Fingerprint detection device, fingerprint detection device control method, and electronic device

Abstract

The present invention relates to the technical field of fingerprint recognition, and particularly to a fingerprint detection device, a control method for the fingerprint detection device, and an electronic device. The fingerprint detection device includes: a display layer and a lower layer, and the lower layer includes: a liquid crystal microlens array layer for separating reflected light at different angles, the liquid crystal microlens array layer including a plurality of liquid crystal microlens units arranged in an array; a collimator layer located on a side of the liquid crystal lens array layer away from the display layer, the collimator layer being configured to collimate the reflected light, the collimator layer including a micropore array layer, the micropore array layer being provided with small holes corresponding to the liquid crystal microlens units one by one; an image sensor for sensing the collimated reflected light; and the focal length of the liquid crystal microlens unit is configured to enable the total characteristic signal-to-noise ratio of the display layer and the lower layer to meet a first condition. The present invention can always maintain the total characteristic signal-to-noise ratio of the display layer and the lower layer at a relatively high level.

Description

Technical Field

[0001] The present invention relates to the technical field of fingerprint recognition, and in particular, to a fingerprint detection device, a control method for the fingerprint detection device, and an electronic device. Background Art

[0002] The under-display fingerprint recognition technology integrates a fingerprint sensor under the display screen. Since there are certain intervals between the pixels of the display screen, these intervals form light leakage areas, so that light can be guaranteed to pass through the display screen. When a user touches the screen with a finger, the screen can emit light to illuminate the finger area, and the reflected light illuminating the fingerprint passes through the gaps between the screen pixels and returns to the image sensor closely attached under the display screen. Fingerprints include ridge areas and valley areas. Since the fingerprint tissue in the ridge areas absorbs light, the light reflected from the ridges will become darker; the light reflected from the valleys is relatively brighter. Therefore, the brightness difference generated by the ridges and valleys can form a fingerprint pattern on the image sensor. The fingerprint sensor set under the display screen precisely realizes the recognition of under-display fingerprints by detecting the reflected light carrying the user's fingerprint information.

[0003] Currently, in fingerprint recognition, a collimator layer is used to collimate the reflected light carrying fingerprint information, so that the reflected light collimated by the collimator layer and reaching the image sensor has a fingerprint area and an imaging area that are basically the same. At the same time, a microlens layer is used to separate the reflected light at different angles. Although the foregoing solutions all help to improve the total characteristic signal-to-noise ratio of the display layer and the underlying layers, the total characteristic signal-to-noise ratio of the display layer and the underlying layers decreases due to the microlens array being easily affected by the environment. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a fingerprint detection device, a control method for the fingerprint detection device, and an electronic device, so as to solve the technical problem that the existing fingerprint recognition technology cannot ensure that the total characteristic signal-to-noise ratio of the display layer and the underlying layers always remains at a high level after changes in the external environment.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a fingerprint detection device, including:

[0007] A display layer and a lower layer, where the lower layer includes:

[0008] A liquid crystal microlens array layer for separating reflected light at different angles, and the liquid crystal microlens array layer includes a plurality of liquid crystal microlens units distributed in an array;

[0009] A collimator layer, located on the side of the liquid crystal lens array layer away from the display layer, for collimating the reflected light. The collimator layer includes a microporous array layer, and the microporous array layer is provided with small holes corresponding to the liquid crystal microlens units one by one;

[0010] An image sensor for sensing the collimated reflected light;

[0011] The focal length of the liquid crystal microlens unit is configured such that the total characteristic signal-to-noise ratio of the display layer and the lower layer satisfies a first condition.

[0012] Preferably, the liquid crystal microlens array layer includes a first substrate, a first electrode layer, an insulating layer, a second electrode layer, a liquid crystal layer, a third electrode layer, and a second substrate layer arranged in sequence from the display layer towards the image sensor. The first electrode layer is a transparent electrode layer, and the second electrode layer includes light-passing holes arranged in an array.

[0013] Preferably, it further includes a first microlens array layer, which is located on the side of the liquid crystal microlens array layer away from the display layer or on the side close to the display layer.

[0014] Preferably, it further includes a polarization element, which is located in the optical path from the display screen to the liquid crystal lens array layer.

[0015] Preferably, the image sensor is a pixelated image sensor.

[0016] Preferably, the cross-section of the small hole is elliptical.

