Method and device for determining the resonance frequency of a chip card

Abstract

The invention relates to a method and a device for determining the resonance frequency of a chip card (10). The chip card (10) is first exposed to a first magnetic field with a predetermined frequency and an increasing field strength, until a response signal (22) emitted by the chip card (10) is detected by a card reader (30). The first field strength applied to the chip card (10) at the time of the emitted response signal (22) is determined. A differential signal (210) is then detected over a predefined field strength range, and a characteristic differential signal profile (205) at or around the first field strength is determined. Further differential signals are then detected for different frequencies over the predetermined field strength range and the characteristic differential signal profile is identified in the further differential signals. From among further differential signals, the differential signal in which the characteristic differential signal profile occurs at the lowest field strength value is identified, and the frequency associated with this differential signal is output as the resonance frequency of the chip card (10).

Description

[0001] Method and device for determining the resonance frequency of a chip card

[0002] Technical area

[0003] The invention relates to a method and a device for determining the resonance frequency of a chip card, in particular for chip cards containing a microcontroller with RFID (radio frequency identification) properties, or a so-called dual-interface chip card.

[0004] background

[0005] Card-shaped data storage devices, especially chip cards, are used in many areas, for example, for cashless payment transactions, as identification documents, or to verify access authorizations. In the context of this description, such data storage devices are referred to as chip cards for all applications.

[0006] A chip card comprises a card body and an integrated circuit embedded in the card body, for example, in the form of a chip module with a chip. The chip module is inserted into a cavity or module opening in the card body.

[0007] Chip cards can contain an integrated electrical oscillating circuit through which energy can be transferred to the chip card's electronic components. This is typically achieved by supplying energy to the oscillating circuit via a magnetic field. This energy can then be used to perform the chip card's processing and contactless communication functions. For example, chip card controllers with RFID functionality can be used. The oscillating circuit is formed by a coil with an additional capacitor on the chip module.

[0008] A chip card can also be a so-called dual interface (DI) card with corresponding functionality, in which the card body is made partially or entirely of metal. Such a card works by using a chip module that contains a coil (coil-on module). This coil couples to the metallic card body.

[0009] Dual-interface chip cards are chip cards that can be used for both contact and contactless communication. When used as bank cards or credit cards, they are typically in the so-called ID-I format (according to ISO 7810). However, the present invention is not limited to this format. Contact communication occurs via exposed contact areas, the so-called contact pad, while contactless communication generally occurs via an antenna coil inside the card body and a resonant circuit as described above. Both the contact areas and the antenna coil are electrically connected to an IC chip.

[0010] Description of the invention

[0011] The task can be considered to be to reliably determine the resonance frequency of a chip card designed for contactless communication.

[0012] This object is achieved by a method and a device for determining the resonance frequency of a chip card. Further embodiments emerge from the dependent claims and the following description.

[0013] According to one aspect, a method for determining the resonant frequency of a chip card is provided. The method comprises the following steps: generating, with an excitation coil, a first magnetic field using a signal output by an excitation unit with a predetermined frequency and a variable field strength over a predetermined field strength range; applying the first magnetic field to the chip card;

[0014] Detecting, with a card reader, a response signal of the chip card while the chip card is in a first position with respect to the excitation coil and the card reader is in a reading position with respect to the chip card;

[0015] Detecting, with a detection unit, a first field strength value of the first magnetic field acting on a measuring coil at the time the card reader detects the response signal, wherein the excitation coil is arranged between the chip card and the measuring coil; Generating, with the excitation coil, a second magnetic field using signals from the excitation unit with the predetermined frequency and the variable field strength over the predetermined field strength range, which contains the first field strength value;Detecting, with the detection unit, a difference signal between a first receiving coil and a second receiving coil over the predetermined field strength range and at the predetermined frequency of the second magnetic field, wherein the excitation coil is arranged between the first receiving coil and the second receiving coil, while the chip card is arranged adjacent to the first receiving coil and the measuring coil is arranged adjacent to the second receiving coil; Identifying, with a control arrangement, a characteristic difference signal curve in the detected difference signal at the first field strength value; Detecting, with the detection unit, further difference signals between the first receiving coil and the second receiving coil over the predetermined field strength range and at different frequencies of the second magnetic field;Identifying, with the control arrangement, the characteristic difference signal curve in the detected further difference signals, as well as a respective field strength value belonging to the characteristic difference signal curve; Determining, with the control arrangement, a lowest field strength value at which the characteristic difference signal curve was identified, as well as the frequency whose associated difference signal contains the characteristic difference signal curve at the lowest field strength value; Outputting, with the control arrangement, the frequency whose associated difference signal contains the characteristic difference signal curve at the lowest field strength value as the resonant frequency of the chip card.

