Method for ultrasonic fingerprint recognition, ultrasonic fingerprint device and electronic equipment
By obtaining the correspondence function between temperature and background signal, the ultrasonic fingerprint signal is calibrated, solving the problem of temperature affecting the background signal and realizing high-definition fingerprint recognition at different temperatures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUIKE (SINGAPORE) HLDG PTE LTD
- Filing Date
- 2022-08-31
- Publication Date
- 2026-06-23
AI Technical Summary
Temperature affects the background signal acquired by the ultrasonic fingerprint device, resulting in a decrease in the signal-to-noise ratio. Existing technologies cannot calibrate the background signal in real time, which affects the clarity of the fingerprint image.
By obtaining a first function that establishes the correspondence between temperature and background signal, the target background signal is determined, and the ultrasonic fingerprint signal is calibrated based on this function, thereby reducing the amount of stored data and improving adaptability and accuracy.
Maintaining fingerprint image clarity at different temperatures reduces signal attenuation and improves the adaptability and accuracy of ultrasonic fingerprint detection.
Smart Images
Figure CN115410237B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of fingerprint recognition, and more specifically, to a method, device, and electronic device for ultrasonic fingerprint recognition. Background Technology
[0002] Ultrasonic fingerprint recognition technology is gradually becoming a mainstream fingerprint unlocking solution due to its advantages such as fast unlocking speed, high accuracy, simple registration, and wide applicability. During ultrasonic fingerprint recognition, the ultrasonic fingerprint device emits ultrasonic signals. These signals pass through the adhesive layer and screen, reaching the screen surface. Reflected by a finger on the screen, they then pass through the layers again and return to the ultrasonic fingerprint device. Because the fingerprint valleys and ridges have different reflectivities to ultrasonic signals, the echo signal collected by the ultrasonic fingerprint device carries fingerprint information. In addition, the ultrasonic fingerprint device also needs to collect the background signal when no finger is pressing on the screen surface. By subtracting the background signal from the echo signal carrying fingerprint information, a clear fingerprint image can be obtained.
[0003] However, temperature affects the magnitude of the background signal acquired by the ultrasonic fingerprint device, and the background signal cannot be acquired in real time; that is, the background signal drifts with temperature, thereby reducing the signal-to-noise ratio of the fingerprint image. Therefore, how to reduce the impact of temperature on ultrasonic fingerprint detection has become a problem that needs to be solved. Summary of the Invention
[0004] This application provides a method, device, and electronic equipment for ultrasonic fingerprint recognition, which can reduce the impact of temperature on ultrasonic fingerprint detection.
[0005] In a first aspect, a method for ultrasonic fingerprint recognition is provided, performed by an ultrasonic fingerprint device disposed under the screen of an electronic device to achieve under-screen ultrasonic fingerprint recognition. The method includes:
[0006] Obtain a first function to represent the correspondence between temperature and a background signal, wherein the background signal is an ultrasonic signal without fingerprint information received when no finger is pressing the screen;
[0007] When a finger presses the screen, the current temperature is acquired, and a target background signal corresponding to the current temperature is determined based on the current temperature and the first function.
[0008] An ultrasonic signal is emitted to the finger, and an ultrasonic fingerprint signal carrying the fingerprint information is received from the finger, wherein the fingerprint image of the finger is obtained based on the difference between the ultrasonic fingerprint signal and the target background signal.
[0009] In this embodiment, during ultrasonic fingerprint recognition, a target background signal corresponding to the current temperature is determined based on a first function representing the correspondence between temperature and background signal. After transmitting an ultrasonic signal to the finger and receiving the ultrasonic fingerprint signal carrying fingerprint information returned by the finger, a fingerprint image of the finger is obtained based on the target background signal and the ultrasonic fingerprint signal. Since the target background signal determined by the first function matches the current temperature, when it is subtracted from the ultrasonic fingerprint signal to cancel out the background signal carried in the ultrasonic fingerprint signal, excessive signal attenuation can be avoided, ensuring the clarity of the fingerprint image and reducing the impact of temperature on ultrasonic fingerprint detection. Furthermore, since this application represents the correspondence between temperature and background signal through a function, the amount of data that needs to be stored is reduced. At the same time, the background signal corresponding to any temperature can be obtained according to the function, making ultrasonic fingerprint detection more adaptable to temperature and more accurate.
[0010] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, each of which corresponds to a multiple first functions. The step of determining the target background signal corresponding to the current temperature based on the current temperature and the first functions includes: determining the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit in the detection unit array.
[0011] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, the detection unit array including multiple subarrays, each subarray corresponding to a multiple first function, and determining the target background signal corresponding to the current temperature based on the current temperature and the first function includes: determining the target background signal corresponding to each detection unit based on the first function corresponding to multiple adjacent subarrays of each detection unit in the detection unit array.
[0012] By merging adjacent detection units, the number of stored first functions can be reduced. During fingerprint detection, the target background signal corresponding to each detection unit can be determined based on the first functions corresponding to multiple subarrays adjacent to each detection unit.
[0013] In one implementation, the target background signal corresponding to each detection unit can be determined by interpolation calculations, such as coefficient interpolation or mean interpolation, based on the first function corresponding to the multiple adjacent subarrays of each detection unit. For example, determining the target background signal corresponding to each detection unit based on the first function corresponding to the adjacent subarrays of each detection unit in the detection unit array includes: performing interpolation calculations on the first function corresponding to each of the multiple adjacent subarrays of each detection unit to obtain the first function corresponding to each detection unit, and determining the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit; or, determining the target background signal corresponding to each of the multiple adjacent subarrays based on the first function corresponding to each of the multiple adjacent subarrays of each detection unit, and performing interpolation calculations on the target background signals corresponding to each of the multiple adjacent subarrays to obtain the target background signal corresponding to each detection unit.
