A fingerprint sensor

Abstract

The present invention discloses a fingerprint sensor, which relates to the field of integrated circuits, and includes a dielectric layer, an excitation signal generator, a control switch, a collection unit, a control circuit, a selection switch, a programmable amplifier, and an analog-to-digital converter; the surface of the collection unit is covered with a dielectric layer, the excitation signal generator is connected to the collection unit through the control switch, the collection unit is connected to the programmable amplifier and the analog-to-digital converter in sequence through the selection switch and converts the output voltage into a digital signal, and the control circuit provides a timing signal and a control signal for the selection switch, the programmable amplifier, and the analog-to-digital converter. Under the premise of ensuring robustness, the present invention avoids direct contact between human fingers and electrical signals, improves the comfort of use, and reduces the packaging cost of the fingerprint sensor and the difficulty of installation when embedded in the whole machine.

Description

Technical Field

[0001] The invention relates to the field of integrated circuits, and in particular to a fingerprint sensor without an external excitation ring. Background Art

[0002] According to the different principles of fingerprint sensors in collecting fingerprint images, fingerprint sensors can be roughly divided into optical fingerprint sensors, semiconductor capacitive fingerprint sensors and ultrasonic fingerprint sensors.

[0003] In order to improve the sensitivity, acquisition speed and anti-static ability of fingerprint sensors, people have developed active fingerprint sensors. Active fingerprint sensors mainly generate excitation signals with certain timing requirements inside the chip. When the finger touches the metal ring, the excitation signal is transmitted to the collected finger through the chip PAD, binding wires and the metal ring installed around the sensor. The finger equivalent capacitance formed between the finger surface and the acquisition point plate is C f The internal reference capacitor Cref of the chip is connected across the input and output terminals of the fingerprint acquisition amplifier, and the finger equivalent capacitance C f , reference capacitor C ref The fingerprint acquisition amplifier forms a capacitor proportional amplifier circuit. Output voltage Where ΔV ex The amplitude of the excitation signal changes. It can be seen that the output voltage is proportional to the size of the finger equivalent capacitance. ref It is connected across the input and output of the reverse amplifier, not the capacitance of the finger collection plate to ground, so C ref The parasitic capacitance in the process can be designed to be very small (typical range is 1~5fF), so that the range of finger equivalent capacitance can be designed to be 0.1fF~1fF, which greatly improves the acquisition sensitivity of the fingerprint sensor. After the absolute value of the finger equivalent capacitance is reduced, the thickness of the chip surface packaging insulation material can be increased to enhance the antistatic ability of the chip. At the same time, the conversion of the output voltage can be completed within one system clock cycle, which greatly improves the speed of fingerprint acquisition. However, the introduction of the external excitation ring increases the cost of chip packaging and the difficulty of installing the chip on the whole machine. The shell of the whole machine is usually grounded, and the excitation ring of the fingerprint sensor needs to be insulated from the shell of the whole machine and cannot be directly in contact. In addition, in the face of different groups of people, in order to obtain good robustness, the excitation signal is often designed as an electrical signal with high current and strong driving force. For some sensitive people, when the finger directly touches the excitation ring, it often brings some tingling sensation, which reduces the comfort of product use.

[0004] Therefore, technicians in this field are committed to developing a fingerprint sensor to obtain good robustness and improve the comfort of use. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to avoid direct contact between human fingers and electrical signals while ensuring robustness, thereby improving the comfort of use, and at the same time reducing the packaging cost of the fingerprint sensor and the difficulty of installation when it is embedded in the whole machine.

[0006] To achieve the above purpose, the inventor has studied the existing active fingerprint sensor. The existing active fingerprint sensor usually introduces an external excitation ring, that is, an installed metal ring. The sensor generates an excitation signal with certain timing requirements. When the finger touches the external excitation ring, the excitation signal is generated by the chip and transmitted to the collected finger through the metal ring. The absolute value of the finger equivalent capacitance of the active fingerprint sensor is small, which can increase the thickness of the insulating material encapsulated on the surface of the fingerprint sensor and enhance the antistatic ability of the chip. At the same time, the conversion of the output voltage can be completed within a system clock cycle, which greatly improves the speed of fingerprint collection. However, the introduction of the external excitation ring increases the cost of chip packaging and the difficulty of installing the chip on the whole machine. The shell of the whole machine is usually grounded. The excitation ring of the fingerprint sensor needs to be insulated from the shell of the whole machine and cannot be directly in contact. In addition, in the face of different groups of people, in order to obtain good robustness, the excitation signal is often designed as an electrical signal with a large current and strong driving force. For some sensitive people, when the finger directly touches the excitation ring, it often brings some tingling sensation, which reduces the comfort of product use.

