Fingerprint sensing device and signal processing method

Abstract

A fingerprint sensing device and a signal processing method. The fingerprint sensing device includes a first analog front-end circuit, a compensation circuit, a correction circuit, and an output circuit. The first analog front-end circuit generates a first image signal from fingerprint data read from a plurality of rows of a fingerprint sensor. The correction circuit receives a first output digital code generated by reading at least one row of the plurality of rows of the fingerprint sensor and calculates a brightness correction value and a relative-illumination correction value from the first output digital code. The compensation circuit modifies the first image signal to generate a second image signal according to the brightness correction value and the relative-illumination correction value. The output circuit is configured to generate a second output digital code from the second image signal.

Description

Technical Field

[0001] This disclosure relates generally to fingerprint recognition, and more specifically, to a fingerprint sensing device and its signal processing method that can enhance fingerprint recognition performance. Background Technology

[0002] Fingerprint sensors are widely used in various electronic devices, such as mobile phones, laptops, and personal digital assistants (PDAs), for fingerprint recognition. Recently, optical fingerprint recognition has become one of the most widely used fingerprint recognition methods, in which an image sensor captures reflected light passing through an optical lens of the fingerprint sensor to generate a fingerprint image signal. However, various noises and offsets can exist in the fingerprint image signal, limiting its signal quality and degrading fingerprint recognition performance.

[0003] With the increasing demand for high-quality fingerprint recognition in recent years, it is necessary to enhance the performance of fingerprint sensing and fingerprint recognition. Summary of the Invention

[0004] A fingerprint sensing device and its signal processing method are disclosed, which can enhance the performance of fingerprint recognition.

[0005] A fingerprint sensing device may include: a readout circuit, a first analog front end (AFE) circuit, a compensation circuit, a correction circuit, and an output circuit. The readout circuit is configured to read fingerprint data from multiple rows of a fingerprint sensor. The AFE circuit is configured to generate a first image signal based on the fingerprint data read from the multiple rows of the fingerprint sensor. The correction circuit is configured to receive a first output digital code generated by reading at least one row of the multiple rows of the fingerprint sensor. The correction circuit is further configured to calculate a luminance correction value and a relative illumination (RI) correction value based on the first output digital code. The compensation circuit is configured to modify the first image signal based on the luminance correction value and the RI correction value to generate a second image signal. The output circuit is configured to generate a second output digital code based on the second image signal.

[0006] The signal processing method may include the following steps: reading fingerprint data from at least one row of a fingerprint sensor to generate a first output digital code; calculating a brightness correction value and a relative illumination (RI) correction value based on the first output digital code; reading fingerprint data from multiple rows of the fingerprint sensor; generating a first image signal based on the fingerprint data read from the multiple rows of the fingerprint sensor; modifying the first image signal based on the brightness correction value and the RI correction value to generate a second image signal; and generating a second output digital code based on the second image signal.

[0007] In some embodiments, the fingerprint sensing device reads at least one row of a fingerprint sensor to obtain a first output digital code, and calculates correction values ​​(i.e., brightness correction values, RI correction values, and gain values) based on the first output digital code. After calculating the correction values, the fingerprint sensing device corrects multiple image signals (or fingerprint image signals) read from the rows of the fingerprint sensor according to the correction values. In this way, offsets caused by different factors are corrected in a single image frame, resulting in fast and accurate fingerprint sensing and recognition. Additionally, the amplitude of the peaks and valleys of the fingerprint in the fingerprint image signal can be enhanced according to the calculated gain value to improve the signal quality of the fingerprint image signal. Furthermore, the full-scale range of the analog-to-digital converter (ADC) can be adjusted according to the calculated gain value to improve the ADC's resolution. In this way, the fingerprint recognition performance of the fingerprint sensing device is improved.

[0008] To make this disclosure easier to understand, several embodiments, illustrated below, are described in detail. Attached Figure Description

[0009] The accompanying drawings are included to further illustrate this disclosure, and are incorporated in and form a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0010] Figure 1 A schematic diagram of a fingerprint sensing device according to some embodiments is shown.

[0011] Figure 2 A flowchart illustrating a signal processing procedure suitable for a fingerprint sensing device according to some embodiments is shown.

[0012] Figure 3 A diagram illustrating the output digital code read from a row of a fingerprint sensor according to some embodiments.

[0013] Figure 4 A graph illustrating the relative response (RI) characteristics of a lens according to some embodiments.

[0014] Figure 5A and Figure 5B An exemplary order for reading multiple rows of a fingerprint sensor is shown according to some embodiments.

[0015] Figure 6A and Figure 6B The diagram illustrates an interpolation operation on fingerprint data read from a predetermined row of a fingerprint sensor, according to some embodiments.

