Fingerprint sensor and method of fingerprint recognition

Abstract

A fingerprint sensor and a fingerprint recognition method are disclosed. The fingerprint recognition method includes: performing a first scan using the fingerprint sensor to obtain an initial scan image; identifying an initial fingerprint image in the initial scan image; setting a local scanning area based on reference points in the initial fingerprint image; performing a second scan on the local scanning area using the fingerprint sensor to obtain a local fingerprint image; and converting the local fingerprint image into a detection physiological signal to obtain a detection result.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a technology for recognizing a fingerprint, and in particular, to a fingerprint sensor and a fingerprint recognition method. BACKGROUND

[0002] With the development of technology, "information security" has become an important consideration for consumers when using electronic devices. Therefore, many electronic devices are designed with a user authentication mechanism to control data access. Among various authentication mechanisms, "fingerprint recognition" is the most common, because "fingerprint recognition" is easy to integrate into electronic devices, and is based on biometric recognition, which has high security.

[0003] However, in recent years, some people still try to crack the fingerprint recognition technology by using "fake fingerprints" (such as optical paper printed with special fingerprints), so the recognition ability of the fingerprint recognition technology must be improved to meet the market's requirements for information security. SUMMARY

[0004] The present disclosure relates to a fingerprint recognition method, comprising: performing a first scan by a fingerprint sensor to obtain an initial scan image; identifying an initial fingerprint image in the initial scan image; setting a local scan area according to a reference point in the initial fingerprint image; performing a second scan by the fingerprint sensor on the local scan area to obtain a local fingerprint image; and converting the local fingerprint image into a detection physiological signal to obtain a detection result.

[0005] The present disclosure also relates to a fingerprint sensor, comprising a sensing circuit and a processing circuit. The sensing circuit comprises a plurality of sensing units, wherein the sensing units are used to form an initial sensing area. The processing circuit is coupled to the sensing circuit and is used to control the sensing circuit to perform a first scan on the initial sensing area to obtain an initial scan image, wherein the initial scan image comprises an initial fingerprint image. The processing circuit is also used to set a local scan area according to a reference point in the initial fingerprint image, and to control the sensing circuit to perform a second scan on the local scan area to obtain a local fingerprint image. The processing circuit is also used to convert the local fingerprint image into a detection physiological signal to obtain a detection result.

[0006] By performing a local scan on the fingerprint image and converting it into a physiological signal for judgment, the processing speed and recognition accuracy of the fingerprint sensor can be effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1A A schematic diagram of a fingerprint sensor according to some embodiments of the present disclosure is shown.

[0008] Figure 1AA partial schematic diagram of a sensing unit according to some embodiments of the present disclosure.

[0009] Figure 2A An image diagram acquired by a fingerprint sensor according to some embodiments of the present disclosure for scanning an initial sensing area.

[0010] Figure 2A An enlarged schematic diagram of an initial fingerprint image according to some embodiments of the present disclosure.

[0011] Figures 3A-3D A schematic diagram of a manner of setting a reference point PR according to some embodiments of the present disclosure.

[0012] Figure 4 A flowchart of a fingerprint recognition method according to some embodiments of the present disclosure.

[0013] Figure 5A A signal diagram of performing a first scan according to some embodiments of the present disclosure.

[0014] Figure 5B A signal diagram of performing a second scan according to some embodiments of the present disclosure.

[0015] Figure 5C A signal diagram of performing a plurality of second scans in succession according to some embodiments of the present disclosure.

[0016] Figure 6 A schematic diagram of a manner of generating a physiological signal according to some embodiments of the present disclosure.

[0017] Figure 7 A signal diagram of simultaneously detecting a plurality of fingerprints according to some embodiments of the present disclosure.

[0018] Figure 8 A physiological signal diagram of simultaneously detecting a plurality of fingerprints according to some embodiments of the present disclosure.

