CN109992154B - Touch screen with full screen fingerprint identification function and fingerprint identification method - Google Patents

Abstract

The invention discloses a touch screen with a full-screen fingerprint recognition function and a fingerprint recognition method. The touch screen includes a screen cover that is in direct contact with fingers, a display screen under the screen cover, and a flexible electrical connection with the display screen. circuit board; the display screen is also provided with a capacitive sensor array integrated in the display screen stack, as a sensor for touch detection and fingerprint detection, the capacitive sensor array includes a first sensing electrode array and a The second sensing electrode array, the first sensing electrode array is also electrically connected to the display element in the display screen stack, and is used for inputting display signals; the flexible circuit board includes a TDDI chip, which is respectively connected with the I/O pins through the I/O pins. The first sensing electrode array is connected to the second sensing electrode array. The touch screen of the present invention integrates three functions of display, touch and fingerprint recognition, no need to separately set the fingerprint recognition hardware module behind the screen, saving the space of the mobile phone, and the technology can also be applied to the liquid crystal display screen.

Description

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

technical field

The invention relates to a touch screen with fingerprint identification function, in particular to a touch screen integrating display, touch and fingerprint identification functions and a full-screen fingerprint identification method.

Background technique

Fingerprint recognition unlocking has become the default solution for most smartphones and is the most important biometric authentication method. From a technical point of view, there are currently several solutions for fingerprint recognition, such as capacitive sensors, optical sensors and ultrasonic sensors. Since the iPhone 5S, the capacitive fingerprint recognition solution has become the mainstream. At present, almost all mobile phone fingerprint recognition is a capacitive sensor solution. Its working principle is that the capacitive sensor set at the home button of the mobile phone is used to collect the user's fingerprint path information, and the thermal sensor is used to assist judgment to realize the fingerprint detection function. The capacitive sensor solution is small in size, low in cost and quick to unlock, so it has become the preferred unlocking method for smartphones. However, since the concept of "full screen" has been popularized, the capacitive solution has gradually been at a disadvantage. Because the concept of a full screen is to maximize the display area, this means that the Home button on smartphones and most of the hardware on the front needs to be removed, and with it disappears the sensors usually placed under these buttons, including capacitive sensor. Since users expect fingerprint recognition to remain on full-screen phones, there must be some way to put a fingerprint sensor somewhere else.

Although the performance and cost advantages of capacitive sensor-based fingerprint identification solutions are irresistible, unfortunately, due to the limitation of power consumption and touch accuracy of capacitive fingerprint identification technology, the existing touch drive channel TX has only dozens of The line is shown in Figure 3, the density is not high, so it cannot be used to detect fingerprints. In addition to capacitive sensors, two other under-screen fingerprint sensors are gaining increasing attention: one is an ultrasonic sensor and the other is an optical sensor, both located behind the screen. Ultrasonic sensor, the penetration of ultrasonic waves is good, and the penetration of the object is strongly related to the thickness, so it is very sensitive to the thickness of the front screen, the screen must be thin enough, otherwise the signal cannot penetrate. A thinner LED display, such as an ultra-thin AMOLED display (Active-matrix organic light-emitting diode, active-matrix organic light-emitting diode or active-matrix organic light-emitting diode), can be used for fingerprint recognition, while a liquid crystal display (LCD) is inherently thick, and it is not easy to achieve accurate and fast recognition results. Another optical sensor needs to transmit the fingerprint image through the screen to the sensor, so generally a thinner LED display such as an AMOLED display is used. Each pixel of the AMOLED display can be controlled independently without a constant backlight. It has the basis of light transmission, and the liquid crystal display has a backlight, and the backlight part cannot transmit the light signal in front of the screen to the back of the screen, so this optical sensor structure cannot be applied to the liquid crystal display. At the same time, due to the poor penetration of light, it is easily affected by the light source and the color of the screen, and the problem of identification errors occurs. Moreover, whether it is an ultrasonic sensor or an optical sensor, a space for setting the sensor needs to be left behind the screen. As the structure of mobile phones develops in a lighter and thinner direction, this space tends to be compressed. Sensor placement presents new challenges.

SUMMARY OF THE INVENTION

Purpose of the invention: In view of the above problems, the present invention proposes a touch screen with a full-screen fingerprint recognition function and a full-screen fingerprint recognition method based on the touch screen, which can perform fingerprint recognition at any position in the touch screen, It can be applied to both LED display and LCD display.