[0016] The method described here can be used to determine the resonant frequency of a chip card designed for contactless information exchange. A chip card, as defined in this description, is functionally defined by its components and their functions and can take any structural form. A device with an embedded integrated circuit, for example, in the form of a chip module with a chip, as well as an electrical resonant circuit that supplies power to the integrated circuit, is considered a chip card.

[0017] The excitation coil, the first receiving coil, the second receiving coil, and the measuring coil are, for example, components of a measuring device. The excitation unit, the card reader, the detection unit, and the control arrangement are also components of the measuring device and are connected to the aforementioned coils to carry out the method steps.

[0018] The method makes it possible to reliably determine the resonance frequency of the chip card and thus to examine both a single chip card and the properties of an entire series of chip cards with a specific design.

[0019] The design of the measuring device is described below. The configuration of each individual coil is predetermined. The excitation unit outputs an electrical signal with a voltage and a current at a specified frequency. This electrical signal is dimensioned such that the coil exposed to the electrical signal generates a magnetic field with the desired field strength, which is expressed in amperes / meter (A / m).

[0020] The magnetic field is used to inject energy into the chip card. Once the chip card has received sufficient energy, the active electronic components of the chip card can begin operating, performing processing operations and generating signals that are sent via a transmitter. This enables information and data exchange between the chip card and the card reader.

[0021] The proportion of energy fed into or transferred from the magnetic field to the chip card is higher the closer the so-called coupling factor is to the value 1. The coupling factor, in turn, is closer to the value 1 the closer the frequency of the magnetic field is to the resonant frequency of the chip card (more precisely: of an oscillating circuit of the chip card). Due to various factors such as component tolerances and / or previously unknown properties of components used, the resonant frequency of the chip card is often not known with the desired accuracy. This has the consequence that the communication between a card reader and a chip card is disrupted (e.g. the connection or data exchange between the card reader and the chip card does not establish or the connection is interrupted) because the card reader operates at a predetermined frequency and the resonant frequency of the chip card deviates from the frequency of the card reader to a not insignificant extent.

[0022] The method described here can be used to reliably determine the resonance frequency of a chip card and then, if necessary, to modify the design of the chip card to achieve a better coupling factor between the magnetic field and the chip card.

[0023] In practice, a card reader generates a magnetic field with a predetermined field strength at a predetermined (fixed) frequency. This magnetic field transfers energy to the chip card. Once the chip card has sufficient energy, it exchanges data with the card reader.

[0024] In the method described here, the magnetic field is not generated by the card reader, but by the excitation coil in cooperation with the excitation unit. The excitation coil is arranged centrally and at the same distance from the receiving coils. The magnetic field generated at this time and in this method step is referred to as the first magnetic field. Both the field strength and the frequency of the first magnetic field can be varied using the excitation unit, because both occur at different times or in different steps in the method. In this case, the card reader is limited to passively receiving the response signal emitted by the chip card. The first magnetic field is generated with increasing field strength, and the chip card's response to this is recorded. It is now known at which field strength value in conjunction with the specified frequency the chip card sends a response signal.However, it is unknown whether the specified frequency of the first magnetic field corresponds to the resonant frequency of the chip card or is close to this resonant frequency. To determine the frequency of a magnetic field that is close to the resonant frequency of the chip card, the behavior of the chip card is first recorded at the specified frequency over a specified field strength range. Subsequently, the behavior of the chip card is recorded over the same field strength range at frequencies deviating from the specified frequency. The frequency for which the best coupling factor between the magnetic field and the chip card was measured is then determined.

[0025] First, the field strength of the first magnetic field is increased at a predetermined frequency in order to determine at which field strength the chip card sends a response signal, which is detected by the card reader. Then, using the excitation coil and the excitation unit, a second magnetic field is generated at the predetermined frequency and with a variable field strength over a predetermined field strength range. The chip card is exposed to this second magnetic field. Due to its properties, the chip card absorbs energy from the second magnetic field and influences the second magnetic field. This influence, in turn, can be detected by the first receiving coil and the second receiving coil. The chip card is adjacent to one of the receiving coils (the first receiving coil).The other receiving coil (the second receiving coil) is arranged at a distance from the first receiving coil, so that the excitation coil lies between the first receiving coil and the second receiving coil. The detection unit detects a signal from each of the first receiving coil and the second receiving coil and forms a difference signal. The detection unit detects a voltage signal from each receiving coil and determines the difference from this. The voltage difference forms the difference signal as voltage versus field strength. This difference signal is an indicator of differences in the magnetic field in the area of ​​the first and second receiving coil. The differences arise because the chip card is arranged adjacent to the first receiving coil and the chip card draws energy from the magnetic field.

