HK1136099A - Device with no radiofrequency contact comprising several antennas and associated antenna selection circuit - Google Patents

Description

Contactless radio frequency device featuring multiple antennas and associated antenna selection circuit

Technical Field

The present invention relates to radio frequency devices (RFID) and, in particular, to contactless radio frequency devices featuring multiple antennas and their associated antenna selection circuitry.

Background

Contactless transceiver devices are currently used in a wide variety of applications. One of these applications is contactless smart cards, which are being increasingly used in various sectors, such as for example the public transport sector. Contactless smart cards have also been developed as payment devices.

The exchange of information between a contactless device and an associated reader is accomplished by the remote transmission of electromagnetic signals between an antenna housed within the contactless device and another antenna located within the reader. For collecting, storing and processing information, the device is equipped with a microcircuit connected to said antenna and is characterized by having a memory area. During the information exchange process, the contactless device is powered by the electromagnetic waves transmitted by the reader.

An increasingly important application of these contactless devices is their use as labels that are affixed to objects to identify the objects when tracking goods or inventory locations. In these applications, the microcircuit of the label affixed to each object contains, in the memory, the data of the object, which allows to index and identify the object and thus ensure traceability.

The label is affixed to the object as it is created and accompanies the object until it is received by the customer. The memory of the microcircuit contains information about the characteristics of the object or about its content in the case of the reservoir. This information can be read by the reader at any time. Currently, the frequencies typically used by readers for exchanging data with tags are Ultra High Frequencies (UHF) from 860MHz to 960MHz, which allows tags to be read at distances greater than 2 meters.

A simple antenna that may be used in a contactless tag, such as those shown in fig. 1 referred to as RFID tag 100, is a dipole antenna 112, which has a dimension of about half a wavelength of the operating frequency. A particular feature of such a dipole is that energy is radiated primarily in a preferred direction perpendicular to the axis of the dipole. As a result, a simple dipole used as an antenna has the major drawback of having directional radiation, which means that the tag cannot function in all directions, but only in certain specific directions.

One solution to eliminate this drawback is to use a combination of antennas, e.g. two dipoles as shown in fig. 2, to approximate uniform or non-directional bulk radiation. In this case, the signals received by each antenna may be added to each other so as to obtain a larger output signal. A first drawback of such systems with multiple antennas is that the energy of the received field is not optimized when one of the received signals is noise. In addition, each signal received is conditioned with a capacitance, which requires space on the integrated circuit. However, the very small size of such circuits means that additional expense is required when components are added thereto.

Disclosure of Invention

It is therefore an object of the present invention to provide an integrated circuit for a contactless radio frequency device that allows the management of signals from multiple antennas in order to improve the radiation of the contactless device.

It is another object of the invention to provide a radio frequency contactless device equipped with an integrated circuit that allows the management of the signals from multiple antennas in order to improve the radiation.

The object of the invention is therefore an integrated circuit for a contactless radio-frequency device, which is connected to a first antenna and a second antenna designed to receive radio-frequency signals from a reader. According to one main characteristic, the integrated circuit comprises a first rectifier circuit and a second rectifier circuit to rectify each radio frequency signal received from the first antenna and the second antenna, respectively, so as to generate two positive output voltages V1 and V2, the rectifier circuits being mounted in parallel so as to select an output voltage value corresponding to a maximum voltage value between V1 and V2.

A second object of the invention is a contactless radio frequency device equipped with an integrated circuit according to the first object.

