Under-screen fingerprint sensing device and control method thereof

Abstract

The application provides an under-screen fingerprint sensing device and a control method thereof. The device comprises a plurality of sub-pixel circuits and a driving control chip. The sub-pixel circuit is composed of two thin film transistors, a liquid crystal pixel and a sensing electrode plate. The sensing electrode plate and the fingerprint of a finger form a sensing capacitor. The self-capacitance sensing circuit is manufactured by using a TFT process. The same circuit is also used to drive the liquid crystal display, so as to achieve the integration of the liquid crystal display and the fingerprint sensing device, and the traditional liquid crystal display can be integrated with the fingerprint collection equipment.

Description

Technical Field

[0001] This invention belongs to the field of under-display fingerprint recognition technology, and particularly relates to an under-display fingerprint sensing device and its control method. Background Technology

[0002] With the widespread use of full-screen phones, under-display optical fingerprint detection technology is mainly used to collect fingerprint images. However, this method can only be used on OLED (Organic Light-Emitting Diode) display panels. Therefore, phones that use LCD (Liquid Crystal Display) display panels, which have lower production costs and better display effects, can only place the fingerprint collection device on the side or back cover, which does not conform to general usage habits.

[0003] Therefore, there is a need for other methods to integrate fingerprint sensing devices on the front of LCD display panels. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide an under-display fingerprint sensing device and a control method thereof, so as to realize the integration of a fingerprint sensing device on the front of an LCD display panel.

[0005] A first aspect of the present invention provides an under-display fingerprint sensing device, comprising: a plurality of sub-pixel circuits and a driving control chip;

[0006] Each sub-pixel circuit includes a first thin-film transistor, a second thin-film transistor, a liquid crystal pixel, and a sensing electrode plate; the drain of the first thin-film transistor is connected to one end of the sensing electrode plate and one end of the liquid crystal pixel, and the gate of the first thin-film transistor is externally connected to a first control signal; the drain of the second thin-film transistor is connected to one end of the sensing electrode plate and one end of the liquid crystal pixel, and the gate of the second thin-film transistor is externally connected to a second control signal; the other end of the liquid crystal pixel and the source of the second thin-film transistor are both externally connected to a reference voltage.

[0007] The drive control chip internally includes an operational amplifier, a charge amplifier, a reset switch, a feedback capacitor, an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC). The source of the first thin-film transistor (TFT) is connected to the negative input of the charge amplifier, the positive input of the charge amplifier is connected to an external reference voltage VREF, and the output of the charge amplifier is connected to the input of the ADC. The source of the first TFT is also connected to the output of the operational amplifier, the negative input of the operational amplifier is connected to its output, and the positive input of the operational amplifier is connected to the output of the DAC. One end of the feedback capacitor and the reset switch is connected to the negative input of the charge amplifier, and the other end of the feedback capacitor and the reset switch is connected to the output of the charge amplifier. The reset switch is controlled by a reset signal.

[0008] As one possible implementation, the other end of the liquid crystal pixel and the source of the second thin-film transistor are both externally connected to reference voltages, including: the other end of the liquid crystal pixel is externally connected to a first reference voltage VCOM, and the source of the second thin-film transistor is externally connected to a second reference voltage VGL.

[0009] As one possible implementation, the other end of the liquid crystal pixel and the source of the second thin-film transistor are both externally connected to a reference voltage signal, including: the other end of the liquid crystal pixel and the source of the second thin-film transistor are connected to the same reference voltage VCOM.

[0010] As one possible implementation, multiple sub-pixel circuits are arranged in n rows and m columns, and a row-by-row control method is adopted;

[0011] The gates of the first thin-film transistors in each row of sub-pixel circuits are connected to form a first electrode, which is used to receive the first control signal of the row; the gates of the second thin-film transistors in each row of sub-pixel circuits are connected to form a second electrode, which is used to receive the second control signal of the row.

[0012] As one possible implementation, the second control signal for each row can be an independent signal, or the second control signal for each row can be the first control signal of the previous row.

[0013] As one possible implementation, a shift register circuit is also included, through which the drive control chip provides the first control signal and the second control signal required by the under-display fingerprint sensing device.

[0014] A second aspect of the present invention provides a control method for an under-display fingerprint sensing device. The method is applied to an under-display fingerprint sensing device as described in the first aspect and any possible implementation thereof, wherein a plurality of sub-pixel circuits in the under-display fingerprint sensing device are arranged in n rows and m columns.

