PROTECTION

Field of the Invention

The present invention relates to a smartcard comprising a biometric sensor. In particular, the present invention relates to ESD-protection in a smartcard.

Background of the Invention

As the development of biometric devices for identity verification, and in particular of fingerprint sensing devices, has led to devices which are made smaller, cheaper and more energy efficient, the range of applications for such devices is increasing.

In particular, capacitive fingerprint sensing devices have been adopted more and more in for example consumer electronic devices due to small form factor, relatively beneficial cost/performance factor and high user acceptance. There is also an increasing interest in using fingerprint sensors in smartcards to enable biometric identification in a card such as a bank card where other types of biometric systems are not applicable.

The integration of fingerprint sensors in smartcards and the like puts new requirements on the fingerprint sensor module for example in terms of energy consumption and wear resistance. Moreover, a smartcard often contains a contact plate for physically connecting the card to a terminal as well as a wireless interface for contactless operation.

Electrostatic discharge (ESD) is a problem for all electronics, and especially so in applications when the user is in contact with the equipment containing the electronics. This is especially true for biometric solutions implemented in smartcards. In a biometric smartcard, the contact communication mode of the card is especially sensitive as the human body is in direct contact with a bezel in close proximity of the fingerprint sensor and where an ESD pulse can be guided via the bezel and the fingerprint sensor to the reader terminal. Thereby, an electrostatic discharge has the potential to damage both the integrated electronics in the smartcard as well as in the point of sales (POS) contact reader.

An existing approach for handling ESD in a smartcard and to protect components in the card is to deflect the ESD pulse directly through ground of the reader by extending the ESD ground in the contact reader through the card to the fingerprint sensor. However, this may expose the card reader to potentially damaging ESD pulses.

Accordingly, it is desirable to improve ESD protection in a smartcard comprising a biometric sensor.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved smartcard comprising integrated ESD-protection.

According to one embodiment of the invention, there is provided a smartcard comprising: a fingerprint sensor module; a microcontroller module; a contact plate comprising externally accessible contacts configured to communicate with a terminal, the contact plate being galvanically connected to the microcontroller module; a wireless interface circuit formed in at least one conductive layer of the smartcard. The wireless interface circuit comprises a first communication interface to the fingerprint sensor module and a second communication interface to the microcontroller module, wherein at least one of the first and second communication interface is a wireless interface, and wherein the wireless interface circuit comprises a capacitive coupling to a ground terminal of the contact plate.

A smartcard can be considered to be any card comprising functionality such as biometric sensing, and smartcards may be used as payment cards, identification cards, access cards and in other applications where a card with built-in functionality is desirable. In the present context, the smartcard comprises a fingerprint sensor module which communicates with the microcontroller module via the wireless interface circuit having at least one wireless interface internally on the smartcard. The fingerprint sensor module comprises at least a fingerprint sensor having an active sensing surface, and the fingerprint sensor may advantageously be a capacitive fingerprint sensor comprising an array of electrically conductive sensing elements. A capacitive fingerprint sensor should be understood to further comprise sensing circuitry connected to sensing elements for reading a signal from the sensing elements. The sensing circuitry may in turn comprise or be connected to readout circuitry for providing a result of the sensing device to an external device for further processing, which in the present case may be included in the fingerprint sensor module. The fingerprint sensor module may also comprise additional passive or active components.

The present invention is based on the realization that the risk of damage to the microcontroller control module, to the contact plate and to a smartcard reader can be significantly reduced by providing a wireless communication interface between the microcontroller module and the fingerprint sensor module. The fingerprint sensor module is thus galvanically isolated from the microcontroller module and subsequently from a card reader terminal.

To comply with the safety requirements of major card manufacturers, only a small portion of the energy of an electrostatic discharge (ESD) is allowed to reach a reader terminal. A fingerprint sensor often comprises a conductive structure such as a bezel to be touched by the finger of the user in order to control the potential of a finger in contact with the sensor. Such a conductive structure may also guide an electrostatic discharge to other components in the smartcard through galvanic connections. Thereby, the smartcard according to the present invention provides significantly improved ESD-protection by galvanically isolating the fingerprint sensor module from the contact plate.

The present invention is further based on the realization that ESD- protection can be even more improved by providing a capacitive coupling between the conductive inlay of a smartcard and a ground terminal of the contact plate. An electrostatic discharge from a finger to the fingerprint sensor which reaches the wireless interface circuit can then be directed to the ground terminal of the contact plate via the capacitive coupling instead of propagating to the microcontroller module where it may damage the microcontroller circuitry. If the smartcard is inserted into a reader terminal, the ground contact of the contact plate will be galvanically connected to a ground terminal of the reader. The capacitive coupling can thereby provide a predefined discharge path through the smartcard, via the contact plate to the reader, which is designed to minimize any discharge damages to the smartcard in case of an ESD.

