Stabilising the contactless power supply of the chip of a chip card and corresponding chip card
A method is implemented by a chip embedded in a chip card to adjust the internal supply voltage of the chip based on the strength of an external electromagnetic field that powers the chip. The internal supply voltage can be lowered by toggling a reduction in the threshold voltage. The chip includes a sensor register displaying a field strength value dependent on the external field strength and the adjusted internal supply voltage. Additionally, a corresponding computer program product, a storage medium containing the computer program product, a method for setting up the chip within the chip card using the storage medium to execute the method for adjusting the internal supply voltage, as well as a chip card featuring the chip, in which the method for adjusting the internal supply voltage of the chip is implemented, are also provided.
1 . A method which is implemented by a chip of a chip card for adjusting the internal supply voltage of the chip based on the field strength of an external electromagnetic field supplying the chip with power,
wherein the internal supply voltage is reducible through activation and deactivation of a threshold voltage reduction, and the chip has a sensor register indicating a field strength value which is dependent on the external field strength and the adjusted internal supply voltage,
wherein the method comprises the following steps:
a step A, comprising activating the threshold voltage reduction for the first time when the field strength value in the sensor register is less than a predetermined first switching threshold;
a step B, comprising deactivating the threshold voltage reduction for the first time as soon as the field strength value in the sensor register is greater than or equal to the first switching threshold; and
a step C, comprising setting a predetermined second switching threshold for each further activation of the threshold voltage reduction while retaining the first switching threshold for each further deactivation of the threshold voltage reduction, wherein the second switching threshold is lower than the first switching threshold.
2 . The method according to claim 1 , wherein the field strength value indicated by the sensor register is evaluated intermittently, and steps A to C are carried out on this basis.
3 . The method according to claim 2 , wherein 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 a continuous evaluation of the sensor register (SR).
4 . The method according to claim 3 , wherein the sensor register is evaluated before the S(WTX) request is transmitted.
5 . The method according to claim 1 , wherein the chip further comprises shunt resistors and a shunt register for controlling the shunt resistors, which can be connected to the chip or disconnected from the chip depending on the present power consumption of the chip, the external field strength and the present internal supply voltage for discharging excess power.
6 . A computer program comprising commands which, when the computer program is executed by a computer by a microcontroller in a chip of a chip card, cause said chip to carry out the steps of the method according to claim 1 .
7 . A storage medium in the form of an internal or external program storage area of a chip of a chip card, comprising commands which, when executed by a computer, by a microcontroller in a chip of a chip card, cause said chip to carry out the steps of the method according to claim 1 .
8 . A method for configuring the chip of a chip card having a storage medium according to claim 7 ,
wherein the internal supply voltage of the chip can be reduced and increased based on the field strength of an external electromagnetic field supplying the chip with power through activation and deactivation of a threshold voltage reduction and the chip has a sensor register, which indicates a field strength value which is dependent on the external field strength and on whether the threshold voltage reduction is activated or deactivated, wherein the method comprises the following steps:
a step a, comprising determining the field strength values in the sensor register depending on the external field strength when the threshold voltage reduction is deactivated, i.e. the internal supply voltage is not reduced, over a field strength range;
a step b, comprising determining the field strength values in the sensor register depending on the external field strength when the threshold voltage reduction is activated, i.e. the internal supply voltage is reduced, over the field strength range;
a step c, comprising predetermining a first switching threshold, below which the threshold voltage reduction is activated for the first time, and subsequently above which the threshold voltage reduction is deactivated once more for the first time;
a step d, comprising predetermining a second switching threshold, below which the threshold voltage reduction is intended to be activated once more, wherein the second switching threshold is lower than the first switching threshold; and
a step e, comprising storing the first switching threshold and the second switching threshold in the storage medium of the chip.
9 . The method according to claim 8 , wherein the field strength range is defined from 0 A/m to 10 A/m.
10 . The method according to claim 9 , wherein, in step d, fluctuations due to the production process of the chip card and/or a coil which is connected to the chip and/or due to the connection technology used to connect the coil to the chip are taken into account.
11 . A chip card having a chip, the internal supply voltage of which is reducible through activation and deactivation of a threshold voltage reduction,
wherein the chip comprises:
a sensor register which indicates a field strength value which is dependent on an external field strength of an external electromagnetic field and the adjusted internal supply voltage;
a storage medium in which a first switching threshold and a second switching threshold are stored, wherein the second switching threshold is lower than the first switching threshold; and
an integrated circuit, which is configured to carry out a method according to claim 1 .
12 . The chip card according to claim 11 , wherein the chip card has a storage area in the storage medium for storing value pairs having field strength values to be indicated in the sensor register and the respective associated external field strength when the threshold voltage reduction is deactivated, i.e. the internal supply voltage is not reduced, and for storing value pairs having field strength values to be indicated in the sensor register and the respective associated external field strength when the threshold voltage reduction is activated, i.e. the internal supply voltage is reduced.
13 . The chip card according to claim 11 , wherein the respective value pairs having the field strength value in the sensor register and the associated external field strength over a field strength range from 0.5 A/m to 7.5 A/m are stored in the storage area when the threshold voltage reduction is activated and the threshold voltage reduction is deactivated.