CN105913049B - Fingerprint acquisition device - Google Patents
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- CN105913049B CN105913049B CN201610345417.0A CN201610345417A CN105913049B CN 105913049 B CN105913049 B CN 105913049B CN 201610345417 A CN201610345417 A CN 201610345417A CN 105913049 B CN105913049 B CN 105913049B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/12—Fingerprints or palmprints
- G06V40/13—Sensors therefor
- G06V40/1306—Sensors therefor non-optical, e.g. ultrasonic or capacitive sensing
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2218/00—Aspects of pattern recognition specially adapted for signal processing
- G06F2218/02—Preprocessing
- G06F2218/04—Denoising
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Abstract
The embodiment of the invention discloses a fingerprint acquisition device, which comprises a fingerprint sensing array, an adjustable gain amplifier, a common-mode voltage compensation circuit, a voltage analog-to-digital converter and a signal processing unit, wherein the fingerprint sensing array is used for acquiring fingerprint information to obtain a voltage signal; the adjustable gain amplifier is used for amplifying the voltage signal to obtain an amplified signal; the common-mode voltage compensation circuit is used for compensating voltage for the amplified signal so as to eliminate common-mode voltage and noise in the amplified signal; a voltage analog-to-digital converter for converting the amplified signal from which the common mode voltage and noise are removed into a digital signal; and the signal processing unit is used for obtaining an initial fingerprint image according to the digital signal and controlling the parameters of the adjustable gain amplifier, the common-mode voltage compensation circuit and the voltage analog-to-digital converter based on the histogram of the initial fingerprint image. By adopting the invention, a clearer fingerprint image can be obtained under the conditions of uneven thickness of the protective layer and larger fingerprint difference among users.
Description
Technical Field
The invention relates to the technical field of computers, in particular to a fingerprint acquisition device.
Background
Referring to fig. 1, fig. 1 is a schematic structural diagram of a fingerprint acquisition device in the prior art, the fingerprint acquisition device includes a protective layer, a glue and a fingerprint sensing array, the fingerprint sensing array (i.e. a fingerprint acquisition chip) is disposed under the protective layer, and the protective layer and the fingerprint sensing array are adhered together by the glue. The principle of the fingerprint acquisition device for acquiring fingerprints is shown in fig. 2, and parasitic capacitance is formed between the finger and the metal electrode on the surface of the fingerprint sensing array. Because the distances from the valleys and the ridges of the finger to the metal electrodes are different, the formed parasitic capacitance is also different, and thus the fingerprint pattern can be reflected by measuring the parasitic capacitance. Because the glue thickness is less, do not consider the influence of glue to parasitic capacitance. The parasitic capacitance between the finger and the metal electrode (hereinafter referred to as finger capacitance Cf) is expressed as: cf ═ Cx x Cy)/(Cx + Cy),
wherein Cx ═ epsilon _ f ═ S)/df, (epsilon _0 ∈ _ x · S)/dx, Cx is the capacitance between the finger and the surface of the protective layer, Cy is the capacitance between the surface of the protective layer and the metal electrode, S is the electrode area, dx is the thickness of the protective layer, df is the distance between the surface of the finger and the surface of the protective layer, epsilon _0 is the vacuum dielectric constant, epsilon _ x is the dielectric constant of the protective layer, and epsilon _ f is the dielectric constant between the finger and the protective layer.
In the research process, the inventor of the technical scheme finds that offset noise is formed because the problem of uneven thickness exists in the manufacturing process of a protective layer and glue in the conventional fingerprint acquisition device, and Cy is different at each position of an acquisition array when the surface of the protective layer is uneven, so that the offset noise needs to be offset.
Disclosure of Invention
The embodiment of the invention discloses a fingerprint acquisition device which can obtain a clearer fingerprint image under the conditions that the thickness of a protective layer is not uniform and the fingerprint difference between users is large.
In a first aspect, an embodiment of the present invention provides a fingerprint acquisition device, where the fingerprint acquisition device includes a fingerprint sensing array, an adjustable gain amplifier, a common-mode voltage compensation circuit, a voltage analog-to-digital converter, and a signal processing unit, where:
the fingerprint sensing array is used for collecting fingerprint information to obtain a voltage signal and outputting the voltage signal to the adjustable gain amplifier;
the adjustable gain amplifier is used for amplifying the voltage signal to obtain an amplified signal;
the common mode voltage compensation circuit is used for compensating voltage for the amplified signal so as to eliminate common mode voltage and noise in the amplified signal;
the voltage analog-to-digital converter is used for receiving the amplified signal with the common-mode voltage and the noise eliminated and converting the amplified signal with the common-mode voltage and the noise eliminated into a digital signal; outputting the digital signal to the signal processing unit;
the signal processing unit is used for obtaining an initial fingerprint image according to the digital signal and judging whether a histogram of the initial fingerprint image meets a preset condition or not; if the digital signal is not satisfied, controlling and adjusting the amplification factor of the adjustable gain amplifier, and at least one of the reference voltage of the voltage analog-to-digital converter and the voltage value compensated by the common-mode voltage compensation circuit until the histogram of the fingerprint image obtained by the signal processing unit according to the digital signal satisfies the preset condition.
