WO2019004904A1

WO2019004904A1 - Fingerprint sensing and body area network communication system

Info

Publication number: WO2019004904A1
Application number: PCT/SE2018/050664
Authority: WO
Inventors: Markus Andersson; Jan Nilsson; Hans THÖRNBLOM
Original assignee: Fingerprint Cards Ab
Priority date: 2017-06-26
Filing date: 2018-06-20
Publication date: 2019-01-03

Abstract

The present invention relates to a combined fingerprint sensing and body area network communication system (102, 400) for communication with an electronic unit (302, 312) using the body (301) of a user as communication medium. The system is operable in two states, a fingerprint sensing state, in which a readout circuitry (902) is controlled to provide sensing signals indicative of a fingerprint pattern, and a body area network communication state in which a communication signal is provided to at least a portion of a sensing arrangement(402) by one of the electronic unit and a body area network communication circuitry (404). The communication signal is transmitted using an alternating reference potential of the sensing arrangement. The communication signal being sent from one of the electronic device(100) and the body area network communication circuitry via the user's body and via the sensing arrangement portion to the other one of the electronic unit and the body area network communication circuitry.

Description

FINGERPRINT SENSING AND BODY AREA NETWORK COMMUNICATION

SYSTEM

Field of the Invention

The present invention relates to a combined fingerprint sensing and body area network communication system for communication with an electronic unit using the body of a user as communication medium. The present invention further relates to an electronic device comprising such a combined system.

Background of the Invention

Various types of biometric systems are used more and more in order to provide for increased security and/or enhanced user convenience.

In particular, fingerprint sensing systems have been adopted in, for example, consumer electronic devices, thanks to their small form factor, high

performance and user acceptance.

There is further an increasing usage of so-called body area networks in which electronic equipment is connected to a network using the body as communication medium. For example, in the medical industry it is has become common to connect e.g. sensors to a patients body for measuring health information from the patient, the information is downloaded via the body area network of the patient. The body area network (so-called BAN) can be used for both downloading information from the electronic equipment and for uploading information to the electronic equipment via the BAN. In order to connect to the BAN, a connection point, e.g. antenna is typically used.

To protect the user, the BAN requires authorization to access the network. This can be implemented by requiring the user to enter a password each time. For higher level of security and a more time efficient way for authorization is to implement a fingerprint sensor for authorization.

US2015/0163221 discloses to use a fingerprint scanner for allowing access to a BAN. In US2015/0163221 , the BAN system comprises a (yellow) ring which is attached to the scanner for connecting the user to the BAN. An electrode is arranged to detect the presence of a user, to thereby control the BAN to send requests and the fingerprint sensor to start scanning for biometric data.

Although the solution proposed by US2015/0163221 provides for access via a fingerprint sensor there still appears to be room for improvement related to integration of BAN components and fingerprint sensor components and to coexistence of the BAN system and the fingerprint sensor.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide a combined fingerprint sensing and body area network communication system with improved integration.

According to a first aspect of the present invention, it is therefore provided a combined fingerprint sensing and body area network

communication system for communication with an electronic unit using the body of a user as communication medium, comprising: a sensing

arrangement comprising: an array of sensing structures each facing a surface of the sensing arrangement and being arranged to capacitively couple to a finger touching the surface of the sensing arrangement; and read-out circuitry connected to each of the sensing structures for providing sensing signals indicative of a capacitive coupling between each sensing structure and a finger in response to a change in potential difference between a sensing structure potential of the sensing structure and a finger potential of the finger. The combined fingerprint sensing and body area network communication system further comprises a supply circuitry for providing a sensing reference potential to the sensing arrangement for alternating a reference potential of the sensing arrangement with respect to a device reference potential of a device comprising the combined fingerprint sensing and body area network communication system, wherein the alternation of the reference potential results in the change in potential difference between the finger potential and the sensing structure potential, and a body area network communication circuitry. The system is controllable between: a fingerprint sensing state, in which the readout circuitry is controlled to provide the sensing signals, and a body area network communication state in which a communication signal is provided to at least a portion of the sensing arrangement by one of the electronic unit and the body area network communication circuitry. The potential of the portion of the sensing arrangement is adapted to follow the sensing reference potential such that the communications signal is

transmitted using an alternating reference potential of the sensing

arrangement. The communication signal being sent from the one of the electronic device and the body area network communication circuitry via the user's body and via the sensing arrangement portion to the other one of the electronic unit and the body area network communication circuitry.

The present invention is based upon the realization that a fingerprint sensor has a suitable functionality for serving as a body area network antenna in addition to sensing of fingerprints. The sensing arrangement is connected to a supply circuitry which has the capability to alter the reference potential of the sensing arrangement. This function of alternating the reference potential may advantageously also be used for sending a

communication signal in the body area network communication state. In other words, no, or only minor modifications has to be made to a present sensing arrangement.

