TW201545072A - Fingerprint sensor - Google Patents

Abstract

When utilizing capacitor sensing effect to detect fingerprint ridges and valleys from tiny changed capacitances, a sensing circuit designed with high sensitivity is required. However, when a sensing circuit has higher sensitivity, the accompanying noises are greater. Such situation is getting worse for pressing type capacitive sensing arrays; wherein, sensing capacitive units and accompanying noises are varied by differences of positions in lines and rows. To improve such issue, the present invention provides not only a circuit arrangement/configuration to decrease possible noises, but also an offset cancellation circuit, having two different capacitors, to optimize noises of sensing capacitors. After signals of fingerprint ridges and valleys are optimized, said signals are arranged to pass an amplifier so as to enhance the magnitude of each of said signals. Hence, through said two capacitors of the offset cancellation circuit, the signal of each sensing electrode is optimized.

Description

Fingerprint sensor

The present invention relates to a fingerprint sensor, and more particularly to a fingerprint sensor having a reinforced design for a fingerprint image of a capacitive fingerprint sensing wafer.

Due to the capacitive fingerprint sensing technology, in addition to maintaining sufficient capacitance signals, it is also necessary to overcome the electrostatic damage when the finger is touched; therefore, on the one hand, in order to generate sufficient capacitance signals, it is necessary to consider when designing a capacitive sensing wafer. Using a sensing electrode with a higher capacitance value and a thin insulating capacitor sensing layer with a higher dielectric constant to avoid the occurrence or influence of other stray capacitance; on the other hand, in order to generate sufficient electrostatic protection, A thicker protective layer and other static elimination designs are required, such as a metal mesh for electrostatic protection. However, when the thickness of the protective layer is increased, the capacitance of the sensing electrode is reduced; therefore, how to optimize the improvement between the capacitive signal and the electrostatic protection becomes the main subject of the capacitive fingerprint sensor. One.

In addition, in order to improve the fingerprint recognition rate, the fingerprint sensing element also evolves from a finger linear sliding induction to a planar pressing induction. However, the planar push-type sensing must overcome the difference in position of the sensing pixels due to different positions, and have different stray capacitances and cause signal transmission differences to avoid gradation of the grayscale of the fingerprint image.

Furthermore, if capacitive sensing is to be used to sense the small capacitance change of the fingerprint peak and the fingerprint valley in the fingerprint, a highly sensitive sensing circuit must be designed. However, the higher the sensitivity of the sensing circuit, the more the accompanying noise increases. Especially for the push-type capacitive sensing array, the sensing capacitor unit and the accompanying noise will be in different rows and columns. The difference in location has changed.

In order to solve the above problems and improve the deficiencies of the prior art, one of the objects of the present invention is to provide a capacitance sensing device having an offset cancellation circuit and improving the parasitic capacitance of the sensing capacitance unit of each pixel through the offset cancellation circuit or The difference between fingers wet and dry, in order to obtain the best signal noise ratio and equal fingerprint grayscale image.

According to an embodiment of the present invention, a fingerprint sensor includes an offset cancellation circuit having an input end and an output end, and the output end is disposed corresponding to the input end, and includes: a first switch, a second switch, a third switch, a fourth switch, a first capacitor, a second capacitor, and a third capacitor. One end of the first switch is connected to the input end; one end of the second switch is connected to the other end of the first switch; one end of the first capacitor is connected to the other end of the first switch, and The second switch is connected in parallel, and one of the other ends is grounded; one end of the second capacitor is connected to the other end of the second switch, and one of the other ends is grounded; one end of the third capacitor and the first switch The other end is connected in parallel with the second switch, and one of the other ends is adjacent to the output end; one end of the third switch is connected between the other end of the third capacitor and the output end, and One of the other ends is grounded; one end of the fourth switch is connected to the end of the second capacitor, and one of the other ends is grounded.

