Fingerprint sensor with charge modification device

Abstract

The fingerprint sensor includes: a plurality of sensing structures arranged in a sensing plane for capacitive sensing of a fingerprint; a charge modification device comprising a plurality of charge modification structures arranged relative to the plurality of sensing structures to form a plurality of capacitors, and a charge modification circuit arranged between the plurality of charge modification structures and the plurality of capacitors, a charge modification circuit coupled to each of the plurality of charge modification structures and controllable to provide a voltage signal to the plurality of charge modification structures, thereby modifying an amount of charge carried by the sensing structure; and a measurement circuit coupled to the plurality of sensing structures for providing a measurement signal indicative of a capacitive coupling between each of the plurality of sensing structures and the finger, where the charge modification device is configured to provide different charge modifications for different ones of the plurality of sensing structures.

Description

Technical Field

[0001] The present invention relates to a fingerprint sensor, to an electronic device comprising the fingerprint sensor, and to a method of acquiring a fingerprint representation. Background Art

[0002] Biometric identification systems are widely used as a means for improving the convenience and security of personal electronic devices such as mobile phones, etc. In particular, fingerprint sensing systems are currently included in most of all newly released personal communication devices such as mobile phones.

[0003] Many electronic devices have various curved surfaces for providing an improved user experience. It would be desirable to provide improved integration of fingerprint sensing capabilities in such electronic devices. Summary of the invention

[0004] In view of the above, it is an object of the present invention to provide improved integration of fingerprint sensing capabilities in electronic devices having at least one curved surface portion.

[0005] According to a first aspect of the present invention, a fingerprint sensor is provided, which includes: a plurality of sensing structures arranged in a sensing plane for capacitive sensing of a fingerprint of a finger placed on a finger receiving surface of the fingerprint sensor; a charge modification device, which includes: a plurality of charge modification structures arranged relative to the plurality of sensing structures to form a plurality of capacitors, each capacitor including a sensing structure in the plurality of sensing structures, a charge modification structure in the plurality of charge modification structures, and a dielectric between the sensing structure and the charge modification structure; and a charge modification circuit coupled to each of the plurality of charge modification structures and controllable to provide a voltage signal to the plurality of charge modification structures, thereby modifying the amount of charge carried by the sensing structure; and a measurement circuit coupled to the plurality of sensing structures for providing a measurement signal indicating the capacitive coupling between each of the plurality of sensing structures and the finger, wherein the charge modification device is configured to provide different charge modifications for different sensing structures in the plurality of sensing structures.

[0006] The present invention is based on the general recognition that in an electronic device using a capacitive fingerprint sensor with a sensing structure arranged in a sensing plane, it would be beneficial to enable a non-planar topography of the finger receiving surface. The inventors have also recognized that the sensing performance of a fingerprint sensor in such a configuration can be improved by adding or subtracting different numbers of charges from a sensing structure arranged to be covered by a dielectric material of different thicknesses.

[0007] Thus, a more uniform signal strength baseline can be achieved across the entire sensing plane, which in turn provides an improved fingerprint image quality. The thereby improved fingerprint image quality can be translated into improved biometric authentication performance of an electronic device incorporating a fingerprint sensor according to an embodiment of the present invention. Furthermore, according to an embodiment of the present invention, compensation for dielectric materials of varying thickness can be performed at the beginning of the measurement chain, which can benefit the measurement performance of the fingerprint sensor, for example in terms of signal-to-noise ratio, also providing improved fingerprint image quality.

[0008] The charge modification device may advantageously be configured to provide a charge modification that is adapted or adaptable to different configurations of the finger receiving surface.

[0009] For a convex finger receiving surface, the thickness of the dielectric material covering the sensing structures will be greater for the centrally located sensing structures than for the peripheral sensing structures. For such a configuration, the charge modification device may be configured to subtract more charge from the peripheral sensing structures than from the centrally located sensing structures. Alternatively, the charge modification device may be configured to add a first charge amount to the peripherally located sensing structures and to add a second charge amount greater than the first charge amount to the centrally located sensing structures. According to another alternative, the charge modification device may be configured to subtract charge from the peripherally located sensing structures and to add charge to the centrally located sensing structures.

[0010] For a concave finger receiving surface, the charge modification should be opposite to that described above for a convex finger receiving surface.

