Fingerprint sensing devices and electronic devices

Abstract

This invention discloses a fingerprint sensing device and an electronic device. The fingerprint sensing device includes: a sensor array comprising a plurality of sensing units arranged in an array; a plurality of amplification circuits correspondingly coupled to the plurality of sensing units for providing a sensing signal indicating capacitive coupling between the sensing unit and the finger; a first signal providing circuit for providing an excitation signal to the plurality of amplification circuits; at least one compensation capacitor arranged in a plurality of sensing units in a selected column of the array; and at least one compensation voltage signal, each of the compensation voltage signals being coupled to a corresponding compensation capacitor. The capacitance value of the corresponding compensation capacitor and / or the voltage value of the compensation voltage signal are set according to the size of the parasitic capacitance in each sensing unit of the selected column, enabling differentiated compensation for sensing units in different columns of the sensor array, thereby improving the phenomenon of excessive offset of the sensing signal in the edge column of the fingerprint sensing device.

Description

Technical Field

[0001] This invention relates to the field of fingerprint recognition technology, and in particular to a fingerprint sensing device and electronic device. Background Technology

[0002] Capacitive fingerprint acquisition technology has been widely used in various electronic devices. Its principle is that the valleys and ridges of the fingerprint have different capacitance values ​​with the sensing unit. The capacitance value is converted into an electrical signal (voltage, current, etc.) by an amplification circuit coupled to the sensing unit, thereby detecting fingerprint features.

[0003] In today's era of full-screen displays in smartphones and other electronic devices, capacitive fingerprint sensors, due to their limited penetration capabilities, cannot support in-display fingerprint recognition. Therefore, most devices utilize rear-mounted or side-mounted fingerprint solutions. Side-mounted fingerprint sensors, which can share a location with the power button, offer a better user experience and are thus more widely adopted.

[0004] However, capacitive fingerprint sensors are affected by edge effects. Sensing units located at the edges of the sensor array have larger parasitic capacitances, resulting in larger sensing signals compared to the central area. When a finger presses on the sensor array, the edge areas are more prone to saturation, causing image distortion. Currently, there are two main solutions: one is to ensure all sensing signals are unsaturated and then correct them using algorithms or software. This not only increases the time required for fingerprint detection and recognition but also reduces the dynamic range and signal-to-noise ratio. The second solution is to use the edge-column sensing units as dummy sensing units, treating the sensing signals generated by the dummy units and their corresponding amplification circuits as invalid signals to ensure sufficient dynamic range. However, with the increasing prevalence of ultra-thin phones, the width limitations for fingerprint modules are becoming more stringent. The width of the AA (Active Area), the recognition area, has decreased from 3mm to 1.5mm or even lower. The dummy sensing unit solution significantly reduces the proportion of usable sensing units, negatively impacting the accuracy and speed of fingerprint detection and recognition.

[0005] Therefore, there is an expectation for an improved fingerprint sensing device and electronic device that can solve the above problems. Summary of the Invention

[0006] In view of the above problems, the purpose of the present invention is to provide a fingerprint sensing device and electronic device that can perform differential compensation on sensing units in different columns of a sensor array, thereby improving the phenomenon of excessive offset of edge column sensing signals.

[0007] According to one aspect of this application, a fingerprint sensing device is provided, comprising: a sensor array including a plurality of sensing units arranged in an array; a plurality of amplification circuits correspondingly coupled to the plurality of sensing units for providing a sensing signal indicating capacitive coupling between the sensing units and a finger; a first signal providing circuit for providing an excitation signal to the plurality of amplification circuits; at least one compensation capacitor disposed in the plurality of sensing units in a selected column of the array; and at least one compensation voltage signal, each of the compensation voltage signals being coupled to a corresponding compensation capacitor.

[0008] Optionally, the capacitance value of the corresponding compensation capacitor and / or the voltage value of the compensation voltage signal are set according to the size of the parasitic capacitance in each sensing unit of the selected column.

[0009] Optionally, the selected column is a column near the edge of the sensor array.

[0010] Optionally, the compensation capacitors located in the same column of the at least one compensation capacitor receive the same compensation voltage signal.