[0016] Figure 7A and Figure 7B A diagram illustrating brightness correction according to some embodiments.

[0017] Figure 8 This describes fingerprint image frames used for RI correction according to some embodiments.

[0018] Figures 9A to 9C A diagram illustrating signal enhancement and full-scale range adjustment according to some embodiments.

[0019] Figure 10 A flowchart illustrating a signal processing method according to some embodiments is provided.

[0020] Explanation of icon numbers

[0021] 100: Fingerprint sensing device;

[0022] 110: Fingerprint sensor / fingerprint sensor array / finger sensor;

[0023] 120: Readout circuit;

[0024] 121: Sensing signal;

[0025] 130: Analog front-end circuit;

[0026] 131: Image signal;

[0027] 140: Compensation circuit;

[0028] 141: Compensation signal;

[0029] 150: Digital-to-analog converter;

[0030] 151: Correction signal;

[0031] 160: Output circuit;

[0032] 162: AFE circuit;

[0033] 164: Analog-to-digital converter;

[0034] 170: Correction circuit;

[0035] 171, 172: Correction values;

[0036] 210, 220, 230, 240, 250, 260, 270, 1010, 1020, 1030, 1040, 1050, 1060: Steps;

[0037] 701, 702: Arrows;

[0038] 801: Fingerprint image frame;

[0039] 1621: Amplified signal;

[0040] AVG: Average value;

[0041] C1, C1', C2, C2', C3, C3', C31, C41, C91, C92: Curves;

[0042] D, D(1), D(N), D(M)_1: Output numeric codes;

[0043] EXPO: Exposure operation;

[0044] FS, FS1, FS2: Full-scale range;

[0045] MAX: Maximum value;

[0046] MIN: Minimum value;

[0047] P1: pixel;

[0048] P0: Center pixel;

[0049] r: distance;

[0050] R: Reset operation;

[0051] R1, R2, R3: Zones;

[0052] R(1), R(N): rows;

[0053] S: Sampling operation;

[0054] T1: Exposure time / Exposure time cycle;

[0055] T2: Exposure time / exposure cycle;

[0056] x, y: coordinates. Detailed Implementation

[0057] It should be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of this disclosure. Furthermore, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered limiting. The use of “comprising,” “including,” or “having,” and variations thereof herein is intended to cover the items listed thereafter and their equivalents, as well as additional items. Unless otherwise limited, the terms “connection,” “coupling,” and “mounting,” and variations thereof, used herein, are used broadly and cover direct and indirect connections, couplings, and mountings.

[0058] Figure 1A schematic diagram of a fingerprint sensing device 100 according to some embodiments is shown. According to some embodiments, the fingerprint sensing device 100 may include a fingerprint sensor 110, a readout circuit 120, an analog front-end (AFE) circuit 130, a compensation circuit 140, a digital-to-analog converter (DAC) 150, an output circuit 160, and a correction circuit 170. The fingerprint sensor array 110 may include a plurality of pixels arranged in rows and columns, and the fingerprint sensor 110 is configured to sense a user's fingerprint. For example, the fingerprint sensor array 110 may be an optical fingerprint sensor that captures an image of a user's fingerprint through the pixels of the fingerprint sensor 110 to generate a sensing signal (or image signal). In some embodiments, the fingerprint sensing device 100 is an optical fingerprint sensing device 100 disposed below a sensor pad or panel of an electronic device (not shown) along with a light source (not shown) and a lens or lens group (not shown). The light source and lens group may be included in or coupled to the optical fingerprint sensing device 100. The light source is configured to emit light toward a touching finger on a sensing pad or panel, and a lens can focus the reflected light from the touching finger onto the fingerprint sensor 110 for generating a sensing signal (or image signal). The lens may comprise a biconvex lens, a convex-concave (positive meniscus) lens, a plano-convex lens, a plano-concave lens, or a combination thereof. The lens may be characterized by a lens pattern, which refers to the relative illumination (RI) of the lens corresponding to the distance from the sensing pixel to the center pixel corresponding to the center of the lens.

[0059] Readout circuitry 120 is coupled to fingerprint sensor 110 and configured to read fingerprint data from pixels of fingerprint sensor 110 to generate sensing signal 121. Readout circuitry 120 can selectively read at least one sensing pixel of fingerprint sensor 110. For example, readout circuitry 120 can read a specific row of fingerprint sensor 110, or can sequentially read multiple rows of fingerprint sensor 110 to generate sensing signal 121. Readout circuitry 120 can output sensing signal 121 to AFE circuitry 130.

