Fingerprint detection device having an edge compensation structure

Abstract

1. A fingerprint detection system (3) for detecting a fingerprint pattern of a finger (26), the fingerprint detection system (3) comprising: a sensor array (7) having a plurality of conductive sensing structures (10); a readout circuit (39) connected to each of the sensing structures (10) for providing a detection signal representative of capacitive coupling between the sensing structures (10) and the finger (26); a first signal supply circuit (49) for supplying a first time-varying voltage (V1(t)) signal to at least a portion of the sensor array (7); at least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) disposed outside the sensor array (7); and a second signal supply circuit (63; 65) for supplying a second time-varying voltage (V2(t)) signal to at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83).

Description

Technical Field

[0001] The present invention relates to a fingerprint detection system and a method for detecting a fingerprint pattern of a finger.

Background Art

[0002] The use frequency of various types of biometric systems is increasing more and more in order to improve security and / or enhance user convenience.

[0003] In particular, fingerprint detection systems have been adopted in consumer electronic devices, for example, for their small form factor, high performance, and user acceptance.

[0004] Among various available fingerprint detection principles (such as capacitance, light, sound, heat, etc.), capacitive detection is most commonly used in applications where size and power consumption are important issues.

[0005] A capacitive fingerprint sensor generally provides a magnitude representing the capacitance between each of a plurality of detection structures and a finger placed on the surface of the fingerprint sensor.

[0006] U.S. Patent No. 9,383,876 discloses a fingerprint detection system including a sensor array having a plurality of detection structures, a readout circuit connected to each of the detection structures to supply a detection signal, and a power supply circuit arranged to supply a substantially constant supply voltage, which is a difference between a high drive potential and a low drive potential, to the readout circuit. The fingerprint detection system according to U.S. Patent No. 9,383,876 is configured such that during operation of the fingerprint detection system, the low drive potential and the high drive potential oscillate in phase with respect to the reference potential of the device including the fingerprint detection system while sufficiently maintaining the power supply voltage.

[0007] U.S. Patent No. 9,152,841 discloses a fingerprint detection system having an excitation signal supply circuit coupled to each detection structure of a detection element that varies the potential of the detection structure to provide a change in the potential difference between a finger and the detection structure. Based on the output from the detection element when such a change in potential difference is provided, the representation of the fingerprint pattern of the finger can be determined.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Even if a fingerprint system as described above can achieve sufficient fingerprint image quality, there is still room for improvement, particularly for very small fingerprint sensors.

[0009] From the above perspective, an object of the present invention is to provide further improved fingerprint detection.

Means for Solving the Problems

[0010] According to a first aspect of the present invention, there is provided a fingerprint detection system for detecting a fingerprint pattern of a finger, comprising: a sensor array having a plurality of conductive detection structures; a readout circuit connected to each of the detection structures for supplying a detection signal representing a capacitive coupling between the detection structure and the finger; a first signal supply circuit for supplying a signal of a first time-varying voltage to at least a part of the sensor array; at least one conductive edge compensation structure disposed outside the sensor array; and a second signal supply circuit for supplying a signal of a second time-varying voltage to the at least one edge compensation structure.

[0011] Each of the plurality of conductive detection structures may preferably be provided in the form of a metal plate, as a result of which a certain kind of parallel plate capacitor is formed by the detection structure (metal plate), the local finger surface, and the dielectric structure covering the detection structure (as well as the air that may locally exist between the local finger structure and the dielectric structure). The detection structure at a position corresponding to a ridge of the fingerprint exhibits a stronger capacitive coupling to the finger than the detection structure at a position corresponding to a valley of the fingerprint.

[0012] The dielectric structure covering the detection structure preferably has a thickness of at least 20 μm and may have a protective dielectric coating with a high dielectric strength to protect the underlying structure from wear and tear and ESD. Even more preferably, the protective coating has a thickness of at least 50 μm. In embodiments, the dielectric structure covering the detection structure may be several hundred μm thick. In such cases, the dielectric structure covering the detection structure may have, for example, a cover glass of the electronic device.

[0013] The readout circuit may supply, for example, an analog detection signal in the form of a voltage level or current representing the capacitive coupling between the finger and the detection structure provided in the sensor array.

[0014] However, according to various embodiments, the readout circuit may have a circuit for converting an analog signal into a digital signal. Such circuits are, for example, a sampling circuit and an analog-to-digital conversion circuit.

[0015] One or both of the first signal supply circuit and the second signal supply circuit may be a switching circuit configured to switch between two or more different potentials supplied to different lines. Alternatively or in combination, one or both of the first signal supply circuit and the second signal supply circuit may include at least one signal source configured to supply a time-varying potential such as a square wave voltage signal or a sine wave voltage signal.

[0016] Furthermore, the first signal supply circuit and the second signal supply circuit may be provided as individual circuits or as a common circuit connected to both the sensor array and / or the readout circuit and an edge compensation structure disposed outside the sensor array.

[0017] Note that both the first time-varying voltage signal and the second time-varying voltage signal vary with respect to the same reference potential, such as the reference potential of a device equipped with a fingerprint detection system. The reference potential of such a device may be referred to as "device ground". In some embodiments, the reference potential of the sensor array - "sensor ground" - may be constant with respect to the device ground, and in other embodiments, the sensor ground may vary with time. In such embodiments, the first time-varying potential may be substantially constant with respect to the sensor ground (while varying with respect to the device ground). Further, note that the potential of the finger is typically at a substantially constant level with respect to the "device ground" for the relevant time scale for obtaining a fingerprint. For example, the user's body actually defines the "device ground" of a portable device that is not connected to some global reference potential (such as mains ground). Such a portable device in which the user's body defines the device ground may be, for example, a mobile communication device or a smart card, etc.

[0018] A first time-varying voltage signal supplied to at least a part of the sensor creates a time-varying potential difference between at least one of the detection structures and the finger. Due to such a time-varying potential difference, the readout circuit can supply a detection signal representing the capacitive coupling between each of the detection structures and the finger.