[0015] This method employs a line-by-line scanning approach, including:

[0016] When liquid crystal display is required, for each row of sub-pixel circuit, the first thin-film transistor is connected through the first control signal of that row, and the second thin-film transistor is disconnected through the second control signal of that row;

[0017] When fingerprint sensing is required, for each row of sub-pixel circuits, the first thin-film transistor is first disconnected by the first control signal of the row, and the second thin-film transistor is connected by the second control signal of the row, while the reset switch is closed to discharge the feedback capacitor; then, the first thin-film transistor is turned on by the first control signal of the row, and the second thin-film transistor and the reset switch are turned off by the second control signal of the row.

[0018] The beneficial effects of the embodiments of the present invention compared with the prior art are as follows:

[0019] The under-display fingerprint sensing device provided in this invention integrates a first thin-film transistor, a second thin-film transistor, a liquid crystal pixel, and a sensing electrode plate in its sub-pixel circuit. Controlled by a first control signal and a second control signal, it achieves both liquid crystal display and fingerprint sensing. Because the self-capacitance sensing circuit is fabricated using thin-film transistor technology, the same circuit is also used to drive the liquid crystal display, thus integrating the liquid crystal display screen and the fingerprint sensing device. This allows a traditional liquid crystal display screen to integrate a fingerprint acquisition device. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the sub-pixel circuit and driving control chip provided in an embodiment of the present invention. Figure 1 ;

[0022] Figure 2 This is a schematic diagram of the sub-pixel circuit and driving control chip provided in an embodiment of the present invention. Figure 2 ;

[0023] Figure 3 This is a schematic diagram of the structure of the under-display fingerprint sensing device provided in an embodiment of the present invention. Figure 1 ;

[0024] Figure 4 This is a schematic diagram of the control logic of the under-display fingerprint sensing device provided in an embodiment of the present invention;

[0025] Figure 5 This is a schematic diagram of the structure of the under-display fingerprint sensing device provided in an embodiment of the present invention. Figure 2 . Detailed Implementation

[0026] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0027] To illustrate the technical solution described in this invention, specific embodiments are described below.

[0028] The present invention aims to provide an integrated display driving and capacitive sensing circuit based on TFT-LCD (Thin Film Transistor; Liquid Crystal Display) technology, enabling traditional liquid crystal displays to integrate fingerprint acquisition devices.

[0029] Please see also Figure 1 and Figure 2 As shown, the connection between a sub-pixel circuit and the driving control chip will be used as an example for explanation.

[0030] The sub-pixel circuit includes a first thin-film transistor (TFT1), a second thin-film transistor (TFT2), a liquid crystal pixel (LC), and a sensing electrode plate (t). The sensing electrode plate (t) together with the fingerprint sensor constitutes the sensing capacitor. The drain of the first thin-film transistor (TFT1) is connected to one end of the sensing electrode plate (t) and one end of the liquid crystal pixel (LC), respectively. The gate of the first thin-film transistor (TFT1) is externally connected to a first control signal (such as...). Figure 1 , Figure 2 Scan in <n>The drain of the second thin-film transistor TFT2 is connected to one end of the sensing electrode plate t and the liquid crystal pixel LC, respectively. The gate of the second thin-film transistor TFT2 is externally connected to a second control signal (such as...). Figure 1 Reset in <n>, Figure 2 Scan in <n-1>The other end of the liquid crystal pixel LC and the source of the second thin-film transistor TFT2 are both externally connected to a reference voltage (such as...). Figure 1 VCOM and VGL in Figure 2 VCOM in the middle.

[0031] The drive control chip internally includes an operational amplifier (OP), a charge amplifier (CA), a reset switch (Reset), and a feedback capacitor (C). F The system consists of an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC). The source of the first thin-film transistor (TFT1) is connected to the negative input of a charge amplifier (CA). The positive input of CA is connected to an external reference voltage VREF. The output of CA is connected to the input of the ADC. The source of TFT1 is also connected to the output of an operational amplifier (OP). The negative input of OP is connected to its output. The positive input of OP is connected to the output of the DAC. The feedback capacitor C... F One end of the reset switch (Reset) is connected to the negative input terminal of the charge amplifier (CA), and the feedback capacitor (C) is connected to the negative input terminal of the charge amplifier (CA). F The other end of the reset switch is connected to the output of the charge amplifier CA.

