JP2006262055A - Antenna module and portable information terminal having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna module capable of suppressing a decrease in communication distance while eliminating a communication problem when approaching a reader / writer.
An antenna module 11 according to the present invention includes a first tuning coil 13A for tuning when separated from a reader / writer and a second tuning coil for tuning when close to the reader / writer. 13B. The first tuning coil 13A is an antenna with a high Q level to secure a communication distance, and the second tuning coil 13B is an antenna design with a suppressed Q level in order to expand the tuning frequency band. It is possible to eliminate a communication failure caused by a shift in the tuning point when the reader / writer is separated from and close to the reader / writer, and a decrease in communication distance can be suppressed.
[Selection] Figure 1

Description

  The present invention relates to an antenna module used in an RFID (Radio Frequency Identification) system and a portable information terminal including the antenna module.

  Conventionally, in the RFID technology represented by a non-contact IC card system, an antenna coil is built in a non-contact IC tag for identification such as an IC card and inductively coupled with a radio wave transmitted from an external reader / writer antenna. Thus, for example, contactless data communication at a communication frequency of 13.56 MHz is performed.

  For this type of non-contact IC tag, for example, an antenna module having an antenna coil formed in a loop shape on the surface of a base substrate is used (see Patent Document 1 below). This antenna module includes a magnetic core member and a metal shield plate as necessary, and can be used by being incorporated in a casing of a portable information terminal such as a cellular phone.

  This antenna module includes a module circuit (signal processing circuit) that processes and generates a signal received or transmitted by an antenna coil. This module circuit is composed of components such as an IC chip including a memory storing information, and is electrically connected to the antenna coil. This module circuit may be incorporated into a control board of a device in which the antenna module is incorporated.

  During communication between the antenna module and the reader / writer, an induced current corresponding to the intensity of the oscillating radio wave from the reader / writer is generated in the antenna coil. This induced current is rectified in the module circuit and converted into an information read voltage. The read information is modulated in the module circuit and transmitted to the reader / writer via the antenna coil.

  FIG. 8 shows a configuration example of a conventional antenna module. The antenna module 1 includes a feeding coil 2, a tuning coil 3 coupled to the feeding coil 2 by mutual induction, and a module circuit 4 connected to the feeding coil 2. The tuning coil 3 has a tuning capacitor 5 and tunes at a predetermined tuning frequency with an external reader / writer.

  The tuning coil 3 in the antenna module 1 is designed to have an antenna characteristic (frequency characteristic) P0 as shown in FIG. 9, for example. In this example, the tuning frequency (tuning point) is designed to be f0, and the maximum resonance sharpness Q0 and the communication distance can be obtained at this frequency. Note that the communication distance generally increases as the resonance sharpness of the tuning coil 3 increases.

  On the other hand, the antenna module 6 shown in FIG. 10 shows an example in which the tuning coil is composed of a power feeding / tuning coil 7 that also serves as a power feeding coil. Also with this configuration, the antenna characteristic P0 as shown in FIG. 9 is obtained.

  By the way, in this type of antenna module (non-contact IC tag), it is known that the tuning point changes depending on the relative distance between them when communicating with the reader / writer. Specifically, compared with the tuning point f0 when the antenna module and the reader / writer are separated from each other, the tuning point when the antenna module is close to the reader / writer is higher than the tuning point f0. Shift to (fp in FIG. 9). Therefore, in the antenna characteristic where the band of the tuning point is narrow, the communication characteristic deteriorates in the proximity of the antenna module and the reader / writer.

  As described above, in the conventional antenna module, although the antenna characteristic with a high Q value can be obtained due to the structure, the deterioration of the communication characteristic when the tuning point is shifted cannot be avoided. In addition, a resistor or the like can be inserted into the tuning coil to lower the Q (damping). However, the output level is lowered, so that the application is limited and cannot be an essential measure.

