JP2008244740A - Rfid tag with improved range - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the operation range by combining an RFID tag which has an rfid integrated circuit and an antenna with a first passive antenna circuit. <P>SOLUTION: A first passive antenna circuit has a first coil and a first capacitor adjusting the passive antenna circuit to the same resonance frequency as the operating frequency of the RFID tag. The first coil has a center opening portion larger than the size of the antenna. The passive antenna circuit is arranged having the antenna provided at the center portion of the coil, preferably, in level to accelerate mutual induction operation. A second passive antenna circuit is basically the same, but larger in size than the first circuit, and the coil of the second passive antenna circuit encloses the first coil to expand the operation range more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to the field of rfid (radio frequency identification) chips and antenna technology. More particularly, the present invention relates to an associated rf query and read device and an rfid chip and antenna with improved communication range.

  Both a general rfid chip and an antenna are incorporated into an ID tag such as that shown and described in US Pat. Is normal. In general, an ID tag is an antenna that is attached to or enclosed in a thin substrate such as a polyethylene terephthalate (PET) substrate as disclosed in US Pat. And rfid chip. The antenna is typically a small loop antenna or a dipole antenna and must be ohmically connected to the rfid chip. A typical loop antenna is a multi-turn planar ohmic conductor formed by any one of several well-known methods. One such technique is silver paste printing on a suitable substrate such as the PET substrate described above. Another well-known technique for forming loop antennas is copper deposition on a substrate implemented at the RCD Technology Corporation of Bethlehem, Pennsylvania. The coil size (coil diameter and thickness) and the number of turns are determined by the specific application requirements, including constraints on the physical size of the ID tag. The function of the antenna provides electromagnetic transmission between the RFID chip and an external inquiry / reading device such as a host CPU, user reading station, etc., and also allows inductive transfer of power from the external device to the RFID chip. It is to supply power to the active circuit elements in the rfid chip.

  Currently, a wide variety of commercially available rfid chips are known, each having standard internal functional components commonly found in rfid integrated circuits. Such standard components include an RF analog section, a CPU, a ROM, and an EEPROM (see FIG. 9.1.1: RFID transponder IC block diagram of Non-Patent Document 1). The rfid chip receives power via the antenna when queried by the external device and communicates with the external device using a standard protocol such as the ISO 14443 protocol or the ISO 15693 protocol. Before installing the ID tag on the object, information for identifying the object to be mounted is written in a ROM (read only memory) incorporated in the rfid chip. Once this information is written to ROM, it cannot be overwritten or rewritten by the interrogation device. The rfid chip is queried by an external query and read device and only supplies information to the external device, i.e. it cannot change the information stored in the ROM.

  An ID tag of the type described above having an rfid chip and an antenna is very useful for object tracking and is currently used in a variety of such applications. Although this technology can be used more theoretically, its practical use has been limited so far due to size and cost constraints. Such restrictions have recently been overcome by improved semiconductor batch processing technology, as ultra-small rfid chips and antennas are now produced at a cost much lower than the cost of the individual objects to be mounted. For example, Hitachi, LTD. Released a mu series rfid chip and antenna in 2004 with a chip size of 0.4 mm x 0.4 mm and at least one-third the price of the rfid chip sold at that time. Other semiconductor manufacturers are following their precedent competitive products.

  FIG. 1 is a plan view of a prior art ID tag 10 having an rfid chip 12 and a single individual antenna 14 that are both elements attached to a substrate 15. The rfid chip 12 is an integrated circuit that includes the normal circuit configuration required for a functional rfid device and is a device that is fabricated independently. These integrated circuit devices are typically manufactured using batch processing techniques well known to those skilled in the art. In general, multiple copies of the basic device design are made on a large semiconductor wafer, after which individual chips are separated from each other and combined with other individual parts.

  In the ID tag 10 of FIG. 1, another individual component is an antenna 14, whereby the circuit configuration of the rfid chip 12 can be communicated with an external inquiry device, and energy is electromagnetically transmitted to the rfid chip 12 and included therein. Power can be supplied to the electronic circuit configuration. The effective operating range of the rf antenna is directly related to the coil area, and the antenna 14 is ideally a multi-turn coil that occupies a much larger area than the rfid chip 12 in order to provide the widest possible operating range. The antenna 14 is typically either a separately formed individual coil that is later bonded to the substrate 15 or a metal layer that is directly deposited on the substrate 15 during coil formation.

