TW201629844A - Fingerprint detection circuit and electronic device - Google Patents

Abstract

In a fingerprint detection circuit disclosed in the present invention, a negative input end of a signal amplifier is connected with a finger capacitance, and a positive input end of the signal amplifier is connected with a reference voltage terminal. The signal amplifier outputs voltage from an output end thereof according to the capacitance value of the finger capacitance. A switch unit is connected with the negative input end and the output end of the signal amplifier respectively, to control the capacitance to be communicated between the negative input end and the output end of the signal amplifier, such that the voltage is in a non-linear relationship with the capacitance value of the finger capacitance. In the fingerprint detection circuit, the voltage output by the signal amplifier is in a non-linear relationship with the finger capacitance (a capacitance to be detected). In a subsequence processing, the voltage output by the signal amplifier is partially linear amplified, to make the SNR (signal to noise ratio) higher and the subsequent calculation easier, so as to improve the fingerprint detection effect. The present invention further discloses an electronic device.

Description

Fingerprint detection circuit and electronic device

The present invention relates to the field of fingerprint detection, and more particularly to a fingerprint detection circuit and an electronic device.

In the field of fingerprint detection, due to the advantages of small size and low power consumption of the capacitive chip type fingerprint detection circuit, such detection circuits are rapidly becoming the first choice in the mobile phone and tablet market. The detecting circuit detects the fingerprint ridge valley information of the finger. Since the distance between the ridge line of the fingerprint and the sensing unit of the fingerprint detecting circuit is relatively close, the distance between the valley line of the fingerprint and the sensing unit of the fingerprint detecting and detecting circuit is far. Therefore, the capacitance formed between the ridge line and the sensing unit and the capacitance formed between the valley line and the sensing unit are different. As long as the above capacitance (hereinafter referred to as finger capacitance) is detected, the ridge characteristics of the fingerprint information can be separated. The output voltage of the fingerprint detecting circuit is linearly proportional to the finger capacitance (capacitance to be measured), and the final result corresponds to the numerical difference between the output voltage of the finger capacitance of the ridge line and the output voltage of the finger capacitance corresponding to the valley line. Very small, and the output voltage corresponding to the finger capacitance needs to be amplified by a certain multiple, then the amplification factor will be limited by the range. If the amplification factor is too large, the output voltage will exceed the range and the data will overflow. The magnification is small, and the ridge line is calculated later. The difference between the corresponding output voltage and the output voltage corresponding to the valley line is small, which is not well recognized, and the fingerprint detection effect is not optimized.

The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention needs to provide a fingerprint detecting circuit and an electronic device. A fingerprint detecting circuit for transmitting an excitation signal to a finger to collect a finger capacitance. The fingerprint detecting circuit includes a signal amplifier, a circuit capacitor and a switching unit. The negative input of the signal amplifier is connected to the finger capacitor, and the forward input of the signal amplifier is connected to the reference voltage terminal. The signal amplifier outputs a voltage from the output of the signal amplifier according to the capacitance value of the finger capacitor. The switching unit is respectively connected to the negative input terminal of the signal amplifier and the output end of the signal amplifier for controlling the circuit capacitance to be connected between the negative input terminal of the signal amplifier and the output end of the signal amplifier, so that the switch unit The relationship between the voltage and the capacitance of the finger capacitance is a non-linear relationship. In the above fingerprint detecting circuit, the relationship between the voltage outputted by the signal amplifier and the finger capacitance (capacitance to be measured) is a nonlinear relationship. In the subsequent processing, the voltage output from the signal amplifier is locally linearly amplified, so that the output ridge line corresponds. The difference between the voltage corresponding to the voltage and the valley line becomes larger, and the signal-to-noise ratio is higher, which makes the subsequent algorithm easier to recognize, thereby improving the fingerprint detection effect. In one embodiment, the reference voltage terminal is a ground terminal, and the fingerprint detecting circuit further includes a power source. The power source is connected to the capacitor through the switch unit, and the switch unit is configured to control