  On the other hand, an antenna coil having a plurality of tuning coils and a tuning circuit that tunes at different tuning points is also known (see Patent Document 2 below). As shown in FIG. 11, the tuning circuit 8 coupled to the feeding coil 2 by mutual induction is composed of a plurality of tuning coils 8a, 8b and 8c. As shown in FIG. 12, the antenna characteristics P1, P2, and P3 of the tuning coils 8a, 8b, and 8c have tuning points at f1 (= f0), f2, and f3, respectively.

  According to this configuration, as shown in FIG. 12, it is possible to widen the tuning frequency band with the individual tuning coils 8a to 8c and obtain the antenna characteristics including the shifted tuning point fp, and the antenna module can be a reader / writer. In order to ensure stable communication performance, the influence of the change in the tuning frequency when close to is eliminated.

JP 2004-364199 A JP 2003-69336 A

  However, in the conventional antenna module (the antenna coil disclosed in Patent Document 2) including a plurality of tuning coils 8a to 8c, as shown in FIG. Since Q is greatly reduced as compared with the antenna characteristic P0, depending on the magnitude of the reduction amount ΔQ0, there is a problem that the communication distance of the antenna module cannot be secured when separated from the reader / writer.

  This is because the tuning coils 8a to 8c each have the same Q level and have different tuning points so that the frequency band is broadened at the expense of the communication distance. In reality, it is required to secure the maximum communication distance while eliminating communication problems when approaching a reader / writer. Therefore, the conventional antenna module sufficiently meets such requirements. It is difficult.

  The present invention has been made in view of the above-described problems, and provides an antenna module that can suppress a decrease in communication distance while eliminating a communication failure when approaching a reader / writer, and a portable information terminal including the antenna module. Let it be an issue.

  In order to solve the above problems, the antenna module of the present invention includes a first tuning coil that is tuned when separated from the external antenna and a second tuning coil that is tuned when close to the external antenna.

  The first tuning coil is intended for tuning when separated from the external antenna (when the communication distance is relatively long), so that the Q (resonance sharpness) value is relatively high so that the longest communication distance can be obtained. High antenna design.

  On the other hand, the second tuning coil is intended to secure a tuning band when close to an external antenna (when the communication distance is relatively short), so an antenna that can spread the tuning frequency band by applying a Q dump. Designed. This is because, as the second tuning coil, it is sufficient to ensure a Q level that can solve the problem at the time of proximity. The tuning point of the second tuning coil may be the same as or different from the tuning point of the first tuning coil.

  Thus, in an antenna module having a plurality of tuning coils with different Q levels, it is possible to keep the amount of decrease in communication distance during communication with an external antenna lower than before. As a result, the necessary communication distance can be ensured while eliminating the communication trouble when close to the external antenna.

  The antenna module according to the present invention is applicable not only to the antenna module for non-contact IC tags but also to the transmission / reception antenna section of the reader / writer. Therefore, when the present invention is applied to an antenna module for a non-contact IC tag, the external antenna corresponds to a transmission / reception antenna section of a reader / writer, and when the present invention is applied to a transmission / reception antenna section of a reader / writer, The antenna corresponds to the antenna coil of the non-contact IC tag.

  Furthermore, the antenna module according to the present invention can include a switching unit that selectively switches between the first tuning coil and the second tuning coil. With this configuration, when the antenna module is separated from the external antenna, the first tuning coil is selected to establish communication between them, while when the antenna module is close to the external antenna, the second tuning coil is selected. In this way, a stable communication state is secured while suppressing the influence of the change in the tuning point.

  As a switching method between the first tuning coil and the second tuning coil, for example, the induced voltage of the tuning coil that changes according to the magnitude of the relative distance between the antenna module and the external antenna is used as a reference. can do. That is, when this voltage level has reached a certain value, the second tuning coil is selected to widen the tuning frequency band, thereby avoiding communication troubles when close. On the other hand, when the voltage level of the tuning coil is lower than the predetermined value, the first tuning coil is selected to suppress the decrease in the Q value and secure the communication distance.

  As described above, according to the present invention, the first tuning coil that is tuned when being separated from the external antenna and the second tuning coil that is tuned when being close to the external antenna are provided. It is possible to secure a stable communication operation by suppressing a decrease in the Q value of the antenna module while solving the communication troubles in FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, an antenna module for a non-contact IC tag that performs non-contact communication with an external reader / writer will be described as an example.