[0060] The AFE circuit 130 is coupled to the readout circuit 120 and configured to generate an image signal 131 based on the sense signal 121 output from the readout circuit 120. The AFE circuit 130 may perform processing operations on the sense signal 121 to generate the image signal 131. For example, the AFE circuit 130 may perform sampling, amplification, and / or compensation operations on the sense signal 121 to reduce noise and improve signal quality. The AFE circuit 130 is configured to output the image signal 131 to the compensation circuit 140. This disclosure does not limit the circuit structure and operation of the AFE circuit 130.

[0061] Compensation circuit 140 is coupled to DAC 150 and AFE circuit 130 to receive image signal 131 from AFE circuit 130 and correction signal 151 from DAC 150. Compensation circuit 140 is configured to compensate image signal 131 according to correction signal 151 to generate compensation signal 141. Compensation circuit 140 may include adder circuitry configured to add correction signal 151 to image signal 131 to generate compensation signal 141. In some embodiments, correction signal 151 is configured to correct offsets caused by brightness variations and offsets caused by lens patterns (i.e., relative illuminance) on image signal 131. Offsets caused by brightness variations may be affected by ambient light intensity and / or light intensity of the panel area where a touching finger is located and / or other factors. Offsets caused by lens patterns may be affected by the optical characteristics (i.e., RI characteristics) of the lens. For example, the central region of a lens (having a shorter distance from the lens center) has a higher relative illuminance than the peripheral region. Therefore, the sensing signal from a pixel corresponding to the central region of the lens typically has higher brightness than the sensing signal from a pixel corresponding to the outer peripheral region of the lens. This will be combined with... Figure 7A , Figure 7B as well as Figure 8 The corrections for offsets caused by brightness variations and offsets caused by lens patterns are described in detail.

[0062] Output circuit 160 is coupled to compensation circuit 140 and configured to generate output digital code D based on compensation signal 141. Output digital code D is a digital representation of a user's fingerprint (i.e., the peaks and valleys of the user's fingerprint) sensed by finger sensor 110. In some embodiments, output circuit 160 includes AFE circuit 162 and analog-to-digital converter (ADC) 164. AFE circuit 162 is configured to amplify compensation signal 141 based on a gain value to generate amplified signal 1621, where the gain value can be calculated by correction circuit 170. In some embodiments, AFE circuit 162 amplifies compensation signal 141 to increase the amplitude of the peaks and valleys of the fingerprint in compensation signal 141 to generate amplified signal 1621. ADC 164 has a full-scale range corresponding to the operating voltage range of ADC 164, and the number of bits of ADC 164 spans the full-scale range of ADC. ADC 164 is coupled to AFE circuit 162 and configured to convert amplified signal 1621 to generate output digital code D. In some embodiments, the full-scale range of the ADC 164 can be adjusted based on a gain value calculated by the correction circuit 170, thereby improving the resolution of the ADC 164. The gain value is represented as a correction value 172 from the output of the correction circuit 170 to the output circuit 160. A description of the adjustment of the gain value, signal enhancement, and full-scale range will follow. Figures 9A to 9C Describe it.

[0063] The correction circuit 170 is coupled to the output circuit 160 and configured to generate correction values ​​171 and 172 according to the output digital code D. Correction value 171 is provided to DAC 150, and DAC 150 converts the digital correction value 171 into a correction signal 151 in analog form. In some embodiments, correction value 171 includes at least one of a luminance correction value and an RI correction value. DAC 150 can convert the luminance correction value and RI correction value in correction value 171 to generate a correction signal 152. Figure 1 The values ​​in the diagram represent the brightness correction signal and the RI correction signal, respectively, as correction signal 151.

[0064] Figure 2 This illustrates a fingerprint sensing device (i.e., according to some embodiments) Figure 1 A flowchart illustrating the signal processing procedure of the fingerprint sensing device 100. (See reference...) Figure 1 and Figure 2 In step 210, the fingerprint sensing device 100 determines the touch area of ​​the user's finger. In step 220, the fingerprint sensing device 100 reads fingerprint data from at least one row (hereinafter referred to as a predetermined row) of the fingerprint sensor 110 to generate an output digital code. Since each row of the fingerprint sensor 110 contains multiple pixels, the output digital code obtained by reading the predetermined row contains multiple pixel output digital codes corresponding to the pixels of the predetermined row. Therefore, the output digital code of the predetermined row can be represented as a curve (i.e., Figure 3 (Curve C31 in the text). Figure 3 A graph illustrating an exemplary curve C31 representing the output digital code obtained by reading a predetermined row of the fingerprint sensor 110 according to some embodiments. The vertical axis of the graph represents the output digital code D, and the horizontal axis of the graph represents the position of the pixels in the predetermined row. Figure 3 The average value AVG, maximum value MAX, and minimum value MIN are further illustrated, where the average value AVG is the average of the pixel output digital codes forming curve C31, the minimum value MIN is the smallest of the pixel output digital codes, and the maximum value MAX is the largest of the pixel output digital codes. The average value AVG, maximum value MAX, or minimum value MIN of the output digital codes can be used to calculate the correction value.

