Stabilization of contactless energy supply of chips of chip card and corresponding chip card

Abstract

The invention relates to a method carried out by a chip (26) of a chip card (10) for adjusting an internal supply voltage (VCC) of the chip (26) on the basis of a field strength of an external electromagnetic field (H) that supplies energy to the chip (26), the internal supply voltage (VCC) being reduced by activating and deactivating a threshold voltage reduction function, and the chip (26) having a sensor register (SR), the sensor register displays a field strength value that is related to an external field strength and a regulated internal supply voltage (VCC). The invention further relates to a corresponding computer program product, to a storage medium having a computer program product, to a method for setting a chip (26) of a chip card (10) having a storage medium for carrying out a method for adjusting an internal supply voltage (VCC) of the chip (26), and to a chip card (10) having a chip (10), a method for regulating an internal supply voltage (VCC) of a chip (26) is implemented in the chip.

Description

Technical Field

[0001] The present invention relates to a method for regulating an internal supply voltage of a chip of a chip card based on the field strength of an external electromagnetic field that supplies energy to the chip, a corresponding computer program product, a storage medium having the computer program product, a method for setting a chip of a chip card having the storage medium to execute the method for regulating the internal supply voltage of the chip, and a chip card having a chip in which the method for regulating the internal supply voltage of the chip is implemented. Background Art

[0002] Chip cards, also called smart cards or IC cards (Integrated Circuit Card, ICC), are card-shaped data carriers that are used in many fields, especially in security-critical applications, such as payment methods for cashless payment transactions, for forgery-proof identification of persons, such as as a certificate, or as proof of authorization, such as for proof of access authorization, to name just a few non-closed examples. For example, ISO / IEC 7810 as an international standard defines four formats for identity documents, ID-1, ID-2, ID-3 and ID-000, of which ID-1 is the known bank card, credit card and check card format.

[0003] A chip card has a card body and an integrated circuit (chip) embedded in the card body, for example in the form of a chip module. The chip module is usually installed in a cavity or module opening of the card body. Therefore, physically, a chip card is a card with a chip installed therein, the chip containing at least one hardware logic, but usually a microprocessor (or microcontroller) and a non-volatile memory (electrically erasable programmable read-only memory EPROM, or electrically rewritable programmable read-only memory EAPROM). The chip card can be controlled by a card reader device provided for this purpose and communicate with the card reader device.

[0004] Consider below a chip card or chip module with an integrated coil, which is provided for contactless or contactless communication via an external electromagnetic field and is supplied with the energy required for its operation by the electromagnetic field; an example here is a chip card controller with "identification by means of electromagnetic waves" functionality (RFID). The chip card considered here can also be a card with dual interface (DI) functionality, i.e. also with electromechanical contacts for contactless communication with an associated reading device. For further information, reference can be made here, for example, to the international standard series ISO / IEC 14443 for contactless chip cards. ISO / IEC 14443 refers to the reading unit as PCD (proximity coupling device) and the chip card as PICC (proximity integrated circuit card), wherein the permissible reading distance within the maximum proximity for reliable reading is a few centimeters to direct placement.

[0005] There is such a chip card, in which in the contactless module also called CL module (CL= ContactLess), the energy management itself must be performed by software. For this purpose, the chip has a sensor register, a shunt register and a power supply voltage register, in which the current field strength detected by the sensor of the external reading electromagnetic field is stored as an absolute value or a relative value, the bit of the shunt register connects or disconnects the additional load resistor in the chip / relative to the chip, and the power supply voltage register can change the internal power supply voltage in the chip. Here, the register is basically a storage area for data, which can be called particularly quickly by the hardware logic or microprocessor (or microcontroller) of the chip, wherein the register is basically a storage location with a physical or logical storage address. Interference with power consumption can thus be performed in the CL module by software. This is necessary because the chip consumes all the energy it obtains from the contactless reading device PCD in the contactless module. If the chip is “saturated”, ie the chip cannot fully convert the input energy into computing power, additional ohmic resistors (shunts) are activated in order to convert the excess energy into heat and thus protect the chip from damage.

[0006] On the contrary, in order to make the chip work in a weaker electromagnetic field, it is feasible to reduce the internal threshold voltage in the chip through software, which is the internal power supply voltage level at which the chip starts to work. The chip thus works internally with a reduced power supply voltage; for example, it no longer works at 1V, but starts working at 0.85V, which is a reduction of 0.15V.

[0007] However, the internal supply voltage of the chip can only be reduced in a weak field. In field strengths exceeding a certain value, for example 1.5 A / m, the supply voltage must be set to a normal value again, i.e. the reduction function must be disabled, because otherwise damage may occur in the chip. The switching point or, more precisely, the switching threshold is important. If the supply voltage reduction function is disabled in an external field strength that is too low, the chip may "stagnate", i.e. fail, due to excessive internal power consumption; by switching to a normal supply voltage, the chip immediately requires more energy, because, for example, transistors consume more energy at a higher supply voltage.

[0008] On the other hand, if the switch to the normal supply voltage is not timely, excessive power consumption may occur due to the high field strength of the external electromagnetic field and the chip may be damaged.

