CN109992154B

CN109992154B - Touch screen with comprehensive screen fingerprint identification function and fingerprint identification method

Info

Publication number: CN109992154B
Application number: CN201910193845.XA
Authority: CN
Inventors: 王磊
Original assignee: Nanjing Guanhai Microelectronic Co ltd
Current assignee: Nanjing Guanhai Microelectronic Co ltd
Priority date: 2019-03-14
Filing date: 2019-03-14
Publication date: 2022-10-21
Anticipated expiration: 2039-03-14
Also published as: CN109992154A

Abstract

The invention discloses a touch screen with a comprehensive screen fingerprint identification function and a fingerprint identification method, wherein the touch screen comprises a screen cover plate directly contacted with a finger, a display screen below the screen cover plate and a flexible circuit board electrically connected with the display screen; the display screen is also internally provided with a capacitive sensor array integrated in the display screen lamination layer and used as a sensor for touch detection and fingerprint detection, the capacitive sensor array comprises a first induction electrode array and a second induction electrode array arranged nearby the first induction electrode array, and the first induction electrode array is also electrically connected with a display element in the display screen lamination layer and used for inputting display signals; the flexible circuit board comprises a TDDI chip which is respectively connected with the first sensing electrode array and the second sensing electrode array through I/O pins. The touch screen integrates three functions of display, touch and fingerprint identification, a fingerprint identification hardware module does not need to be arranged behind the screen independently, the space of a mobile phone is saved, and the technology can also be applied to a liquid crystal display screen.

Description

Touch screen with comprehensive screen fingerprint identification function and fingerprint identification method

Technical Field

The present invention relates to a touch screen with fingerprint recognition function, and more particularly, to a touch screen integrating display, touch and fingerprint recognition functions and a method for full-screen fingerprint recognition.

Background

Fingerprint identification unlocking has become the default scheme of most smart phones and is the most important biometric authentication mode. From the technical point of view, at present, fingerprint identification has several solutions such as a capacitive sensor, an optical sensor and an ultrasonic sensor. From the iPhone 5S, the capacitive fingerprint identification scheme becomes the mainstream, and almost all mobile phones have capacitive fingerprint identification at present. The working principle is that a capacitance sensor arranged at the Home key of the mobile phone is used for collecting the finger line information of a user, and a thermosensitive sensor is used for assisting judgment to realize the fingerprint detection function. The capacitive sensor scheme is small in size, low in cost and quick in unlocking, and therefore becomes the first-choice unlocking mode of the intelligent machine. However, since the "full screen" concept began to prevail, the capacitive solution was gradually at a disadvantage. Since the full screen concept is to maximize the display area, this means that the Home key and most of the hardware on the front side of the smartphone need to be removed, and the sensors typically placed under these keys, including capacitive sensors, disappear. Since the user expects that fingerprint identification can continue to remain on the full-screen handset, the fingerprint sensor must somehow be placed somewhere else.

Although the performance and cost advantages of the fingerprint identification scheme based on the capacitive sensor are irresistible, unfortunately, due to the limitations of power consumption and the factors such as touch accuracy of the capacitive fingerprint identification technology, the existing touch driving channel TX only has dozens of lines as shown in fig. 3, and the density is not high, so that the capacitive fingerprint identification scheme cannot be used for detecting fingerprints. In addition to capacitive sensors, two other types of underscreen fingerprint sensors are increasingly focused: one is an ultrasonic sensor, and the other is an optical sensor, which are both arranged behind the screen. Ultrasonic sensors, which have good ultrasonic wave permeability and are strongly related to the permeability and thickness of objects, are sensitive to the thickness of the front screen, and the screen must be thin enough, otherwise the signal cannot penetrate. A thinner LED display screen, such as an ultra-thin AMOLED display screen (Active-matrix organic light-emitting diode or Active-matrix organic light-emitting diode), may be used to implement fingerprint identification, while a Liquid Crystal Display (LCD) is inherently thicker and is not easy to achieve accurate and fast identification. Another optical sensor needs to transmit a fingerprint image to a sensor through a screen, so a relatively thin LED display screen such as an AMOLED display screen is generally adopted, each pixel of the AMOLED display screen can be independently controlled, constant backlight is not needed, a light-transmitting base is provided, a liquid crystal display screen is provided with backlight, and a backlight part cannot transmit an optical signal in front of the screen to the back of the screen, so that the optical sensor structure cannot be applied to the liquid crystal display screen. Meanwhile, because the light has poor penetrability, the light is easily influenced by the light source and the color of the screen, and the problem of wrong identification occurs. Moreover, both the ultrasonic sensor and the optical sensor require a space for disposing the sensor behind the screen, and in the case of the mobile phone structure being developed in the direction of lighter and thinner, the space tends to be compressed, thereby bringing new challenges to the placement of these sensors.