[0017] Preferably, the first condition is that the total characteristic signal-to-noise ratio of the display layer and the lower layer is the largest.

[0018] Preferably, the first condition is that the total characteristic signal-to-noise ratio of the display layer and the lower layer is greater than a first threshold.

[0019] In a second aspect, the present invention further provides a control method for a fingerprint detection device, and the method includes the following steps:

[0020] S1: Adjust the focal length of the liquid crystal microlens unit to obtain the total characteristic signal-to-noise ratio of the display layer and the lower layer at different focal lengths;

[0021] S2: Select the largest total characteristic signal-to-noise ratio as the target total characteristic signal-to-noise ratio;

[0022] S3: Obtain the focal length corresponding to the target total characteristic signal-to-noise ratio as the focal length of the liquid crystal microlens unit.

[0023] In a third aspect, the present invention further provides another control method for a fingerprint detection device, and the method includes the following steps:

[0024] S01: Obtain the first threshold value;

[0025] S02: Obtain the total characteristic signal-to-noise ratio of the current display layer and the lower layer of the liquid crystal microlens unit;

[0026] S03: Compare the total characteristic signal-to-noise ratio of the current display layer and the lower layer with the first threshold value;

[0027] S04: If the total characteristic signal-to-noise ratio of the current display layer and the lower layer is less than the first threshold value, adjust the focal length of the liquid crystal microlens unit.

[0028] In a fourth aspect, the present invention provides an electronic device, including a processor and the fingerprint detection device described in the first aspect.

[0029] Beneficial effects: The fingerprint detection device, the control method of the fingerprint detection device, and the electronic device of the present invention use a liquid crystal microlens array to separate reflected light at different angles, so that the reflected light obliquely incident from adjacent regions cannot pass through the collimator layer. At the same time, the collimator layer is used to collimate the reflected light carrying the user's fingerprint information, so that the area where the reflected light forms an image on the image sensor corresponds one-to-one with the area where the finger touches the display screen, thereby reducing the interference of light in other areas and significantly improving the imaging effect. The present invention also uses the characteristic that the focal length of the liquid crystal microlens array can be adjusted by the driving voltage to dynamically configure the focal length of the liquid crystal microlens unit according to the current total characteristic signal-to-noise ratio, so that the total characteristic signal-to-noise ratio of the display layer and the underlying layers always meets the requirements for accurate fingerprint recognition, effectively avoiding the adverse impact on the fingerprint recognition effect caused by the change of the total characteristic signal-to-noise ratio of the display layer and the underlying layers due to environmental changes. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to these drawings, and these are all within the protection scope of the present invention.

[0031] Figure 1 It is a schematic structural diagram of the fingerprint detection device in Embodiment 1 of the present invention;

[0032] Figure 2 It is a schematic structural diagram of the liquid crystal microlens array in Embodiment 1 of the present invention;

[0033] Figure 3 It is a schematic diagram of the reflected light converging on the image sensor after being adjusted by the liquid crystal microlens array;

[0034] Figure 4 It is a schematic diagram of the change in the focusing position of a kind of reflected light after the ordinary microlens array is affected by the environment;

[0035] Figure 5 It is a schematic diagram of the change in the focusing position of the reflected light after the ordinary microlens array is affected by the environment;

[0036] Figure 6 It is a schematic diagram that light incident obliquely from different directions will generate a phase difference after passing through the same aperture position of the liquid crystal microlens;

[0037] Figure 7 It is a schematic structural diagram of the microlens array in a regular hexagonal arrangement in Embodiment 1 of the present invention;

[0038] Figure 8 It is a schematic structural diagram of the microlens array in a rectangular arrangement in Embodiment 1 of the present invention;

[0039] Figure 9 It is a flowchart of a control method for a fingerprint detection device according to the present invention;

[0040] Figure 10 It is a flowchart of another control method for a fingerprint detection device according to the present invention. Detailed implementation manners

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or sequence between these entities or operations. In the description of the present invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "comprising..." do not exclude the existence of additional identical elements in the process, method, article or device including the said elements. If there is no conflict, the embodiments of the present invention and the various features in the embodiments can be combined with each other, and all are within the protection scope of the present invention.