[0014] In one implementation, the first function is a polynomial B(T) = P0 + P1 × T + P2 × T 2 +……+Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
[0015] In one implementation, the method further includes: receiving multiple background signals at multiple temperatures respectively; and performing fitting calculations based on the values of the multiple temperatures and the multiple background signals to obtain the polynomial B(T).
[0016] In one implementation, the method further includes: obtaining a second function representing the correspondence between temperature and flight time, wherein the flight time is the time elapsed from the emission of the ultrasonic signal to its reception; receiving multiple background signals at multiple temperatures includes: determining the flight time corresponding to each of the multiple temperatures based on the multiple temperatures and the second function; and receiving the multiple background signals at the multiple temperatures based on the flight time corresponding to each of the multiple temperatures.
[0017] Temperature also affects the time-of-flight of ultrasonic signals. In this embodiment, multiple time-of-flight intervals corresponding to multiple temperatures are determined according to a second function representing the relationship between temperature and time-of-flight. Background signals are then received at different temperatures based on the corresponding time-of-flight intervals. Since the time-of-flight intervals determined by the second function are temperature-matched, optimal background signals can be received. Furthermore, because the relationship between temperature and time-of-flight is represented by a function, the amount of data that needs to be stored is reduced. Simultaneously, the time-of-flight interval corresponding to any temperature can be obtained from the second function, making ultrasonic fingerprint detection more adaptable to temperature and more accurate.
[0018] In one implementation, the method further includes: when a finger presses the screen, determining a target time of flight corresponding to the current temperature based on the current temperature and the second function; receiving the ultrasonic fingerprint signal carrying the fingerprint information returned by the finger includes: receiving the ultrasonic fingerprint signal based on the target time of flight.
[0019] Since the ultrasonic fingerprint signal is received based on the target time of flight matched with the current temperature, both the background signal and the ultrasonic fingerprint signal are calibrated for temperature. By subtracting the ultrasonic fingerprint signal from the background signal, a clear fingerprint image can be obtained.
[0020] In one implementation, the second function is the polynomial F(T) = A0 + A1 × T + A2 × T 2 +……+An×T n T and F(T) are the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial.
[0021] In one implementation, the first function is stored in the memory of the electronic device, or in the one-time programmable OTP memory or electronic fuse EFUSE memory of the ultrasonic fingerprint device.
[0022] Secondly, an ultrasonic fingerprint device is provided, wherein the ultrasonic fingerprint device is disposed under the screen of an electronic device to realize under-screen ultrasonic fingerprint recognition, the ultrasonic fingerprint device comprising:
[0023] The processing module is configured to: acquire a first function representing the correspondence between temperature and a background signal, wherein the background signal is an ultrasonic signal without fingerprint information received when no finger is pressing the screen; acquire the current temperature when a finger presses the screen, and determine a target background signal corresponding to the current temperature based on the current temperature and the first function; and,
[0024] The detection module is used to emit ultrasonic signals to the finger and receive ultrasonic fingerprint signals carrying the fingerprint information returned by the finger, wherein the fingerprint image of the finger is obtained based on the difference between the ultrasonic fingerprint signal and the target background signal.
[0025] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, each of which corresponds to a multiple first functions. The processing module is specifically used to: determine the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit in the detection unit array.
[0026] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, the detection unit array including multiple sub-arrays, each sub-array corresponding to a multiple first function, and the processing module is specifically used to: determine the target background signal corresponding to each detection unit based on the first functions corresponding to multiple adjacent sub-arrays of each detection unit in the detection unit array.
[0027] In one implementation, the processing module is specifically used to: perform interpolation calculations on the first functions corresponding to the plurality of adjacent subarrays of each detection unit to obtain the first function corresponding to each detection unit, and determine the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit; or, determine the target background signal corresponding to each of the plurality of adjacent subarrays based on the first functions corresponding to the plurality of adjacent subarrays of each detection unit, and perform interpolation calculations on the target background signals corresponding to the plurality of adjacent subarrays to obtain the target background signal corresponding to each detection unit.
[0028] In one implementation, the first function is a polynomial B(T) = P0 + P1 × T + P2 × T 2 +……+Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
[0029] In one implementation, the detection module is further configured to: receive multiple background signals at multiple temperatures respectively; the processing module is further configured to: perform fitting calculations based on the values of the multiple temperatures and the multiple background signals to obtain the polynomial B(T).
[0030] In one implementation, the processing module is further configured to: obtain a second function representing the correspondence between temperature and flight time, wherein the flight time is the time elapsed from the transmission of the ultrasonic signal to its reception; the detection module is specifically configured to: determine the flight time corresponding to each of the plurality of temperatures based on the plurality of temperatures and the second function; and receive the plurality of background signals at the plurality of temperatures respectively based on the flight time corresponding to each of the plurality of temperatures.
[0031] In one implementation, the processing module is further configured to: determine a target flight time corresponding to the current temperature based on the current temperature and the second function when a finger presses the screen; the detection module is specifically configured to: receive the ultrasonic fingerprint signal based on the target flight time.
[0032] In one implementation, the second function is the polynomial F(T) = A0 + A1 × T + A2 × T 2 +……+An×T n T and F(T) are the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial.
[0033] In one implementation, the first function is stored in the memory of the electronic device, or in the one-time programmable OTP memory or electronic fuse EFUSE memory of the ultrasonic fingerprint device.
[0034] Thirdly, an electronic device is provided, comprising: a display screen; and an ultrasonic fingerprint device according to the second aspect or any possible implementation thereof, the ultrasonic fingerprint device being disposed below the display screen to achieve under-display ultrasonic fingerprint recognition. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the transmission of ultrasonic signals in a screen stack.