the power source to charge the circuit capacitor and control the circuit capacitor to be disconnected from the power source. In one embodiment, the switch unit includes a first switch and a second switch. The first switch includes a first selection end, a first power end, and a first connection end, the first selection end is connected to one end of the circuit capacitor, and the first power end is connected to the first pole of the power source, the first connection end Connect the negative input of the signal amplifier. The second switch includes a second selection end connected to the other end of the circuit capacitor, and a second power connection end connected to the second pole of the power source, the second connection The terminal is connected to the output of the signal amplifier. The first selection end is connected to the first connection end and disconnected from the first power supply end, and the second selection end is connected to the second connection end and disconnected from the second power supply end, so that the circuit is capacitively connected to the signal The negative input of the amplifier is coupled to the output of the signal amplifier and the circuit capacitor is disconnected from the power supply. Or the first selection end is connected to the first power supply end and disconnected from the first connection end, the second selection end is connected to the second power supply end and disconnected from the second connection end, so that the power source is the circuit capacitor Charging. In one embodiment, the capacitance value of the finger capacitance is determined by the following formula: Vo=(Vc−Vt*Cx/Ci), where Vo is the voltage, Vt is the voltage amplitude of the excitation signal, and Cx is the finger. The capacitance of the capacitor, Ci is the capacitance of the capacitor of the circuit, and Vc is the voltage across the capacitor of the circuit. In one embodiment, the fingerprint detecting circuit further includes a power source, the reference voltage terminal is an output end of the power source, and the switching unit is connected in parallel with the capacitor. The switching unit is disconnected to capacitively connect the circuit between the negative input of the signal amplifier and the output of the signal amplifier. The switching unit is closed such that the circuit capacitance is not connected between the negative input of the signal amplifier and the output of the signal amplifier. In one embodiment, the capacitance value of the finger capacitance is determined by the following formula: Vo=(Vs−Vt*Cx/Ci), where Vo is the voltage, Vt is the voltage amplitude of the excitation signal, and Cx is the finger. The capacitance value of the capacitor, Ci is the capacitance value of the circuit capacitor, and Vs is the voltage of the power source. In one embodiment, the fingerprint detection circuit further includes a sample and hold circuit and an analog to digital converter coupled between the output of the signal amplifier and the analog to digital converter. An electronic device includes a fingerprint detection circuit for transmitting an excitation signal to a finger to collect a finger capacitance. The fingerprint detecting circuit includes a signal amplifier, a circuit capacitor and a switching unit. The negative input of the signal amplifier is connected to the finger capacitor, and the forward input of the signal amplifier is connected to the reference voltage terminal. The signal amplifier outputs a voltage from the output of the signal amplifier according to the capacitance value of the finger capacitor. The switching unit is respectively connected to the negative input terminal of the signal amplifier and the output end of the signal amplifier for controlling the circuit capacitance to be connected between the negative input terminal of the signal amplifier and the output end of the signal amplifier, so that the switch unit The relationship between the voltage and the capacitance of the finger capacitance is a non-linear relationship. In one embodiment, the reference voltage terminal is a ground terminal, and the fingerprint detecting circuit further includes a power source. The power source is connected to the circuit capacitor through the switch unit, and the switch unit is configured to control the power source to charge the circuit capacitor and control the circuit capacitor to be disconnected from the power source. In one embodiment, the fingerprint detecting circuit further includes a power source, the reference voltage terminal is an output end of the power source, and the switch unit is connected in parallel with the circuit capacitor. The switching unit is disconnected to capacitively connect the circuit between the negative input of the signal amplifier and the output of the signal amplifier. The switching unit is closed such that the circuit capacitance is not connected between the negative input of the signal amplifier and the output of the signal amplifier. In one embodiment, the fingerprint detection circuit further includes a sample and hold circuit and an analog to digital converter coupled between the output of the signal amplifier and the analog to digital converter. The additional aspects and advantages of the invention will be set forth in part in the description which follows.

