TWI718667B - Optical fingerprint collection method and optical fingerprint sensing device and handheld device using the same - Google Patents

Abstract

An optical fingerprint collection method for compensating the sensing output voltage of one of an optical sensor array to overcome the influence of ambient light on the optical sensor array when sensing fingerprints. The method includes: using a digital analogy The conversion unit generates a substrate compensation voltage according to a compensated digital value; uses an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensed output voltage and the substrate compensation voltage; and uses an analog to digital conversion unit to convert the analog voltage into An output digital value for an application processor to perform a fingerprint processing program.

Description

Optical fingerprint collection method and optical fingerprint sensing device and handheld device using the same

The present invention relates to a fingerprint collection method, in particular to an optical fingerprint collection method.

With the popularity and vigorous development of mobile devices, many mobile devices have been equipped with fingerprint recognition devices on the touch display panel, such as optical fingerprint recognition devices or capacitive fingerprint recognition devices.

The optical fingerprint identification device mainly includes a sensing panel and a readout chip, where the sensor panel has a photodiode sensing array to convert the light sensing signal into a voltage signal, and the readout chip is It includes an analog front end circuit (Analog Front End; AFE) and an analog-to-digital converter (ADC). The analog front end circuit is used to collect and amplify all of the photodiode sensing array. Said voltage signal, the analog-to-digital conversion unit is used to convert the amplified analog voltage signal into a digital voltage signal, and then upload it to an application processor through a serial peripheral interface (Serial Peripheral Interface; SPI) for subsequent processing .

Please also refer to FIGS. 1a to 1b. FIG. 1a shows a fingerprint sensing signal (including a substrate voltage V _{b) generated by a conventional readout chip on an optical fingerprint sensor panel in a low light environment.} And a fingerprint signal V _f ) a schematic diagram of an analog-to-digital conversion operation; and Fig. 1b shows the fingerprint sensing signal generated by the conventional read-out chip on the optical fingerprint sensor panel in a strong light environment A schematic diagram of performing the analog-to-digital conversion operation.

As shown in FIG. 1a, in a low light environment, the substrate voltage V _b has a low level, so _{that the voltage range of the fingerprint signal V f} falls in the low potential area of an ADC (analog-to-digital converter); and, as shown in FIG. As shown in 1b, in a strong light environment, the substrate voltage V _b has a high level, so _{that the voltage range of the fingerprint signal V f} falls in the high potential area of the ADC. That is to say, for the same fingerprint signal V _f , its base voltage V _b will vary greatly due to the strong and weak changes of the ambient light, which forces the ADC to have high resolution to smoothly transfer the fingerprint signal. V _{f is} converted into a digital signal for an application processor to perform a fingerprint processing program.

However, the design of a high-resolution analog-to-digital conversion unit is difficult, and a more complex calibration algorithm is required to ensure its performance. In addition, serial peripheral interfaces also need to spend more time uploading more data to the application processor.

In order to solve the above-mentioned problems, a novel optical fingerprint collection method is urgently needed in this field.

One objective of the present invention is to disclose an optical fingerprint acquisition method, which can generate a base compensation voltage by a compensation digital value to offset the influence of ambient light on the base voltage of the fingerprint sensing signal.

Another object of the present invention is to disclose an optical fingerprint collection method, which can eliminate the need for a high-resolution analog-to-digital conversion unit to reduce the difficulty of chip design and save design cost.

Another object of the present invention is to disclose an optical fingerprint sensing device, which can overcome the influence of ambient light on an optical sensor array when sensing fingerprints by a simple circuit.

Another object of the present invention is to disclose a handheld device that can overcome the influence of ambient light on an optical sensor array when sensing fingerprints by a simple circuit.