Preferably, the fingerprint sensor further includes an inductive circuit having an inductive input end and an inductive output end, the inductive output end is disposed opposite the inductive input end, and the inductive output end is coupled to the input end And comprising: a first inductive switch, a second inductive switch, a reference capacitor, a stray capacitance, and a sensing electrode. One end of the first inductive switch is connected to the inductive input end; one end of the second inductive switch is connected to one end of the first inductive switch; one end of the reference capacitor is connected to the other end of the first inductive switch Connected and connected in parallel with the second inductive switch, and one of the other ends is grounded; one end of the stray capacitance is connected to one end of the second inductive switch, and one of the other ends is grounded; one end of the sensing electrode The other end of the second inductive switch is connected and connected in parallel with the stray capacitance, and one of the other ends can be regarded as a ground.

Preferably, the sensing circuit has a substrate, and the substrate has a plurality of floating electrodes between the sensing electrodes. The stray capacitance generated by the substrate can be shielded by the plurality of floating electrodes to avoid affecting the sensing capacitance formed by the sensing electrode and reduce the stray capacitance of the sensing circuit as a whole.

Preferably, the capacitance value of the first capacitor and the capacitance value of the second capacitor are adjustable. The ratio of the second capacitor to the first capacitor is adjusted to be equal to the ratio of the stray capacitance to the reference capacitor, so that the output voltage signal can cancel the voltage of the fingerprint valley and retain the signal of the fingerprint peak, thereby improving the fingerprint. The quality of sensing.

The purpose, technical contents, features, and effects achieved by the present invention will become more apparent from the detailed description of the appended claims.

Please refer to FIG. 1, which shows the component architecture of the fingerprint sensor 1 according to an embodiment of the present invention. The fingerprint sensor 1 includes an inductive insulating layer 10, a plurality of sensing electrodes 12, a row of multiplexers 14, a column of multiplexers 16, a controller 18, and an offset cancellation circuit 60. The plurality of sensing electrodes 12 are adjacent to the inductive insulating layer 10, and are electrically connected to the row multiplexer 14, the column multiplexer 16, and the offset eliminating circuit 60, and the row multiplexer 14 and the column multiplexer 16 are connected. It is electrically connected to the controller 18. In more detail, each of the sensing electrodes 12 is a pixel, and the plurality of sensing electrodes 12 form a specific pixel array, and the specific pixel array has a specific number of rows and a specific number of columns, and the row multiplexer 14 And the column multiplexer 16 outputs a signal of the plurality of sensing electrodes 12 in a specific order generated by the preset program to the offset canceling circuit 60 according to a preset program and the control of the controller 18. The offset cancellation circuit 60 filters out or reduces the influence of the stray/parasitic capacitance, thereby outputting a processed signal to the processor 100, and the processor 100 is configured to convert the processed signal to be available. The processor 100, other processors (not shown), or information that the user can interpret. Preferably, the offset cancellation circuit 60 is coupled to the processor 100 with a processing signal amplifier (not shown). Preferably, the offset cancellation circuit 60 is electrically connected to the row multiplexer 14 or the column multiplexer 16 to output the processed signal to the processor 100.

Referring to FIG. 2A, a circuit and a use state of the sensing electrode 12 according to an embodiment of the present invention are shown. One end of the inductive insulating layer 10 is provided with a sensing electrode 12, and one end of the inductive insulating layer 10 is contacted by at least one finger 1000 of a user. The sensing circuit 12 is connected to an inductive circuit 20. The sensing circuit 20 has an inductive input terminal 22 and an inductive output terminal 24, and includes a first inductive switch 30, a second inductive switch 32, a reference capacitor 40, and a stray. Capacitor 42; wherein the stray capacitance 42 is a capacitance generated by the sensing electrode 12 and an adjacent circuit (such as a transistor, a signal line or other electronic component, etc.), and the stray capacitance 42 can be represented as shown in FIG. 2A. When the finger 1000 of the user contacts the sensing insulating layer 10, a corresponding sensing capacitor 44 is formed between the sensing electrode 12 and the fingerprint peak 1000A of the finger 1000 and the fingerprint valley 1000B; that is, the sensing electrode 12 A fingerprint peak sensing capacitor 44A and a fingerprint valley sensing capacitor 44B are formed corresponding to a fingerprint peak 1000A and a fingerprint valley 1000B, respectively. In more detail, the inductive output terminal 24 is disposed opposite to the inductive input terminal 22; one end of the first inductive switch 30 is coupled to the inductive input terminal 22; and one end of the second inductive switch 32 is coupled to the other end of the first inductive switch 30; One end of the reference capacitor 40 is connected to the other end of the first inductive switch 30, and is connected in parallel with the second inductive switch 32, and one of the other ends is grounded; one end of the stray capacitance 42 and one of the second inductive switches 32 The other end is connected, and one of the other ends is grounded; one end of the sensing electrode 12 or the sensing capacitor 44 (44A, 44B) is connected to the other end of the second inductive switch 32, and is connected in parallel with the stray capacitance 42, and one of them The other end can be considered as ground. Preferably, the inductive output 24 of the inductive circuit 20 can be further coupled to an amplifier 50. Preferably, the amplifier 50 includes a current mirror (not shown) and a source follower (not shown). It should be noted that in one embodiment, the sensing electrode 12 is one of the main components of the sensing circuit 20; that is, the sensing circuit 20 includes the sensing electrode 12.