[0011] Different charge modifications for different sensing structures can be achieved by various configurations of the charge modification device. Different sensing structures can exhibit different capacitive couplings with the charge modification structure, and / or the charge modification circuit can be configured to provide different voltage signals to the charge modification structure capacitively coupled to different sensing structures.

[0012] A fingerprint sensor according to an embodiment of the present invention may include a dielectric material covering a sensing plane of the fingerprint sensor, the dielectric material having a non-uniform thickness profile defining the topography of a finger receiving surface of the fingerprint sensor.

[0013] The dielectric material may be provided, for example, in the form of a suitably shaped window against which the planar surface of the fingerprint sensor according to an embodiment of the invention is pressed or glued. Alternatively or in combination, the dielectric material may be molded onto the sensing surface of the fingerprint sensor, thereby practically ensuring that there is no air gap between the sensing plane and the finger receiving surface.

[0014] According to a second aspect of the present invention, there is provided a method for acquiring a fingerprint representation using a fingerprint sensor having a finger receiving surface to be contacted by a finger, the fingerprint sensor comprising: a plurality of sensing structures arranged in a sensing plane; a charge modification device comprising: a plurality of charge modification structures, the plurality of charge modification structures being arranged relative to the plurality of sensing structures to form a plurality of capacitors, each capacitor comprising a sensing structure in the plurality of sensing structures, a charge modification structure in the plurality of charge modification structures, and a dielectric between the sensing structure and the charge modification structure; and a charge modification circuit coupled to each of the plurality of charge modification structures and controllable to provide a voltage signal to the plurality of charge modification structures, thereby modifying the amount of charge carried by the sensing structure; and a measurement circuit coupled to the plurality of sensing structures for providing a measurement signal indicating the capacitive coupling between each of the plurality of sensing structures and the finger; and a dielectric material covering the sensing plane, the dielectric material having a non-uniform thickness profile defining the topography of the finger receiving surface of the fingerprint sensor. The method comprises the following steps: acquiring a first group of measurement signals from a first group of sensing structures among a plurality of sensing structures covered by a dielectric material with a thickness within a first thickness range, and providing a first charge modification to the first group of sensing structures by a charge modification device; and acquiring a second group of measurement signals from a second group of sensing structures among a plurality of sensing structures covered by a dielectric material with a thickness within a second thickness range, the second thickness range only including thicknesses greater than the first thickness range, and providing a second charge modification to the second group of sensing structures by the charge modification device.

[0015] In summary, an embodiment of the present invention therefore relates to a fingerprint sensor, which includes: a plurality of sensing structures, which are arranged in a sensing plane for capacitive sensing of fingerprints; a charge modification device, which includes: a plurality of charge modification structures, which are arranged relative to the plurality of sensing structures to form a plurality of capacitors; and a charge modification circuit, which is coupled to each of the plurality of charge modification structures and can be controlled to provide a voltage signal to the plurality of charge modification structures, thereby modifying the amount of charge carried by the sensing structure; and a measurement circuit, which is coupled to the plurality of sensing structures for providing a measurement signal indicating the capacitive coupling between each of the plurality of sensing structures and a finger, wherein the charge modification device is configured to provide different charge modifications for different sensing structures in the plurality of sensing structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings showing example embodiments of the invention, in which:

[0017] Figure 1is an illustration of an exemplary electronic device in the form of a mobile phone including a fingerprint sensor in accordance with an embodiment of the present invention;

[0018] Figure 2 yes Figure 1 an enlarged view of a portion of an electronic device;

[0019] FIG. 3A to FIG. 3B yes Figure 1 and Figure 2 A perspective view of a fingerprint sensor included in a mobile phone in;

[0020] Figure 4 yes Figure 1 and Figure 2 A partially opened perspective schematic diagram of a fingerprint sensor included in a mobile phone in;

[0021] Figure 5 yes Figure 4 A schematic cross-sectional view of a fingerprint sensor in FIG.