The embodiments of the present invention are described in detail below, and the examples of the embodiments are illustrated in the drawings, wherein the same or similar reference numerals indicate the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are intended to be illustrative of the invention and are not to be construed as limiting. In the description of the present invention, it is to be understood that the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defining "first" or "second" may include one or more of the described features either explicitly or implicitly. In the description of the present invention, the meaning of "a plurality" is two or more unless specifically and specifically defined otherwise. In the description of the present invention, it should be noted that the terms "installation", "connected", and "connected" are to be understood broadly, and may be fixed or detachable, for example, unless otherwise explicitly defined and defined. Connected, or integrally connected; may be mechanically connected, or may be electrically connected or may communicate with each other; may be directly connected or indirectly connected through an intermediate medium, may be internal communication of two elements or interaction of two elements relationship. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood on a case-by-case basis. The disclosure below provides many different embodiments or examples for implementing the different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of the specific examples are described below. Of course, they are merely examples and are not intended to limit the invention. In addition, the present disclosure may repeat reference numerals and/or reference letters in different examples, which are for the purpose of simplicity and clarity, and do not indicate the relationship between the various embodiments and/or settings discussed. Moreover, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art will recognize the use of other processes and/or the use of other materials. Referring to FIG. 1 , a fingerprint detecting circuit 100 according to a first preferred embodiment of the present invention includes a signal amplifier 102 , a circuit capacitor 104 , a switching unit 106 , a power source 108 , a sample and hold circuit 110 , and an analog to digital converter 112 . When acquiring a fingerprint, in conjunction with FIG. 2, the fingerprint detecting circuit 100 can transmit an excitation signal to the finger 500 to collect the finger capacitance 114. For example, the fingerprint detecting circuit 100 can output the excitation signal through the signal generator 116 and transmit an excitation signal to the finger 500 through a transmitting electrode (not shown). The excitation signal can be an alternating current signal, such as an alternating current signal of a sine wave, a square wave or a triangular wave. The voltage amplitude of the AC signal is Vt (hereinafter referred to as an excitation voltage), and the frequency of the AC signal is S. The finger capacitance 114 refers to a capacitance formed between the fingerprint of the finger 500 and the fingerprint sensor 502. For example, a ridge line capacitance is formed between the ridge line of the fingerprint and the fingerprint sensor 502, and the valley line of the fingerprint and the fingerprint sensor 502 A valley capacitance is formed between them. The ridge capacitance and the valley capacitance can be collectively referred to as a finger capacitance 114, that is, a capacitance to be measured. For example, in conjunction with FIG. 2, the fingerprint sensor 502 includes a bezel 504 and a two-dimensional detection array 508 that is composed of a plurality of fingerprint sensing units 506. The bezel 504 surrounds the two-dimensional detection array 508 and provides an excitation signal (e.g., an alternating current signal) to the finger 500 upon fingerprint detection. For example, the bezel 504 can be coupled to the transmit electrode to output the excitation signal. Fingerprint sensing unit 506 completes the acquisition of a single pixel of the fingerprint image. For example, each fingerprint sensing unit 506 is typically about 50 um * 50 um in size. The size of the capacitor 114 formed between the fingerprint sensing unit 506 and the finger 500 represents the feature of the ridge or valley line of the fingerprint, so that all of the sensing units 506 of the detection array 508 and the plurality of finger capacitors 114 formed by the finger 500 represent The ridge valley feature of the fingerprint image. In the present embodiment, the signal amplifier 102 corresponds to one fingerprint sensing unit 506, and outputs a voltage corresponding to the finger capacitance. The negative input of the signal amplifier 102 is coupled to the finger capacitor 114. The forward input of the signal amplifier 102 is coupled to a reference voltage terminal 118. The signal amplifier 102 is output from the signal amplifier 102 based on the capacitance of the finger capacitor 114. Terminal output voltage. In this embodiment, the reference voltage terminal 118 is the ground terminal, that is, the forward input terminal of the signal amplifier 102 is connected to the ground terminal 118. The circuit capacitance 104 can be an internal capacitance or other capacitance of the fingerprint sensor, and the capacitance value of the circuit capacitance 104 is generally fixed. The switch unit 106 is