[0011] Optionally, the fingerprint sensing device further includes a second signal providing circuit configured to provide the compensation voltage signal synchronously with the excitation signal.

[0012] Optionally, the second signal providing circuit includes a plurality of signal generating units, each of which is configured to provide the compensation voltage signal to the compensation capacitors of the corresponding column.

[0013] Optionally, the selected columns include a first column and a second column that are physically symmetrical in the sensor array, wherein the compensation voltage signal received by the compensation capacitor of the first column and the compensation voltage signal received by the compensation capacitor of the second column originate from the same signal generation unit.

[0014] Optionally, the signal generation unit includes: a voltage generation circuit configured to provide a first voltage; a second switch, with a first terminal receiving the first voltage and a second terminal providing the compensation voltage signal; and a third switch coupled between the second terminal of the second switch and ground; wherein the second switch and the third switch are alternately turned on to generate a compensation voltage signal with a high level of the first voltage and a low level of 0V.

[0015] Optionally, the voltage generation circuit is selected from a digital-to-analog converter circuit.

[0016] Optionally, the signal generation unit includes: an operational amplifier circuit, wherein a first input terminal of the operational amplifier circuit receives the excitation signal and an output terminal provides the compensation voltage signal; a first impedance network, wherein the first impedance network is coupled between a second input terminal of the operational amplifier circuit and ground; and a second impedance network, wherein the second impedance network is connected in parallel between a second input terminal and an output terminal of the operational amplifier circuit.

[0017] Optionally, the ratio of the first impedance network and / or the second impedance network can be changed to adjust the amplitude of the compensation voltage signal.

[0018] Optionally, between the compensation capacitor and the amplification circuit, there is also: a seventh switch, the first end of which is coupled to the compensation capacitor and the second end of which is coupled to the amplification circuit; and a fifth switch and a sixth switch connected in series between the first voltage and ground, the intermediate node of which is coupled to the compensation capacitor.

[0019] According to another aspect of this application, an electronic device is provided, including a fingerprint sensing device as described in any of the preceding claims.

[0020] Optionally, the electronic device further includes a power button configured to control the opening and / or closing of the electronic device or a portion thereof; wherein the projection of the sensor array in the fingerprint sensing device onto the plane of the power button partially or completely overlaps with the power button.

[0021] In the fingerprint sensing device provided by the present invention, the compensation voltage signal and / or compensation capacitor correspond to the parasitic capacitance value in the sensing unit, thereby changing the compensation signal provided to the amplification circuit, reducing or eliminating the offset of the sensing signal caused by excessive parasitic capacitance value, and effectively improving the flatness of the fingerprint image.

[0022] Optionally, to address the issue of large parasitic capacitance in the edge column sensing units of the sensor array, a scheme is adopted whereby a signal generation unit generates a compensation voltage signal corresponding to the parasitic capacitance and / or adjusts the capacitance value of the compensation capacitor in the sensing unit. This can generate a corresponding compensation signal and perform differentiated compensation for sensing units in different columns, thereby improving the phenomenon that excessive capacitance value of the edge column parasitic capacitance leads to excessive shift in the sensing signal and improving the flatness of the acquired fingerprint image.

[0023] Optionally, the black borders of the sensor array are mainly caused by edge effects. The fingerprint images collected by the sensing units in the non-edge columns have good flatness. Therefore, in some application scenarios, only the edge columns can be differentiated to reduce circuit complexity.

[0024] Optionally, the sensing units of the sensor array have a certain degree of symmetry, and the capacitance of their parasitic capacitance also has a certain degree of symmetry. The same signal generation unit can be selected to drive columns with the same or similar compensation voltage signals. For example, the leftmost column and the rightmost column can use the same signal generation unit, thereby simplifying the circuit, reducing the chip area and production cost. Attached Figure Description

[0025] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0026] Figure 1 A schematic diagram of the electronic device is shown;

[0027] Figure 2 Show Figure 1 A schematic structural diagram of the sensor array in a fingerprint sensing device;

[0028] Figure 3 The circuit schematic of a prior art detection unit is shown;

[0029] Figure 4 This diagram shows the structure of a finger pressure sensor array.