[0026] The behavior of the chip card is detected over the larger field strength range by detecting the difference signal between the first receiving coil and the second receiving coil, which are exposed to the generated second magnetic field.

[0027] From this difference signal, a characteristic difference signal waveform is identified, indicating the point at which the chip card receives sufficient energy to begin operating. This is typically also the point at which the card reader detects the response signal from the chip card. This characteristic difference signal waveform indicates the point at which the chip card receives sufficient energy from the magnetic field to send the response signal. For example, the characteristic difference signal waveform is the beginning of a sudden increase or decrease in the value of the difference signal, indicating that the chip card is absorbing energy from the magnetic field.

[0028] We now know which value of the field strength is necessary at the given frequency for the chip card to start operating and send a response signal, as well as the influence of the chip card on the magnetic field (the difference signal) at the given frequency and over a given field strength range.

[0029] To determine the resonant frequency of the chip card, or to approximate it, additional differential signals are recorded over the same specified field strength range at different frequencies. This step serves to identify the field strength values ​​at the different frequencies at which the chip card sends the response signal. The lower the field strength at which the chip card sends the response signal, the higher the coupling factor between the magnetic field and the chip card, and the closer the frequency of the magnetic field is to the resonant frequency of the chip card.

[0030] To determine this resonant frequency with the highest possible accuracy, the characteristic difference signal curve at which the chip card sent the response signal is identified in all difference signals recorded at different frequencies across the specified field strength range. Then, for each characteristic difference signal curve, the corresponding field strength value is identified, and the control system determines the lowest field strength value at which the characteristic difference signal curve was identified. Using this information, the control system can determine the frequency of the corresponding difference signal, which contains the characteristic difference signal curve at the lowest field strength value, and output this frequency as the chip card's resonant frequency.

[0031] If a measuring tower is used that is designed to measure the field strength at a given measuring frequency, for example 13.56 MHz, a correction factor can be applied to the measured field strength for measurements at other frequencies. As described here, the measuring tower can be operated at different frequency values ​​within a frequency range. Depending on the design of the measuring tower, the measured field strength at different frequencies can be adjusted in the form of a correction factor, for example as a factor that is multiplicatively applied to the measured field strength value. If, for example, a field strength measurement deviates from the stated 13.56 MHz at 16 MHz, the correction value determined for this frequency is applied to the field strength measured at 16 MHz.

[0032] According to one embodiment, the predetermined field strength range for generating the first magnetic field and the second magnetic field is between 0 A / m and 7.5 A / m.

[0033] The predetermined field strength range does not necessarily extend over the entire range from 0 A / m to 7.5 A / m (preferably including both of these values), but may also extend over only a part of it, in particular if the first magnetic field is generated in order to check at which field strength value the chip card first sends a response signal that is received by the card reader.

[0034] The chip cards tested in this method can, for example, be designed to transmit a response signal when the magnetic field has a field strength of 1.5 A / m. It is not impossible for a chip card to transmit the response signal at a lower field strength. Thus, for example, a field strength range from 0 A / m to 2 A / m or from 0 A / m to 1.5 A / m (both inclusive) can be used to generate the first magnetic field.

[0035] However, to detect the differential signal between the first receiving coil and the second receiving coil, the entire field strength range from 0 A / m to 7.5 A / m is preferably used. This allows the variation of the differential signal to be detected over the entire field strength range, and the behavior of the chip card (i.e., the influence of the chip card on the differential signal) to be detected accordingly over the entire field strength range.

[0036] According to a further embodiment, the card reader is removed from the reading position after detecting the response signal with the card reader and before generating the second magnetic field.

[0037] In other words, the card reader is initially required to detect the response signal from the chip card. Once the response signal and the associated first field strength value of the first magnetic field have been detected, the card reader can be removed from its reading position. Thus, the card reader is also removed from the detection range of the first receiving coil and the second receiving coil and does not affect the process of detecting the differential signal between the first receiving coil and the second receiving coil.

[0038] According to a further embodiment, the characteristic difference signal curve at the first field strength value corresponds to a voltage curve of the difference signal in an environment of the first field strength value.