[0019] BRIEF DESCRIPTION OF DRAWINGS

[0020] 100: fingerprint sensor

[0021] 110: sensing circuit

[0022] 111: sensing unit

[0023] 120: processing circuit

[0024] 130: scanning circuit

[0025] 140: reading circuit

[0026] 141: integrator

[0027] 142: analog-to-digital converter

[0028] Tc: heart rhythm cycle

[0029] GL: scan line

[0030] RL: read line

[0031] F: finger

[0032] W1: on switch

[0033] C1: capacitor

[0034] D1: light sensing element

[0035] SR: detection signal

[0036] stv: start signal

[0037] ckv: scan signal

[0038] oe: enable signal

[0039] Sp: physiological signal detected

[0040] SA-SC: physiological signal detected

[0041] P10: initial scan image

[0042] P11-P13: initial fingerprint image

[0043] PR: reference point

[0044] R10-R30: local scan area

[0045] Y1-Y3: scan height

[0046] P11A: initial sub-area

[0047] P11B: fingerprint vector

[0048] IM1-IMN: local fingerprint image

[0049] F10: scan cycle

[0050] F20: scan cycle

[0051] F21: local detection period

[0052] F71-F72: scan cycle

[0053] T11-T13: detection period

[0054] T21-T23: detection period

[0055] T50: Distribution Time

[0056] S401-S409: Steps Detailed Implementation

[0057] Several embodiments of the present invention will be disclosed below with reference to the accompanying drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and elements will be shown in the drawings in a simple schematic manner.

[0058] In this document, when an element is referred to as a “connection” or “coupled,” it may mean an “electrical connection” or “electrical coupling.” “Connection” or “coupled” can also be used to indicate the operation or interaction between two or more elements. Furthermore, although terms such as “first,” “second,” etc., are used herein to describe different elements, these terms are merely used to distinguish elements or operations described using the same technical terminology. Unless the context clearly indicates otherwise, these terms do not specifically refer to or imply any order or sequence, nor are they intended to limit the invention.

[0059] Figure 1A The diagram shows a fingerprint sensor 100 according to a partial embodiment of the present disclosure. The fingerprint sensor 100 includes a sensing circuit 110 and a processing circuit 120. The sensing circuit 110 includes a plurality of sensing units 111, which are used to form an initial sensing area. In one embodiment, the sensing circuit 110 may be a fingerprint sensing panel, and may be integrated into a display panel or disposed in one area of ​​the display panel (e.g., the sensing units 111 are respectively placed above or below thin-film transistors corresponding to the display panel). When a user touches the fingerprint sensor 100 with their finger F, the sensing circuit 110 uses the principle of optical reflection to project a light signal and receive the reflected signal. Based on the pulse waveform in the reflected signal, a corresponding fingerprint image can be converted. Since those skilled in the art will understand the technology and principles of acquiring fingerprint images using optical technology, further details are omitted here.

[0060] The processing circuit 120 is coupled to the sensing circuit 110 via the scanning circuit 130 and the reading circuit 140 to control the sensing circuit 110 to scan the initial sensing area. Specifically, the processing circuit 120 generates a start signal stv, a scan signal ckv, and an enable signal oe to sequentially drive multiple scan lines GL (e.g., ...) through the scanning circuit 130. Figure 1A (From top to bottom) At the same time, multiple reading lines RL are sequentially turned on by the reading circuit 140 to read the detection signal transmitted from each sensing unit 111.

[0061] Figure 1B Fig. 1 1 shows a partial schematic diagram of a sensing unit 1 1 1 according to some embodiments of the present disclosure. In one embodiment, the sensing unit 1 1 1 comprises a capacitor C1 and a light sensing element D1 (e.g., a photodiode). When the sensing unit 1 1 1 is in sensing, the processing circuit 120 turns on the switch W1 through the corresponding scan line GL. At this time, the light sensing element D1 of the sensing unit 1 1 1 is turned on by the light signal, and a current is generated according to the voltage Vb1 and the electric energy in the capacitor C1. The reading circuit 140 receives the current through the integrator 141. The integrator 141 receives the signal from the reading line RL and outputs a detection signal SR according to the voltage Vb2 and through the analog-to-digital converter 142. The processing circuit 120 can convert the detection signal SR into a corresponding fingerprint image according to the detection signal SR.

[0062] Figure 2A Fig. 12 shows a schematic diagram of an image acquired by the fingerprint sensor 100 for scanning an initial sensing area according to some embodiments of the present disclosure. In one embodiment, the processing circuit 120 first performs a "first scan" on the initial sensing area to obtain an initial scan image P10 corresponding to the entire initial sensing area. The initial scan image P10 comprises at least one initial fingerprint image. In Figure 1A In the embodiment shown, since the user simultaneously contacts the fingerprint sensor 100 with three fingers, the initial scan image P10 will comprise three initial fingerprint images P1 1 -P13. The processing circuit 120 can determine the initial fingerprint images P1 1 -P13 included in the initial scan image P10 through image recognition technology. For example, the processing circuit 120 can determine the regions in the initial scan image P10 that are similar to fingerprints, or determine the regions in the initial scan image P10 that have a gray scale value lower than or higher than a preset value (e.g., white represents no object contact), to identify the initial fingerprint images P1 1 -P13.