An additional advantage of the present invention is that the number of galvanic contacts on the smartcard can be reduced, thereby simplifying manufacturing of the smartcard. The conductive inlays in a smartcard which form the wireless interfaces are easily patterned during manufacturing of the smartcard. In comparison, forming a galvanic contact between components on the smartcard requires both proper alignment of components and often also a heating step for forming the electrical contact, which may complicate the manufacturing process since plastic layers of the smartcard typically are sensitive to heat. Accordingly, the suggested implementation using one or more wireless interfaces instead of galvanic connections will facilitate an increased yield in smartcard manufacturing and assembly.

According to one embodiment of the invention, the first communication interface comprises a first inductive coil arranged in the fingerprint sensor module and a second inductive coil arranged in a conductive layer of the smartcard. The second inductive coil is thereby part of the wireless interface circuit.

According to one embodiment of the invention, the second communication interface comprises a third inductive coil arranged in a conductive layer of the smartcard and a fourth inductive coil arranged in the microcontroller module. The third inductive coil is thereby part of the wireless interface circuit. The first and/or the second communication interface is thereby an inductively coupled wireless communication interface comprising two inductive coils which are arranged adjacent to each other so that a change of current in one of the coils is detected by the other coil, thereby enabling wireless communication between the two coils. Inductive coils can also be referred to as inductive antennas.

According to one embodiment of the invention, the first communication interface comprises a first pair of capacitive patch antennas arranged in the fingerprint sensor module and a second pair of capacitive patch antennas arranged in a conductive layer of the smartcard. The second pair of capacitive patch antennas are thereby part of the wireless interface circuit.

According to one embodiment of the invention, the second communication interface comprises a third pair of capacitive patch antennas arranged in a conductive layer of the smartcard and a fourth pair of capacitive patch antennas arranged in the microcontroller module. The third pair of capacitive patch antennas are thereby part of the wireless interface circuit.

The first and/or the second communication interface can thereby be a capacitively coupled wireless communication interface comprising at least two overlapping capacitive plates which are arranged so that a change in voltage on a first plate is detected by the second plate and which results in a detectable change in voltage on the second plate, thereby enabling wireless communication between the two plates. Capacitive plates can also be referred to as capacitive patch antennas. Moreover, the capacitively coupled wireless communication interface is at least partially implemented in one or more conductive layers of the smartcard.

In the present context, each pair of capacitive patch antennas refer to two separate capacitive plates configured to communicate with two corresponding opposing capacitive plates located in a different conductive layer of the smartcard or in a component integrated in the smartcard. The reason for using a pair of capacitive antennas instead of a single antenna is that communication is typically performed differentially. In differential signaling, information is transmitted as the relative difference in voltage between the two capacitive plates for a pair of capacitive patch antennas.

According to one embodiment of the invention, the first communication interface comprises a galvanic coupling between the fingerprint sensor module and the wireless interface circuit.

According to one embodiment of the invention, the second communication interface comprises a galvanic coupling between the microcontroller module and the wireless interface circuit. Even though each wireless connection improves the ESD-protection properties of the smartcard it is possible to use both wireless and galvanic interfaces in a smartcard to good effect.

According to one embodiment of the invention, the capacitive coupling between the wireless interface circuit and the ground terminal comprises parallelly arranged conductive wires located in a conductive layer of the smartcard. Thereby, it is possible to form a capacitive coupling using a single conductive layer of the smartcard.

According to one embodiment of the invention the capacitive coupling between the wireless interface circuit and the ground terminal comprises overlapping conductive wires located in two different conductive layers of the smartcard.

The smartcard may further comprise a first dielectric material located between the conductive wires, where first dielectric material has a first dielectric constant which is higher than a second dielectric constant of a second dielectric material in of the smartcard. The first dielectric material may be located adjacent to the second dielectric material of the smartcard, or the first dielectric material may be located in a first layer of the smartcard and the second dielectric material may be located in a second layer of the smartcard. In an example embodiment, the second dielectric material may be located only between plates of a capacitive patch antenna of the smartcard.