[0030] Figure 5 A schematic diagram of a prior art sensor array with black borders is shown;

[0031] Figure 6 Show Figure 5 A graph showing the correspondence between the column mean and column number of the sensor array;

[0032] Figure 7 A schematic structural diagram of a fingerprint sensing device according to an embodiment of the present invention is shown;

[0033] Figure 8 A circuit diagram of the detection unit according to an embodiment of the present invention is shown;

[0034] Figure 9a Show Figure 7 A circuit diagram of the signal generation unit in the first embodiment;

[0035] Figure 9b Show Figure 7 Circuit structure diagram of the signal generation unit in the second embodiment;

[0036] Figure 10 A circuit diagram of a detection unit according to another embodiment of the present invention is shown;

[0037] Figure 11 Show Figure 10 Signal timing diagram of the detection unit. Detailed Implementation

[0038] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements or modules are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0039] It should be understood that, in the following description, "circuit" may include single or combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by the programmable circuit. When an element or circuit is said to be "coupled to" another element or "coupled between" two nodes, it can be directly coupled to the other element or there may be intermediate elements; the coupling between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly coupled to" another element, it means that there are no intermediate elements between them.

[0040] Furthermore, certain terms are used in this patent specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This patent specification and claims do not distinguish components based on differences in name, but rather on differences in function.

[0041] Furthermore, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0042] Figure 1 The diagram illustrates the structure of an electronic device, which includes a screen 10 and a fingerprint sensor 20. The fingerprint sensor 20 is used, for example, to unlock the electronic device and / or authorize transactions performed on the electronic device. The electronic device can be a portable electronic device such as a mobile phone or tablet. The fingerprint sensor 20 can be located on the side of the electronic device and shares a position with the power button.

[0043] Figure 2 Show Figure 1A schematic structural diagram of the sensor array of a fingerprint sensing device. The sensor array 100 includes a plurality of sensing units 300 arranged in an array and a sealing ring 400. Each sensing unit 300 can be considered as a pixel. The sealing ring 400 is coupled to a preset voltage, for example, to protect the sensor array 100 and prevent external electrical signals from adversely affecting the sensor array 100. In this embodiment, the sealing ring 400 is disposed on the outer edge of the plurality of sensing units 300. It should be understood that the sealing ring 400 may also be disposed below the plurality of sensing units 300.

[0044] Figure 3 A circuit schematic of a prior art detection unit is shown. The detection unit 301 includes an amplifier circuit 310 and a sensing unit 300. The sensing unit 300 is coupled to a finger to form a detection capacitor Cs and is coupled to the module ground of the fingerprint sensing device 20 to form a parasitic capacitance Cp. The detection unit 301 also includes a feedforward capacitor Cf coupled between the first input terminal and the output terminal of the amplifier circuit 310.

[0045] The positive input terminal of amplifier circuit 310 receives the excitation signal Vtx generated by the first signal supply circuit, the negative input terminal is coupled to the first terminal of parasitic capacitance Cp and detection capacitance Cs, and the output terminal generates a sensing signal Vout. The second terminals of parasitic capacitance Cp and detection capacitance Cs are grounded. It is easy to obtain the change in sensing signal Vout.

[0046]

[0047] See Figure 4 , Figure 4 This diagram shows the structure of a finger pressure sensor array, combined with... Figure 2 , Figure 3 This paper further explains the image distortion that occurs when the existing fingerprint sensing device 20 collects fingerprints. Figure 4 The diagram shows a cross-sectional view of a finger 901 and a sensor array 100. The sensing unit 300 is also selected, for example, from a sampling plate. When the finger 901 presses against the sensor array 100, the valleys or ridges of the fingerprint couple with the sensing unit 300 to form detection capacitances Cs1 to Csn. Each sensing unit 300 is modularly coupled to form parasitic capacitances Cp1 to Cpn. Due to edge effects, the closer the column containing the sensing unit 300 is to the boundary of the sensor array 100, the larger its parasitic capacitance Cp.