coupled to the negative input of the signal amplifier 102 and the output of the signal amplifier 102 for controlling the circuit capacitor 104 to communicate with the output of the signal amplifier 102 and the output of the signal amplifier 102. Between the ends, the relationship between the voltage and the capacitance value of the finger capacitor 114 is a non-linear relationship. Specifically, the power source 108 is connected to the circuit capacitor 104 through the switch unit 106. The switch unit 106 is configured to control the power source 108 to charge the circuit capacitor 104 and control the circuit capacitor 104 to be disconnected from the power source 108. The power source 108 can be an internal power source of the fingerprint detection circuit 100, for example, a first pole of the power source 108, and a second pole of the power source. Further, the switch unit 106 includes a first switch S1 and a second switch S2. The first switch S1 includes a first selection terminal A1, a first power supply terminal B1, and a first connection terminal C1. The first selection terminal A1 is connected to one end of the circuit capacitor 104. The first power terminal B1 is connected to the power source 108. In one pole, the first connection terminal C1 is connected to the negative input terminal of the signal amplifier 102. The second switch S2 includes a second selection terminal A2, a second power supply terminal B2, and a second connection terminal C2. The second selection terminal A2 is connected to the other end of the circuit capacitor 104. The second power terminal B2 is connected to the power source 108. The second terminal, the second terminal C2 is connected to the output of the signal amplifier 102. The first connection end A1 is connected to the first connection end C1 and disconnected from the first power supply end B1, and the second selection end A2 is connected to the second connection end C2 and disconnected from the second power supply end B2, so that the Circuit capacitance 104 is coupled between the negative input of signal amplifier 102 and the output of signal amplifier 102, and causes circuit capacitor 104 to be disconnected from power supply 108. The first selection terminal A1 is connected to the first power supply terminal B1 and disconnected from the first connection terminal C1, and the second selection terminal A2 is connected to the second power terminal B2 and disconnected from the second connection terminal C2, so that the first selection terminal A1 is disconnected from the second connection terminal C2. Power source 108 charges the circuit capacitor 104. At this point, the power supply 108 charges the circuit capacitor 104 with a certain voltage across the circuit capacitor 104. The sample and hold circuit 110 is coupled between the output of the signal amplifier 102 and the analog to digital converter 112. The sample and hold circuit 110 is for amplifying the voltage output from the output of the signal amplifier 102 by a set multiple. The analog to digital converter 112 is used to convert the amplified voltage into a value and save it. The fingerprint detection circuit 100 can also include a digital signal processor (not shown) that processes the digital signal, the digital signal processor being coupled to the output of the analog to digital converter 112. The voltage output from the output of the digital signal amplifier 102 facilitates subsequent calculations. The capacitance value of the finger capacitance is determined by the following formula: Vo=(Vc-Vt*Cx/Ci), where Vo is the voltage, Vt is the excitation voltage, Cx is the capacitance value of the finger capacitance 114, and Ci is the circuit. The capacitance value of the capacitor 104, Vc, is the voltage across the circuit capacitor 104. As can be seen from the equation, the relationship between the voltage Vo output by the signal amplifier 102 and the capacitance value Cx of the finger capacitor 114 is nonlinear. When the fingerprint detecting circuit 100 is initialized, the first selection terminal A1 is connected to the first power terminal B1, the second selection terminal A2 is connected to the second power terminal B2, and the second power terminal B2 is connected to the anode of the power source 108, and the first power terminal B1 is connected. The negative terminal of the power source 108 is connected, and the circuit capacitor 104 is charged by the power source 108. After charging, the voltage across circuit capacitor 104 is Vc. In this example, Vc = Vs, and Vs is the voltage of the power supply. When the finger capacitor 114 is initialized, both ends are grounded, and the signal generator 116 is grounded (Vt is grounded). Then, the first selection terminal A1 is connected to the first connection terminal C1, the second selection terminal A2 is connected to the second connection terminal C2, and the circuit capacitor 104 is connected between the negative input terminal of the signal amplifier 102 and the output terminal of the signal amplifier 102. At this time, the voltage Vo outputted from the output terminal of the signal amplifier 102 is Vc, and the initialization operation is completed. In the process of fingerprint collection by the fingerprint detecting circuit 100, the signal generator 116 raises the excitation voltage Vt, and charges the finger capacitor 114 during the rising process. The charged charge is the electric quantity Q=Vt*Cx, due to the virtual shortness