[0019] At least one edge compensation structure may be a conductive structure disposed relatively close to the detection structure and at the edge of the sensor array. For example, at least one edge compensation structure may be disposed such that it is less than 0.5 mm from the edge of the sensor array. Advantageously, at least one edge compensation structure may be disposed such that it is less than 0.1 mm from the edge of the sensor array (the edge of the detection structure closest to the edge of the sensor array).

[0020] The overall capacitive coupling that can be detected by the detection structure depends not only on the local distance between the detection structure and the finger but also on other conductive structures near the detection structure. For example, as described in U.S. Patent No. 9,152,841, the contribution to the overall capacitive coupling from adjacent detection structures can be significantly reduced by controlling the potential of the adjacent detection structures that varies according to the potential of the currently active (one or more) detection structures in the detection mode. However, the detection structures arranged at the edge of the sensor array are not surrounded by adjacent detection structures. As a result, a strong and sometimes non-uniform capacitive coupling occurs between the detection structure and the surrounding proximity near the middle of the sensor array. This affects the fingerprint image (or other display) formed based on the detection signal from the readout circuit. For relatively large fingerprint sensors, such an effect is ignored or sufficiently compensated through image processing or the like. For relatively small (and thus cost-effective) fingerprint sensors, the effect becomes even more important in order for the fingerprint sensor to provide good image quality for the entire area of the sensor array.

[0021] The inventor of the present application has realized that such edge effects can be reduced by providing at least one edge compensation structure with low conductivity outside the sensor array and supplying a signal of a time-varying voltage to the at least one edge compensation structure.

[0022] According to various embodiments, the second signal supply circuit is configured to supply the second time-varying voltage signal in synchronization with the first time-varying voltage signal. The second time-varying voltage signal may, for example, advantageously be substantially in phase with the first time-varying voltage signal.

[0023] According to an embodiment, the second time-varying voltage signal may be made to be held substantially constant at a point in time when the potential difference between the detection structure at the edge of the sensor array and the adjacent edge compensation structure is at least related to the detection of the capacitive coupling between the detection structure and the finger. Thereby, the influence of the parasitic capacitance on the structure near the detection structure can be significantly reduced.

[0024] The time point related to detection may vary depending on the detection method used, and those skilled in the art can determine such a time point without undue burden, for example, based on circuit simulation. For example, in the case of so-called correlation double sampling where the detection signal is sampled at two sampling times, the sampling time may be the time point related to detection.

[0025] According to an embodiment, the readout circuit is a plurality of detection circuits, and each of the plurality of detection circuits is disposed below each set of detection structures of the plurality of detection structures and connected to each set of detection structures of the plurality of detection structures. A plurality of detection circuits, and a signal routing and adjustment circuit for routing and / or adjusting signals to and / or from the plurality of detection circuits. The signal routing and adjustment circuit is disposed at least partially under at least one edge compensation structure.

[0026] The above-described signal routing and adjustment circuit may have, for example, a signal line of a control signal for a detection circuit, a status signal, a signal line of a detection signal from the detection circuit, an amplifier, a sampler, a multiplexer, an analog-to-digital conversion circuit, digital control logic, a memory, and / or an interface circuit.

[0027] In these embodiments, the desired edge compensation can be realized while only using the sensor real estate already used for other functions. This means that the desired edge compensation can be realized with little additional cost to the fingerprint detection system.

[0028] In an embodiment, the above-described set of detection structures may be a single detection structure in which each detection structure has a dedicated detection circuit. In other embodiments, the above-described set of detection structures may have a plurality of detection structures such that each detection circuit is sequentially connected to the detection structures for four or eight detection structures.

[0029] In an embodiment of the fingerprint detection system according to the present invention, advantageously, the sensor array, the readout circuit, and at least one edge compensation structure are included in the fingerprint sensor component.

[0030] In these embodiments, the fingerprint sensor component includes a component substrate, an active circuit formed on the component substrate, and a plurality of metal layers on the active circuit.

[0031] The component substrate may advantageously be a semiconductor substrate such as a silicon substrate, and the active circuit may be provided on the substrate by various processes including p-doping and / or n-doping and the addition of conductive layer stacks.

[0032] Alternatively, the component substrate may be an insulating substrate. In such embodiments, the active circuit can be formed using thin-film technology.

[0033] The above-described metal layers on the active circuit may be separated by insulating layers sandwiched between the metal layers. Interconnections may be provided using techniques known per se to realize electrical contacts between different metal layers at selected positions.

[0034] In an embodiment, the plurality of detection structures and at least one conductive edge compensation structure are advantageously formed on the uppermost metal layer of the plurality of metal layers. Alternatively, at least one edge compensation structure may be provided on the uppermost metal layer covering the detection structure using a post-process that may be performed, for example, during the packaging of the fingerprint sensor component.

[0035] In various embodiments, further, the detection structures of the sensor array are arranged in rows and columns, the fingerprint detection system includes a plurality of edge compensation structures, and the plurality of edge compensation structures each have a plurality of left adjacent edge compensation structures arranged to the left of the corresponding row among the rows and a plurality of right adjacent edge compensation structures arranged to the right of the corresponding row among the rows. Each of the left adjacent edge compensation structures may be substantially aligned with the corresponding row of the detection structures, and each of the right adjacent edge compensation structures may be substantially aligned with the corresponding row of the detection structures.

[0036] It should be noted that the terms "row" and "column" used herein do not specify the dimensions or orientation of the sensor array. A row may have the same number of columns, more columns than columns, or fewer columns than columns. All rows / columns do not necessarily have the same number of detection structures, and this often occurs.

[0037] The second signal supply circuit is connected to each of the left adjacent edge compensation structures and each of the right adjacent edge compensation structures, and is controllable to supply a signal of a second time-varying voltage to a set of the left adjacent edge compensation structures and / or a set of the right adjacent edge compensation structures. The (one or more) sets of adjacent edge compensation structures to which the signal of the second time-varying voltage is supplied may be selected in consideration of the (one or more) detection structures that are currently active. For example, when simultaneously controlling all the detection structures of the detection structures in a predetermined row to exhibit a time-varying potential, a signal of a second time-varying voltage may be simultaneously supplied to at least the left adjacent edge compensation structure and the right adjacent edge compensation structure that are substantially aligned with the row of the detection structures.