[0007] In view of the above-mentioned shortcomings of active fingerprint sensors, the inventors have designed a fingerprint sensor by adopting a method of modulating the power supply of an internal fingerprint acquisition amplifier with an excitation signal while retaining its advantages. Therefore, in the first embodiment of the present invention, a fingerprint sensor is provided, including a dielectric layer, an excitation signal generator, a control switch, an acquisition unit, a control circuit, a selection switch, a programmable amplifier (PGA) and an analog-to-digital converter (ADC); the surface of the acquisition unit is covered with a dielectric layer, the excitation signal generator is connected to the acquisition unit through the control switch, the acquisition unit is connected to the programmable amplifier (PGA) and the analog-to-digital converter (ADC) in sequence through the selection switch and converts the output voltage into a digital signal, and the control circuit provides timing signals and control signals for the selection switch, the programmable amplifier (PGA) and the analog-to-digital converter (ADC).

[0008] Furthermore, in the fingerprint sensor in the above embodiment, the dielectric layer also includes a passivation layer and a packaging material.

[0009] Furthermore, in the fingerprint sensor in any of the above embodiments, the acquisition unit includes an acquisition plate, a reset switch, an internal reference capacitor C b And fingerprint collection amplifier, collection plate and reset switch, internal reference capacitor C bConnected to the fingerprint collection amplifier circuit.

[0010] Furthermore, in the fingerprint sensor in the above embodiment, the internal reference capacitor C b , ranging from 1 to 5fF;

[0011] Furthermore, in the fingerprint sensor of any of the above embodiments, the surface of the finger contacts the dielectric layer, and a finger equivalent capacitance is generated between the finger surface and the collecting electrode, and the value is C f .

[0012] Furthermore, in the fingerprint sensor in the above embodiment, the finger equivalent capacitance C f The range is 0.1fF~1fF;

[0013] Furthermore, in the fingerprint sensor in the above embodiment, the excitation signal generator generates an excitation signal, which is connected to the fingerprint acquisition amplifier through a control switch to serve as a power supply for the fingerprint acquisition amplifier.

[0014] Furthermore, in the fingerprint sensor in the above embodiment, the excitation signal is composed of a periodic square wave of high and low levels, the high level is 3.3V, and the low level is 1.5V.

[0015] Furthermore, in the fingerprint sensor in the above embodiment, the fingerprint acquisition amplifier operates in the linear amplification region.

[0016] Furthermore, in the fingerprint sensor in the above embodiment, the voltage of the acquisition plate is used as the input of the fingerprint acquisition amplifier, and changes synchronously with the power supply voltage, with only a DC level V gs .

[0017] Furthermore, in the fingerprint sensor in the above embodiment, the reset switch is closed in the initial stage of acquisition, and the circuit is in a reset state.

[0018] Furthermore, in the fingerprint sensor in any of the above embodiments, the digital signal is usually 8 bits.

[0019] In the second embodiment of the present invention, the inventor further optimized the design of the fingerprint acquisition amplifier, including an amplifier stage, a current mirror group, an internal fixed current source, an NMOS tube 1, an NMOS tube 2, and a first-level output buffer stage. The current mirror group is connected to the internal fixed current source to derive a bias current, and the first-level output buffer stage buffers the output voltage of the fingerprint acquisition amplifier.

[0020] Furthermore, in the fingerprint sensor in the above embodiment, the amplification stage of the fingerprint acquisition amplifier includes an input amplifier tube, a cascode tube, a current source load 1 and a current source load 2 connected in sequence, and the amplification stage is in a saturation region during the period of the excitation signal.

[0021] Furthermore, in the fingerprint sensor in the above embodiment, the above current mirror group includes a PMOS tube 1, a PMOS tube 2 and a PMOS tube 3.