[0039] The characteristic differential signal curve, which represents the curve of the differential signal (as the voltage difference between the voltage values ​​of the first and second receiving coils) when the response signal is transmitted by the chip card, corresponds, for example, to a voltage curve of the differential signal around the first field strength value. The characteristic differential signal curve corresponds, for example, to the curve of the differential signal between -5% and +5% of the measured first field strength value when the response signal is detected. It is conceivable to also detect the characteristic differential signal curve in other field strength ranges around the first field strength value, for example, from -10% to +10% of the first field strength value.In particular, the characteristic difference signal curve is extracted from the difference signal in a field strength range that allows recognition of the characteristic difference signal curve in the difference signals acquired at other frequency values.

[0040] According to a further embodiment, the different frequencies of the second magnetic field at which the further difference signals are detected between the first receiving coil and the second receiving coil are distributed around the predetermined frequency at which the first magnetic field is generated such that some frequencies are higher and others lower than the predetermined frequency at which the first magnetic field is generated.

[0041] For example, the frequencies of the second magnetic field can be distributed symmetrically around the predetermined frequency with which the first magnetic field is generated. This means, for example, that in a first further measurement, the second magnetic field is generated at a specific frequency across the entire field strength range, and the difference signal is recorded, whereby the specific frequency with which the second magnetic field is generated is a specific frequency value lower than the predetermined frequency of the first magnetic field. In a second further measurement, the frequency is higher than the predetermined frequency of the first magnetic field by the same specific frequency value. In this way, the entire frequency range under investigation can gradually move away from the predetermined frequency of the first magnetic field, both upwards and downwards.

[0042] The frequencies of the second magnetic field can deviate in steps of 0.1 MHz from the specified frequency at which the first magnetic field is generated.

[0043] According to a further embodiment, the predetermined frequency at which the first magnetic field is generated is 13.56 MHz.

[0044] According to a further embodiment, the chip card has a chip module which has a microcontroller with RFID properties or a dual interface chip.

[0045] According to a further aspect, a measuring device for determining the resonance frequency of a chip card is specified. The measuring device has the following components: a measuring tower comprising a first carrier plate, a second carrier plate, a third carrier plate, a first receiving coil arranged on the first carrier plate, a second receiving coil arranged on the third carrier plate, an excitation coil arranged on the second carrier plate, and a measuring coil. The second carrier plate is arranged between the first carrier plate and the third carrier plate. The first carrier plate is designed to receive and hold the chip card in a predetermined position. The measuring coil is arranged on the third carrier plate such that the measuring coil and the chip card are at the same distance from the excitation coil in the predetermined position.The measuring device further comprises a card reader, an excitation unit, a detection unit, and a control arrangement. The control arrangement is connected to the card reader, the excitation unit, and the detection unit and is configured to control the card reader, the excitation unit, and the detection unit such that the method is carried out as described herein.

[0046] According to one embodiment, a first distance between the predetermined position of the chip card and the excitation coil is equal to a second distance between the measuring coil and the excitation coil.

[0047] According to a further embodiment, the first receiving coil and the second receiving coil are equidistant from the excitation coil.

[0048] The measuring device executes the method described here. It should therefore be understood that the steps described in connection with the method can be implemented as functions of the measuring device or the control arrangement. These steps or functions will not be repeated here; rather, reference is made to the explanations in the context of the method.

[0049] In addition to the information described here, the differential signal can also provide further information about the operation and function of the chip card. For example, it is possible to determine at what magnetic field strength the chip card operates in saturation, and further energy absorbed from the magnetic field can no longer be supplied to the chip and must be dissipated as waste heat. The differential signal indicates at what field strength this point is reached. This makes it possible to determine whether a chip card can even withstand a required maximum magnetic field strength without being damaged by overheating.

[0050] Short description of the characters

[0051] Some details are described in more detail below using the attached drawings. The illustrations are schematic and not to scale. Like reference numerals refer to like or similar elements. They show:

[0052] Fig. 1 is a schematic representation of a so-called dual-interface chip card; Fig. 2 is a schematic representation of a chip card;

[0053] Fig. 3 is a schematic diagram of a chip module;

[0054] Fig. 4 is a schematic representation of a measuring device;

[0055] Fig. 5 is a schematic representation of a diagram with a

[0056] differential signal;

[0057] Fig. 6 is a schematic representation of a diagram with several difference signals recorded at different frequencies of a magnetic field;

[0058] Fig. 7 is an enlarged section of the illustration in Fig. 6, showing the characteristic differential signal waveforms of several differential signals at a field strength leading to the response signal of a chip card;

[0059] Fig. 8 is a schematic representation of the steps of a method for determining the resonance frequency of a chip card.