[0063] The processing circuit 120 can further analyze and process each initial fingerprint image to determine whether the initial fingerprint image is generated by a real finger or belongs to a fake fingerprint. Figure 2B Fig. 13 shows a zoomed-in schematic diagram of the initial fingerprint image P1 1 according to some embodiments of the present disclosure. The processing circuit 120 can obtain a reference point PR for each initial fingerprint image. The reference point PR can be the center point of the initial fingerprint image P1 1, or the region with the highest density in the initial fingerprint image P1 1. The manner of setting the reference point PR will be described in subsequent paragraphs.

[0064] As mentioned above, the processing circuit 120 sets a local scanning area R10 for the corresponding initial fingerprint image P11 according to the reference point PR. The processing circuit 120 controls the sensing circuit 110 to perform one or more "second scans" on the local scanning area R10 to obtain one or more local fingerprint images.

[0065] In an embodiment, the aforementioned "local scanning area R10" is a region centered at the reference point PR and has an area smaller than the initial sensing area. In an embodiment, the processing circuit 120 sets a scanning height Y1 according to the reference point PR along a first direction (e.g., the vertical direction as shown) of the fingerprint sensor 100 to form the local scanning area R10, where the first direction is the same as the arrangement direction of the plurality of scanning lines. Similarly, the processing circuit 120 can set scanning heights Y2 and Y3 for the initial fingerprint images P12 and P13, respectively, to form local scanning areas R20 and R30. Figure 2A

[0066] In an embodiment, the aforementioned "second scan" is more accurate than the "first scan". In other words, the first scanning frequency (update rate) of the first scan is lower than the second scanning frequency of the second scan.

[0067] By performing local scanning on the initial fingerprint image P11, the fingerprint sensor 100 can save scanning time. In an embodiment, since the local scanning area R10 is the center position of the initial fingerprint image P11, a higher accuracy scan is performed on this position, and the fingerprint image can be more accurately identified as being generated by a real finger.

[0068] In addition, after obtaining the local fingerprint images for each of the initial fingerprint images P11-P13, the processing circuit 120 further converts each local fingerprint image into a detection physiological signal to determine the authenticity of the fingerprint and generate a detection result. If the detection physiological signal is within a standard signal range pre-stored in the processing circuit 120, it means that the initial fingerprint image is generated by a real finger. If the detection physiological signal is not within the standard signal range, it means that the initial fingerprint image can be a fake fingerprint. The detection physiological signal can be a heartbeat, a heart rate value / period, or a pulse value. For example, if the detected heart rate value is between 1 and 1.6, it is normal and the corresponding initial fingerprint image can continue to the subsequent identity recognition procedure. Conversely, if the detected heart rate value is 0.2 or 5, since this data does not match the physiological characteristics of a normal person, it can be considered as a fake fingerprint. The manner of converting the local fingerprint image into a detection physiological signal will be described in subsequent paragraphs.

[0069] ​As mentioned above, the fingerprint sensor 100 of the present disclosure can be applied to detect a single fingerprint, or to detect multiple fingerprints simultaneously. For example, if a user places multiple fingers on the initial detection area at the same time, the sensing circuit 110 sets a corresponding reference point for each initial fingerprint image P11-P13, and performs a second scan respectively.

[0070] The following describes a way of setting the reference point PR in some embodiments of the present disclosure. Referring to FIGS. 3A-3D, the processing circuit 120 first divides the initial fingerprint image P11 into multiple initial sub-areas P11A, for example, divides the initial fingerprint image P11 into multiple rectangular areas with the same area as the initial sub-areas P11A. As shown, each initial sub-area P11A records one or more fingerprint segments. These fingerprint segments can be converted into multiple fingerprint vectors P11B through image recognition technology. The processing circuit 120 can set the reference point PR by comparing the distribution differences of the fingerprint vectors P11B in each initial sub-area P11A.