Drawings

These objects, objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

fig. 1 shows a tag equipped with an RFID antenna of the dipole type;

fig. 2 shows a tag equipped with two antennas;

FIG. 3 is a schematic diagram of the communication between an RFID tag and a reader;

fig. 4 shows a circuit diagram of a radio frequency receiving system of an integrated circuit according to the invention;

FIG. 5 shows a circuit diagram of a radio frequency receiving system of an integrated circuit according to a specific example of the present invention;

fig. 6 shows a circuit diagram of a radio frequency receiving system of an integrated circuit according to the invention;

FIG. 7 shows a circuit diagram of a radio frequency receiving system of an integrated circuit according to a specific example of the present invention;

FIG. 8 shows a first tag according to a first embodiment of the invention;

FIG. 9 shows a second label according to the first embodiment of the invention;

FIG. 10 is a view of a label according to the present invention positioned on both sides of a three-dimensional object;

FIG. 11 is a view of a label according to the present invention prior to being positioned on three sides of a three-dimensional object according to a first method; and

fig. 12 is a view of a label according to the present invention positioned on three sides of a three-dimensional object according to a first method.

Detailed Description

According to a preferred embodiment of the invention, the contactless radio frequency device is a Radio Frequency (RFID) identification tag as shown in fig. 2 and 3, which is constituted by a support 10 on which support 10 an integrated circuit 12 connected to two antennas 14 and 18 is placed. The support 11 is a support preferably made of a flexible material, such as a fibrous material like paper or a synthetic material. Each antenna is a dipole type antenna made of two wires (wires). The first antenna 14 is made of the wires 13 and 15 and the second antenna 18 is made of the wires 17 and 19. The antennas 14 and 18 of the label 10 are printed on the support 11 by screen printing, flexo printing, rotogravure printing, offset printing or ink jet printing of the antennas 14 and 18. The antenna is made of epoxy-based conductive ink filled with silver or gold particles or made of conductive polymer. The antennas 14 and 18 are preferably dipole antennas having a size of about half a wavelength of the operating frequency. Each antenna is connected to the integrated circuit by means of contacts 23, 25, 27 and 29 of the chip, the wires 13 and 15 of the antenna 14 are connected to the contacts 23 and 25 of the integrated circuit, and the wires 17 and 19 of the antenna 18 are connected to the contacts 27 and 29 of the integrated circuit. The contacts 23 and 25 of the integrated circuit are connected to a first receiving system and the contacts 27 and 29 are connected to a second receiving system. The integrated circuit is characterized by having a memory area containing information required for traceability or personal identification of objects, for example, which can be read by a reader by Ultra High Frequency (UHF) electromagnetic wave exchange of about 1GHz, and in particular greater than 860MHz (a frequency of 1GHz according to the ISO 18000-6 standard and a frequency of 2.45GHz according to the ISO 18000-4 standard).

During the information exchange, the integrated circuit is powered by electromagnetic waves transmitted by the reader. When an RFID tag enters the field of the reader, a voltage is induced on each antenna. This UHF voltage is then processed in order to produce a positive and continuous voltage designed to power the circuit, and a positive voltage with a suitable rate of change in order to be able to demodulate the information transmitted by the reader. When the problem is to generate energy for the circuit, we refer to a rectifier, and when the problem is to recover information modulated in amplitude, we refer to envelope detection. Considering that similar descriptions apply to modulated signals representing information, we will describe in detail the processing of signals intended to power a circuit, since the processing of a first supply signal and a second signal corresponding to the modulated information is similar. But the differences will be explained. The peak value of the induced voltage in each antenna depends on the position of the antenna and, therefore, on the orientation of the tag relative to the reader antenna orientation. For example, in the case shown in FIG. 3, the tag is positioned relative to the Radio Frequency (RF) field emitted by antenna 32 of reader 30 in such a way that the voltage induced in antenna 14 is less than the voltage induced in antenna 18. In practice, the radiation of a dipole antenna is very low along the antenna axis (i.e., along the y-axis with reference to fig. 3) and is maximum in a plane through its center and perpendicular to the antenna (i.e., the (x, z) plane).