Disclosure of Invention

The invention aims to: in order to solve the problems, the invention provides a touch screen with a comprehensive screen fingerprint identification function and a comprehensive screen fingerprint identification method based on the touch screen.

The technical scheme is as follows: the technical scheme adopted by the invention is a touch screen with a comprehensive screen fingerprint identification function, which comprises a screen cover plate directly contacted with a finger, a display screen below the screen cover plate and a flexible circuit board electrically connected with the display screen; the display screen is also internally provided with a capacitive sensor array integrated in the display screen lamination layer and used as a sensor for touch detection and fingerprint detection, the capacitive sensor array comprises a first induction electrode array and a second induction electrode array arranged nearby the first induction electrode array, and the first induction electrode array is also electrically connected with a display element in the display screen lamination layer and used for inputting display signals; the flexible circuit board comprises a TDDI chip used for processing display signals, touch signals and fingerprint scanning signals, and the TDDI chip is connected with the first sensing electrode array and the second sensing electrode array through I/O pins of the TDDI chip. The display screen can adopt a high-definition or full-high-definition display screen.

Furthermore, the first sensing electrode array is a plurality of data lines distributed in parallel, and the second sensing electrode array is a plurality of signal lines perpendicular to the data lines. The second sensing electrode array is arranged above the plane of the data line or in the same plane of the data line. When the two electrodes are arranged in different layers, a capacitive sensor unit is formed at the intersection position of the two electrodes for the mutual capacitance type induction principle, wherein one electrode is used for driving, and the other electrode is used as an induction electrode to output a detection signal. When the two electrodes are arranged in the same layer, the capacitance change of the two electrodes to the ground is output as a detection signal according to a self-capacitance type induction principle, and the cost of the display screen corresponding to the scheme is lower.

The smart phone assembled and manufactured by the touch screen with the comprehensive screen fingerprint identification function does not need to be additionally provided with hardware related to fingerprint unlocking on the front panel of the smart phone.

The invention also provides a method for fingerprint identification by using the touch screen, which integrates display, touch and fingerprint identification functions by using a TDDI chip time division multiplexing capacitive sensor and comprises the following steps:

(1) The TDDI chip controls the first sensing electrode array to send display signals to the display element, and the display screen displays images.

(2) In the interval time of each frame of image display, the display element is turned off, the TDDI chip detects the capacitance change of partial capacitive sensors uniformly distributed on the whole display screen, the coordinates of touch points in a plane are calculated according to touch detection signals generated by the capacitance change, and the finger position is positioned; the number of the partial capacitive sensors is less than 1/100 of the number of all the capacitive sensors.

(3) After the finger is positioned at the position of the finger, fingerprint detection signals generated by capacitance changes of all the capacitive sensors near the position of the finger are detected, the fingerprint detection signals are analyzed and compared by a TDDI chip, fingerprint identification is completed, and a display element is turned off in the detection process. This step is performed at the current frame after the finger position is located or at the interval of the next frame image display.

