equivalent circuit shown in FIG. 11.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a system configuration of an RFID system 1 according to the first embodiment of the present invention. As shown in FIG. 1, the RFID system 1 includes an RFID 2 and an RFID reader 3.

  The RFID 2 includes an IC chip 21 and a filter 22 and is mounted on a wireless communication device such as a mobile phone or an IC card. The IC chip 21 has a transmission terminal Tx, a reception terminal Rx, and a ground terminal G. Between the transmission terminal Tx and the ground terminal G, an inductor L1 and a capacitor C1 are connected in series in this order. The filter 22 includes the inductor L1 and the capacitor C1. The reception terminal Rx is connected to a connection point between the inductor L1 and the capacitor C1.

  The RFID reader 3 has a coil L2, and reads information stored in the IC chip 21 in the RFID 2. When reading is performed, the coil L2 is brought close to the inductor L1. Then, the RFID reader 3 sends a signal modulated by data including a read command to the coil L2. Further, after sending the modulated signal, an unmodulated signal is sent over a predetermined time. These signals are received by the IC chip 21 via magnetic coupling between the coil L2 and the inductor L1.

  The IC chip 21 includes a rectifier circuit, a communication circuit, and a memory. The rectifier circuit receives a single-ended signal through the receiving terminal Rx, and rectifies the signal into a direct current. The communication circuit operates using this direct current as a power source, first interprets the modulation signal, and reads data from the memory according to the interpretation result. Then, the reflected signal of the non-modulated signal is modulated by the read data and is transmitted as a single-ended signal through the transmission terminal Tx. The RFID reader 3 receives this signal via the magnetic coupling between the coil L2 and the inductor L1 and demodulates it to obtain data stored in the memory in the IC chip 21.

  The filter 22 functions as a low-pass filter by the inductor L1 and the capacitor C1, and prevents high-frequency spurious from being emitted during transmission. The resonance frequency of the filter 22 is set to a resonance frequency substantially equal to the RFID operating frequency of 13.56 MHz. Note that “substantially equal” means that it is sufficient if at least a signal having an operating frequency is allowed to pass while a necessary minimum high-frequency spurious signal can be removed. Usually, it is set to about 14 MHz which is slightly higher than 13.56 MHz. In this case, the inductance of the inductor L1 and the capacitance of the capacitor C1 are 0.33 μH and 390 pF, respectively.

  As the inductor L1, a coil component made of a planar spiral coil formed on a resin body is used. FIG. 2A is a top view of the coil component 40 including the inductor L1, and FIG. 2B is a cross-sectional view taken along the line A-A 'of FIG. As shown in these drawings, the coil component 40 includes a magnetic substrate 41 made of a magnetic material such as ferrite, a resin body 42 formed on the upper surface thereof, embedded in the resin body 42, and an inductor L1. A planar spiral coil 43 is provided. The magnetic substrate 41 is also provided in the space portion in the center of the planar spiral coil 43. The inner peripheral end 43-1 and the outer peripheral end 43-2 of the planar spiral coil 43 are connected to the transmission terminal Tx and the capacitor C1 through lead conductors 43a and 43b and a wiring pattern on a substrate (not shown), respectively.

  The coil component 40 is characterized in that it does not have a magnetic substrate on the upper surface of the resin body 42. As a result, the inductor L2 can be magnetically coupled to the inductor L2 by bringing the inductor L2 closer to the upper surface.

  In the RFID 2 according to the present embodiment, the inductor L1 serving as the filter 22 for EMC countermeasures also functions as an antenna, and a configuration corresponding to the external antenna 102 shown in FIGS. 10A and 10B is not provided. . Since the external antenna 102 is not provided, the matching circuit 105 for connecting the external antenna 102 is not necessary in the RFID 2, and as a result, the number of parts is reduced as compared with the configuration of FIG. .

Note that there is no need to provide a matching circuit between the filter 22 and the IC chip 21 as in the example of FIGS. This is an impedance Z ₁ and Z ₂ shown in FIG. 1, because the imaginary part becomes almost the same value. For the real part, is substantially the impedance Z ₂ 0, since the value itself of the internal resistance of the impedance Z ₁ in the IC chip 21, but necessary to match occurs depending on the size of the internal resistance of the IC chip 21, this Matching can be realized simply by inserting a resistance element in series with the capacitor C1. Hereinafter, the impedances Z ₁ and Z ₂ will be described in detail while specifically showing them.

First, the case where the internal resistance of the IC chip 21 is 5Ω will be described. In this case, the impedance _{Z 1} is a 5.0-j0.0Ω.

FIG. 3A is an equivalent circuit of the filter 22 shown in FIG. 3 (b) is a diagram showing the results of calculating the impedance Z ₂ with reference to the equivalent circuit shown in FIG. 3 (a). However, in the calculation, the inductance of the inductor L1 and the capacitance of the capacitor C1 were set to 0.33 μH and 390 pF, respectively.