[0048] Cp1>Cp2>Cp3>...Cpm <Cpm+1<CpM+2<...Cpn

[0049] Where Cpm is the parasitic capacitance of the sensing unit closest to the center column, and Cpn is the parasitic capacitance of the sensing unit in the rightmost column, combined with formula (1), it can be seen that when the change in excitation signal Vtx ΔVtx, detection capacitor Cs, and feedforward capacitor Cf are constant, the larger the parasitic capacitance Cp, the larger the change in sensing signal Vout ΔVout, which is equivalent to adding an offset to ΔVout, increasing its signal strength, thereby causing the fingerprint image edge to turn black, commonly known as a black border, such as Figure 5 As shown. Figure 5 The diagram shows a prior art sensor array with black borders, from left to right: column 1, column 2, column 3, ..., column n-2, column n-1, and column n. Further details can be found in the documentation. Figure 6 , Figure 6 Show Figure 5 The graph showing the correspondence between the column mean and column number of the sensor array 100 shows that the column mean shifts larger closer to the edge of the array. Specifically, the first and nth columns have the largest shifts, followed by the second and (n-1)th columns, and so on. Figure 5 In the text, the closer the column is to the edge, the darker the color and the more obvious the black border.

[0050] To address the aforementioned problems, embodiments of the present invention provide an improved fingerprint sensing device, see below. Figure 7 and Figure 8 . Figure 7 A schematic structural diagram of a fingerprint sensing device according to an embodiment of the present invention is shown. Figure 8 The circuit diagram of the detection unit according to an embodiment of the present invention is shown. The detection unit 302 includes an amplifier circuit 320 and a sensing unit 306. The sensing unit 306 is coupled with a finger to form a detection capacitor Cs and coupled with the module ground of the fingerprint sensing device 20 to form a parasitic capacitor Cp. The detection unit 302 also includes a feedforward capacitor Cf coupled between the first input terminal and the output terminal of the amplifier circuit 310 and a switch S1.

[0051] The fingerprint sensing device 20 includes a sensor array 101, an amplifier circuit 320, a compensation capacitor Cc, a first signal providing circuit (not shown), and a second signal providing circuit 500.

[0052] The sensor array 101 includes a plurality of sensing units 306 arranged in an array, each sensing unit 306 being considered a pixel. A plurality of amplification circuits 320 are correspondingly coupled to the plurality of sensing units 306, and a compensation capacitor Cc is disposed, for example, in a plurality of sensing units 306 in a selected column of the sensor array 101. A first signal providing circuit provides an excitation signal Vtx to the amplification circuits 320, and a second signal providing circuit 500 includes a plurality of signal generating units 501 corresponding to the selected column, for providing a compensation voltage signal Vcx to the compensation capacitor Cc of the corresponding column.

[0053] Optionally, the fingerprint sensing device 20 further includes a sealing ring (not shown), which is coupled to a preset voltage, for example, to protect the sensor array 100 and prevent external electrical signals from adversely affecting the sensor array 100. In this embodiment, the sealing ring is disposed on the outer edge of the sensor array 101.

[0054] See Figure 8 The detection unit 302 also includes a switch S1, and the amplifier circuit 320 includes a first input terminal, a second input terminal, and an output terminal. For example, the amplifier circuit 320 can be a common differential amplifier. The first input terminal of the amplifier circuit 330 is a negative input terminal, and the second input terminal is a positive input terminal, or vice versa.

[0055] The positive input terminal of amplifier circuit 312 receives the excitation signal Vtx generated by the first signal providing circuit, the negative input terminal is coupled to the first terminal of detection capacitor Cs, and the output terminal generates a sensing signal Vout, which is used to indicate the detection capacitor Cs formed by the coupling between sensing unit 306 and the finger. The second terminal of detection capacitor Cs is grounded. The first terminal of feedforward capacitor Cf is coupled to the output terminal of amplifier circuit 320, and the second terminal is coupled to the negative input terminal of amplifier circuit 320. The first terminal of parasitic capacitor Cp is coupled to the second terminal of feedforward capacitor Cf, and the second terminal is grounded. The first terminal of switch S1 is coupled to the first terminal of feedforward capacitor Cf, and the second terminal is coupled to the second terminal of feedforward capacitor Cf.