[0038] In an embodiment, the plurality of edge compensation structures include a plurality of left distal edge compensation structures each disposed to the left of a corresponding one of the left adjacent edge compensation structures, and a plurality of right distal edge compensation structures each disposed to the right of a corresponding one of the right adjacent edge compensation structures.

[0039] The second signal supply circuit is connected to each of the left distal edge compensation structures and each of the right distal edge compensation structures, and is controllable to supply a signal of a third time-varying voltage to a set of the left distal edge compensation structures and / or a set of the right distal edge compensation structures.

[0040] The signal of the third time-varying voltage may be the same as the signal of the second time-varying voltage. However, alternatively, the amplitude of the signal of the third time-varying voltage may be larger than the amplitude of the signal of the second time-varying voltage.

[0041] In various embodiments of the fingerprint detection system according to the present invention, the first signal supply circuit can be controlled to supply a signal of a first time-varying voltage to a set of detection structures of a plurality of detection structures.

[0042] To implement such a "swinging pixel" operation, the first signal supply circuit may be connectable to each detection structure directly or via a so-called virtually grounded amplifier configuration.

[0043] In the latter structure, the readout circuit includes a plurality of detection circuits. Each detection circuit of the plurality of detection circuits is connected to a plurality of detection circuits each connected to a set of detection structures of the plurality of detection structures. Each detection circuit of the plurality of detection circuits includes an amplifier. The amplifier has a first input connected to a set of detection structures, a second input, an output, and a feedback capacitor between the first input and the output. The amplifier is configured such that a substantially identical electrical change occurs at the first input as a result of a change in the potential of the second input. The first signal supply circuit is connected to the second input.

[0044] The amplifier may advantageously be a charge amplifier known per se.

[0045] The first signal supply circuit may be configured to supply a first time-varying voltage to the second input, thereby varying the potential of the (one or more) detection structures of the set of detection structures connected to the first input of the amplifier with respect to the potential of the finger.

[0046] In an embodiment, the fingerprint detection system includes a semiconductor substrate, the amplifier includes a transistor formed on a wall portion of the semiconductor substrate, the transistor has a gate that constitutes a first input portion, the interface between the wall portion and the semiconductor substrate is configured to prevent current from flowing between the wall portion and the semiconductor substrate, and the first signal supply circuit is further connected to the wall portion. In these embodiments, the influence of the detection of the parasitic capacitance between the (one or more) detection structures and the wall portion can be reduced.

[0047] The semiconductor substrate is preferably a doped semiconductor substrate, and the wall portion may be a part of a substrate doped with a polarity opposite to that of the semiconductor substrate (when the semiconductor substrate is p-doped, the wall portion is n-doped, and when the semiconductor substrate is n-doped, the wall portion is p-doped). This is one way to realize an interface between the wall portion and the semiconductor substrate configured to prevent current from flowing between the wall portion and the substrate. In particular, the wall portion and the substrate may be held at a potential such that no current flows through the diode formed at the interface between the substrate and the wall portion.

[0048] Alternatively, an insulating layer may be provided between the substrate and the wall portion, for example, in the form of a thin film of glass. Such an insulating layer also prevents current from flowing between the wall portion and the substrate.

[0049] In various embodiments of the fingerprint detection system according to the present invention, the fingerprint detection system may further include a fingerprint detection circuit connected to at least one edge compensation structure and supplying a fingerprint detection signal representing a capacitive coupling between the at least one edge compensation structure and a finger.

[0050] According to a second aspect of the present invention, there is provided a method for detecting a fingerprint pattern of a finger using a fingerprint detection system including a sensor array having a plurality of conductive detection structures, a readout circuit connected to each of the detection structures, a first signal supply circuit, at least one conductive edge compensation structure disposed outside the sensor array, and a second signal supply circuit, the method comprising: controlling the first signal supply circuit to supply a first time-varying voltage signal to at least a part of the sensor array; controlling the second signal supply circuit to supply a second time-varying voltage signal to at least one edge compensation structure; and controlling the readout circuit to supply a detection signal representing a capacitive coupling between the detection structure and the finger.

[0051] Other embodiments and effects obtained according to the second aspect of the present invention are very similar to those described for the first aspect of the present invention.

[0052] These aspects and other aspects of the present invention will be described in more detail with reference to the accompanying drawings showing exemplary embodiments of the present invention.

Brief Description of the Drawings

[0053]

FIG. 1A

FIG. 1B

FIG. 2A

FIG. 2B

FIG. 2C

FIG. 3

FIG. 4A

FIG. 4B

FIG. 5

FIG. 6A

FIG. 6B

FIG. 6C

DETAILED DESCRIPTION OF THE INVENTION

[0054] In this detailed description, various embodiments of the fingerprint detection system and method according to the present invention will be mainly described with reference to a fingerprint detection system in which the potential of a set of detection structures is controlled to vary with respect to the sensor ground and the sensor ground is constant with respect to the device ground. In particular, an example in which all detection elements / pixels in a row / column are read out simultaneously will be described. Further, some exemplary examples of the edge compensation structure will be shown.

[0055] It should be noted that this does not in any way limit the scope defined by the appended claims, which similarly have a fingerprint detection system capable of realizing the potential difference between the detection structure and the finger, for example, by supplying a fingerprint sensor component having a reference potential that varies with time with respect to the device ground. Further, for example, other detection forms in which other groups of detection elements are read out simultaneously or the detection elements are read out individually may be used. Many other structures of the (one or more) edge compensation structures are possible.

[0056] FIG. 1A linearly shows a mobile phone 1 as a first example of an electronic device including a fingerprint detection system 3 according to an embodiment of the present invention. The fingerprint detection system 3 may be used, for example, to unlock the mobile phone 1 and / or permit a transaction executed using the mobile phone or the like.

[0057] FIG. 1B linearly shows a smart card 5 as a second example of an electronic device including a fingerprint detection system 3 according to an embodiment of the present invention.