[0071] In an embodiment, the reference point PR is the center of the fingerprint. As shown, since the fingerprint vectors present a distribution similar to a vortex shape, the fingerprint vectors at the center of the fingerprint present an elliptical distribution. That is, the slopes of each fingerprint segment near the center are different. Therefore, the processing circuit 120 can first identify the fingerprint vectors P11B in the same initial sub-area P11A, and calculate the slopes of all the fingerprint vectors P11B. According to the slope differences of the fingerprint vectors P11B in each initial sub-area P11A (for example, the more similar the slopes of all the fingerprint vectors P11B in the initial sub-area P11A, the smaller the difference), the processing circuit 120 selects the initial sub-area P11A with the largest slope difference as the reference point PR.

[0072] Figure 4 FIG. 4 shows a flowchart of a fingerprint recognition method according to some embodiments of the present disclosure. Referring to FIG. 4, in step S401, the processing circuit 120 controls the sensing circuit 110 to perform a first scan on the initial detection area to obtain an initial scan image P10. Figures 1A-4 In step S401, the processing circuit 120 controls the sensing circuit 110 to perform a first scan on the initial detection area to obtain an initial scan image P10.

[0073] Figure 5A FIG. 5 shows a signal schematic diagram of performing the first scan in some embodiments of the present disclosure. The processing circuit 120 provides a start signal stv to the scanning circuit 130 to start scanning in a scanning period F10. The scanning circuit 130 drives the sensing unit 111 to perform detection according to the scanning signal ckv and the enable signal oe to generate a detection signal SR (for example, a voltage signal) as shown in FIG. 5. Figure 1BThe current value of the illustrated embodiment). In an embodiment, the resolution of the fingerprint sensor 100 is 1500, i.e. has 1500 scan lines, when both the scan signal ckv and the enable signal oe are at the enabled level, i.e. the corresponding sensing unit 111 is detected.

[0074] In step S402, the processing circuit 120 identifies at least one initial fingerprint image P11-P13 in the initial scan image P10. In an embodiment, the sensing circuit 110 divides the image area that meets the "fingerprint" characteristics using image recognition technology, and marks as the initial fingerprint image P11-P13.

[0075] In step S403, the processing circuit 120 obtains the reference point PR of the initial fingerprint image P11-P13. As described above, the reference point PR can be the center point of the initial fingerprint image P11-P13, or the area with the highest fingerprint density in the initial fingerprint image P11-P13, or obtained by analyzing the fingerprint vector.

[0076] In step S404, the processing circuit 120 sets the local scan area R10-R30 according to the obtained reference point PR, respectively. As described above, in an embodiment, the processing circuit 120 sets the scan height Y1-Y3 (i.e. the number of scan lines GL) with the reference point PR as the center to define the local scan area R10-R30.

[0077] In step S405, the processing circuit 120 performs at least one second scan on the local scan area R10-R30 to obtain the local fingerprint image, respectively. Figure 5B The signal diagram shown is the second scan performed in some embodiments of the present disclosure. The processing circuit 120 provides the start signal stv, the scan signal ckv and the enable signal oe to the scanning circuit 130 to start scanning in the scan period F20, which is less than the scan period F10. Among them, the enable signal oe will only be triggered when the "scan line GL corresponding to the local scan area R10 / R20 / R30" is driven (i.e. the local detection period F21, corresponding to the scan height Y1 / Y2 / Y3) to Figure 2A For example, when the scanning circuit 130 scans to the scan line of the scan height Y1, the enable signal oe is triggered to enable the reading circuit 140 to generate the detection signal SR.

[0078] In some embodiments, the second scan can be a "continuous collection". In other words, the sensing circuit 110 will perform multiple second scans on the local scan area R10-R30 at multiple detection time points to obtain multiple local fingerprint images. For example, Figure 2A For example, the processing circuit 120 will obtain multiple local fingerprint images corresponding to the same local scan area R10.

[0079] Figure 5C The diagram shown illustrates the signals from multiple consecutive second scans performed in some embodiments of this disclosure. Figure 5C The waveform in the figure omits the signal waveform when the sensing circuit does not acquire the scanned image (i.e., the scanning time corresponding to areas other than the local scan area R10 to R30). Figure 5C In this process, the processing circuit 120 controls the sensing circuit 110 to perform multiple second scans on the same local scanning area R10 to sequentially acquire multiple local fingerprint images IM1 to IMN. In some embodiments, the distribution time T50 of the continuously acquired multiple time points may be less than two seconds, but this disclosure is not limited thereto.

[0080] In step S406, the processing circuit 120 converts the local fingerprint image into a detected physiological signal. In one embodiment, the processing circuit 120 can identify the user's blood vessels, pulse, or heart rhythm / beat based on the local fingerprint image. Figure 5C In the embodiment shown, the processing circuit 120 analyzes multiple local fingerprint images IM1 to IMN to generate detection physiological signals.