Furthermore the sensing arrangement is perfectly positioned to function as a connection means (i.e. an antenna) for connecting to an electronic unit with the user body as a transmission medium. Such

"connection means" may be any portion of the sensing arrangement including the die of the sensing arrangement. The location of the sensing arrangement for the BAN-transmission is advantageous since it will be touched by the finger for fingerprint acquisition thus thereby providing sufficient physical contact between the finger and the sensing arrangement for serving as an antenna for the BAN system. Furthermore, it has been realized that the BAN communication circuitry and the sensing arrangement may disturb each other, therefore the combined fingerprint sensing and body area network communication system operates in two separate states so that they do not interfere with each other.

Advantageously, by using existing hardware in the fingerprint sensor, also for the BAN signal transmission, the need for additional hardware is reduced for the combined system compared to prior art system. Since the fingerprint sensor system is already adapted for capacitive coupling to the finger, the BAN system (i.e. the body area network communication circuitry) may advantageously use this functionality also for communicating with the electronic unit in contact with the user's body.

The electronic device may, for example, be a portable electronic device, such as a mobile phone, a smart watch, an electronic door lock, or a chip card (a so-called smart card). Furthermore, the electronic device may be a sub-system comprised in a more complex apparatus, such as a vehicle.

The sensing structures may, for example, be capacitive sensing structures, each providing a measure indicative of the capacitive coupling between that particular sensing structure and a finger surface touching the sensor surface. Sensing structures at locations corresponding to ridges in the fingerprint will exhibit a stronger capacitive coupling to the finger than sensing structures at locations corresponding to valleys in the fingerprint. Both one and two-dimensional sensors are possible and within the scope of the invention.

The read-out circuitry may include circuitry for converting analog signals to digital signals. Such circuitry may include at least one analog to digital converter circuit. In such embodiments, the fingerprint sensing system may thus provide a fingerprint pattern signal as a digital signal. In other embodiments, the fingerprint pattern signal may be provided as an analog signal. For example, the signals may be analog or digital values indicative of a voltage, which may in turn be proportional to the capacitance of the capacitor constituted by the finger (or other conductive object in the vicinity of the finger detecting structure), the finger detecting structure and the dielectric material there between. The sensed fingerprint pattern may be used for various purposes, such as biometric enrollment or authentication, or fingerprint pattern based navigation etc.

That the read-out circuitry is connected to each of the sensing structures in such a way that the sensing structure potential substantially follows the sensing reference potential of the sensing arrangement should be understood to mean that a change of the sensing reference potential results in a substantially corresponding change in the sensing structure potential. Depending on the configuration of the read-out circuitry, the sensing structure potential may be substantially the same as the sensing reference potential, or there may be a substantially constant potential difference between the sensing reference potential and the sensing structure potential.

The sensing reference potential may for example be provided to alter the sensor ground of the sensing arrangement in relation to an electronic device ground, for example via a device connection interface for connection of the fingerprint sensing system to an electronic device, the device connection interface including a device reference potential input for receiving a device reference potential from the electronic device.

The electronic unit may be any electrical unit which is operable to send and/or receive signals. The electronic unit is arranged so that it can communicate with the body area network communication circuitry (BAN communication circuitry) via the user's body, thus the signal travels through the user's body. The BAN may for example follow the standard IEEE 802.15.6 (Body Area Network) which is part of the 802.15 (Wireless Personal Area Network) series.

The transition between the fingerprint sensing state and the body area network communication state may be controlled by a host control unit, for example a control unit comprised in the electronic device comprising the combined fingerprint sensing and BAN communication system.

A dielectric structure which may cover the sensing structures may advantageously be at least 20 pm thick and have a high dielectric strength to protect the underlying structures of the fingerprint sensing device from wear and tear as well as ESD (electrostatic discharge). Even more

advantageously, the dielectric structure may be at least 50 pm thick or even several hundred pm thick. For instance, the dielectric structure may be at least partly constituted by a structural part of the electronic device, such as a cover glass or a laminate.

According to embodiments of the invention, the portion of the sensing arrangement may be the entire sensing arrangement. Accordingly, the sensing reference potential is altered for the entire sensing arrangement which thereby provides the advantages that the entire sensing arrangement may serve to transmit or receive the communication signal in the body area network communication state. Thereby, the area of the "antenna" formed by the entire sensing arrangement is relatively large which provides for improved coupling to the user's body compared to a smaller area antenna.

In embodiments of the invention, in the body area network

communication state, the communication signal may be provided to the portion of the sensing arrangement only by the body area network

communication circuitry, wherein the communication signal is being sent from the body area network communication circuitry via the user's body and via the portion of the fingerprint sensor to the electronic unit. In other words the system may be configured to only send the communication signal, from the electronic device to the electronic unit via the user's body and the sensing arrangement.

The communication signal may be sent from the portion of the sensing arrangement by modulating the sensing reference potential for acting as a carrier signal. In other words, the alternating reference potential of the sensing arrangement is used both for providing the change in potential difference between the user's finger and the sensing structures in the fingerprint sensing state, and for acting as a carrier signal for sending the communication signal.