Technical solution: The technical solution adopted in the present invention is a touch screen with a full-screen fingerprint recognition function. The touch screen includes a screen cover that is in direct contact with fingers, a display screen below the screen cover, and an electric circuit connected to the display screen. connected flexible circuit board; the display screen is also provided with a capacitive sensor array integrated in the display screen stack, as a sensor for touch detection and fingerprint detection, the capacitive sensor array includes a first sensing electrode array and a A second sensing electrode array nearby, the first sensing electrode array is also electrically connected to the display element in the display screen stack for inputting display signals; the flexible circuit board includes a device for processing display signals, touch signals and a TDDI chip for fingerprint scanning signals, the TDDI chip is respectively connected with the first sensing electrode array and the second sensing electrode array through its I/O pins. The display screen can be a high-definition or full-high-definition liquid crystal display.

Further, 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 where the data lines are located, or is arranged in the same plane of the data lines. When two kinds of electrodes are arranged in different layers, it is based on the principle of mutual capacitance induction, and a capacitive sensor unit is formed at the intersection of the two electrodes. When the two electrodes are arranged in the same layer, it is a self-capacitance induction principle, and the capacitance change of the two electrodes to the ground is output as a detection signal, and the display screen corresponding to this solution has a lower cost.

The smart phone assembled and manufactured using the above-mentioned touch screen with a full-screen fingerprint recognition function does not need to add hardware related to fingerprint unlocking on the front panel of the mobile phone.

The present invention also provides a method for fingerprint identification using the above-mentioned touch screen, which realizes the integration of display, touch and fingerprint identification functions through a TDDI chip time-division multiplexing capacitive sensor, including the following steps:

(1) The first sensing electrode array is controlled by the TDDI chip to send a display signal to the display element, and the display screen displays an image.

(2) In the interval of each frame of image display, turn off the display element, the TDDI chip detects the capacitance change of some capacitive sensors evenly distributed on the entire display screen, and calculates the plane according to the touch detection signal generated by the capacitance change The coordinates of the inner touch point are used to locate the position of the finger; the number of the partial capacitive sensors accounts for less than 1/100 of the number of all capacitive sensors.

(3) After locating the position of the finger, detect the fingerprint detection signal generated by the capacitance change of all capacitive sensors near the position of the finger, and analyze and compare the TDDI chip to complete the fingerprint identification. During the detection process, the display element is turned off. break. This step is performed in the current frame after positioning the finger position or in the interval time between the next frame of image display.

Beneficial effects: Compared with the prior art, the present invention has the following advantages: 1. Using a TDDI chip, three functions of display, touch and fingerprint recognition are integrated, and a separate fingerprint recognition sensor hardware module behind the screen is not required, saving mobile phone space ;2. The fingerprint recognition function is integrated in the screen, and the fingerprint detection process will not be affected by the backlight, so that it can be applied to both LED displays, such as AMOLED, and LCD liquid crystal displays, suitable for all kinds of conventional displays. 3. The solution of positioning first and then identification is adopted, and the sensor module is reused, which saves the sensor or processor module, low power consumption and low cost; 4. Combined with multi-touch, multiple fingerprints can be realized at the same time. identify.

Description of drawings

1 is a schematic structural diagram of a touch screen used in the present invention;

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

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

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

FIG. 5 is a schematic diagram of the principle of fingerprint detection performed by a mutual capacitance capacitive sensor;

FIG. 6 is a schematic structural diagram of two electrodes of a self-capacitance capacitive sensor.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

The touch screen with full-screen fingerprint recognition function according to the present invention is shown in FIG. 1 , including a screen cover 1 that is in direct contact with the finger, a display screen 2 under the screen cover, and a display screen 2 connected to the screen cover. the flexible circuit board 3.

Since the thickness of the screen cover 1 itself will cause the sensor to not collect enough signals, the screen cover 1 should be made as thin as possible, reaching the level of 100 microns, so as to improve the sensitivity of the capacitive touch display screen.