Each antenna is thus connected to a stage of the integrated circuit by means of a contact, and this corresponds to a radio frequency receiver system. Thus, an integrated circuit connected to two antennas is characterized by having two radio frequency receiving systems. According to fig. 4, the voltage induced by the antenna 14 is rectified by a rectifier circuit 40, the rectifier circuit 40 being characterized by a first diode 41 and a second diode 42. Similarly, the voltage induced by the antenna 18 is rectified by a rectifier circuit 50, the rectifier circuit 50 being characterized by a first diode 51 and a second diode 52. The rectifier circuits 40 and 50 may also use transistors mounted as diodes or other components that ensure the same function. The rectified output voltage of antenna 14 is a positive and constant voltage V1, while the rectified output voltage of antenna 18 is a voltage V2. The integrated circuit according to the invention enables optimization of the capacitance 60 required for regulating the output voltage applied to the terminals of the load 70 of the integrated circuit of the RFID tag, since the two rectifier circuits 40 and 50 are mounted in parallel, so that the conductors 15 and 17 of the antennas 14 and 18, respectively connected to the contacts 25 and 27 of the chip 12, are connected together by means of an ohmic connection. In fact, in the case of an integrated circuit connected to two antennas according to the prior art, each rectifier circuit requires a capacitance which, in terms of surface, can represent approximately two thirds of the surface of the rectifier circuit. As a result, the integrated circuit according to the invention, although comprising two rectifier circuits, uses only one capacitor and saves approximately two thirds of the surface area representing the surface of the rectifier circuits.

The values of V1 and V2 change depending on the positioning of the RFID tag relative to the reader's antenna, so that we always obtain two positive non-zero voltage values, such as V1> V2 or V2> V1. Assuming that the output voltage V2 of antenna 18 is greater than the output voltage V1 of antenna 14, the current provided by voltage V2 and through forward biased diode 52 can only flow through load 70 as long as the circuit through diode 42 is open when diode 42 is reverse biased (in the locked direction) in this situation. Referring to fig. 5, diode 42 is thus equivalent to an open switch, which results in an open circuit of the circuit through diode 42.

Conversely, if V1> V2, diode 52 will be reverse biased, while diode 42 will be forward biased. The current provided by the voltage V1 cannot flow through the diode 52, which is equivalent to an open circuit switch, but only through the load 70.

The voltage induced in the antenna associated with the rectifier with the diode forward biased is therefore the voltage applied to the load 70 to power the circuit and exchange information from the reader. The integrated circuit according to the invention thus facilitates the selection of the maximum voltage between the voltage V1 from the antenna 14 and the voltage V2 from the antenna 18, which in the example illustrated in fig. 5 is the voltage V2. The selected maximum output voltage is then adjusted by the capacitor 60 to power the load 70 of the integrated circuit of the RFID tag 10. In which case no voltage from the other antenna is used.

The voltage induced in each antenna that produces a second signal corresponding to the modulated information is processed by two circuits, referred to as envelope detectors, similar to rectifier circuits 40 and 50. However, the envelope detector circuit has a cut-off frequency for the output signal that is greater than the cut-off frequency of the rectifier circuit designed to process the input signal. As a result, the output voltages V1 and V2 are not constant, but change at a speed suitable for the output of the modulation signal. For a signal corresponding to modulated information, the integrated circuit according to the invention presents the advantage of picking up only a "good" signal when one of the voltages induced in one of the antennas is noise, such as a spurious peak. In the case of an integrated circuit that adds induced voltages, the resulting signal will contain interference that may cause communication errors.

Considering that the integrated circuit for processing an input signal according to the invention requires only one capacitor, it has the advantage of saving space in respect of the integrated circuit for processing a modulated information signal. In addition, even when one of the signals received by one of the antennas is noise, the integrated circuit according to the present invention can process the modulated information signal without communication error as long as the amplitude of the noise is lower than that of the signal received by the other antenna.

The antenna used may be any type of antenna without departing from the scope of the invention.

In addition, the tag equipped with the integrated circuit according to the invention can be positioned without orientation restrictions on any type of support, such as a tray, a carton. The integrated circuit according to the invention can also be used in any contactless device.