According to another embodiment of the invention, in the body area network communication state, the communication signal may be provided to the portion of the sensing arrangement only by the electronic unit, wherein the communication signal is being sent from the electronic unit via the user's body and via the portion of the sensing arrangement to the body area network communication circuitry. In other words the system may be configured to only receive the communication signal, from the electronic unit to the electronic device via the user's body and the sensing arrangement.

In one embodiment, the body area network communication circuitry may be in an at least partly inactive mode in the fingerprint sensing state. In this way, the interference between the BAN communication circuitry and the sensing arrangement is reduced. The at least partly inactive mode may for example be that the BAN communication circuitry may not communicate with the electronic unit on the user's body, thus receive signals from the electronic unit or send signals to the electronic unit, in the fingerprint sensing state. The BAN communication circuitry may however, communicate with other external devices in the at least partly inactive mode, for example to send information to the cloud or to a stationary or mobile electronic device.

According to one embodiment, the sensing arrangement may further comprise control circuitry, wherein a transition between the states is controlled by the control circuitry. Thus, the sensing arrangement, e.g. a fingerprint sensor, may be the master in the system, and the BAN- communication circuitry thus serves as a slave, thereby being controlled by the control circuitry of the sensing arrangement.

In one embodiment, the sensing arrangement may be configured to provide an instruction signal to the body area network communication circuitry for allowing the body area network communication circuitry to send the communication signal to the electronic unit via the user's body and the sensing arrangement or to receive the communication signal from the electronic unit. The instruction signal thus provides an efficient

implementation for reducing the interference between the BAN

communication circuitry and the sensing arrangement.

In one embodiment, the sensing arrangement may be configured to instruct the body area network communication circuitry to be in an at least partly inactive mode during a time slot in which the system is in the fingerprint sensing state.

According to embodiments of the invention, the sensing signals may be sampled in a first frequency range, and the communication signal may be sent in a second frequency range different from the first frequency range, wherein the communication signal is being sent at least partly during a time during which overlaps with a time duration at which said sensing signals are sampled. The fingerprint sensing state and the body area network

communication state is in this case separated by operating in different frequency bands. For example, the body area network communication circuitry may operate (e.g. send and/or receive signals) at frequencies in the range of 100 MHz up to e.g. 10 GHz, whereas the read-out circuitry may operate at frequencies lower than 100 MHz. For reducing interference between the two states, a filter circuit may be suitable provided.

According to another embodiment, the body area network

communication circuitry may comprise a transceiver for communicating information obtained from the electronic device and comprised in the communication signal to an external electronic device. In other words, the body area network communication circuitry may communicate with devices other than the electronic unit in the BAN. For example, the body area network communication circuitry may send information read form the electronic unit on the user's body to an external communication center e.g. a server or a central computer, or even to a body area network communication circuitry of a second BAN. The transceiver may transmit signals wirelessly to external devices.

The body area network communication circuitry may also comprise a transceiver for sending signals to the electronic unit.

According to one embodiment, the system may be configured to:

perform, in the a fingerprint sensing state, a user authentication procedure to authenticate the user, when the result of the authentication procedure indicates a successful authentication of the user, read, using the body area network communication circuitry, information from the electronic unit. Thus, the sensing arrangement may sense the fingerprint pattern of the user's finger in the fingerprint sensing state to acquire a verification representation from a fingerprint image, if the verification representation matches an enrolment representation previously enrolled by the user; the system may proceed to read information from the electronic unit connected to the BAN. Note that the BAN may have more than one electronic unit connected to it.

According to a second aspect of the present invention, there is provided an electronic device comprising a control unit and a combined fingerprint sensing and body area network system according to any one of the embodiments of the previous aspect, and a control unit for: providing an authentication request for the finger to the fingerprint sensing and body area network communication system; receiving an authentication signal from the fingerprint sensing and body area network communication system; and performing at least one action if the authentication signal indicates

authentication success.

The electronic device may advantageously be a mobile phone.

However, other electronic devices are of course thinkable such as tablets, laptops desktop computers, electronic door locks, etc.

Further embodiments of, and effects obtained through this second aspect of the present invention are largely analogous to those described above for the first aspect of the invention.

Within the context of the invention, the expression "fingerprint image" should be interpreted broadly and to include both a regular "visual image" of a fingerprint of a finger as well as a set of measurements relating to the finger when acquired using the fingerprint sensor. In addition, the expression

"control unit" should be understood to include any type of computing device, such as an ASIC, a micro-processor, etc. It should also be understood that the actual implementation of such a control unit may be divided between a plurality of devices/circuits.

In the context of the present application, an "enrolment representation" and/or a "verification representation" of a fingerprint image may be any information extracted from the fingerprint image, which is useful for assessing the similarity between fingerprint images acquired at different times. For instance, the enrolment/verification representation of the fingerprint image may comprise descriptions of fingerprint features (such as so-called minutiae) and information about the positional relationship between the fingerprint features. Alternatively, the representation of the fingerprint image may be the image itself, or a compressed version of the image. For example, the image may be binarized and/or skeletonized.