[0022] Figure 6 Schematically illustrates an example embodiment of a fingerprint sensor according to the present invention;

[0023] Figure 7 Schematically shows Figure 6 A first example configuration of a measurement circuit and a charge modification device in a fingerprint sensor;

[0024] FIG. 8A to FIG. 8D Schematically shows Figure 6 Different configurations of charge modification devices in fingerprint sensors; and

[0025] 9A to 9C Schematically shows Figure 6 Other configurations of the charge modification device in the fingerprint sensor. DETAILED DESCRIPTION

[0026] In this detailed description, various embodiments of fingerprint sensors according to the present invention are described primarily with reference to fingerprint sensor components including semiconductor-based capacitive fingerprint sensor integrated circuits (ICs). It should be noted that fingerprint sensors according to embodiments of the present invention do not need to be overmolded by dielectric materials, and the topography of the finger receiving surface can be alternatively implemented using separate parts attached to or appropriately arranged relative to the fingerprint sensor. In addition, the finger receiving surface of the fingerprint sensor is primarily illustrated as a convex surface. It should be noted that, as defined by the claims, the present invention is not limited to any particular shape or configuration of the finger receiving surface. In addition, the fingerprint sensor is not necessarily elongated, but can be any other shape, such as square or circular, etc. In addition, it should be understood that the mobile phone in the figure is only an example of an electronic device that can include a fingerprint sensor according to an embodiment of the present invention. Fingerprint sensors according to embodiments of the present invention can be advantageously included in many other electronic devices, including, for example, computers, electronic watches and other gadgets, and smart cards, etc.

[0027] Figure 1 Schematically shows an electronic device (here, in the form of a mobile phone 1) comprising a device housing 3 and a fingerprint sensor 5. Figure 1 As can be seen in FIG. 1 , the device housing 3 has a convex portion 7 with an opening 9. The fingerprint sensor 5 is arranged in the opening 9 and also exhibits a convex shape. The convex shape of the fingerprint sensor 5 can substantially follow the convex shape of the convex portion 7 of the device housing 3 at least at the opening 9. This is Figure 2 It can be better seen in the enlarged view of the part.

[0028] FIG. 3A to FIG. 3B yes Figure 1 and Figure 2 A perspective view of a fingerprint sensor 5 included in a mobile phone 1 in FIG.

[0029] Figure 3A 1 is a perspective view showing the top surface 11 and side surface 13 of the fingerprint sensor 5. Figure 3A As can be seen in FIG. 1 , the fingerprint sensor 5 in this particular example configuration is elongated, having a length l and a width w.

[0030] Figure 3B 1 is a perspective view showing the component bottom surface 15 and side surface 13 of the fingerprint sensor 5. Figure 3B As can be seen in FIG. 1 , the fingerprint sensor 5 has a component conductor pattern 17 on the component bottom surface 15 . Figure 3B In the embodiment of the present invention, the component conductor pattern 17 is defined as having a plurality of component connection pads 19 (only one of which is formed by Figure 3B The reference numerals in the figure indicate a land grid array (land grid array) in order to avoid cluttering the drawing.

[0031] Figure 4 is Figure 1 The mobile phone 1 in the embodiment includes and Figure 3A and Figure 3B FIG. 5 is a schematic perspective view of a partially opened fingerprint sensor 5 shown in FIG. Figure 4 The fingerprint sensor 5 includes a substrate 21, a fingerprint sensor die 23 and a dielectric material 25. The substrate 21 has a substrate top surface 27 and a substrate bottom surface 29. The substrate top surface 27 has a dielectric material 25. Figure 4 The top surface conductor pattern of the bonding pad 31 is visible in FIG. Figure 4 The bottom surface 29 of the substrate has a structure that can constitute the above reference Figure 3B The fingerprint sensor die 23 has a die top surface 33, a die bottom surface 35, and a side surface 37 connecting the die top surface 33 and the die bottom surface 35. The die top surface 33 includes a planar sensing surface 39. The die bottom surface 35 of the fingerprint sensor die 23 is bonded to the substrate top surface 27 of the substrate 21. Figure 4 As schematically indicated in FIG. 1 , the fingerprint sensor die 23 also includes a die connection pad 43 that is electrically connected to the bonding pad 31 on the substrate top surface 27 of the substrate 21. This electrical connection can be made using, for example, Figure 4 The dielectric material 25 covers the sensing surface 39 and the side surface 37 of the fingerprint sensor die 23, and the portion of the substrate top surface 27 of the substrate 21 that is not covered by the fingerprint sensor die 23. Figure 4 As schematically indicated in FIG. 1 , the dielectric material 25 exhibits a convex shape above the sensing surface 39 of the fingerprint sensor die 23. Figure 4 As schematically indicated in FIG. 4 , the fingerprint sensor 5 may optionally additionally comprise a colored coating 47 on top of the dielectric material 25 .