  The ID tag 10 of FIG. 1 is generally constructed by first manufacturing the rfid chip 12 and the antenna 14 as separate parts, attaching the parts 12 and 14 to the substrate 15 and electrically connecting the antenna 14 to the rfid chip 12. Is done. Therefore, two ohmic connection pads 16 and 17 to which the free ends 18 and 19 of the antenna 14 are joined are manufactured on the rfid chip 12.

  Although the manufacturing process of the ID tag 10 looks simple and easy, in practice it is difficult to carry out this process with high repeatability. This difficulty is mainly due to the small dimensions of the connection pads on the rfid chip and the free ends 18, 19 of the antenna 14 need to be accurately positioned on the pads 16, 17 prior to the process bonding step. And the need for an accurate mechanical ohmic connection between the antenna end and the connection pad. The production cost of an ID tag of the type seen in FIG. 1 is estimated to be one third for the rfid chip 12, one third for the antenna 14, and one third for assembly. As the physical size of the rfid chip is reduced, the difficulty and cost of assembling a correctly functioning ID tag will increase accordingly.

  FIG. 2 shows one of the latest methods used in the art to alleviate the difficulty in assembling an ID tag having a single rfid chip and antenna component. As can be seen in the figure, the rfid chip 22 and the antenna 24 integrally formed on the substrate 25 are manufactured in the ID tag 20. Since the antenna 24 is formed with the rfid chip 22 during the chip fabrication process, an ohmic connection is automatically formed between the rfid chip 22 and the free end of the antenna 24. This “coil-on-chip” method eliminates costly bonding steps and associated difficulties.

  While the “coil-on-chip” solution does indeed alleviate the problems associated with joining individual parts in the ID tag assembly process, it places severe restrictions on the effective operating range of ID tags fabricated according to this technology. “Coil-on-chip” ID tags are fabricated using integrated circuit batch processing techniques, but the size of the antenna is significantly limited to the size of the die produced. For example, the published operating range of commercially available “coil-on-chip” ID tags is limited to a maximum distance of 3.0 mm. While this is suitable for some special applications, such a narrow operating range is inappropriate for most of the applications currently envisioned for ID tags.

  One of the attempts to expand the operating range of the “coil-on-chip” ID tag is “Radio Frequency Identification Responder with Integrated Antenna” issued July 31, 2001, whose disclosure is incorporated by reference. Patent Document 3 of Japanese Patent Application Laid-Open No. H11-228707. According to the teaching of this reference, an antenna is formed on a chip mounted above or below the rfid chip. The antenna has several coil turns that together form a helical coil having an axis parallel to the body surface of the rfid chip. In order to increase the inductance of the antenna coil and the operating range of the ID tag, a high permeability layer is formed on the antenna chip. Although this structure certainly extends the operating range of “coil-on-chip” ID tags, it requires several additional processing steps, which can increase manufacturing costs and affect yield, and is relatively narrow in scope. Only an antenna can be obtained.

  Thus, current RFID tags with discrete integrated circuit chips and antennas and various “coil-on-chip” s still have serious shortcomings that limit the effective operating range with associated interrogation and reading devices. It is.

US Pat. No. 6,154,137 US Pat. No. 6,373,708 B1 US Pat. No. 6,268,796 1999 IEEE International Solid State Circuit Conference Public Relations 0-7803-5129-0 / 99

  The present invention includes a method and system for providing an RFID tag with an extended range over known ID tags with comparable dimensions.

  The present invention in terms of apparatus includes a combination of RFID tags including an rfid integrated circuit and an antenna having an operating frequency, wherein the first passive antenna circuit includes a first multi-turn coil and a first coil connected to the first coil. Including a capacitor. The passive antenna circuit has a resonance frequency that is substantially the same as the operating frequency of the RFID tag.