(First embodiment)
1 and 2 show a first embodiment of the present invention. Here, FIG. 1 is a schematic configuration diagram of the antenna module 11 of the present embodiment, and FIG. 2 is a diagram for explaining antenna characteristics of the antenna module 11.

  The antenna module 11 of the present embodiment includes a feeding coil 12, a tuning circuit 13 coupled to the feeding coil 12 by mutual induction, and a module circuit 14 connected to the feeding coil 12. The tuning circuit 13 has a tuning capacitor 15 and tunes with a reader / writer (not shown) at a predetermined tuning frequency. As a result, the antenna module 11 performs non-contact communication with the reader / writer.

  The tuning circuit 13 includes a first tuning coil 13A that is tuned when being separated from the reader / writer, a second tuning coil 13B that is tuned when being close to the reader / writer, a tuning capacitor 15, and a Q dump resistor 16. ing.

  The first tuning coil 13A is designed to have an antenna characteristic P11A as shown by a solid line in FIG. 2, for example. In this example, the first tuning coil 13A is designed in the same manner as the tuning coil 3 described with reference to FIG. 8, and the tuning point is set to the communication frequency f0 (for example, 16.76 MHz) when separated from the reader / writer. Has been. That is, the first tuning coil 13A is intended for tuning when separated from the reader / writer (when separated from the reader / writer), and can obtain a relatively high resonance sharpness Q1 that increases the communication distance. The antenna design.

  The second tuning coil 13B is designed to have an antenna characteristic P11B as indicated by a one-dot chain line in FIG. In this example, the tuning point is designed at the tuning point f0 of the first tuning coil 13A, and the resonance sharpness Q2 (<Q1) is obtained at this frequency.

  Since the second tuning coil 13B is intended to secure a tuning band when close to the reader / writer, the second tuning coil 13B has an antenna design that applies a Q dump to push the tuning frequency band. This is because the second tuning coil 13B does not require a long communication distance, and it is sufficient to secure a Q level that can solve the problem at the time of proximity.

  In the present embodiment, a tuning band including the frequency fp is secured as shown in FIG. 2 by connecting the Q dump resistor 16 in parallel to the second tuning coil 13B. The size of the Q dump resistor 16 is not particularly limited, as long as the tuning band can be expanded to a necessary frequency range, and Q2 can be secured so that communication can be established in the vicinity of the external reader / writer.

  The formation conditions such as the line width, the number of turns, and the material of the first and second tuning coils are appropriately set according to the specifications.

  The module circuit 14 is a signal processing circuit unit for processing and generating a signal received or transmitted by the tuning circuit 13, and is mainly composed of an IC component in which a memory storing information, an arithmetic circuit, a modulation / demodulation circuit and the like are integrated. ing. The module circuit 14 is connected to a feeding coil 12 coupled to the tuning circuit 13 by mutual induction, and is modularized together with the feeding coil 12 and the tuning circuit 13.

  These feeding coil 12 and tuning circuit 13 are arranged and formed on the same substrate. In particular, in the present embodiment, the tuning circuit 13 is arranged on the inner peripheral side of the feeding coil 12. In the tuning circuit 13, the first tuning coil 13A and the second tuning coil 13B are adjacent to each other, and the second tuning coil 13B is disposed on the inner peripheral side of the first tuning coil 13A. At this time, the module circuit 14 can be mounted on the same substrate.

  Thereby, it is possible to reduce the size and thickness of the antenna module 11 that is a module body of the feeding coil 12, the tuning circuit 13, and the module circuit 14, and to save space inside the small and thin casing of the portable information terminal. It becomes possible to mount with.

  In the antenna module 11 of the present embodiment configured as described above, an induction current corresponding to the intensity of the oscillating radio wave from the reader / writer is generated in the tuning circuit 13 during communication with the reader / writer. This induced current is supplied to the module circuit 14 via the power feeding coil 12, and is rectified in the module circuit 14 and converted into an information read voltage. The read information is modulated in the module circuit 14 and transmitted to the reader / writer via the feeding coil 12 and the tuning circuit 13.