[0081] Figure 6 The diagram illustrates a method for generating a detection physiological signal according to some embodiments of the present disclosure. In one embodiment, each local fingerprint image IM1-IMN has multiple pixels (e.g., grayscale values). The processing circuit 120 calculates the average pixel value of pixels at the same location in the local fingerprint images IM1-IMN, and then generates a detection physiological signal Sp based on the average pixel value. In other embodiments, the processing circuit 120 may also calculate the median pixel value of pixels at the same location in the local fingerprint images IM1-IMN, and then generate a detection physiological signal Sp based on the median pixel value. The processing circuit 120 may generate the detection physiological signal Sp using photoplethysmogram (PPG).

[0082] like Figure 6 As shown, after analyzing multiple local fingerprint images IM1 to IMN, the processing circuit 120 can convert them into a detection physiological signal Sp. In this embodiment, the detection physiological signal Sp is the heart rhythm cycle Tc, but the content of this disclosure is not limited thereto. Since those skilled in the art can understand the method of converting fingerprint images into physiological signals, it will not be described in detail here.

[0083] In step S407, the processing circuit 120 judges whether the detected physiological signal Sp conforms to the standard signal range. If the detected physiological signal Sp conforms to the standard signal range, it means that the corresponding fingerprint is a real finger. In step S408, the processing circuit 120 performs an identity recognition procedure (e.g., judges whether the initial fingerprint image corresponding to the detected physiological signal Sp is identical to the verification fingerprint previously stored by the user) according to the initial fingerprint image corresponding to the detected physiological signal Sp.

[0084] If the detected physiological signal Sp does not conform to the standard signal range, it means that the corresponding fingerprint is a fake fingerprint. In step S409, the processing circuit 120 generates a prompt message (e.g., "Please contact the sensing area directly with your finger") and does not perform an identity recognition procedure using the initial fingerprint image corresponding to the detected physiological signal Sp.

[0085] As mentioned above, the fingerprint sensor 100 of the present disclosure can be applied to detect a single fingerprint or to detect multiple fingerprints simultaneously. Figure 7 Fig. 6 shows a signal diagram for detecting multiple fingerprints simultaneously in some embodiments of the present disclosure. By outputting the enabling signal oe, the processing circuit 120 can detect different local scanning areas in multiple scanning periods F71, F72 through the sensing circuit 110 to receive the detection signals SR and convert multiple local fingerprint images. As shown, in the detection periods T11, T21, the processing circuit 120 obtains multiple local fingerprint images IMA1-IMA2 corresponding to the same local scanning area through the sensing circuit 110.

[0086] Similarly, in the detection periods T12, T22, the processing circuit 120 obtains multiple local fingerprint images IMB1-IMB2 corresponding to the same local scanning area through the sensing circuit 110. In the same way, in the detection periods T13, T23, the processing circuit 120 obtains multiple local fingerprint images IMC1-IMC2 corresponding to the same local scanning area through the sensing circuit 110.

[0087] Figure 8 Fig. 7 shows a signal diagram for detecting multiple fingerprints simultaneously in some embodiments of the present disclosure. Figure 7 Fig. 8 shows a signal diagram of the detection physiological signals SA-SC converted from the local fingerprint images. In this embodiment, the detection physiological signals SA-SC are used to present the heart rhythm period. Since the detection physiological signal SB does not have a periodic change (i.e., does not have a heart rhythm period at all), it can be easily identified that the detection physiological signal SB does not have the physiological change that a real finger should have and can be identified as a fake fingerprint.

[0088] The elements, method steps or technical features in the foregoing embodiments can be combined with each other without being limited to the order of the textual description or the order shown in the drawings in the present disclosure.

[0089] While the present disclosure has been disclosed in terms of embodiments as above, it will be apparent that various variations and modifications can be made to the embodiments without departing from the spirit and scope of the present disclosure, and it is to be understood that the present disclosure is not limited to the specific embodiments disclosed.