To achieve the foregoing objective, an optical fingerprint collection method is proposed to compensate the sensing output voltage of one of an optical sensor array to overcome the influence of ambient light on the optical sensor array when sensing fingerprints. The method includes: using a digital analog conversion unit to generate a substrate compensation voltage according to a compensation digital value; using an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensing output voltage and the substrate compensation voltage; and using an analog digital The conversion unit converts the analog voltage into an output digital value for an application processor to perform a fingerprint processing program.

In one embodiment, the compensation digital value is determined based on an average value of at least one previous digital value of the sensed output voltage.

In one embodiment, the compensation digital value is determined according to a digital value generated by a pre-fingerprint collection procedure.

In one embodiment, the pre-fingerprint collection procedure does not overlap or partially overlap with a subsequent fingerprint collection procedure.

To achieve the foregoing objective, the present invention further provides an optical fingerprint sensing device having an optical sensor array and a sensing circuit for driving the optical sensor array, the sensing circuit having a digital-to-analog conversion unit , An analog front-end circuit and an analog-to-digital conversion unit, and is used to implement an optical fingerprint acquisition method to compensate the sensing output voltage of one of the optical sensor arrays to overcome ambient light on the optical sensor array The method for sensing the influence of fingerprints includes: using the digital-to-analog conversion unit to generate a base compensation voltage based on a compensation digital value; using the analog front-end circuit to generate an analog based on the voltage difference between the sensing output voltage and the base compensation voltage Voltage; and using the analog-to-digital conversion unit to convert the analog voltage into an output digital value for an application processor to perform a fingerprint processing program.

In one embodiment, the compensation digital value is determined based on at least one previous digital value of the sensed output voltage.

In one embodiment, the compensation digital value is determined according to a digital value generated by a pre-fingerprint collection procedure.

In one embodiment, the pre-fingerprint collection procedure does not overlap or partially overlap with a subsequent fingerprint collection procedure.

In addition, the present invention also provides a handheld device having a central processing unit and a display device. The display device has the aforementioned optical fingerprint sensing device, wherein the central processing unit is used to communicate with the display device.

In one embodiment, the handheld device is a smart phone or a portable computer.

In order to enable your reviewer to further understand the structure, features and purpose of the present invention, the drawings and detailed descriptions of preferred specific embodiments are attached.

Please refer to FIG. 2, which illustrates a flowchart of an embodiment of the optical fingerprint collection method of the present invention, wherein the optical fingerprint collection method is used to compensate the output voltage of one of the optical sensor arrays to overcome the environment The influence of light on the optical sensor array when sensing fingerprints, the method includes:

Step a: Utilize a digital-to-analog conversion unit to generate a base compensation voltage according to a compensation digital value;

Step b: using an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensing output voltage and the substrate compensation voltage; and

Step c: Use an analog-to-digital conversion unit to convert the analog voltage into an output digital value for an application processor to perform a fingerprint processing program.

In step a, the compensation digital value can be determined by an average value of at least one previous digital value of the sensed output voltage. For example, the compensation digital value can be a digital value generated by a pre-fingerprint collection procedure Decided. In addition, in possible embodiments, the pre-fingerprint collection procedure may not overlap or partially overlap with a subsequent fingerprint collection procedure. In other words, because the fingerprint collection procedure can be divided into steps such as reset, exposure and signal collection, the subsequent fingerprint collection procedure can be carried out after the pre-fingerprint collection procedure, or while the pre-fingerprint collection procedure is still in progress ( Or just after completing) the signal acquisition step.

In step b, the analog front-end circuit is used to perform an amplifying operation on the voltage difference between the sensing output voltage and the substrate compensation voltage to generate an analog voltage. In a preferred embodiment, the analog front-end circuit is a switched capacitor subtraction circuit.

In step c, the analog-to-digital conversion unit is used to convert the analog voltage into an output digital value for an application processor to perform a fingerprint processing program. Since the base voltage of the sensing output voltage has been removed in step b, the analog-to-digital conversion unit can generate digital fingerprint information without having to configure a high-bit resolution.

Please refer to FIG. 3, which shows a block diagram of an embodiment of the optical fingerprint sensing device of the present invention.