[0032] Figure 5 yes Figure 4 The fingerprint sensor in 5 is along Figure 4 Schematic cross-sectional view of the portion taken along line AA' in FIG. Figure 4 In addition to the description, Figure 5 A through-hole 49 electrically connecting the top surface conductor pattern of the substrate 21 with the bottom surface conductor pattern 17 of the substrate 21 is schematically shown. Figure 5 Also indicated is an advantageous configuration of the convex shape of the dielectric material 25. Figure 5 As indicated in , the top surface (finger receiving surface) of the fingerprint sensor 5 exhibits a convex shape with a radius of curvature R. The radius of curvature R of the fingerprint sensor 5 may be adapted to substantially follow the radius of curvature of the convex portion 7 of the device housing 3 of the electronic device 1 .

[0033] Figure 6 is a schematic cross-sectional view of a fingerprint sensor 5 according to an example embodiment of the present invention, comprising a dielectric material 25 having a non-uniform thickness profile defining the topography (in this case a convex topography) of a finger receiving surface 51 of the fingerprint sensor 5. The fingerprint sensor 5 comprises a plurality of conductive sensing structures, here in the form of metal plates 41 arranged in a uniform array configuration in a sensing plane - the sensing surface 39 mentioned above - for capacitive sensing of a fingerprint of a finger 53 placed on the finger receiving surface 51 of the fingerprint sensor 5.

[0034] The plurality of conductive sensing structures 41 include a first group 41a, a second group 41b, and a third group 41c of sensing structures. The first group 41a of sensing structures is arranged to be covered by a thickness of the dielectric material 25 within a first thickness range d1-d2; the second group 41b of sensing structures is arranged to be covered by a thickness of the dielectric material 25 within a second thickness range d3-d4, the second thickness range d3-d4 only including thicknesses greater than the first thickness range d1-d2; and the third group 41c of sensing structures is arranged to be covered by a thickness of the dielectric material 25 within a third thickness range d2-d3, the third thickness range d2-d3 being between the first thickness range and the second thickness range.

[0035] The capacitive coupling between the sensing structure 41 of the fingerprint sensor 5 and the finger 53 placed on the finger receiving surface 51 is a measure of the capacitance of the capacitor formed by the sensing structure 41, the finger 53 and the dielectric material 25 between the sensing structure 41 and the finger surface. Figure 6 In the configuration in , the maximum capacitance (resulting from good contact of the ridges of the finger pattern with the finger receiving surface 51) can be considered to be proportional to the surface area of ​​the sensing structure 41 and inversely proportional to the distance between the sensing structure and the finger surface.

[0036] As in Figure 6 As schematically indicated in FIG. 1 , the fingerprint sensor 23 further comprises a charge-modification device 57 and a sensor coupled to the sensing structure 41 for providing a measurement signal S indicating the capacitive coupling between the sensing structure 41 and the finger 53. m The measuring circuit 58 is provided.

[0037] exist Figure 6 In the embodiment, the charge modification device 57 is arranged to provide three different charge modifications, such as Figure 6 It should be understood that this is merely an illustration to help understand the embodiment, and the charge modification device does not necessarily have different physical configurations in different parts thereof.

[0038] The different charge modifications 57a to 57c provided by the charge modification device 57 may be permanent, or the charge modification device 57 may be controllable to vary the charge modification for all sensing structures 41 or for different groups of sensing structures. This optional controllability of the charge modification device 57 is determined by Figure 6 The dashed arrow 59 in FIG.

[0039] Thus, the measurement circuit 58 may provide a first set of measurement signals from the first group 41a of sensing structures subjected to the first charge modification indicated by 57a, a second set of measurement signals from the second group 41b of sensing structures subjected to the second charge modification indicated by 57b, and a third set of measurement signals from the third group 41c of sensing structures subjected to the third charge modification indicated by 57c, so that a fingerprint representation S including the first set of measurement signals, the second set of measurement signals, and the third set of measurement signals can be formed. m .

