A method and a system for reducing the influence of disturbing signals in transponder applications

Abstract: In a transponder application comprising at least one transponder (11) and at least one interrogating reader, this reader has at least two receiving units so disposed, for instance at different distances, relatively to the transponder, that signals from the same are received at different levels by the receiving units. By combination, e.g. by subtraction, of the received signals, disturbing signals received at practically the same level are eliminated while the difference of useful transponder signals is available. This substantially improves system performance in transponder applications and allows to increase the operating distance between reader and transponder.

Description: The invention relates to a method for reducing the effect of disturbance signals in a system including a transponder and a reader. The invention further relates to an identification system comprising at least one transponder and at least one reader. Transponders are electronic circuits containing information used for identification of animals, for identification of any type of object, for attaching dedicated information to any type of item in logistics processes, etc. Transponders are used in combination with a reader device which communicates with said transponder and makes the information stored in the transponder available to the user of said information. In certain cases there is also the possibility that said reader device sends information to the transponder, where said information may also be stored in the transponder memory (Read-Write systems, etc.). Typically, transponders have little energy at their disposal for internal handling of their information (e.g. read / write operations) and for transmitting the required information to the interrogating reader device: So-called active transponders have an internal energy source (a battery or the like) which, however, usually is quite small due to size, weight and cost restrictions, while so-called passive transponders do not have an internal energy source but make use of the energy of the interrogating field. While the problem solved with this invention is of prime interest for passive transponders, also active transponders may benefit: Due to the very limited energy received by the interrogating reader from a transponder, a consequence of the above outlined internal energy restriction within the transponder, the reception of the information transmitted by the transponder is prone to be disturbed by sources of disturbance in the environment of an interacting system comprising a transponder and a reader. If the frequency of a disturbing signal is very close or even identical with the frequency of the signal provided by the transponder to transmit information to the interrogating reader, the reader may not be able to properly assess this information. Since the energy level of the signal received by the interrogating reader from the transponder is rather low, reception of such a signal can easily be disturbed even by relatively weak disturbance sources. In real world applications such a disturbance often significantly decreases the achievable reading distance between transponder and reading device, sometimes even down to almost zero, thereby heavily compromising the transponder system performance. In view of the foregoing the main aim of the instant invention is to provide a method and a system for substantially reducing the negative effect of disturbance signals on the operation of a system comprising a transponder and a reader. According to a first aspect of the invention this aim is attained with the method defined by claim 1. Preferred embodiments of this method are defined by claims 2-9. According to a second aspect of the invention this aim is attained with the system defined by claim 10. Preferred embodiments of this system are defined by claims 11-13. The main advantage of the invention is that it makes possible to practically eliminate the influence of disturbing signals, to improve substantially the performance of a transponder reader system, and to increase the operating distance between reader and transponder in such a system. Fig. 1 schematically shows a preferred embodiment of the invention, wherein a transponder 11 is apt to emit a transponder signal X and to communicate with an interrogating reader which comprises two receiving units 12 respectively 13 of similar or identical design. The lines connecting transponder 11 to receiving units 12, 13 represent the transmission links between them and the letters p, q represent the respective transmission function coefficients. Each of receiving units 12, 13 comprises or consists substantially of a coil antenna. The coil antennas of receiving units 12, 13 are for instance located at different distances from transponder 11. In Fig. 1 block 14 represents a source 14 of a noise or disturbance signal N. The lines connecting disturbance source 14 to receiving units 12, 13 represent the transmission links between them and the letters x, y represent the respective transmission function coefficients. Source 14 is assumed to be located at a much greater distance or at a different angle from receiving units 12 and 13 of the reader. For this reason x is approximately equal to y, and therefore the energy levels of the disturbance signals xN respectively yN which are received by both receiving units are substantially the same. Within the context of this description the term "transponder signal" means the signal emitted by a single transponder or by a plurality of transponders. Since the receiving units 12, 13 are located at different distances from transponder 11, p is larger or much larger than q, and therefore the energy levels of the transponder signals pX respectively qX which are received by receiving units 12 respectively 13 are substantially different. Receiving unit 12 provides a first output signal U12. Receiving unit 13 provides a second output signal U13. Output signals U12 respectively U13 comprise each a transponder signal component, pX respectively qX, and a disturbance signal component, xN respectively yN. As can be appreciated from Fig. 1 output signals U12 respectively U13 are combined in a suitable way, e.g. by connecting the outputs of receiving units 12, 13 to respective inputs of e.g. a summing amplifier 15 in order to generate a third output signal S which comprises a transponder signal component which is much larger than a disturbance signal component of output signal S. This is achieved e.g. by forming the difference of output signals U12 and U13. Thereby the disturbance signal component of output signal S is practically canceled (xN - yN ≈ 0 for x ≈ y), whereas the transponder signal component (pX - qX ≈ mX with p » q) of output signal S is large enough for suitable operation of the transponder reader system. Output signal S thus has a maximal ratio of transponder-signal level to disturbance signal level. The energy source for the transponder - a battery in the case of active transponders or the energizing field of the reading device in the-case of passive transponders - is not discussed here. Depending on the specific implementation of the system, an amplitude and/or phase correction of the output signals of receiving units 12, 13 may be suitable or necessary. If the phase of the output signals of receiving units 12, 13 does not differ much, the effect of the invention is always in favor of the transponder signal and decreases disturbances. If pX /xN is greater than qX / yN, then (pX+xN)-((qX+yN)*A) with A being an amplitude correction factor, then A can be adjusted, preferably by a suitable control system, in order to decrease the effect of disturbance signal by bringing Nx and Ny in the same order of magnitude in level. Even if the performance of the two receiving units and/or the distance x and y are different, the disturbance can be reduced by adjusting amplitude factor A, where factor A may also be < 1. As the transponder signals pX and qX received by receiving units 12, 13 may be different in phase and as the receiving units 12, 13 may introduce different phase relationships due to different quality factors, different inductance, different filters, etc., it may be advisable to adjust the phase relationship between receiving units 12, 13 or to make this phase relationship adjustable for maximum suppression of the disturbance signal component of output signal S and for maximum useful transponder signal component of output signal S respectively. Amongst the various possible designs of receiving units, the use of coil antennas is preferred. Similar coils wound in the same direction may be used connected in series or parallel with opposite polarity or coils wound in opposite directions may directly be connected together in series or parallel, or a coil wound in the shape of an 8 (eight) with identical loops may be used, wherein the signals received by the loops are subtracted. Of course, the subtraction together with any correction such as phase correction or amplitude adjustment may be effected by electronic means of the reader. In a more general representation of a system according to the invention, the reader of the system according to Fig. 1 may include one or more transmitting units 16 which provide the necessary signals to activate, energize and/or control the operation of transponder 11. In a preferred embodiment the one or more transmitting units are used only for transmission, but not for reception. Transponder 11 can be a single transponder or can be formed by a group of transponders.

