Abstract:
A method for assisting with positioning of an electromagnetic transponder by a user with respect to a terminal, wherein: a first value of the current in an oscillating circuit of the terminal is periodically measured; a second value of a ratio between a no-load value of this current, stored when no transponder is in the field of the terminal, and the first value, is calculated; and pieces of information intended for the user are controlled according to said second value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Stage of international patent application number PCT/FR2012/050842, filed on Apr. 18, 2012, which claims the priority benefit of French patent application number 11/54861, filed on Jun. 3, 2011, which applications are hereby incorporated by reference to the maximum extent allowable by law. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Embodiments generally relate to systems using transponders, that is, transceivers (generally mobile) capable of communicating in a contactless and wireless manner with a terminal. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Electromagnetic transponder systems are more and more used with the coming up of mobile telecommunication devices equipped with near field communication (NFC) routers. In such devices, the mobile equipment may be used both as a transponder reader, for example, as a contactless chip card reader and, conversely, as an actual transponder for a near field communication with a terminal, for example, another mobile device, an access terminal, etc. 
         [0006]    A recurring issue in the use of electromagnetic transponders is, for the quality of the communication, the distance separating the transponder from the reader. 
         [0007]    In particular, a natural reflex of the bearer of the transponder (for example, of the contactless chip card) is to press the card against the reader surface. This pressure may even be strong enough to fold the card. This results in mechanical stress on the chip card which is capable of damaging the antenna generally formed of a conductive winding embedded in the card, or of damaging the contacts between the antenna and the chip. 
         [0008]    Further, the positioning of the transponder is often not optimal for the system operation. 
       SUMMARY 
       [0009]    It would be desirable to have means enabling to avoid that a user submits a transponder to unnecessary mechanical stress. 
         [0010]    It would further be desirable to optimize the communication between a transponder (be it a chip card or a mobile device equipped with an NFC router operating as a transponder) and a terminal. 
         [0011]    An embodiment overcomes all or part of the disadvantages of known transponder systems. 
         [0012]    An embodiment provides a method for assisting with positioning of an electromagnetic transponder by a user with respect to a terminal, wherein: 
         [0013]    a first value of the current in an oscillating circuit of the terminal is periodically measured; 
         [0014]    a second value of a ratio between a no-load value of this current, stored when no transponder is in the field of the terminal, and the first value, is calculated; and 
         [0015]    pieces of information intended for the user are controlled according to said second value. 
         [0016]    According to an embodiment, said second value is compared with two thresholds surrounding value 2. 
         [0017]    According to an embodiment, the thresholds are selected according to operating parameters around an optimum coupling position in which the communication between the transponder and the terminal is considered to be optimal. 
         [0018]    According to an embodiment, when said value of the ratio is between the two thresholds, the terminal notifies the user to no longer modify the distance between the transponder and the terminal. 
         [0019]    According to an embodiment, the second value is successively compared with the two thresholds to define whether the user should increase or decrease the distance between the terminal and the transponder. 
         [0020]    According to an embodiment, said second value is compared with the value of said ratio calculated in a previous measurement to determine whether the distance between the transponder and the terminal varies. 
         [0021]    According to an embodiment, said pieces of information indicate to the user whether he should decrease or increase the distance between the transponder and the terminal or not modify this distance. 
         [0022]    An embodiment provides an electromagnetic transponder read terminal comprising means capable of implementing the method. 
         [0023]    An embodiment also provides a cell phone comprising such a terminal. 
         [0024]    The foregoing and other objects, features, and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  very schematically shows an example of a transponder near-field communication system; 
           [0026]      FIG. 2  is a simplified block diagram of the terminal of  FIG. 1 ; 
           [0027]      FIG. 3  is a simplified block diagram of the transponder of  FIG. 1 ; 
           [0028]      FIG. 4  illustrates an example of the variation of the voltage across the resonant circuit of the transponder according to a normalized coupling; 
           [0029]      FIGS. 5A ,  5 B, and  5 C illustrate an embodiment of the method for assisting the communication between a transponder and a reader; 
           [0030]      FIG. 6  illustrates the variation of a current ratio in the oscillating circuit of the reader according to the coupling; and 
           [0031]      FIG. 7  is a block diagram illustrating an implementation mode of the communication assistance method. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The same elements have been designated with the same reference numerals in the different drawings. For clarity, only those steps and elements which are useful to the understanding of the described embodiments have been shown and will be detailed. In particular, the origin and the destination of the data transmitted in communications between a transponder and a terminal have not been detailed, the described embodiments being compatible with any usual communication. 