Various ways of extracting such verification representation or enrolment representation from a fingerprint image are well-known to a person of ordinary skill in the relevant art.

In summary, the present invention relates to a combined fingerprint sensing and body area network communication system for communication with an electronic unit using the body of a user as

communication medium. The system is operable in two states, a fingerprint sensing state, in which a readout circuitry is controlled to provide sensing signals indicative of a fingerprint pattern, and a body area network

communication state in which a communication signal is provided to at least a portion of the sensing arrangement by one of the electronic unit and a body area network communication circuitry. The communication signal is

transmitted using an alternating reference potential of the sensing

arrangement. The communication signal being sent from one of the electronic device and the body area network communication circuitry via the user's body and via the sensing arrangement portion to the other one of the electronic unit and the body area network communication circuitry.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled addressee 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 mobile phone comprising a combined fingerprint sensing and body area network system according to an example embodiment of the present invention;

Fig 2 conceptually shows a combined fingerprint sensing and body area network communication system comprised in the electronic device in fig 1 ;

Fig. 3a-b each illustrates an exemplary application for the combined fingerprint sensing and body area network communication system;

Fig 4 is a schematic block diagram of an embodiment of a combined fingerprint sensing and body area network communication system;

Fig. 5 is an exemplary timing diagram for a coexistence signal;

Fig. 6a-b are conceptual block diagrams of the embodiments of the combined fingerprint sensing and body area network communication system;

Fig 7 is a schematic cross section view of a portion of a fingerprint sensing and body area network communication system; and

Figs 8a-b are graphs schematically illustrating the relation between the sensing reference potential and the sensing signal output by the charge amplifier in Fig. 7, as well as exemplary sampling times.

Detailed Description of Example Embodiments

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout. For example, various embodiments of the fingerprint sensing and body area network communication system according to the present invention are mainly described with reference to an electronic device in the form of a mobile phone. Although this is convenient for many applications, it should be noted that many other kinds of electronic devices such as desktop computers, tablets, laptops, or stationary devices e.g. at hospitals for downloading health information from a patient, or electronic door locks.

Turning now to the drawings and to Fig 1 in particular, there is schematically illustrated an electronic device according to embodiments of the present invention, in the form of a mobile phone 100 with a combined fingerprint sensing and body area network communication system 102 and a display unit 104 with a touch screen interface 106. In this embodiment the combined fingerprint sensing and body area network communication system 102 and the display unit 104 are together arranged at the front side of the mobile phone 100. The combined fingerprint sensing and body area network communication system 102 may, for example, be used for unlocking the mobile phone 100 and/or for authorizing transactions carried out using the mobile phone 100, or for downloading health information from a patient carrying a medical electronic device such as a sensor on his/her body or for unlocking a door equipped with an electronic door lock. The combined fingerprint sensing and body area network communication system 102 may of course also be placed on the backside or on the side of the mobile phone 100.

Preferably and as is apparent for the skilled person, the mobile phone 100 shown in Fig. 1 further comprises a first antenna for WLAN/Wi-Fi communication, a second antenna for telecommunication communication, a microphone, a speaker, and a phone control unit. Further hardware elements are of course possibly comprised with the mobile phone. It should furthermore be noted that the invention may be applicable in relation to any other type of portable electronic device, such as a laptop, a remote control, a tablet computer, or any other type of present or future similarly configured device.

With reference to Fig. 2, there is conceptually illustrated a somewhat enlarged view of the combined fingerprint sensing and body area network communication system 102. In the case of employing a capacitive sensing technology, the sensing arrangement of the combined fingerprint sensing and body area network communication system 102 is configured to comprise a large plurality of sensing structures, preferably arranged as a two-dimensional array. The two-dimensional array may have sizes depending on the planned implementation and in an embodiment 160x160 pixels are used. Other sizes are of course possible and within the scope of the invention, including two- dimensional array with less pixels as compared to the above example. A single sensing structure (also denoted as a pixel) is in Fig. 2 indicated by reference numeral 202.

Fig. 3a schematically shows an implementation of the combined fingerprint sensing and body area network system 102 integrated in an electronic device 100. There is shown an electronic unit 302 arranged in contact with a user's body 301 . The combined fingerprint sensing and body area network system 102 comprises a sensing arrangement (not shown in Fig. 3) such that a body area network communication circuitry (not shown in Fig. 3) (e.g. comprising a transceiver) can communicate with the electronic unit 302 via the user's body and any portion of the sensing arrangement. The user's body serves as a conduction medium. The sensing arrangement comprises sensing structures which are used for sensing a fingerprint pattern of the user.