[0058] FIG. 2A linearly shows an exemplary embodiment of a fingerprint detection system according to the present invention in the form of a semiconductor-based fingerprint sensor 3. As can be seen from FIG. 2A, the fingerprint sensor 3 includes a sensor array 7, an interface 9 that receives power for the operation of the fingerprint sensor 3 and interacts with a processing circuit provided in an electronic device such as the mobile phone 1 of FIG. 1A or the smart card 5 of FIG. 1B. The sensor array 7 includes a number of detection structures 10 (only one of the detection structures is labeled with a reference number to avoid confusion in the drawing). As linearly shown in an enlarged view of the fingerprint sensor 3 of FIG. 2A, the fingerprint sensor 3 further includes an edge compensation structure, and the edge compensation structure includes a left adjacent edge compensation structure 11, a right adjacent edge compensation structure 13, a left distal edge compensation structure 15, a right distal edge compensation structure 17, an upper adjacent edge compensation structure 19, a lower adjacent edge compensation structure 21, an upper distal edge compensation structure 23, and a lower distal edge compensation structure 25.

[0059] Even if not visible in FIG. 2A, the fingerprint sensor 3 further includes a readout circuit, a first signal supply circuit, and a second signal supply circuit. Examples of these parts of the fingerprint sensor 3 will be further described later with reference to FIGS. 2B and 2C.

[0060] FIG. 2B is a partial cross-section of the fingerprint sensor 3 along line A-A' shown in FIG. 2, with a finger placed on the upper side of the dielectric structure 28 covering the sensor array 7. The surface of the finger 26 includes ridge lines 30 that contact the dielectric structure 28 and valley lines 32 that are spaced apart from the dielectric structure 28.

[0061] Referring to FIG. 2B, the fingerprint sensor 3 includes a doped semiconductor component substrate 27, an active circuit 29 formed on the component substrate 27, and a metal layer 31 on the active circuit 29. The detection structure 10 and the edge compensation structure (the left adjacent edge compensation structure 11 and the right adjacent edge compensation structure 13 are visible in FIG. 2B) described above are formed on the uppermost metal layer 33. The above-described readout circuit may be at least partially formed using the active circuit 29. As linearly shown in FIG. 2B, the portion 35 of the active circuit 29 below the detection structure 10 may be used to form a detection circuit that detects the capacitive coupling between the detection structure 10 and the finger 26. Another portion 37 of the active circuit 29 below the edge compensation structures 11, 15 may be used to form a signal routing and adjustment circuit that routes and / or adjusts signals to and / or from a plurality of detection circuits of the first portion of the active circuit 29.

[0062] By arranging the edge compensation structures 11, 15 and the signal routing and adjustment circuit, etc. in the same place, the surface area of the fingerprint sensor 3 is not increased by providing the edge compensation structure.

[0063] FIG. 2B is at a substantially accurate ratio to show a realistic example of the relative dimensions of the dielectric structure / protective film 28, the detection structure 10, and the ridge 30 and valley 32 of the finger 26. As can be seen, the dielectric structure / protective film 28 is somewhat thick to protect the underlying structure from damage and ESD. Needless to say, the protective film 28 is important for the robustness of the fingerprint sensor 3. From the relative dimensions of FIG. 2B, the capacitance between the detection structure 10 and the finger 26 is very small, especially compared to the parasitic capacitance between the detection structure 10 and other conductive structures adjacent to the detection structure 10. Examples of such conductive structures include adjacent detection structures, additional metal structures, the active semiconductor circuit 29, and the component substrate 27.

[0064] An exemplary form of the above-described readout circuit including the detection circuit and the signal routing and adjustment circuit will be described with reference to FIG. 2C, which is a circuit diagram of a part of the fingerprint sensor components in FIGS. 2A and 2B.

[0065] As linearly shown in FIG. 2C, the above-described readout circuit 39 connected to each detection structure 10 of the sensor matrix 7 has a detection circuit 41 and a signal routing and adjustment circuit 43.

[0066] Referring to FIG. 2C, each detection circuit 41 includes a charge amplifier 45, a selection circuit functionally shown as a simple selection switch 47 here to be able to obtain a detection signal from the detection circuit 41, and a first signal supply circuit 49 that can be controlled to supply a signal V1(t) of a first time-varying voltage to the detection structure 10 as will be described in more detail later.

[0067] The charge amplifier 45 is linearly shown by at least one amplification stage here as an operational amplifier (op-amp) 51. The amplification stage has a first input part (negative input part) 53 connected to the detection structure 10, a second input part (positive input part) 55 connected to the first signal supply circuit 49, and an output part 57. Further, the charge amplifier 45 includes a feedback capacitor 59 connected between the first input part 53 and the output part 57, and a reset circuit functionally shown as a switch 61 to enable controlled discharge of the feedback capacitor 59. The charge amplifier 45 may be reset by operating the reset circuit 61 to discharge the feedback capacitor 59.

[0068] In a common case of the op-amp 51, the potential of the first input part 53 follows the potential supplied to the second input part. Depending on a specific amplification form, the potential of the first input part 53 may be substantially the same as the potential of the second input part 55, or there may be a substantially constant offset between the first input part 53 and the second input part 55.

[0069] By using the first signal supply circuit 49, a signal V1(t) of a first time-varying voltage with respect to a reference potential (sensor ground) can be supplied to the detection structure 10.

[0070] The first signal supply circuit 49 may be realized, for example, as a plurality of controllable switches configured to controllably connect to voltage lines each selecting a second input portion 55 (to have mutually different voltages with respect to the sensor ground). Alternatively, the first signal supply circuit 49 may be directly connectable to the detection structure 10 to directly supply the signal V1(t) of the first time-varying voltage to the detection structure 10.

[0071] By controlling the first signal supply circuit 49, a selected potential corresponding to the desired function of a specific detection structure 10 can be supplied to the detection structure 10, as will be described in more detail later.

[0072] Here, each detection circuit 41 is shown as being connected to a single detection structure 10 respectively, but it should be noted that alternatively each detection circuit 41 may be common to a group of detection structures of the detection structure.