As understood from FIG. 3 (b), the real part of the impedance _{Z 2} is always approximately 0.0. On the other hand, although the imaginary part changes depending on the frequency, it becomes about −2.0Ω at the RFID operating frequency of 13.56 MHz. Therefore, the impedance Z ₂ at the operating frequency of 13.56 MHz is Z ₂ = 0.0−j2.0Ω.

Comparing the impedance Z ₁ and Z _2, which is almost equal to the real part imaginary part both. From this, it is understood that it is not necessary to provide a matching circuit as shown in FIG. 10B between the filter 22 and the IC chip 21.

  Next, a case where the internal resistance of the IC chip 21 is 30Ω will be described.

FIG. 4 is a diagram showing a system configuration of the RFID system in this case. Since the impedance _{Z 3} is made of a 30.0-j0.0Ω shown in FIG. 4, when compared with the impedance _Z 2 = _0.0-j2.0Ω described above, the difference of the real part is slightly larger. Therefore, in order to cancel this difference and match the impedance, a resistance element is inserted in series with the capacitor C1 as shown in FIG. Thus, it is possible to increase the real part of the impedance Z _4, it is possible to match the impedance.

FIG. 5A is an equivalent circuit of the filter 22 shown in FIG. 5 (b) is a diagram showing the results of calculating the impedance Z ₄ with reference to the equivalent circuit shown in Figure 5 (a). However, in the calculation, the resistance value of the resistor R1 was set to 30Ω. Further, the inductor L1 and the capacitor C1 are the same as those in FIG.

As understood from FIG. 5 (b), the real part of the impedance _{Z 4} is always substantially 30.0. On the other hand, the imaginary part is not changed from the case of FIG. 3B, and is about −2.0Ω at the RFID operating frequency of 13.56 MHz. Therefore, the impedance Z ₂ at the operating frequency of 13.56 MHz is Z ₂ = 30.0−j2.0Ω. Therefore, when compared with impedance Z ₃ = 30.0−j0.0Ω, it is understood that the real part has almost the same value and is matched.

  FIG. 6 is a diagram showing a system configuration of the RFID system 1 according to the second embodiment of the present invention. The difference between the RFID system 1 shown in FIG. 1 and the RFID system 1 shown in FIG. 1 is that the RFID 2 has a booster 23 provided between the inductor L1 and the coil L2. Hereinafter, this difference will be mainly described.

  Since the inductor L1 is also used for a filter, the inductance (component size) is not so large and a long communication distance cannot be obtained. The booster 23 is installed to extend the communication distance of the RFID 2.

  The booster 23 has a booster coil L3 and a capacitor C3, and the booster coil L3 is magnetically coupled to both the inductor L1 and the coil L2. The booster coil L3 and the capacitor C3 constitute an LC resonance circuit. The inductance of the booster coil L3 and the capacitance of the capacitor C3 are determined such that the resonance frequency of the booster 23 is substantially equal to the operating frequency of 13.56 MHz of the RFID2. Note that the inductance (component size) of the booster coil L3 is set to a value that is considerably larger than the inductance (component size) of the inductor L1 and that allows a sufficient communication distance.

  FIG. 7A is a top view of the booster 23. In the figure, only the conductor patterns (upper layer conductor pattern 60 and lower layer conductor pattern 61 described later) among the components of the booster 23 are shown. FIG. 7B shows only the lower conductor pattern 61 extracted from FIG. 7A. 8A is a cross-sectional view of the booster 23 corresponding to the line BB ′ in FIG. 7A, and FIG. 8B corresponds to the line CC ′ in FIG. 3 is a cross-sectional view of a booster 23. FIG.

  A region D shown in FIGS. 7A and 8A and 8B shows the position of the coil component 40 shown in FIG. The coil component 40 is installed just below the lower conductor pattern 61 (back side of the paper) with the exposed surface of the planar spiral coil 43 (inductor L1) facing the booster 23. The RFID reader 3 (FIG. 6) is disposed above the booster 23 (on the front side of the page).

  As shown in FIGS. 8A and 8B, the booster 23 includes an upper layer conductor pattern 60, a lower layer conductor pattern 61, through-hole conductors 62 and 63, and a resin substrate 64.

  The upper conductor pattern 60 is a conductor pattern formed on the upper surface of the resin substrate 64, and has a planar spiral structure as shown in FIG. On the other hand, the lower conductor pattern 61 is a conductor pattern formed on the lower surface of the resin substrate 64. As shown in FIGS. 8A and 8B, the inner peripheral end 60a of the upper layer conductor pattern 60 is electrically connected to one end portion 61a of the lower layer conductor pattern 61 through a through-hole conductor 62 provided in the resin substrate 64. Connected. Similarly, the outer peripheral end 60b of the upper layer conductor pattern 60 is electrically connected to the other end 61b of the lower layer conductor pattern 61 through a through-hole conductor 63 provided in the resin substrate 64, as shown in FIG. Connected to.