[0036] Figure 2 This is a schematic flowchart of an ultrasonic fingerprint recognition method according to an embodiment of this application.
[0037] Figure 3 This is a schematic diagram showing the correspondence between flight time and pixel value.
[0038] Figure 4 This is a schematic diagram of the process of obtaining the first function.
[0039] Figure 5 This is a schematic diagram of the B(T) curve obtained by fitting multiple background signals with multiple temperatures.
[0040] Figure 6 yes Figure 2 The diagram shows a possible flow of an ultrasonic fingerprint recognition method.
[0041] Figure 7 These are fingerprint images obtained under different conditions, with calibrated and uncalibrated flight times at different temperatures.
[0042] Figure 8 It is the function B corresponding to each detection unit. i,j One possible way to store (T).
[0043] Figure 9 This is a schematic diagram of merging adjacent detection units.
[0044] Figure 10 This is a schematic diagram of interpolation between adjacent detection units.
[0045] Figure 11 This is a schematic block diagram of an ultrasonic fingerprint device according to an embodiment of this application. Detailed Implementation
[0046] The technical solutions in this application will now be described with reference to the accompanying drawings.
[0047] Ultrasonic fingerprint recognition can be considered a type of under-display fingerprint (UDF). Figure 1 The transmission of ultrasonic signals in the screen stack is shown, such as Figure 1 As shown, the ultrasonic fingerprint device 3 is positioned below the screen 1. For example, the stacked layers of screen 1 include an upper cover plate 101, a polarizer 102, a quarter-glass slide 103, an OLED light-emitting layer 104, and a lower cover plate 105. The transmitted signal (TX signal) of the ultrasonic fingerprint device 3 needs to pass through the stacked layers of screen 1 to reach the finger 2 above screen 1. After being reflected or scattered on the surface of finger 2, it passes through the stacked layers of screen 1 again and returns to the ultrasonic fingerprint device 3. Due to the difference in reflectivity of the fingerprint valleys and ridges of finger 2 to sound waves, the received signal (RX signal) carries the fingerprint information of the finger. The data collected by the ultrasonic fingerprint device 3 at this time is called raw data. In addition, the RX signal also includes the background signal reflected back from the stacked layers of screen 1. When no finger 2 is pressing on screen 1, the RX signal is the background signal; the data collected by the ultrasonic fingerprint device 3 at this time is called base data. Subtracting the raw data from the base data yields a clear fingerprint image.
[0048] The detection electrode in the ultrasonic fingerprint device 3 is affected by temperature, and the signal strength it receives drifts with temperature changes. This means the base data drifts with temperature, reducing the signal-to-noise ratio of the fingerprint image. For example, in mobile devices such as mobile phones, wearable devices, tablets, and computers, the ambient temperature often varies significantly, and real-time base data acquisition is not possible. To ensure a satisfactory unlocking experience for users, it is necessary to maintain fingerprint recognition rates at different temperatures; therefore, temperature drift calibration of the base data is required.
[0049] Therefore, this application provides an ultrasonic fingerprint recognition method that uses a first function representing the correspondence between temperature and background signal to calibrate the background signal, thereby reducing the influence of temperature on ultrasonic fingerprint detection.
[0050] Figure 3 This is a schematic flowchart illustrating an ultrasonic fingerprint recognition method according to an embodiment of this application. Method 100 is executed by an ultrasonic fingerprint device 3, which is disposed below the screen 1 of an electronic device to achieve under-screen ultrasonic fingerprint recognition. Figure 3 As shown, method 100 includes some or all of the following steps.
[0051] In step 110, a first function is obtained to represent the correspondence between temperature and background signal.
[0052] In step 120, when a finger presses the screen, the current temperature is obtained, and the target background signal corresponding to the current temperature is determined based on the current temperature and the first function.
[0053] In step 130, an ultrasonic signal is emitted to the finger, and an ultrasonic fingerprint signal carrying fingerprint information is received from the finger.
[0054] The background signal is an ultrasonic signal that does not carry fingerprint information and is received when no finger is pressing the screen. The ultrasonic fingerprint signal includes an effective signal carrying fingerprint information and a background signal. By subtracting the ultrasonic fingerprint signal from the background signal, the fingerprint information of the finger can be obtained. The background signal is a target background signal corresponding to the current temperature.
[0055] It should be understood that Raw Data can be obtained by processing the ultrasonic fingerprint signal, and Base Data can be obtained by processing the background signal. Subtracting the ultrasonic fingerprint signal from the background signal is equivalent to subtracting the Raw Data from the Base Data.
[0056] In this embodiment, during ultrasonic fingerprint recognition, a target background signal corresponding to the current temperature is determined based on a first function representing the correspondence between temperature and background signal. After transmitting an ultrasonic signal to the finger and receiving the ultrasonic fingerprint signal carrying fingerprint information returned by the finger, a fingerprint image of the finger is obtained based on the target background signal and the ultrasonic fingerprint signal. Since the target background signal determined by the first function matches the current temperature, when it is subtracted from the ultrasonic fingerprint signal to cancel out the background signal carried in the ultrasonic fingerprint signal, excessive signal attenuation can be avoided, ensuring the clarity of the fingerprint image and reducing the impact of temperature on ultrasonic fingerprint detection. Furthermore, since this application represents the correspondence between temperature and background signal through a function, the amount of data that needs to be stored is reduced. At the same time, the background signal corresponding to any temperature can be obtained according to the function, making ultrasonic fingerprint detection more adaptable to temperature and more accurate.