Although there is here only shown a single electronic unit 302 in Fig. 3a, there may in practice be more than one electronic unit arranged in contact with the user's body and which can communicate (signals denoted 304) via the user's body 301 with the body area network communication circuitry. The body area network communication circuitry may comprise a transceiver (not shown) for sending signals (denoted 306) to an external device 308 such as a control unit located remotely. The signals provided to the externals device may for example be data obtained from the electronic unit 302. The

transceiver may communicate via wires or wirelessly (e.g. BlueTooth, IR, Wifi, etc.) with the external device 308. Fig. 3b schematically illustrates another possible implementation of the combined fingerprint sensing and body area network system 102. In Fig. 3b, the combined fingerprint sensing and body area network system 102 is used for unlocking an electronic lock 312 on a door 314. In such an application, an authentication signal 304 may be sent from the combined fingerprint sensing and body area network system 102 through the user's body to the electronic lock 312 in order to unlock (or lock) the electronic lock 312 on the door 314. The authentication signal 304 will of course be recognizable by a control circuitry in the electronic lock 312, the control circuitry being configured to control the lock 312 to be in a locked state or an unlocked state.

Accordingly, the combined fingerprint sensing and body area network system 102 advantageously enables a secure way of transmitting

authentication signals to electronic units (e.g. lock 312 or unit 302).

Furthermore, another advantageous security aspect is that it is not necessary to store the sensitive fingerprint enrolment data at the lock 312 (or at another electronic unit 302) which may constitute a security risk.

Fig. 4 schematically shows a block diagram of an embodiment of the invention. In Fig. 4, the sensing arrangement 402 comprised in a fingerprint sensor of the combined fingerprint sensing and body area network system 400 is configured to communicate with the body area network communication circuitry 404 to instruct the body area network communication circuitry 404 when to read data from the electronic unit (see Fig. 3a-b) or send signals to the electronic unit 302 arranged on or near the user's body.

In the fingerprint sensing state, the sensing arrangement is provided with a sensing reference potential, and the read-out circuitry of the sensing arrangement is configured to provide sensing signals indicative of the capacitive coupling between a finger and the sensing structures. The sensing arrangement is configured to instruct the body area network communication circuitry 404 when it is allowed to read/send signals from/to the electronic unit via the fingerprint sensor. This can be performed by sending an instruction signal CS (see also Fig. 5) to the body area network communication circuitry 404. Fig. 5 schematically illustrates a timing diagram of a "coexistence signal", i.e. the instruction signal (CS), e.g. a control signal provided by the sensing arrangement to the body area network communication circuitry for controlling transitions between the fingerprint sensing state and the body area network communication state. During a first time slot ti the combined fingerprint sensing and body area network communication system is in a fingerprint sensing state. After time t-i, the sensing arrangement may have finished sensing a fingerprint pattern of a user's finger, and may thus allow the body area network communication circuitry to communicate with the electronic unit via the sensing arrangement, thereby the system transitions to the body area network communication state.

The transition is initiated by the sensing arrangement which is the master in the system; consequently the body area network communication circuitry is the slave. Thus, first (during t-i) the fingerprint pattern is read, subsequently (during t₂), the electronic unit is read by the body area communication circuitry, or a communication signal is sent to the electronic unit from the body area network communication circuitry. In the fingerprint sensing state, the body area network communication circuitry is in an at least partly inactive mode, thereby not communicating with the electronic unit in contact with the user's body via the sensing arrangement. Optionally, after time t₂, the system returns to the fingerprint sensing state. The control signal described in Fig. 5 may be provided either by the sensing arrangement or by a host electronic device to the body area network communication circuitry.

Alternatively, the sensing signals may be sampled simultaneously as that the communication signal is sent or received. The fingerprint sensing state and the body area network communication state is in this case separated by operating in different frequency bands. For reducing

interference between the two states, a filter circuit may be suitable provided e.g. between the sensing arrangement and the body area communication circuitry.

Fig. 6a is a conceptual overview of embodiments of the combined fingerprint sensing and body area communication system 400. A set of switching circuitries, here functionally illustrate as switches 608 and 609 controls whether the supply circuitry 804 or the body area network

communication circuitry 404 is connected to a supply interface 602 of the sensing arrangement 402.

In the fingerprint sensing state, the sensing arrangement 402 receives a supply voltage from the supply circuitry 804 as the substantially constant difference between a sensor ground potential SGND and a sensor supply potential SVDD. The sensor ground potential SGND and the sensor supply potential SVDD vary together in relation to device ground DGND. In the fingerprint sensing state, the switches 608 and 609 is thus in a state in which the supply circuitry 804 is connected to a supply voltage input 605 and to a sensor reference potential input 604 of the supply interface 602 of the sensing arrangement 402.

In the body area network communication state, the switching circuitries 608 and 609 connects the body area network communication circuitry 404 to the supply interface 602 such that the body area network communication circuitry 404 may provide a communication signal to at least one of the supply voltage input 605 and the sensor reference potential input 604 of the supply interface 602 (this state of the switches are shown in fig. 6a). The body area network communication circuitry 404 may thereby provide a supply voltage to the supply interface 602 for the purpose of sending a communication signal from the body area network communication circuitry 404 to the sensing arrangement 402, which communication signal is provided to an electronic unit (not shown) via a user's body. Similarly the body area network

communication circuitry 404 may be connected to the supply interface 602 for receiving a communication signal from the electronic unit via the user's body and the sensing arrangement 402.