         [0033]      FIG. 1  very schematically shows an example of a communication and remote-supply system comprising a terminal  1  or read and/or write terminal, and a transponder  2 . 
         [0034]    Generally, terminal  1  comprises a series oscillating circuit, formed of an inductance L 1  in series with a capacitor C 1  and a resistor R 1 . This series oscillating circuit is controlled by a device  11  comprising, among others and without this being a limitation, an amplifier or antenna coupler and a transmission control and exploitation circuit especially comprising a modulator/demodulator and a command and data processing circuit (generally, a microprocessor). Device  11  generally communicates with different input/output circuits (keyboard, display, element of exchange with a server, etc.) and/or processing circuits, not shown. The elements of terminal  1  most often draw the power necessary to their operation from a supply circuit (not shown) connected, for example, to the power line distribution system (mains) or to a battery (for example, that of an automobile vehicle or of a portable telephone or computer). 
         [0035]    A transponder  2  capable of cooperating with terminal  1  comprises an oscillating circuit, for example, parallel, formed of an inductance L 2  in parallel with a capacitor C 2  between two input terminals  22  and  23  of a control and processing circuit  21 . Terminals  22  and  23  are, in practice, connected to input terminals of a rectifying element (not shown in  FIG. 1 ) having output terminals forming terminals for supplying the circuits internal to the transponder. Such circuits generally comprise a memory and a modulator for transmitting data to the terminal. According to the transponder type (depending on the application and on the tasks that it is supposed to perform), these circuits may also comprise a demodulator of the signals that may be received from the terminal, a microprocessor, and various other processing circuits. 
         [0036]    The oscillating circuits of the terminal and of the transponder are generally tuned to a same frequency corresponding to the frequency of an excitation signal of the oscillating circuit of the terminal. This high-frequency signal (for example, at 13.56 MHz) is used not only as a data transmission carrier from the terminal to the transponder, but also as a remote-supply carrier for the transponders located in the field of the terminal. When a transponder  2  is in the field of terminal  1 , a high-frequency voltage is generated between terminals  21  and  23  of the resonant circuit of the transponder. This voltage is used to provide the power supply voltage of electronic circuits  21  of the transponder. 
         [0037]      FIG. 2  is a block diagram of an embodiment of a terminal  1 . As indicated previously, the terminal comprises an oscillating circuit formed of an inductance or antenna L 1  in series with a capacitive element C 1  and with a resistive element R 1 . In the example of  FIG. 2 , these elements are connected between an output terminal  12  of an amplifier or antenna coupler  14  and a terminal  13  at a reference voltage (generally the ground). In  FIG. 2 , resistor R 1  is assumed to be comprised in block  14 . An element  15  for measuring the current in the oscillating circuit is interposed, for example, between capacitive element C 1  and ground  13 . Measurement element  15  belongs to a phase regulation loop which will be described hereafter. Amplifier  14  receives a high-frequency transmission signal E originating from a modulator  16  (MOD) which receives a reference frequency (signal OSC), for example, from a quartz oscillator (not shown). Modulator  16  receives, if need be, a data signal Tx to be transmitted and, in the absence of any data transmission from the terminal, provides the high-frequency carrier (for example, at 13.56 MHz) capable of remotely supplying a transponder. Capacitive element C 1  preferably is a variable-capacitance element controllable by a signal CTRL. The phase of the current in antenna L 1  is regulated with respect to a reference signal. This regulation is a regulation of the high-frequency signal, that is, of the carrier signal corresponding to signal E in the absence of data to be transmitted. The regulation is performed by varying capacitance C 1  of the oscillating circuit of the terminal to maintain the current in antenna L 1  in constant phase relationship with the reference signal. The reference signal for example corresponds to signal OSC provided by the oscillator to the modulator. Signal CTRL originates from a circuit  17  (COMP) having the function of detecting the phase shift with respect to the reference signal and to accordingly modify the capacitance of element C 1 . The phase measurement is, for example, performed from a measurement of current I in the oscillating circuit by means of measurement element  15 . In the shown example, this element is formed of a current transformer comprising a primary winding  151  between element C 1  and ground terminal  13 , and a secondary winding  152  having a first terminal directly connected to ground and having its other terminal providing a signal MES indicative of the result of the measurement. A current-to-voltage conversion resistor  153  is connected in parallel with secondary winding  152 . The result of measurement MES is sent to comparator  17 , which accordingly controls the value of capacitive element C 1  by means of signal CTRL. 