[0040] exist Figure 6 , only three different charge modifications are shown. It will be appreciated that this is primarily for ease of illustration and explanation. The charge modification device 57 may advantageously be configured to implement a greater number of charge modifications. In particular, it may be advantageous to provide a substantially continuous gradient of charge modifications across the length and / or width of the fingerprint sensor. For example, a different charge modification may be provided for each row or column of the sensing structure 41, thereby producing a "smooth" compensation for sensitivity variations caused by varying thicknesses of the dielectric material 25 above the sensing surface 29.

[0041] The fingerprint sensor 5 may be included in a fingerprint sensing system, which also includes a fingerprint sensor controller coupled to the fingerprint sensor 5 to control the operation of the fingerprint sensor 5. The fingerprint sensor controller is not explicitly shown in the drawings, but it will be clear to those skilled in the art that the fingerprint sensor controller may be included in an electronic device such as Figure 1 In the mobile phone 1 in. Therefore, the fingerprint sensing system mentioned above may partially include the circuit included in the electronic device. According to one embodiment, the fingerprint sensor controller may be included in the fingerprint sensor module integrated in the electronic device (mobile phone 1), and according to another embodiment, the function of the fingerprint sensor controller may be at least partially implemented by the main controller of the electronic device.

[0042] In an embodiment, the fingerprint sensor controller may be configured to control the charge modification device 57 of the fingerprint sensor 5 to provide an initial charge modification distribution between the sensing structures 41 by means of a control signal 59. Based on the measurement signal obtained using the initial charge modification distribution, the fingerprint sensor controller may determine an updated charge modification distribution between the sensing structures 41, and control the charge modification device 57 to provide an updated charge modification distribution by means of the control signal 59.

[0043] Figure 7 Schematically shows Figure 6 A first exemplary configuration of a charge modification device 57 and a measurement circuit 58 in a fingerprint sensor of FIG. Figure 7 The measuring circuit 58 includes an amplifier circuit 63 and an analog-to-digital converter (ADC) circuit 65. Figure 7 As schematically indicated in FIG. 1 , the amplification circuit 63 receives input from one or several sensing structures 41 and provides an amplified analog signal to the ADC circuit 65. The ADC circuit 65 outputs a digital measurement signal S m The input from the sensing structure 41 is related to the charge (or change in charge) carried by the sensing structure 41. The charge (or change in charge) carried by the sensing structure 41 during the measurement operation in turn depends on the capacitive coupling between the sensing structure 41 and the finger 53. In addition to the difference in distance to the surface of the finger 53 due to the fingerprint topography, the capacitive coupling is also affected by the thickness of the dielectric material 25 covering the sensing structure 41. In order to compensate for this common-mode effect on the capacitive coupling, the charge modification device 57 is configured to provide different charge modifications for different sensing structures 41.

[0044] Continue to refer to Figure 7 , the charge modification device 57 includes a plurality of charge modification structures 67 and a charge modification circuit 69 coupled to each charge modification structure 67. For simplicity of description, Figure 7 Only one charge modification structure 67 is shown in the schematic diagram. FIG. 8A to FIG. 8D , FIG. 9A to FIG. 9B and FIG. 10 further describe various configurations of the charge modification device 57 .

[0045] like Figure 7As shown, its charge modification structure 67 is arranged relative to its associated sensing structure 41 to form a capacitor with a capacitance C, which includes the sensing structure 41, the charge modification structure 67 and a dielectric between the sensing structure 41 and the charge modification structure 67. The charge modification circuit 69 is coupled to the charge modification structure 67 (coupled to all charge modification structures included in the charge modification device 57) and can be controlled to provide a voltage signal V to the charge modification structure 67. The charge modification circuit 69 can include at least one controllable voltage source, such as one or more DACs (digital-to-analog converters). Each group 41a to 41c of the sensing structure 41 can have one controllable voltage source, or there can be fewer voltage sources, each with several individually controllable outputs. Depending on the desired charge modification distribution, a simpler solution may also be sufficient. For example, a voltage source with two outputs with different voltages can be combined with a string of resistors (at least one resistor) to form an intermediate voltage (at least one). If necessary, using a string of resistors, a substantially continuous voltage distribution between the charge modification structures can be achieved.