[0032] In this embodiment, display driving and fingerprint sensing operate in a time-division multiplexing manner. When display is required, TFT1 is turned on, and the chip provides a driving voltage to the liquid crystal pixel LC through TFT1, enabling the sub-pixel circuit to generate a specified light transmittance. When fingerprint sensing is required, TFT2 is turned on first to reset, restoring the liquid crystal pixel LC and the sub-pixel circuit, such as the sensing electrode plate t, to the reference voltage. Then, TFT1 is turned on, and the chip drives the sub-pixel circuit to the VREF voltage. Since the depth of fingerprint ridges varies, the size of the resulting sensing capacitance also varies, and the amount of charge required to drive the sensing capacitance to the VREF voltage also varies. The chip can detect the fingerprint ridges and acquire a fingerprint image by detecting the amount of driving charge.

[0033] As one possible implementation, such as Figure 1 As shown, the other end of the liquid crystal pixel LC and the source of the second thin film transistor TFT2 are both externally connected to reference voltages, including: the other end of the liquid crystal pixel LC is externally connected to a first reference voltage VCOM, and the source of the second thin film transistor TFT2 is externally connected to a second reference voltage VGL.

[0034] In this embodiment, typically, multiple under-display fingerprint sensing sub-circuits are arranged and combined, and a row-by-row control method is used. Taking the sub-pixel circuit in the nth row and mth column as an example, see [link to documentation]. Figure 1 This displays the work done during the nth row of the task. <n>When the voltage changes from VGL to VGH, TFT1 is turned on. The chip converts the display data into a drive voltage via DAC, and then the OP outputs the drive voltage to the Data. <m>, the liquid crystal LC generates a corresponding transmittance after receiving the input voltage. During the fingerprint detection, first, the Reset <n>the potential of the liquid crystal capacitor (C LC , equivalent capacitance at the liquid crystal pixel LC) and the sensing capacitor (C t , equivalent capacitance at the sensing electrode plate t) is fixed at an initial voltage value VGL, while the reset signal Reset is high, the detection circuit in the chip is also reset, and the switch is closed to discharge the feedback capacitor C f , and then the Reset <n> / Reset goes low, Scan <n>Pull high, chip pair Data <m>The driving VREF voltage, due to the conservation of charge, the charge transferred to the output of the CA by the sub-pixel circuit driving, the output voltage generated is:

[0035]

[0036] Finally, the output voltage is converted by the ADC to generate the detection data Sensing data. In the embodiment, the second control signal of each row can be an independent signal provided by the driving control chip.

[0037] In the structure shown in Figure 1 The formed under-screen fingerprint sensing device is as shown in Figure 3 The gate of the first thin film transistor TFT1 in each row of sub-pixel circuits is connected to form a first electrode, and the first electrode is used to receive the first control signal Scan <n>; the gate of the second thin film transistor TFT2 in each row of sub-pixel circuits is connected to form a second electrode, and the second electrode is used for receiving a second control signal Reset of the nth row <n>The specific control logic can refer to the above description and Figure 4 The detailed description is omitted here.

[0038] In the embodiment of the application, the chip needs to output Scan<1~n> and Reset<1~n>, which will consume too many pins and increase the chip area in the application of high-resolution display screen. Figure 1 Figure 3 In the embodiment of the application, the chip needs to output Scan<1~n> and Reset<1~n>, which will consume too many pins and increase the chip area in the application of high-resolution display screen.

[0039] Therefore, the embodiment shown in FIG. 4 is provided, in which the other end of the liquid crystal pixel LC and the source level of the second thin film transistor TFT2 are connected with a reference voltage signal, and the embodiment can further include that after the other end of the liquid crystal pixel LC and the source level of the second thin film transistor TFT2 are connected, the same reference voltage VCOM is connected. Figure 2 Figure 5 In the embodiment of the application, the chip needs to output Scan<1~n> and Reset<1~n>, which will consume too many pins and increase the chip area in the application of high-resolution display screen.