[0042] Embodiment 1:

[0043] As Figure 1 shown, Embodiment 1 of the present invention discloses a fingerprint detection device. The fingerprint detection device includes a display layer 10 and a lower layer. The display layer 10 may be a self-luminous display screen, which uses a display unit with self-luminous property as a display pixel. For example, the display screen may be an Organic Light-Emitting Diode (OLED) display screen or a Micro-LED display screen. When using an OLED display screen, the fingerprint detection device described in this embodiment can use the display unit (i.e., the OLED light source) of the OLED display screen located in the fingerprint detection area as an excitation light source for fingerprint detection. When a finger presses on the fingerprint detection area, the display screen emits a beam of light towards the finger to be detected above the fingerprint detection area. The light is reflected on the surface of the finger to form a reflected light 50 or scattered through the finger to form a scattered light. In other alternative embodiments, the display screen 120 may also be a Liquid Crystal Display (LCD) or other passive light-emitting display screens, which are not limited in this application embodiment.

[0044] In addition, the display screen may also be a display screen with touch function, that is, a touch display screen. Using a display screen with touch function, it can not only display images of the electronic device, but also detect touch operations such as touch or press of the user, and control the electronic device according to the detected touch operations. This type of touch display screen can provide a human-computer interaction interface for users.

[0045] In addition, a transparent layer may be provided above the display layer 10. The transparent layer covers the surface of the display layer 10 to protect the display layer 10. The transparent layer may be a glass cover layer, a sapphire cover layer, etc.

[0046] The lower layer includes:

[0047] A liquid crystal microlens array layer 20 for separating reflected lights 50 at different angles. The liquid crystal microlens array layer 20 includes a plurality of liquid crystal microlens units 82 distributed in an array; the liquid crystal microlens units 82 in the liquid crystal microlens array layer 20 can be driven by voltage to zoom.

[0048] A collimator layer 30 located on the side of the liquid crystal lens array layer away from the display layer 10. The collimator layer 30 is used to collimate the reflected light 50. The collimator layer 30 includes a micropore array layer, and the micropore array layer is provided with small holes 31 corresponding to the liquid crystal microlens units 82 one by one;

[0049] The aforementioned collimator layer 30 may include a plurality of collimation units. Among the reflected light 50 reflected from the finger ridge region 61 and the valley region 62, the light rays that are perpendicularly incident on the collimation units can pass through and be received by the image sensor 40 below, while the light rays with too large an incident angle are attenuated after multiple reflections inside the collimation units. Therefore, each optical sensing unit on the image sensor 40 can basically only receive the reflected light 50 reflected from the fingerprint pattern directly above it, thereby effectively improving the image resolution, further improving the fingerprint recognition effect, and enabling the fingerprint detection device to more accurately detect the fingerprint image of the finger. The collimator layer 30 of this embodiment may adopt a micro-hole array layer, and a plurality of small holes 31 arranged in an array are provided on the micro-hole array layer, and the small holes 31 serve as the aforementioned collimation units. Since the small holes 31 of the micro-hole array layer correspond one-to-one with the liquid crystal microlens units 82, the collimation units of the collimator layer 30 also correspond one-to-one with the liquid crystal microlens units 82. The region between adjacent small holes 31 is an opaque light-shielding region, and this light-shielding region can block the light obliquely incident through the adjacent region and avoid the interference of light in the adjacent region.

[0050] As Figure 3 shown, this embodiment adopts a structure in which the liquid crystal microlens units 82 are correspondingly arranged above the small holes 31 of the micro-hole array layer one by one, so that the reflected light 50 incident on the liquid crystal microlens units 82 at certain specific angles (such as perpendicular to the liquid crystal microlens units 82) can pass through the small holes 31 of the micro-hole array layer after being converged by the liquid crystal microlenses, while the reflected light 50 incident on the liquid crystal microlenses obliquely from an adjacent region relative to the liquid crystal microlens units 82 falls on the light-shielding region of the micro-hole array layer and thus cannot reach the corresponding region of the image sensor 40. In this way, the liquid crystal microlens units 82 can separate the reflected light 50 at different angles, so that only the reflected light 50 in the region corresponding to the small holes 31 of the micro-hole array layer can reach the corresponding region of the image sensor 40 after being collimated by the micro-hole array, thereby achieving the effect of a narrow field of view. In this way, the region where the reflected light 50 forms an image on the image sensor 40 corresponds one-to-one with the region where the finger touches the display screen, thereby reducing the interference of light in other regions and significantly improving the imaging effect.