Specifically, the output of the fingerprint sensing array is connected to the input of the adjustable gain amplifier, the output signal of the adjustable gain amplifier is merged with the output signal of the common mode voltage compensation circuit and then connected to the input of the voltage analog-to-digital converter, the output of the voltage analog-to-digital converter is connected to the input of the signal processing unit, and the signal processing unit may further be provided with three channels individually connected to the adjustable gain amplifier, the common mode voltage compensation circuit and the voltage analog-to-digital converter for controlling the adjustable gain amplifier, the common mode voltage compensation circuit and the voltage analog-to-digital converter. Furthermore, the fingerprint sensing array, the adjustable gain amplifier, the common mode voltage compensation circuit, the voltage analog-to-digital converter and the signal processing unit can be Integrated in the same Application Specific Integrated Circuit (ASIC), so that the material cost can be continuously saved, and the time for fingerprint acquisition can be shortened as much as possible.
The fingerprint sensing array can be a semiconductor fingerprint sensor based on a semiconductor silicon capacitance effect technology, the semiconductor fingerprint sensor comprises a semiconductor pressure-sensitive sensor, a semiconductor temperature sensing sensor, a semiconductor capacitance type fingerprint sensor and the like, and the embodiment of the invention focuses on the condition that the semiconductor fingerprint sensor is the semiconductor capacitance type fingerprint sensor.
The adjustable gain amplifier may include one amplifying element, or may include a plurality of amplifying elements, where the amplifying elements may be a PNP transistor, an NPN transistor, or the like, and when a plurality of amplifying elements exist, the amplifying elements may be connected in series. It should be noted that the amplification factor of the adjustable gain amplifier can be adjusted in time as needed, for example, the adjustable gain amplifier is set as a switched capacitor amplifier, so that the amplification factor can be controlled by controlling the on and off of a capacitor switch.
The common mode voltage compensation circuit is used for outputting an analog voltage signal, the common mode voltage compensation circuit can be embodied as a digital-to-analog conversion circuit, and the analog voltage signal can be output from the output end of the common mode voltage compensation circuit after a digital voltage signal is input to the input end of the common mode voltage compensation circuit.
The voltage analog-to-digital converter may be a pipeline analog-to-digital converter, may also be a successive approximation analog-to-digital converter, and may of course also be another analog-to-digital converter. The resolution Q of the voltage adc may be a Least Significant Bit (LSB) voltage, that is, the resolution Q of the voltage adc is equal to a voltage measurement range of the voltage adc divided by a discrete number of voltage intervals, the voltage measurement range is also called a full-scale voltage range, which is equal to a reference voltage of the voltage adc, and the number of voltage intervals is equal to 2 to the power of M, where M is the number of bits of the voltage adc, so adjusting the reference voltage of the voltage adc can adjust the total voltage measurement range of the voltage adc and the resolution of an output signal. For example, if an 8-bit voltage analog-to-digital converter can measure in the range of 0v to 10v, the resolution Q of the output signal is equal to 10/2^8, i.e., 10/256. Further, the reference voltage of the voltage analog-to-digital converter can be adjusted timely according to needs.
By operating the fingerprint collecting device, the fingerprint collecting device can analyze the histogram of the collected fingerprint image through the signal processing unit, judge whether the voltage range of the fingerprint image falls into a proper position in the voltage measuring range of the voltage analog-to-digital conversion circuit, if the voltage range of the fingerprint image does not fall into the proper position, send a control signal to at least one functional unit of the adjustable gain amplifier, the common mode voltage compensation circuit and the voltage analog-to-digital converter through the signal processing unit, control and adjust the amplification factor of the adjustable gain amplifier, or control and adjust the compensation voltage of the common mode voltage compensation circuit and/or control and adjust the reference voltage of the voltage analog-to-digital converter, so that the voltage range of the fingerprint image falls into the proper position in the voltage measuring range of the voltage analog-to-digital conversion circuit, and thus, a clearer fingerprint image can still be obtained under the condition that the thickness of the protective layer is not uniform and the fingerprint difference among users is large.