[0057] The first function used to represent the relationship between temperature and flight time can be implemented in various forms. For example, the first function can be a polynomial B(T) = P0 + P1 × T + P2 × T 2 +……+Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
[0058] The first function may be stored, for example, in the memory of an electronic device; or in a one-time programmable (OTP) memory or an electronic fuse (EFUSE) memory in the ultrasonic fingerprint device 3.
[0059] The first function B(T) can be obtained by fitting the sample data. For example, method 100 further includes: receiving multiple background signals at multiple temperatures respectively; and performing fitting calculations based on the values of the multiple temperatures and multiple background signals to obtain the polynomial B(T).
[0060] After obtaining the correspondence between temperature and background signal, multiple temperatures and their corresponding background signals are used as sample data, and a polynomial B(T) is obtained by fitting the data. The richer the sample data, the more accurate the fitted polynomial B(T). To obtain the best sample data, in some implementations, when receiving multiple background signals at multiple temperatures, it is necessary to calibrate the flytime used to receive the background signals based on the temperature, i.e., the time it takes for the ultrasonic signal to travel from transmission to reception.
[0061] Specifically, since the speed of sound is also affected by temperature, the flight time of the ultrasonic signal drifts with temperature changes. By configuring the flight time of the ultrasonic signal in the ultrasonic fingerprint device 3, the received signal can be optimized. For example, as... Figure 3 As shown, the horizontal axis represents the time-of-flight, and the vertical axis represents the pixel value of the fingerprint image. The ultrasonic signal in the ultrasonic fingerprint device 3 typically varies according to a sine or cosine law, with a pulse period of T. When the ultrasonic fingerprint device 3 receives the signal, it needs to integrate a segment of the signal within the pulse period T, for example, integrating a segment of the signal within a time interval T / 2 between the peak and trough. When temperature changes cause changes in the speed of sound, if the time-of-flight is not calibrated, the ultrasonic fingerprint device 3 may start integrating the signal from different positions when performing fingerprint recognition at different temperatures, resulting in different signal quantities received by the ultrasonic fingerprint device 3 at different temperatures. Figure 3 The relationship between pixel values and time of flight is shown. The ultrasonic fingerprint device 3 receives signals at temperature T1 according to time of flight FCP1. The final integrated signal is... Figure 2 The segment from point A to point B represents time T / 2; the ultrasonic fingerprint device 3 receives the signal at temperature T2 according to time-of-flight FCP2, then the final integrated signal is Figure 1 The T / 2 time interval is shown from point C to point D. Typically, fingerprint recognition aims to integrate this T / 2 time interval (peak to trough or trough to peak) to maximize the received signal. If the temperature at which the ultrasonic fingerprint signal is received differs from the temperature at which the background signal is received, the flight time will also differ. This can introduce more aliasing during the difference between Raw Data and Base Data, leading to signal attenuation and affecting the clarity of the fingerprint image. Therefore, the flight time needs to be calibrated for different temperature environments to optimize signal reception and improve fingerprint image clarity.
[0062] In one implementation, method 100 further includes: obtaining a second function representing the correspondence between temperature and flight time; wherein receiving multiple background signals at multiple temperatures includes: determining the flight time corresponding to each of the multiple temperatures based on the multiple temperatures and the second function; and receiving multiple background signals at the multiple temperatures based on the flight time corresponding to each of the multiple temperatures.
[0063] In this embodiment, multiple flight times corresponding to multiple temperatures are determined according to a second function representing the correspondence between temperature and flight time, and background signals are received at different temperatures based on the corresponding flight times. Since the flight time determined by the second function is temperature-matched, optimal background signals can be received; furthermore, because the correspondence between temperature and flight time is represented by a function, the amount of data that needs to be stored is reduced, and the flight time corresponding to any temperature can be obtained according to the second function, making ultrasonic fingerprint detection more adaptable to temperature and more accurate.
[0064] In one implementation, method 100 further includes: when a finger presses the screen, determining a target flight time corresponding to the current temperature based on the current temperature and a second function; wherein, in step 130, receiving an ultrasonic fingerprint signal carrying fingerprint information returned by the finger includes: receiving the ultrasonic fingerprint signal based on the target flight time.
[0065] Since it's impossible to predict when a user will perform fingerprint recognition, background signals cannot be acquired in real time. Therefore, the background signal used for current fingerprint recognition is a pre-acquired background signal, such as pre-stored background signals corresponding to different temperatures. During fingerprint recognition, a target background signal corresponding to the current temperature T is determined based on the current temperature T and a first function, and a target time-of-flight corresponding to the current temperature T is determined based on a second function. The ultrasonic fingerprint signal is then received based on this target time-of-flight. Since both the target time-of-flight used to receive the ultrasonic fingerprint signal and the time-of-flight used to acquire the target background signal corresponding to temperature T are calibrated based on temperature T, a clear fingerprint image can be obtained by subtracting the raw data from the base data.
[0066] In other words, the purpose of calibrating the flight time based on temperature is to ensure that the ultrasonic fingerprint signal received at the current temperature T and the background signal corresponding to the current temperature T are both segments of the ultrasonic signal at the same position, thereby avoiding signal attenuation caused by the difference between Raw Data and Base Data and ensuring the clarity of the fingerprint image.
[0067] For example, when the ultrasonic fingerprint device 3 receives a signal based on the calibrated time of flight, the time of flight ensures that the received signal of the ultrasonic fingerprint device 3 at different temperatures includes the signal quantity corresponding to the peak and trough. That is, the ultrasonic fingerprint device 3 integrates the signal quantity between the peak and trough or between the trough and the peak, thereby maximizing the signal quantity of the ultrasonic fingerprint signal received by the ultrasonic fingerprint device 3.