Preferably, referring further to FIG. 2B, an arrangement of the sensing electrode 12 and the reference capacitor 40 according to an embodiment of the present invention is shown. The components of each of the sensing electrodes 12 and their corresponding sensing circuits 20 are disposed between the row multiplexer 14 and the column multiplexer 16 (shown in FIG. 1) between the row scanning lines 140 and the column scanning lines 160. The first inductive switch 30, the second inductive switch 32, and the reference capacitor 40 are disposed on either side of the sensing electrode 12; that is, the first inductive switch 30, the second inductive switch 32, and the reference capacitor 40 The non-overlapping configuration between the sensing electrode 12 and the sensing electrode 12; and the non-overlapping configuration between the first inductive switch 30, the second inductive switch 32, and the reference capacitor 40 and the sensing electrode 12 can be avoided under the sensing electrode 12 There are other first inductive switches 30, second inductive switches 32, or reference capacitors 40 that may have a fixed voltage to avoid excessive noise capacitance. Preferably, as shown in FIG. 2C, the sensing circuit 20 has a substrate 26 with a plurality of floating electrodes 28 between the substrate 26 and the sensing electrodes 12 to shield the stray capacitance generated from the substrate 26 to avoid The sensing capacitor 44 formed by the sensing electrode 12 is affected, and the stray capacitance 42 of the entire sensing circuit 20 is reduced. Preferably, the floating electrode 28 is a metal electrode. Preferably, an insulating material 200 is disposed between the sensing electrode 12 and the substrate 26. Wherein, the reference capacitor 40 utilizes the characteristics of the gate thin oxide layer in the MOS (Metal Oxide Semiconductor) capacitor of the transistor, thereby reducing the area and volume of the reference capacitor 40, and simultaneously increasing the capacitance of the reference capacitor 40; The area and volume of the reference capacitor 40 are reduced, thereby increasing the area that the sensing electrode 12 can be distributed, and increasing the value of the sensing capacitance. With the above configuration, the capacitance values of the reference capacitor 40 and the sensing capacitor 44 can be increased, and the influence of the stray capacitance 42 on the overall sensing circuit 20 can be reduced.