Claims: A method for reducing the effect of disturbance signals in a system including a transponder and a reader, said method comprising using a reader having a first receiving unit (12) and a second receiving unit (13) for receiving a signal emitted by a transponder (11), said first and second receiving units (12, 13) receiving both also a disturbance signal emitted by a disturbance source (14), the energy levels of the transponder signals which are received by said first and second receiving units (12, 13) being substantially different, the energy levels of the disturbance signals which are received by said first and second receiving units (12, 13) being substantially the same, said first receiving unit (12) providing a first output signal and said second receiving unit (13) providing a second output signal, each of said first and second output signals comprising a transponder signal component and a disturbance signal component, and combining said output signals of said first and second receiving units in order to generate a third output signal (S) comprising a transponder signal component which is much larger than a disturbance signal component of said third output signal (S). A method according to claim 1, wherein said output signals of said first and said second receiving units (12, 13) are corrected for phase difference in order to optimize the suppression of the disturbance signal component of said third output signal. A method according to claim 1 or 2, wherein said output signals of said first and said second receiving units (12, 13) are adjusted for amplitude difference in order to optimize the suppression of the disturbance signal component of said third output signal. A method according to any one of claims 1 to 3, wherein said third output signal (S) is formed by subtracting the output signal of one of the receiving units (12, 13) from the output signal of the other receiving unit. A method according to any one of claims 1 to 3, wherein said first and said second receiving units (12, 13) are so configured that their output signals are of opposite polarity, and wherein these output signals are added. A method according to any one of claims 1 to 5, wherein the reader comprises more than two receiving units (12, 13) for reception of transponder signals and one or more transmitting units (16). A method according to any one of claims 1 to 6, wherein the reader comprises more than one transmitting unit (16) for transmission of energizing signals. A method according to any one of claims 1 to 7, wherein the energizing signal or signals is/are modulated for transmission of data from the reader to the transponder (11). A method according to any one of claims 1 to 8, wherein the adjustment of the optimal ratio of the two or more output signals provided by the receiving units (11, 13) is effected automatically in order to maximize the signal-to-noise ratio of said third output signal (S). An identification system comprising at least one transponder (11) which is able to emit a transponder signal, at least one reader, said reader having at least two receiving units (12, 13) which able to receive said transponder signal, said receiving units (12, 13) being also able to receive a disturbance signal emitted by a disturbance source (14), said receiving units (12, 13) being so arranged with respect to said transponder (11) that the energy levels of the transponder signals which are received by said first and second receiving units (12, 13) are substantially different, said receiving units (12, 13) being so arranged with respect to said disturbance source (14) that the energy levels of the disturbance signals which are received by said first and second receiving units (12, 13) are substantially the same, said first receiving unit (12) providing a first output signal and said second receiving unit (13) providing a second output signal, each of said first and second output signals comprising a transponder signal component and a disturbance signal component, and means (15) for combining said output signals of said first and second receiving units (12, 13) in order to generate a third output signal (S) comprising a transponder signal component which is much larger than a disturbance signal component. A system according to claim 10, wherein each of the two receiving units (12, 13) comprises a coil, the coils of both receiving units are similar, and the combination of the output signals of the receiving units is obtained by winding the coil of one of the receiving units clockwise and the coil of the other receiving unit counterclockwise and by connecting both coils in series or parallel. A system according to claim 10, wherein each of the two receiving units (12, 13) comprises a coil, the coils of both receiving units being similar, wound clockwise or counterclockwise, connected in series or parallel, and being so configured that the output signals delivered by the receiving units are of opposite polarity. A system according to claim 10, wherein the two receiving units (12, 13) comprise one coil wound in a shape of an 8 (eight) in order to divide said one coil in two coils adapted to provide output signals having a phase difference of 180 degrees between them.

Inventors: ISHII TAKAMASA, JOBIN JEAN-MARC, STEGMAIER PETER, ISHII, TAKAMASA, JOBIN, JEAN- MARC, STEGMAIER, PETER
Applicants: DATAMARS SA
Application year: 2000
Main classification: G06K7
IPC codes: H04B1, G06K7, H04B7