[0065] exist Figure 2 In step 230, a correction value is calculated based on the output digital code of the predetermined row, wherein the correction value may include at least one of a brightness correction value, a lens pattern correction value, and a gain value. This can be achieved by the correction circuit of the fingerprint sensing device 100 (i.e., Figure 1 The correction circuit 170 in the middle performs the calculation of the correction value in step 230.

[0066] In some embodiments, the correction circuit 170 is configured to calculate a brightness correction value based on the output digital code of a predetermined line, the full-scale range of the ADC 164, and the number of bits of the ADC 164 (or the number of bits of the DAC 150). In an example, the brightness correction value ΔDAC is calculated according to equation (1). LM , where AVG is the average (or mean) of the pixel output digital codes obtained by reading a predetermined row, FS is the full-scale range of ADC 164, ADCbit is the number of bits of ADC 164, and DACbit is the number of bits of DAC 150. In another instance, the average value AVG in equation (1) can be replaced by the maximum value MAX or the minimum value MIN among the pixel output digital codes of the output digital codes.

[0067]

[0068] Luminance correction value ΔDAC LM This can correspond to the image signal (i.e., Figure 1 The shift amount (i.e., voltage level or current level) of the image signal 131 in the image is used to correct the offset caused by brightness changes. The brightness correction value ΔDAC LM It can be converted into a brightness correction signal by DAC 150 and used to compensate the image signal by compensation circuit 140.

[0069] In some embodiments, the correction circuit 170 is further configured to calculate an RI correction value based on the output digital code of the predetermined row and the number of bits of the ADC 164 (or the number of bits of the DAC 150). Since the output digital code is obtained by reading all pixels contained in the predetermined row of the fingerprint sensor, the output digital code obtained by reading the predetermined row reflects the RI response of the entire surface of the lens. Based on the RI response of the lens (or the output digital code obtained by reading the predetermined row), the correction circuit 170 can calculate an RI correction value (also called an anti-RI gain value) corresponding to each pixel of the predetermined row. For example, the correction circuit 170 can calculate the RI correction value ΔDAC corresponding to each pixel of the predetermined row according to equation (2). RI ΔRI(r) is the distance from the target pixel to the center pixel corresponding to the center point of the lens, ΔRI(r) is the difference between the RI corresponding to the target pixel and the RI corresponding to the center pixel, ADCbit is the number of bits of ADC 164, and DACbit is the number of bits of DAC 150. Figure 4 Exemplary values ​​of r and ΔRI(r) are shown on a graph of the output digital code (i.e., curve C41) obtained by reading a predetermined line of the fingerprint sensor 110. Figure 4 The vertical and horizontal axes of the graph represent the output numeric code and pixel position, respectively.

[0070]

[0071] RI correction value ΔDAC RI (r) can indicate the image signal (i.e., Figure 1 The image signal 131 in the image sensor is shifted by an amount (i.e., voltage level or current level) to correct for the offset caused by the RI characteristics of the lens. Due to the RI characteristics, pixels corresponding to the central region of the lens typically have higher brightness than pixels corresponding to the outer peripheral region of the lens (due to the offset caused by the RI characteristics). In some embodiments, for all pixels in a row of the fingerprint sensor 110, the RI correction value ΔDAC is used. RI (r) is not fixed. Instead, the RI correction value ΔDAC RI (r) can vary depending on the distance r from the pixel to the center pixel. Therefore, a lookup table can be used to store the RI correction value ΔDAC for each pixel of the fingerprint sensor 110 based on the distance r from the pixel to the center pixel. RI (r). The lookup table can store the fingerprint sensor 110 and the RI correction value ΔDAC. RI The lookup table represents a one-to-one relationship between pixels (r). In other words, when the fingerprint sensor 110 has n pixels, there are n RI correction values ​​ΔDAC in the lookup table. RI (r).

[0072] In some embodiments, the correction circuit 170 is configured to calculate a gain value G based on the difference between the full-scale range of the ADC 164 and the swing range of the compensation signal 141. For example, the gain value G can be calculated according to equation (3), where FS is the full-scale range of the ADC 164 and dsig is the swing range of the compensation signal 141. The swing range dsig defines the range of the peaks and valleys of the fingerprint in the compensation signal 141, and is shown as... Figures 9A to 9C The range in the equation is from (FS / 2+dsig) to (FS / 2-dsig).

[0073]

[0074] The gain value G can be used to enhance the amplitude of the peaks and valleys of the fingerprint in the compensation signal (i.e., the higher AFE gain of AFE circuit 162) and / or improve the resolution of ADC 164 (the higher ADC gain of ADC 164).