[0060] Detailed description

[0061] Fig. 1 shows a schematic plan view of a dual-interface chip card 10 in ID-I format with a card body 11. An antenna coil 19 and a chip module 12 are arranged in the card body 11 of the chip card 10. The antenna coil 19 has a contact connection 19-1, 19-2 at each of its two open ends, via which the antenna coil 19 is conductively connected to the chip module 12. The antenna coil 19 is used for contactless communication between an external card reader 30 (see Fig. 4) and the chip module 12. For contact-based communication with the chip module 12, the chip module 12 has a contact pad 19-3 with several separate contact areas.

[0062] Fig. 2 shows a chip card 10 with a card body 11 in an alternative embodiment. The card body 11 can be made of a plastic such as PVC, polycarbonate, or the like. The card body can comprise a metallic layer (not shown here), the main surfaces of which can each be covered with a plastic layer. A metallic layer can be present, for example, in the form of a core or a layer of a stainless steel alloy, for example, with a thickness of 400 μm. The thickness of the card body

[0063] For example, 11 can be between 50 pm and 920 pm.

[0064] The chip card 10 comprises a chip module 12, which is inserted into a main surface 13 of the card body 11 or the chip card 10. The chip module 12 can be inserted into a module opening or cavity. The cavity can comprise a central blind hole and a peripheral edge region. Here, the cavity is concealed by the inserted chip module 12. The chip module 12 can be glued or otherwise secured in the cavity, for example, held therein by a clamping force.

[0065] Chip module 12 contains a coil 16. Coil 16 typically has a plurality of turns, for example, approximately 12 to 16 turns. The turns run, for example, concentrically around a chip or an electronic circuit of chip module 12. The width of a turn can be 50 μm to 70 μm, and the spacing between two turns can be 100 μm. The turns can have copper thicknesses of up to approximately 30 μm.

[0066] The chip can be implemented, for example, in the form of an integrated circuit and is, for example, in a potting compound on the underside of the chip module

[0067] 12. The integrated circuit is supplied with power and / or signals via the coil. This allows an electromagnetic field to be coupled into the coil. For example, the integrated circuit can be or contain a chip card controller with RFID functionality.

[0068] Fig. 3 shows an equivalent circuit diagram of the chip module 12 of the chip card 10. The chip module 12 comprises the integrated circuit 14, for example in the form of a chip. The integrated circuit 14 can, for example, be soldered onto the chip module 12 or applied to the chip module 12 using flip-chip assembly. The integrated circuit 14 contains a card controller for the chip card 10. The integrated circuit 14 typically contains a processor for executing control functions for the chip card 10 and for communication, and for executing computing operations, for example, for security functions. Furthermore, the integrated circuit 14 contains a memory area for storing and / or making data available.

[0069] The integrated circuit 14 further contains a capacitor 15 with a suitable capacitance, which influences the resonant frequency of the oscillating circuit. The capacitance is in the range of a few pF, for example, 78 pF. The coil 16 is connected in parallel with the integrated circuit 14.

[0070] Coil 16 and capacitor 15 of integrated circuit 14 form an oscillating circuit. This oscillating circuit allows chip module 12 to communicate with a reader external to chip card 10 (see, for example, card reader 30 in Fig. 4), a production machine, or even a measuring device (see Fig. 4, measuring tower 20). The reader applies energy to coil 16 via an electromagnetic field, thereby activating and operating integrated circuit 14. Coil 16 functions in the same way as antenna coil 19 in Fig. 1.

[0071] The integrated circuit 14 has a processor 17, whose operating speed or computing power depends on the applied field strength. When the electromagnetic field strength reaches a minimum, the processor 17 and the integrated circuit 14 start operating. As the field strength increases, the operating frequency of the processor 17 and the integrated circuit 14 also increases, and thus the processing speed. Beyond a certain threshold frequency, the operating frequency no longer increases. The processor 17 and the integrated circuit 14 are in saturation and operate at maximum frequency.

[0072] Thus, a correlation can be established between different values ​​of the electromagnetic field strengths and a corresponding performance of the integrated circuit 14 or the processor 17 located therein.

[0073] The chip card 10 can be a so-called D1 card, with a high-quality connection technology between the integrated circuit 14 and the coil 16. This is preferably either a soldered connection or a welded connection.

[0074] In addition, this chip card 10 can be equipped with an operating system (OS) that can receive and send data at a predetermined carrier frequency, for example 13.56 MHz.