With reference to the first aspect, in a first possible implementation manner of the first aspect, the controlling, by the signal processing unit, the adjusting of the amplification factor of the adjustable gain amplifier, and at least one of a reference voltage of the voltage analog-to-digital converter and a voltage value compensated by the common mode voltage compensation circuit specifically includes:
when the voltage range of the histogram of the initial fingerprint image exceeds the voltage measurement range of the voltage analog-to-digital converter, the reference voltage of the voltage analog-to-digital converter is increased, or the amplification factor of the adjustable gain amplifier is reduced;
when the proportion of the voltage range of the histogram of the initial fingerprint image in the voltage measurement range of the voltage analog-to-digital converter is smaller than a preset proportion, the reference voltage of the voltage analog-to-digital converter is adjusted to be low, or the amplification factor of the adjustable gain amplifier is increased.
With reference to the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the common-mode voltage compensation circuit includes a digital-to-analog conversion circuit.
With reference to the first aspect or the first possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the adjustable gain amplifier is formed by serially connecting multiple stages of adjustable gain amplification circuits.
With reference to the third possible implementation manner of the first aspect, in a fourth possible implementation manner of the first aspect, the adjustable gain amplifier is a switched capacitor amplifier.
With reference to the first aspect or the first possible implementation manner of the first aspect, in a fifth possible implementation manner of the first aspect, the voltage analog-to-digital converter is a pipeline analog-to-digital converter or a successive approximation analog-to-digital converter.
With reference to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner of the first aspect, the resolution of the voltage analog-to-digital converter is a least significant bit LSB voltage.
With reference to the first aspect or the first possible implementation manner of the first aspect, in a seventh possible implementation manner of the first aspect, the signal processing unit controls and adjusts an amplification factor of the adjustable gain amplifier, and at least one of a reference voltage of the voltage analog-to-digital converter and a voltage value compensated by the common mode voltage compensation circuit is specifically:
calculating a voltage width of a voltage range in the histogram;
calculating the voltage width of the voltage measurement range of the voltage analog-to-digital converter;
judging the magnitude relation between the voltage width of the voltage range and the voltage width of the voltage measurement range;
when the voltage width of the voltage range is larger than that of the voltage measurement range, the reference voltage of the voltage analog-to-digital converter is increased, or the amplification factor of the adjustable gain amplifier is reduced, so that the voltage width of the voltage range is equal to that of the voltage measurement range;
when the voltage width of the voltage range is smaller than that of the voltage measurement range, the reference voltage of the voltage analog-to-digital converter is adjusted to be low, or the amplification factor of the adjustable gain amplifier is increased, so that the voltage width of the voltage range is equal to that of the voltage measurement range.
With reference to the seventh possible implementation manner of the first aspect, in an eighth possible implementation manner of the first aspect, when the voltage width of the voltage range is equal to the voltage width of the voltage measurement range, the signal processing unit is further configured to:
acquiring a maximum value and a minimum value of a voltage range in the histogram;
calculating a middle value of the voltage range according to the maximum voltage value and the minimum voltage value;
calculating a voltage difference value between the middle value of the voltage range and the middle value of the voltage measurement range of the voltage analog-to-digital converter;
determining a compensation voltage according to the voltage difference value;
and sending a control signal to the common mode voltage compensation circuit to control the common mode voltage compensation circuit to output a voltage with the same magnitude as the compensation voltage.
With reference to the eighth possible implementation manner of the first aspect, in a ninth possible implementation manner of the first aspect, the fingerprint sensing array, the adjustable gain amplifier, the common-mode voltage compensation circuit, the voltage analog-to-digital converter, and the signal processing unit are integrated in a same application specific integrated circuit ASIC.