In the fingerprint sensing state, the body area network communication circuitry 404 may be inactive. A sensor controller (not shown) or an external host may be configured to control the body area network communication circuitry 404 to be active or in-active. Furthermore, the fingerprint sensing state, the switching circuitries 608 and 609 disconnects the body area network communication circuitry 404 from the sensing arrangement 402 which advantageously reduces interference between the body area network communication circuitry and the sensing arrangement in the fingerprint sensing state.

Although not explicitly shown in the drawings, the body area network communication circuitry 404 and the supply circuitry 804 may optionally be provided as a single unit, e.g. the body area network communication circuitry 404 may comprise the supply circuitry 804 or vice versa. Accordingly, the body area network communication circuitry 404 may comprise its own supply circuitry for modulating a voltage potential, or the body area network communication circuitry 404 may utilize the supply circuitry 804.

Now turning to fig. 6b which is another conceptual overview of embodiments of the invention. A difference between Fig.6a and Fig. 6b is that in Fig. 6b, a switching circuit 603 is arranged such that the sensor reference potential input 604 may be connected to the sensor supply input 605 in the body area network communication state, i.e. when the switching circuitries is in a state in which the body area network communication circuitry 404 is connected to the supply interface 602. In other words, the switching circuit 603 is configured to connect the sensor ground input 604 and the sensor supply input 605 which means there will be a substantially zero potential difference between the sensor ground potential SGND and a sensor supply potential SVDD.

Fig. 7 is a schematic cross section view of a portion of a fingerprint sensing and body area network communication system 400 according to embodiments of the invention with a finger 19 placed on top of the sensing arrangement 402 of the combined fingerprint sensing and body area network communication system 400. The combined fingerprint sensing and body area network communication system 400 further comprises a body area network communication circuitry 404 connected to the sensing arrangement 402 via switching circuitries 608 and 609 as is described in more detail with reference to Figs. 6a-b. The finger 19 has a finger potential FGND. As is schematically shown in fig 7, the combined fingerprint sensing and body area network

communication system 400 comprises a plurality of sensing structures 202, here in the form of metal plates underneath a dielectric structure 24, and read-out circuitry 902 connected to each of the sensing structures 202. In the example embodiment of fig 3, the read-out circuitry comprises a plurality of charge amplifiers 901 , a multiplexer 39, a sampling circuitry 220, an ADC 809, and selection circuitry, here functionally illustrated as a simple selection switch 40 for allowing selection/activation of different sensing elements 8.

The charge amplifier 901 comprises at least one amplifier stage, here schematically illustrated as an operational amplifier (op amp) 41 having a first input (negative input) 42 connected to the sensing structure 202, a second input (positive input) 43 connected to sensor ground SGND, and an output 44. In addition, the charge amplifier 901 comprises a feedback capacitor 45 connected between the first input 42 and the output 44, and reset circuitry, here functionally illustrated as a switch 46, for allowing controllable discharge of the feedback capacitor 45. The charge amplifier 901 may be reset by operating the reset circuitry 46 to discharge the feedback capacitor 45.

As is often the case for an op amp 41 , the potential at the first input 42 follows the potential applied to the second input 43. Depending on the particular amplifier configuration, the potential at the first input 42 may be substantially the same as the potential at the second input 43, or there may be a substantially fixed offset between the potential at the first input 42 and the potential at the second input 43.

In fig 7, a sensing arrangement controller 802 is shown to control the selection circuitry 40, the multiplexer 39, the sampling circuitry 220 and the ADC 809. The sensing arrangement controller 802 may be an external controller comprised in the host electronic device or it may be integrated in the combined fingerprint sensing and body area network communication system 400. The sensing arrangement controller 802 may also be configured to control the transition between the fingerprint sensing state the body area network communication state. The change in potential difference between the finger 19 and the sensing structure 202 may be provided in different ways. For example, a supply circuitry 804 of the host device, e.g. the electronic device 100 may provide the sensing reference potential (SGND) to the sensing arrangement Alternatively, the sensing reference potential may be provided directly to the sensing arrangement or via an interface circuitry, or by a supply circuitry 804 local to the combined fingerprint sensing and body area network

communication system 400. The supply circuitry 804 is connected to a reference ground connection SGND of the sensing arrangement 402.

Thereby, the change in potential difference between the finger 19 and the sensing structure 202 is achieved by providing the sensing reference signal to the reference ground connection SGND such that the ground potential of the sensing arrangement follows the sensing reference signal.