  Since the first coil has a basically spiral structure with a central opening larger than the size of the antenna, the passive antenna circuit and the RFID tag are guided by the first coil with the antenna provided in the central opening. Assembled in a deployed state for interaction. When assembled, the first coil is essentially in the same plane as the antenna.

  In an alternative embodiment, the present invention further includes a second passive antenna circuit including a second multi-turn coil and a second capacitor, wherein the second passive antenna circuit has a resonance frequency that is approximately the same as the resonance frequency of the first passive antenna circuit. have. The second multi-turn coil has an outer diameter of the first coil so that the first and second passive antenna circuits are assembled with the first coil provided in the central opening of the second coil so as to mutually induce each other. It has a basically helical structure with a larger central opening. When assembled, the first and second coils are essentially on the same plane.

Viewed from a process perspective, the present invention includes a method for extending the operating range of an RFID tag having an rfid integrated circuit and an antenna, the method comprising:
(A) providing an RFID tag having an rfid integrated circuit and an antenna having an operating frequency;
(B) providing a passive antenna circuit having a first multi-turn coil and a first capacitor connected to the first coil and having a resonance frequency substantially the same as the operating frequency;
(C) combining the RFID tag and the passive antenna so as to mutually induce between the first coil and the passive antenna;
including.

  The first coil has a central opening that is larger than the size of the antenna, and the combining step (c) preferably includes positioning the first coil with the central opening surrounding the antenna. The combining step (c) also preferably includes the step of placing the antenna and the first coil essentially on the same plane.

This method further
(D) providing a second passive antenna circuit having a second multi-turn coil and a second capacitor connected to the second coil and having a resonance frequency substantially the same as the resonance frequency of the first passive circuit;
(E) combining the first passive antenna circuit and the second passive antenna circuit to mutually induct between the first coil and the second coil;
including.

  The second coil has a central opening larger than the size of the first coil, and the combining step (e) includes positioning the second coil with the central opening surrounding the first coil. preferable. The combination step (e) preferably includes a step of arranging the first coil and the second coil basically on the same plane.

  The present invention provides a much wider operating range than known devices while realizing all the advantages of a “coil-on-chip” ID tag and discrete component RFID tag. This expansion of the operating range is estimated to be five times as large as known RFID tags.

  For a further understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying drawings.

  In the drawing, FIG. 3 is a schematic diagram showing the principle of the present invention. As can be seen, the “coil-on-chip” RFID tag 30 has an rfid integrated circuit chip 32 and an integrated antenna 34 fabricated on an integrated circuit board 35. Arranged adjacent to the antenna 34 is a passive antenna circuit 36 having a coil 37 and a tuning capacitor 38. The coil 37 has a much larger area than the chip antenna 34, and the two elements are arranged so as to mutually induce each other.

  The resonant frequency of the passive antenna circuit 36 is selected by the tuning capacitor 38 so as to coincide with the resonant frequency of the circuit including the rfid integrated circuit 32 and the chip antenna 34 so that mutual inductive coupling is maximized.

  When an inquiry signal of the operating frequency selected for the RFID tag 30 is transmitted within the range of the passive antenna circuit 36, the inquiry signal is detected by the passive antenna circuit 36 and transmitted to the chip antenna 34 and the rfid integrated circuit 32. The When the integrated circuit 32 transmits a response to the interrogation signal, this response is first transmitted by the chip antenna 34, detected by the passive antenna circuit 36, and transmitted to the remote interrogation system. Since the range of the passive antenna circuit 36 is considerably wider than the range of the RFID tag 30, the operation range of the RFID tag 30 can be greatly expanded to about 5 times the normal operation range by adding the passive antenna circuit 36.