The integrated circuit according to the invention is particularly suitable for labels that are attached to several sides of a three-dimensional object, such as a carton. Fig. 6 shows such a tag 10 and is characterized by having two axes 33-35 and 37-39 intersecting each other at a point 30 preferably located at the center of the tag. The two axes 33-35 and 37-39 are preferably perpendicular to each other and are preferably the axes of symmetry of the contactless tag. The two axes 33-35 and 37-39 divide the contactless tag into 4 zones 45, 46, 47 and 48. The wires 13, 15, 17 and 19 of the antenna are placed on the support 11 so that they do not overlap at the intersection 30 of the two axes 33-35 and 37-39 and so that they do not intersect at least one of the half-axes 33, 35, 37 or 39. According to the example shown, the half-shafts 37 do not intersect any antenna wire in this case. In addition, the integrated circuit is positioned such that it does not overlap one of the axes 33-35, 37-39. The axes 33-35, 37-39 may be marked with a color line on one side of the label 10. The label is characterized by a protective layer on the antenna support, which is the support for printed logos or other items, and an adhesive layer covered with a removable silicone-treated paper.

Fig. 7 shows the same tag with the same arrangement of antenna wires with respect to the axis as in the previous figure, but with a different antenna wire.

According to fig. 8, the non-contact tag 10 is affixed to both sides of a three-dimensional object such as a paper cassette 500. In this regard, the label may preferably be folded along axes 33-35 such that axes 33-35 overlap edges 510 defining sides 501 and 502 of the carton. The portion of the tag on side 501 of carton 500 is comprised of regions 46 and 47, which include the entire conductor 13 of antenna 14 and the entire conductor 19 of antenna 18, as well as a small portion of conductors 15 and 17. The portion of the tag located on the second side 502 of the carton 500 is comprised of regions 44 and 48, which include a major portion of the conductor 15 of antenna 14, and a major portion of the conductor 17 of antenna 18.

The non-contact tag 10 may also be affixed to three sides of a three-dimensional object such as a carton. In this case, the positioning of the label can be done in two ways, either removing a portion of the label or covering a portion of the label. These two ways are shown in figures 9 and 10 and 11 and 12 respectively.

According to fig. 10, the contactless tag 10 is cut along half-shafts 37 up to the point of intersection 30, and preferably folded along axes 33-35. The label 10 is then positioned on the carton 600 so that the intersection point 30 of the two axes of the label overlaps one corner of the carton 600 as shown in figure 10, with half-axis 35 overlapping the edge 610 of the carton 600 and half-axis 39 overlapping the edge 630 of the carton. Portion 46, located on side 601 of carton 600, includes a major portion of wire 19 of antenna 14 and a minor portion of wire 15 of antenna 14. Portion 47, which is located on second side 602 of carton 600, includes the entire conductive line 13 and a small portion of conductive lines 15, 17, and 19 of antenna 14, and integrated circuit 12. Portion 45 of the label on third side 603 of carton 600 overlies portion 48 of label 10. In this way, the portion of the tag located on the third side comprises the main part of the conductor 15 of the antenna 14 and the main part of the conductor 17 of the antenna 18.

In order to place the non-contact tag on three sides of a three-dimensional object, such as a carton, a portion of the tag may also be removed. In this case, according to fig. 11, the label is cut along half-axes 33 and 37 up to point of intersection 30, and area 48 is separated from label 10. In this way, a major portion of the wire 17 of the antenna 18 is removed. The wires 15 and 17 are connected together and the wire 15 serves as a second wire for the antenna 14 and also for the antenna 18.