         [0038]    In the embodiment illustrated in  FIG. 2 , comparator  17  uses the same phase demodulator (not shown) as that which is used to demodulate the signal originating from the transponder and which is possibly received by the oscillating circuit. Accordingly, comparator  17  provides a signal Rx giving back a possible retromodulation of the data received from a transponder to a block  18  symbolizing the rest of the electronic circuits of the terminal. 
         [0039]    The response time of the phase regulation loop is selected to be sufficiently long to avoid disturbing the possible retromodulation from a transponder and sufficiently short as compared with the speed at which a transponder passes in the field of the terminal. One can speak of a static regulation with respect to the modulation frequencies (for example, a 13.56-MHz frequency of the remote supply carrier and a 847.5-kHz retromodulation frequency used to transmit data from the transponder to the terminal). 
         [0040]    As a variation of the current transformer of  FIG. 2 , other current measurement elements may be used (for example, a resistor). 
         [0041]    An example of a phase regulation terminal is described in document EP-A-0857981. 
         [0042]      FIG. 3  shows an embodiment of a transponder  2 . Between terminals  22  and  23  of the oscillating circuit (inductance and antenna L 2  and capacitive element C 2  in parallel), is connected a rectifying element  25 , for example, a fullwave rectifying bridge. The rectified outputs of bridge  25  are interconnected by a smoothing capacitive element C 25  and provide a voltage V 25  to a circuit  26  (ALIM) for managing the transponder power supply. Circuit  26  supplies the other transponder circuits, symbolized by a block  27 , with the power necessary to their operation. Elements  25 , C 25 ,  26 , and  27  are, in  FIG. 1 , comprised in block  21 . Circuit  27  samples data between terminals  22  and  23  of the resonant circuit to be able to demodulate the possible data received from the terminal before rectification. Further, circuit  27  comprises so-called retromodulation capacitive and/or resistive elements, not shown, capable of modulating the load (LOAD) formed by the transponder on the field generated by the terminal. This load modification translates, on the terminal side, as a modification of the current or of the voltage of its oscillating circuit (assuming that amplifier or antenna coupler  14 , in  FIG. 2 , is capable of providing a constant current). This current or voltage modification, detected by the current transformer ( 15 ,  FIG. 2 ) or by any other measurement element (for example, the voltage measurement across capacitive element C 1 ), enables the terminal to decode the data received from the transponder. 
         [0043]    The fact that the phase is regulated on the terminal side enables using current and voltage measurements in the oscillating circuit of the terminal to deduce information relative to the transponder coupling when it is in the field of the terminal. 
         [0044]    Such information takes into account, in particular, the coupling between the transponder and the terminal, that is, the coefficient of the coupling between the oscillating circuit of the terminal and that of the transponder. This coupling coefficient essentially depends on the distance separating the transponder from the terminal. The coupling coefficient, designated as k, between the oscillating circuits of a transponder and of a terminal, always ranges between 0 and 1. 
         [0045]    In the embodiments which will be described, different relations between the electric quantities measureable by the terminal in different configurations of operation with a transponder are used to assist the user in positioning the transponder with respect to the terminal. 
         [0046]    The position where the transponder is placed against the terminal is considered as the maximum coupling position. Indeed, the antennas of the transponder and of the terminal cannot be brought closer to each other, unless the terminal package is eliminated. 
         [0047]    It is now known that an optimum coupling position k opt , corresponding to the position at which voltage V C2  recovered across the transponder (more specifically across its antenna) is maximum, exists between the terminal and the transponder. This optimum coupling position does not necessarily correspond to the maximum coupling position. 
         [0048]      FIG. 4  shows an example of the shape of voltage V C2  recovered on the transponder side according to normalized coupling k/k opt . 
         [0049]    The curve starts from the origin of ordinates (zero voltage) for a zero coupling. This corresponds to a distance from the transponder to the terminal such that no signal can be sensed by the transponder. Voltage V C2  reaches a maximum V C2opt  for an optimum coupling coefficient k opt  (k/k opt =1), then decreases to an intermediate value V C2(1)  reached at coupling 1. The maximum coupling position is at a given location of this curve, but not necessarily at the optimum coupling position. This in particular depends on the different values of the capacitive and resistive elements. 
         [0050]    Other remarkable points of the curve of  FIG. 4  are points of inflexion where ratio k/k opt  is respectively equal to 1/√{square root over (3)} and to √{square root over (3)} and where voltage V C2  has the same value on the transponder side. 
         [0051]    Relations expressing voltage value V C2  according to the ratio of the current coupling to the optimum coupling and linking these values to current I in the oscillating circuit of the terminal have become usual. For example, such relations are provided in document EP-A-2114019 (B8723-07-RO-225). 