  In the tuning circuit 13, when the relative distance between the reader / writer and the antenna module 11 is relatively long, contactless communication mainly using the first tuning coil 13A is performed. The antenna characteristic P11A of the first tuning coil 13A is affected by the second tuning coil 13B, and the resonance sharpness Q0 when the second tuning coil 13B does not exist (antenna characteristic P0 of the tuning coil 3 shown in FIG. 8). Compared to lower. However, since the Q values of the first and second tuning coils 13A and 13B are different from each other, the Q reduction amount ΔQ1 (FIG. 2) is the same as that described with reference to FIGS. The amount of decrease Q in the antenna module is smaller than ΔQ0 (ΔQ1 <ΔQ0).

  On the other hand, the antenna module 11 communicates with the reader / writer mainly using the second tuning coil 13B. The antenna characteristic P11B of the second tuning coil 13B has a broad tuning band that includes the communication frequency fp when close to the reader / writer, so that the antenna module and the reader / writer are close to each other. A stable communication operation is ensured by absorbing the deviation of the tuning frequency.

  Therefore, according to the present embodiment, the necessary communication distance can be secured while eliminating the communication trouble when close to the reader / writer, so that a stable and reliable communication operation environment corresponding to a wide communication distance is provided. Thus, it is possible to improve the reliability of the RFID.

  In the antenna module 11 having the above-described configuration, the first tuning coil 13 </ b> A can also serve as the power feeding coil 12. FIG. 3 shows an example of the configuration. The power feeding / tuning coil 17 corresponds to a first tuning coil that is tuned when separated from the reader / writer.

  In this case, the second tuning coil 13B is disposed adjacent to the inner peripheral side of the power feeding / tuning coil 17 and is coupled to the coil 17 by mutual induction. A tuning capacitor 15 is provided in both the coils 17 and 13B. Even with such a configuration, the same effects as described above can be obtained.

(Second Embodiment)
4 and 5 show a second embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  The antenna module 21 of the present embodiment differs from the first embodiment described above in the configuration of the tuning circuit 23. That is, in the present embodiment, the tendency of the tuning frequency deviation that occurs when approaching the reader / writer is grasped in advance, and the tuning point of the first tuning coil 23A and the tuning frequency of the second tuning coil 23B are matched to the frequency band. The point is different.

  As described above, the tuning point at the time of proximity to the reader / writer shifts to a higher frequency side than the tuning point at the time of separation, so the second tuning coil at a frequency higher than the tuning point of the first tuning coil 23B. 23B tuning point is set. FIG. 5 shows an example in which the tuning point of the second tuning coil 23B is set to 18.53 MHz with respect to the tuning point f0 (16.76 MHz) of the first tuning coil 23A.

  According to the present embodiment, the same effects as those of the first embodiment described above can be obtained, and the antenna characteristic P21A of the first tuning coil 23A and the first effect can be compared with those of the first embodiment described above. Interference with the antenna characteristic P21B of the two tuning coil 23B can be suppressed, so that the reduction amount ΔQ2 of the resonance sharpness Q1 of the first tuning coil 23A can be further reduced.

(Third embodiment)
6 and 7 show a third embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  The antenna module 31 of the present embodiment includes a first tuning coil 33A that is tuned when being separated from the reader / writer, and a second tuning coil 33B that is tuned when being close to the reader / writer. The first tuning coil 33 </ b> A and the second tuning coil 33 </ b> B each independently have a function as a power feeding coil, and are each electrically connected to the module circuit 34 independently.

  The first tuning coil 33A and the second tuning coil 33B are set to the same tuning point f0 (16.76 MHz). The second tuning coil 33B is a Q dump coil in which a Q dump resistor 16 is connected in parallel. As shown in FIG. 7, the resonance sharpness Q1 of the first tuning coil 33A is the second tuning coil. The resonance sharpness Q2 of 33B is higher. The first tuning coil 33A and the second tuning coil 33B are arranged at a distance from each other in order to reduce the coupling due to mutual induction.