[0051] In addition, the fingerprint recognition device of this embodiment further includes a first microlens array layer, which is located on the side of the liquid crystal microlens array layer away from the display layer or on the side close to the display layer. The first microlens array layer can adopt other microlens arrays that do not require voltage driving, that is, a liquid crystal microlens array is added on the basis of the original ordinary microlens array to form a combination of an ordinary microlens array and a liquid crystal microlens array, and each liquid crystal microlens unit 82 corresponds to an ordinary microlens unit 81. The liquid crystal microlens array is first arranged above or below the ordinary microlens array. During normal operation, the ordinary microlens array is used for focusing. When the total feature signal-to-noise ratio changes, the driving voltage of the liquid crystal lens can be changed to finely adjust the focal length of the combination of the entire ordinary microlens array and the liquid crystal microlens array, so as to improve the total feature signal-to-noise ratio. Since the liquid crystal microlens array only needs to finely adjust the focal length, the change range of the focal length of the liquid crystal microlens can be reduced, and the response time can be improved.

[0052] An image sensor 40, configured to sense the collimated reflected light 50; the image sensor 40 is a TFT-based organic imaging device. The TFT-based organic imaging device is an organic imaging device manufactured on a TFT-based electronic readout substrate. The organic imaging device can be an organic semiconductor photodiode array. The organic semiconductor photodiode can be made of a stack of evaporated ultra-thin (e.g., <100nm) films of organic substances such as chloro-boron (e.g., SubPc / C-60).

[0053] The focal length of the liquid crystal microlens unit 82 is configured to make the total feature signal-to-noise ratio of the display layer 10 and the lower layers meet the first condition.

[0054] According to the Gaussian formula 1 / s + 1 / l = 1 / f, when the light field is a narrow field of view and the image distance l is constant, changing the object distance s does not affect the total feature signal-to-noise ratio of the touch display layer 10 and the underlying layers, while changing the focal length f will cause the signal-to-noise ratio to decrease. Since the microlens array is easily affected by the environment, such as temperature, which changes the focal length of the microlens, the focusing position of the light changes from the position in Figure 3 to the position in Figure 4 or Figure 5 The total feature signal-to-noise ratio of the touch display layer 10 and the underlying layers decreases. When the total feature signal-to-noise ratio of the touch display layer 10 and the underlying layers is relatively low, the image effect collected by the image sensor 40 is poor, which will affect the accuracy of fingerprint recognition. In response to this, this embodiment utilizes the characteristic that the focal length of the liquid crystal microlens array can be adjusted by the driving voltage to dynamically configure the focal length of the liquid crystal microlens unit 82 according to the current total feature signal-to-noise ratio so that the total feature signal-to-noise ratio of the display layer 10 and the underlying layers meets the requirements of fingerprint recognition.

[0055] The foregoing first condition may be that the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer is maximized. That is, the focal length value at which the liquid crystal microlens unit 82 is configured is the focal length value corresponding to the maximum total characteristic signal-to-noise ratio of the display layer 10 and the lower layer. The maximum total characteristic signal-to-noise ratio of the display layer 10 and the lower layer here means that within the variable focal length range of the liquid crystal lens, the variable focal length characteristic of the liquid crystal microlens is used to scan the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer, and all the total characteristic signal-to-noise ratios obtained by the scanning are compared, and the maximum value among them is selected. When the focal length of the liquid crystal microlens unit 82 makes the total characteristic signal-to-noise ratio of the display layer 10 and the following layers equal to this maximum value, the foregoing first condition is satisfied. By adopting the foregoing condition, the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer can be maintained at the optimal level all the time by dynamically adjusting the focal length of the liquid crystal microlens unit 82 by the system, so that the fingerprint detection device can have the best recognition effect regardless of how the external environment changes.

[0056] In addition, the foregoing first condition may also be that the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer is greater than a first threshold. By adopting the foregoing condition, the minimum total characteristic signal-to-noise ratio of the display layer 10 and the lower layer that meets the requirement can be obtained as the first threshold according to the accuracy requirement of fingerprint recognition. The system detects the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer. When the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer is lower than the set first threshold, the focal length of the liquid crystal microlens is adjusted until the current total characteristic signal-to-noise ratio of the display layer 10 and the lower layer is higher than the set first threshold. By adopting the foregoing method, the focal length of the liquid crystal microlens unit 82 can be configured according to the specific requirements of fingerprint recognition without repeatedly adjusting the focal length to scan the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer. This not only ensures the accuracy of the fingerprint detection device during long-term use but also saves system overhead. The first threshold may be different in different application scenarios or can be flexibly adjusted according to different accuracy requirements of fingerprint recognition.