[0022] Furthermore, in the fingerprint sensor in the above embodiment, the value of the internal fixed current source is 10uA.

[0023] Furthermore, in the fingerprint sensor in the above embodiment, PMOS tube 1 is connected in a diode manner to provide bias voltage to PMOS tube 2, PMOS tube 3 and cascode tube, ensuring that PMOS tube 2, PMOS tube 3 and cascode tube operate in the saturation region.

[0024] Furthermore, in the fingerprint sensor in the above embodiment, the bias currents derived from the PMOS tube 2 and the PMOS tube 3 flow through the NMOS tube 1 and the NMOS tube 2 connected in a diode manner, respectively, to provide bias voltages to the current source load 2 and the current source load 1 of the amplifier stage, respectively, to ensure that the current source load 1 and the current source load 2 operate in the saturation region.

[0025] Furthermore, the diode connection is a connection method in which the gate and the drain are short-circuited.

[0026] Furthermore, the current source load 1 and the current source load 2 are NMOS tubes.

[0027] Furthermore, in the fingerprint sensor in the above embodiment, during the period of the excitation signal, the bias current inside the amplifier stage does not change, and the gate-source voltage V gs The input voltage of the fingerprint acquisition amplifier changes synchronously with the excitation signal (which is also the power supply of the fingerprint acquisition amplifier at this time), and the difference is only a DC level V gs That is, the power supply of the fingerprint acquisition amplifier is modulated by the excitation signal, which indirectly realizes the excitation of the finger equivalent capacitance.

[0028] In the third embodiment of the present invention, the inventor designed a circuit using the fingerprint sensor in the above embodiment.

[0029] In the fourth embodiment of the present invention, the inventor uses the fingerprint sensor in any of the above embodiments to design a fingerprint collection method, which includes the following steps:

[0030] S001, start collecting, the reset switch changes from closed to open;

[0031] S002, the excitation signal generates a level difference;

[0032] S003, select the collection unit that has completed fingerprint collection by selecting the switch;

[0033] S004. The output voltage of the acquisition unit is converted into a digital signal through a programmable amplifier (PGA) and an analog-to-digital converter (ADC).

[0034] In step S002, the level difference is ΔV ex , the charge change on the finger equivalent capacitor is ΔV ex ×C f According to the principle of charge conservation and negative feedback, the charge change on the finger equivalent capacitance is equal to the reference capacitance C b The charge on the out ×C b =ΔV ex ×C f ,get

[0035] The present invention stimulates the finger equivalent capacitance by modulating the power supply of the internal fingerprint acquisition amplifier through an excitation signal. During the entire cycle of the excitation signal, the fingerprint acquisition amplifier operates in the linear amplification region and the amplitude of the excitation signal is consistent with the amplitude of the excitation signal of the traditional active fingerprint sensor, so that the fingerprint acquisition sensitivity is consistent with the traditional active fingerprint sensor, and the acquisition speed and anti-static ability are also the same. The present invention eliminates the external excitation ring of the traditional active fingerprint sensor, saves the packaging cost of the fingerprint sensor, and reduces the installation difficulty and installation cost when the external excitation ring is embedded in the whole machine. At the same time, it avoids direct contact between human fingers and electrical signals, making it more convenient and comfortable to use, and avoiding interference introduced by the external excitation ring, thereby improving the fingerprint acquisition quality and making the acquisition performance more robust.

[0036] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a diagram illustrating a conventional active fingerprint sensor according to an exemplary embodiment;

[0038] Figure 2 is a diagram illustrating a fingerprint sensor according to an exemplary embodiment;

[0039] Figure 3 is a diagram illustrating a fingerprint acquisition amplifier of a fingerprint sensor according to an exemplary embodiment;

[0040] Figure 4 is a schematic diagram illustrating a circuit according to an exemplary embodiment;

[0041] Figure 5 is a flow chart illustrating a fingerprint collection method according to an exemplary embodiment. DETAILED DESCRIPTION

[0042] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0043] In the drawings, components with the same structure are indicated by the same numerical reference numerals, and components with similar structures or functions are indicated by similar numerical reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the illustration clearer, the thickness of the components is schematically exaggerated in some places in the drawings.

