CN114882541A

CN114882541A - Fingerprint sensing device and electronic equipment

Info

Publication number: CN114882541A
Application number: CN202210548036.8A
Authority: CN
Inventors: 李伟江; 杨俊�; 陈飞祥; 桑田
Original assignee: Chipone Technology Beijing Co Ltd
Current assignee: Chipone Technology Beijing Co Ltd
Priority date: 2022-05-18
Filing date: 2022-05-18
Publication date: 2022-08-09

Abstract

The invention discloses a fingerprint sensing device and an electronic device, wherein the fingerprint sensing device comprises: a sensor array including a plurality of sensing units arranged in an array; a plurality of amplifying circuits coupled to the plurality of sensing units, respectively, for providing sensing signals indicative of capacitive coupling between the sensing units and a finger; a first signal providing circuit for providing a stimulus signal to the plurality of amplifying circuits; at least one compensation capacitance arranged in a plurality of sense cells of a selected column in the array; and at least one compensation voltage signal, wherein each compensation voltage signal is coupled with a corresponding compensation capacitor, the capacitance value of the corresponding compensation capacitor and/or the voltage value of the compensation voltage signal are/is set according to the size of the parasitic capacitor in each sensing unit of the selected column, so that differential compensation can be performed on the sensing units of different columns in the sensor array, and the phenomenon of overlarge offset of edge column sensing signals in the fingerprint sensing device is improved.

Description

Fingerprint sensing device and electronic equipment

Technical Field

The present invention relates to the field of fingerprint identification technologies, and in particular, to a fingerprint sensing device and an electronic device.

Background

The principle of the capacitive fingerprint collection technology is that the sizes of capacitances between valleys and ridges of a fingerprint and a sensing unit are different, and capacitance values are converted into electrical signals (voltage, current, and the like) through an amplifying circuit coupled to the sensing unit, so as to detect fingerprint characteristics.

When electronic equipment such as a mobile phone and the like pursues a full-face screen, a capacitive fingerprint sensing device cannot support fingerprint identification under the screen due to limited penetration capacity, and a solution of back fingerprints and side fingerprints is mostly adopted. Wherein, the side fingerprint can with the power key sharing position, experience better relatively, therefore the popularization degree is higher.

However, capacitive fingerprint sensing devices suffer from edge effects, and sensing cells located at the edge regions of the sensor array have larger parasitic capacitances, resulting in sensing signals generated by them being also larger relative to the middle region. When a finger presses on the sensor array, the edge area is more likely to saturate, causing image distortion. At present, two main solutions are provided, one is to ensure that all sensing signals are not saturated, and then the sensing signals are repaired through an algorithm or software, so that the time required by fingerprint detection and fingerprint identification is increased, and the dynamic range of the fingerprint detection is reduced and the signal-to-noise ratio is reduced. The second is to use the sensing units in the edge row as dummy sensing units (dummy), and to use the sensing signals generated by the dummy sensing units and the corresponding amplifying circuits as invalid signals to process, so as to ensure sufficient dynamic range. However, as ultra-thin mobile phones are gradually popularized, the limitation on the width of a fingerprint module is more and more severe, the width of an aa (active area) area, i.e., an identification area, has been reduced from 3mm to 1.5mm or even lower, and the solution of adopting a pseudo sensing unit results in a significant reduction in the number of sensing units which can be actually used, which adversely affects the accuracy and speed of fingerprint detection and fingerprint identification.

Accordingly, an improved fingerprint sensing device and electronic device are desired, which can solve the above problems.

Disclosure of Invention

In view of the foregoing problems, an object of the present invention is to provide a fingerprint sensing device and an electronic apparatus, which can compensate for differences between sensing units in different rows in a sensor array, so as to improve the phenomenon of excessive deviation of sensing signals in edge rows.