Please refer to FIG. 3, which shows a circuit diagram of the sensing circuit 20 and the offset canceling circuit 60 of the fingerprint sensor according to an embodiment of the invention. Because of the influence of the stray capacitance 42, the sensing circuit 20 generates a considerable degree of offset signal after charge sharing, which affects the correctness and identification of the signal interpretation; therefore, in order to improve the problem of the offset signal, the present invention introduces An offset cancellation circuit 60 is coupled to the sense circuit 20. The offset cancellation circuit 60 has an input terminal 62 and an output terminal 64, and includes a first switch 70, a second switch 72, a third switch 74, a first capacitor 80, and a second capacitor 82. And a third capacitor 84. The output terminal 64 is disposed corresponding to the input terminal 62, and the sensing output terminal 24 of the sensing circuit 20 is connected to the input terminal 62 of the offset canceling circuit 60; one end of the first switch 70 is connected to the input terminal 62; and one end of the second switch 72 One end of the first switch 70 is connected to the other end of the first switch 70; one end of the first capacitor 80 is connected to the other end of the first switch 70, and is connected in parallel with the second switch 72, and one of the other ends is grounded; the second capacitor 82 One end is connected to one end of the second switch 72, and one of the other ends is grounded; one end of the third capacitor 84 is connected to the other end of the first switch 70, and is connected in parallel with the second switch 72, and one of them The other end is connected to the output end 64; one end of the third switch 74 is connected between the other end of the third capacitor 84 and the output end 64, and one of the third switches 74 is grounded at the other end; one end of the fourth switch 76 is connected The end of the second capacitor 82, and one of the other ends is grounded. Preferably, a circuit connection switch 90 is connected in series between the induction circuit 20 and the offset cancellation circuit 60; in more detail, the circuit connection switch 90 is connected between the inductive output terminal 24 and the input terminal 62. Preferably, the output 64 of the offset cancellation circuit 60 is electrically coupled to the processor 100. Preferably, a circuit output switch 92 is disposed between the offset cancellation circuit 60 and a processor 100. Preferably, the output 64 of the offset cancellation circuit 60 can be connected in series with an amplifier 52. Preferably, one end of the circuit output switch 92 is connected to the other end of the third capacitor 84 and the third switch 74, and one of the circuit output switches 92 is connected to the output end 64.