[0044] In order to improve the comfort of using fingerprint sensors, enhance the robustness of fingerprint collection, and reduce costs while maintaining the sensitivity of fingerprint collection, the inventors studied traditional active fingerprint sensors, such as Figure 1 As shown, it includes a dielectric layer 107 composed of a passivation layer and a packaging material, an excitation signal generator 101, an external excitation ring 104, a collection unit 116, a control circuit 112, a selection switch 113, a programmable amplifier (PGA) 114, and an analog-to-digital converter (ADC) 115; the control circuit 112 provides timing signals and control signals for the unit collection circuit 116, the selection switch 113, the programmable amplifier (PGA) 114 and the analog-to-digital converter (ADC) 115, the surface of the collection unit 116 is covered with the dielectric layer 107, the excitation signal generator 101 is connected to the collection unit 116, and the collection unit 116 is connected to the programmable amplifier (PGA) 114 and the analog-to-digital converter (ADC) 115 in sequence through the selection switch 113 and converts the output voltage into a digital signal.

[0045] The excitation signal generator 101 is integrated with the fingerprint sensor. Since the generated excitation signal requires a large current driving capability, its ground terminal 102 is processed separately from the ground 103 of the fingerprint acquisition amplifier to prevent the noise injected into the ground from interfering with the fingerprint acquisition effect. The excitation signal is transmitted to the collected finger through an external excitation loop.

[0046] The acquisition unit 116 includes an acquisition plate 105, a reset switch 108, and a reference capacitor C b 109, fingerprint acquisition amplifier 111 and power supply 110 of fingerprint acquisition amplifier, the area of ​​acquisition plate 105 is 50um*50um; reset switch 108 is closed in the initial stage of acquisition, the circuit is in reset state, reference capacitor C bThe range of 109 is 1 to 5 fF, and the voltage of the power supply 110 of the fingerprint acquisition amplifier is 1.8 V or 3.3 V; when the finger surface contacts the dielectric layer 107, a finger equivalent capacitance 106 is generated between the finger surface and the acquisition electrode 105, and the value is C f , ranging from 0.1fF to 1fF.

[0047] When fingerprint collection starts, the reset switch 108 is first switched from closed to open, and then the excitation signal generates a level difference ΔV ex According to the charge conservation and negative feedback principle, the charge change on the finger equivalent capacitor 106 is equal to the reference capacitor C b The charge on the out ×C b =ΔV ex ×C f ,get The unit that has completed fingerprint collection is selected by selecting switch 113, V out The digital signal is converted into a digital signal by a programmable amplifier (PGA) 114 and an analog-to-digital converter (ADC) 115. The digital signal is usually 8 bits. It can be seen that the output digital signal size is similar to the value C of the finger equivalent capacitance 106. f Directly proportional.

[0048] When the finger touches the external excitation ring 104, the excitation signal is generated inside the chip and transmitted to the collected finger through the external excitation ring 104. The absolute value of the fingerprint equivalent capacitance is small, which increases the thickness of the insulating material packaged on the surface of the fingerprint sensor and enhances the antistatic ability of the chip. At the same time, the conversion of the output voltage is completed within one system clock cycle, which greatly improves the speed of fingerprint collection. However, the inventors found that the introduction of the external excitation ring increases the cost of fingerprint sensor packaging and the difficulty of installation on the whole machine. The casing of the whole machine is usually grounded, and the external excitation ring of the fingerprint sensor needs to be insulated from the casing of the whole machine and cannot be directly in contact. In addition, in the face of different groups of people, in order to obtain good robustness, the excitation signal is often designed as an electrical signal with a large current and strong driving force. For some sensitive people, when the finger directly touches the excitation ring, it often brings some tingling sensation, which reduces the comfort of product use.

[0049] The inventors considered improving the traditional active fingerprint sensor by modulating the power supply of the internal fingerprint acquisition amplifier with an excitation signal to stimulate the finger equivalent capacitance. Figure 2As shown, it includes a dielectric layer 107, an excitation signal generator 101, a control switch 203, a collection unit 116, a control circuit 112, a selection switch 113, a programmable amplifier (PGA) 114 and an analog-to-digital converter (ADC) 115; the surface of the collection unit 116 is covered with the dielectric layer 107, the excitation signal generator 101 is connected to the collection unit 116 through the control switch 203, the collection unit 116 is connected to the programmable amplifier (PGA) 114 and the analog-to-digital converter (ADC) 115 in sequence through the selection switch 113 and converts the output voltage into a digital signal, and the control circuit 112 provides a timing signal and a control signal for the selection switch 113, the programmable amplifier (PGA) 114 and the analog-to-digital converter (ADC) 115.