[0057] In this embodiment, for the convenience of focal length adjustment, the focal lengths of the liquid crystal microlens units 82 in the liquid crystal microlens array can be adjusted uniformly. For example, the same set of driving voltages is used to drive all the liquid crystal microlens units 82.

[0058] Due to the different properties of the liquid crystal microlens units 82 in each region during the manufacturing process, or due to the different properties of each liquid crystal microlens unit 82, the total characteristic signal-to-noise ratios of different regions are different, or the total characteristic signal-to-noise ratios of different small holes 31 are different. In this embodiment, the focal length of the liquid crystal microlens can also be adjusted in different regions, or the focal length of each liquid crystal microlens unit 82 can be adjusted individually. For example, different driving voltages are used to adjust the focal length of the liquid crystal microlenses in different regions. Another example is to configure an independent driving voltage for each liquid crystal microlens unit 82, so as to independently adjust the focal length of each liquid crystal microlens unit 82. By adopting the foregoing method, the property differences of different liquid crystal microlens units 82 can be overcome, so that the focal length of each liquid crystal microlens unit 82 can meet the conditions of the corresponding total characteristic signal-to-noise ratio.

[0059] The fingerprint detection device of this embodiment can also be provided with a transparent isolation layer 70 between the microporous array layer and the image sensor 40, and the transparent isolation layer 70 is used to separate the microporous array layer and the image sensor 40 by a certain distance.

[0060] In addition, since the refractive index of liquid crystal molecules is related to the incident angle, and the pretilt angle of the liquid crystal molecules in the liquid crystal microlens unit is fixed and rotates in the same direction with the voltage, a phase difference will be generated after the light obliquely incident from different directions passes through the same aperture position of the liquid crystal microlens. As Figure 6 shown, the liquid crystal microlens exhibits different optical powers for light incident from different directions. In this embodiment, the cross-section of the foregoing small hole 31 is set to be elliptical to avoid the foregoing problem. In other embodiments, the foregoing small hole 31 can also be circular or other shapes, which are not limited here. Next, the specific structure of the liquid crystal microlens array applied to the foregoing fingerprint detection device will be introduced. As Figure 2 The foregoing liquid crystal microlens array layer 20 includes a first substrate 21, a first electrode layer 22, an insulating layer 23, a second electrode layer 24, a liquid crystal layer 25, a third electrode layer 26, and a second substrate 27 arranged in sequence from the display layer 10 towards the image sensor 40. The first electrode layer 22 and the third electrode layer 26 are transparent electrode layers, and the second electrode layer 24 is provided with light-passing holes 241 arranged in an array.

[0061] Among them, the first electrode layer 22 and the third electrode layer 26 are made of transparent electrodes, such as ITO electrodes, AZO electrodes, etc. The aforementioned light passing hole 241 can be a circular light passing hole 241, and in other embodiments, it can also be a light passing hole 241 with other symmetrical shapes, such as a rectangular light passing hole 241, a regular polygon light passing hole 241, etc., which are not limited here. Among them, the third electrode layer 26 is used as the common electrode of the liquid crystal microlens to provide a reference voltage for the first electrode layer 22 and the second electrode layer. The third electrode layer 26 and the second electrode layer 24 are separated by a liquid crystal layer 25, and the hole-shaped electrode and the second electrode unit are separated by a relatively thin insulating layer 23 to insulate the first electrode layer 22 and the second electrode layer 24, so that the liquid crystal microlens array can maintain a relatively small thickness. The first substrate 21 and the second substrate 27 are used as the support structures of the liquid crystal microlens element and can be made of transparent materials with a certain strength and stiffness, such as glass substrates, plastic substrates, etc. To maintain the shape of the liquid crystal layer 25, spacers for supporting the liquid crystal layer 25 can also be provided in the liquid crystal layer 25 in this embodiment.