According to an aspect of the present application, there is provided a fingerprint sensing device comprising: a sensor array including a plurality of sensing units arranged in an array; a plurality of amplifying circuits coupled to the plurality of sensing units, respectively, for providing sensing signals indicative of capacitive coupling between the sensing units and a finger; a first signal providing circuit for providing a stimulus signal to the plurality of amplifying circuits; at least one compensation capacitance arranged in a plurality of sense cells of a selected column in the array; and at least one compensation voltage signal, each of the compensation voltage signals coupled to a respective compensation capacitor.

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

Optionally, the selected column is a column of the sensor array near an edge.

Optionally, the compensation voltage signals received by the compensation capacitors located in the same column in the at least one compensation capacitor are the same.

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

Optionally, the second signal providing circuit comprises a plurality of signal generating units, each configured to provide the compensation voltage signal to the compensation capacitance of the corresponding column.

Optionally, the selected columns include a first column and a second column that are physically symmetric 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 are from the same signal generation unit.

Optionally, the signal generating unit includes: a voltage generation circuit configured to provide a first voltage; a second switch, a first end receiving the first voltage, a second end providing the compensation voltage signal; a third switch coupled between a second terminal of the second switch and ground; 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.

Optionally, the voltage generating circuit is selected from digital-to-analog conversion circuits.

Optionally, the signal generating unit includes: the first input end of the operational amplification circuit receives the excitation signal, and the output end of the operational amplification circuit provides the compensation voltage signal; a first impedance network coupled between the second input terminal of the operational amplification circuit and ground; a second impedance network coupled in parallel between a second input terminal and an output terminal of the operational amplification circuit.

Optionally, a ratio of the first impedance network and/or the second impedance network is changed to adjust the amplitude of the compensation voltage signal.

Optionally, between the compensation capacitor and the amplifying circuit, the method further includes: a seventh switch, a first terminal of which is coupled to the compensation capacitor, and a second terminal of which is coupled to the amplifying circuit; and a fifth switch and a sixth switch sequentially coupled in series between the first voltage and ground, an intermediate node of the fifth switch and the sixth switch being coupled to the compensation capacitor.

According to another aspect of the application, there is provided an electronic device comprising a fingerprint sensing apparatus as described in any of the above.

Optionally, the electronic device further comprises: a power key configured to control turning on and/or off of functions of the electronic device or a part of the electronic device; and the projection of the sensor array in the fingerprint sensing device on the plane where the power key is located is partially or completely coincided with the power key.

In the fingerprint sensing device provided by the invention, the compensation voltage signal and/or the compensation capacitor correspond to the capacitance value of the parasitic capacitor in the sensing unit, so that the compensation signal provided to the amplifying circuit is changed, the deviation of the sensing signal caused by the overlarge capacitance value of the parasitic capacitor is weakened or eliminated, and the flatness of the fingerprint image is effectively improved.

Optionally, for the problem that the parasitic capacitance of the sensing unit in the edge row in the sensor array is large, a scheme that the signal generation unit generates a compensation voltage signal corresponding to the parasitic capacitance and/or adjusts a capacitance value of the compensation capacitance in the sensing unit is adopted, so that a corresponding compensation signal can be generated, and differential compensation is performed on the sensing units in different rows, so that the phenomenon that the sensing signal is shifted too much due to the fact that the capacitance value of the parasitic capacitance in the edge row is too large is improved, and the flatness of the acquired fingerprint image is improved.

Optionally, the black edge of the sensor array is mainly caused by the edge effect, and the fingerprint image acquired by the sensing units in the non-edge rows has better flatness, so that in some application scenarios, only the edge rows can be compensated differentially, and the circuit complexity is reduced.

Optionally, the sensing units of the sensor array have certain symmetry, the capacitance values of the parasitic capacitances thereof also have symmetry, and the same signal generation unit can be selected to drive the columns with the same or similar compensation voltage signals, for example, the leftmost column and the rightmost column adopt the same signal generation unit, thereby simplifying the circuit, and reducing the chip area and the production cost.