[0046] The product of capacitance C and voltage V determines the modification (reduction or addition) of the charge carried by sensing structure 41 . To control the charge modification, capacitance C or voltage V or both capacitance C and voltage V may be controlled, as indicated by control signal 59 .

[0047] Despite Figure 7 4. One amplifier circuit is shown connected to a single sensing structure 41, but it should be noted that this is not necessarily the case, and for example, one amplifier circuit may be connected (selectively connectable) to a plurality of sensing structures 41.

[0048] FIG. 8A to FIG. 8D Schematically shows Figure 6 Different example configurations of the charge modification device 57 in the fingerprint sensor of FIG. In particular, FIG. 8A to FIG. 8D Different arrangements of the charge modifying structure 67 relative to the sensing structure 41 that is charge modified by the charge modifying structure 67 are shown.

[0049] exist FIG. 8A to FIG. 8D In each of the three groups of four sensing structures are shown. From left to right, the sensing structures 41 of these groups are respectively from Figure 6 The first group 41a, Figure 6 The third group 41c, and Figure 6 The second group 41b in.

[0050] It should be noted again that there may advantageously be far more than three groups of sensing structures with different charge modifications in a fingerprint sensor, and references herein to first, second and third groups of sensing structures are primarily intended to simplify the description.

[0051] exist Fig. 8A In FIG. 6 , as can be seen from the finger receiving surface of the fingerprint sensor, the charge modification structure 67 is a conductive structure arranged below the sensing plane. Fig. 8A As can be seen in FIG. 6 , there is one charge modifying structure 67 for each sensing structure 41. Each charge modifying structure forms a capacitor together with its associated sensing structure 41. Since the overlapping area between the sensing structure and its associated charge modifying structure is different for different groups 41a to 41c of sensing structures, the capacitances C1 to C3 are different for different groups 41a to 41c. Fig. 8A In the example configuration of , the capacitance C1 for the peripheral first group 41a of sensing structures is greater than the capacitance C3 for the centrally located second group 41b of sensing structures, and greater than the capacitance C2 for the intermediate group 41c. Therefore, if the same voltage signal is provided to all charge modifying structures 67, more charge can be subtracted from the peripheral sensing structures than from the centrally located sensing structures. Therefore, as Figure 6 As shown in , for a fingerprint sensor 5 having a convex finger receiving surface, the charge baseline can be flattened. If the charge modification is performed by adding charge instead, the size relationship between the charge modification structures for different groups 41a to 41c of sensing structures can be as follows Fig. 8A The opposite of what is shown in .

[0052] like Figure 8B As schematically indicated in , the charge modification structure 67 may be common to a group of sensing structures 41 .

[0053] exist Figure 8C In the embodiment, the charge modification structure 67 is also shared by a group of sensing structures 41 . Figure 8C Configuration and Figure 8B The configuration in FIG. 4 is different in that the charge modification structure 67 and the sensing structure 41 are arranged in the same plane.

[0054] exist Fig.8D In the configuration, the overlapping area between the sensing structure 41 and its associated charge modification structure 67 is the same for different groups 41a to 41c of sensing structures, which means that the capacitance C is the same for different groups 41a to 41c (assuming that the dielectric thickness between the sensing structure 41 and the associated charge modification structure 67 is the same for different groups 41a to 41c of sensing structures). Fig.8D In the example configuration of Fig.8D 41a to 41c) is controlled to provide different voltage signals V1 to V3 to the charge modifying structures associated with the sensing structures in different groups 41a to 41c of sensing structures. Fig.8DIn an example configuration, the voltage V1 for the peripheral first group 41a of sense structures can be greater than the voltage V3 for the centrally located second group 41b of sense structures, and greater than the voltage V2 for the intermediate group 41c. Thus, more charge can be subtracted from (or added to) the peripheral sense structures than from the centrally located sense structures.

[0055] It should be noted again that a greater number of different voltages may advantageously be present across the fingerprint sensor to provide a more precise charge modification that is better adapted to the contours of the finger receiving surface.

[0056] 9A to 9C Schematically shows Figure 6 Other example configurations of the charge modification device 57 in the fingerprint sensor 5. 9A to 9C For the sensing structures in the first group 41a of sensing structures and the sensing structures in the second group 41b of sensing structures (see Figure 6 ), showing a schematic cross section of the fingerprint sensor 5. 9A to 9C As can be seen in , these example configurations of the charge modification device 57 include two charge modification structures 67 a - 67 b for each sensing structure 41 .