[0062] When the liquid crystal microlens array works, working voltages are applied to each electrode layer, generating a non-uniform electric field distribution in the liquid crystal region. Under the action of the non-uniform electric field, the liquid crystal molecules undergo non-uniform deflection, resulting in a non-uniform change in the refractive index spatial distribution, thereby focusing the light beam at a specific position. When the control voltage changes, the focal position of the microlens changes, thus completing the control process of the focal position of the liquid crystal microlens. To form the aforementioned electric field for driving the liquid crystal microlens array, in this embodiment, a first driving voltage V1 can be connected between the first electrode layer 22 and the third electrode layer 26, and a second driving voltage V2 can be connected between the second electrode layer 24 and the third electrode layer 26. And the first driving voltage V1 and the second driving voltage V2 are independent driving voltages, so the values of the first driving voltage V1 and the second driving voltage V2 can be independently adjusted respectively. In this embodiment, the focal length value of the liquid crystal microlens array can be adjusted by adjusting the values of the first driving voltage V1 and the second driving voltage V2.

[0063] The liquid crystal microlens array of this embodiment adopts the aforementioned structure and driving method, which can make the focal length increase monotonically with the driving voltage, the focal length adjustment is very convenient, and the focal length can be adjusted within the positive and negative ranges. Therefore, by using the liquid crystal microlens array of this embodiment, the aforementioned total feature signal-to-noise ratio can be conveniently scanned, so that the total feature signal-to-noise ratio between the display layer 10 and the lower layer in the fingerprint detection device can always be maintained at a relatively high level.

[0064] The aforementioned second electrode layer 24 may also be a structure including a plurality of electrode units, and a light passing hole is correspondingly provided for each electrode unit. Each electrode unit and other functional layers of the liquid crystal microlens array together form the aforementioned liquid crystal microlens unit 82. Each electrode unit may adopt an independent driving voltage, that is, the second driving voltage V2 of each electrode unit can be independently adjusted, so that the focal lengths of the respective liquid crystal microlens units 82 can be adjusted according to the aforementioned total characteristic signal-to-noise ratio.

[0065] The aforementioned liquid crystal microlens units 82 may be arranged in a rectangular array or a regular hexagonal array. As Figure 8 shown, when the liquid crystal microlens units 82 are arranged in a rectangular array, the geometric centers of the liquid crystal microlens units 82 (i.e., the geometric centers of the light passing holes 241) are located at the positions of the four vertices of the rectangle. As Figure 7 shown, when the liquid crystal microlens units 82 are arranged in a regular hexagonal array, the geometric centers of the liquid crystal microlens units 82 (i.e., the geometric centers of the light passing holes 241) are located at the positions of the six vertices of the regular hexagon.

[0066] The aperture of the light passing hole 241 of the aforementioned liquid crystal microlens unit 82 is 50um to 5um, and different apertures can be selected according to different requirements. According to the Fresnel approximation, the focal length of the lens is:

[0067]

[0068] wherein d LC is the thickness of the liquid crystal layer 25, and δn is determined by the potential difference between the center and the edge of the lens. For example d LC = 15um, 0.2 ≤ f ≤ ∞. The distance between the lenses is P, where the distance between the lenses satisfies

[0069] In this embodiment, the image sensor 40 is a pixelated image sensor 40. Using the aforementioned collimator layer 30 can collimate the reflected light 50. This collimation process can make the area of the finger surface in contact with the transparent cover layer correspond one-to-one with the image formed on the pixelated image sensor 40, and can solve the problem that the incident light and the reflected light 50 cannot correspond. Even for the reflected light 50 lines collimated by the collimator layer 30 and reaching the pixelated image sensor 40, the fingerprint area and the imaging area reflected are basically the same.

[0070] The fingerprint detection device of this embodiment further includes a polarization element, such as a polarizer, which is located in the optical path from the display screen to the liquid crystal lens array layer. The reflected light 50 is filtered by the polarization element before passing through the liquid crystal microlens array, and only the light beam in a specified direction can pass through the polarization element and reach the liquid crystal microlens array. If the polarization element is not provided, the light flux of the sensor when the liquid crystal microlens is not working can be taken first. Then take the light flux of the sensor when the liquid crystal microlens is working. Among them It includes part of the light flux when the liquid crystal microlens is not working, that is Using The total light flux modulated by the liquid crystal microlens can be obtained.