[0050] The improved fingerprint sensor removes the external excitation ring 104 of the traditional active fingerprint sensor, and the excitation signal is connected to the acquisition unit 116 through the control switch 203. Specifically, the power supply 110 of the fingerprint acquisition amplifier in the traditional active fingerprint sensor is replaced, and the excitation signal is used to excite the power supply end of the fingerprint acquisition amplifier; the excitation signal is composed of a periodic square wave of high and low levels, with a high level of 3.3V and a low level of 1.5V. The inventor optimizes the internal design of the fingerprint acquisition amplifier to ensure that the amplifier works in the linear amplification area during the excitation signal cycle. Since the bias is fixed, the input end 204 of the fingerprint acquisition amplifier changes synchronously with the power supply voltage, with only a difference of a DC level V gs Assume that the high and low level difference of the excitation signal is the same as that of the traditional active fingerprint sensor, which is ΔV ex , then the charge change on the finger equivalent capacitor is still ΔV ex ×C f According to the principle of charge conservation and negative feedback, the charge change on the finger equivalent capacitance is equal to the reference capacitance C b The charge on the out ×C b =ΔV ex ×C f ,get Then, the acquisition unit 116 that has completed the fingerprint acquisition is selected by selecting the switch 113, and the output voltage V out The digital signal is converted into an 8-bit digital signal by a programmable amplifier (PGA) 114 and an analog-to-digital converter (ADC) 115. The output digital signal is equal to the finger equivalent capacitance C f Therefore, the improved fingerprint sensor achieves the same collection sensitivity as the traditional active fingerprint sensor.

[0051] The inventor continues to design the circuit of the fingerprint acquisition amplifier 111, such as Figure 3As shown, it includes an amplifier stage 330, a current mirror group 320, an internal fixed current source 301, an NMOS tube 1 308, an NMOS tube 2 306, and a first-level output buffer stage 311. The current mirror group 320 is connected to the internal fixed current source 301 to derive a bias current, and the first-level output buffer stage 311 buffers and outputs the output voltage of the fingerprint acquisition amplifier 111. The amplifier stage 330 of the fingerprint acquisition amplifier includes an input amplifier tube 310, a cascode tube 305, a current source load 1 307, and a current source load 2 309 connected in sequence. The amplifier stage 330 is in a saturation region during the period of the excitation signal; the current mirror group 320 includes a PMOS tube 1 302, a PMOS tube 2 303, and a PMOS tube 3 304. The internal fixed current source 301 is 10uA, and the PMOS tube 1 302 is connected in a diode manner to provide bias voltage to the PMOS tube 2 303, the PMOS tube 3 304 and the cascode tube 305, ensuring that the PMOS tube 2, the PMOS tube 3 and the cascode tube work in the saturation region. The bias current derived from the PMOS tube 2 303 and the PMOS tube 3 304 flows through the NMOS tube 1 308 and the NMOS tube 2 306 connected in a diode manner, respectively, to provide bias voltage to the current source load 2 309 and the current source load 1 307 of the amplifier stage, respectively, ensuring that the current source load 1 307 and the current source load 2 309 work in the saturation region. During the cycle of the excitation signal, the bias current inside the amplifier stage 330 does not change, and the gate-source voltage V of the input amplifier tube 310 gs The input voltage of the fingerprint acquisition amplifier 111 changes synchronously with the excitation signal (which is also the power supply of the fingerprint acquisition amplifier 111 at this time), and the difference is only a DC level V gs Therefore, the excitation signal is used to modulate the power supply of the fingerprint acquisition amplifier, which indirectly realizes the excitation of the finger equivalent capacitance.

[0052] The inventor has designed a circuit using the fingerprint sensor in the above embodiment. Figure 4 As shown, the fingerprint sensor and the microcontroller unit (MCU) are connected to realize the fingerprint recognition function. The MCU can be replaced by a single-chip unit or chip with computing and processing functions.