The display screen 2 is provided with a capacitive sensor array integrated in the display screen stack, which serves as a sensor for touch detection and a sensor for fingerprint detection. Specifically, it is integrated in the TFT circuit layer, which can be embedded in the circuit layer, or part of it can be embedded in the TFT circuit layer, and the other part can be arranged above it. The capacitive sensor array includes a number of parallel distributed data lines 4 and a number of parallel distributed signal lines 5 perpendicular thereto. One solution is that the data line 4 (data line) is located in the TFT circuit, and the signal line 5 is arranged above the display basic unit (the display basic unit is generally arranged in order from top to bottom as color filter glass, color filter, TFT circuit, Substrate glass, color caster and backlight), the two are perpendicular to each other. In this scheme, the two electrodes are arranged on different layers, which is based on the principle of mutual capacitance induction. At this time, a capacitor is formed at the intersection of the data line 4 and the signal line 5. The data line 4 is used as the driver, and the signal line 5 is used as the output of the sensing electrode. detection signal. Another solution is that the data line 4 and the signal line 5 are located in the same layer, for example, they are both in the TFT circuit. The capacitance change to the ground formed by the data line 4 and the signal line 5 is output as a detection signal, and the display screen corresponding to this solution has a lower cost. Data lines 4 are also electrically connected to display elements in the display stack for inputting display signals. This precise and compact structure makes the data line 4 multiplexed multiple times, and is used as the source input of the display unit during display, as the touch emitter during touch detection, and as the electrode of the capacitive sensor during fingerprint detection. Moreover, in order to achieve accurate fingerprint scanning in this structure, the data line 4 needs to meet the density requirement of 20 pieces/mm. In terms of resolution, a high-definition (HD) or full high-definition (FHD screen) liquid crystal display can be used. This display screen has 1000-2000 data lines, and the density is about 40 lines/mm, which can meet the above requirements.

The flexible circuit board 3 includes a TDDI chip, and the TDDI chip is respectively connected to the data line array and the signal array through its I/O pins. TDDI (Touch and Display Driver Integration) chip, namely touch and display driver integrated chip, is used to process display, touch and fingerprint scanning signals. This chip integrates the touch chip and the display chip into a single chip, reducing display noise and making the display screen thinner overall. The TDDI chip uses the method of time division multiplexing to control the data line 4 to perform pixel display, touch detection and fingerprint detection. As shown in Figure 2, the display segment (display) is used to display images, and the data line 4 is used to control the display of screen pixels during this period. There is a period of time between the two display segments, and the interval is used as a touch scan segment (touch). During this period of time, the data line 4 is used for finger touch positioning and fingerprint scanning. The TDDI chip compares the fingerprint information to complete the fingerprint identification. The software program corresponding to the above process is executed by the TDDI chip, and the program is stored in a storage medium readable by the chip.

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

(1) The TDDI chip controls the data line (data line) arranged in the touch display screen to send the source signal for display to the display element in the display area (active area) at intervals, and the display screen displays the image. As shown in the display segment (display) in FIG. 2 . During this time, the TDDI chip controls the display of the screen pixels through the data line. At this time, the function of the data line is equivalent to the source line in the ordinary display screen, and the screen pixels display corresponding colors under its control.

(2) In the interval of each frame of image display, turn off the display element, the TDDI chip detects the capacitance change of some capacitive sensors evenly distributed on the entire display screen, and calculates the plane according to the touch detection signal generated by the capacitance change The coordinates of the touch point within, locate the finger position. As shown in FIG. 3 , it is a schematic diagram of the density of the data lines controlled by the TDDI chip during touch positioning. Because the density of capacitive sensors required to locate the finger position is not large, among thousands of data lines on the display screen, one for every dozens of data lines is enough to locate it. In the mutual capacitance structure, this part of the data line is used as the touch emitter TX to drive the touch detection, and the position where the capacitive sensor is formed on the corresponding signal line is used as the touch receiver RX to output the detection signal. In the self-capacitance structure, it is also necessary to detect signal lines equivalent to the number of data lines. Calculated according to the sensor array composed of millions of capacitive sensor units on the display screen, the number of the above-mentioned part of the capacitive sensors accounts for less than 1/100 of the total number of capacitive sensors in the screen.

(3) After locating the position of the finger, detect the fingerprint detection signal generated by the capacitance change of all capacitive sensors near the position of the finger, and analyze and compare the TDDI chip to complete the fingerprint identification. During the detection process, the display element is turned off. break. This step is performed in the current frame after positioning the finger position or in the interval time between the next frame of image display. If it is performed in the interval time between the next frame of image display after the finger position is located, it will not interfere with the display or finger positioning. During detection, all data lines and signal lines (horizontal and vertical) near the position of the finger are used as the electrodes of the fingerprint capacitive sensor. Detecting fingerprints requires high-density data lines, as shown in Figure 4, and requires all data lines near the fingerprint. Near the fingerprint, you can choose a circular area with a diameter of 1-4cm with the finger position as the center.