As shown in FIG. 3, an optical fingerprint sensing device 100 has an optical sensor array 110, a sensing circuit 120 for driving the optical sensor array 110, and an application processor 130.

The optical sensor array 110 is used to generate a sensing output voltage V _S when sensing a fingerprint.

The sensing circuit 120 has a digital-to-analog conversion unit 120a, an analog front-end circuit 120b, and an analog-to-digital conversion unit 120c, and is used to perform an optical fingerprint collection method to sense the output voltage V of the optical sensor array 110 _S is compensated to overcome the ambient light effect on the optical sensor array 110 upon sensing a fingerprint, the method comprising: using a digital to analog conversion unit 120a generates a base offset voltage V _b by a compensation digital value D _b; using analog front-end _{The circuit 120b generates an analog voltage V A} according to the voltage difference between the sensed output voltage V _S and the substrate compensation voltage V _b ; and uses the analog-to-digital conversion unit 120c to convert the analog voltage V _A into an output digital value D _OUT for supplying the processor 130 performs a fingerprint processing program.

The compensation digital value D _b can be determined by an average value of at least one previous digital value of the _{sensed output voltage V S. For example, the compensation digital value D b} can be determined by a digital value generated by a pre-fingerprint collection procedure. In addition, in a possible embodiment, the pre-fingerprint collection procedure may not overlap or partially overlap with a subsequent fingerprint collection procedure. In other words, because the fingerprint collection procedure can be divided into steps such as reset, exposure and signal collection, the subsequent fingerprint collection procedure can be carried out after the pre-fingerprint collection procedure, or while the pre-fingerprint collection procedure is still in progress ( Or just after completing) the signal acquisition step.

In addition, the analog front-end circuit 120b is used to perform an amplifying operation on the voltage difference between the _{sensing output voltage V S} and the substrate compensation voltage V _{b to generate the analog voltage V A.} In a preferred embodiment, the analog front-end circuit 120b is a switched capacitor subtraction circuit.

In addition, the analog-to-digital conversion unit 120c is used to perform an analog-to-digital conversion operation _{on the analog voltage V A.} Since the analog front-end circuit 120b has sensing output voltage V _S of the substrate is removed, therefore, ADCs unit 120c may generate a digital fingerprint is the information to be arranged without high bit resolution.

Based on the above description, the present invention further discloses a handheld device.

Please refer to FIG. 4, which shows a block diagram of an embodiment of the handheld device of the present invention.

As shown in FIG. 4, a handheld device 200 has a central processing unit 210 and a display device 220. The display device 220 has an optical fingerprint sensing device 100 as shown in FIG. 3, wherein the central processing unit 210 is used for Communicate with the display device 220.

In addition, the handheld device 200 can be a smart phone or a portable computer.

With the design disclosed above, the present invention has the following advantages:

1. The optical fingerprint acquisition method of the present invention can generate a substrate compensation voltage by a compensation digital value to offset the influence of ambient light on the substrate voltage of the fingerprint sensing signal.

2. The optical fingerprint collection method of the present invention can eliminate the need for a high-resolution analog-to-digital conversion unit to reduce the difficulty of chip design and save design costs.

3. The optical fingerprint collection device of the present invention can overcome the influence of ambient light on an optical sensor array when sensing fingerprints by a simple circuit.

4. The handheld device of the present invention can overcome the influence of ambient light on an optical sensor array when sensing fingerprints by a simple circuit.

The disclosure in this case is a preferred embodiment, and any partial changes or modifications that are derived from the technical ideas of the case and can be easily inferred by those who are familiar with the art will not deviate from the scope of the patent right of the case.

In summary, regardless of the purpose, means and effects of this case, it is shown that it is very different from the conventional technology, and its first invention is suitable for practicality, and it does meet the patent requirements of the invention. I implore the examiner to observe it and grant the patent as soon as possible. Society is for the best prayer.