Drawings

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

fig. 1 shows a schematic structural diagram of an electronic device;

FIG. 2 shows a schematic block diagram of a sensor array of the fingerprint sensing device of FIG. 1;

FIG. 3 shows a circuit schematic of a prior art detection cell;

FIG. 4 shows a schematic diagram of a finger press sensor array;

FIG. 5 shows a schematic black-edge view of a prior art sensor array;

FIG. 6 is a graph illustrating the column mean versus column number for the sensor array of FIG. 5;

figure 7 shows a schematic block diagram of a fingerprint sensing device according to an embodiment of the present invention;

FIG. 8 shows a circuit schematic of a detection cell of an embodiment of the invention;

fig. 9a shows a circuit configuration diagram of the signal generating unit of the first embodiment in fig. 7;

fig. 9b shows a circuit configuration diagram of the signal generating unit of the second embodiment in fig. 7;

fig. 10 shows a circuit configuration diagram of a detection unit according to another embodiment of the present invention;

fig. 11 shows a signal timing diagram of the detection unit in fig. 10.

Detailed Description

Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In the various figures, the same elements or modules are denoted by the same or similar reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale.

It should be understood that in the following description, "circuitry" may comprise singly or in combination hardware circuitry, programmable circuitry, state machine circuitry, and/or elements capable of storing instructions executed by programmable circuitry. When an element or circuit is referred to as being "coupled" to another element or circuit is "coupled" between two nodes, it may be directly coupled or coupled to the other element or intervening elements may be present, and the coupling between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly coupled" to another element, it is intended that there are no intervening elements present.

Also, certain terms are used throughout the description and claims to refer to particular components. As one of ordinary skill in the art will appreciate, manufacturers may refer to a component by different names. This patent specification and claims do not intend to distinguish between components that differ in name but not function.

Moreover, it is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Fig. 1 shows a schematic structural view of an electronic device comprising a screen 10 and a fingerprint sensing arrangement 20, the fingerprint sensing arrangement 20 being used, for example, for unlocking the electronic device and/or for performing an authorization or the like on the electronic device when performing a transaction. The electronic device may be a portable electronic device such as a mobile phone or a tablet computer, and the fingerprint sensing device 20 may be disposed at a side of the electronic device and share a common location with the power key.

FIG. 2 shows a schematic block diagram of a sensor array of the fingerprint sensing device of FIG. 1. The sensor array 100 includes a plurality of sensing cells 300 arranged in an array, and a seal ring (sealing) 400, and each sensing cell 300 may be regarded as one pixel. The seal ring 400 is coupled to a predetermined voltage, for example, for protecting the sensor array 100 and preventing the sensor array 100 from being adversely affected by external electrical signals. In the present embodiment, the sealing ring 400 is disposed outside the edges of the plurality of sensing cells 300, and it should be understood that the sealing ring 400 may also be disposed below the plurality of sensing cells 300.

Fig. 3 shows a circuit schematic of a prior art detection unit. The detecting unit 301 comprises an amplifying circuit 310 and a sensing unit 300, wherein the sensing unit 300 is coupled to the finger to form a detecting capacitor Cs, and is coupled to the module ground of the fingerprint sensing device 20 to form a parasitic capacitor Cp. The detection unit 301 further comprises a feed forward capacitor Cf coupled between the first input terminal and the output terminal of the amplification circuit 310.

The amplifying circuit 310 has a positive input terminal receiving the driving signal Vtx generated by the first signal providing circuit, a negative input terminal coupled to the parasitic capacitor Cp and a first terminal of the detecting capacitor Cs, and an output terminal generating the sensing signal Vout. The second terminals of the parasitic capacitor Cp and the sensing capacitor Cs are grounded. Easy availability, sensing the variation of signal Vout