Through the configuration of the sensing circuit 20 and the offset canceling circuit 60 of the fingerprint sensor 1 of the present invention, the fingerprint sensor 1 of the present invention can be used to sense the fingerprint of a user, and the following steps 1 to 5 are described: Step 1 When the fingerprint is detected, that is, when a sensing capacitor 44 is formed between the user's finger and the sensing electrode 12, the sensing input terminal 22 inputs a first induced voltage, the first sensing switch 30 is turned on, and the second sensing switch 32 is turned on. The first switch 70 is disconnected, and the reference capacitor 40 has a first voltage difference V _O1 at both ends. The value of the first induced voltage is V _b , and the reference capacitor 40 has a capacitance value C _o , and the value of the first voltage difference V _O1 is substantially equal to the value of the first induced voltage. Step 2: When the reference capacitor 40 has a first voltage difference V _O1 at both ends, the first inductive switch 30 is turned off, the second inductive switch 32 is turned on, and the first switch 70 is turned off, thereby generating the first The charge sharing at one time causes the reference capacitor 40, the stray capacitance 42, and the sense capacitor 44 to have a second voltage difference V _O2 at both ends. The stray capacitance 42 has a capacitance value C _p , and the induction capacitor 44 has a capacitance value C _S , and the value of the second voltage difference V _O2 can be expressed as the following formula (1): V _O2 = V _b C _o / (C _o + C _p + C _S ) (1) Preferably, in step one or step two, the third switch 74 is preset to be turned on, so that there is no voltage difference across the third capacitor 84. Step 3: After the sensing circuit 20 has the second voltage difference V _O2 , the first sensing switch 30 is turned off, the second sensing switch 32 is turned on, the first switch 70 is turned on, and the second switch 72 is When the third switch 74 is turned off, the fourth switch 76 is turned on, and after the third capacitor 84 stores a certain amount of power, the third switch 74 and the fourth switch 76 that are preset to the on state are turned off. The conversion is turned off so that the sampling capacitor voltage difference is substantially equal to the value of the second voltage difference V _O2 . In more detail, because the third switch 74 is turned off, the third capacitor 84 having the specific power does not reproduce the charging or discharging effect, so that the sampling voltage difference between the two ends of the third capacitor 84 is maintained constant. A value that is equal to the value of the second voltage difference V _O2 . Step 4: When both ends of the third capacitor 84 have the sampling voltage difference, the first inductive switch 30 is turned on, the second inductive switch 32 is turned off, the first switch 70 is turned on, and the second switch 72 is turned on. The third switch 74 is disconnected, the fourth switch 76 is open, and the second input voltage is input to the sensing input terminal 22, so that the end of the third capacitor 84 generates a first voltage V _EA1 at one end. The value of the first voltage V _EA1 is substantially equal to the value of the second induced voltage; and the sampling voltage difference based on the two ends of the third capacitor 84 is maintained at the value of the second voltage difference V _O2 , and the third capacitor 84 The other end generates an _external first voltage V _EB1 . In an embodiment, if the value of the second induced voltage is equal to the value of the first induced voltage, the value of the other first voltage V _EB1 can be expressed by the following equation (2): V _EB1 = V _b (C _p + C _S ) / (C _o + C _p + C _S ) (2) From the equation (2), it should be noted that, in an ideal case, the value of the stray capacitance 42 C _p =0; When a fingerprint valley is sensed, an ideal state of the fingerprint peak signal V _IDEA-A and an ideal state of the fingerprint valley signal V _IDEA-B are obtained as shown in the following equations (2a) and (2b), respectively. _IDEA-A = V _b (C _SA ) / (C _o + C _SA ) (2a) V _IDEA-B = V _b (C _SB ) / (C _o + C _SB ) (2b) where, when ideally , valleys of the fingerprint due to a very small capacitance value C _SB 44B of the ideal state of the valleys of the fingerprint signal V _IDEA-B approaches zero, thus making the ideal fingerprint peak signal V _IDEA-a to the ideal state of valleys of the fingerprint signal V _{IDEA A} large ratio is generated between _-B , and the image of the fingerprint peak and the fingerprint valley can be easily recognized and clearly generated by the general signal processing. However, in practice, the value C _p of the stray capacitance 42 in the other first voltage V _EB1 of the fingerprint (2) as a fingerprint identification output signal cannot be omitted, so that the conventional fingerprint sensor measures The difference between the fingerprint peak signal and the fingerprint valley signal is not large enough, which results in poor recognition performance or poor image resolution and uneven gray scale after recognition. In view of this, the following step 5 of the present invention utilizes the configuration of each component in the offset cancellation circuit 60 to eliminate or reduce the influence of the stray capacitance 42 on the output signal, thereby improving the fingerprint sensor 1 of the present invention to correctly recognize the fingerprint. The signal of the peak and the fingerprint valley, and thereby produce a clear image. Step 5 After the second induced voltage is input, and the third capacitor 84 generates the first voltage V _EA1 and the other end voltage V _EB1 , the first switch 70 is disconnected to make the charge of the offset cancel circuit 60 Stored and retained in the first capacitor 80; wherein, if the first capacitor 80 has a capacitance value C _{S / H} , and if the value of the second induced voltage is equal to the value of the first induced voltage, the first capacitor 80 storage one charge Q _{S / HC} can be expressed as the following formula (3): Q _{S / HC} = C _{S / H} V _b (3) Next, the second switch 72 is turned on, thereby generating a second charge sharing such that the end of the third capacitor 84 generates a second voltage V _EA2 at one end; wherein, if the second capacitor 82 has a The capacitance value C _OS , the second voltage V _EA2 can be expressed as the following equation (4): V _EA2 = V _b (C _{S / H} ) / (C _{S / H} + C _OS ) (4) and based on the third capacitor 84 The sampling voltage difference between the two ends is still maintained as the value of the second voltage difference V _O2 , and the other end of the third capacitor 84 generates a second voltage V _EB2 which can be expressed by the following equation (5): V _EB2 = V _b ( C _p +C _S )/(C _o +C _p +C _S )-V _b C _OS /(C _S/H +C _OS ) (5) where the second voltage V _EB2 at the other end of equation (5) is a stray capacitance elimination equation with respect to the other end of the second voltage V _EB1 of equation (2) .

In an embodiment, the second voltage V _EB2 obtained according to the foregoing step 5 is a bias cancellation voltage or the so-called processed signal, and the processed signal can be transmitted to a processor 100. Alternatively, in another embodiment, the processed signal is optionally transmitted to the processor 100 via an amplifier 52 or a signal converter (not shown).