[0068] The second function used to represent the relationship between temperature and flight time can be implemented in various forms. For example, the second function can be a polynomial F(T) = A0 + A1 × T + A2 × T 2 +……+An×T n T and F(T) represent the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial. Based on the current temperature T, the corresponding flight time F(T) can be calculated. The second function can be stored, for example, in the memory of an electronic device; or in the OTP memory or EFUSE memory of the ultrasonic fingerprint device 3.
[0069] The second function F(T) can be obtained by fitting sample data. For example, multiple flight times corresponding to multiple temperatures can be obtained, and the polynomial F(T) can be obtained by fitting the multiple temperatures and multiple flight times.
[0070] In other words, when obtaining the correspondence between temperature and flight time, the correspondence between flight time and received signal, as well as the correspondence between temperature and received signal, can be obtained in advance. Then, based on multiple signal values received at multiple flight times and multiple signal values received at multiple temperatures, the correspondence between multiple temperatures and multiple flight times can be determined. By using multiple temperatures and their corresponding multiple flight times as sample data and fitting them, a polynomial F(T) can be obtained.
[0071] Figure 4 The process of obtaining the first function is illustrated. As an example, the ultrasonic fingerprint device 3, which is attached to the screen 1, can be placed in a temperature-controlled chamber. Assume the temperature range of the chamber is [-20℃, 50℃], the humidity is 40%, and the temperature change amount STEP = 5℃. Figure 4 As shown, the process may include the following steps.
[0072] In step 101, the flight time is corrected according to the first function.
[0073] For example, the flight time corresponding to a given temperature can be determined based on the temperature and the stored polynomial F(T).
[0074] In step 102, a background signal is received based on the flight time.
[0075] In step 103, it is determined whether the temperature has reached 50°C.
[0076] If the temperature does not reach 50°C, proceed to step 140; if the temperature reaches 50°C, proceed to step 105.
[0077] In step 104, the temperature of the incubator is adjusted based on STEP = 5°C.
[0078] In step 105, a first function, such as a polynomial B(T), is fitted based on the correspondence between multiple temperatures and multiple background signals, and then stored. It should be understood that in this embodiment, the storage of the first and second functions can be either direct storage of the polynomial B(T) or F(T), or storage of the coefficients in B(T) and F(T).
[0079] Figure 5 The diagram shows a polynomial B(T) curve calculated by fitting multiple background signals to multiple temperatures. The horizontal axis represents temperature, and the vertical axis represents the mean of the base data. Since most screens use a similar layered structure, the correspondence between the base data and temperature can be represented by B(T). For example, based on... Figure 5 The sample points shown in the figure are fitted to obtain B(T) with a degree m = 6. The degrees of the constant term and each of the multiple terms are P0 = 10720, P1 = 132.2, P2 = -4.2507, P3 = -0.3729, P4 = 0.0067, P5 = 0.0001, and P6 = 0.000002, respectively. That is, B(T) = 10720 + 132.2 × T - 4.2507 × T 2 -0.3729×T 3 +0.0067×T 4 +0.0001×T 5 +0.000002×T 6 When performing fingerprint recognition, if the current temperature T is detected, the current temperature T is substituted into B(T) to obtain the Base Data corresponding to the current temperature T. By subtracting the Raw Data from the Base Data, a clear fingerprint image can be obtained.
[0080] The polynomial B(T) can be obtained before the mass production of the ultrasonic fingerprint device 3 and stored in the ultrasonic fingerprint device 3 or electronic device. When the ultrasonic fingerprint device 3 performs fingerprint recognition, B(T) can be directly called to obtain the target background data corresponding to the current temperature. Furthermore, the ultrasonic fingerprint device 3 can also correct B(T), for example, by correcting the coefficients in B(T) based on a certain period or event trigger.
[0081] Figure 6 It shows Figure 2 The illustrated method represents one possible procedure for ultrasonic fingerprint recognition. Figure 6 As shown, the process may include the following steps.
[0082] In step 201, B(T) and F(T) are obtained.
[0083] In step 202, it is detected whether a finger is pressing on screen 1.
[0084] Specifically, if it is determined that a finger is pressing on screen 1, step 103 is executed; otherwise, the process continues to wait for the finger to press on screen 1.
[0085] In step 203, the temperature information detected by the temperature sensor is read.
[0086] In step 204, the corresponding target background signal is determined based on the current temperature and B(T).
[0087] In step 205, the corresponding target flight time is determined based on the current temperature and F(T).
[0088] In step 206, the ultrasonic fingerprint signal is received based on the target time of flight.
[0089] Specifically, the ultrasonic detection device 3 emits an ultrasonic signal to the finger above the screen 1, and immediately begins to receive the ultrasonic fingerprint signal returned by the finger after the target flight time, until all ultrasonic fingerprint signals within the predetermined time period have been received.
[0090] In step 207, a fingerprint image is obtained based on the ultrasonic fingerprint signal and the target background signal.
[0091] B(T) is obtained by fitting the correspondence between multiple temperatures and multiple background signals based on the calibrated flight time. Thus, the target background signal is the background signal corresponding to the current temperature. Meanwhile, the ultrasonic fingerprint signal is received based on the target flight time corresponding to the temperature. Therefore, the fingerprint image obtained based on the ultrasonic fingerprint signal and the target background signal is clearer.
[0092] For example, Figure 7 The images show fingerprint images obtained at different temperatures with and without background signal calibration using the method described above. The first row, from left to right, shows fingerprint images obtained without background signal calibration at -20℃, 0℃, 20℃, 30℃, and 50℃; the second row, from left to right, shows fingerprint images obtained with background signal calibration using the method described above at -20℃, 0℃, 20℃, 30℃, and 50℃. It can be seen that with background signal calibration, the fingerprint image quality is significantly improved, and the fingerprint image is clearer.