[0040] In the embodiment of the application, the chip needs to output Scan<1~n> and Reset<1~n>, which will consume too many pins and increase the chip area in the application of high-resolution display screen. <n>Input, change to Scan <n-1>i.e. the first control signal Scan of the (n-1)th row <n-1>Also as the second control signal of the nth row, and VGL is changed to VCOM, other signals remain unchanged. First, during the display period, when the (n-1)th row is scanned, the TFT2 of the nth row is turned on, the voltage difference between the liquid crystal LC is reset to zero, and the minimum light transmittance is generated. After that, the nth row is scanned to turn on TFT1, and the specified driving voltage is input to the liquid crystal LC to generate the specified light transmittance. Therefore, in a frame of display image, the display color of each row will be temporarily changed to black when the previous row is scanned, but due to the visual persistence of the human eye, the color change in this period (less than 10us) will not be felt by the human eye. The working mode during the fingerprint detection period is the same as that of the first embodiment, except that the VGL voltage is changed to the VCOM voltage, and the output voltage is also changed relatively:

[0041]

[0042] It can be seen that the under-screen fingerprint sensing device provided by the embodiment of the present application integrates the first thin film transistor, the second thin film transistor, the liquid crystal pixel and the sensing electrode plate, and controls through the first control signal and the second control signal, so as to realize liquid crystal display and fingerprint sensing. Since the self-capacitance sensing circuit is manufactured by using the thin film transistor process, the same circuit is also used to drive the liquid crystal display, realizes the integration of the liquid crystal display screen and the fingerprint sensing device, and makes the traditional liquid crystal display screen be able to integrate the fingerprint collection equipment.

[0043] As a possible implementation manner, the driving control chip further comprises a shift register circuit, and the driving control chip provides the first control signal and the second control signal required by the under-screen fingerprint sensing device through the shift register circuit.

[0044] In the embodiment, the signals of Scan<0~n> are generated by the driving control chip, but in order to further reduce the pin number of the driving control chip, a shift register circuit can be manufactured on the glass to generate the signals of Scan<0~n>, and the driving control chip only needs to output the control signals (such as a start signal and a clock signal) required by the shift register circuit, so that the pin number of the chip can be greatly reduced. The reference voltage VREF, the reference voltage and the reset signal are directly generated by the driving control chip, and do not need to pass through the shift register circuit.

[0045] The embodiment of the application has the innovative point of providing a display driving and capacitive sensing integrated circuit based on TFT-LCD technology, using TFT technology to manufacture a self-capacitive sensing circuit, and the same circuit is also used to drive liquid crystal display, so as to achieve the integration of the liquid crystal display and the fingerprint sensing device, and make the traditional liquid crystal display screen can integrate the fingerprint collection equipment. Since the maturity of the LCD display screen is quite high, its cost and display effect are better than the OLED display screen, once the fingerprint detection technology and the liquid crystal display technology are integrated, the fingerprint collection can be realized on the front of the LCD display screen, and the convenience of fingerprint identification is improved.

[0046] The embodiment of the application provides a control method of the under-screen fingerprint sensing device.

[0047] The plurality of sub-pixel circuits in the under-screen fingerprint sensing device are arranged as n rows and m columns.

[0048] The method adopts the row-by-row scanning mode, and includes the following steps.

[0049] When the liquid crystal display is needed, for each row of sub-pixel circuits, the first thin film transistor is connected through the first control signal of the row, and the second thin film transistor is disconnected through the second control signal of the row.

[0050] When the fingerprint sensing is needed, for each row of sub-pixel circuits, the first thin film transistor is disconnected through the first control signal of the row, and the second thin film transistor is connected through the second control signal of the row, and the feedback capacitor is discharged by closing the reset switch; then, the first thin film transistor is turned on through the first control signal of the row, and the second thin film transistor is disconnected and the reset switch is disconnected through the second control signal of the row.

[0051] The detailed steps can refer to the description in the device embodiment described above, and will not be described here.

[0052] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the application.

[0053] The above embodiments are only used to illustrate the technical solutions of the application, but not limit it; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application, and should be included in the protection scope of the application. < / n> ​​< / n> < / n> < / m> < / n> < / n> < / n> < / m> < / n> < / n> < / n>