The label 10 is then positioned on the carton 700 so that the intersection point 30 of the two axes of the label overlaps the corner of the carton 700, half-axis 35 overlaps the edge 710 of the carton 700 and half-axis 39 overlaps the edge 730 of the carton, as shown in figure 12. The portion 46 of the tag located on the side 701 of the carton 700 includes the main portion of the wire 19 of the antenna 14 and a small portion of the wire 15 of the antenna 14. The portion of the tag located on the second side 702 of the carton 700 is comprised of area 47 and includes the entire conductive line 13 of antenna 14 and a small portion of conductive lines 15, 17 and 19 and integrated circuit 12. The portion of the tag located on the third side 703 of the carton 700 is comprised of region 45 and includes a major portion of the conductive line 15 of the antenna 14. The two wires 15 and 17 of the respective antennas 14 and 18 are connected together, the antenna 14 being composed of the wires 13 and 15 and the antenna 18 being composed of the wires 19 and 15. Depending on the range of influence of the field emitted by the reader, the integrated circuit 12 is powered by an antenna 14 consisting of the conductors 13 and 15 or by an antenna 18 consisting of the conductors 19 and 15.

Generally, the two shafts 33-35 and 37-39 are used as shafts along which the label can be folded, and the half shafts 37 can be cut without hindering the operation of the label. In order to make it easy to mount the label on two or three sides of a three-dimensional object such as a carton, the half shafts 33, 35, 37 and 39, which are folding or shearing shafts, may be formed in advance, i.e., the label may be folded along the shafts in advance during the manufacturing process.

When a tag according to the invention is placed on two or three sides of a three-dimensional object, the reader exchanges data with at least one of the two antennas. In fact, if only the maximum of the two voltages of the input signal of the antenna is selected, whether or not one of the two antennas is shielded, one of the two antennas will transmit a particular radiation with respect to the reader with respect to the other antenna, and this antenna powers the integrated circuit. The integrated circuit is thus powered by the antenna 14 or by the antenna 18, depending on the range of influence of the field emitted by the reader.

Claims (12)

1. An integrated circuit (12) for a contactless radio frequency device, the integrated circuit (12) being connected to a first antenna (14) and a second antenna (18) designed to receive radio frequency signals from a reader,

characterized in that said integrated circuit (12) comprises a first rectifier circuit (40) and a second rectifier circuit (50) to rectify each radio frequency signal received from said first antenna (14) and said second antenna (18) respectively so as to generate two positive output voltages V1 and V2, said rectifier circuits (40 and 50) being mounted in parallel so as to select an output voltage value corresponding to a maximum voltage value between V1 and V2.

2. An integrated circuit (12) as claimed in claim 1, wherein the selected maximum output voltage is regulated by a capacitor (60).

3. An integrated circuit (12) as claimed in any of claims 1 or 2, wherein the regulated voltage output from the capacitor (60) is applied to a load (70) for powering the circuit and for transmitting information.

4. An integrated circuit (12) as claimed in any one of claims 1 to 3, characterized by a memory area containing information required for traceability of objects or for identifying persons, for example.

5. The integrated circuit (12) of claim 4, wherein the information can be read from the reader by exchange of Ultra High Frequency (UHF) electromagnetic waves.

6. A contactless radio frequency device characterized by an integrated circuit (12) according to any of claims 1 to 5.

7. Contactless radio frequency device according to claim 6, wherein the antennas (14 and 18) are dipole type antennas.

8. The contactless radio frequency device according to any of claims 6 or 7, wherein the antenna is printed on a support (11).

9. The contactless radio frequency device according to any of the claims 6 to 8, wherein the support (11) is made of paper.

10. A device as claimed in any one of claims 6 to 9, which is a radio frequency identification tag (RFID) or a contactless tag.

11. The contactless tag (10) of claim 10, sized to be affixed to one or more sides of a three-dimensional object, each portion of the tag located on one of the sides of the object wholly or partially containing at least one conductor of one of the antennas (14 and 18) such that any side may participate in data exchange with the reader regardless of the orientation of the tag relative to the reader.

12. A contactless tag according to claim 11, characterized by having two axes 33-35 and 37-39 along which said tag can be folded, cutting half-shafts 37 without hindering the operation of said tag.