[0075] Fig. 4 shows a schematic diagram of a measuring device 100 for determining the resonant frequency of a chip card 10. The measuring device 100 is constructed, for example, according to ISO / IEC 14443. Via an excitation coil 21, the electromagnetic field strength of the magnetic field H generated by the excitation coil 21 is first scanned or adjusted at a predetermined frequency, for example 13.56 MHz, within a predetermined field strength range, for example from 0 A / m to 7.5 A / m. From a certain field strength, the chip card 10 receives sufficient energy for the chip module 12 to begin operation and receive and send information. For example, when the chip card receives sufficient energy, it transmits a signal (also: response signal) 22 in the form of a data packet, for example an activation sequence, a so-called ATS, which is received by the card reader 30.

[0076] The control arrangement 60 controls the excitation unit 40 so that it outputs an electrical signal with a predetermined voltage, current and frequency to the excitation coil 21 so that the magnetic field is generated with the corresponding or desired field strength and frequency.

[0077] The card reader 30 transmits the data received from the chip card 10 to the control arrangement 60. Likewise, the detection unit 50 transmits the measured values ​​it detects (signal at the measuring coil 25 and the difference signal between the first receiving coil and the twenty-third second receiving coil 24) to the control arrangement 60.

[0078] Because chip card 10 and measuring coil 25 are arranged at the same distance from excitation coil 21, the field strength detected by measuring coil 25 also corresponds to the field strength applied to chip card 10. Thus, control arrangement 60 is able to determine the field strength at which chip card 10 receives sufficient energy to transmit response signal 22.

[0079] In the described construction, the chip card 10, the excitation coil 21 and the measuring coil 25 are preferably arranged along an axis, ie they are arranged linearly, and the excitation coil 21 is arranged centrally and at the same distance between the chip card 10 and the measuring coil 25.

[0080] Once the field strength of the magnetic field at which the chip card 10 sends the response signal two 20 is known, the card reader 30 can be removed from the reading position shown in Fig. 4. The control arrangement 60 now controls the excitation unit 40 such that, at the predetermined frequency, a magnetic field with increasing field strength is generated within a predetermined field strength range. The chip card 10 is still in the position shown in Fig. 4. The detection unit 50 now detects a voltage signal output by the first receiving coil 23 and the second receiving coil 24 and determines therefrom a difference signal as the difference between the voltage at the first receiving coil and the voltage at the second receiving coil.Since the chip card 10 is arranged adjacent to the first receiving coil 23, the chip card 10 draws energy from the magnetic field at this position, thereby influencing a voltage signal output by the first receiving coil 23, depending on the energy absorbed by the chip card 10. The greater the amount of energy the chip card 10 absorbs from the magnetic field, the greater the difference signal between the first receiving coil 23 and the second receiving coil 24 becomes. The difference signal is detected over a predetermined field strength range. This results in a difference signal 210 as shown in Fig. 5.

[0081] Fig. 5 shows a diagram 200 in which the difference signal 210 is plotted as a curve of the voltage 201 between the first receiving coil and the second receiving coil against the field strength 202 of the magnetic field. Various operating points of the chip card 10 can be derived from this difference signal 210. At 203, the chip card 10 operates in an analog range, at 204 a reset function is enabled, and at 205 the chip card 10 begins to absorb energy from the magnetic field and is capable of exchanging data and sending the response signal 22. In the present example, this is the case at a field strength value of 0.55 A / m. At 206, the chip card 10 is fully operational and can receive data, execute operations, and send data.

[0082] From the measurement using card reader 30, the field strength value at which chip card 10 sent response signal 22 is known. This field strength value associated with response signal 22 is now identified in diagram 200 of Fig. 5 in differential signal 210, and the profile of differential signal 210 at this field strength value is defined as the characteristic differential signal profile. In the illustration of Fig. 5, this is the region of differential signal 210 in which the value of the differential signal increases sharply at 205.

[0083] Now, additional difference signals 210 are acquired for different magnetic field frequencies using the same measurement setup and over the same field strength range. These additional difference signals are shown in diagram 200 in Fig. 6. It can be seen that, quantitatively speaking, the difference signals for different frequencies have slightly different profiles. This is due to the fact that the coupling factor between the magnetic field and the chip card varies for different magnetic field frequencies, and thus the energy input into the chip card also varies.

[0084] In any case, it can be seen from the illustration in Fig. 6 that the characteristic differential signal curve, at which the voltage value of the measured differential signal between the first receiving coil and the second receiving coil rises sharply at 205, occurs at different field strength values. From these multiple differential signals, the one can now be identified in which the characteristic differential signal curve 205 occurs at the lowest field strength (i.e., furthest to the left in the illustration in Fig. 6). The frequency associated with the identified differential signal is closest to the resonant frequency of the chip card, which results from the fact that the chip card has absorbed sufficient energy at the lowest field strength to transmit the response signal.