When the finger is pressed on the surface of the capacitive touch screen, the peaks and valleys of the fingerprint will affect the charge distribution ratio on the upper and lower electrodes of the internal capacitance of the screen. Therefore, the charge ratios on the upper and lower electrodes at the positions corresponding to the peaks and valleys of the fingerprint are different. This difference is used to reproduce the fingerprint. The principle of fingerprint detection by mutual capacitance sensor is shown in Figure 5. The data line 4 and the signal line 5 are used as the upper electrode and the lower electrode of the capacitive sensor unit respectively. The data line is used as the signal transmitter (TX) when the mutual capacitive touch works, and the LCD In the middle VCOM is subdivided into many signal lines, in AMLED, ELVSS is subdivided into many blocks as signal lines, and the signal line is also the touch receiving end (RX) when the mutual capacitive touch works.

The present invention makes full use of the data line of the pixel source, and multiplexes the data line through time division to make it serve as the display source and touch emission in different steps. electrode (TX), the capacitive electrode plate of the fingerprint detection sensor. When it is necessary to detect fingerprints, firstly use hundreds of uniform capacitive sensors to detect finger touch, locate the position of the finger, and then perform fingerprint detection on all capacitive sensors near the position of the finger, which greatly improves the data density of the finger position. More than tenfold increase in density for detecting fingerprint data. The detected fingerprint data is analyzed by the fingerprint detection algorithm in the TDDI chip, the similarity with the registered fingerprint is calculated, and the matching result of the two fingerprints is finally obtained, realizing full-screen fingerprint recognition. This solution adopts fixed-point increase in density, and the power consumption is only a few tenths of a relatively comprehensive increase in density. Combined with multi-point touch, the present invention can also realize simultaneous identification of multiple fingerprints. Since its sensing principle is not affected by the backlight of the display, both LED and LCD screens can be used, with strong versatility.

The smart phone assembled and manufactured using the above-mentioned touch screen with a full-screen fingerprint recognition function does not need to add hardware related to fingerprint unlocking on the front panel of the mobile phone, and requires fewer manufacturing parts. This means a more simplified manufacturing process and a lighter and more compact body structure, and it has strong competitiveness in the existing mobile phone market.

Claims (1)

1. A method for fingerprint identification using a touch screen, the touch screen comprising a screen cover plate (1) in direct contact with a finger, a display screen (2) below the screen cover plate (1), and a display screen (2) below the screen cover plate (1). 2) The electrically connected flexible circuit board (3); the display screen (2) is further provided with a capacitive sensor array integrated in the display screen stack, as a sensor for touch detection and fingerprint detection, the capacitive sensor array It includes a first sensing electrode array and a second sensing electrode array arranged near it, and the first sensing electrode array is also electrically connected to the display element in the display screen stack for inputting display signals; the flexible circuit board ( 3) comprising a TDDI chip for processing display signals, touch signals and fingerprint scanning signals, the TDDI chip is respectively connected with the first sensing electrode array and the second sensing electrode array through its I/O pins; the first sensing The 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) perpendicular to the data lines (4); The integration of display, touch and fingerprint recognition functions using capacitive sensors includes the following steps: (1) controlling the first sensing electrode array to send a display signal to the display element through the TDDI chip, and the display screen (2) displays an image; (2) In the interval of each frame of image display, turn off the display element, the TDDI chip detects the capacitance change of some capacitive sensors evenly distributed on the entire display screen, and calculates the plane according to the touch detection signal generated by the capacitance change The coordinates of the inner touch point to locate the finger position; (3) After locating the position of the finger, detect the fingerprint detection signal generated by the capacitance change of all capacitive sensors near the position of the finger, and analyze and compare the TDDI chip to complete the fingerprint identification. During the detection process, the display element is turned off. break; The number of some capacitive sensors uniformly distributed on the entire display screen described in the step 2 accounts for less than 1/100 of the number of all capacitive sensors; The step 3 is performed in the current frame after the finger position is located.

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