[0073] As linearly shown in FIG. 2C, the fingerprint sensor 3 includes a second signal supply circuit 63 and a third signal supply circuit 65. The second signal supply circuit 63 is connected to the left proximity edge compensation structure 11 to supply the signal V2(t) of the second time-varying voltage to the left proximity edge compensation structure 11, and the third signal supply circuit 65 is connected to the left distal edge compensation structure 15 to supply the signal V3(t) of the third time-varying voltage to the left distal edge compensation structure 15.

[0074] When detecting the capacitive coupling between the detection structure 10 and the finger 26, the first signal supply circuit 49 is controlled to supply the signal V1(t) of the first time-varying voltage with respect to the sensor ground to the second input portion 55.

[0075] In FIG. 2C, finger 26 is linearly shown as being “grounded”. The finger “ground” may be different from the sensor ground. For example, finger 26 may be at the ground potential of an electronic device (such as the mobile phone of FIG. 1A or the smart card 5 of FIG. 1B) that includes fingerprint sensor 3. Alternatively, the body may be considered to have a large electrical “mass” such that the potential of the finger remains substantially constant when the potential of detection structure 10 varies.

[0076] As a result of the above-described change in the potential difference between detection structure 10 and finger 26, a detection signal Vs is generated at output portion 57 of charge amplifier 45.

[0077] When the readout circuit is controlled to detect the capacitive coupling between the selected detection structure 10 and finger 26, selection switch 47 is closed to connect output portion 57 of charge amplifier 45 to readout line 65. Readout line 65, which can be a common readout line for a row or column of detection array 7, is shown connected to multiplexer 67 in FIG. 2C. As linearly shown in FIG. 2C, other readout lines that supply detection signals from other rows / columns of fingerprint sensor 3 are also connected to multiplexer 67.

[0078] Detection signal Vs is demodulated by sample - hold circuit 69. The output portion of sample - hold circuit 69 is connected to analog - to - digital converter 71 to provide a digital display of the measured values for each of the selected detection structures 10 of the analog DC voltage signal output by sample - hold circuit 69.

[0079] As linearly shown in FIG. 2C, multiplexer 67, sample - hold circuit 69, and analog - to - digital converter 71 may be included in signal routing and conditioning circuit 43 disposed under the edge compensation structure.

[0080] FIG. 3 is a linear diagram of an exemplary detection pattern of the fingerprint sensor components of FIGS. 2A-2C. In FIG. 3, a simplified sensor array 7 having a very small number of columns is shown linearly. It should be understood that the sensor array 7 of FIG. 3 is merely an example for illustration and that the sensor array 7 may advantageously have a much larger number of columns.

[0081] In the detection pattern of FIG. 3, a fingerprint pattern of a finger (not shown in FIG. 3) is detected row by row (the "rows" and "columns" are interchangeable). A detection structure 10a of one row is shown as being used for detection, and detection structures 10b-c of adjacent rows are shown as being used to "guard" to reduce the influence of parasitic capacitive coupling between adjacent detection structures. In this particular form of excitation, a detection structure 10d outside the band defined by the detection structures 10a-c of the three shown rows is held at the sensor ground potential.

[0082] In the detection pattern of FIG. 3, the selected edge compensation structure is used to compensate for the difference in the electrical environment of the detection structures used to perform detection near the edge of the sensor array 7 compared to the detection structures used to perform detection closer to the middle of the sensor array 7. In this particular example, three left adjacent edge compensation structures 11a-c, three right adjacent edge compensation structures 13a-c, three left distal edge compensation structures 15a-c and three right distal edge compensation structures 17a-c are used to compensate for the influence of the edges, as will be described in more detail later.

[0083] A first exemplary mode of operation for the fingerprint detection pattern of FIG. 3 will be described mainly with reference to the linear timing diagram of FIG. 4A in addition to the display of FIG. 2.

[0084] As shown for the simplified detection operation of FIG. 4A, the first signal supply circuit 49 is controlled to supply the signal V1(t) of the first time-varying voltage to the detection structure 10a used to detect the capacitive coupling between the finger and the detection structures 10b-c used for the guard. Similarly, the second signal supply circuit 63 is controlled to supply the signal V2(t) of the second time-varying voltage to the proximity (left 11a-c and right 13a-c) edge compensation structures, and the third signal supply circuit 65 is controlled to supply the signal V3(t) of the third time-varying voltage to the distal (left 15a-c and right 17a-c) edge compensation structures. The remaining detection structures 10d and edge compensation structures 11d, 13d, 15d, 17d are all held at sensor ground (SGND). The detection circuit 41 and the signal routing and conditioning circuit 42 are controlled to detect the capacitive coupling between the detection structure 10a used for detection and the finger 26 and to route and condition the signal representing this capacitive coupling.

[0085] In the first exemplary operation mode of FIG. 4A, the signal V1(t) of the first time-varying voltage, the signal V2(t) of the second time-varying voltage, and the signal V3(t) of the third time-varying voltage are substantially the same.

[0086] In the second exemplary operation mode of FIG. 4B, the signal V1(t) of the first time-varying voltage and the signal V2(t) of the second time-varying voltage are substantially the same, and the signal V3(t) of the third time-varying voltage exhibits a voltage swing that is twice that of the first V1(t) and the second V2(t).

[0087] FIG. 5 is a diagram showing the respective effects of the signal patterns of FIG. 4A compared to the fingerprint image obtained without edge compensation. and FIG. 4B The figure shows the average pixel values (solid curve 73) measured for the last 14 columns of the fingerprint sensor 3 according to an embodiment of the present invention with respect to the inactive edge compensation structure (the edge compensation structure held at sensor ground), the operation mode of FIG. 4A (dashed curve 75), and the operation mode of FIG. 4B (dotted curve 77).

[0088] The figure shows the average pixel values (solid curve 73) measured for the last 14 columns of the fingerprint sensor 3 according to an embodiment of the present invention with respect to the inactive edge compensation structure (the edge compensation structure held at sensor ground), the operation mode of FIG. 4A (dashed curve 75), and the operation mode of FIG. 4B (dotted curve 77).

[0089] As can be seen from FIG. 5, when edge compensation is not applied, the pixel values from the detection structures closest to the edges of the sensor array 7 are significantly different from the pixel values from the detection structures closer to the middle of the sensor array. The operation mode of FIG. 4A has already achieved a significant improvement, and the operation mode of FIG. 4B can almost completely remove the influence of the edges.