[0075] After calculating the correction value in step 230, step 240 is executed. In step 240, fingerprint data from multiple rows of the fingerprint sensor 110 are read sequentially to generate an image signal. (Reference) Figure 1 and Figure 2 The readout circuit 120 and the AFE circuit 130 can read and amplify fingerprint data from the rows of the fingerprint sensor 110 to generate an image signal 131.

[0076] Figure 5A and Figure 5B This illustrates a fingerprint sensor (i.e., according to some embodiments) for reading fingerprint sensors. Figure 1 An exemplary order of multiple rows R(1) to row R(N) of the fingerprint sensor 110 in the image. (See reference...) Figure 1 and Figure 5A The fingerprint sensing operation for reading each of rows R(1) to R(N) of the fingerprint sensor 110 includes a reset operation R, an exposure operation EXPO, and a sampling operation S. The reset operation R, exposure operation EXPO, and sampling operation S of each fingerprint sensing operation are executed sequentially to read data from each row of the fingerprint sensor 110. The reset operation R is configured to reset at least one pixel of the fingerprint sensor 110. The exposure operation EXPO is performed after the reset operation to expose at least one pixel during the exposure time period. The sampling operation S samples the image signal to generate an output digital code D.

[0077] refer to Figure 5A A fingerprint sensing operation is performed to read fingerprint data from a predetermined row R(M) to generate an output digital code D(M). The output digital code D(M) of the predetermined row R(M) is used to calculate correction values, such as brightness correction values, RI correction values, and gain values. In some embodiments, the predetermined row R(M) is the center row of the fingerprint sensor 110. After calculating the correction value based on the output digital code D(M), a fingerprint sensing operation is performed to sequentially read fingerprint data from the other rows of the fingerprint sensor 110, starting from the adjacent row R(M+1). In other words, after reading row R(M) and calculating the correction value, rows R(M+1) to R(N) and rows R(1) to R(M-1) are read sequentially to generate an image signal of the user's fingerprint. The image signal generated by reading rows R(M+1) to R(N) and rows R(1) to R(M-1) is corrected by the correction value to generate output digital codes D(1) to D(N).

[0078] refer to Figure 5B , Figure 5A Fingerprint sensing operation and Figure 5B The difference between the fingerprint sensing operations is the order in which rows R(1) to R(N) of the fingerprint image 110 are read. Figure 5B In the process, after obtaining the output digital code D(M) and calculating the correction value, the rows of the fingerprint sensor 110 are read sequentially from the top row R(1) to the bottom row R(N). Figure 5A Fingerprint sensing operation and Figure 5BAnother difference between the fingerprint sensing operations is that two predetermined rows R(M) are read, where the first read generates an output digit code D(M) and the second read generates an output digit code D(M)_1. Because the time exposure difference between the two reads of the predetermined row R(M) is relatively long, an interpolation operation can be performed to estimate the output digit code D(M)_1 in the second read. In this way, the fingerprint sensing device can accurately estimate the digit code D(M)_1 in the second read.

[0079] Interpolation can be Figure 6A The figure shown illustrates intra-interpolation. Figure 6A The horizontal axis of the graph shows the exposure time, and Figure 6A The vertical axis of the graph shows the output digital code D output by the fingerprint sensing device. When a predetermined row R(M) is read at exposure time T1, the output digital code D(M) is output. Therefore, when a predetermined row R(M) is read at exposure time T2, the output digital code D(M)_1 should be proportional to the difference between exposure time T2 and exposure time T1. In some embodiments, an internal interpolation operation for calculating the output digital code D(M)_1 is defined in equation (4), where T1 and T2 are exposure time periods, D(M) is the output digital code when a predetermined row R(M) is read at exposure time period T1, and D(M)_1 is the output digital code when a predetermined row R(M) is read at exposure time period T2.

[0080]

[0081] In some alternative embodiments, the interpolation operation may be Figure 6B The diagram illustrates extra-interpolation. Therefore, the output numeric code D(M)_1 corresponding to a predetermined row R(M) can be estimated based on the output numeric codes corresponding to adjacent rows (i.e., rows R(M+1) and R(M-1)). This disclosure does not limit the techniques used to perform extra-interpolation. Any technique that infers the value / code of a row from the values / codes of adjacent rows should fall within the scope of this disclosure.