By implementing the embodiment of the invention, the fingerprint acquisition device can analyze the histogram of the acquired fingerprint image through the signal processing unit, judge whether the voltage range of the fingerprint image falls into a proper position in the voltage measurement range of the voltage analog-to-digital conversion circuit, if the voltage range of the fingerprint image does not fall into the proper position, send a control signal to at least one functional unit of the adjustable gain amplifier, the common mode voltage compensation circuit and the voltage analog-to-digital converter through the signal processing unit, control and adjust the amplification factor of the adjustable gain amplifier, or control and adjust the compensation voltage of the common mode voltage compensation circuit and/or control and adjust the reference voltage of the voltage analog-to-digital converter, so that the voltage range of the fingerprint image falls into the proper position in the voltage measurement range of the voltage analog-to-digital conversion circuit, and thus, a clearer fingerprint image can still be obtained under the condition that the thickness of the protective layer is not uniform and the fingerprint difference among users is large.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of a prior art fingerprint acquisition device;
FIG. 2 is a schematic diagram of a fingerprint acquisition device in the prior art for acquiring fingerprints;
fig. 3 is a schematic structural diagram of a fingerprint acquisition device according to an embodiment of the present invention;
FIG. 4 is a histogram of a fingerprint image provided by an embodiment of the present invention;
FIG. 5 is a histogram of a fingerprint image according to an embodiment of the present invention;
fig. 6 is another histogram of a fingerprint image according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It is to be understood that the terminology used in the embodiments of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. In addition, the terms "first," "second," "third," and "fourth," etc. in the description and claims of the invention and the above-described drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a fingerprint capturing device according to an embodiment of the present invention, the fingerprint capturing device includes a fingerprint sensing array 301, an adjustable gain amplifier 302, a common mode voltage compensation circuit 303, a voltage adc 304 and a signal processing unit 305, wherein an output of the fingerprint sensing array 301 is connected to an input of the adjustable gain amplifier 302, a signal of an output of the adjustable gain amplifier 302 is merged with a signal of an output of the common mode voltage compensation circuit 303 and then connected to an input of the voltage adc 304, an output of the voltage adc 304 is connected to an input of the signal processing unit 305, and the signal processing unit 305 may further include three channels individually connected to the adjustable gain amplifier 302, the common mode voltage compensation circuit 303 and the voltage adc 304, for individually connecting the adjustable gain amplifier 302, the common mode voltage compensation circuit 303 and the voltage adc 304 to the fingerprint capturing device, The common mode voltage compensation circuit 303 and the voltage analog-to-digital converter 304 perform control. Further, the fingerprint sensing array 301, the adjustable gain amplifier 302, the common mode voltage compensation circuit 303, the voltage analog-to-digital converter 304 and the signal processing unit 305 may be Integrated in a same Application Specific Integrated Circuit (ASIC), so that material cost may be continuously saved and time for fingerprint acquisition may be shortened as much as possible.
The fingerprint sensing array 301 is configured to collect fingerprint information input by a user, obtain a voltage signal, and output the voltage signal to the adjustable gain amplifier 302. The fingerprint sensing array 301 may be a semiconductor fingerprint sensor based on a semiconductor silicon capacitance effect technology, the semiconductor fingerprint sensor includes a semiconductor pressure-sensitive sensor, a semiconductor temperature-sensitive sensor, a semiconductor capacitive fingerprint sensor, and the like.
The adjustable gain amplifier 302 is used for inputting the voltage signal output by the fingerprint sensing array 301, and since the capacitance formed between the finger print and the sensing point in the fingerprint sensing array 301 is very small, the formed small voltage is easily affected by the noise of the circuit, the obtained voltage signal needs to be amplified by the adjustable gain amplifier 302 to obtain an amplified signal, and the adjustable gain amplifier 302 outputs the amplified signal after obtaining the amplified signal. The adjustable gain amplifier 302 may include one amplifying element, or may include a plurality of amplifying elements, which may be PNP transistors, NPN transistors, etc., and when a plurality of amplifying elements exist, the plurality of amplifying elements may be connected in series. It should be noted that the amplification factor of the adjustable gain amplifier 302 can be adjusted in time as needed, for example, the adjustable gain amplifier 302 is configured as a switched capacitor amplifier, so that the on and off of a capacitor switch can be controlled to control the amplification factor.
The common mode voltage compensation circuit 303 is configured to output a voltage signal to be superimposed with the amplified signal output by the adjustable gain amplifier 302, so as to eliminate noise in the amplified signal, where a process problem of the fingerprint sensing array 301 may cause certain noise, and related circuits may also generate certain noise, and the noise may affect the effect of a subsequent fingerprint image, so that the noise needs to be compensated, that is, eliminated. The common mode voltage compensation circuit 303 is also configured to output the amplified signal with the noise removed to the voltage analog-to-digital converter 304. It should be noted that the common mode voltage compensation circuit 303 may be specifically a digital-to-analog conversion circuit, and that the input end of the common mode voltage compensation circuit 303 inputs a digital voltage signal, that is, an analog voltage signal is output from the output end of the common mode voltage compensation circuit 303.
The voltage analog-to-digital converter 304 is configured to input the amplified signal with the noise removed, convert the input signal into a digital signal, and output the digital signal to the signal processing unit 305. The voltage adc 304 may be a pipeline adc, a successive approximation adc, or other adcs. The resolution Q of the voltage adc 304 can be a Least Significant Bit (LSB) voltage, that is, the resolution Q of the voltage adc 304 is equal to a voltage measurement range of the voltage adc 304 divided by a discrete number of voltage intervals, which is also called a full-scale voltage range, which is equal to a reference voltage of the voltage adc 304, and the number of voltage intervals is equal to 2 to the power of M, where M is the number of bits of the voltage adc 304, so adjusting the reference voltage of the voltage adc 304 can adjust the total voltage measurement range of the voltage adc 304 and the resolution of the output signal. For example, if an 8-bit voltage analog-to-digital converter 304 can measure in the range of 0v to 10v, the resolution Q of the output signal is equal to 10/2^8, i.e., 10/256. Further, the reference voltage of the voltage analog-to-digital converter 304 can be adjusted in time according to the needs.