100: Optical fingerprint sensor

110: Optical sensor array

120: Sensing circuit

130: application processor

120 a: digital-to-analog conversion unit

120 b: analog front-end circuit

120 c: analog to digital conversion unit

200: Handheld device

210: Central Processing Unit

220: display device

Step a: Use a digital-to-analog conversion unit to generate a base compensation voltage according to a compensation digital value

Step b: Use an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensing output voltage and the substrate compensation voltage

Step c: Use an analog-digital conversion unit to convert the analog voltage into an output digital value for an application processor to perform a fingerprint processing program

FIG. 1a shows a schematic diagram of a conventional read-out chip performing an analog-to-digital conversion operation on a fingerprint sensing signal generated by an optical fingerprint sensing panel in a low light environment. FIG. 1b shows a schematic diagram of the conventional read-out chip of FIG. 1a performing the analog-to-digital conversion operation on the fingerprint sensing signal generated by the optical fingerprint sensing panel under a strong light environment. Fig. 2 shows a flowchart of an embodiment of the optical fingerprint collection method of the present invention. FIG. 3 shows a block diagram of an embodiment of the optical sensing device of the present invention. FIG. 4 is a block diagram of an embodiment of the handheld device of the present invention.

Step a: Use a digital-to-analog conversion unit to generate a base compensation voltage according to a compensation digital value

Step b: Use an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensing output voltage and the substrate compensation voltage

Step c: Use an analog-digital conversion unit to convert the analog voltage into an output digital value for an application processor to perform a fingerprint processing program

Claims (8)

An optical fingerprint acquisition method for compensating the sensing output voltage of one of an optical sensor array to overcome the influence of ambient light on the optical sensor array when sensing fingerprints. The method includes: using a digital analogy The conversion unit generates a substrate compensation voltage according to a compensation digital value; uses an analog front-end circuit to generate an analog voltage according to the voltage difference between the sensed output voltage and the substrate compensation voltage; and uses an analog-digital conversion unit to convert the analog voltage into An output digital value is used by an application processor to perform a fingerprint processing procedure; wherein the compensation digital value is determined according to a digital value generated by a pre-fingerprint collection procedure. For the optical fingerprint collection method described in item 1 of the scope of patent application, the compensation digital value is determined based on an average value of at least one previous digital value of the sensing output voltage. For the optical fingerprint collection method described in item 1 of the scope of patent application, the pre-fingerprint collection procedure does not overlap or partially overlap with a subsequent fingerprint collection procedure. An optical fingerprint sensing device having an optical sensor array and a sensing circuit for driving the optical sensor array, the sensing circuit having a digital analog conversion unit, an analog front-end circuit and an analog digital The conversion unit is used to perform an optical fingerprint acquisition method to compensate the sensing output voltage of one of the optical sensor arrays to overcome the influence of ambient light on the optical sensor array when fingerprints are sensed, the method The method includes: using the digital-to-analog conversion unit to generate a substrate compensation voltage according to a compensation digital value; using the analog front-end circuit to generate an analog voltage according to the voltage difference between the sensing output voltage and the substrate compensation voltage; and using the analog-to-digital conversion unit The analog voltage is converted into an output digital value for an application processor to perform a fingerprint processing procedure; wherein the compensation digital value is determined according to a digital value generated by a pre-fingerprint collection procedure. According to the optical fingerprint sensing device described in item 4 of the scope of patent application, the compensation digital value is determined based on at least one previous digital value of the sensing output voltage. For the optical fingerprint sensing device described in item 4 of the scope of patent application, the pre-fingerprint collection procedure does not overlap or partially overlap with a subsequent fingerprint collection procedure. A handheld device having a central processing unit and a display device, the display device having the optical fingerprint sensing device as described in any one of claims 4 to 6, wherein the central processing unit is used for Communicate with the display device. For example, the handheld device described in item 7 of the scope of patent application is a smart phone or a portable computer.

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