[0057] First go to Fig.9A , the first charge modifying structure 67a has a relatively large surface area and is the same for each sensing structure 41 in the first group 41a and the second group 41b (generally across the entire fingerprint sensor 5). The second charge modifying structure 67b has a relatively small surface area and is the same for each sensing structure 41 in the first group 41a and the second group 41b (generally across the entire fingerprint sensor 5). Fig.9A As schematically indicated in FIG. 1 , a first relatively large charge modifying structure 67a is connected to charge modifying circuitry 69 for sensing structures 41 in a first group 41a of sensing structures, and a second relatively small charge modifying structure 67b is connected to charge modifying circuitry 69 for sensing structures 41 in a second group 41 of sensing structures. The connections between the charge modifying structures and the charge modifying circuitry may be controllable or hardwired. Fig.9A The configuration of the charge modification device in the embodiment enables a simplified circuit design and can provide some adjustability of the fingerprint sensor 5 for different finger receiving surface topography (at least in the above-mentioned connection controllable embodiment).

[0058] Now refer to Fig. 9B , wherein the configuration of the charge modification device 57 is schematically shown Fig.9A The configuration in FIG. 5 differs in that the first charge modification structure 67a for each sensing structure 41 has a surface area that depends on the position of the sensing structure 41 in the fingerprint sensor 5. Fig. 9BIn the exemplary configuration of , the first charge modification structure 67a has a larger surface area for the sensing structures in the first group 41a of sensing structures than for the sensing structures in the second group 41b of sensing structures. On the other hand, for each sensing structure 41, the second charge modification structure 67b for each sensing structure 41 has the same surface area. Fig. 9B As shown in FIG. 5 , the charge modification device 57 further comprises a controllable switch 70 for each sensing element 41 , allowing selection of which charge modification structure (if any) is used for the sensing structure 41 . Fig. 9B By configuring the charge modification device in the same fingerprint sensor IC, the same fingerprint sensor IC can be optimized for a flat finger receiving surface and for a curved finger receiving surface. In addition, for example, a setup with the same surface dimensions of the charge modification structure for each sensing structure 41 can be used for production testing and calibration, etc., and another setup can be used to obtain fingerprint representations.

[0059] Fig. 9C Another example configuration of the charge modification device 57 is schematically shown, enabling improved adaptability to different finger receiving surface contours and / or variations in production.

[0060] Fig. 9C The configuration of the charge modification device 57 in the above reference Fig. 9B The configuration described in the embodiment of the present invention differs in that there is a first switch 73 and a second switch 75 for each sensing structure 41. By selectively activating the switches 73, 75 and optionally also adjusting the voltages supplied to the charge modification structures 67a of different sizes and the charge modification structures 67b of uniform size, respectively, the charge modification can be adapted to all finger receiving surface profiles that can be expressed or approximated as a second-order polynomial. This greatly increases the adaptability of the fingerprint sensor to different products with different requirements in terms of the surface profile of the finger receiving surface.

[0061] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A fingerprint sensor, comprising: a plurality of sensing structures arranged in a sensing plane for capacitive sensing of a fingerprint of a finger placed on a finger receiving surface of the fingerprint sensor; A charge modification device, the charge modification device comprising: a plurality of charge modifying structures arranged relative to the plurality of sensing structures to form a plurality of capacitors, each capacitor comprising a sensing structure of the plurality of sensing structures, a charge modifying structure of the plurality of charge modifying structures, and a dielectric between the sensing structure and the charge modifying structure; and a charge modification circuit coupled to each of the plurality of charge modification structures and controllable to provide a voltage signal to the plurality of charge modification structures; and a measurement circuit coupled to the plurality of sensing structures for providing a measurement signal indicative of a capacitive coupling between each of the plurality of sensing structures and the finger, The charge modification device is configured to provide different charge modifications for different sensing structures among the plurality of sensing structures.

2. The fingerprint sensor according to claim 1, wherein: Each of the plurality of charge modifying structures is a conductive structure disposed below the sensing plane as viewed from the finger receiving surface.