The capacitive properties of the capacitive wire connection can be tailored by changing the length of the parallel or overlapping wire path, the dimensions of the wires and the distance between the wires. For ESD- protection purposes it is desirable to have a high capacitance to ground to more easily guide an ESD pulse to ground. On the other hand, a large capacitance to ground leads to higher attenuation of a high frequency signal used for communication. There is thus a trade-off between contradicting requirements for the capacitive coupling to ground. However, by selecting different dielectric materials for different capacitors in the circuit, the ESD protection can be maximized while minimizing the attenuation of the signal. Furthermore, the dielectric material of the capacitor intended to guide a ESD pulse to ground should have a sufficiently high dielectric strength so that the dielectric is not damaged by an ESD pulse. The discharge path is also determined by wire inductances of the inductive couplings, and it is therefore desirable to design the circuit as a whole to achieve the preferred discharge path to ground.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig. 1 schematically illustrates a smartcard comprising a fingerprint sensor module according to an embodiment of the invention;

Figs. 2A-B schematically illustrates a smartcard according to an embodiment of the invention;

Figs. 3A-B schematically illustrates a smartcard according to an embodiment of the invention;

Figs. 4A-B schematically illustrates a smartcard according to an embodiment of the invention; and Figs. 5A-B schematically illustrates a smartcard according to an embodiment of the invention.

Detailed Description of Example Embodiments

In the present detailed description, various embodiments of the smartcard and method for controlling communication in a smartcard according to the present invention are mainly described with reference to a smartcard comprising a capacitive fingerprint sensor embedded therein.

Fig. 1 schematically illustrates a smartcard 100 in the form of a payment card comprising a fingerprint sensor module 102 according to an embodiment of the invention. The smartcard 100 is provided with means for wireless communication with a reader terminal such as a point-of-sale (POS) terminal 104.

Figs. 2A-B to 5A-B schematically illustrate a smartcard 100 according to an embodiment of the invention where the respective Figs. 2A, 3A, 4A and 5A are circuit schematics describing components of the smartcard 100 and Figs. 2B, 3B, 4B, and 5B are exemplary illustrations of how an electrically conductive inlay of the smartcard 100 can be configured to achieve the described functionality.

The smartcard 100 can be considered to be formed as a laminate structure comprising a plurality of non-conductive layers, such as one or more core layers and outer layers on respective sides of the core layer(s).

Typically, the smartcard 100 will also comprise one or more electrically conductive layers embedded within the smartcard 100 to route signals between different parts of the card, to form antennas for energy harvesting and communication and also to form electrical components in the card. An electrically conductive layer of the smartcard can also be referred to as an inlay or a conductive inlay.

With reference to Figs. 2A-B, the smartcard 100 comprises a fingerprint sensor module 102 comprising a first inductive coil 201 , a microcontroller module 214, and a contact plate 216 comprising externally accessible contacts configured to communicate with a terminal, the contact plate being galvanically connected to the microcontroller module 214. The first inductive coil 201 of the fingerprint sensor module 102 may be arranged on an outer surface of the fingerprint sensor module 102 on either side of the fingerprint sensor module 102 or it may be embedded within the fingerprint sensor module 102, allowing the fingerprint sensor module 102 to communicate wirelessly with other components using the first inductive coil 201.

The contact plate 216 may be of the type commonly used in payment cards having contact pads configured according to ISO/IEC 7816-2 where the contact plate is capable of communicating with a reader terminal when in physical contact with the reader terminal. The contact plate 216, contact pads and /or the contact area may also be referred to as an “ISO-plate”.

In addition to controlling communication via the contact plate 216, the microcontroller module 214 may further comprise a secure element, SE, used in fingerprint authentication and the microcontroller module 214 may also be configured to control communication with and/or operation of the fingerprint sensor module 102. Thereby, there is no need for a separate secure element or for a specific controller for the fingerprint sensor module 102. However, some or all of the described functionalities may equally well be integrated in the fingerprint sensor module 102 or be provided as separate modules in the smartcard.

Moreover, the microcontroller module 214 may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the microcontroller module 214 includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device. The smartcard further comprises a wireless interface circuit 211 formed in at least one conductive layer of the smartcard 100. The wireless interface circuit 211 comprises a first communication interface 221 connecting the wireless interface circuit 211 to the fingerprint sensor module 102 and a second communication interface 222 connecting the wireless interface circuit 211 to the microcontroller module 214. Thereby, communication between the fingerprint sensor module 102 and the microcontroller module 214 is enabled via the wireless interface circuit 211. According to the invention, at least one of the first and second communication interface 221 , 222, is a wireless interface. In the embodiment illustrated in Figs. 2A-B, both the first and second communication interfaces 221 , 222, are wireless communication interfaces in the form of inductively coupled interfaces.

In the embodiment illustrated in Figs. 2A-B, the first communication interface 221 comprises a first inductive coil 201 arranged in the fingerprint sensor module 102 and a second inductive coil 202 arranged in a conductive layer of the smartcard 100, and the second communication interface 222 comprises a third inductive coil 203 arranged in a conductive layer of the smartcard and a fourth inductive coil 202 arranged in the microcontroller module 214.