In more detail, when a sensing electrode 12 is a fingerprint peak 1000A, the value of the corresponding fingerprint peak sensing capacitor 44A is C _SA , which corresponds to one of the fingerprint voltage peaks generated by the second voltage V _EB2 . The value of the voltage-eliminating output voltage V _A can be expressed by the following equation (6): V _A = V _b {[(C _SA +C _P )/(C _o +C _p +C _SA )]-[C _OS /(C _S/H +C _OS )]} (6) When a sensing electrode 12 is a fingerprint valley 1000B, the value of the corresponding fingerprint valley sensing capacitor 44B is C _SB , which corresponds to the other second voltage V _{EB2 .} The value of one of the generated fingerprint valley bias elimination output voltages V _B can be expressed by the following equation (7): V _B = V _b {[(C _SB + C _P ) / (C _o + C _p + C _SB )] -[C _OS /(C _S/H +C _OS )]} (7) where, since the value C _SB of the fingerprint valley sensing capacitor 44B is much smaller than the value of the reference capacitor 40 C _o and the value of the stray capacitance 42 C _p Therefore, equation (7) can omit the value C _{SB of the} fingerprint valley sensing capacitor 44B and simplify the following equation (8): V _B V _b {[C _p /(C _o +C _p )]-[C _OS /(C _S/H +C _OS )]} (8) wherein, in an embodiment, the second capacitor 82 is designed and first the ratio of the capacitance 80 C _{OS /} C _S / _H 42 is substantially equal to the stray capacitance and the reference capacitance ratio C _p / C _o 40, the offset canceling the valleys of the fingerprint of the output voltage V _B of the zero bias fingerprint peaks Eliminating the value of the output voltage V _A can be expressed as the following equation (9): V _A = (V _b C _o C _SA )/[(C _o +C _p +C _SA )(C _o +C _p )] = (V _b C _SA )/[(C _o +C _p +C _SA )(1+C _p /C _o )] (9)

Preferably, the values of the first capacitor 80 and the second capacitor 82 are adjustable, and thereby can be set according to the difference between the different reference capacitors 40 and the stray capacitances 42 of the sensing electrodes 12 at different positions. Adjusting the corresponding first capacitor 80 and the second capacitor 82 to increase the ratio of the fingerprint peak offset canceling output voltage V _A to the fingerprint valley offset canceling output voltage V _B , in particular, causing the fingerprint valley offset to eliminate the output voltage V _B It is equal to zero or close to zero, so that the difference between the fingerprint peak and the sensing signal of the fingerprint valley is more obvious and a clearer image is produced. In an embodiment, the first capacitor 80 and the second capacitor 82 respectively have at least two different size capacitance values, thereby adjusting the ratio of the value of the first capacitor 80 to the value of the stray capacitance 42 and adjusting the second capacitor 82. The ratio of the value to the value of the reference capacitor 40 is such that the value of the fingerprint valley bias cancellation output voltage V _B is equal to zero, approaches zero, or the bias voltage of the opposite fingerprint peak eliminates the output voltage V _A which is negligible in signal processing. Or clearly identified to achieve the optimization of the fingerprint sensing signal. Preferably, in an embodiment, the first capacitor 80 and the second capacitor 82 respectively have at least three different size capacitance values.

It is noted that, in order to achieve a ratio of the second capacitor 82 and the capacitor 80 of the first C _{OS /} C _S / _H ratio is substantially equal to the stray capacitance C _p / C _o 42 and 40 of the reference capacitance can be used in the manufacturing process through Corresponding type of capacitor. For example, if the reference capacitor 40 and the stray capacitance 42 are respectively a transistor capacitor and an electrode plate capacitor, a transistor capacitor and an electrode plate capacitor can be respectively used as the second capacitor 82 and the first capacitor. 80. Thereby, the offset of each capacitor in the process can be simulated, and the offset can be corrected by the offset cancel circuit 60. However, it should be noted that the second capacitor 80 is not limited to the transistor type capacitor, and the second capacitor 80 may be other types of capacitors, such as a polysilicon capacitor (PIP Capacitor) or a metal-insulated metal capacitor (MIM Capacitor). And the second capacitor 80 is not limited to the types of capacitors exemplified above.

Preferably, referring to FIG. 2B, each row or column of the specific pixel array is configured with a corresponding offset cancellation circuit 60 for adjusting the first capacitor 80 and the second for each individual electrical characteristic of each row or column. The capacitor 82, in turn, improves the identification accuracy and image sharpness of the fingerprint sensor. Preferably, each of the specific pixels is configured with a corresponding offset cancellation circuit 60.