[0093] The ultrasonic fingerprint device 3 typically includes an array of detection units consisting of multiple detection units, where the background signal received by each detection unit changes similarly with respect to temperature. Further, the detection unit array can be divided into multiple subarrays, such as 2×2 subarrays, 3×3 subarrays, or 4×4 subarrays, etc. Embodiments of this application provide two methods for determining the target background signal corresponding to each detection unit. Based on the target background signal corresponding to each detection unit and the ultrasonic fingerprint signal received by that detection unit, the pixel value of that detection unit can be obtained.
[0094] In Method 1, multiple detection units can correspond to multiple first functions respectively. In this case, in step 120, the target background signal corresponding to the current temperature is determined according to the current temperature and the first function, including: determining the target background signal corresponding to each detection unit according to the first function corresponding to each detection unit in the detection unit array.
[0095] In Method 2, to reduce the number of stored first functions, multiple subarrays correspond to multiple first functions. In this case, in step 120, the target background signal corresponding to the current temperature is determined based on the current temperature and the first functions. This includes determining the target background signal corresponding to each detection unit based on the first functions corresponding to multiple adjacent subarrays of each detection unit in the detection unit array. By binning adjacent detection units, the number of stored first functions is reduced. During fingerprint detection, the target background signal corresponding to each detection unit can be determined based on the first functions corresponding to multiple adjacent subarrays.
[0096] For example, interpolation calculations are performed on the first functions corresponding to multiple adjacent subarrays of each detection unit to obtain the first function corresponding to each detection unit, and the target background signal corresponding to each detection unit is determined based on the first function corresponding to each detection unit.
[0097] For example, based on the first function corresponding to each of the multiple adjacent subarrays of each detection unit, the target background signal corresponding to each of the multiple adjacent subarrays is determined, and interpolation calculation is performed on the target background signal corresponding to each of the multiple adjacent subarrays to obtain the target background signal corresponding to each detection unit.
[0098] The following, combined with Figures 8 to 10 The description details how the target background signal corresponding to each detection unit is obtained according to method 2. The ultrasonic fingerprint device 3 includes an array of M rows × M columns of detection units. This detection unit array includes M / N subarrays, and each subarray consists of N rows × N columns of detection units. Figure 8 The first function B corresponding to each detection unit is shown. i,j(T) is a possible storage method, where i and j are the row and column positions of the detection unit in the detection unit array, respectively, T is the temperature, and B is the value of temperature. i,j (T)=p 0(i,j) +p 1(i,j) ×T+p 2(i,j) ×T 2 +….+p (n-1)(i,j) ×T n-1 +p n(i,j) ×T n , Figure 8 The number of matrices in the middle is equal to B i,j The total number of constant terms and coefficients of higher-order terms that need to be stored in (T) is taken as an example of n+1 matrices, corresponding to B respectively. i,j The constant term and coefficients of the n higher-order terms in (T).
[0099] To save storage space, adjacent pixels are binning to reduce B. i,j (T) or B i,j The number of coefficients stored in (T). For example... Figure 9 As shown, each N rows × N columns of detection units form a subarray. Figure 9 The subarray is represented by a black dot, forming M / N rows × M / N columns.
[0100] In practical applications, the target background signal corresponding to each detection unit can be determined based on the first function corresponding to each subarray adjacent to each detection unit. For example, the background signal corresponding to each detection unit can be determined by using the first function corresponding to each of the multiple subarrays adjacent to each detection unit through interpolation or other methods. Figure 10 As shown, when calculating the target background signal of the detection unit in the i-th row and j-th column, the four subarrays adjacent to this detection unit are subarray A, subarray B, subarray C, and subarray D. The first function B corresponding to this detection unit... i,j The coefficient p of the linear term in (T) 1(i,j) For example, the coefficients of the constant term and other terms are calculated similarly. If the coefficients of the first-order terms in the first function corresponding to subarrays A, B, C, and D are Q1, Q2, Q3, and Q4 respectively, then p 1(i,j)= k1×Q1+k2×Q2+k3×Q3+k4×Q4, where k1, k2, k3, and k4 are the interpolated values obtained by interpolating the coefficients of the first term in the first function corresponding to subarrays A, B, C, and D, respectively. k1, k2, k3, and k4 are related to the distance or area formed between the detection unit and subarrays A, B, C, and D, respectively. For example, if k1+k2+k3+k4=1, the detection unit is closest to subarray A and forms the smallest area, so k1 is the smallest; the detection unit is farthest from subarray D and forms the largest area, so k4 is the smallest. After obtaining all coefficients in a similar manner, the first function B corresponding to the detection unit can be determined. i,j (T).
[0101] When a finger is detected pressing on screen 1, the ultrasonic fingerprint signal is received, and the corresponding B for each detection unit is calculated based on the current temperature T. i,j (T) is obtained, and the target background signal corresponding to the detection unit is obtained. Based on the background signal and the received ultrasonic fingerprint signal of the finger, the fingerprint image of the finger can be obtained.
[0102] For temperatures outside the temperature range, such as [-20℃, 50℃] mentioned above, it can be determined by adjusting B. i,j (T) is used to expand the target background signal, for example, Taylor expansion.
[0103] Of course, multiple background signals can also be determined based on the first function corresponding to each of the multiple adjacent subarrays of the detection unit, and the target background signal of the detection unit can be calculated based on the multiple background signals corresponding to the multiple adjacent subarrays. That is, Q1, Q2, Q3 and Q4 mentioned above can also be replaced by the background signals calculated by subarray A, subarray B, subarray C and subarray D based on their respective first functions.
[0104] This application also provides an ultrasonic fingerprint device, such as Figure 11 As shown, the ultrasonic fingerprint device 3 is located below the screen 1 of the electronic device to realize under-screen ultrasonic fingerprint recognition. The ultrasonic fingerprint device 3 includes a processing module 310 and a detection module 320.