Claims

1. An under-display fingerprint sensing device, characterized in that, include: Multiple sub-pixel circuits and driving control chips; Each sub-pixel circuit includes a first thin-film transistor, a second thin-film transistor, a liquid crystal pixel, and a sensing electrode plate; The drain of the first thin-film transistor is connected to the sensing electrode plate and one end of the liquid crystal pixel, respectively, and the gate of the first thin-film transistor is connected to a first control signal; the drain of the second thin-film transistor is connected to the sensing electrode plate and one end of the liquid crystal pixel, respectively, and the gate of the second thin-film transistor is connected to a second control signal; the other end of the liquid crystal pixel and the source of the second thin-film transistor are both connected to a reference voltage. The drive control chip internally includes an operational amplifier, a charge amplifier, a reset switch, a feedback capacitor, an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC). The source of the first thin-film transistor (TFT) is connected to the negative input terminal of the charge amplifier, the positive input terminal of the charge amplifier is connected to an external reference voltage VREF, and the output terminal of the charge amplifier is connected to the input terminal of the ADC. The source of the first TFT is also connected to the output terminal of the operational amplifier, the negative input terminal of the operational amplifier is connected to its output terminal, and the positive input terminal of the operational amplifier is connected to the output terminal of the DAC. One end of the feedback capacitor and the reset switch is connected to the negative input terminal of the charge amplifier, and the other end of the feedback capacitor and the reset switch is connected to the output terminal of the charge amplifier. The reset switch is controlled by a reset signal. The liquid crystal display and fingerprint sensing operate in a time-division multiplexing manner. When performing liquid crystal display, the first thin-film transistor is turned on, and the chip provides driving voltage to the liquid crystal pixels through the first thin-film transistor. When performing fingerprint sensing, the second thin-film transistor is turned on first to reset, restoring the liquid crystal pixels and sub-pixel circuits such as the sensing electrode plate to the reference voltage. Then, the first thin-film transistor is turned on, and the chip drives the sub-pixel circuits to the VREF voltage. The chip detects the fingerprint ridges by detecting the amount of driving charge and acquires the fingerprint image.

2. The under-display fingerprint sensing device as described in claim 1, characterized in that, The other end of the liquid crystal pixel and the source of the second thin film transistor are both externally connected to reference voltages, including: the other end of the liquid crystal pixel is externally connected to a first reference voltage VCOM, and the source of the second thin film transistor is externally connected to a second reference voltage VGL.

3. The under-display fingerprint sensing device as described in claim 1, characterized in that, The other end of the liquid crystal pixel and the source of the second thin film transistor are both externally connected to a reference voltage signal, including: the other end of the liquid crystal pixel and the source of the second thin film transistor are connected to the same reference voltage VCOM.

4. The under-display fingerprint sensing device as described in any one of claims 1-3, characterized in that, Multiple sub-pixel circuits are arranged in n rows and m columns, and are controlled row by row. The gates of the first thin-film transistors in each row of sub-pixel circuits are connected to form a first electrode, which is used to receive a first control signal for that row; the gates of the second thin-film transistors in each row of sub-pixel circuits are connected to form a second electrode, which is used to receive a second control signal for that row.

5. The under-display fingerprint sensing device as described in claim 4, characterized in that, The second control signal for each row can be an independent signal, or the second control signal for each row can be the first control signal of the previous row.

6. The under-display fingerprint sensing device as described in claim 4, characterized in that, It also includes a shift register circuit, through which the drive control chip provides the first control signal and the second control signal required by the under-display fingerprint sensing device.

7. A control method for an under-display fingerprint sensing device, characterized in that, The method is applied to the under-display fingerprint sensing device as described in any one of claims 1-6, wherein the plurality of sub-pixel circuits in the under-display fingerprint sensing device are arranged in n rows and m columns; The method employs a line-by-line scanning approach, including: When liquid crystal display is required, for each row of sub-pixel circuit, the first thin-film transistor is connected through the first control signal of that row, and the second thin-film transistor is disconnected through the second control signal of that row; When fingerprint sensing is required, for each row of sub-pixel circuits, the first thin-film transistor is first disconnected by the first control signal of the row, and the second thin-film transistor is connected by the second control signal of the row. At the same time, the reset switch is closed to discharge the feedback capacitor. Then, the first thin-film transistor is turned on by the first control signal of the row, and the second thin-film transistor and the reset switch are turned off by the second control signal of the row. The liquid crystal display and fingerprint sensing operate in a time-division multiplexing manner. When performing liquid crystal display, the first thin-film transistor is turned on, and the chip provides driving voltage to the liquid crystal pixels through the first thin-film transistor. When performing fingerprint sensing, the second thin-film transistor is turned on first to reset, restoring the liquid crystal pixels and sub-pixel circuits such as the sensing electrode plate to the reference voltage. Then, the first thin-film transistor is turned on, and the chip drives the sub-pixel circuits to the VREF voltage. The chip detects the fingerprint ridges by detecting the amount of driving charge and acquires the fingerprint image.

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