of the operational amplifier. According to the principle of disconnection, the voltage Vo outputted by the signal amplifier 102 is lowered, and the circuit capacitor 104 is charged with the same amount of charge to ensure that the input end of the operational amplifier is maintained at ground potential. At this time, the electric quantity Q charged to the circuit capacitor 104 is (Vc - Vo) * Ci = Vt * Cx, so the voltage output from the signal amplifier 102 is Vo = Vc - Vt * Cx / Ci. When the voltage Vo enters the sample-and-hold circuit 110, it is amplified by a factor of n and enters the final detection voltage Va=n* (Vc-Vt*Cx/Ci) of the analog-to-digital converter 112. For example, if a finger 500 is placed on the fingerprint sensor 502, the output voltage of the fingerprint ridge line corresponds to the output voltage Vo1=-2V, and the output voltage corresponding to the fingerprint valley line is assumed for this finger 500. The first voltage is equal to the output voltage corresponding to the fingerprint ridge (hereinafter referred to as the second voltage) by 15%, that is, the second voltage Vo2 = -1.7V. If the input range of the analog-to-digital converter 112 is 0~-5V, the sample-and-hold circuit 110 can be amplified by a maximum of 2.5 times (n=2.5), the amplified first voltage Va1=-5V, and the amplified second voltage Va2= -4.25V, Va1-Va2 = -0.75V. When detecting the fingerprint by the fingerprint detecting circuit 100 of the present invention, it is assumed that the voltage Vc of the two ends when the circuit capacitor 104 is initialized is 1.5 V, and the first voltage Vo1 becomes 1.5-2=-0.5 V during the acquisition process, and the second voltage is obtained. Vo2 becomes 1.5-1.7=-0.2V. At this time, the sample and hold circuit 110 can be amplified by 10 times, the amplified first voltage Va1 = -5V, the amplified second voltage Va2 = -2V, Va1 - Va2 = -3V, and the difference is amplified by the difference - 3/-0.75=4 times. The two output voltages are 60% different and are amplified by a factor of four. At this time, the difference between the two output voltages collected by the fingerprint detecting circuit 100 is relatively large, the signal-to-noise ratio is higher, and the subsequent algorithm is easier to recognize. Therefore, taking the first voltage as an example, it can be determined whether the first voltage Vo1 is greater than or equal to -0.5 V (set value), and if so, the first voltage can be used for the formation of a finger fingerprint image. If not, the fingerprint detecting circuit 100 can adjust the first voltage Vo1 by adjusting at least one of the excitation voltage Vt and the voltage Vc across the circuit capacitor 104. The setting of the set value may take into consideration factors such as the range of the analog-to-digital converter 112, the excitation voltage Vt, and the safe voltage range of the voltage Vc across the circuit capacitor 104. In summary, in the fingerprint detecting circuit 100, the relationship between the voltage outputted by the signal amplifier 102 and the finger capacitance 114 is nonlinear, and in the subsequent processing, the voltage output from the signal amplifier 102 is locally linearly amplified to make the output The difference between the voltage corresponding to the ridge line and the voltage corresponding to the valley line becomes larger, and the signal-to-noise ratio is higher, which makes the subsequent algorithm easier to recognize, thereby improving the fingerprint detection effect. Referring to FIG. 3, the fingerprint detecting circuit 200 of the second preferred embodiment of the present invention includes a signal amplifier 202, a capacitor 204, a switching unit 206, a power source (not shown), a sample and hold circuit 210, and an analog to digital converter 212. The fingerprint detecting circuit 200 of the present embodiment can transmit the excitation signal to the finger 500 by using the fingerprint sensor 502 disclosed in the first embodiment to collect the finger capacitance 214. The negative input terminal of the signal amplifier 202 is connected to the finger capacitor 214. The forward input terminal of the signal amplifier 202 is connected to the reference voltage terminal 216. The signal amplifier 202 is output from the output of the signal amplifier 202 according to the capacitance value of the finger capacitor 214. The output voltage. In this embodiment, the reference voltage terminal 216 is the output end of the power source, that is, the forward input terminal of the signal amplifier 202 is connected to the power source. The circuit capacitance 204 can be an internal capacitance or other capacitance of the fingerprint sensor, and the capacitance of the circuit capacitance 204 is generally fixed. The switch unit 206 is coupled to the negative input of the signal amplifier 202 and the output of the signal amplifier 202 for controlling the circuit capacitor 204 to communicate with the output of the signal amplifier 202 and the output of the signal amplifier 202. Between the terminals, the relationship between the voltage and the capacitance value of the finger capacitance 214 is a nonlinear relationship. Specifically, the switch unit 206 is connected in parallel with the circuit capacitor 204. The switching unit 206 is disconnected to connect the circuit capacitor 204 between the negative input of the signal amplifier 202 and the output of the signal amplifier 202. The switching unit 206 