[0105] Processing module 310 is configured to acquire a first function representing the correspondence between temperature and a background signal, wherein the background signal is an ultrasonic signal without fingerprint information received when no finger is pressing the screen; when a finger presses the screen, it acquires the current temperature and determines a target background signal corresponding to the current temperature based on the current temperature and the first function; and,
[0106] The detection module 320 is used to emit an ultrasonic signal to the finger and receive an ultrasonic fingerprint signal carrying the fingerprint information returned by the finger, wherein the fingerprint image of the finger is obtained based on the difference between the ultrasonic fingerprint signal and the target background signal.
[0107] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, each of which corresponds to a multiple first function. The processing module 310 is specifically used to: determine the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit in the detection unit array.
[0108] In one implementation, the ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, the detection unit array including multiple subarrays, each subarray corresponding to a multiple first function, and the processing module 310 is specifically used to: determine the target background signal corresponding to each detection unit based on the first functions corresponding to multiple adjacent subarrays of each detection unit in the detection unit array.
[0109] In one implementation, the processing module 310 is specifically used to: perform interpolation calculations on the first functions corresponding to the plurality of adjacent subarrays of each detection unit to obtain the first function corresponding to each detection unit, and determine the target background signal corresponding to each detection unit based on the first function corresponding to each detection unit; or, determine the target background signal corresponding to each of the plurality of adjacent subarrays based on the first functions corresponding to the plurality of adjacent subarrays of each detection unit, and perform interpolation calculations on the target background signals corresponding to the plurality of adjacent subarrays to obtain the target background signal corresponding to each detection unit.
[0110] In one implementation, the first function is a polynomial B(T) = P0 + P1 × T + P2 × T 2 +……+Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
[0111] In one implementation, the detection module 320 is further configured to: receive multiple background signals at multiple temperatures respectively; the processing module 310 is further configured to: perform fitting calculations based on the values of the multiple temperatures and the multiple background signals to obtain the polynomial B(T).
[0112] In one implementation, the processing module 310 is further configured to: acquire a second function representing the correspondence between temperature and flight time, wherein the flight time is the time elapsed from the transmission of the ultrasonic signal to its reception; the detection module 320 is specifically configured to: determine the flight time corresponding to each of the plurality of temperatures based on the plurality of temperatures and the second function; and receive the plurality of background signals at the plurality of temperatures respectively based on the flight time corresponding to each of the plurality of temperatures.
[0113] In one implementation, the processing module 310 is further configured to: determine a target flight time corresponding to the current temperature based on the current temperature and the second function when a finger presses the screen; the detection module 320 is specifically configured to: receive the ultrasonic fingerprint signal based on the target flight time.
[0114] In one implementation, the second function is the polynomial F(T) = A0 + A1 × T + A2 × T 2 +……+An×T n T and F(T) are the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial.
[0115] In one implementation, the first function is stored in the memory of the electronic device, or in the OTP memory or EFUSE memory of the ultrasonic fingerprint device.
[0116] This application also provides an electronic device, which includes a display screen 1 and an ultrasonic fingerprint device 3 as described in any of the above embodiments. The ultrasonic fingerprint device 3 is disposed below the display screen 1 to realize under-display ultrasonic fingerprint recognition.
[0117] By way of example and not limitation, the electronic devices in this application can be portable or mobile computing devices such as terminal devices, mobile phones, tablets, laptops, desktop computers, gaming devices, in-vehicle electronic devices, or wearable smart devices, as well as other electronic devices such as electronic databases, automobiles, and automated teller machines (ATMs). The wearable smart devices include fully functional, large-sized devices that can achieve complete or partial functionality without relying on a smartphone, such as smartwatches or smart glasses, as well as devices that focus on only a specific type of application function and require cooperation with other devices such as smartphones, such as various smart bracelets and smart jewelry for vital sign monitoring.
[0118] It should be noted that, without conflict, the various embodiments and / or technical features described in this application can be arbitrarily combined with each other, and the resulting technical solutions should also fall within the protection scope of this application.
[0119] The systems, apparatuses, and methods disclosed in the embodiments of this application can be implemented in other ways. For example, some features of the method embodiments described above can be ignored or not performed. The apparatus embodiments described above are merely illustrative, and the division of units is only a logical functional division. In actual implementation, there may be other division methods, and multiple units or components may be combined or integrated into another system. In addition, the coupling between units or between components can be direct coupling or indirect coupling, including electrical, mechanical, or other forms of connection.
[0120] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process and technical effects of the above-described apparatus and equipment can be referred to the corresponding processes and technical effects in the foregoing method embodiments, and will not be repeated here.
[0121] It should be understood that the specific examples in the embodiments of this application are only for the purpose of helping those skilled in the art to better understand the embodiments of this application, and are not intended to limit the scope of the embodiments of this application. Those skilled in the art can make various improvements and modifications based on the above embodiments, and all such improvements or modifications fall within the protection scope of this application.
[0122] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A method for ultrasonic fingerprint recognition, characterized in that, Performed by an ultrasonic fingerprint device disposed under the screen of an electronic device to achieve under-screen ultrasonic fingerprint recognition, the method includes: Obtain a first function to represent the correspondence between temperature and a background signal, wherein the background signal is an ultrasonic signal without fingerprint information received when no finger is pressing the screen; When a finger presses the screen, the current temperature is acquired, and a target background signal corresponding to the current temperature is determined based on the current temperature and the first function. An ultrasonic signal is emitted to the finger, and an ultrasonic fingerprint signal carrying the fingerprint information is received from the finger, wherein the fingerprint image of the finger is obtained based on the difference between the ultrasonic fingerprint signal and the target background signal; The ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, the detection unit array including multiple sub-arrays, each sub-array corresponding to a multiple first function. The step of determining the target background signal corresponding to the current temperature based on the current temperature and the first function includes: Interpolation calculations are performed on the first functions corresponding to the multiple adjacent subarrays of each of the plurality of detection units to obtain the first function corresponding to each detection unit. Based on the first function corresponding to each detection unit, the target background signal corresponding to each detection unit is determined. The first function corresponding to each detection unit is related to the following parameters: the distance between each detection unit and its multiple adjacent subarrays or the area formed therein.