It should be noted that the term "substantially equal" as used in the above description covers the range of errors that may occur due to actual operation or signal measurement of circuit-related components, and the term "equal" as recited in the claims of the present invention. It should be defined and understood to include a reasonable margin of error. Preferably, the reasonable error range is within ±20%.

The embodiments described above are only intended to illustrate the technical idea and the features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the contents of the present invention and to implement the present invention. That is, the equivalent variations or modifications made by the spirit of the present invention should still be included in the scope of the present invention.

1‧‧‧Finger sensor
10‧‧‧Induction insulation
12‧‧‧Induction electrodes
14‧‧‧ multiplexer
16‧‧‧ column multiplexer
18‧‧‧ Controller
20‧‧‧Induction circuit
22‧‧‧Induction input
24‧‧‧inductive output
30‧‧‧First sensor switch
32‧‧‧Second sensor switch
40‧‧‧ reference capacitor
42‧‧‧Stray capacitance
44‧‧‧Inductive Capacitance
44A‧‧‧Finger peak induction capacitance
44B‧‧‧Finger Valley Sensing Capacitance
50‧‧‧Amplifier
52‧‧‧Amplifier
60‧‧‧Offset elimination circuit
62‧‧‧ input
64‧‧‧output
70‧‧‧First switch
72‧‧‧second switch
74‧‧‧ Third switch
76‧‧‧fourth switch
80‧‧‧first capacitor
82‧‧‧second capacitor
84‧‧‧ third capacitor
90‧‧‧Circuit connection switch
92‧‧‧Circuit output switch
100‧‧‧ processor
140‧‧‧ scan lines
160‧‧‧ column scan line
1000‧‧‧ fingers
1000A‧‧‧Fingerprint Peak
1000B‧‧‧Fingerprint Valley

1 is a schematic view showing a fingerprint sensor according to an embodiment of the present invention. 2A is a schematic view showing a sensing electrode and a use state of a fingerprint sensor according to an embodiment of the present invention. 2B is a schematic view showing the arrangement of the sensing electrodes and the reference capacitors of the fingerprint sensor according to an embodiment of the invention. 2C is a schematic diagram showing a plurality of floating electrodes between a substrate and a sensing electrode of a fingerprint sensor according to an embodiment of the invention. 3 is a schematic diagram showing an inductive circuit and an offset canceling circuit of a fingerprint sensor according to an embodiment of the present invention.

20‧‧‧Induction circuit

22‧‧‧Induction input

24‧‧‧inductive output

30‧‧‧First sensor switch

32‧‧‧Second sensor switch

40‧‧‧ reference capacitor

42‧‧‧Stray capacitance

44‧‧‧Inductive Capacitance

50‧‧‧Amplifier

52‧‧‧Amplifier

60‧‧‧Offset elimination circuit

62‧‧‧ input

64‧‧‧output

70‧‧‧First switch

72‧‧‧second switch

74‧‧‧ Third switch

76‧‧‧fourth switch

80‧‧‧first capacitor

82‧‧‧second capacitor

84‧‧‧ third capacitor

90‧‧‧Circuit connection switch

92‧‧‧Circuit output switch

100‧‧‧ processor

Claims (10)