[0082] exist Figure 2 In step 250, brightness correction is performed according to the correction value (i.e., the brightness correction value ΔDAC). LM Corrects the offset caused by noise and brightness variations in image signal 131. (Reference) Figure 1 and Figure 2 The DAC 150 can output the brightness correction value ΔDAC. LM It is converted into a brightness correction signal; and the compensation circuit 140 uses the correction signal 151 to compensate the image signal 131 to generate the compensation signal 141. Figure 7AThe output digital codes (i.e., curves C1, C2, and C3) prior to performing luminance correction according to some embodiments are shown, and Figure 7B The output digital codes (i.e., curves C1′, C2′, and C3′) after brightness correction are shown. Figure 7A and Figure 7B In the diagram, the horizontal axis represents the pixel position in each row of the fingerprint sensor 110, and the vertical axis represents the output numeric code from each row. Figure 7A Before brightness correction, the output digital codes (i.e., curves C1, C2, and C3) may span the full-scale range FS of the ADC 164. Brightness correction is configured to shift curves C1, C2, and C3 towards the center of the full-scale range (i.e., approximately FS / 2) corresponding to the brightness correction value ΔDAC. LM The amount of shift. Figure 7A Arrows 701 and 702 indicate the shift of curves C1, C2, and C3 towards the center of the full-scale range (FS / 2). After brightness correction, curves C1, C2, and C3 are shifted towards the center of the full-scale range (FS / 2) to become... Figure 7B Curves C1′, C2′, and C3′ are shown in the figure. Figure 7A and Figure 7B As illustrated, the output digital codes (i.e., curves C1, C2, and C3) read from the rows of the fingerprint sensor 110 are shifted toward and locked at the center of the ADC 164 (approximately FS / 2). In this way, the offset caused by brightness variations and noise is eliminated, the resolution of the ADC 164 is improved, and the performance of fingerprint sensing and recognition is enhanced.

[0083] exist Figure 2 In step 260, RI correction is performed according to the correction value (i.e., the RI correction value ΔDAC). RI (r)) Corrects the offset caused by the lens's RI characteristics. Reference Figure 1 and Figure 2 The DAC 150 can correct the RI value ΔDAC. RI (r) is converted into an RI correction signal; and the compensation circuit 140 uses the RI correction signal to compensate the image signal 131 to generate the compensation signal 141. If a lookup table is used to store the RI correction value ΔDAC corresponding to each pixel of the fingerprint sensor 110... RI (r), then the corresponding RI correction value ΔDAC stored in the lookup table can be used. RI(r) Correct the fingerprint data from each pixel. In some embodiments, for each pixel of the fingerprint sensor 110, a distance r from the pixel to the center pixel (the center pixel corresponding to the center of the lens) is determined, and a correction value ΔDAC corresponding to the distance r is determined. RI (r) (or anti-RI value) is used to correct fingerprint data read from pixels. For example, reference Figure 8 , Figure 8 The image frame 801, read from the pixels of the fingerprint sensor 110, shows the distance from pixel P1 to the center pixel P0, which can be calculated based on the pixel coordinates x and y. Therefore, a correction value ΔDAC corresponds to the distance r. RI (r) can be used to compensate for fingerprint data read from pixel P1. For example... Figure 8 As illustrated, fingerprint image frame 801 can be divided into multiple regions R1, R2, and R3, wherein a correction value ΔDAC is used to correct the fingerprint data read from the pixels of each of regions R1, R2, and R3. RI (r) can be different. Generally, the pixels in the outer peripheral areas (i.e., areas R2 and R3) should be adjusted more than the pixels in the central area R1 to compensate for the higher relative illumination (RI) characteristics in the central area. As a result of RI correction, the offset caused by the RI characteristics of the lens is removed from the compensation signal (i.e., compensation signal 141).

[0084] After performing luminance correction and RI correction in steps 250 and 260, the image signal is compensated (i.e., Figure 1 The offset on the image signal 131 in the image signal, and the offset on the compensation signal (i.e., Figure 1 The peaks and valleys of the fingerprint are preserved in the compensation signal 141. Figure 2 In step 270, signal enhancement is performed based on the gain value G to amplify the amplitude of the peaks and valleys of the fingerprint in the compensation signal 141. (See reference...) Figure 1 and Figure 2 The gain G can be provided to the output circuit 160, and the AFE circuit 162 of the output circuit 160 is configured to amplify the compensation signal 141 according to the gain G. In some embodiments, the AFE circuit 162 can multiply the compensation signal 141 with the gain G to generate an amplified signal 1621 at the output of the AFE circuit 162. However, this disclosure is not limited thereto, and any technique for amplifying the compensation signal 141 according to the gain G falls within the scope of this disclosure.