  FIG. 4 shows a first embodiment of the present invention having a single passive antenna circuit 40. As seen in the figure, the passive antenna circuit 40 includes a multi-turn coil 42 coupled at each end to a separate plate of a tuning capacitor 44. Coil 42 has a central opening that is large enough to accommodate an RFID tag, such as tag 30. The coil 42 may be formed in a desired form such as the above silver paste printing or copper deposition technique. Capacitor 44 may be an individual component element or an element formed using semiconductor fabrication techniques (deposition, masking, etching, etc.). The value of the capacitor 44 is carefully selected so that the resonant frequency of the passive antenna circuit 40 matches the operating frequency of the RFID tag 30. The RFID tag 30, the antenna 42, and the capacitor 44 are preferably attached to some kind of common attachment surface (not shown), which is usually an attachment substrate made of a suitable material. For example, if the embodiment of FIG. 4 is designed for use with clothing, the mounting surface is typically a paper tag for clothing. Similarly, if the embodiment of FIG. 4 is designed to be used in a small package, the mounting surface is typically the surface of the product package itself.

  In operation, when an interrogation signal is transmitted within the passive antenna circuit 40 at the operating frequency selected for the RFID tag 30, the interrogation signal is detected by the passive antenna circuit 40, and the chip antenna 34 and the rfid integrated circuit. 32. When the integrated circuit 32 sends a response to the interrogation signal, this response is first transmitted by the chip antenna 34, detected by the passive antenna circuit 36, and transmitted to the remote interrogation system. Since the range of the passive antenna circuit 40 is considerably wider than the range of the RFID tag 30, the addition of the passive antenna circuit 40 greatly expands the operation range of the RFID tag 30 to about 5 times the normal operation range.

  FIG. 5 shows a second embodiment of the present invention having two passive antenna circuits. As can be seen in the figure, the first passive antenna circuit 40 is arranged to surround the RFID tag 30 in the same manner as shown in FIG. The second large passive antenna circuit 50 has a relatively large induction coil 52 that is ohmically connected to the plate of the second capacitor 54 at each end. The central opening of the coil 52 is large enough to accommodate the coil 42 of the first passive antenna circuit 40. By selecting an appropriate value of the capacitor 54, the passive antenna circuit 50 is tuned to the same frequency as the first passive antenna circuit 40. The structure of the antenna 52 and the capacitor 54 is basically the same as that of the coil 42 and the capacitor 44 except that the dimension of the coil 52 is considerably larger than the dimension of the coil 42.

  The operation of the embodiment of FIG. 5 is similar to that already described for the embodiment of FIG. When the inquiry signal of the operating frequency selected for the RFID tag 30 is transmitted within the range of the second passive antenna circuit 50, the inquiry signal is detected by the second passive antenna circuit 50 and transmitted to the first antenna circuit 40. And transmitted to the chip antenna 34 and the rfid integrated circuit 32. When the integrated circuit 32 sends a response to the interrogation signal, this response is first transmitted by the chip antenna 34, detected by the passive antenna circuit 40, transmitted to the second passive antenna circuit 50, and transmitted to the remote inquiry system. . Since the range of the second passive antenna circuit 50 is considerably wider than the range of the first passive antenna circuit and the RFID tag 30, the addition of the second passive antenna circuit 50 further expands the operating range of the embodiment of FIG.

  The number of turns of the passive coils 42, 52, the width of the individual coil straight sections, and the spacing between the coil turns is a matter of design choice. Generally, the coils 42, 52 are such that the area of the coil is much larger than the surrounding element to provide sufficient physical space for the enclosed element and an inductance that is significantly greater than the inductance of the chip coil 34. Dimensions should be selected. However, the outer diameter of the passive coil should be suitable for the size of the object to which the tag is attached. Thus, for example, if a tag is used for tracking small jewelry, the outer diameter of the passive coil should be smaller than the size of the jewelry.

  It should be noted that the passive antenna circuits 40 and 50 need not be precisely concentric with the RFID tag 30. In order to promote significant electromagnetic interaction between the induction coils, it is sufficient that the passive antenna coils 42, 52 are approximately centered relative to the chip coil 34 and relative to each other. As a result, the assembly of the RFID tag and one or two passive antenna circuits does not need to be a precision matching process, thus reducing assembly costs. In addition, passive antenna circuits can be manufactured at a very low cost, so adding one or more passive antenna circuits to an RFID tag does not add substantial cost to the product and increases the operating range of the RFID tag. Enlarge greatly.