3. The fingerprint sensor according to claim 1 or 2, wherein: Each sensing structure of the plurality of sensing structures is a metal plate; and Each charge modifying structure of the plurality of charge modifying structures is a metal plate.

4. A fingerprint sensor according to any one of the preceding claims, wherein: Each charge modifying structure of the plurality of charge modifying structures together with its associated sensing structure forms one capacitor of the plurality of capacitors.

5. A fingerprint sensor according to any one of the preceding claims, wherein: The plurality of capacitors include: a first set of capacitors having a first capacitance; and A second set of capacitors having a second capacitance different from the first capacitance.

6. The fingerprint sensor according to claim 5, wherein: Each capacitor of the first set of capacitors exhibits a first overlap area between a sensing structure and a charge modifying structure included in the capacitor; and Each capacitor of the second set of capacitors exhibits a second overlap area between a sensing structure and a charge modifying structure included in the capacitor that is different than the first area.

7. A fingerprint sensor according to any one of the preceding claims, wherein: The charge modification circuit is configured to provide different voltage signals to different charge modification structures.

8. The fingerprint sensor according to claim 7, wherein: The charge modification circuit includes a controllable voltage source.

9. The fingerprint sensor according to claim 8, wherein: The charge modification circuit comprises: a first output coupled to a first set of charge modifying structures to provide a first voltage signal to each charge modifying structure in the first set of charge modifying structures; and A second output is coupled to a second set of charge modifying structures to provide a second voltage signal to each charge modifying structure in the second set of charge modifying structures.

10. The fingerprint sensor according to claim 9, wherein: The charge modification circuit comprises: a third output coupled to a third set of charge modifying structures to provide a third voltage signal to each charge modifying structure in the third set of charge modifying structures; a first resistor coupled between the first output and the third output; and A second resistor is coupled between the second output and the third output.

11. The fingerprint sensor according to claim 9 or 10, wherein: The charge modification circuit comprises: a first independently controllable voltage source coupled to each charge modifying structure in the first set of charge modifying structures; and A second independently controllable voltage source is coupled to each charge modifying structure in the second set of charge modifying structures.

12. A fingerprint sensor according to any one of the preceding claims, wherein: The fingerprint sensor includes a dielectric material covering the sensing plane of the fingerprint sensor, the dielectric material having a non-uniform thickness profile defining the topography of the finger receiving surface of the fingerprint sensor.

13. The fingerprint sensor according to claim 12, wherein: The charge modification device is configured to provide: a first charge modification for a sensing structure covered by a thickness of the dielectric material within a first thickness range; as well as A second charge modification for a sensing structure covered by a thickness of the dielectric material within a second thickness range, the second thickness range comprising only thicknesses greater than the first thickness range.

14. An electronic device comprising: a device housing having a curved portion with an opening; as well as According to the fingerprint sensor of claim 12 or 13, the fingerprint sensor is arranged in an opening of the bent portion of the device housing.

15. A method of acquiring a fingerprint representation using a fingerprint sensor having a fingerprint receiving surface to be contacted by a finger, the fingerprint sensor comprising: a plurality of sensing structures arranged in a sensing plane; A charge modification device, the charge modification device comprising: a plurality of charge modifying structures arranged relative to the plurality of sensing structures to form a plurality of capacitors, each capacitor comprising a sensing structure of the plurality of sensing structures, a charge modifying structure of the plurality of charge modifying structures, and a dielectric between the sensing structure and the charge modifying structure; and a charge modification circuit coupled to each of the plurality of charge modification structures; and a measurement circuit coupled to the plurality of sensing structures for providing a measurement signal indicative of a capacitive coupling between each of the plurality of sensing structures and the finger; and a dielectric material covering the sensing plane, the dielectric material having a non-uniform thickness profile defining the topography of the finger receiving surface of the fingerprint sensor, The method comprises the following steps: Acquiring a first set of measurement signals from a first set of sensing structures of the plurality of sensing structures covered by a thickness of the dielectric material within a first thickness range, while providing a first charge modification to the first set of sensing structures by the charge modification device; and A second set of measurement signals is obtained from a second group of sensing structures among the plurality of sensing structures covered by a thickness of the dielectric material within a second thickness range, wherein the second thickness range only includes thicknesses greater than the first thickness range, while a second charge modification is provided to the second group of sensing structures by the charge modification device.

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