[0085] Figure 9A and Figure 9B This is a magnified diagram illustrating the compensation signal 141 according to some embodiments based on the gain value G. The vertical axis of the diagram represents the output digital code D, and the horizontal axis represents the pixel position in the row of the fingerprint sensor 110. In this example, the output digital code corresponding to the compensation signal 141 is... Figure 9AThis is represented by curve C91. For example... Figure 9A Hezhong Figure 9B As illustrated, curve C92 is generated by amplifying curve C91 based on gain G, where the peak-to-valley difference (or swing range) of curve C92 is greater than that of curve C91. In other words, AFE circuit 162 can increase the peak-to-valley difference of the fingerprint, thereby improving the signal quality of compensation signal 141. The swing range of the amplified curve C92 can be less than or equal to the full-scale range FS1 of ADC 164.

[0086] In some embodiments, the full-scale range FS1 of the ADC 164 can be adjusted according to the gain G to improve the resolution of the ADC 164. (See reference...) Figure 9A and Figure 9C The full-scale range FS1 of the ADC 164 is adjusted to a new full-scale range FS2 based on the gain G, wherein the full-scale range FS2 is smaller than the full-scale range FS1. In this way, the resolution of the ADC 164 can be improved, and the fingerprint recognition performance of the fingerprint sensing device 100 can be enhanced. In some embodiments, the adjustment amount of the full-scale range is greater as the gain G increases. This disclosure does not limit the adjustment amount of the full-scale range of the ADC 164.

[0087] Figure 10 This is a flowchart of a signal processing method applicable to a fingerprint sensing device according to some embodiments. In step 1010, fingerprint data is read from a predetermined row of a fingerprint sensor to generate a first output digital code. In step 1020, a brightness correction value and a relative illumination (RI) correction value are calculated based on the first output digital code. In steps 1030 and 1040, fingerprint data from multiple rows of an optical fingerprint sensor is read, and a first image signal is generated based on the fingerprint data read from the multiple rows of the optical fingerprint sensor. In step 1050, the first image signal is modified based on the brightness correction value and the RI correction value to generate a second image signal. In step 1060, a second output digital code is generated based on the second image signal.

[0088] In the above embodiments, correction values, such as brightness correction values, RI correction values, and gain values, are calculated based on the first output digital code read from a predetermined row of the fingerprint sensor. These correction values ​​are used to correct multiple image signals (or fingerprint image signals) read from the rows of the fingerprint sensor. In this way, offsets caused by different factors are corrected within a single image frame, resulting in fast and accurate fingerprint sensing and recognition. Furthermore, the amplitude of the peaks and valleys of the fingerprint in the fingerprint image signal can be enhanced based on the calculated gain value to improve the signal quality of the fingerprint image signal. Additionally, the full-scale range of the ADC can be adjusted based on the calculated gain value to improve the ADC's resolution. In this way, the fingerprint recognition performance of the fingerprint sensing device is improved.

[0089] For those skilled in the art, various modifications and variations can be made to the structure of the embodiments of this disclosure without departing from the scope or spirit of this disclosure. In view of the foregoing, it is intended that this disclosure cover modifications and variations thereof, provided that such modifications and variations fall within the scope of the appended claims and their equivalents.

Claims

1. A fingerprint sensing device, comprising: The readout circuit is configured to read fingerprint data from multiple rows of the fingerprint sensor; A first analog front-end circuit is configured to generate a first image signal based on the fingerprint data read from the plurality of rows of the fingerprint sensor; The correction circuit is configured as follows: Receive a first output digital code generated by reading at least one of the plurality of rows of the fingerprint sensor; as well as Calculate the luminance correction value and relative illuminance correction value based on the first output digital code; A compensation circuit is configured to modify the first image signal according to the brightness correction value and the relative illumination correction value to generate a second image signal; The output circuit is configured to generate a second output digital code based on the second image signal; as well as A digital-to-analog converter, coupled to the correction circuit, is configured to convert the luminance correction value and the relative illuminance correction value into a luminance correction signal and a relative illuminance correction signal, wherein the luminance correction signal and the relative illuminance correction signal are analog signals. The compensation circuit includes an adder circuit coupled to the digital-to-analog converter and the first analog front-end circuit, and the adder circuit is configured to add the luminance correction signal and the relative illumination correction signal to the first image signal to generate the second image signal.

2. The fingerprint sensing device of claim 1, wherein the correction circuit is further configured to calculate a gain value based on the first output digital code.

3. The fingerprint sensing device according to claim 2, wherein the output circuit comprises: A second analog front-end circuit, coupled to the compensation circuit, is configured to amplify the second image signal according to the gain value to generate a third image signal; as well as An analog-to-digital converter, coupled to the second analog front-end circuit, is configured to convert the third image signal to generate the second output digital code. The correction circuit is configured to calculate the gain value based on the full-scale range of the analog-to-digital converter and the swing range of the second image signal, wherein the full-scale range of the analog-to-digital converter corresponds to the operating voltage range of the analog-to-digital converter.