[0090] It should be understood that the actual effect of edge compensation depends on other factors such as the form of the dielectric structure 28 between the detection structure 10 and the finger 26. It should also be noted that further improvements can be achieved by adding other columns / rows of the edge compensation structure and / or adjusting the signals supplied to the edge compensation structure and / or controlling the number and form of the edge compensation structures to which the voltage signals are supplied. Thus, by controlling / programming one or more voltage signals supplied to the edge compensation structure and / or the active form (arrangement and / or number) of the edge compensation structure, the edge compensation structure can be individually adjusted for various applications and / or solutions for packaging.

[0091] Finally, some examples of alternative forms of the edge compensation structure will be briefly described with reference to FIGS. 6A - 6C.

[0092] FIG. 6A linearly shows a fingerprint sensor 3 in which individually controllable edge compensation structures 79 extend along the entire length of each edge of the sensor array 7. The edge compensation structure 79 may be formed in the same metal layer as the detection structure 10, or may be added in a post-process before providing a dielectric structure (protective film) to the fingerprint sensor 3.

[0093] FIG. 6B linearly shows a fingerprint sensor 3 provided with a single edge compensation structure 81 as a frame or bezel around the sensor array 7. Regarding the form of FIG. 6A, the edge compensation structure 81 may be formed in the same metal layer as the detection structure 10, or may be added in a post-process before providing a dielectric structure (protective film) to the fingerprint sensor 3.

[0094] FIG. 6C linearly shows the fingerprint sensor 3 with the edge compensation structure 83 provided on the upper side of the dielectric structure (protective film) of the fingerprint sensor 3 as a frame or bezel around the sensor array 7.

[0095] Those skilled in the art to realize the present invention are by no means limited to the preferred embodiments described above. On the contrary, many changes and modifications are possible within the scope of the appended claims.

[0096] In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may perform the functions of a plurality of items recited in the claims. The fact that certain means are recited in mutually different dependent claims does not indicate that these means cannot be used advantageously in combination. A computer program may be stored / distributed on a suitable medium such as an optical recording medium or a solid-state medium provided together with or as part of other hardware, but may also be distributed in other forms such as the Internet or other wired or wireless communication systems. The reference numbers in the claims should not be construed as limiting the scope. The invention disclosed in this specification includes the following. [Item 1] A fingerprint detection system (3) for detecting a fingerprint pattern of a finger (26), comprising: A sensor array (7) having a plurality of conductive detection structures (10); A readout circuit (39) connected to each of the detection structures (10) for supplying a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26); A first signal supply circuit (49) for supplying a signal of a first time-varying voltage (V 1 (t)) to at least a part of the sensor array (7); At least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) disposed outside the sensor array (7); A second signal supply circuit (63; 65) for supplying a signal of a second time-varying voltage (V 2 (t)) to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83); A fingerprint detection system (3) comprising the above. [Item 2] The fingerprint detection system (3) according to Item 1 above, wherein the second signal supply circuit (63; 65) is configured to supply a signal of the second time-varying voltage (V 2 (t)) in synchronization with a signal of the first time-varying voltage (V 1 (t)). [Item 3] The readout circuit (39) comprises: A plurality of detection circuits (41), each of the plurality of detection circuits being disposed below each set of the detection structures (10) of the plurality of detection structures and connected to each set of the detection structures (10) of the plurality of detection structures; A signal routing and adjustment circuit (43) for routing and / or adjusting signals to and / or from the plurality of detection circuits (41); Comprising; The fingerprint detection system (3) according to Item 1 or 2 above, wherein the signal routing and adjustment circuit (43) is at least partially disposed under the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83). [Item 4] The sensor array (7), the readout circuit (39), and the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) are the fingerprint detection system (3) according to any one of items 1 to 3 included in the fingerprint sensor component. [Item 5] The fingerprint sensor component includes a component substrate, an active circuit formed on the component substrate, and a plurality of metal layers on the active circuit, and is the fingerprint detection system (3) according to item 4 above. [Item 6] The plurality of detection structures and the at least one edge compensation structure are formed on the uppermost metal layer of the plurality of metal layers, and are the fingerprint detection system (3) according to item 5 above. [Item 7] The detection structures (10) of the sensor array (7) are arranged in rows and columns, the fingerprint detection system (3) includes a plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25), and the plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25) include a plurality of left adjacent edge compensation structures (11) each arranged to the left of the corresponding row among the rows, and a plurality of right adjacent edge compensation structures (13) each arranged to the right of the corresponding row among the rows, and are the fingerprint detection system (3) according to any one of items 1 to 6 above. [Item 8] The second signal supply circuit (63; 65) is connected to each of the left adjacent edge compensation structures (11) and each of the right adjacent edge compensation structures (13), and supplies the second time-varying voltage (V 2 (t)) signal to the set of left adjacent edge compensation structures (11a-c) and / or the set of right adjacent edge compensation structures (13a-c), and is controllable as such, and is the fingerprint detection system (3) according to item 7 above. [Item 9] The second signal supply circuit (63; 65) supplies the second time-varying voltage (V 2 (t)) signal to at least one (11a-c) of the left adjacent edge compensation structures aligned with one row (10a-c) of the detection structures and at least one (13a-c) of the right adjacent edge compensation structures aligned with the one row of the detection structures simultaneously, and is controllable as such, and is the fingerprint detection system (3) according to item 8 above. [Item 10] The plurality of edge compensation structures include a plurality of left distal edge compensation structures (15) each arranged to the left of the corresponding one of the left adjacent edge compensation structures (11), A plurality of right distal edge compensation structures (17), each disposed to the right of a corresponding one of the right adjacent edge compensation structures (13); The fingerprint detection system (3) according to any one of Items 7 to 9 above, comprising the same. [Item 11] The second signal supply circuit (63; 65) is connected to each of the left distal edge compensation structures (15) and each of the right distal edge compensation structures (17), and is connected to a set (15a-c) of the left distal edge compensation structures and / or a set (17a-c) of the right distal edge compensation structures. The fingerprint detection system (3) according to Item 10 above, which is controllable to supply a signal of a third time-varying voltage (V 3 (t)). [Item 12] The first signal supply circuit (49) is controllable to supply a signal of the first time-varying voltage (V 1 (t)) to a set (10a-c) of the detection structures of the plurality of detection structures. The fingerprint detection system (3) according to any one of Items 1 to 11 above. [Item 13] The readout circuit (39) includes a plurality of detection circuits (41), and each detection circuit of the plurality of detection circuits includes a plurality of detection circuits (41) connected to each set of the detection structures (10) of the plurality of detection structures. Each detection circuit (41) of the plurality of detection circuits includes a charge amplifier (45). The charge amplifier (45) includes a first input part (53) connected to the set of the detection structures, a second input part (55), an output part (57), and a feedback capacitor between the first input part (53) and the output part (57). The charge amplifier (45) is configured such that a substantially same electrical change occurs in the first input part (53) as a result of a change in the potential of the second input part (55). The first signal supply circuit (49) is connected to the second input part (55). The fingerprint detection system (3) according to Item 12 above. [Item 14] The fingerprint detection system includes a semiconductor substrate (27). The charge amplifier (45) includes a transistor formed on a wall part of the semiconductor substrate (27). The transistor has a gate that constitutes the first input part. An interface between the wall part and the semiconductor substrate is configured to prevent a current from flowing between the wall part and the semiconductor substrate. The first signal supply circuit (49) is further connected to the wall part. The fingerprint detection system (3) according to Item 13 above. [Item 15] The fingerprint detection system is A fingerprint detection system (3) according to any one of the above items 1 to 14, further comprising a fingerprint detection circuit connected to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) and supplying a fingerprint detection signal representing a capacitive coupling between the at least one edge compensation structure and the finger (26). [Item 16] A sensor array (7) having a plurality of conductive detection structures (10), A readout circuit (39) connected to each of the detection structures (10), A first signal supply circuit (49), At least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) disposed outside the sensor array (7), A second signal supply circuit (63; 65), A method for detecting a fingerprint pattern of a finger (26) using a fingerprint detection system (3) comprising: Controlling the first signal supply circuit (49) to supply a first time-varying voltage signal (V 1 (t)) to at least a part of the sensor array (7); Controlling the second signal supply circuit (63; 65) to supply a second time-varying voltage signal (V 2 (t)) to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83); Controlling the readout circuit (39) to supply a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26). A method comprising the steps of.