[0009] Since the field strength changes of the external field cannot be predicted well, the difficulty of regulating the internal supply voltage is additionally increased. Therefore, the mere fact that a person holds the chip card in the reading range already produces fluctuations in the CL field, especially since the transaction can last up to 1 second. If, for example, the transaction is carried out at a point of sale (POS) terminal as a PCD, the method has an additional effect. In a first step, the POS terminal is first activated. In a second step, the customer manually brings the chip card to the POS terminal. During the time period until the card reaches its final position on the POS terminal, the CL field acting on the position of the chip card changes continuously. In addition, the POS terminal itself can also be moved manually by the salesperson towards the chip card.

[0010] All of the aforementioned circumstances relating to regulating the internal supply voltage of the chip together with fluctuations in the field strength of the external electromagnetic field during the above-described typical sequence of a payment process present a reason for transaction interruptions at the POS terminal. Summary of the invention

[0011] The invention is therefore based on the object of proposing a method for ensuring a power supply that is as stable as possible to a chip of a chip card having an adjustable internal supply voltage that is dependent on the field strength of an external electromagnetic field that supplies the chip card with energy.

[0012] The technical problem is solved by the independent claims. Designs and further developments of the invention are given in the dependent claims. Features and details described in connection with the method according to the invention also apply in connection with the chip card, computer program and storage medium according to the invention and vice versa, respectively, so that reference can always be made to each other with respect to the disclosure of the individual inventive aspects.

[0013] The basic idea of ​​the invention is to control the internal supply voltage of a chip of a chip card by means of a software-controlled control loop so that the energy supply of the chip remains as stable as possible when external field strength fluctuations are “observed” by the chip card.

[0014] The design of the software-controlled regulation proposed here of the internal supply voltage required for chip operation by activating or deactivating the internal supply voltage reduction function requires a number of technical considerations and insights, which are explained below.

[0015] As mentioned at the beginning of this article, for the chip card considered here, the voltage threshold value can be lowered by software, from which the chip starts to work, so that the chip can already be used in weaker electromagnetic fields. In fact, the chip works internally with a reduced supply voltage here. The activation of the internal supply voltage reduction function, i.e. the reduction of the threshold voltage, should only be performed in weak fields so that the chip is not damaged in higher external field strengths. That is, when the external field strength exceeds a certain value, the threshold voltage reduction function should be deactivated again and the internal supply voltage should therefore be set to a normal value again.

[0016] However, the inventors have determined that a reduction in the internal supply voltage also affects all sensors of the chip and thus also the sensor registers which display the current external electromagnetic field strength. This is shown schematically by way of an example.

[0017] Assume that the internal supply voltage of the chip is not reduced, that is, the threshold voltage reduction function is not activated, and there is an external field strength of 1A / m. For example, the value displayed by the sensor register is "0x03". If the threshold voltage reduction function is activated at this time, that is, the internal supply voltage is reduced, then when the external field strength is also 1A / m, the value displayed by the sensor register is "0x07". Therefore, the threshold voltage reduction function causes the sensor register to display an external field strength to the chip that is higher than the actual external field strength. As mentioned above, the threshold voltage can only be reduced in a weak electromagnetic field. When the field strength exceeds a certain value, assuming for example 1.5A / m, the threshold voltage must be increased again, that is, the reduction function must be deactivated, and the internal supply voltage is adjusted back to a normal value, because otherwise damage may occur in / on the chip. For this reason, the switching threshold is crucial, because if the threshold voltage reduction function is deactivated when the external field strength is too low, that is, the threshold voltage reduction function is deactivated too early, the chip will "stagnate" due to its excessive internal power consumption, because the chip converts more energy at the normal internal supply voltage. If the threshold voltage reduction function is disabled too late, the chip may be damaged due to excessive power consumption.

[0018] Since the field strength fluctuations of the external electromagnetic field that provides energy to the chip depend on different factors and are therefore hardly predictable, the software-supported regulation of the internal supply voltage by activating / deactivating the threshold voltage reduction function becomes more difficult. The fact that the chip card is guided by a person through the reading range in the direction of the POS terminal and the transaction may take up to 1 second already causes field strength fluctuations of the external CL field. In addition, at the POS terminal, the salesperson usually also moves the POS terminal as a handheld device towards the customer's chip card, so that both the chip card and the POS terminal are moving during the transaction. Finally, the contactless payment transaction process at the POS terminal inevitably leads to field strength fluctuations of the CL field. Usually in a first step, the POS terminal is first activated, and in a second step, the customer brings the chip card to the POS terminal and, if necessary, the salesperson also brings the POS terminal to the chip card. During the time period when the card reaches its final position at the POS terminal, the CL field seen by the chip card itself changes as the distance between the chip card and the POS terminal changes.

[0019] All of the above technical relationships and processes must be taken into account so that transactions at the POS terminal are not interrupted as much as possible due to excessive fluctuations in the chip's internal power supply voltage.