Has the advantages that: compared with the prior art, the invention has the following advantages: 1. the TDDI chip is utilized, three functions of display, touch control and fingerprint identification are integrated, a separate fingerprint identification sensor hardware module behind a screen is not needed, and the space of the mobile phone is saved; 2. the fingerprint identification function is integrated in the screen, and the fingerprint detection process is not influenced by backlight, so that the fingerprint identification function can be applied to an LED display screen, such as AMOLED, and an LCD (liquid crystal display), is suitable for various conventional display screens at present, and has strong universality; 3. the scheme of positioning and identifying is adopted, the sensor module is multiplexed, the sensor, namely the processor module is saved, the power consumption is low, and the cost is low; 4. and by combining multi-point touch control, simultaneous identification of multiple fingerprints can be realized.

Drawings

FIG. 1 is a schematic diagram of a touch screen structure used in the present invention;

FIG. 2 is a schematic diagram of time division multiplexing of display and touch control in the method of the present invention;

FIG. 3 is a schematic diagram of the density of data lines (data lines) controlled during touch positioning according to the present invention;

FIG. 4 is a schematic diagram of the density of data lines (data lines) controlled during fingerprint identification according to the present invention;

FIG. 5 is a schematic diagram of a capacitive sensor for fingerprint detection;

fig. 6 is a schematic diagram of two electrode structures of the self-capacitance type capacitive sensor.

Detailed Description

The technical scheme of the invention is further explained by combining the drawings and the embodiment.

The touch screen with the comprehensive screen fingerprint identification function has the structural schematic diagram shown in fig. 1, and comprises a screen cover plate 1 directly contacted with a finger, a display screen 2 below the screen cover plate, and a flexible circuit board 3 connected with the display screen 2.

The thickness of the screen cover plate 1 can cause that the sensor can not collect enough signals, the screen cover plate 1 should be made as thin as possible, the thickness reaches hundreds of microns, and the sensitivity of the capacitive touch display screen is improved.

The display screen 2 is provided with a capacitive sensor array integrated in the display screen laminate, which is used as a sensor for touch detection and a sensor for fingerprint detection. In particular integrated in the TFT circuit layer, may be embedded in the circuit layer or may be partially embedded in the TFT circuit layer with another portion disposed thereon. The capacitive sensor array comprises a plurality of data lines 4 (data lines) distributed in parallel and a plurality of signal lines 5 distributed in parallel and perpendicular to the data lines. In one embodiment, the data line 4 (data line) is disposed in a TFT circuit, and the signal line 5 is disposed above a display unit (the display unit is generally arranged in order of a color filter glass, a color filter, a TFT circuit, a substrate glass, a color polarizing plate, and backlight illumination from top to bottom) which are perpendicular to each other. In this scheme, two electrodes are disposed at different layers, and a mutual capacitance type sensing principle is adopted, in which a capacitor is formed at a position where the data line 4 and the signal line 5 intersect, the data line 4 serves as a drive, and the signal line 5 serves as a sensing electrode to output a detection signal. Alternatively, the data lines 4 and the signal lines 5 are in the same layer, for example, in a TFT circuit, and they are perpendicular to each other and woven together in a crossing manner, as shown in fig. 6, which is a self-capacitance sensing principle, and the capacitance change to ground formed by the data lines 4 and the signal lines 5 is output as a detection signal, and this scheme corresponds to a lower cost display screen. The data line 4 (data line) is also electrically connected to the display element in the display screen stack for inputting a display signal. The precise and compact structure enables the data lines 4 to be multiplexed for multiple times, and the data lines are used as source input of the display unit during display, as touch emitters during touch detection, and as electrodes of the capacitive sensor during fingerprint detection. Moreover, the structure needs the data lines 4 to meet the density requirement of 20/mm to realize accurate fingerprint scanning. From the viewpoint of resolution, a High Definition (HD) or full high definition (FHD screen) liquid crystal display screen may be employed. The display screen is provided with 1000-2000 data lines, the density is about 40 lines/mm, and the requirements can be met.