Claims

1. A fingerprint detection system (3) for detecting a fingerprint pattern of a finger (26), a sensor array (7) having a plurality of conductive detection structures (10), wherein the detection structures arranged at the edges of the sensor array are not surrounded by adjacent detection structures, the sensor array (7); A first time-varying voltage (V 1 (t)) to at least a part of the sensor array (7); and a first signal supply circuit (49) for supplying a signal of at least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) arranged outside the sensor array (7) adjacent to the detection structures arranged at the edges of the sensor array; a readout circuit (39) connected to each of the detection structures (10) for supplying a detection signal representing a capacitive coupling between the detection structures (10) and the finger (26) and not connected to the at least one edge compensation structure; The signal of the second time-varying voltage (V 2 (t)) is synchronized with the signal of the first time-varying voltage (V 1 (t)) and supplied to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) by a second signal supply circuit (63; 65); comprising the readout circuit (39) is a plurality of detection circuits (41), each of the plurality of detection circuits being arranged below each set of the detection structures (10) of the plurality of detection structures and connected to each set of the detection structures (10) of the plurality of detection structures, the plurality of detection circuits (41); a signal routing and conditioning circuit (43) for routing and / or conditioning signals to and / or from the plurality of detection circuits (41); comprising the signal routing and conditioning circuit (43) is at least partially arranged under the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) of the fingerprint detection system (3).

2. The fingerprint detection system (3) according to claim 1, wherein the sensor array (7), the readout circuit (39) and the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) are included in a fingerprint sensor component.

3. The fingerprint sensor component is a component substrate, an active circuit formed on the component substrate, a plurality of metal layers on the active circuit; The fingerprint detection system (3) according to claim 2, comprising

4. The fingerprint detection system (3) according to claim 3, wherein the plurality of detection structures and the at least one edge compensation structure are formed on the uppermost metal layer of the plurality of metal layers.

5. A fingerprint detection system (3) for detecting a fingerprint pattern of a finger (26), A sensor array (7) having a plurality of conductive detection structures (10), wherein the detection structures arranged at the edges of the sensor array are not surrounded by adjacent detection structures, the sensor array (7), and A first signal supply circuit (49) for supplying a signal of a first time-varying voltage (V1(t)) to at least a part of the sensor array (7); At least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) arranged outside the sensor array (7) adjacent to the detection structures arranged at the edges of the sensor array; A readout circuit (39) connected to each of the detection structures (10) for supplying a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26) and not connected to the at least one edge compensation structure; A second signal supply circuit (63; 65) for supplying a signal of a second time-varying voltage (V2(t)) to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) in synchronization with the signal of the first time-varying voltage (V1(t)); Comprising The detection structures (10) of the sensor array (7) are arranged in rows and columns; The fingerprint detection system (3) comprises a plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25), and the plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25) are A plurality of left adjacent edge compensation structures (11) each arranged to the left of the corresponding row of the rows; A plurality of right adjacent edge compensation structures (13) each arranged to the right of the corresponding row of the rows; A fingerprint detection system (3) having.

6. The second signal supply circuit (63; 65) is connected to each of the left proximity edge compensation structures (11) and each of the right proximity edge compensation structures (13), and the second time-varying voltage (V 2 The fingerprint detection system (3) according to claim 5, which is controllable to supply a signal of (t)) to a set (11a-c) of the left proximity edge compensation structures and / or a set (13a-c) of the right proximity edge compensation structures.

7. The second signal supply circuit (63; 65) supplies the second time-varying voltage (V 2 (t)) signals to at least one (11a-c) of the left proximity edge compensation structures aligned with one row (10a-c) of the detection structures and at least one (13a-c) of the right proximity edge compensation structures aligned with the one row of the detection structures simultaneously. The fingerprint detection system (3) according to claim 6, which is controllable to do so.