[0020] A first aspect of the invention relates to a method for regulating an internal supply voltage of a chip of a chip card based on the field strength of an external electromagnetic field supplying energy to the chip, wherein the method is implemented by a chip. The internal supply voltage of the chip can be reduced by activating and deactivating a threshold voltage reduction function. The chip has a sensor register which displays a field strength value which is correlated with the field strength of the external electromagnetic field and the regulated internal supply voltage. The method has the following steps:

[0021] - Step A, activating the threshold voltage reduction function for the first time when the field strength value in the sensor register is less than a predetermined first switching threshold;

[0022] - step B, deactivating the threshold voltage reduction function for the first time once the field strength value in the sensor register is greater than or equal to the first switching threshold; and

[0023] - Step C, setting a predetermined second switching threshold value for each reactivation of the threshold voltage lowering function while maintaining the first switching threshold value for each reactivation of the threshold voltage lowering function, wherein the second switching threshold value is smaller than the first switching threshold value.

[0024] In order to activate and deactivate the function of reducing the threshold voltage in order to change the internal supply voltage of the chip, a threshold register can be provided, which can be written to activate and deactivate the function of reducing the threshold voltage. Activate or deactivate a specific bit of a storage location in a working memory that can be assigned to a microprocessor or microcontroller of the chip, for example, wherein the internal supply voltage unit of the chip is controlled accordingly via this bit.

[0025] It is understandable that the field strength value of the external field strength of the external electromagnetic field displayed in the sensor register of the chip refers to the field strength value at the location of the chip card; usually the chip card has corresponding components used as one or more antennas to couple with the external electromagnetic field, such as a coil integrated in the card body of the chip card and / or the chip module of the chip.

[0026] For example, typical electromagnetic field strengths for communication between a chip of a chip card and a contactless reading device (PCD or CL reader) are in the range between 1.5 A / m and 7.5 A / m.

[0027] For example, the chip can be an integrated circuit with a microcontroller or a microprocessor; in principle, the integrated circuit can also implement all necessary functions as pure hardware logic, for example, as an application-specific integrated circuit (ASIC) or as a field programmable gate array (FPGA).

[0028] In order to ensure the best possible regulation of the chip's internal supply voltage, the sensor register values ​​should be analyzed in sufficiently short time intervals. On this basis, the threshold voltage can be adjusted and, if necessary, the shunt resistor can be switched on or off to dissipate possible excess power in the chip. Based on the following technical considerations, the inventors suggest designing the clock for analyzing the sensor register values ​​as follows.

[0029] The chip card usually starts to work when it is about 5 cm away from the center of the PCD or POS terminal. At 3 cm from the center, the field strength at the location of the chip card exceeds 2 A / m for most POS terminals. The maximum movement speed for the card user with one arm to bring the chip card close to the POS terminal is about 0.59 m / s; this movement speed only applies to linear movements, i.e. without stopping. This means that for the field strength range of 0 A / m to 2 A / m, a regulation within a range of 2 cm needs to be designed. This results in a time window of less than 200 ms, within which sufficiently precise regulation must be performed. To ensure this regulation, the sensor register should be analyzed at the latest every 35 ms.

[0030] The field strength values ​​in the sensor register of the chip of the chip card can be evaluated intermittently, preferably at intervals of 30 ms to 40 ms, particularly preferably approximately every 35 ms. On this basis, the above steps A to C are performed, ie the threshold voltage is activated or deactivated as required or desired.

[0031] A particularly efficient implementation is to use the S(WTX) or SWTX command "Frame Wait Time Extension Request" of the T=CL protocol according to ISO / IEC 7816-4 as a trigger for the continuous evaluation of the sensor registers. The SWTX command is a request for more time to process the command, i.e., to extend the predetermined waiting time in order to prevent communication interruptions. This makes it possible to omit further interruptions or continuous checking of the sensor registers.

[0032] The sensor register is preferably checked before the S(WTX) request is sent. This has the advantage that the characteristics of the load modulation can be adjusted according to the field strength. That is, in a preferred embodiment, the sensor register is evaluated before the S(WTX) request is sent.

[0033] The chip preferably has a switchable internal or external shunt resistor, which can be connected to the chip or disconnected from the chip according to the current power consumption of the chip and the external field strength in order to discharge excess energy. The connection or disconnection of the shunt resistor to the chip can be controlled by a corresponding shunt register, the bits of which are respectively assigned to a specific shunt resistor, and for example, a set bit ("1") connects the assigned shunt resistor to the chip so that part of the current excess energy in the shunt resistor is converted into heat.

[0034] According to the invention, the above method is implemented as software control in a hardware logic in a chip of the chip card, such as a microcontroller or a microprocessor or an ASIC or an FPGA.

[0035] A second aspect of the invention relates to a computer program (product) comprising instructions which, when executed by a computer, in particular a microcontroller or microprocessor in a chip of a chip card, cause the computer to perform the steps of the method according to the first aspect of the invention.

[0036] A third aspect of the present invention relates to a (computer-readable) storage medium, in particular a storage medium in the form of a program storage area of ​​a chip of a chip card, in which instructions are stored, which, when executed by a computer, in particular a microcontroller or microprocessor in the chip of a chip card, cause the computer to perform the steps of the method according to the first aspect of the present invention.