         [0052]    It is provided to exploit these relations to assist the user holding the transponder in placing it at an optimal distance from the terminal or reader to optimize the communication. 
         [0053]    The position corresponding to a zero coupling ( FIG. 4 ) corresponds to a position of the terminal with no transponder. Current I ( FIG. 2 ) in the antenna or the oscillating circuit of the terminal has a so-called no-load value, noted I V  or I NO-LOAD . 
         [0054]    As indicated, for example, in above-mentioned document EP-A-2114019, the ratio of current coupling k to optimum coupling k opt  is linked to the no-load current and to the current value, noted I, of current I by the following relation: 
         [0000]      ( k/k   opt ) 2   =I   V   /I− 1. 
         [0055]    This relation may also be written as: 
         [0000]        I   V   /I =( k/k   opt ) 2 +1. 
         [0056]    In the optimum coupling position (k=k opt ), the current is I opt =I V /2. Further, there appears from the above formula that, in optimum coupling position, ratio I V /I=2. 
         [0057]      FIGS. 5A ,  5 B, and  5 C illustrate, in simplified representations of respective positions of a terminal  1  and of a transponder  2 , an embodiment of the positioning assistance method for optimizing communications. 
         [0058]    Terminal  1  is assumed to be a mobile telecommunication device of cell phone or smartphone type and transponder  2  is assumed to be a chip card. All that will be described however also applies to the case where the transponder is a telecommunication terminal equipped with an NFC router and where terminal  1  is another mobile device operating in reader mode or is a fixed terminal, etc. 
         [0059]    According to this embodiment, the relative information of ratio I V /I of the no-load current to the current in the oscillating circuit of terminal  1  is exploited to determine whether the transponder needs to be brought closer to or further away from the terminal. It should be noted that, when it is spoken of bringing the transponder closer to or further away from the terminal, this may correspond to moving a terminal away from or closer to the transponder, for example, in the case of a fixed transponder (transponder integrated to posters or the like). 
         [0060]    The example of  FIG. 5A  corresponds to a position in which transponder  2  should be moved closer to terminal  1 . A display  19  of the terminal displays a message (REDUCE DISTANCE) for the user and/or emits a sound signal (BEEP) by means of a loudspeaker  19 ′. A first sound signal frequency or a first sound pulse train is for example provided. 
         [0061]      FIG. 5B  illustrates the case where the transponder should be moved away from the terminal (for example, the case where it would be laid on the terminal and where the optimum coupling position would not correspond to this maximum coupling). In this case, display  19  displays a different message (INCREASE DISTANCE) for the user and/or emits a sound signal at another frequency or a sound pulse train (beeps) at another frequency than in the case of  FIG. 5A . 
         [0062]      FIG. 5C  illustrates the case where transponder  2  is in a position of optimum coupling with respect to terminal  1 . In this case, display  19  notifies it to the user, for example, by a STOP-type message and/or by a different sound signal (for example, a continuous sound signal or a signal at a different frequency than in the two previous cases). 
         [0063]      FIG. 6  illustrates the variation of ratio I V /I according to coupling k. 
         [0064]    This curve is remarkable in that it is linear from the zero coupling (I V /I=1) through the point where the optimum coupling provides a ratio I V /I=2. Two other remarkable points appear on the curve of  FIG. 6 . These points are the points of inflexion in the curve of  FIG. 4 . In the positions corresponding to these points of inflexion, this translates, on the terminal side, as a current ratio I V /I respectively equal to 1.33 (k=k opt /√{square root over (3)}) and 4 (k={square root over (3)}·k opt ). 
         [0065]    It is also known that value V C2max  is reached for a value of current coupling k which is either lower or greater than the optimum coupling. 
         [0066]    Then, measuring current I and knowing no-load current I V  is sufficient to determine current coupling k with respect to optimum coupling k opt . 
         [0067]    It should be noted that when it is spoken of measuring current I, the obtaining of data representative of current I is considered. However, a measurement of the current is preferred to a measurement of the voltage, which is more difficult to compare. 
         [0068]    In a situation where current I is lower than half the no-load current (I V /I&gt;2), the current coupling is greater than optimum coupling k opt  (area B,  FIG. 6 ). The optimal coupling then corresponds to a transponder position more remote from the terminal than when it is laid on it. In other words, the optimum coupling may be reached by drawing the transponder away from the terminal, and there exists a distance between the transponder and the terminal for which recovered voltage V C2  reaches maximum V C2opt . Maximum V C2opt  does not correspond to value V C2max  and value V C2max  is lower than value V C2opt . 