[0056] The first terminal of the compensation capacitor Cc receives the compensation voltage signal Vcx, and the second terminal is coupled to the negative input terminal of the amplifier circuit 320. The compensation capacitor Cc generates a compensation signal based on the compensation voltage signal Vcx and provides it to the negative input terminal of the amplifier circuit 320. In this embodiment, the compensation voltage signal Vcx and the excitation signal Vtx have the same period and duty cycle, but their amplitudes can be the same or different.

[0057] Switch S1 is turned on or off according to a reset signal, such that when the excitation signal Vtx changes, the sensing signal Vout also changes, thereby converting the capacitance of the sensing capacitor Cs into an electrical signal. It is easy to see that the change in the sensing signal Vout...

[0058]

[0059] According to formula (2), we need to let Then it is necessary Simplification yields When the change in excitation signal Vtx ΔVtx, the feedforward capacitor Cf, and the compensation capacitor Cc are constant, there is a definite mapping relationship between the change in compensation voltage signal Vcx ΔVcx and the parasitic capacitance Cp. The signal generation unit 501 can generate the corresponding compensation voltage signal Vcx according to the capacitance value of the parasitic capacitance Cp in different columns of detection units 302, so as to ensure... This mechanism improves the phenomenon that excessive parasitic capacitance Cp leads to excessive deviation of the sensing signal Vout, weakens or eliminates the deviation of the sensing signal Vout caused by edge effects, and effectively improves the flatness of the fingerprint image.

[0060] In one feasible embodiment, the compensation voltage signal Vcx can be fixed, and the capacitance value of the compensation capacitor Cc can be adjusted to change the compensation signal. This can also improve the phenomenon that the excessive parasitic capacitance Cp causes the sensing signal Vout to deviate too much. It should be understood that, depending on the needs of the actual application scenario, both the compensation voltage signal Vcx and the compensation capacitor Cc can be adjusted simultaneously to change the compensation signal.

[0061] Optionally, the circuit structure diagram of the signal generation unit 501 is as follows: Figure 9a As shown, the system includes a digital-to-analog converter (DAC), switch S2, and switch S2b. The first terminal of switch S2 is coupled to the output of the DAC, and the second terminal provides a compensation voltage signal Vcx. Switch S2b is coupled between the second terminal of switch S2 and ground. The DAC provides a voltage Vc. Switches S2 and S2b are alternately turned on and off to generate a square wave signal with a high level of Vc and a low level of 0V, i.e., the compensation voltage signal Vcx. By adjusting the value of the voltage Vc output by the DAC, compensation voltage signals Vcx of different amplitudes can be obtained. In this embodiment, the compensation voltage signal Vcx and the excitation signal Vtx have the same period and duty cycle, but their amplitudes can be the same or different.

[0062] In one feasible embodiment, the compensation voltage signal Vcx can be fixed, and the compensation signal can be changed by adjusting the capacitance value of the compensation capacitor Cc. This can also improve the phenomenon that the excessively large capacitance value of the parasitic capacitor Cp causes the sensing signal Vout to deviate too much.

[0063] It should be understood that, depending on the needs of the actual application scenario, the compensation signal can also be changed by simultaneously adjusting the compensation voltage signal Vcx and the compensation capacitor Cc.

[0064] according to Figure 4Analysis shows that the parasitic capacitance Cp of the sensing unit closer to the edge is larger, that is, Cp1 > Cp2 > Cp3 >... Cpm < Cpm+1 < CpM+2 <... Cpn. Then, only by applying the corresponding compensation voltage signal Vcx such that Vcx1 > Vcx2 > Vcx3 >.. Vcxm < Vcxm+1 < Vcxm+2 <... Vcxn can the offset of the sensing signal Vout caused by the different capacitance values of the parasitic capacitance Cp be eliminated. Exemplarily, Figure 7 In it, Vcx1 > Vcx2 > Vcx3, and Vcxn is approximately equal to Vcx1.

[0065] Optionally, Figure 9b shows Figure 7 The circuit structure diagram of the signal generation unit in the second embodiment. The signal generation unit 502 includes an operational amplifier circuit OPA, an impedance network Z1, and an impedance Z2. The positive input terminal of the operational amplifier circuit OPA receives the excitation signal Vtx, the negative input terminal is coupled to the first end of the impedance network Z1, and the output terminal is used to provide the compensation voltage signal Vcx. The second end of the impedance network Z1 is grounded. The first end of the impedance network Z2 is coupled to the output terminal of the operational amplifier circuit OPA, and the second end is coupled to the first end of the impedance network Z1. By adjusting the parameters of the impedance network Z1 and the impedance network Z2, compensation voltage signals Vcx with different amplitudes can be obtained.