Referring to fig. 4, fig. 4 shows a schematic structural diagram of a finger pressing sensor array, and with reference to fig. 2 and fig. 3, further description is made on image distortion occurring when a fingerprint is captured by the fingerprint sensing device 20 in the prior art. Fig. 4 shows a cross-sectional view of a finger 901 and the sensor array 100, the sensing unit 300 is further selected from a sampling pad, for example, and when the finger 901 presses the sensor array 100, the valleys or ridges of the fingerprint are coupled with the sensing unit 300 to form the sensing capacitances Cs1 to Csn. Each sensing cell 300 is coupled to the ground to form parasitic capacitances Cp 1-Cpn, wherein the parasitic capacitances Cp are larger as the sensing cell 300 is closer to the sensor array 100 due to the edge effect, i.e. the sensing cell 300 is located in the column, i.e. the parasitic capacitances Cp are larger

Cp1>Cp2>Cp 3>...Cpm<Cpm+1<CpM+2<...Cpn

Where Cpm is the parasitic capacitance of the sensing unit closest to the center column, Cpn is the parasitic capacitance of the sensing unit of the rightmost column, and when the variation Δ Vtx of the stimulus signal Vtx, the detection capacitance Cs, and the feed-forward capacitance Cf are fixed, the larger the parasitic capacitance Cp is, the larger the variation Δ Vout of the sense signal Vout is, which is equivalent to superimposing an offset (offset) on Δ Vout, and the signal amount thereof becomes larger, thereby causing the edge of the fingerprint image to be blackened, commonly referred to as a black edge, as shown in fig. 5. FIG. 5 shows a schematic black-edged diagram of a prior art sensor array, in order from left to right, of a first column, a second column, a third column … …, a n-2 th column, a n-1 th column, and an nth column. Further, referring to fig. 6, fig. 6 shows a column mean value and column number correspondence diagram of the sensor array in fig. 5, it can be seen that the column mean shift of the sensor array 100 is larger closer to the edge, that is, the column mean shift of the first column and the nth column is the largest, the column of the second column and the nth-1 is the second, and so on, the column corresponding to fig. 5 is darker in color and more obvious in black edge.

In order to solve the above problems, embodiments of the present invention provide an improved fingerprint sensing device, see fig. 7 and 8. Fig. 7 shows a schematic block diagram of a fingerprint sensing device according to an embodiment of the present invention, and fig. 8 shows a schematic circuit diagram of a detection unit according to an embodiment of the present invention. The detecting unit 302 includes an amplifying circuit 320 and a sensing unit 306, wherein the sensing unit 306 is coupled to the finger to form a detecting capacitor Cs, and is coupled to the module ground of the fingerprint sensing device 20 to form a parasitic capacitor Cp. The detection unit 302 further includes a feed-forward capacitor Cf coupled between the first input terminal and the output terminal of the amplification circuit 310, and a switch S1.

The fingerprint sensing device 20 comprises a sensor array 101, an amplifying circuit 320, a compensation capacitance Cc, a first signal providing circuit (not shown) and a second signal providing circuit 500.

The sensor array 101 includes a plurality of sensing units 306 arranged in an array, and each sensing unit 306 may be regarded as one pixel. The amplifying circuits 320 are correspondingly coupled to the sensing units 306, and the compensation capacitor Cc is disposed in the sensing units 306 of a selected row in the sensor array 101, for example. The first signal supply circuit supplies the excitation signal Vtx to the amplification circuit 320, and the second signal supply circuit 500 includes a plurality of signal generating units 501 corresponding to selected columns for supplying the compensation voltage signal Vcx to the compensation capacitors Cc of the corresponding columns.

Optionally, the fingerprint sensing device 20 further comprises a sealing ring (not shown), for example coupled to a preset voltage, for protecting the sensor array 100 and preventing the sensor array 100 from being adversely affected by external electrical signals. In this embodiment, the seal ring is disposed outside the edge of the sensor array 101.

Referring to fig. 8, the detection unit 302 further includes a switch S1, and the amplifying circuit 320 includes a first input terminal, a second input terminal, and an output terminal. For example, the amplifying circuit 320 may be a general 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.