         [0069]    If current I is greater than I V /2 (I V /I&lt;2), the current coupling is lower than the optimum coupling (area A,  FIG. 6 ). This means that optimum coupling k opt  corresponds to a transponder position closer to the terminal. In other words, the optimum coupling may be reached by drawing the transponder closer to the terminal. 
         [0070]    In the two above cases, the transponder to be remotely supplied cannot in principle benefit from the possible voltage maximum V C2opt  to ensure an optimal communication. 
         [0071]      FIG. 7  is a simplified flowchart of an embodiment of the positioning assistance method illustrated in  FIGS. 5A to 5C  and taking advantage of the curve of  FIG. 6 . 
         [0072]    A periodic measurement (block  31 , MES I i ) of current value I i  of the current in the terminal is performed. The measurement periodicity is selected to be as short as possible while remaining compatible with the time necessary to exploit the measurements (to execute the method between two measurements). Current value I i  is then compared (block  32 , I i =I V ?) with the no-load value. In case they are equal (output Y of block  32 ), this means that no transponder is present in the terminal field and the method loops back onto a next measurement of the current value of the current (block  33 , NEXT i ). 
         [0073]    When a transponder is in the field of the terminal, the no-load value is no longer equal to the current value (output N of block  32 ). 
         [0074]    The ratio of the no-load current to current value I i  is then calculated and a comparison (block  34 , I V /I i =I V /I i−1 ?) of this value with the ratio calculated at the previous iteration (i- 1 ) is performed. This test amounts to determining whether the distance between the transponder and the terminal varies. 
         [0075]    If the distance varies (output N of block  34 ), that is, the user moves one of the two elements with respect to the other, it is determined whether the current ratio is within an acceptable range defined by two thresholds MIN and MAX around the ratio equal to 2, that is, around the optimum coupling with an acceptable tolerance. To achieve this, it is for example started by comparing whether the current is lower than the lower threshold (block  35 , I V /I i &lt;MIN?). If it is (output Y of block  35 ), this means that the two elements have to be brought closer to each other (block  36 , REDUCE DISTANCE). If it is not (output N of block  35 ), current value I V /I i  is compared with the maximum threshold (block  37 , I V /I i &gt;MAX?). If maximum threshold MAX is exceeded (output Y of block  37 ), this means that the transponder should be moved away from the terminal since the optimum coupling point has been passed (block  38 , INCREASE DISTANCE). In both cases, a subsequent measurement is performed to verify whether the user has effectively taken the instruction into account (block  33 , NEXT i ). 
         [0076]    If the transponder is within the acceptable distance range (output N of block  37 ), it is displayed or indicated to the user that this position is correct and the he does not need to move any more (block  39 , STOP). 
         [0077]    If the transponder no longer moves with respect to the terminal (output Y of block  34 ), its position with respect to the optimum coupling is examined. For example, it is started by checking whether it is too distant (block  40 , I V /I i &lt;MIN?). If it is (output Y of block  40 ), this means that, although the transponder has been pressed against the terminal, the optimum coupling position cannot be reached by bringing the transponder closer, generally because of the terminal package. The user is then requested to stop (block  39 ). 
         [0078]    If the motionless position corresponds to a position greater than the minimum, it is checked (block  41 , I V /I i &gt;MAX?) whether ratio I V /I i  is greater than the maximum value. If it is (output Y of block  41 ), the user is notified that he should move the transponder away from the terminal (block  38 ). If it is not, he is told to no longer move since the transponder then is within the acceptable range between thresholds MIN and MAX. 
         [0079]    The selection of thresholds MIN and MAX depends on the application and is also performed to provide a hysteresis, which avoids for the notification system to permanently vary. Indeed, it could have been envisaged to directly compare the threshold with value 2. However, this would in practice result, due to the fact that the object is held by a user and is thus sensitive to the displacement of his hand, in an unstable system. 
         [0080]    Various embodiments have been described, many variations and modifications will occur to those skilled in the art. In particular, the selection of the thresholds acceptable for the current ratio and the periodicity of the measurements and of the iterations is within the abilities of those skilled in the art according to the application. Further, the inequality relations may correspond to strict or non-strict inequalities. Further, other notification means than sound or visual indicators may be used. For example, a system causing a vibration of the transponder in the case where it is a mobile telecommunication device equipped with an NFC router and stopping the vibration when the reached position is correct or, conversely, causing a vibration thereof once this reached position is correct, may be provided. Further, the practical implementation of embodiments is within the abilities of those skilled in the art based on the functional indications given hereabove and by using hardware and software tools currently present in transponder systems. 
         [0081]    Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.