[0085] Fig. 7 shows an enlarged view of diagram 200 from Fig. 6 to identify the characteristic signal curve 205 for the multiple differential signals. In this illustration in Fig. 7, the arrow of reference numeral 205 points to the differential signal that increases sharply at the lowest field strength value.

[0086] Fig. 8 shows a schematic representation of the steps of a method 300 for determining the resonant frequency of a chip card 10, as also described with reference to Figs. 4 to 7. In a step 302, a first magnetic field H is generated with an excitation coil 21 using a signal output by an excitation unit 40 with a predetermined frequency and a variable field strength over a predetermined field strength range. In a step 304, the first magnetic field H is applied to the chip card 10. In a step 306, a response signal 22 is detected with a card reader 30 while the chip card 10 is in a first position with respect to the excitation coil 21 and the card reader 30 is in a reading position with respect to the chip card 10.In a step 308, a first field strength value of the first magnetic field H acting on a measuring coil 25 is detected by a detection unit 50 at the time when the card reader 30 detects the response signal 22, with the excitation coil 21 arranged between the chip card 10 and the measuring coil 25. In a step 310, a second magnetic field H is generated with the excitation coil 21 using signals from the excitation unit 40 with the predetermined frequency and the variable field strength over the predetermined field strength range containing the first field strength value.In a step 312, the detection unit 50 detects a difference signal 210 between a first receiving coil 23 and a second receiving coil 24 over the predetermined field strength range and at the predetermined frequency of the second magnetic field H, wherein the excitation coil 21 is arranged between the first receiving coil 23 and the second receiving coil 24, while the chip card 10 is arranged adjacent to the first receiving coil 23 and the measuring coil 25 is arranged adjacent to the second receiving coil 24. In a step 314, a control arrangement 60 is used to identify a characteristic difference signal curve 205 in the detected difference signal 210 at the first field strength value. In a step 316, the detection unit 50 detects further difference signals 210 between the first receiving coil 23 and the second receiving coil 24 over the predetermined field strength range and at different frequencies of the second magnetic field H.In a step 318, the control arrangement 60 identifies the characteristic difference signal curve 205 in the detected additional difference signals 210, as well as a respective field strength value associated with the characteristic difference signal curve 205. In a step 320, the control arrangement 60 determines a lowest field strength value at which the characteristic difference signal curve 205 was identified, as well as the frequency whose associated difference signal 210 contains the characteristic difference signal curve 205 at the lowest field strength value. In a step 320, the control arrangement 60 outputs the frequency whose associated difference signal 210 contains the characteristic difference signal curve 205 at the lowest field strength value as the resonant frequency of the chip card 10.

[0087] Additionally, it should be noted that "comprising" or "having" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations.

[0088] List of reference symbols

[0089] 10 chip card

[0090] 11 Card body

[0091] 12 chip module

[0092] 13 Main area

[0093] 14 integrated circuit

[0094] 15 Capacitor

[0095] 16 coil

[0096] 17 processor

[0097] 18 storage

[0098] 19 Antenna coil

[0099] 19-1 Contact connection

[0100] 19-2 Contact connection

[0101] 19-3 Contact pad

[0102] 20 measuring tower

[0103] 21 Excitation coil

[0104] 22 card signal

[0105] 23 first receiving coil

[0106] 24 second receiving coil

[0107] 25 measuring coil

[0108] 28-1 first carrier plate

[0109] 28-2 second carrier plate

[0110] 28-3 third carrier plate

[0111] 30 card readers

[0112] 40 excitation unit

[0113] 50 recording units

[0114] 60 Tax Order

[0115] 100 measuring device

[0116] 200 diagram

[0117] 201 Voltage Field strength Operating point (RF analog range) Operating point (reset enabled) Operating point, characteristic differential signal curve (T-CL communication, resonance frequency) Internal control Signal curve, differential signal (voltage vs. field strength) Procedure -322 process steps