The amplifying circuit 312 has a positive input terminal receiving the stimulus signal Vtx generated by the first signal providing circuit, a negative input terminal coupled to a first terminal of the detecting capacitor Cs, an output terminal generating a sensing signal Vout for indicating the detecting capacitor Cs formed by the coupling between the sensing unit 306 and the finger, and a second terminal of the detecting capacitor Cs connected to ground. The feed forward capacitor Cf has a first terminal coupled to the output terminal of the amplifier circuit 320 and a second terminal coupled to the negative input terminal of the amplifier circuit 320. The parasitic capacitor Cp has a first terminal coupled to the second terminal of the feedforward capacitor Cf, and a second terminal grounded. The switch S1 has a first terminal coupled to the first terminal of the feedforward capacitor Cf and a second terminal coupled to the second terminal of the feedforward capacitor Cf.

The compensation capacitor Cc has a first terminal receiving the compensation voltage signal Vcx and a second terminal coupled to the negative input terminal of the amplifying circuit 320. The compensation capacitor Cc generates a compensation signal according to the compensation voltage signal Vcx, which has the same period and duty cycle as the excitation signal Vtx and has the same or different amplitude, and provides the compensation signal to the negative input terminal of the amplifying circuit 320.

The switch S1 is turned on or off according to a reset signal, for example, so that when the stimulus signal Vtx changes, the sensing signal Vout also changes to convert the capacitance of the sensing capacitor Cs into an electrical signal. Easy availability, sensing the variation of signal Vout

According to the formula (2), the order is

Then it is necessary to

Simple and available

When activatingWhen the variation Δ Vtx of the excitation signal Vtx, the feed-forward capacitor Cf, and the compensation capacitor Cc are fixed, a certain mapping relationship exists between the variation Δ Vcx of the compensation voltage signal Vcx and the parasitic capacitor Cp, and the signal generating unit 501 may generate the corresponding compensation voltage signal Vcx according to the capacitance values of the parasitic capacitors Cp in the detecting units 302 in different rows, so as to ensure that the parasitic capacitors Cp in different rows are in parallel with each other

Therefore, the phenomenon that the offset of the sensing signal Vout is overlarge due to overlarge capacitance value of the parasitic capacitance Cp is improved, the offset of the sensing signal Vout caused by the edge effect is weakened or eliminated, and the flatness of the fingerprint image is effectively improved.

In a possible embodiment, the compensation voltage signal Vcx can be fixed, and the capacitance of the compensation capacitor Cc can be adjusted to change the compensation signal, which can also improve the phenomenon that the sensing signal Vout is shifted too much due to the capacitance of the parasitic capacitor Cp being too large. It should be understood that the compensation voltage signal Vcx and the compensation capacitor Cc may be adjusted simultaneously to change the compensation signal according to the requirements of the practical application scenario.

Alternatively, the circuit structure of the signal generating unit 501 is shown in fig. 9a, and includes a digital-to-analog converter DAC, a switch S2, and a switch S2 b. The switch S2 has a first terminal coupled to the output terminal of the DAC and a second terminal for providing the compensation voltage signal Vcx. The switch S2b is coupled between the second terminal of the switch S2 and ground. The digital-to-analog converter DAC is used for providing a voltage Vc, and the switch S2 and the switch S2b are alternately turned on and off to generate a square wave signal with Vc at a high level and 0V at a low level, i.e., a compensation voltage signal Vcx. By adjusting the value of the voltage Vc output by the digital-to-analog converter DAC, compensation voltage signals Vcx with 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, and may have the same or different amplitudes.

In a possible embodiment, the compensation voltage signal Vcx can be fixed, and the capacitance of the compensation capacitor Cc can be adjusted to change the compensation signal, so as to also improve the phenomenon that the sensing signal Vout is shifted too much due to the capacitance of the parasitic capacitor Cp being too large.

It should be understood that the compensation voltage signal Vcx and the compensation capacitor Cc may be adjusted simultaneously to change the compensation signal according to the requirements of the practical application scenario.