The signal processing unit 305 is configured to obtain an initial fingerprint image according to the digital signal, and determine whether a histogram of the initial fingerprint image satisfies a preset condition.
Specifically, the signal processing unit 305 inputs the digital signal output by the voltage analog-to-digital converter 304, processes the digital signal to obtain a fingerprint image, and the fingerprint image obtained at the beginning is an initial fingerprint image, the signal processing unit 305 may obtain a histogram of the initial fingerprint image, and then determine whether the histogram of the initial fingerprint image satisfies a preset condition, for example, determine whether a voltage range of the initial fingerprint image in the histogram (a horizontal axis of the histogram represents the voltage range of the fingerprint image) exceeds a voltage measurement range of the voltage analog-to-digital converter 304, and if so, it indicates that the histogram of the initial fingerprint image does not satisfy the preset condition, and fig. 4 is a schematic diagram illustrating that the voltage range of the initial fingerprint image exceeds the voltage measurement range of the voltage analog-to-digital converter 304. For another example, it is determined whether the ratio of the voltage range of the initial fingerprint image to the voltage measurement range of the voltage analog-to-digital converter 304 is smaller than a preset ratio (the size of the ratio may be set according to actual needs, for example, set to 60%), if so, it indicates that the histogram of the initial fingerprint image does not satisfy the preset condition, and fig. 5 is a schematic diagram that the ratio of the voltage range of the fingerprint image to the voltage measurement range of the voltage analog-to-digital converter 304 is smaller than the preset ratio. For another example, it is determined whether the voltage range of the initial fingerprint image is centered within the voltage measurement range of the voltage analog-to-digital converter 304, if the voltage range deviates far from the middle position, it indicates that the histogram of the initial fingerprint image does not satisfy the predetermined condition (for example, the difference between the middle value of the voltage range of the initial fingerprint image and the middle value of the voltage measurement range of the voltage analog-to-digital converter 304 within a predetermined range indicates that the predetermined condition is satisfied), and fig. 6 is a schematic diagram of the middle position of the voltage range of the initial fingerprint image within the voltage measurement range of the voltage analog-to-digital converter 304. Of course, other determination conditions may also be set, and the other determination conditions are not illustrated here.
The signal processing unit 305 is further configured to control and adjust the amplification factor of the adjustable gain amplifier 302, at least one of the reference voltage of the voltage analog-to-digital converter 304 and the voltage value compensated by the common mode voltage compensation circuit 303 when it is determined that the histogram of the initial fingerprint image does not satisfy the preset condition, until the histogram of the fingerprint image obtained by the signal processing unit 305 according to the digital signal satisfies the preset condition.
Specifically, if the histogram of the initial fingerprint image does not satisfy the preset condition, the signal processing unit 305 controls to adjust the amplification factor of the adjustable gain amplification circuit, or controls to adjust the reference voltage of the voltage analog-to-digital converter 304, or adjusts the voltage value compensated by the common mode voltage compensation circuit 303; until the histogram of the fingerprint image newly generated by the signal processing unit 305 can satisfy the preset condition.
For example, when the maximum value in the voltage range of the fingerprint image shown in fig. 4 is larger than the maximum value in the voltage measurement range of the voltage analog-to-digital converter 304, and the minimum value in the voltage range of the fingerprint image is smaller than the minimum value in the voltage measurement range of the voltage analog-to-digital converter 304 (which is often the case when the saturation of the fingerprint is too high), the signal processing unit 305 may send a control signal to the voltage analog-to-digital converter 304 to increase the reference voltage of the voltage analog-to-digital converter 304 based on the path established between the signal processing unit and the voltage analog-to-digital converter 304; or the signal processing unit 305 may send a control signal to the adjustable gain amplifier 302 to reduce the amplification of the adjustable gain amplifier 302 based on the path established with the adjustable gain amplifier 302, so that the voltage range of the initial fingerprint image eventually falls within the voltage measurement range of the voltage analog-to-digital converter 304.
When the voltage range of the fingerprint image shown in fig. 5 falls within the voltage measurement range of the voltage adc 304 and the voltage range of the fingerprint image occupies a smaller proportion of the voltage measurement range of the voltage adc 304 (which is often the case when the saturation of the fingerprint is too low), the signal processing unit 305 may send a control signal to the voltage adc 304 to lower the reference voltage of the voltage adc 304 based on the path established between the voltage adc 304 and the signal processing unit 305; or the signal processing unit 305 may send a control signal to the adjustable gain amplifier 302 to increase the amplification of the adjustable gain amplifier 302 based on the path established with the adjustable gain amplifier 302, so that the voltage range of the initial fingerprint image is increased to a preset value in proportion to the voltage measurement range of the voltage analog-to-digital converter 304.