[0071] In addition, the fingerprint detection device of this embodiment further includes a processor, which processes the fingerprint information detected by the image sensor 40. The processor can be a Central Processing Unit (CPU), or other general-purpose processors, single-chip microcomputers, ARM, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0072] Embodiment 2

[0073] As Figure 9 shown, this embodiment provides a control method for a fingerprint detection device, which is used to control the aforementioned fingerprint detection device. The method includes the following steps:

[0074] S1: Adjust the focal length of the liquid crystal microlens unit 82 to obtain the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer at different focal lengths;

[0075] Specifically, the focal length of the liquid crystal microlens unit 82 can be adjusted by adjusting the aforementioned first driving voltage and second driving voltage. The focal length of the liquid crystal microlens unit 82 can be changed from near to far. During the change of the focal length of the liquid crystal microlens unit 82, the total characteristic signal-to-noise ratio of the display layer 10 and the lower layer corresponding to the focal length is detected, that is, the total characteristic signal-to-noise ratio of the liquid crystal microlens unit 82, the display layer 10 and the lower layer is scanned.

[0076] S2: Select the largest total characteristic signal-to-noise ratio as the target total characteristic signal-to-noise ratio;

[0077] In this step, a series of overall feature signal-to-noise ratios detected during the focal length adjustment process of the aforementioned liquid crystal microlens unit 82 are compared to obtain the maximum overall feature signal-to-noise ratio, which is used as the optimal overall feature signal-to-noise ratio of the liquid crystal microlens unit 82. Subsequent focal length adjustments are targeted at the value of this overall feature signal-to-noise ratio.

[0078] S3: Obtain the focal length corresponding to the target overall feature signal-to-noise ratio as the focal length of the liquid crystal microlens unit 82.

[0079] Based on the corresponding relationship between the overall feature signal-to-noise ratio and the focal length detected during the previous focal length adjustment process, find the focal length corresponding to the target overall feature signal-to-noise ratio, and then adjust the driving voltage to make the focal length of the liquid crystal microlens unit 82 reach this focal length value.

[0080] Using the aforementioned method, regardless of the impact of the external environment on the current overall feature signal-to-noise ratio, the control method of this embodiment can keep the overall feature signal-to-noise ratios of the display layer 10 and the lower layer at the optimal values. The overall feature signal-to-noise ratio can be measured at regular intervals of a preset time, or when the external environment changes.

[0081] Embodiment 3

[0082] As Figure 10 shown, this embodiment provides another control method for a fingerprint detection device. The control method includes the following steps:

[0083] S01: Obtain the first threshold;

[0084] In this step, according to the accuracy requirements of fingerprint recognition, the minimum overall feature signal-to-noise ratio of the display layer 10 and the lower layer that allows the fingerprint detection device to accurately recognize fingerprints is obtained as the first threshold. Subsequent dynamic adjustments are based on the aforementioned first threshold as the standard.

[0085] S02: Obtain the current overall feature signal-to-noise ratio of the display layer 10 and the lower layer of the liquid crystal microlens unit 82;

[0086] S03: Compare the size of the current overall feature signal-to-noise ratio of the display layer 10 and the lower layer with the first threshold;

[0087] S04: If the current overall feature signal-to-noise ratio of the display layer 10 and the lower layer is less than the first threshold, then adjust the focal length of the liquid crystal microlens unit 82.

[0088] The fact that the current overall feature signal-to-noise ratio of the display layer 10 and the lower layer is less than the first threshold indicates that the current overall feature signal-to-noise ratio is too small to meet the requirements of fingerprint detection accuracy. At this time, it is necessary to adjust the focal length of the liquid crystal microlens unit 82 so that the overall feature signal-to-noise ratio is increased to a level greater than or equal to the first threshold.

[0089] If the total feature signal-to-noise ratio of the current display layer 10 and the lower layer is greater than or equal to the first threshold, it indicates that the current feature signal-to-noise ratio can meet the requirements of fingerprint detection accuracy. At this time, it is not necessary to adjust the focal length of the liquid crystal microlens unit 82.

[0090] Using the foregoing method does not require scanning the total feature signal-to-noise ratio from beginning to end. Only adjustment is needed when the total feature signal-to-noise ratio does not meet the standard, which can not only ensure that the total feature signal-to-noise ratio of the display layer 10 and the lower layer meets the requirements of fingerprint recognition, but also reduce the system overhead.