From the analysis of fig. 4, it can be seen that the sensing unit parasitic capacitance Cp closer to the edge is larger, i.e. Cp1> Cp2> Cp 3>. Cpm < Cpm +1< Cpm + 2.. Cpn, only the corresponding compensation voltage signal Vcx needs to be applied, so that Vcx1> Vcx2> Vcx 3>. Vcx m < Vcx m +1< Vcx m + 2.. Vcx n can be eliminated, and the offset of the sensing signal Vout caused by the different capacitance values of the parasitic capacitance Cp can be eliminated. Illustratively, in FIG. 7, Vcx1> Vcx2> Vcx 3, Vcxn is approximately equal to Vcx 1.

Alternatively, fig. 9b shows a circuit configuration diagram of the signal generating unit of the second embodiment in fig. 7. The signal generation unit 502 includes an operational amplification circuit OPA, an impedance network Z1, and an impedance Z2. The operational amplifier circuit OPA has a positive input receiving the driving signal Vtx, a negative input coupled to a first end of the impedance network Z1, an output for providing the compensation voltage signal Vcx, and a second end grounded to the impedance network Z1. The impedance network Z2 has a first terminal coupled to the output terminal of the OPA and a second terminal coupled to the first terminal 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.

In the signal generating unit 501 shown in fig. 9a, in order to ensure that the excitation signal Vtx and the compensation voltage signal Vcx have the same period and duty ratio, the on-time and the off-time of the switch S2 and the switch S2b need to be strictly controlled, but the signal generating unit 502 of this embodiment uses the excitation signal Vtx as one of the inputs, so as to directly obtain the compensation voltage signal Vcx having the same period and duty ratio as the excitation signal Vtx, and obtain the compensation voltage signals Vcx with different amplitudes by only adjusting the impedance Z1 network and the impedance Z2, so that the circuit structure and the operating logic are simpler.

Further, fig. 10 shows a schematic circuit diagram of a detection unit according to a second embodiment of the present invention, and fig. 11 shows a timing diagram of signals of the detection unit in fig. 10. As shown in fig. 10 and 11, the detecting unit 303 includes an amplifying circuit 330 and a sensing unit 306, the sensing unit 306 is coupled with the finger to form a detecting capacitor Cs, and is coupled with the module ground of the fingerprint sensing device 20 to form a parasitic capacitor Cp. The detection unit 302 further includes a feed-forward capacitor Cf coupled between the first input terminal and the output terminal of the amplification circuit 310, a switch S1, and a compensation circuit 510.

The amplifying circuit 330 includes a first input terminal, a second input terminal, and an output terminal. For example, the amplifying circuit 330 may be a general 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.

The amplifying circuit 330 has a first input terminal coupled to the first terminal of the detecting capacitor Cs, and a second input terminal receiving the driving signal Vtx; the second terminal of the detection capacitor Cs is grounded. The feed-forward capacitor Cf and the switch S1 are coupled in parallel between the first input terminal and the output terminal of the amplifying circuit 330.

The compensation circuit 510 is coupled to the first input terminal of the amplifying circuit 330, and is used for providing the charge to the detection capacitor Cs when the switch S1 is in the open state.

In the present embodiment, the control period Tctr1 of the stimulus signal Vtx includes a first time period Ts1 (i.e., T0-T2 time periods) and a second time period Ts2 (i.e., T2-T4 time periods). When the excitation signal Vtx is level-inverted in the control period TCtr1, the switch S1 is switched from the on state to the off state. The switch S1 transitions from the off state to the on state at the end of the first time period Ts1 and the second time period Ts2 by the actuation signal Vtx.

Specifically, at time T1, the excitation signal Vtx flips from low to high, at which time the switch S1 transitions from an on state to an off state.

At time T2, i.e., the end of the first time period Ts1, the switch S1 transitions from the off state to the on state.

At time T3, the excitation signal Vtx transitions from a high level to a low level, at which time the switch S1 transitions from an on state to an off state.

At time T4, which is the end of the second time period Ts2, the switch S1 transitions from the off state to the on state.