When the maximum value of the voltage range over which the fingerprint image shown in figure 6 appears is greater than the maximum value of the voltage measurement range of the voltage analog-to-digital converter 304, but the minimum value of the voltage range of the fingerprint image is greater than the minimum value of the voltage measurement range of the voltage analog-to-digital converter 304 (the minimum value of the voltage range of the fingerprint image is less than the minimum value of the voltage measurement range of the voltage analog-to-digital converter 304, but the maximum value of the voltage range of the fingerprint image is less than the maximum value of the voltage measurement range of the voltage analog-to-digital converter 304), the signal processing unit 305 can send a control signal to the common mode voltage compensation circuit 303 to adjust the magnitude of the compensation voltage output by the common mode voltage compensation circuit 303 based on the path established between the signal processing unit and the common mode voltage compensation circuit 303, such that the middle of the voltage range of the initial fingerprint image is near the middle of the voltage measurement range of the voltage analog-to-digital converter 304. Further, when the middle value of the voltage range of the initial fingerprint image is close to the middle value of the voltage measurement range of the voltage analog-to-digital converter 304, if the situation shown in fig. 4 and 5 occurs again, the signal processing unit 305 can control the amplification factor of the adjustable gain amplifier 302 or the reference voltage of the voltage analog-to-digital converter 304 to solve the problem.
Alternatively, if it appears that the voltage width of the voltage range in the histogram is different from the voltage width of the voltage measurement range of the voltage analog-to-digital converter 304, and the middle value of the voltage range is far from the middle value of the voltage measurement range, the processing may be performed by the following procedure:
the first step is as follows: the signal processing unit 305 calculates the voltage width of the voltage range in the histogram.
The second step is that: the signal processing unit 305 calculates the voltage width of the voltage measurement range of the voltage analog-to-digital converter 304.
The third step: the signal processing unit 305 determines the magnitude relationship between the voltage width of the voltage range and the voltage width of the voltage measurement range.
The fourth step: when the voltage width of the voltage range is larger than the voltage width of the voltage measurement range, the signal processing unit 305 increases the reference voltage of the voltage analog-to-digital converter 304 or decreases the amplification factor of the adjustable gain amplifier 302 so that the voltage width of the voltage range is equal to the voltage width of the voltage measurement range;
when the voltage width of the voltage range is smaller than the voltage width of the voltage measurement range, the signal processing unit 305 decreases the reference voltage of the voltage analog-to-digital converter 304 or increases the amplification factor of the adjustable gain amplifier 302 so that the voltage width of the voltage range is equal to the voltage width of the voltage measurement range.
The fifth step: when the voltage width of the voltage range is equal to the voltage width of the voltage measurement range, the signal processing unit 305 acquires the voltage range maximum value and the voltage minimum value in the histogram.
And a sixth step: the signal processing unit 305 calculates a middle value of the voltage range from the voltage maximum value and the voltage minimum value.
The seventh step: the signal processing unit 305 calculates a voltage difference value between the middle value of the voltage range and the middle value of the voltage measurement range of the voltage analog-to-digital converter 304.
Eighth step: the signal processing unit 305 determines a compensation voltage from the voltage difference.
The ninth step: the signal processing unit 305 sends a control signal to the common mode voltage compensation circuit 303 to control the common mode voltage compensation circuit 303 to output a voltage having the same magnitude as the compensation voltage.
It should be noted that the above-mentioned schemes of the first step to the ninth step are only an optional scheme, and the same or similar beneficial effects can be achieved by adjusting the order of these steps, or omitting some steps, or replacing some steps with other similar steps in the actual operation process. In the embodiment of the present invention, the "voltage width" is generally applied to a voltage range, and if the voltage range is 0v to 10v, the corresponding voltage width is (10-0) to 10 v; if the voltage ranges from 20v to 100v, the corresponding voltage width is (100-20) ═ 80 v.
Alternatively, the middle value of the voltage range of the fingerprint image may be calculated by a preset algorithm based on the maximum value and the minimum value of the voltage range of the fingerprint image, and the middle value of the voltage measurement range of the voltage analog-to-digital converter 304 may be calculated by a preset algorithm based on the maximum value and the minimum value of the voltage measurement range of the voltage analog-to-digital converter 304. The magnitude of the compensation voltage may also be calculated based on the difference between the middle of the voltage range of the fingerprint image and the middle of the voltage measurement range of the voltage analog-to-digital converter 304.