[0053] like Figure 5 As shown, the inventor uses the fingerprint sensor in any of the above embodiments to design a fingerprint collection method, including the following steps:

[0054] S001, start collecting, reset switch 108 changes from closed to open;

[0055] S002, the excitation signal generates a level difference, the value is ΔV ex , the charge change on the finger equivalent capacitor is ΔV ex ×Cf According to the principle of charge conservation and negative feedback, the charge change on the finger equivalent capacitance is equal to the reference capacitance C b The charge on the out ×C b =ΔV ex ×C f ,get

[0056] S003, selecting the collection unit 116 that has completed fingerprint collection through the selection switch 113;

[0057] S004 , the output voltage of the acquisition unit 116 is converted into a digital signal through a programmable amplifier (PGA) 114 and an analog-to-digital converter (ADC) 115 .

[0058] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A fingerprint sensor, characterized in that: The invention comprises a dielectric layer, an excitation signal generator, a control switch, a collection unit, a control circuit, a selection switch, a programmable amplifier PGA and an analog-to-digital converter ADC; the surface of the collection unit is covered with the dielectric layer, the excitation signal generator is connected to the collection unit through the control switch, the collection unit is connected to the programmable amplifier PGA and the analog-to-digital converter ADC in sequence through the selection switch and converts the output voltage into a digital signal, and the control circuit provides a timing signal and a control signal for the selection switch, the programmable amplifier PGA and the analog-to-digital converter ADC; the collection unit comprises a collection plate, a reset switch, an internal reference capacitor and a fingerprint acquisition amplifier, the acquisition plate and the reset switch, the internal reference capacitor Connected to the fingerprint acquisition amplifier circuit, the voltage of the acquisition plate is used as the input of the fingerprint acquisition amplifier, and changes synchronously with the power supply voltage, with only a DC level difference. The fingerprint acquisition amplifier includes an amplifier stage, a current mirror group, an internal fixed current source, an NMOS tube 1, an NMOS tube 2, and a first-level output buffer stage. The current mirror group is connected to the internal fixed current source to derive a bias current. The first-level output buffer stage buffers and outputs the output voltage of the fingerprint acquisition amplifier. During the cycle of the excitation signal, the bias current inside the amplifier stage does not change, and the gate-source voltage of the input amplifier tube The input voltage of the fingerprint acquisition amplifier changes synchronously with the excitation signal, with only a DC level difference. That is, the power supply of the fingerprint acquisition amplifier is modulated by the excitation signal, which indirectly realizes the excitation of the finger equivalent capacitance.

2. The fingerprint sensor according to claim 1, characterized in that: The excitation signal generator generates an excitation signal, which is connected to the fingerprint acquisition amplifier through the control switch to serve as a power supply for the fingerprint acquisition amplifier.

3. The fingerprint sensor according to claim 2, characterized in that: The excitation signal is composed of a periodic square wave of high and low levels, the high level is 3.3V, and the low level is 1.5V.

4. The fingerprint sensor according to claim 1, characterized in that: The amplification stage of the fingerprint acquisition amplifier includes an input amplifier tube, a cascode tube, a current source load 1 and a current source load 2 which are connected in sequence.

5. The fingerprint sensor according to claim 4, characterized in that: The current mirror group includes a PMOS tube 1, a PMOS tube 2 and a PMOS tube 3.

6. The fingerprint sensor according to claim 5, characterized in that: The bias currents derived from the PMOS tube 2 and the PMOS tube 3 flow through the NMOS tube 1 and the NMOS tube 2 respectively connected in a diode manner, and provide bias voltages to the current source load 2 and the current source load 1 respectively, ensuring that the current source load 1 and the current source load 2 operate in the saturation region.

7. A circuit, characterized in that: Comprising a fingerprint sensor as described in any one of claims 1-6.

8. A fingerprint collection method, characterized in that: Using the fingerprint sensor as described in any one of claims 1 to 6 comprises the following steps: S001, start collecting, the reset switch changes from closed to open; S002, the excitation signal generates a level difference; S003, select the collection unit that has completed fingerprint collection by selecting the switch; S004. The output voltage of the acquisition unit is converted into a digital signal through a programmable amplifier and an analog-to-digital converter.

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