In the present embodiment, the compensation circuit 510 includes a switch S4, a switch S5, a switch S6, and a compensation capacitor Cc. The first terminal of the compensation capacitor Cc receives the compensation voltage signal Vcx, the second terminal is coupled to the first terminal of the switch S6, and the second terminal of the switch S6 is coupled to the first input terminal of the amplifying circuit 330. The switch S4 and the switch S5 are sequentially coupled in series between the first voltage Vdda and ground, and the intermediate node of the switches S4 and S5 is coupled to the second terminal of the compensation capacitor Cc. The stimulus signal Vcc is synchronized with the stimulus signal Vtx, and has the same period and duty ratio. The stimulus signal Vcc may be the same or different in magnitude from the stimulus signal Vtx.

In the present embodiment, the switch S1 and the switch S6 are alternately turned on. When the excitation signal Vtx is inverted from the low level to the high level in the control period Tctr1, the switch S4 is switched from the on state to the off state, and at the end of the control period Tctr1, the switch S4 is switched from the off state to the on state.

In the time period from T0 to T1, the switches S1 and S4 are turned on, the switches S5 and S6 are turned off, and the total charge on the capacitor

Q1＝(Vdda-0)*Cc

During the time period T1 to T2, the switch S1, the switch S4 and the switch S5 are turned off, the switch S6 is turned on, and the total charge on the capacitor

Q2＝(Vtx-0)*(Cs+Cp)+(Vtx-Vout2)*Cf

At time T1, the driving signal Vtx is inverted from low to high, the charge on the capacitor is redistributed, and Q1 is Q2 according to the principle of charge conservation

In the time period from T2 to T3, the switches S1 and S5 are turned on, the switches S5 and S6 are turned off, and the total charge on the capacitor

Q3＝(Vtx-0)*(Cs+Cp)+(0-Vcx)*Cc

In the time period from T3 to T4, the switch S1, the switch S4 and the switch S5 are turned off, the switch S6 is turned on, and the total charge on the capacitor

Q4＝(0-Vout2)*Cf

At time T3, the excitation signal Vtx is inverted from high to low, the charge on the capacitor is redistributed, and Q3 is equal to Q4 according to the principle of charge conservation, so that the voltage of the capacitor is increased

Can obtain the product

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 Δ C, such that

Need to make sure that

Is easy to obtain

Similar to the detecting unit 302, the compensation voltage signal Vcx varies according to the capacitance of the parasitic capacitor Cp, so as to vary the compensation signal provided to the amplifying circuit 330, reduce or eliminate the offset of the sensing signal Vout caused by the edge effect, and effectively improve the flatness of the fingerprint image.

In summary, in the fingerprint sensing device provided by the present invention, for the problem that the parasitic capacitance of the edge row sensing unit in the sensor array is large, the scheme that the signal generating unit generates the compensation voltage signal corresponding to the parasitic capacitance and/or adjusts the capacitance value of the compensation capacitance in the sensing unit is adopted, so that the corresponding compensation signal can be generated, and differential compensation is performed on the sensing units in different rows, thereby improving the phenomenon that the capacitance value of the edge row parasitic capacitance is too large to cause too large sensing signal offset, and improving the flatness of the acquired fingerprint image.

Optionally, the black edge of the sensor array is mainly caused by the edge effect, and the fingerprint image acquired by the sensing units in the non-edge rows has better flatness, so that in some application scenarios, only the sensing units in the edge rows can be compensated differentially, and the circuit complexity is reduced.

Optionally, the sensing units of the sensor array have a certain symmetry, the capacitance values of the parasitic capacitances thereof also have symmetry, and the same signal generation unit can be selected to drive the columns with the same or similar compensation voltage signals, for example, the left-most column and the right-most column adopt the same signal generation unit, thereby simplifying the circuit, and reducing the chip area and the production cost.