A fingerprint sensor includes: an offset cancellation circuit having an input end and an output end, wherein the output end is disposed corresponding to the input end, and includes: a first switch, one end of which is connected to the input end a second switch, one end of which is connected to the other end of the first switch; a first capacitor, one end of which is connected to the other end of the first switch, and is connected in parallel with the second switch, and One of the other ends is grounded; a second capacitor has one end connected to the other end of the second switch, and one of the other ends is grounded; a third capacitor, one of the ends and the first switch The end is connected and connected in parallel with the second switch, and one of the other ends is connected to the output end; a third switch, one end of which is connected between the other end of the third capacitor and the output end, third One of the switches is grounded at the other end; and a fourth switch has one end connected to the end of the second capacitor, and one of the other ends is grounded. The fingerprint sensor of claim 1, further comprising: a sensing circuit having an inductive input end and an inductive output end, wherein the inductive output end is disposed opposite the inductive input end, and the inductive output end is coupled to the The input end is connected in series, and comprises: a first inductive switch, one end of which is connected to the inductive input terminal; and a second inductive switch, one of the ends of which is connected to one end of the first inductive switch; a reference capacitor, One end is connected to the other end of the first inductive switch, and is connected in parallel with the second inductive switch, and one of the other ends is grounded; a stray capacitance, one end of which is connected to one end of the second inductive switch And one of the other ends is grounded; and a sensing electrode, one end of which is connected to the other end of the second inductive switch, and is connected in parallel with the stray capacitance, and one of the other ends is grounded. The fingerprint sensor of claim 2, further comprising an inductive insulating layer, a row of multiplexers, a column of multiplexers, and a controller; the plurality of sensing electrodes are adjacent to the inductive insulating layer, and the plurality of The sensing electrode is electrically connected to the row multiplexer and the column multiplexer, and the row multiplexer and the column multiplexer are electrically connected to the controller. The fingerprint sensor of claim 2, wherein the sensing circuit has a substrate, and the substrate has a plurality of floating electrodes between the sensing electrodes. The fingerprint sensor of claim 2, wherein when the sensing electrode forms a sensing capacitor, the sensing input terminal inputs a first induced voltage, and the first sensing relationship is turned on, and the second sensing is turned on. The relationship is disconnected, the first open relationship is open, and the reference capacitor has a first voltage difference at both ends; when the reference voltage has the first voltage difference across the reference capacitor, the first inductive relationship is off. The second inductive relationship is turned on, the first open relationship is off, the reference capacitor, the stray capacitance, and the sensing capacitor have a second voltage difference at both ends; when the sensing circuit has the second After the voltage difference, the first inductive open relationship is off, the second inductive open relationship is on, the first open relationship is on, the second open relationship is off, and the third open relationship is on. The fourth open relationship is turned on, and after the third capacitor stores a specific power, the third and fourth switches that are preset to be in an on state are turned into off, so that the third capacitor is The terminal has a sampling voltage difference, and the sampling voltage difference is equal to the second voltage difference a value; when the two ends of the third capacitor have the sampling voltage difference, the first inductive open relationship is on, the second inductive open relationship is off, the first open relationship is on, and the second The open relationship is disconnected, the third open relationship is open, the fourth open relationship is open, and the second input voltage is input to the sensing input end, so that the end of the third capacitor generates a first voltage at one end, The third capacitor generates an other terminal first voltage; when the third capacitor generates the first voltage of the terminal and the other terminal voltage, the first open relationship is disconnected, so that the offset cancellation circuit The charge is stored in the first capacitor; the second switch is turned on, the end of the third capacitor generates a second voltage at one end, and the other end of the third capacitor generates a second voltage at the other end. The fingerprint sensor of claim 5, wherein the value of the first induced voltage is V _b , the value of the second induced voltage is equal to the value of the first induced voltage, and the reference capacitor has a capacitance value C _o , the stray capacitance has a capacitance value C _p , the induction capacitance has a capacitance value C _S , the first capacitance has a capacitance value C _S/H , and the second capacitance has a capacitance value C _OS , the other The value of the second voltage of the terminal is V _b (C _p + C _S ) / (C _o + C _p + C _S ) - V _b C _OS /(C _S/H +C _OS ). The fingerprint sensor according to any one of the preceding claims, wherein the sensing capacitor and the second capacitor are formed by a transistor capacitor, and the stray capacitance and the first capacitor are It is formed by an electrode plate capacitor. The fingerprint sensor of any one of claims 1 to 6, wherein the capacitance value of the first capacitor and the capacitance value of the second capacitor are adjustable. The fingerprint sensor of claim 7, wherein the sensing capacitor and the second capacitor are formed by a transistor capacitor, and the stray capacitance and the first capacitor are formed by an electrode plate capacitor. The fingerprint sensor of any one of claims 2 to 6, wherein a ratio of the second capacitance to the first capacitance is equal to a ratio of the stray capacitance to the reference capacitance.