Optionally, the signal processing unit 305 may calculate a maximum gray scale difference of the fingerprint image according to a maximum value and a minimum value of a voltage range of the fingerprint image, where the gray scale difference needs to be distributed as much as possible within the voltage measurement range of the voltage analog-to-digital converter 304 to achieve balance between contrast and saturation of the entire fingerprint image, and further, the signal processing unit 305 may determine the amplification factor of the adjustable gain amplifier 302 by combining the gray scale difference and the voltage measurement range of the voltage analog-to-digital converter 304. Further, the signal processing unit 305 may also be a reference voltage of the voltage analog-to-digital converter 304 based on a difference between a maximum value and a minimum value of the voltage range of the fingerprint image.
In the fingerprint capturing apparatus 30 shown in fig. 3, the fingerprint capturing apparatus 30 may analyze the histogram of the captured fingerprint image through the signal processing unit 305, determine whether the voltage range of the fingerprint image falls into a proper position within the voltage measurement range of the voltage analog-to-digital converter 304, and if the voltage range of the fingerprint image does not fall into the proper position, send a control signal to at least one functional unit of the adjustable gain amplifier 302, the common mode voltage compensation circuit 303 and the voltage analog-to-digital converter 304 through the signal processing unit 305, control to adjust the amplification factor of the adjustable gain amplifier, or control to adjust the compensation voltage of the common mode voltage compensation circuit 303 and/or control to adjust the reference voltage of the voltage analog-to-digital converter 304, so that the voltage range of the fingerprint image falls into a proper position within the voltage measurement range of the voltage analog-to-digital converter 303, thus, a clearer fingerprint image can be obtained even when the thickness of the protective layer is not uniform and the fingerprint difference between users is large.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. And the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
The above embodiments are only for illustrating the preferred embodiments of the present invention, and the scope of the present invention should not be limited thereby, and those skilled in the art can understand that all or part of the processes of the above embodiments can be implemented and equivalents thereof can be made according to the claims of the present invention, and still fall within the scope of the invention.
Claims (7)
1. A fingerprint collection device is characterized by comprising a fingerprint sensing array, an adjustable gain amplifier, a common-mode voltage compensation circuit, a voltage analog-to-digital converter and a signal processing unit, wherein the output of the fingerprint sensing array is connected with the input of the adjustable gain amplifier, the signal of the output of the adjustable gain amplifier is merged with the signal of the output of the common-mode voltage compensation circuit and then is connected with the input of the voltage analog-to-digital converter, the output of the voltage analog-to-digital converter is connected with the input of the signal processing unit, and the signal processing unit is independently connected with the adjustable gain amplifier, the common-mode voltage compensation circuit and the voltage analog-to-digital converter, wherein:
the fingerprint sensing array is used for collecting fingerprint information to obtain a voltage signal and outputting the voltage signal to the adjustable gain amplifier;
the adjustable gain amplifier is used for amplifying the voltage signal to obtain an amplified signal;
the common mode voltage compensation circuit is used for compensating voltage for the amplified signal so as to eliminate common mode voltage and noise in the amplified signal;
the voltage analog-to-digital converter is used for receiving the amplified signal with the common-mode voltage and the noise eliminated and converting the amplified signal with the common-mode voltage and the noise eliminated into a digital signal; outputting the digital signal to the signal processing unit;
the signal processing unit is configured to obtain an initial fingerprint image according to the digital signal, and determine whether a histogram of the initial fingerprint image meets a preset condition, where the preset condition includes any one of: the voltage range of the histogram of the initial fingerprint image does not exceed the voltage measurement range of the voltage analog-to-digital converter; the proportion of the voltage range of the histogram of the initial fingerprint image in the voltage measurement range of the voltage analog-to-digital converter is larger than a preset proportion; and the voltage range of the histogram of the initial fingerprint image is centered within the voltage measurement range of the voltage analog-to-digital converter;
if the initial fingerprint image does not meet the preset condition, controlling and adjusting the amplification factor of the adjustable gain amplifier, and at least one of the reference voltage of the voltage analog-to-digital converter and the voltage value compensated by the common-mode voltage compensation circuit until the histogram of the initial fingerprint image obtained by the signal processing unit according to the digital signal meets the preset condition;
the controlling and adjusting the amplification factor of the adjustable gain amplifier comprises: calculating the maximum gray difference of the initial fingerprint image according to the maximum value and the minimum value of the voltage range of the initial fingerprint image, and determining the amplification factor of the adjustable gain amplifier by combining the gray difference and the voltage measurement range of the voltage analog-to-digital converter;