The first communication interface 221 further comprises a capacitor 219 for tuning the frequency of the wireless interface circuit 211 . The capacitor 219 can be referred to as a tuning capacitor 219 which is formed by the parasitic capacitance between adjacent wires of the conductive inlay.

Moreover, the wireless interface circuit 211 comprises a capacitive coupling 223a-b to a ground terminal of the contact plate 216. It should the noted that the capacitances in practice are physically distributed capacitances between the wires. In principle, all of the inductances and capacitances are distributed properties. The circuit schematic uses a so-called lumped component approximation to create a circuit diagram representative of the functionality of the circuit.

The smartcard 100 further comprises an inductively coupled wireless communication interface in the form of an antenna loop 212 inductively coupled to a fifth inductive coil 205 of the microcontroller module 214. The antenna loop 212 comprises a sixth inductive coil 206 arranged to communicate with the fifth inductive coil 205, a tuning capacitor 220 and a seventh inductive coil 207 configured to communicate with an eighth inductive coil 208 of the external reader terminal 104. Preferably, the wireless interface circuit 211 is configured to communicate at a first frequency and the antenna loop 212 is configured to communicate at a second frequency different from the first frequency in order to avoid interference therebetween.

The first frequency is preferably higher than second frequency, meaning that communication between the microcontroller module 214 and the fingerprint sensor module 102 is performed at a higher frequency than the communication between the microcontroller module 214 and an external terminal 104. The first frequency may for example be in the range of 30 MHz to 900 MHz (VHF/UHF range) and the second frequency is 13.56 MHz which is the common frequency for NFC.

An advantage of having a higher carrier frequency is that the bandwidth scales with the carrier frequency. NFC operates at 13.56 MHz with a bandwidth slightly lower than 1 MHz. By increasing the carrier frequency by a factor of 10, the bandwidth increases by the same factor which is desirable to achieve the bandwidth required in communication between the microcontroller module 214 and the fingerprint 102 sensor, which is substantially higher than the bandwidth for standard NFC-communication at 13.56 MHz.

Moreover, the second frequency is preferably different from an overtone of the first frequency. Using two frequencies where the higher frequency is not an overtone of the lower frequency reduces the risk of crosstalk and other disturbances between the two wireless interfaces operating at the different frequencies. Moreover, the first frequency is preferably at least ten times higher than the second frequency in order to provide a data transfer rate required for communication between the fingerprint sensor module 102 and the microcontroller module Fig. 2B illustrates an example configuration of a conductive inlay showing the wireless interface circuit 211 , the antenna loop 212 and second, third, sixth and seventh inductive coils 202, 203, 206 and 207 of the smartcard 100. Fig. 2B further illustrates the outline of the fingerprint sensor module 102 and the microcontroller module 214. Moreover, the capacitors 223a-b coupling the wireless interface circuit 211 to a ground terminal of the contact plate 216 are shown as distributed wire capacitances which are galvanically coupled 224a-b to the contact plate, either directly or via terminals of the microcontroller module 214.

Figs. 3A-B illustrate an example embodiment which in many respects is similar to what is shown in Figs. 2A-B and described above. The difference in Figs. 3A-B is that the antenna loop 212 is galvanically connected to the microcontroller module 214, and the antenna loop 212 thereby comprises a single inductive coil 305 for wireless communication with an external terminal 104.

Figs. 4A-B schematically illustrates a circuit schematic and a conductive inlay of a smartcard 100 where the first communication interface 221 comprises a first pair of capacitive patch antennas 401 a-b arranged in the fingerprint sensor module and a second pair of capacitive patch antennas 402a-b arranged in a conductive layer of the smartcard, and the second communication interface 222 comprises a third pair of capacitive patch antennas 403a-b arranged in a conductive layer of the smartcard and a fourth pair of capacitive patch antennas 404a-b arranged in the microcontroller module 214. The wireless interface circuit 211 further comprises first and second inductive coils 405a-b configured to tune the frequency of the wireless interface circuit 211 .

In Figs. 5A-B, the first and second communication interfaces 221 , 222 are similar to what is illustrated in Fig. 4A-B and described above. The different from the embodiment of Fig. 4A-B is that the antenna loop 212 is galvanically connected to the microcontroller module 214, and the antenna loop 212 thereby comprises a single inductive coil 305 for wireless communication with an external terminal 104. Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the smartcard may be omitted, interchanged or arranged in various ways, the smartcard yet being able to perform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.