[0037] A fourth aspect of the invention relates to a method for setting a chip of a chip card having a computer-readable storage medium according to the third aspect of the invention. The internal supply voltage of the chip can be reduced and increased again by activating and deactivating a threshold voltage reduction function of the internal supply voltage of the chip, in particular in a threshold register, based on the field strength of an external electromagnetic field that supplies energy to the chip. The chip has a sensor register that displays a field strength value that is dependent on the external field strength of the external electromagnetic field and whether the threshold voltage reduction function is activated or deactivated. The method has the following steps:

[0038] - step a, determining a field strength value in a sensor register according to the external field strength over a field strength range, when the threshold voltage reduction function is deactivated and therefore the internal supply voltage is not reduced;

[0039] - step b, determining a field strength value in the sensor register according to the external field strength over said field strength range when the threshold voltage reduction function is activated and thus the internal power supply voltage is reduced;

[0040] - step c, predetermining a first switching threshold, below which the threshold voltage reduction function is activated for the first time, and, when the first switching threshold is subsequently exceeded, the threshold voltage reduction function is deactivated again for the first time;

[0041] - step d, predetermining a second switching threshold below which the threshold voltage lowering function should be reactivated, wherein the second switching threshold is lower than the first switching threshold; and

[0042] - Step e, storing the first switching threshold and the second switching threshold in a storage medium of the chip.

[0043] The field strength range may be defined as 0 A / m to 10 A / m and preferably 0.5 A / m to 7.5 A / m.

[0044] In step d, fluctuations caused by the manufacturing process of the chip card and / or the coil connected to the chip circuit and / or the connection technology for connecting the coil to the chip can be taken into account.

[0045] For example, the first switching threshold can be 2 A / m. It has been determined that in the case of fluctuations in the manufacturing process of the chip card, the relevant value in the sensor register can shift within a range of + / - 0.1 A / m. In addition to this range, the coil and the connection technology used to connect the coil to the chip circuit can also cause fluctuations. When soldering is used as the connection technology, these values ​​are very small, when using flexible bump technology, these values ​​can be larger, for example + / - 0.4 A / m.

[0046] A fifth aspect of the invention relates to a chip card having a chip whose supply voltage can be reduced by activating and deactivating a function for reducing a threshold voltage of an internal supply voltage of the chip. To this end, the chip has:

[0047] - a sensor register, which displays a field strength value which is related to the external field strength of the external electromagnetic field and the regulated internal supply voltage;

[0048] - a storage medium in which a first switching threshold and a second switching threshold are stored, wherein the second switching threshold is smaller than the first switching threshold; and

[0049] - A chip configured to perform the method according to the first aspect of the invention.

[0050] The chip card can have a storage area in which a value pair is stored, the value pair having a field strength value in a sensor register and an associated external field strength when the threshold voltage reduction function is deactivated and the internal power supply voltage is not reduced, and a value pair is stored in the storage area in which the value pair has a field strength value in a sensor register and an associated external field strength when the threshold voltage reduction function is activated and the internal power supply voltage is reduced.

[0051] Preferably, corresponding value pairs having a field strength value in the sensor register and an associated external field strength are stored in the memory area over a field strength range of 0 A / m to 10 A / m and preferably 0.5 A / m to 7.5 A / m with an activated threshold voltage reduction function and a deactivated threshold voltage reduction function.

[0052] The method proposed above can be used to provide a chip card of the type described in the invention, in which the stability of the energy supply of the chip on the chip card is improved. This is manifested in that the chip internally "stagnates" less or no longer occurs, i.e. too little energy due to too low a voltage, or the chip is not destroyed or damaged due to overheating. This greatly increases the probability that a complete transaction can be carried out using a chip card having a chip according to the invention, despite or in the event of fluctuations in external field strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention is exemplarily described below with reference to the accompanying drawings. In the accompanying drawings:

[0054] Figure 1 shows a simplified schematic exploded view of a dual interface (DI) chip card;

[0055] Figure 2 Shows Figure 1 A simplified functional block diagram of a chip module of a chip card;

[0056] Figure 3 A simplified illustration of a chip card in contactless mode is shown, which chip card is brought to a POS terminal, for example, for a payment process, wherein the POS terminal generates an electromagnetic field for supplying energy to the chip card and for communicating with the chip card;

[0057] Figure 4 A flow chart of a method according to the invention is shown for setting a chip of a chip card for applying a software-implemented, Figure 6 control methods;

[0058] Figure 5 Shown by Figure 4 An example diagram of a correlation between external field strengths in a sensor register of a chip of a chip card determined by the method of FIG. 1 with an activated function for reducing the threshold voltage and a deactivated function for reducing the threshold voltage;

[0059] Figure 6 A flow chart of a method according to the invention for regulating an internal supply voltage of a chip of a chip card as a function of the field strength of an external electromagnetic field which supplies the chip with energy, in order to implement a control method according to the invention implemented by software, is shown; and

[0060] Figure 7 An illustration of a control method for activating and deactivating a threshold voltage reduction function according to a correlation between field strengths displayed in a sensor register when the threshold voltage reduction function is activated and when the threshold voltage reduction function is deactivated, respectively, is shown. DETAILED DESCRIPTION

[0061] Figure 1 The basic structure of a dual-interface chip card 10 is shown by way of example. The example diagram is from: M. Roland and M. Hölzl, "Evaluation of Contactless Smartcard Antennas", Technical Report, Computing Research Repository (CoRR), arXiv:1507.06427[cs.CR], page 17, University of Applied Sciences Upper Austria, JR-Center u'smile, July 2015.