Claims

Patent claims 1 . Method (300) for determining the resonance frequency of a chip card (10), the method comprising the following steps: Generating (302), with an excitation coil (21), a first magnetic field (H) using a signal output by an excitation unit (40) with a predetermined frequency and a variable field strength over a predetermined field strength range; Applying (304) the first magnetic field (H) to the chip card (10); detecting (306), with a card reader (30), a response signal (22) of the chip card (10) while the chip card (10) is in a first position with respect to the excitation coil (21) and the card reader (30) is in a reading position with respect to the chip card (10); Detecting (308), with a detection unit (50), a first field strength value of the first magnetic field (H) acting on a measuring coil (25) at the time when the card reader (30) detects the response signal (22), wherein the excitation coil (21) is arranged between the chip card (10) and the measuring coil (25); Generating (310), with the excitation coil (21), a second magnetic field (H) using signals from the excitation unit (40) with the predetermined frequency and the variable field strength over the predetermined field strength range which contains the first field strength value; Detecting (312), with the detection unit (50), a difference signal (210) between a first receiving coil (23) and a second receiving coil (24) over the predetermined field strength range and at the predetermined frequency of the second magnetic field (H), wherein the excitation coil (21) is arranged between the first receiving coil (23) and the second receiving coil (24), while the chip card (10) is arranged adjacent to the first receiving coil (23) and the measuring coil (25) is arranged adjacent to the second receiving coil (24); Identifying (314), with a control arrangement (60), a characteristic difference signal curve (205) in the detected difference signal (210) at the first field strength value; Detecting (316), with the detection unit (50), further difference signals (210) between the first receiving coil (23) and the second receiving coil (24) over the predetermined field strength range and at different frequencies of the second magnetic field (H); Identifying (318), with the control arrangement (60), the characteristic difference signal curve (205) in the detected further difference signals (210), as well as a respective field strength value belonging to the characteristic difference signal curve (205); Determining (320), with the control arrangement (60), a lowest field strength value at which the characteristic difference signal curve (205) was identified, as well as the frequency whose associated difference signal (210) contains the characteristic difference signal curve (205) at the lowest field strength value; Outputting (322), with the control arrangement (60), the frequency whose associated difference signal (210) contains the characteristic difference signal curve (205) at the lowest field strength value, as the resonance frequency of the chip card (10).

2. The method (300) according to claim 1, wherein the predetermined field strength range for generating the first magnetic field and the second magnetic field is between 0 A / m and 7.5 A / m.

3. Method (300) according to claim 1 or 2, wherein after detecting (306) the response signal (22) with the card reader (30) and before generating (310) the second magnetic field, the card reader (30) is removed from the reading position.

4. Method (300) according to one of the preceding claims, wherein the characteristic difference signal curve (205) in the first Field strength value corresponds to a voltage curve of the difference signal (210) in an environment of the first field strength value.

5. The method (300) according to any one of the preceding claims, wherein the different frequencies of the second magnetic field at which the further difference signals are detected between the first receiving coil (23) and the second receiving coil (24) are distributed around the predetermined frequency at which the first magnetic field is generated, such that some frequencies are higher and others are lower than the predetermined frequency at which the first magnetic field is generated.

6. The method (300) according to any one of the preceding claims, wherein the predetermined frequency at which the first magnetic field is generated is 13.56 MHz.

7. The method (300) according to any one of the preceding claims, wherein the chip card (10) comprises a chip module (12) which comprises a microcontroller with RFID properties or a dual interface chip.

8. Measuring device (100) for determining the resonance frequency of a chip card (10), the measuring device (100) comprising: a measuring tower (20) comprising a first carrier plate (28-1), a second carrier plate (28-2), a third carrier plate (28-3), a first receiving coil (23) arranged on the first carrier plate (28-1), a second receiving coil (24) arranged on the third carrier plate (28-3), an excitation coil (21) arranged on the second carrier plate (28-2), and a measuring coil (25), wherein the second carrier plate (28-2) is arranged between the first carrier plate (28-1) and the third carrier plate (28-3), wherein the first carrier plate (28-1) is designed to receive and hold the chip card (10) in a predetermined position, and wherein the measuring coil (25) is arranged on the third carrier plate (28-3) such that the measuring coil (25) and the chip card (10) in the predetermined position have an equal distance from the excitation coil (25); a card reader (30); an excitation unit (40); a detection unit (50), a control arrangement (60) which is connected to the card reader (30), the excitation unit (40), and the detection unit (50); wherein the control arrangement (60) is designed to control the card reader (30), the excitation unit (40), and the detection unit (50) such that the method according to one of claims 1 to 7 is carried out.

9. Measuring device (100) according to claim 8, wherein a first distance between the predetermined position of the chip card (10) and the excitation coil (21) is equal to a second distance between the measuring coil (25) and the excitation coil (21).

10. Measuring device (100) according to claim 8 or 9, wherein the first receiving coil (23) and the second receiving coil (24) are equidistant from the excitation coil (25).

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