At least when the fingerprint sensing and body area network system 400 is in a fingerprint sensing state, a sensing reference potential (SGND) is provided to the sensing arrangement in the form of a sensing reference signal alternating, in relation to the device reference potential DGND of the electronic device, between a first sensing reference potential V_L and a second sensing reference potential V_H. Since the finger potential FGND is

substantially constant in relation to the device reference potential DGND (for example through an electrical connection between the electronic device and the hand of the user), and the potential of the sensing structure 202

substantially follows the potential at the second input 43 of the charge amplifier 901 , the time-varying, in relation to the device reference potential DGND, potential SGND at the second input 43 results in a time-varying potential difference between the sensing structure 202 and the finger 19.

A change in potential difference between the sensing structure 202 and the finger 19 will in turn result in a change of the charge carried by the sensing structure 202 that is indicative of the capacitive coupling between the finger 19 and the sensing structure 202. The sensing signal V_s provided at the output 44 of the charge amplifier 901 will be indicative of this change of charge carried by the sensing structure 202 and thus of the local capacitive coupling between the finger 19 and the sensing structure 202.

Between sensing operations, the feedback capacitor 45 needs to be reset (the charge across the feedback capacitor 45 is equalized). This is carried out using the reset switch 46.

When the indicated sensing element 8 is selected for sensing, the selection switch 40 is closed to connect the output of the charge amplifier to the readout line 48. The readout line 48 is connected to the multiplexer 39. As is schematically indicated in fig 7, additional readout lines providing sensing signals from other groups of sensing elements are also connected to the multiplexer 39.

At least the operation of the reset switch 46 and the sampling of the sensing signal V_s need to be synchronized with changes of the sensor ground potential SGND in relation to the device ground potential DGND. In the example embodiment of fig 7, this synchronization is handled by the sensing arrangement controller 802.

An exemplary timing relation between sensing reference signal SGND, operation of the reset switch 46 and sampling of the sensing signal V_s using the sampling circuit 220 will be described below with reference to figs 8a-b.

Fig 8a shows the sensing reference potential (the sensor ground potential SGND) in relation to the device ground potential DGND. As described above, the potential of the sensing structure 202 in relation to the device ground potential DGND will exhibit substantially the same behavior, and fig 8b schematically shows the sensing signal V_s.

Referring first to fig 8a, the sensor ground potential SGND goes from the second sensing reference potential V_H to the first sensing reference potential V_L, in relation to the device ground potential DGND, at T-i , and then goes back from V_L to V_H at T₂. These transitions are controlled by a timing signal provided from the combined fingerprint sensing and body area network communication system 400. Such timing signal may be provided in various ways known to the skilled person, for example from a timing circuitry comprising e.g. a controllable clock, a state machine, a pulse generator and the like for forming timing signal.

A first delay Δίι after first transition, at T-i, the reset switch 46 is operated to bring the charge amplifier 901 to such a state (enabled state) that the output provides a signal if the charge on the sensing plate 202 changes. A second delay Δί₂ after first transition, the sampling circuit 220 is controlled to sample the sensing signal a first time, resulting in a first sampled value S-i.

When the sensor ground potential SGND goes from low to high at T₂, there will be a change in the charge on the sensing plate 202 resulting from capacitive coupling with the finger 19. This change in charge is translated into a change in the voltage provided by the charge amplifier 901 , that is, a change in the sensing signals V_s.

A third delay Δί₃ after the second transition, at T₂, the sampling circuit 22 is controlled to sample the sensing signal a second time, resulting in a second sampled value S₂. The difference between S₂ and Si is a measure indicative of the capacitive coupling between the sensing plate 202 and the finger 19. This capacitive coupling may also be used by the body area communication circuitry for transmitting and receiving signals to/from an electronic unit in contact with a user's body.

For transmitting a communication signal in the body area network communication state, the desired signal to be sent to the electronic unit is provided by the body area network communication circuitry 404 to the sensing arrangement 402. The signal is transmitted to the electronic unit by controlling the sensing reference potential as described above, in other words, the modulation of the sensing reference potential is used to form a capacitive coupling between the sensing arrangement and the electronic unit in contact with the user's body such that the communication signal may be sent from the body area network communication circuitry to the electronic unit via the user's body. In the same way, e.g. by utilizing the capacitive coupling between the sensing arrangement and the user's body, a signal may be received by the body area network communication circuitry from the electronic unit. Since the sensing reference potential is provided to the sensor ground SGND, the potential of the entire sensing arrangement 402 is altered which means that any part of the sensing arrangement including the sensor ground plane, sensor die, sensing structures, etc, may be used for sending and receiving signals in the body area network communication state.

The body area network communication circuitry may share the sampling circuit 220 and the ADC 809 with the sensing arrangement or it may comprise its own sampling circuit and ADC, although not shown here.

The sensing arrangement may advantageously be manufactured using CMOS technology, but other techniques and processes may also be feasible. For instance, an insulating substrate may be used and/or thin-film technology may be utilized for some or all process steps needed to manufacture the sensing arrangement.

A control unit or controller in the invention may include a

microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit or controller may also, or instead, each 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 control unit or controller 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. It should be understood that all or some parts of the functionality provided by means of the control unit or controller (or generally discussed as "processing circuitry") may be at least partly integrated with the fingerprint sensor, or may be part of the electronic device.