The flexible circuit board 3 comprises a TDDI chip which is respectively connected with the data line array and the signal array through I/O pins of the TDDI chip. The TDDI (Touch and Display Driver Integration) chip is a Touch and Display Driver Integration chip for processing Display, touch and fingerprint scan signals. The touch control chip and the display chip are integrated into a single chip, so that the display noise is reduced, and meanwhile, the whole display screen is thinner. The TDDI chip controls the data lines 4 to perform pixel display, touch detection, and fingerprint detection by using a time division multiplexing method. As shown in fig. 2, a display segment (display) is used for displaying an image, and the data lines 4 are used for controlling the display of the pixels of the screen during this period. A time interval exists between two display segments (displays), the time interval is used as a touch scanning segment (touch), the data lines 4 are used for touch positioning and fingerprint scanning of fingers in the time interval, and then the TDDI chip compares fingerprint information to finish fingerprint identification. The software program corresponding to the above process is executed by the TDDI chip, and the program is stored in the storage medium readable by the chip.

In this embodiment, the fingerprint identification method based on the touch screen includes the following steps:

(1) The TDDI chip controls a data line (data line) arranged in the touch display screen to send source signals for displaying to display elements in a display area (active area) at intervals, and the display screen displays images. As shown in the display segment (display) in fig. 2. During the period, the TDDI chip controls the display of the screen pixels through the data line (data line). At this time, the data line (data line) functions as a source line in a common display screen, and the screen pixels display corresponding colors under the control of the source line.

(2) And in the interval time of each frame of image display, the display element is turned off, the TDDI chip detects the capacitance change of partial capacitive sensors uniformly distributed on the whole display screen, the coordinates of touch points in a plane are calculated according to touch detection signals generated by the capacitance change, and the position of a finger is positioned. Fig. 3 is a schematic diagram showing the density of data lines controlled by the TDDI chip during touch positioning. Since the capacitive sensor density required to locate the finger position is not large, it is sufficient to locate every dozen data lines of the thousands of data lines of the display screen. In the mutual capacitance structure, the data line (data line) is used as a touch emitter TX to drive touch detection, and the position on the corresponding signal line where the capacitive sensor is formed is used as a touch receiver RX to output a detection signal. In the self-contained structure, it is also necessary to detect the number of signal lines corresponding to the number of data lines. The method is calculated by forming a sensor array by millions of capacitive sensor units on a display screen, wherein the number of the partial capacitive sensors accounts for less than 1/100 of the number of all capacitive sensors in the screen.

(3) After the finger is positioned at the position of the finger, fingerprint detection signals generated by capacitance changes of all the capacitive sensors near the position of the finger are detected, the fingerprint detection signals are analyzed and compared by a TDDI chip, fingerprint identification is completed, and a display element is turned off in the detection process. This step is performed at the current frame after the finger position is located or at the interval of the next frame image display. If the image is displayed in the interval time of the next frame after the finger position is positioned, the display or the finger positioning is not interfered. During detection, all data lines and signal lines (horizontal and vertical) near the position of the finger are used as polar plates of the fingerprint capacitance sensor. Detecting a fingerprint requires a high density of data lines, as shown in fig. 4, requiring all data lines in the vicinity of the fingerprint to be used. A circular area with the diameter of 1-4cm taking the position of the finger as the center of a circle can be selected near the fingerprint.

When a finger is pressed on the surface of the capacitive touch screen, the wave crests and the wave troughs of the fingerprint influence the charge distribution ratio on the upper electrode and the lower electrode of the capacitor in the screen, so that the charge ratio on the upper electrode and the lower electrode at the positions corresponding to the wave crests and the wave troughs of the fingerprint is different, and the fingerprint is reproduced through the difference. The principle of fingerprint detection by a mutual capacitance type capacitive sensor is shown in fig. 5. The data lines 4 and the signal lines 5 respectively serve as upper and lower electrode plates (upper electrode, lower electrode) of the capacitive sensor unit, the data lines (data lines) serve as signal emitting ends (TX) during mutual capacitance touch operation, VCOM is subdivided into a plurality of signal lines in LCD, ELVSS is subdivided into a plurality of signal lines in AMLED, and the signal lines also serve as touch receiving ends (RX) during mutual capacitance touch operation.