4. The fingerprint sensing device according to claim 3, wherein The fingerprint sensing device is further configured to adjust the full-scale range of the analog-to-digital converter according to the gain value.

5. The fingerprint sensing device according to claim 1, wherein... At least one of the plurality of rows is the center row of the fingerprint sensor.

6. The fingerprint sensing device according to claim 5, wherein After calculating the brightness correction value and the relative illumination correction value based on the first output digital code, the fingerprint sensing device is configured to sequentially read the fingerprint data from the plurality of rows of the fingerprint sensor, starting from adjacent rows of the at least one row of the fingerprint sensor.

7. The fingerprint sensing device according to claim 5, wherein After calculating the brightness correction value and the relative illumination correction value based on the first output digital code, the fingerprint sensing device is configured to sequentially read the fingerprint data from the plurality of rows of the fingerprint sensor, starting from the top row to the bottom row of the plurality of rows.

8. The fingerprint sensing device according to claim 7, wherein The fingerprint sensing device is configured to read at least one row of the fingerprint sensor in a first read and a second read. The fingerprint sensing device is further configured to perform an interpolation operation to estimate the output numeric code of the at least one row in the second reading based on the output numeric code of the at least one row in the first reading.

9. The fingerprint sensing device according to claim 3, wherein The fingerprint sensor's at least one row comprises multiple pixels. The first output numeric code includes multiple pixel numeric codes corresponding to the plurality of pixels, and The correction circuit is configured to calculate the brightness correction value based on the average value of the plurality of pixel digital codes, the full-scale range of the analog-to-digital converter, and the number of bits of the analog-to-digital converter.

10. The fingerprint sensing device according to claim 3, wherein The correction circuit is configured to calculate the relative illumination correction value based on the number of bits of the analog-to-digital converter and the distance from the pixel of the fingerprint sensor to the center pixel of the fingerprint sensor, wherein the center pixel of the fingerprint sensor corresponds to the center point of the lens of the fingerprint sensing device.

11. A signal processing method, comprising: Fingerprint data is read from at least one row of the fingerprint sensor to generate a first output numeric code; Calculate the luminance correction value and relative illuminance correction value based on the first output digital code; Fingerprint data is read from multiple rows of the fingerprint sensor; A first image signal is generated based on the fingerprint data read from the plurality of rows of the fingerprint sensor; The first image signal is modified according to the brightness correction value and the relative illumination correction value to generate the second image signal; as well as A second output digital code is generated based on the second image signal. Modifying the first image signal according to the brightness correction value and the relative illumination correction value to generate the second image signal includes: The luminance correction value and the relative illuminance correction value are converted into a luminance correction signal and a relative illuminance correction signal, wherein the luminance correction signal and the relative illuminance correction signal are analog signals; and The brightness correction signal and the relative illumination correction signal are added to the first image signal to generate the second image signal.

12. The signal processing method according to claim 11, wherein generating the second output digital code based on the second image signal comprises: Calculate the gain value based on the first output numeric code; The second image signal is amplified according to the gain value to generate a third image signal; as well as The third image signal is converted to generate the output digital code. The gain value is calculated based on the full-scale range of the first output digital code from the analog-to-digital converter and the swing range of the second image signal, and the full-scale range of the analog-to-digital converter corresponds to the operating voltage range of the analog-to-digital converter.

13. The signal processing method according to claim 12, further comprising: The full-scale range of the analog-to-digital converter is adjusted according to the gain value.

14. The signal processing method of claim 11, wherein at least one of the plurality of rows is the center row of the fingerprint sensor.

15. The signal processing method of claim 11, wherein reading the fingerprint data from the plurality of rows of the fingerprint sensor comprises: The fingerprint data is read sequentially from the plurality of rows of the fingerprint sensor, starting from the adjacent row of the at least one row of the fingerprint sensor.

16. The signal processing method of claim 11, wherein reading the fingerprint data from the plurality of rows of the fingerprint sensor comprises: The fingerprint data is read sequentially from the multiple rows of the fingerprint sensor, starting from the top row to the bottom row of the multiple rows.

17. The signal processing method according to claim 12, wherein... The fingerprint sensor's at least one row comprises multiple pixels. The first output numeric code includes multiple pixel numeric codes read from the plurality of pixels, and The brightness correction value is calculated based on the average value of the plurality of pixel digital codes, the full-scale range of the analog-to-digital converter, and the number of bits of the analog-to-digital converter.

18. The signal processing method according to claim 12, wherein... The relative illumination correction value is calculated based on the number of bits of the analog-to-digital converter and the distance from the pixel of the fingerprint sensor to the center pixel of the fingerprint sensor, wherein the center pixel of the fingerprint sensor corresponds to the center point of the lens of the fingerprint sensing device.

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