The control functionality of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwire system. Embodiments within the scope of the present disclosure include program products comprising machine-readable medium for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium.

Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine- readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

Additionally, 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.

In addition, variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Furthermore, 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.

Claims

1 . A combined fingerprint sensing and body area network communication system (102, 400) for communication with an electronic unit (302, 312) using the body (301 ) of a user as communication medium, characterized by comprising:

- a sensing arrangement (402) comprising:

- an array of sensing structures (202) each facing a surface of the sensing arrangement and being arranged to capacitively couple to a finger touching said surface of the sensing arrangement; and

- read-out circuitry (902) connected to each of said sensing structures for providing sensing signals indicative of a capacitive coupling between each sensing structure and a finger (19) in response to a change in potential difference between a sensing structure potential of said sensing structure and a finger potential of said finger,

- a supply circuitry (804) for providing a sensing reference potential to said sensing arrangement for alternating a reference potential of said sensing arrangement with respect to a device reference potential of a device comprising said combined fingerprint sensing and body area network communication system, wherein said alternation of the reference potential results in said change in potential difference between said finger potential and said sensing structure potential,

- a body area network communication circuitry (404), wherein the system is controllable between:

- a fingerprint sensing state, in which said readout circuitry is controlled to provide said sensing signals, and

- a body area network communication state in which a communication signal is provided to at least a portion of the sensing arrangement by one of the electronic unit and the body area network communication circuitry,

the potential of said portion of the sensing arrangement is adapted to follow said sensing reference potential such that said communication signal is transmitted using an alternating reference potential of the sensing arrangement,

the communication signal being sent from said one of the electronic device and the body area network communication circuitry via the user's body and via said sensing arrangement portion to the other one of the electronic unit and the body area network communication circuitry.

2. The combined fingerprint sensing and body area network communication system according to claim 1 , wherein the portion of the sensing arrangement is the entire sensing arrangement.

3. The combined fingerprint sensing and body area network communication system according to any one of claim 1 or 2, wherein, in said body area network communication state,

said communication signal is provided to said portion of the sensing arrangement only by said body area network communication circuitry, wherein the communication signal is being sent from said body area network communication circuitry via the user's body and via said portion of the sensing arrangement to the electronic unit.

4. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, wherein in said body area network communication state,

said communication signal is sent from said portion of the sensing arrangement by modulating the sensing reference potential for acting as a carrier signal.

5. The combined fingerprint sensing and body area network communication system according to any one of claim 1 or 2, wherein, in said body area network communication state,

said communication signal is provided to said portion of the sensing arrangement only by said electronic unit, wherein the communication signal is being sent from said electronic unit via the user's body and via said portion of the sensing arrangement to the body area network communication circuitry.

6. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, wherein said body area network communication circuitry is in an at least partly inactive mode in said fingerprint sensing state.

7. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, wherein said sensing arrangement further comprises sensing arrangement controller (802), wherein a transition between said states is controlled by said sensing arrangement controller.

8. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, wherein said sensing arrangement is configured to provide an instruction signal to said body area network communication circuitry for allowing the body area network communication circuitry to send said communication signal to the electronic unit via the user's body and the sensing arrangement or to receive said communication signal from said electronic unit.

9. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, wherein said sensing arrangement is configured to instruct the body area network communication circuitry to be in an at least partly inactive mode during a time slot during which said system is in said fingerprint sensing state.

10. The combined fingerprint sensing and body area network communication system according to any one of claims 1 to 8, wherein said sensing signals are sampled in a first frequency range, and the communication signal is sent in a second frequency range different from the first frequency range, wherein the communication signal is being sent at least partly during a time during which overlaps with a time duration at which said sensing signals are sampled.

1 1 . The combined fingerprint sensing and body area network communication system according to anyone of the preceding claims, wherein said body area network communication circuitry comprises a transceiver for sending information obtained from said electronic unit and comprised in the communication signal to an external electronic device.

12. The combined fingerprint sensing and body area network communication system according to anyone of the preceding claims, wherein said body area network communication circuitry comprises a transceiver for sending communication signals to said electronic unit.

13. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, configured to:

- perform, in said a fingerprint sensing state, a user authentication procedure to authenticate the user,

- when the result of the authentication procedure indicates a successful authentication of the user, read, using the body area network communication circuitry, information from said electronic unit.

14. The combined fingerprint sensing and body area network communication system according to any one of the preceding claims, comprising a switching circuit (603) configured to, in said body area communication state, connect a sensor ground input of the sensing arrangement with a sensor supply input of the sensing arrangement.

15. An electronic device (100), compris - a fingerprint sensing and body area network communication system according to any one of claim 1 to 14; and

- a control unit for:

- providing an authentication request for said finger to the fingerprint sensing and body area network communication system;

- receiving an authentication signal from the fingerprint sensing and body area network communication system; and

- performing at least one action if said authentication signal indicates authentication success.

16. The electronic device according to claim 15, wherein the electronic device is a mobile phone.