the signal processing unit controls and adjusts the amplification factor of the adjustable gain amplifier, and at least one of the reference voltage of the voltage analog-to-digital converter and the voltage value compensated by the common mode voltage compensation circuit specifically includes: calculating a voltage width of a voltage range in the histogram; calculating the voltage width of the voltage measurement range of the voltage analog-to-digital converter; judging the magnitude relation between the voltage width of the voltage range and the voltage width of the voltage measurement range; when the voltage width of the voltage range is larger than that of the voltage measurement range, the reference voltage of the voltage analog-to-digital converter is adjusted to be high so that the voltage width of the voltage range is equal to that of the voltage measurement range; when the voltage width of the voltage range is smaller than that of the voltage measurement range, the reference voltage of the voltage analog-to-digital converter is adjusted to be low so that the voltage width of the voltage range is equal to that of the voltage measurement range; the reference voltage of the voltage analog-to-digital converter refers to a voltage measurement range of the voltage analog-to-digital converter, the voltage measurement range is divided by discrete voltage intervals to be equal to the resolution of the voltage analog-to-digital converter, the discrete voltage intervals are equal to the power M of 2, and M is the digit of the voltage analog-to-digital converter;
when the voltage width of the voltage range is equal to the voltage width of the voltage measurement range, the signal processing unit is further configured to: acquiring a voltage maximum value and a voltage minimum value in the histogram; calculating a middle value of the voltage range according to the maximum voltage value and the minimum voltage value; calculating a voltage difference value between the middle value of the voltage range and the middle value of the voltage measurement range of the voltage analog-to-digital converter; determining a compensation voltage according to the voltage difference value; sending a control signal to the common mode voltage compensation circuit to control the common mode voltage compensation circuit to output a voltage with the same magnitude as the compensation voltage;
the fingerprint sensing array, the adjustable gain amplifier, the common-mode voltage compensation circuit, the voltage analog-to-digital converter and the signal processing unit are integrated in the same Application Specific Integrated Circuit (ASIC).
2. The fingerprint acquisition device according to claim 1, wherein the signal processing unit controls and adjusts amplification of the adjustable gain amplifier, and at least one of a reference voltage of the voltage analog-to-digital converter and a voltage value compensated by the common mode voltage compensation circuit is specifically:
when the voltage range of the histogram of the initial fingerprint image exceeds the voltage measurement range of the voltage analog-to-digital converter, the reference voltage of the voltage analog-to-digital converter is increased, or the amplification factor of the adjustable gain amplifier is reduced;
when the proportion of the voltage range of the histogram of the initial fingerprint image in the voltage measurement range of the voltage analog-to-digital converter is smaller than a preset proportion, the reference voltage of the voltage analog-to-digital converter is adjusted to be low, or the amplification factor of the adjustable gain amplifier is increased.
3. The fingerprint acquisition device of claim 1 or 2, wherein the common mode voltage compensation circuit comprises a digital-to-analog conversion circuit.
4. The fingerprint acquisition device according to claim 1 or 2, wherein the adjustable gain amplifier is formed by connecting multiple stages of adjustable gain amplification circuits in series.
5. The fingerprint acquisition device of claim 4, wherein the adjustable gain amplifier is a switched capacitor amplifier.
6. The fingerprint acquisition device according to claim 1 or 2, wherein the voltage analog-to-digital converter is a pipeline analog-to-digital converter or a successive approximation analog-to-digital converter.
7. The fingerprint acquisition device of claim 6, wherein the resolution of the voltage analog-to-digital converter is Least Significant Bit (LSB) voltage.
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| SE2051062A1 (en) * | 2020-09-10 | 2022-03-11 | Fingerprint Cards Anacatum Ip Ab | Fingerprint sensor arrangement with different measurement circuitry configurations |
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| CN108596060B (en) * | 2018-04-12 | 2021-10-15 | 上海思立微电子科技有限公司 | Fingerprint image processing method, fingerprint identification device and electronic equipment |
| CN108460371A (en) * | 2018-04-16 | 2018-08-28 | 北京中天维科技有限公司 | A kind of fingerprint sensor acquisition system and method |
| CN111027516B (en) * | 2019-12-25 | 2024-01-26 | 北京集创北方科技股份有限公司 | Biological characteristic image acquisition device, biological characteristic image acquisition method and intelligent equipment |
| CN112233410B (en) * | 2020-10-14 | 2021-04-13 | 深圳市康冠商用科技有限公司 | Automatic gain level selection method and device, computer equipment and storage medium |
| CN112637510A (en) * | 2021-03-05 | 2021-04-09 | 南京智谱科技有限公司 | Scene self-adaptive image gain adjusting method, system and device and electronic equipment |
| TWI831017B (en) * | 2021-06-09 | 2024-02-01 | 大陸商北京集創北方科技股份有限公司 | Capacitive fingerprint collection module, fingerprint identification device and information processing device |
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