[0066] Figure 9a In the signal generation unit 501 shown, to ensure that the excitation signal Vtx and the compensation voltage signal Vcx have the same period and duty cycle, the on-time and off-time of the switches S2 and S2b need to be strictly controlled. However, the signal generation unit 502 of this embodiment uses the excitation signal Vtx as one of the inputs and can directly obtain the compensation voltage signal Vcx with the same period and duty cycle as the excitation signal Vtx. Only by adjusting the impedance Z1 network and the impedance network Z2 can compensation voltage signals Vcx with different amplitudes be obtained, and the circuit structure and operation logic are simpler.

[0067] Furthermore, Figure 10 shows the circuit schematic diagram of the detection unit according to the second embodiment of the present invention, Figure 11 shows Figure 10 the signal timing diagram of the detection unit in. As Figure 10 and Figure 11 shown, the detection unit 303 includes an amplifier circuit 330 and a sensing unit 306. The sensing unit 306 forms a detection capacitor Cs by coupling with a finger and forms a parasitic capacitance Cp by coupling with the module ground of the fingerprint sensing device 20. The detection unit 302 also includes a feedforward capacitor Cf, a switch S1, and a compensation circuit 510 coupled between the first input terminal and the output terminal of the amplifier circuit 310.

[0068] The amplifier circuit 330 includes a first input terminal, a second input terminal, and an output terminal. For example, the amplifier circuit 330 can be a common differential amplifier. The first input terminal of the amplifier circuit 330 is a negative input terminal, and the second input terminal is a positive input terminal, or vice versa.

[0069] The first input terminal of the amplifier circuit 330 is coupled to the first terminal of the detection capacitor Cs, and the second input terminal receives the excitation signal Vtx; the second terminal of the detection capacitor Cs is grounded. The feedforward capacitor Cf and the switch S1 are connected in parallel between the first input terminal and the output terminal of the amplifier circuit 330.

[0070] The compensation circuit 510 is coupled to the first input terminal of the amplifier circuit 330 and is used to provide charge to the detection capacitor Cs when the switch S1 is in the open state.

[0071] In this embodiment, the control period Tctr1 of the excitation signal Vtx includes a first time period Ts1 (i.e., the time interval T0 to T2) and a second time period Ts2 (i.e., the time interval T2 to T4). When the excitation signal Vtx undergoes a level flip within the control period Tctr1, the switch S1 transitions from the on state to the off state. At the end of the first time period Ts1 and the second time period Ts2, the switch S1 transitions from the off state to the on state.

[0072] Specifically, at time T1, the excitation signal Vtx flips from low level to high level, at which time the switch S1 changes from the on state to the off state.

[0073] At time T2, which is the end of the first time period Ts1, switch S1 switches from the open state to the on state.

[0074] At time T3, the excitation signal Vtx flips from high level to low level, and at this time, switch S1 changes from the on state to the off state.

[0075] At time T4, which is the end of the second time period Ts2, switch S1 switches from the open state to the on state.

[0076] In this embodiment, the compensation circuit 510 includes switches S4, S5, and S6, and a compensation capacitor Cc. The first terminal of the compensation capacitor Cc receives the compensation voltage signal Vcx, and its second terminal is coupled to the first terminal of switch S6. The second terminal of switch S6 is coupled to the first input terminal of the amplifier circuit 330. Switches S4 and S5 are connected in series between the first voltage Vdda and ground, and the intermediate node between switches S4 and S5 is coupled to the second terminal of the compensation capacitor Cc. The excitation signal Vcc is synchronized with the excitation signal Vtx, having the same period and duty cycle. The amplitudes of the excitation signal Vcc and the excitation signal Vtx may be the same or different.

[0077] In this embodiment, switches S1 and S6 are alternately turned on. When the excitation signal Vtx flips from low level to high level during the control cycle Tctr1, switch S4 changes from the on state to the off state. At the end of the control cycle Tctr1, switch S4 changes from the off state to the on state.