The invention fully utilizes the data line (data line) of the pixel source electrode (source), and the data line (data line) is multiplexed in a time-sharing way to respectively serve as the source electrode (source), the touch emitter (TX) and the capacitance plate of the fingerprint detection sensor in different steps. When the fingerprint needs to be detected, the finger touch detection is firstly carried out by using hundreds of uniform capacitance sensors, the position of the finger is positioned, then the fingerprint detection is carried out on all the capacitance sensors near the position of the finger, the data density of the position of the finger is greatly improved, and the density is improved by more than dozens of times to detect the fingerprint data. And analyzing the detected fingerprint data through a fingerprint detection algorithm in the TDDI chip, calculating the similarity between the detected fingerprint data and the registered fingerprint data, and finally obtaining a matching result of the two fingerprints to realize full-screen fingerprint identification. The scheme adopts fixed-point density improvement, and the power consumption of the density is improved by only one dozen times compared with the overall density improvement. The invention combines multi-point touch control, and can also realize simultaneous identification of multiple fingerprints. Because the sensing principle is not influenced by the backlight of the display screen, both the LED and the LCD screen can be used, and the universality is strong.

The smart phone which is manufactured by assembling the touch screen with the comprehensive screen fingerprint identification function does not need to add hardware related to fingerprint unlocking on the front panel of the smart phone, and needs fewer manufacturing parts. This means a more simplified manufacturing process and a lighter and more compact body structure, which is very competitive in the existing mobile phone market.

Claims

1. A method for fingerprint identification by using a touch screen comprises the following steps that the touch screen comprises a screen cover plate (1) which is in direct contact with a finger, a display screen (2) below the screen cover plate (1) and a flexible circuit board (3) which is electrically connected with the display screen (2); the display screen (2) is also internally provided with a capacitive sensor array integrated in the display screen lamination layer and used as a sensor for touch detection and fingerprint detection, the capacitive sensor array comprises a first induction electrode array and a second induction electrode array arranged nearby the first induction electrode array, and the first induction electrode array is also electrically connected with a display element in the display screen lamination layer and used for inputting display signals; the flexible circuit board (3) comprises a TDDI chip for processing display signals, touch signals and fingerprint scanning signals, and the TDDI chip is respectively connected with the first sensing electrode array and the second sensing electrode array through I/O pins of the TDDI chip; the first sensing electrode array is a plurality of data lines (4) distributed in parallel, and the second sensing electrode array is a plurality of signal lines (5) vertical to the data lines (4); the method is characterized in that integration of display, touch control and fingerprint identification functions is realized through a TDDI chip time-sharing multiplexing capacitive sensor, and the method comprises the following steps:

(1) The TDDI chip controls the first sensing electrode array to send display signals to the display element, and the display screen (2) displays images;

(2) In the interval time of each frame of image display, the display element is turned off, the TDDI chip detects the capacitance change of partial capacitive sensors uniformly distributed on the whole display screen, the coordinates of touch points in a plane are calculated according to touch detection signals generated by the capacitance change, and the finger position is positioned;

(3) After the finger is positioned to the position of the finger, fingerprint detection signals generated by capacitance changes of all the capacitive sensors near the position of the finger are detected, the fingerprint detection signals are analyzed and compared by a TDDI chip to finish fingerprint identification, and a display element is turned off in the detection process;

the number of the partial capacitive sensors uniformly distributed on the whole display screen in the step 2 is less than 1/100 of the number of all the capacitive sensors;

step 3 is performed after the finger position is located in the current frame.