[0062] Figure 1 A chip card 10 is shown with a card body 12. The card body 12 may include a metal layer 13, the main surfaces of which may each be covered with a plastic layer 14. For example, the metal layer 13 may be in the form of a card core or a refined steel alloy layer, for example with a thickness of 400 μm. The thickness of the card body 12 may be, for example, between 50 μm and 920 μm.

[0063] The chip card 10 also includes a chip module 20, which is mounted in a recess 16 in the card body 12 or in a main surface of the chip card 10. The recess 16 can be a module opening or a cavity and includes a central blind hole and a surrounding edge region. The chip module 20 can be bonded in the cavity by means of an adhesive layer or adhesive pad 18.

[0064] In the metal layer 13, it is possible to set (in Figure 1 A gap (not shown) is provided, which extends from the circumferential surface or outer edge of the card body 12 to the cavity to avoid eddy currents in the metal layer 13.

[0065] The chip module 20 is arranged on a so-called module strip 23 and can be connected to a coil 30, which is also integrated in the card body 12, and / or the chip module itself has a coil 22, wherein a metal layer or ferrite layer 24 is arranged between the chip 26 and the coil 22. The coil 30 extends about 3 to 6 windings in the plane of the card around the chip module 20. The coil 22 extends concentrically about 12 to 16 windings in the plane of the chip module 20 around the chip 26 of the chip module 20.

[0066] For example, the chip 26 of the chip module 20 can be implemented in the form of an electronic integrated circuit or circuit and can be fixed on the bottom side of the chip module 20, for example, encapsulated in a potting material. The chip module 20 and thus the chip 26 can be supplied with energy from the outside by the coil 30 or the coil 22 without contact and / or receive or send communication signals. For this purpose, Figure 3 As shown, an external electromagnetic field H can be coupled into the coils 30 and / or 22. For example, the chip 26 can be a chip card controller with RFID (radio frequency identification) functionality in the form of a microcontroller or microprocessor or essentially contain such a chip card controller.

[0067] To avoid ambiguity, it should be pointed out that in Figure 1 The chip module 20 is shown twice: once in the installed position on the right side above the groove 16, and once in its upper left part, flipped 180 degrees to show the back side. Figure 1 The upper side shown in the mounting position in FIG. 1 has a contact area 21 with metal contacts, which is used for contact communication and energy supply of the chip module 20; Figure 1 The chip card 10 shown in the figure is designed as a dual interface (DI) chip card, which is used for contact operation in addition to the contactless mode concerned here. It goes without saying that the improvements proposed here mainly relate to chip cards of the type described in the invention in the contactless mode, and the invention is also applicable to purely contactless chip cards.

[0068] Figure 2Shows Figure 1 A simplified functional block diagram of a chip card 10 is shown.

[0069] The integrated circuit of the chip 26 of the chip module 20 generally includes a microprocessor 40 for executing the control functions and communication functions of the chip card 10 and, if necessary, also a cryptographic processor (not explicitly shown) for executing arithmetic operations for security functions. In addition, the integrated circuit includes various memory circuits for storing and / or providing data. For example, there is a RAM memory 44 as a short-term working memory for the microprocessor 40, a ROM memory 46 for the operating system of the microprocessor 40, and an EEPROM or EAPROM memory 48 as an application memory for the application program of the chip card 10.

[0070] exist Figure 3 In the wireless interface unit 50 and Figure 1 The coil 30 is connected to the wireless interface unit 50 and also includes a capacitor 52. The coil 30 is connected to the capacitor 52 of the wireless interface unit 50. The inductance of the coil 30 and the capacitance of the capacitor 52 form a resonant circuit, which is designed for wireless communication with the chip 26 of the chip card 10 and the wireless energy supply device for a specific carrier frequency; for example, the carrier frequency can be 13.56 MHz.

[0071] The wireless interface device 50 also includes a sensor 54, which is arranged to detect a physical variable related to the field strength of an external electromagnetic field H, which is coupled to the resonant circuit formed by the coil 30 and the capacitor 52. The field strength values ​​detected by the sensor 54 are continuously written by the wireless interface unit 50 into a sensor register SR of the chip 26; as described elsewhere, the register can in principle be a writable storage location and can therefore also be located in the RAM memory 44 of the chip 26. However, the register can also be a dedicated hardware register of the microprocessor 40. Figure 2 In FIG. 1 , the sensor register SR is explicitly shown as a separate unit only for the sake of clarity.

[0072] The wireless interface unit 50 also comprises a voltage regulating unit 56 arranged to regulate the internal supply voltage VCC of the chip 26. In the example shown, the wireless interface unit 50 also comprises all functions for providing the chip 26 with the internal supply voltage VCC fed from the external electromagnetic field H.