[0078] During the time interval T0 to T1, switches S1 and S4 are on, while switches S5 and S6 are off. The total charge on the capacitor...

[0079] Q1=(Vdda-0)*Cc

[0080] During the time period T1 to T2, switches S1, S4, and S5 are open, while switch S6 is closed, and the total charge on the capacitor...

[0081] Q2=(Vtx-0)*(Cs+Cp)+(Vtx-Vout2)*Cf

[0082] At time T1, the excitation signal Vtx flips from low to high, and the charge on the capacitor is redistributed. According to the principle of charge conservation, Q1 = Q2, therefore...

[0083]

[0084] During the time period from T2 to T3, switches S1 and S5 are on, and switches S5 and S6 are off. The total charge on the capacitor...

[0085] Q3=(Vtx-0)*(Cs+Cp)+(0-Vcx)*Cc

[0086] During the time interval T3 to T4, switches S1, S4, and S5 are open, while switch S6 is closed, and the total charge on the capacitor...

[0087] Q4=(0-Vout2)*Cf

[0088] At time T3, the excitation signal Vtx flips from high to low, and the charge on the capacitor is redistributed. According to the principle of charge conservation, Q3 = Q4, therefore...

[0089]

[0090] achievable Wherein, the detection capacitance Cs is, for example, equal to the sum of the background (base) capacitance Cs0 and the fingerprint ridge-valley difference capacitance ΔC, to make need Easy to obtain

[0091]

[0092] Similar to the detection unit 302, the compensation voltage signal Vcx changes according to the capacitance value of the parasitic capacitance Cp, thereby changing the compensation signal provided to the amplifier circuit 330, reducing or eliminating the offset of the sensing signal Vout caused by the edge effect, and effectively improving the flatness of the fingerprint image.

[0093] In one feasible embodiment, the compensation voltage signal Vcx can be fixed, and the capacitance value of the compensation capacitor Cc can be adjusted to change the compensation signal. This can also improve the phenomenon that the excessive parasitic capacitance Cp causes the sensing signal Vout to deviate too much. It should be understood that, depending on the needs of the actual application scenario, both the compensation voltage signal Vcx and the compensation capacitor Cc can be adjusted simultaneously to change the compensation signal.

[0094] In summary, the fingerprint sensing device provided by this invention addresses the problem of large parasitic capacitance in the edge column sensing units of the sensor array by employing a signal generation unit to generate a compensation voltage signal corresponding to the parasitic capacitance and / or adjusting the capacitance value of the compensation capacitor in the sensing unit. This generates a corresponding compensation signal and performs differentiated compensation for sensing units in different columns, thereby improving the phenomenon that excessively large capacitance value of the edge column parasitic capacitance leads to excessive sensing signal offset and improving the flatness of the acquired fingerprint image.

[0095] Optionally, the black borders of the sensor array are mainly caused by edge effects. The fingerprint images collected by the sensing units in the non-edge columns have good flatness. Therefore, in some application scenarios, differential compensation can be performed only on the edge columns of sensing units to reduce circuit complexity.

[0096] Optionally, the sensing units of the sensor array have a certain degree of symmetry, and the capacitance of their parasitic capacitance also has symmetry. The same signal generation unit can be selected to drive columns with the same or similar compensation voltage signals. For example, the leftmost column and the rightmost column use the same signal generation unit, thereby simplifying the circuit, reducing the chip area and production cost.

[0097] Furthermore, those skilled in the art will understand that the terms “during,” “when,” and “when…” used herein in relation to circuit operation are not strict terms indicating an action that occurs immediately upon the initiation of a startup action, but rather that there may be some small but reasonable delay or one or more delays, such as various propagation delays, between the startup action and the reaction action initiated by it. The terms “approximately” or “substantially” used herein mean that an element value is expected to be close to the declared value or position. However, as is well known in the art, there are always small deviations that make it difficult for the value or position to be strictly the declared value. It has been properly determined in the art that a deviation of at least ten percent (10%) (or at least twenty percent (20%) for semiconductor doping concentration) is a reasonable deviation from the described accurate ideal target. When used in conjunction with signal states, the actual voltage value or logic state of the signal (e.g., “1” or “0”) depends on whether positive or negative logic is used.