Furthermore, those of ordinary skill in the art will appreciate that the words "during", "when" and "when … …" as used herein in relation to the operation of a circuit are not strict terms referring to actions occurring immediately upon initiation of a startup action, but rather there may be some small but reasonable delay or delays, such as various transmission delays, between them and the reactive action (action) initiated by the startup action. The words "about" or "substantially" are used herein to mean that the value of an element (element) has a parameter that is expected to be close to the stated value or position. However, as is well known in the art, there is always a slight deviation that makes it difficult for the value or position to be exactly the stated value. It has been well established in the art that a deviation of at least ten percent (10%) for a semiconductor doping concentration of at least twenty percent (20%) is a reasonable deviation from the exact ideal target described. When used in conjunction with a signal state, the actual voltage value or logic state (e.g., "1" or "0") of the signal depends on whether positive or negative logic is used.

In accordance with the present invention, as set forth above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The scope of the invention should be determined with reference to the appended claims and their equivalents.

Claims

1. A fingerprint sensing device comprising:

a sensor array including a plurality of sensing units arranged in an array;

a plurality of amplifying circuits coupled to the plurality of sensing units, respectively, for providing sensing signals indicative of capacitive coupling between the sensing units and a finger;

a first signal supply circuit for supplying a stimulus signal to the plurality of amplification circuits;

at least one compensation capacitance arranged in a plurality of sense cells of a selected column in the array; and

at least one compensation voltage signal, each of the compensation voltage signals coupled to a respective compensation capacitor.

2. The fingerprint sensing device according to claim 1, wherein a capacitance value of said compensation capacitance and/or a voltage value of said compensation voltage signal corresponding is set in dependence of a size of a parasitic capacitance in each sensing cell of said selected column.

3. The fingerprint sensing device according to claim 1, wherein said selected column is a column of said sensor array near an edge.

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

5. The fingerprint sensing device according to claim 4, further comprising a second signal providing circuit configured to provide said compensation voltage signal synchronously with said excitation signal.

6. The fingerprint sensing device according to claim 5, wherein said second signal providing circuit comprises a plurality of signal generating units, each signal generating unit being configured to provide said compensation voltage signal to a compensation capacitance of a corresponding column.

7. The fingerprint sensing device according to claim 6, wherein said selected columns comprise a first column and a second column that are physically symmetric in said sensor array, wherein a compensation voltage signal received by a compensation capacitance of said first column and a compensation voltage signal received by a compensation capacitance of said second column are from the same signal generation unit.

8. The fingerprint sensing device according to claim 6, wherein said signal generation unit comprises:

a voltage generation circuit configured to provide a first voltage;

a second switch, a first end receiving the first voltage, a second end providing the compensation voltage signal;

a third switch coupled between a 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.

9. The fingerprint sensing device according to claim 8, wherein said voltage generation circuit is selected from digital to analog conversion circuits.

10. The fingerprint sensing device according to claim 6, wherein said signal generation unit comprises:

the first input end of the operational amplification circuit receives the excitation signal, and the output end of the operational amplification circuit provides the compensation voltage signal;

a first impedance network coupled between the second input terminal of the operational amplification circuit and ground;

a second impedance network coupled in parallel between a second input terminal and an output terminal of the operational amplification circuit.

11. The fingerprint sensing device according to claim 10, wherein the ratio of said first impedance network and/or said second impedance network is varied to adjust the amplitude of said compensation voltage signal.

12. The fingerprint sensing device according to claim 1, between said compensation capacitance and said amplification circuit, further comprising:

a seventh switch, a first terminal of which is coupled to the compensation capacitor, and a second terminal of which is coupled to the amplifying circuit; and

and the middle node of the fifth switch and the sixth switch is coupled to the compensation capacitor.

13. An electronic device comprising the fingerprint sensing device according to any one of claims 1 to 12.

14. The electronic device of claim 13, further comprising:

a power key configured to control turning on and/or off of functions of the electronic device or a part of the electronic device; wherein,

the projection of the sensor array in the fingerprint sensing device on the plane where the power key is located is partially or completely coincided with the power key.