Claims

1. A method for fingerprint identification, comprising: performing a first scan by a fingerprint sensor to obtain an initial scan image; identifying at least one initial fingerprint image in the initial scan image; setting at least one local scan region according to a reference point in the at least one initial fingerprint image; performing at least one second scan by the fingerprint sensor on the at least one local scan region to obtain at least one local fingerprint image; and converting the at least one local fingerprint image into a detection physiological signal to obtain a detection result, wherein the method for setting the at least one local scan region according to the reference point in the at least one initial fingerprint image comprises: dividing the at least one initial fingerprint image into a plurality of initial sub-regions, wherein the initial sub-regions record a plurality of fingerprint vectors; and comparing a plurality of distribution differences of the fingerprint vectors between the initial sub-regions to set the reference point, wherein the method for comparing the distribution differences of the fingerprint vectors between the initial sub-regions comprises: identifying a plurality of slope differences of the fingerprint vectors of the initial sub-regions; setting a corresponding one of the initial sub-regions as the reference point according to a maximum one of the slope differences, wherein the method for converting the at least one local fingerprint image into the detection physiological signal comprises: calculating a plurality of average pixels of the local fingerprint images; and calculating the detection physiological signal according to the average pixels of the local fingerprint images, wherein the method for setting the at least one local scan region according to the reference point in the at least one initial fingerprint image comprises: setting the at least one local scan region along a first direction with the reference point as a center.

2. The method for fingerprint identification of claim 1, wherein the method for performing the at least one second scan on the at least one local scan region to obtain the at least one local fingerprint image further comprises: performing a plurality of the second scans on the at least one local scan region at a plurality of detection time points to obtain a plurality of the local fingerprint images.

3. The method for fingerprint identification of claim 2, wherein a distribution time of the detection time points is less than two seconds.

4. The method for fingerprint identification of claim 1, wherein a first scan frequency of the first scan is lower than a second scan frequency of the at least one second scan.

5. The method for fingerprint identification of claim 1, wherein the method for converting the at least one local fingerprint image into the detection physiological signal to obtain the detection result comprises: judging whether the detection physiological signal conforms to a standard signal range.

6. The method for fingerprint identification of claim 1, wherein the initial scan image comprises a plurality of the initial fingerprint images, and the method for fingerprint identification further comprises: setting the reference point of each of the initial fingerprint images by the fingerprint sensor, wherein the fingerprint sensor performs the at least one second scan for the reference point of each of the initial fingerprint images respectively.

7. A fingerprint sensor, comprising: a sensing circuit comprising a plurality of sensing units, wherein the sensing units are used to form an initial sensing region; and a processing circuit coupled to the sensing circuit and configured to control the sensing circuit to perform a first scan on the initial sensing area to obtain an initial scan image, wherein the initial scan image comprises at least one initial fingerprint image; wherein the processing circuit is further configured to set at least one local scan area according to a reference point in the at least one initial fingerprint image, and to control the sensing circuit to perform at least one second scan on the at least one local scan area to obtain at least one local fingerprint image; and wherein the processing circuit is further configured to convert the at least one local fingerprint image into a detection physiological signal to obtain a detection result, wherein the at least one initial fingerprint image is divided into a plurality of initial sub-areas, and the initial sub-areas record a plurality of fingerprint vectors; the processing circuit is further configured to compare a plurality of distribution differences of the fingerprint vectors between the initial sub-areas to set the reference point, wherein the processing circuit is configured to identify a plurality of slope differences of the fingerprint vectors of the initial sub-areas, and to set a corresponding one of the initial sub-areas as the reference point according to a maximum one of the slope differences, wherein the processing circuit is further configured to calculate a plurality of average pixels of the local fingerprint images, and to calculate the detection physiological signal according to the average pixels of the local fingerprint images, wherein the processing circuit is configured to set the at least one local scan area along a first direction centered on the reference point.

8. The fingerprint sensor of claim 7, wherein the processing circuit is further configured to perform the second scan on the at least one local scan area multiple times at a plurality of detection time points to obtain a plurality of the local fingerprint images.

9. The fingerprint sensor of claim 8, wherein a distribution time of the detection time points is less than two seconds.

10. The fingerprint sensor of claim 7, wherein a first scan frequency of the first scan is lower than a second scan frequency of the at least one second scan.

11. The fingerprint sensor of claim 7, wherein the processing circuit is configured to determine whether the detection physiological signal meets a standard signal range to generate the detection result.

12. The fingerprint sensor of claim 7, wherein the initial scan image comprises a plurality of the initial fingerprint images, the processing circuit is configured to set the reference point of each of the initial fingerprint images, and the sensing circuit is configured to perform the at least one second scan for the reference point of each of the initial fingerprint images, respectively.

Images