  On the other hand, the module circuit 34 is provided with a switching circuit 35 that selectively switches between the first tuning coil 33A and the second tuning coil 33B. The example of FIG. 6 shows a state where the switching circuit 35 selects the first tuning coil 33A. Switching between the first tuning coil 33A and the second tuning coil 33B is performed based on the output of a detection unit (not shown) that detects the induced voltage generated in these coils.

  That is, the induced voltage generated by the first and second tuning coils 33A and 33B varies depending on the relative distance (communication distance) between the reader / writer and a larger induced voltage is generated as the distance between the two is closer.

  Therefore, when the voltage level is lower than a certain value, the first tuning coil 33A is selected to suppress a decrease in the communication distance between the two. On the other hand, when the voltage level has reached a certain value, the tuning frequency band can be expanded and stable communication operation can be ensured by selecting the second tuning coil 33B.

  As mentioned above, although each embodiment of this invention was described, of course, this invention is not limited to these, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in each of the embodiments described above, the Q dump resistor is inserted in order to widen the tuning frequency band of the second tuning coils 13B, 23B, and 33B, but instead of this, the separation distance from the first tuning coil is increased. A method of forming the second tuning coil with a material having a large coil resistance is also applicable.

  In each of the above embodiments, the antenna modules 11, 21, and 31 according to the present invention have been described by taking the antenna module for a non-contact IC tag as an example. However, the present invention is not limited thereto, and transmission / reception of the reader / writer is performed. Of course, the present invention can be applied to the antenna portion.

  Furthermore, the antenna module according to the present invention may be configured to serve both as an antenna module for a non-contact IC tag and an antenna module for a reader / writer. In this case, the feeding coil and the tuning circuit can be used in common for the tag and the reader / writer.

It is a schematic block diagram of the antenna module 11 by the 1st Embodiment of this invention. It is a figure explaining the frequency characteristic of the antenna module. It is a figure which shows the modification of a structure of the antenna module. It is a schematic block diagram of the antenna module 21 by the 2nd Embodiment of this invention. It is a figure explaining the frequency characteristic of the antenna module. It is a schematic block diagram of the antenna module 31 by the 3rd Embodiment of this invention. It is a figure explaining the frequency characteristic of the antenna module 31. FIG. It is a schematic block diagram of the conventional antenna module. It is a figure explaining the frequency characteristic of the conventional antenna module. It is a schematic block diagram of the other conventional antenna module. It is a schematic block diagram of the conventional antenna module provided with two or more tuning coils. It is a figure explaining the frequency characteristic of the antenna module of FIG.

Explanation of symbols

  11, 21, 31 ... antenna module, 12 ... feeding coil, 13, 23 ... tuning circuit, 13A, 23A, 33A ... first tuning coil, 13B, 23B, 33B ... second tuning coil, 14, 34 ... module circuit, 15 ... tuned capacity, 16 ... Q dump resistor.

Claims (9)

An antenna module for contactless communication that tunes to an external antenna,
A first tuning coil that is tuned when separated from the external antenna;
An antenna module comprising: a second tuning coil that is tuned when close to the external antenna. The antenna module according to claim 1, wherein a resonance sharpness (Q) of the first tuning coil is higher than a resonance sharpness of the second tuning coil. The antenna module according to claim 2, wherein a Q dump resistor is connected in parallel to the second tuning coil. The antenna module according to claim 1, wherein the first tuning coil and the second tuning coil are disposed adjacent to each other. The antenna module according to claim 4, wherein the first tuning coil and the second tuning coil are both formed on the same substrate. The antenna module according to claim 1, further comprising switching means for selectively switching between the first tuning coil and the second tuning coil. The antenna module according to claim 1, wherein the first tuning coil also serves as a feeding coil. The antenna module according to claim 1, wherein the external antenna is a reader / writer. An antenna module for non-contact communication having a first tuning coil that is tuned when separated from an external antenna and a second tuning coil that is tuned when close to the external antenna is incorporated in the housing. A portable information terminal.

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