[0073] The voltage regulating unit 56 is configured to provide a predetermined "normal" power supply voltage VCC when the chip 26 starts up when the external energy supply is sufficient. The voltage regulating unit 56 can be controlled by the power supply voltage register VCCR in a manner that the function of reducing the voltage threshold of the internal power supply voltage VCC is activated or deactivated by the power supply voltage register VCCR. Thus, by reducing the internal power supply voltage VCC, the chip 26 can already start up in a weaker external electromagnetic field H, thereby entering a working state more quickly.

[0074] Finally, the chip 26 also has an internal or external shunt resistor, which can be connected or disconnected from the chip 26 according to the current difference between the power absorbed from the external magnetic field H and the power currently converted by the chip 26, so as to discharge the excess power as heat, thereby avoiding overheating and damage to the chip 26. The shunt resistor can also be controlled by a dedicated shunt resistor register SR-R, in that each individual bit of the register controls the connection or disconnection of the associated shunt resistor; as described above with respect to the sensor register SR, the register can in principle be a writable storage location and is therefore also located in the RAM memory 44 of the chip 26. However, the register can also be a dedicated hardware register of the microprocessor 40. In Figure 2 , the shunt resistor register SR-R is explicitly shown as a separate unit for clarity only.

[0075] Figure 3 It is explained how the chip 26 can communicate with a POS terminal reading device 60 which is external to the chip card 10 by means of a resonant circuit as an antenna. The control circuit 61 of the reading device 60 is also configured to create an electromagnetic field H by means of a coil 64, thereby coupling energy into the coil 30 of the chip card 10, by which the integrated circuit of the chip 26 is activated and operated. The wireless interface unit 50 of the chip card 10 generates an internal supply voltage VCC for the chip 26 via the external electromagnetic field H of the reading device 60.

[0076] The microprocessor 40 of the chip 26 is started from the minimum electromagnetic field strength. The operating frequency of the microprocessor 40 and therefore its processing speed can be increased with increasing field strength. Starting from a certain electromagnetic field strength, the operating frequency is no longer increased. At this point, the microprocessor 40 reaches a saturated state and runs at a maximum frequency. If the energy coupled by the field strength of the external electromagnetic field H exceeds the energy that can be converted by the microprocessor 40, this energy must be consumed by the switchable shunt resistor Rn to avoid damage to the chip 26.

[0077] Figure 4 A flow chart of a method according to the invention is shown for setting a chip of a chip card for applying a Figure 6A control method implemented by software according to the present invention.

[0078] By the following method, for example Figure 1-Figure 3 The chip 26 of the chip card 10 in the embodiment of the present invention can be used to apply the control method implemented by software in order to stabilize the internal supply voltage of the chip 26, wherein the lowering function of the threshold voltage of the internal supply voltage can be activated and deactivated by correspondingly writing into the threshold register of the chip 26 as a function of the field strength of the external electromagnetic field H supplying energy to the chip 26, thereby reducing and raising the internal supply voltage of the chip 26 again. For this purpose, the chip 26 has a sensor register SR which displays a field strength value which depends on the external field strength of the external electromagnetic field H and whether the threshold voltage is currently activated or deactivated.

[0079] The method for setting up the chip 26 has the following steps for this purpose:

[0080] In a first step a, it is determined how the sensor register SR behaves depending on the field strength present at the location of the chip card 10. In this step, the threshold voltage is not reduced. That is, in step a, a value pair is determined between the field strength value displayed in the sensor register SR and the actual external field strength when the threshold voltage is deactivated and the internal supply voltage VCC is not reduced. The determined value pair can be stored in a memory area of ​​the chip 26 of the chip card 10 for further use.

[0081] In a second step b, the process is repeated, but this time the threshold voltage lowering function is activated.

[0082] The measurements in steps a and b are preferably carried out in a field range of 0.5 A / m to 7.5 A / m.

[0083] In step c, a first switching threshold is predetermined, below which the threshold voltage reduction function is to be activated for the first time and above which the threshold voltage reduction function is to be deactivated again for the first time.

[0084] In step d, a second switching threshold is predetermined, below which the threshold voltage reduction function should be reactivated, wherein the second switching threshold is lower than the first switching threshold (0x0F).

[0085] In step e, the first switching threshold value and the second switching threshold value are stored in a storage medium of the chip so that these values ​​can be used in the future during operation of the chip card 10 .

[0086] Figure 5 Shown by Figure 4The difference between the external field strength of the external electromagnetic field H determined in the method described and the value displayed in the sensor register SR of the chip 26 of the chip card 10 for each activation of the lowering function ΔS of the threshold voltage ON case and for the threshold voltage reduction function disabled ΔS OFF An example diagram of the association of the situation.

[0087] Figure 5 It is shown that the value of the sensor register SR depends on the field strength of the external electromagnetic field H and the regulated internal supply voltage.