[0091] Embodiment 4

[0092] This embodiment provides an electronic device, which includes a processor and the fingerprint detection device in Embodiment 1. The foregoing electronic device can be a portable or mobile computing device such as a smart phone, a notebook computer, a tablet computer, a game device, etc., and other electronic devices such as an electronic database, an automobile, a bank Automated Teller Machine (ATM), etc.

[0093] The above is a detailed introduction to the fingerprint detection device, the fingerprint detection device control method, and the electronic device provided by the embodiments of the present invention.

[0094] It should be clear that the present invention is not limited to the specific configurations and processes described and illustrated above. For the sake of brevity, the detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and illustrated as examples. However, the method process of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art can make various changes, modifications, and additions, or change the order between steps after understanding the spirit of the present invention.

[0095] The functional blocks shown in the above structure block diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, etc. When implemented in software, the elements of the present invention are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted via a data signal carried by a carrier wave on a transmission medium or a communication link. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical discs, hard disks, fiber optic media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0096] It should also be noted that the exemplary embodiments mentioned in the present invention describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above steps, that is, the steps can be executed in the order mentioned in the embodiments, can be different from the order of the embodiments, or several steps can be executed simultaneously.

[0097] As described above, the above are only specific embodiments of the present invention. Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working processes of the systems, modules, and units described above can refer to the corresponding processes of the foregoing method embodiments and will not be repeated herein. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A fingerprint detection device, characterized in that, Comprising: A display layer and a lower layer, the lower layer comprising: A liquid crystal microlens array layer for separating reflected light at different angles, the liquid crystal microlens array layer comprising a plurality of liquid crystal microlens units arranged in an array; A collimator layer located on the side of the liquid crystal lens array layer away from the display layer, the collimator layer for collimating the reflected light, the collimator layer comprising a micropore array layer provided with small holes corresponding one-to-one to the liquid crystal microlens units; An image sensor for sensing the collimated reflected light; The focal length of the liquid crystal microlens unit is configured such that the total characteristic signal-to-noise ratio of the display layer and the lower layer satisfies a first condition; The first condition is that the total characteristic signal-to-noise ratio of the display layer and the lower layer is greater than a first threshold; It further comprises a polarization element located in the optical path from the display screen to the liquid crystal microlens array layer.

2. The fingerprint detection device according to claim 1, wherein The liquid crystal microlens array layer comprises a first substrate, a first electrode layer, an insulating layer, a second electrode layer, a liquid crystal layer, a third electrode layer and a second substrate layer arranged in sequence from the display layer towards the image sensor, the first electrode layer and the third electrode layer being transparent electrode layers, and the second electrode layer comprising light-passing holes arranged in an array.

3. The fingerprint detection device according to claim 1, wherein It further comprises a first microlens array layer located on the side of the liquid crystal microlens array layer away from the display layer or on the side close to the display layer.

4. The fingerprint detection device according to claim 1, wherein The image sensor is a pixelated image sensor.

5. The fingerprint detection device according to claim 1, wherein The cross-section of the small hole is elliptical.

6. The fingerprint detection device according to any one of claims 1 to 5, characterized in that, The first condition is that the total characteristic signal-to-noise ratio of the display layer and the lower layer is the largest.

7. A control method for a fingerprint detection device according to any one of claims 1 to 6, characterized in that, Comprising the following steps: S1: Adjust the focal length of the liquid crystal microlens unit to obtain the total characteristic signal-to-noise ratio of the display layer and the lower layer at different focal lengths; S2: Select the largest total characteristic signal-to-noise ratio as the target total characteristic signal-to-noise ratio; S3: Obtain the focal length corresponding to the target total characteristic signal-to-noise ratio as the focal length of the liquid crystal microlens unit.

8. The control method of the fingerprint detection device according to any one of claims 1 to 6, characterized in that, Comprising the following steps: S01: Obtain the first threshold; S02: Obtain the current total characteristic signal-to-noise ratio of the display layer and the lower layer of the liquid crystal microlens unit; S03: Compare the current total characteristic signal-to-noise ratio of the display layer and the lower layer with the first threshold; S04: If the current total characteristic signal-to-noise ratio of the display layer and the lower layer is less than the first threshold, then adjust the focal length of the liquid crystal microlens unit.

9. An electronic device, characterized in that, Comprising a processor and the fingerprint detection device according to any one of claims 1 to 6.

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