[0098] As described above, these embodiments of the present invention do not exhaustively describe all details, nor do they limit the invention to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. The scope of protection of this invention should be determined by the scope defined in the claims and their equivalents.

Claims

1. A fingerprint sensing device, comprising: A sensor array comprising multiple sensing units arranged in an array, wherein the sensing units are coupled to a finger to form a detection capacitance and coupled to the module to form a parasitic capacitance; A plurality of amplification circuits corresponding to the plurality of sensing units are used to provide a sensing signal indicating capacitive coupling between the sensing unit and the finger, and the amplification circuits are coupled to the detection capacitor and the parasitic capacitance; A first signal providing circuit is used to provide an excitation signal to the plurality of amplifier circuits; At least one compensation capacitor is arranged in a plurality of sensing units in a selected column of the array, the compensation capacitor being coupled to the amplification circuit, and the compensation capacitor being independent of the detection capacitor and the parasitic capacitance; as well as At least one compensation voltage signal, each of which is coupled to a corresponding compensation capacitor. Specifically, the capacitance value of the compensation capacitor and / or the voltage value of the compensation voltage signal are set according to the magnitude of the parasitic capacitance in each sensing unit of the selected column. The compensation voltage signal and the excitation signal have the same period and duty cycle.

2. The fingerprint sensing device according to claim 1, wherein, The selected column is the column near the edge of the sensor array.

3. The fingerprint sensing device according to claim 1, wherein, The compensation capacitors located in the same column of the at least one compensation capacitor receive the same compensation voltage signal.

4. The fingerprint sensing device according to claim 3, wherein, It also includes a second signal providing circuit, configured to provide the compensation voltage signal synchronously with the excitation signal.

5. The fingerprint sensing device according to claim 4, wherein, The second signal providing circuit includes a plurality of signal generating units, each of which is configured to provide the compensation voltage signal to the compensation capacitors in the corresponding column.

6. The fingerprint sensing device according to claim 5, wherein, The selected columns include a first column and a second column that are physically symmetrical in the sensor array, wherein the compensation voltage signal received by the compensation capacitor of the first column and the compensation voltage signal received by the compensation capacitor of the second column come from the same signal generation unit.

7. The fingerprint sensing device according to claim 5, wherein, The signal generation unit includes: A voltage generation circuit is configured to provide a first voltage; The second switch has a first terminal that receives the first voltage and a second terminal that provides the compensation voltage signal. The third switch is coupled between the second terminal of the second switch and ground; wherein... The second switch and the third switch are turned on alternately to generate a compensation voltage signal with a high level of the first voltage and a low level of 0V.

8. The fingerprint sensing device according to claim 7, wherein, The voltage generation circuit is selected from digital-to-analog converter circuits.

9. The fingerprint sensing device according to claim 5, wherein, The signal generation unit includes: An operational amplifier circuit, wherein the first input terminal of the operational amplifier circuit receives the excitation signal and the output terminal provides the compensation voltage signal; A first impedance network is coupled between the second input terminal of the operational amplifier circuit and ground; The second impedance network is connected in parallel between the second input terminal and the output terminal of the operational amplifier circuit.

10. The fingerprint sensing device according to claim 9, wherein, The amplitude of the compensation voltage signal is adjusted by changing the ratio of the first impedance network and / or the second impedance network.

11. The fingerprint sensing device according to claim 1, further comprising, between the compensation capacitor and the amplification circuit: The seventh switch has its first end coupled to the compensation capacitor and its second end coupled to the amplifier circuit. as well as A fifth switch and a sixth switch are connected in series between the first voltage and ground, and the intermediate node of the fifth switch and the sixth switch is coupled to the compensation capacitor.

12. An electronic device comprising a fingerprint sensing device as described in any one of claims 1 to 11.

13. The electronic device according to claim 12, further comprising: The power button is configured to control the electronic device or some functions of the electronic device to be turned on and / or off; wherein... The projection of the sensor array in the fingerprint sensing device onto the plane where the power button is located partially or completely overlaps with the power button.

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