[0088] The threshold voltage reduction function activates ΔS ON , the chip 26 has been started in advance. The sensor register SR of the chip 26 has displayed the external field strength value 0x01 at 0.6 A / m, and has displayed the value 0x03 at the external field strength of 1.0 A / m. In contrast, at the normal internal power supply voltage, that is, when the threshold voltage reduction function is disabled ΔS OFF In this case, the sensor register displays the value 0x03 at 1.3A / m.

[0089] according to Figure 5 It can be seen that the reduction in threshold voltage deactivates the function ΔS OFF In order to prevent the chip 26 from overheating internally due to the reduction in the threshold voltage of the internal power supply voltage VCC, the threshold voltage reduction function must be disabled at 2 A / m at the latest, for example.

[0090] Figure 6 A flow chart of a method according to the invention is shown for adjusting the internal supply voltage of a chip of a chip card as a function of the field strength of an external electromagnetic field which supplies energy to the chip, in order to implement a control method according to the invention implemented by software.

[0091] Figure 6 The method is implemented by the chip 26 of the chip card 10 and is used to adjust the internal supply voltage VCC of the chip 26 according to the field strength of the external electromagnetic field H that supplies energy to the chip 26. The internal supply voltage VCC can be reduced by activating and deactivating the threshold voltage reduction function. For example, Figure 2 As shown, the chip 26 has a sensor register SR which displays a field strength value which depends on the current external field strength and the currently set internal supply voltage VCC.

[0092] The method itself has the following steps:

[0093] In step A, the threshold voltage reduction function is activated for the first time as soon as the field strength value displayed in the sensor register SR is less than a predetermined first switching threshold value, 0x1F in the example.

[0094] In step B, the threshold voltage reduction function is deactivated for the first time as soon as the field strength value displayed in the sensor register SR is greater than or equal to a first switching threshold value, 0x1F in the example.

[0095] In step C, for each reactivation of the threshold voltage reduction function, a predetermined second switching threshold value, in the example 0x07, is adjusted, wherein for each re-deactivation of the threshold voltage reduction function, the first switching threshold value, in the example 0x1F, remains unchanged. The second switching threshold value, in the example 0x07, is smaller than the first switching threshold value, in the example 0x1F.

[0096] Figure 7 Considerations underlying the software-implemented control method according to the invention for activating and deactivating the threshold voltage reduction function as a function of the correlation between the field strengths displayed in the sensor register when the threshold voltage reduction function is activated and when the threshold voltage reduction function is deactivated are described.

[0097] exist Figure 7 The switching range SB at 2 A / m is indicated in FIG. It has been determined that fluctuations ΔC during the production of the chip 26 lead to a shift of the value in the sensor register SR within the range of + / - 0.1 A / m. In addition to this fluctuation range, the coil 30 or 22 and the connection technology used also cause fluctuations ΔL. In solder connection technology, the fluctuation values ​​are very small, for example, in flexible bump or flexible bump technology, higher values ​​of + / - 0.4 A / m have been determined.

[0098] FIG. 7 shows that in the field strength range of 1.8 A / m to 2.2 A / m, the sensor register SR on the exemplary chip card 10 can be deactivated by a reduction in the threshold voltage ΔS OFF has a value of 0x1F. The threshold voltage reduction function activates ΔS ON The characteristics are present to the same degree when the above values ​​are equal. This range is not to be regarded as a “range of variation”.

[0099] The first switching threshold is predetermined here at a sensor register value of 0x1F. If the sensor register SR shows a value less than 0x1F, the threshold voltage reduction function is activated; if the value is >= 0x1F, the threshold voltage reduction function should be deactivated again.

[0100] but Figure 7 Now it is shown that the reduction in the threshold voltage disables the function ΔS OFF When the sensor register value drops to 0x0F, this may immediately cause the threshold voltage reduction function to activate ΔS ON Therefore, the inventors propose to re-deactivate ΔSOFF The threshold voltage reduction function reduces the switching threshold for activation of the threshold voltage reduction function to avoid control instability due to toggling. Figure 7 In the example case shown, the ΔS ON The second switching threshold of the threshold voltage reduction function may be set to 0x07.

[0101] Thus, the method described above can be used to improve chip cards of the type described in the invention, because by adjusting the lowering function of the threshold voltage of the internal supply voltage VCC by software, an improved stability of the energy supply of the chip 26 of the chip card 10 can be ensured. As a result, during use, for example at a POS terminal, the chip 26 is less likely to "stagnate" internally or not at all, and the risk of damage to the chip 26 due to overheating is also reduced. In short, the possibility of being able to perform a complete transaction at a POS terminal 60 with a chip card 10 having a chip 26 according to the invention when the external field strength fluctuates is increased.

Claims

1. A method implemented by a chip (26) of a chip card (10) for regulating an internal supply voltage (VCC) of the chip (26) based on the field strength of an external electromagnetic field (H) supplying energy to the chip (26), wherein: The internal supply voltage (VCC) can be reduced by activating and deactivating the threshold voltage reduction function, and the chip (26) has a sensor register (SR) which displays a field strength value which is related to the external field strength and the adjusted internal supply voltage (VCC), wherein the method comprises the following steps: - Step A, activating the threshold voltage reduction function for the first time when the field strength value in the sensor register (SR) is less than a predetermined first switching threshold (0x1F); - Step B, once the field strength value in the sensor register (SR) is greater than or equal to the first switching threshold value (0x1F), the threshold voltage reduction function is disabled for the first time; and - Step C, setting a predetermined second switching threshold value (0x07) for each reactivation of the threshold voltage lowering function while maintaining the first switching threshold value (0x1F) for each reactivation of the threshold voltage lowering function, wherein the second switching threshold value (0x07) is smaller than the first switching threshold value (0x1F).