2. The method according to claim 1, characterized in that, The first function is the polynomial B(T) = P0 + P1×T + P2×T 2 +……+ Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
3. The method according to claim 2, characterized in that, The method further includes: Multiple background signals are received at multiple temperatures respectively; Based on the values of the multiple temperatures and the multiple background signals, a fitting calculation is performed to obtain the polynomial B(T).
4. The method according to claim 3, characterized in that, The method further includes: Obtain a second function to represent the correspondence between temperature and flight time, where the flight time is the time elapsed from the transmission of the ultrasonic signal to its reception. The method of receiving multiple background signals at multiple temperatures includes: Based on the plurality of temperatures and the second function, the flight time corresponding to each of the plurality of temperatures is determined; The plurality of background signals are received at the plurality of temperatures respectively, based on the flight time corresponding to each of the plurality of temperatures.
5. The method according to claim 4, characterized in that, The method further includes: When a finger presses the screen, the target flight time corresponding to the current temperature is determined based on the current temperature and the second function; Receiving the ultrasonic fingerprint signal carrying the fingerprint information returned by the finger includes: The ultrasonic fingerprint signal is received based on the target flight time.
6. The method according to claim 4, characterized in that, The second function is the polynomial F(T) = A0 + A1×T + A2×T 2 +……+ An×T n T and F(T) are the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial.
7. The method according to any one of claims 1 to 6, characterized in that, The first function is stored in the memory of the electronic device, or in the one-time programmable OTP memory or electronic fuse EFUSE memory of the ultrasonic fingerprint device.
8. An ultrasonic fingerprint device, characterized in that, The ultrasonic fingerprint device is disposed under the screen of the electronic device to achieve under-screen ultrasonic fingerprint recognition. The ultrasonic fingerprint device includes: The processing module is configured to: acquire a first function representing the correspondence between temperature and a background signal, wherein the background signal is an ultrasonic signal without fingerprint information received when no finger is pressing the screen; acquire the current temperature when a finger presses the screen, and determine a target background signal corresponding to the current temperature based on the current temperature and the first function; and, The detection module is used to emit ultrasonic signals to the finger and receive ultrasonic fingerprint signals carrying the fingerprint information returned by the finger, wherein the fingerprint image of the finger is obtained based on the difference between the ultrasonic fingerprint signal and the target background signal; The ultrasonic fingerprint device includes a detection unit array composed of multiple detection units, the detection unit array including multiple sub-arrays, each sub-array corresponding to a multiple first function, and the processing module is specifically used for: Interpolation calculations are performed on the first functions corresponding to the multiple adjacent subarrays of each of the plurality of detection units to obtain the first function corresponding to each detection unit. Based on the first function corresponding to each detection unit, the target background signal corresponding to each detection unit is determined. The first function corresponding to each detection unit is related to the following parameters: the distance between each detection unit and its multiple adjacent subarrays or the area formed therein.
9. The ultrasonic fingerprint device according to claim 8, characterized in that, The first function is the polynomial B(T) = P0 + P1 × T + P2 × T 2 +……+ Pm×T m T and B(T) are the temperature and its corresponding background signal, respectively. P0 is the constant term of the polynomial, P1 to Pm are the coefficients of the polynomial, and m is the degree of the polynomial.
10. The ultrasonic fingerprint device according to claim 9, characterized in that, The detection module is also used to: receive multiple background signals at multiple temperatures respectively; The processing module is further configured to: perform fitting calculations based on the values of the plurality of temperatures and the plurality of background signals to obtain the polynomial B(T), and determine the first function based on the polynomial B(T).
11. The ultrasonic fingerprint device according to claim 10, characterized in that, The processing module is also used for: Obtain a second function to represent the correspondence between temperature and flight time, where the flight time is the time elapsed from the transmission of the ultrasonic signal to its reception. The detection module is specifically used for: Based on the plurality of temperatures and the second function, the flight time corresponding to each of the plurality of temperatures is determined; The plurality of background signals are received at the plurality of temperatures respectively, based on the flight time corresponding to each of the plurality of temperatures.
12. The ultrasonic fingerprint device according to claim 11, characterized in that, The processing module is also used for: When a finger presses the screen, the target flight time corresponding to the current temperature is determined based on the current temperature and the second function; The detection module is specifically used for: The ultrasonic fingerprint signal is received based on the target flight time.
13. The ultrasonic fingerprint device according to claim 11, characterized in that, The second function is the polynomial F(T) = A0 + A1×T + A2×T 2 +……+ An×T n T and F(T) are the temperature and its corresponding flight time, respectively. A0 is the constant term of the polynomial, A1 to An are the coefficients of the polynomial, and n is the degree of the polynomial.
14. The ultrasonic fingerprint device according to any one of claims 8 to 13, characterized in that, The first function is stored in the memory of the electronic device, or in the one-time programmable OTP memory or electronic fuse EFUSE memory of the ultrasonic fingerprint device.
15. An electronic device, characterized in that, include: Display screen; as well as, According to any one of claims 8 to 14, the ultrasonic fingerprint device is disposed below the display screen to realize under-screen ultrasonic fingerprint recognition.