8. The plurality of edge compensation structures are A plurality of left distal edge compensation structures (15) each arranged to the left of the corresponding one of the left adjacent edge compensation structures (11); A plurality of right distal edge compensation structures (17) each arranged to the right of the corresponding one of the right adjacent edge compensation structures (13); The fingerprint detection system (3) according to any one of claims 5 to 7, comprising.

9. The second signal supply circuit (63; 65) is connected to each of the left distal edge compensation structures (15) and each of the right distal edge compensation structures (17), and a third time-varying voltage (V 3 The fingerprint detection system (3) according to claim 8, which is controllable to supply a signal of (t)) to the set (15a-c) of the left distal edge compensation structures and / or the set (17a-c) of the right distal edge compensation structures.

10. The readout circuit (39) is A plurality of detection circuits (41), each of the plurality of detection circuits being disposed below each set of the detection structures (10) of the plurality of detection structures and connected to each set of the detection structures (10) of the plurality of detection structures; A signal routing and adjustment circuit (43) for routing and / or adjusting signals to and / or from the plurality of detection circuits (41); Comprising; The fingerprint detection system (3) according to any one of claims 5 to 9, wherein the signal routing and adjustment circuit (43) is at least partially disposed under the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83).

11. The fingerprint detection system (3) according to claim 10, wherein the sensor array (7), the readout circuit (39), and the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) are included in a fingerprint sensor component.

12. The fingerprint sensor component, A component substrate; An active circuit formed on the component substrate; A plurality of metal layers on the active circuit; The fingerprint detection system (3) according to claim 11, comprising.

13. The fingerprint detection system (3) according to claim 12, wherein the plurality of detection structures and the at least one edge compensation structure are formed on the uppermost metal layer of the plurality of metal layers.

14. The first signal supply circuit (49) is capable of controlling to supply a signal of the first time-varying voltage (V 1 (t)) to the set (10a-c) of the detection structures of the plurality of detection structures. The fingerprint detection system (3) according to any one of claims 1 to 13.

15. The readout circuit (39) includes a plurality of detection circuits (41), each detection circuit of the plurality of detection circuits including a plurality of detection circuits (41) connected to each set of the detection structures (10) of the plurality of detection structures, Each detection circuit (41) of the plurality of detection circuits includes a charge amplifier (45), the charge amplifier (45) having a first input part (53) connected to the set of the detection structures, a second input part (55), an output part (57), and a feedback capacitor between the first input part (53) and the output part (57), and the charge amplifier (45) is configured such that a substantially identical electrical change occurs in the first input part (53) as a result of a change in the potential of the second input part (55). The fingerprint detection system (3) according to claim 14, wherein the first signal supply circuit (49) is connected to the second input part (55).

16. The fingerprint detection system includes a semiconductor substrate (27). The charge amplifier (45) includes a transistor formed on a wall portion of the semiconductor substrate (27), and the transistor has a gate that constitutes the first input portion. The interface between the wall portion and the semiconductor substrate is configured to prevent current from flowing between the wall portion and the semiconductor substrate. The fingerprint detection system (3) according to claim 15, wherein the first signal supply circuit (49) is further connected to the wall portion. **Claim 17** A sensor array (7) having a plurality of conductive detection structures (10), wherein the detection structures arranged at the edge of the sensor array are not surrounded by adjacent detection structures, the sensor array (7), At least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) arranged outside the sensor array (7) adjacent to the detection structures arranged at the edge of the sensor array; A readout circuit (39) connected to each of the detection structures (10) to supply a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26) and not connected to the at least one edge compensation structure; A second signal supply circuit (63; 65); A method for detecting a fingerprint pattern of the finger (26) using a fingerprint detection system (3) comprising: Step of controlling a first signal supply circuit (49) to supply a first time-varying voltage signal (V 1 (t)) to at least a part of the sensor array (7); The second time-varying voltage signal (V 2 (t)) is synchronized with the first time-varying voltage signal (V1(t)) and supplied to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83), and controlling the second signal supply circuit (63; 65) for this purpose Controlling the readout circuit (39) to supply a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26); Comprising: The readout circuit (39) A plurality of detection circuits (41), each of the plurality of detection circuits being arranged below each set of the detection structures (10) of the plurality of detection structures and connected to each set of the detection structures (10) of the plurality of detection structures; A signal routing and adjustment circuit (43) for routing and / or adjusting signals to and / or from the plurality of detection circuits (41); Comprising: The signal routing and adjustment circuit (43) is arranged at least partially under the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83). **Claim 18** A sensor array (7) having a plurality of conductive detection structures (10), wherein the detection structures arranged at the edge of the sensor array are not surrounded by adjacent detection structures, the sensor array (7), At least one conductive edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) arranged outside the sensor array (7) adjacent to a detection structure arranged at an edge of the sensor array A readout circuit (39) connected to each of the detection structures (10) for supplying a detection signal representing a capacitive coupling between the detection structure (10) and a finger (26) and not connected to the at least one edge compensation structure A second signal supply circuit (63; 65) A method for detecting a fingerprint pattern of the finger (26) using a fingerprint detection system (3) comprising Controlling a first signal supply circuit (49) to supply a first time-varying voltage signal (V1(t)) to at least a part of the sensor array (7) Controlling the second signal supply circuit (63; 65) to supply a second time-varying voltage signal (V2(t)) to the at least one edge compensation structure (11; 13; 15; 17; 19; 21; 23; 25; 79; 81; 83) in synchronization with the first time-varying voltage signal (V1(t)) Controlling the readout circuit (39) to supply a detection signal representing a capacitive coupling between the detection structure (10) and the finger (26) Comprising The detection structures (10) of the sensor array (7) are arranged in rows and columns The fingerprint detection system (3) comprises a plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25), and the plurality of edge compensation structures (11; 13; 15; 17; 19; 21; 23; 25) are A plurality of left adjacent edge compensation structures (11) each arranged to the left of the corresponding row of the rows A plurality of right adjacent edge compensation structures (13) each arranged to the right of the corresponding row of the rows A method having

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