2. The method according to claim 1, characterized in that The field strength values ​​displayed by the sensor register (SR) are analyzed intermittently, preferably at time intervals of 30 ms to 40 ms, particularly preferably approximately every 35 ms, and steps A to C are carried out based thereon.

3. The method according to claim 1 or 2, characterized in that The command “Frame Wait Time Extension Request”, S(WTX) request, of the T=CL protocol according to ISO / IEC 7816-4 is used as a trigger for the continuous evaluation of the sensor register (SR).

4. The method according to claim 3, characterized in that Analysis of the sensor register (SR) is performed before sending an S(WTX) request.

5. The method according to any one of claims 1 to 4, characterized in that The chip (26) also has a shunt resistor (R) and a shunt register (RR) for controlling the shunt resistor (R), wherein the shunt resistor is connected to the chip (26) or disconnected from the chip (26) to discharge excess energy according to the current power consumption of the chip (26), the external field strength and the current internal power supply voltage (VCC).

6. A computer program comprising instructions which, when executed by a computer, in particular a microcontroller (40) in a chip (26) of a chip card (10), cause the computer to carry out the steps of the method according to one of claims 1 to 5.

7. A storage medium, in particular a storage medium in the form of an internal or external program storage area of ​​a chip (26) of a chip card (10), comprising instructions which, when executed by a computer, in particular a microcontroller (40) in the chip (26) of the chip card (10), cause the computer to perform the steps of a method as described in one of claims 1 to 5.

8. A method for providing a chip (26) of a chip card (10) with a storage medium as claimed in claim 7, wherein: The internal power supply voltage (VCC) of the chip (26) can be reduced and increased by activating and deactivating the threshold voltage reduction function based on the field strength of the external electromagnetic field (H) supplying energy to the chip (26), and the chip (26) has a sensor register (SR) which displays the field strength value, which is related to the external field strength and whether the threshold voltage reduction function is activated or deactivated, wherein the method has the following steps: - step a, determining a field strength value in a sensor register (SR) according to the external field strength over a field strength range, when the threshold voltage reduction function is disabled and therefore the internal power supply voltage (VCC) is not reduced; - step b, determining a field strength value in a sensor register (SR) according to the external field strength over said field strength range when the threshold voltage reduction function is activated and thus the internal power supply voltage (VCC) is reduced; - step c, predetermining a first switching threshold value (0x0F), below which the threshold voltage reduction function is activated for the first time, and next above which the threshold voltage reduction function is deactivated for the first time; - step d, predetermining a second switching threshold value (0x07), below which the threshold voltage reduction function should be reactivated, wherein the second switching threshold value (0x07) is less than the first switching threshold value (0x0F); and - Step e, storing the first switch threshold value (0x0F) and the second switch threshold value (0x07) in a storage medium of the chip (26).

9. The method according to claim 8, characterized in that A field strength range of from 0 A / m to 10 A / m and preferably from 0.5 A / m to 7.5 A / m is defined.

10. The method according to claim 8 or 9, characterized in that In step d, fluctuations due to the manufacturing process of the chip card (10) and / or the coil (30, 22) connected to the chip (26) circuit and / or the connection technology connecting the coil (30, 22) to the chip (26) circuit are taken into account.

11. A chip card (10) having a chip (26) whose internal supply voltage (VCC) can be reduced by activating and deactivating a threshold voltage reduction function, wherein: The chip (26) has: - a sensor register (SR) displaying a field strength value which is related to the external field strength of the external electromagnetic field (H) and to the regulated internal supply voltage (VCC); - a storage medium in which a first switching threshold value (0x0F) and a second switching threshold value (0x07) are stored, wherein the second switching threshold value (0x07) is smaller than the first switching threshold value (0x0F); and - an integrated circuit (14) which is designed to carry out the method according to one of claims 1 to 5.

12. The chip card (10) as claimed in claim 11, characterized in that The chip card (10) has a storage area in a storage medium, in which value pairs including field strength values ​​to be displayed in a sensor register (SR) and respectively assigned external field strengths are stored when the threshold voltage reduction function is deactivated and the internal power supply voltage (VCC) is not reduced, and in which value pairs including field strength values ​​to be displayed in a sensor register (SR) and respectively assigned external field strengths are stored when the threshold voltage reduction function is activated and the internal power supply voltage (VCC) is reduced.

13. The chip card (10) as claimed in claim 11 or 12, characterized in that Corresponding value pairs with field strength values ​​in the sensor register (SR) and the associated external field strength are stored in the memory area over a field strength range of 0.5 A / m to 7.5 A / m with the threshold voltage reduction function activated and the threshold voltage reduction function deactivated.

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