  By using the booster 23 as described above, the magnetic field generated in the inductor L1 of the RFID 2 is amplified by the booster 23 and reaches the coil L2 of the RFID reader 3. Further, the magnetic field generated in the coil L2 of the RFID reader 3 reaches the inductor L1 via the booster coil L3 having a larger inductance than the inductor L1. Therefore, according to the RFID system 1 according to the second embodiment, a sufficient communication distance can be obtained even when the inductance (component size) of the inductor L1 is small.

  FIG. 9 is a diagram showing a system configuration of the RFID system 1 according to the third embodiment of the present invention. The difference between the RFID system 1 shown in the figure and the RFID system 1 shown in FIG. 6 is that a differential IC chip 24 is used instead of the single-end IC chip 21. Along with this change, the EMC countermeasure filter 22 is also replaced with a differential type filter 25. Hereinafter, these differences will be mainly described.

  The IC chip 24 has a transmission terminal Tx1 (first transmission terminal), a transmission terminal Tx2 (second transmission terminal), a reception terminal Rx, and a ground terminal G. The filter 25 includes an inductor L4 (first inductor), an inductor L5 (second inductor), and a capacitor C4.

  The inductor L4 and the capacitor C4 are connected in series between the transmission terminal Tx1 and the ground terminal G in this order, and constitute a low-pass filter. The inductor L5 is connected between the transmission terminal Tx2 and a connection point between the inductor L4 and the capacitor C4, and constitutes a low-pass filter together with the capacitor C4. The reception terminal Rx is also connected to the connection point of the inductor L4 and the capacitor C4.

  The inductors L4 and L5 are each configured by the coil component 40 (FIG. 2) described above. Therefore, by arranging these coil components 40 and bringing the booster coil L3 closer to the upper surface, the inductors L4 and L5 and the booster coil L3 can be magnetically coupled.

  The IC chip 24 is the same as the IC chip 21 in that it includes a rectifier circuit, a communication circuit, and a memory. The IC chip 24 modulates the reflection signal of the non-modulated signal with the data read from the memory according to the instruction of the RFID reader 3, and sends it as a differential signal through the transmission terminals Tx1 and Tx2. The RFID reader 3 receives this signal via the magnetic coupling between the coils L4 and L5 and the inductor L3, and the magnetic coupling between the inductor L3 and the coil L2, and demodulates the signal to the memory in the IC chip 21. Get stored data.

  In the RFID 2 according to the present embodiment, the inductors L4 and L5 functioning as the filter 25 for EMC countermeasures also function as an antenna, and a configuration corresponding to the external antenna 102 shown in FIGS. 10 (a) and 10 (b) is provided. I can't. Therefore, the number of parts is reduced.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to such embodiment at all, and this invention can be implemented in various aspects in the range which does not deviate from the summary. Of course.

  For example, although the above embodiment has been described on the assumption that the operating frequency of RFID is 13.56 MHz, the present invention can also be applied to RFID using other operating frequencies. In that case, of course, the inductance of each inductor and the capacitance of each capacitor are appropriately changed.

  In the above embodiment, an IC chip is used, but other types of integrated circuits such as a circuit (TFT circuit) including a TFT (Thin Film Transistor) may be used instead of the IC chip.

1 RFID system 2 RFID
3 RFID reader 21, 24 IC chip 22, 25 Filter 23 Booster 40 Coil component 41 Magnetic substrate 42 Resin body 43 Planar spiral coil 43a, 43b Lead conductor 60 Upper layer conductor pattern 61 Lower layer conductor pattern 62, 63 Through hole conductor 64 Resin substrate

Claims (4)

An RFID that is magnetically coupled to an RFID reader,
An integrated circuit having a transmission terminal and a ground terminal;
A filter having a resonance frequency substantially equal to the operating frequency,
The filter includes an inductor and a capacitor connected in series between the transmission terminal and the ground terminal ,
The transmission terminal includes first and second transmission terminals,
The inductor includes first and second inductors,
The first inductor is connected between the first transmission terminal and the ground terminal;
The second inductor is connected between the second transmission terminal and the ground terminal,
Wherein the first and second inductors, RFID, characterized in Rukoto by the RFID reader and the magnetic coupling. A resin body formed on the magnetic substrate;
2. The RFID according to claim 1, wherein each of the first and second inductors includes a planar spiral coil embedded in the resin body. Further equipped with a booster coil,
3. The RFID according to claim 1, wherein the first and second inductors are magnetically coupled to the RFID reader via the booster coil. A wireless communication device comprising the RFID according to any one of claims 1 to 3 .

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