  An ID tag fabricated in accordance with the teachings of the present invention benefits from the “coil-on-chip” ID tag, omitting the joining step primarily involving the antenna coil and rfid chip, and using only a single passive antenna circuit. Sometimes it provides the cost advantage of being able to process large batches while providing an extended operating range that is estimated to be five times higher than the known “coil-on-chip” ID tag.

  Although the invention has been described with respect to particular preferred implementations, various modifications, alternative constructions, and equivalents may be employed without departing from the spirit of the invention. For example, although the present invention has been described with respect to “coil-on-chip” RFID tags, the use of RFI tags with discrete rfid integrated circuits and antennas is fully contemplated. Further, although the passive coils 44 and 54 are illustrated and described as single layer coils, if desired, two or more layers of coils each having a number of turns may be employed. Moreover, although the present invention has been illustrated and described with respect to a closed loop coil, a dipole antenna is also contemplated. Therefore, the above should not be construed as limiting the invention, which is defined by the appended claims.

It is a top view of a prior art ID tag having an rfid chip and a separate antenna. FIG. 6 is a plan view of a prior art ID tag having an rfid chip and an integrally formed antenna. 1 is a schematic diagram of an ID tag having an rfid chip and a passive antenna according to the present invention. FIG. It is a top view which shows 1st embodiment of this invention which has a single passive antenna. FIG. 6 is a plan view illustrating an alternative embodiment of the present invention having an additional passive antenna.

Explanation of symbols

  30 “Coil-on-Chip” RFID Tag / RFID Chip with Antenna, 32 RFID Integrated Circuit Chip, 34 Integrated Antenna, 35 Substrate, 36 Passive Antenna, 37 Coil, 38 Tuning Capacitor, 40 Single Passive Antenna Circuit / First Passive Antenna Circuit, 42 passive antenna / multiturn coil, 44 capacitor, 50 second passive antenna circuit, 52 coil, 54 second capacitor

Claims (12)

  A first passive antenna circuit including a multi-turn first coil and a first capacitor connected to the first coil and combined with an RFID tag having an rfid integrated circuit and an antenna having an operating frequency, A first passive antenna circuit having a resonance frequency that is substantially the same as an operating frequency, wherein the first coil has a central opening that substantially surrounds the RFID tag and is arranged for inductive interaction with the antenna.   The invention of claim 1, wherein the first coil is on the same plane as the antenna.   The invention of claim 1, wherein the first coil has a spiral structure.   And a second passive antenna circuit including a second multi-turn coil and a second capacitor, wherein the second passive antenna circuit has a resonance frequency substantially the same as the resonance frequency of the first passive antenna circuit, 2. The invention of claim 1, wherein the second multi-turn coil has a central opening substantially surrounding the first coil and is arranged to inductively interact with the first coil.   5. The invention of claim 4 wherein the second coil is essentially coplanar with the first coil.   The invention of claim 4, wherein the second coil has a basically spiral structure. A method capable of expanding the operating range of an RFID tag having an rfid integrated circuit and an antenna,
(F) providing an RFID tag having an rfid integrated circuit and an antenna having an operating frequency;
(G) providing a passive antenna circuit having a multi-turn first coil and a first capacitor connected to the first coil and having a resonance frequency substantially the same as the operating frequency;
(H) combining the RFID tag and the passive antenna circuit to induce mutual induction between the first coil and the antenna;
Including methods.   The first coil has a central opening larger than the size of the antenna, and the combined step (c) includes positioning the first coil with the central opening surrounding the antenna. Item 7. The method according to Item 7.   8. The method of claim 7, wherein the combining step (c) comprises placing the antenna and the first coil essentially on the same plane. further,
(D) providing a second passive antenna circuit having a second multi-turn coil and a second capacitor connected to the second coil, wherein the second passive antenna circuit is the first passive circuit; A step having a resonance frequency substantially the same as the resonance frequency; and
(E) combining the first passive antenna circuit and the second passive antenna circuit to mutually induct between the first coil and the second coil;
The method of claim 7 comprising:   The second coil has a central opening larger than the size of the first coil, and the combined step (e) positions the second coil with the central opening surrounding the first coil. The method of claim 10 comprising steps.   11. The method of claim 10, wherein the combined step (e) comprises placing the first coil and the second coil essentially on the same plane.

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