is closed such that the circuit capacitance 204 is not connected between the negative input of the signal amplifier 202 and the output of the signal amplifier 202. The connection can be understood as a connection and conduction. In the present embodiment, when the switch unit 206 is closed, the circuit capacitance 204 is connected between the negative input terminal of the signal amplifier 202 and the output terminal of the signal amplifier 202, but the circuit capacitance 204 is Switch unit 206 is shorted such that circuit capacitance 204 is not conducted between the negative input of signal amplifier 202 and the output of signal amplifier 202. The switch unit 206 includes a first connection end D1 and a second connection end D2. The first connection terminal D1 is connected to one end of the circuit capacitor 204 and is connected between the finger capacitor 214 and the negative input terminal of the signal amplifier 202. The second connection terminal D2 is connected to the other end of the circuit capacitor 204 and is connected to the output terminal of the signal amplifier 202. The switching unit 206 is disconnected to connect the circuit capacitor 204 between the negative input terminal of the signal amplifier 202 and the output terminal of the signal amplifier 202, that is, the first connection terminal D1 and the second connection terminal D2 are disconnected. The switch unit 206 is closed such that the capacitor is disconnected between the negative input terminal of the signal amplifier 202 and the output of the signal amplifier 202, that is, the first connection terminal D1 is connected to the second connection terminal D2. Thus, the output of the signal amplifier 202 outputs a voltage equal to the voltage of the power supply. The circuit capacitance 204 is shorted and not connected between the negative input of the signal amplifier 202 and the output of the signal amplifier 202, and has no effect on the voltage output at the output of the signal amplifier 202. The sample and hold circuit 210 is coupled between the output of the signal amplifier 202 and the analog to digital converter 212. The sample and hold circuit 210 is configured to amplify the voltage outputted from the output of the signal amplifier 202 by a set multiple. The analog to digital converter 212 is configured to convert the amplified voltage into a value and save it. The fingerprint detection circuit 200 can also include a digital signal processor (not shown) that processes the digital signal, the digital signal processor being coupled to the output of the analog to digital converter 212. The voltage output from the output of the digital signal amplifier 202 facilitates subsequent calculations. The capacitance value of the finger capacitance 214 is determined by the following formula: Vo = (Vs - Vt * Cx / Ci), where Vo is the voltage outputted from the output of the signal amplifier 202, and Vt is the voltage amplitude of the excitation signal (excitation voltage) Cx is the capacitance value of the finger capacitor 214, Ci is the capacitance value of the circuit capacitor 204, and Vs is the voltage of the power source. It can be seen from the formula that the relationship between the voltage Vo output by the signal amplifier 202 and the capacitance value Cx of the finger capacitance 214 is a nonlinear relationship. When the fingerprint detecting circuit 100 is initialized, the switch unit 206 is closed, the finger capacitor 214 is initialized with both ends grounded, and the signal generator 218 is grounded (Vt is grounded). At this time, the voltage output from the output of the signal amplifier 202 is Vo=Vs, and the initialization operation is completed. In the process of fingerprint collection by the fingerprint detecting circuit 200, the switching unit 206 is turned off, and the signal generator 218 causes the excitation voltage Vt to rise, and during the rising process, the finger capacitor 214 is charged, and the charged charge is the electric quantity Q=Vt*Cx due to The principle of the virtual short-circuit of the op amp, the voltage Vo output by the signal amplifier 202 will drop, charging the circuit capacitor 204 with the same amount of charge to ensure that the input end of the op amp is maintained at the Vs potential. At this time, the electric quantity Q charged to the circuit capacitor 204 is (Vs - Vo) * Ci = Vt * Cx, so the voltage output from the signal amplifier 202 Vo = Vs - Vt * Cx / Ci. When the voltage Vo enters the sample-and-hold circuit 210, it is amplified by a factor of n and enters the final detection voltage Va=n* (Vs-Vt*Cx/Ci) of the analog-to-digital converter 212. Therefore, the voltage Vo output from the signal amplifier 202 can be adjusted by adjusting at least one of the excitation voltage Vt and the voltage Vs of the power source. In summary, in the fingerprint detecting circuit 200, the relationship between the voltage outputted by the signal amplifier 202 and the finger capacitance 214 is nonlinear, and in the subsequent processing, the voltage output from the signal amplifier 202 is locally linearly amplified to make the output The difference between the voltage corresponding to the ridge line and the voltage corresponding to the valley line becomes larger, and the signal-to-noise ratio is higher, which makes the subsequent algorithm easier to recognize, thereby improving the fingerprint detection effect. Referring to FIG. 4 and in conjunction with FIGS. 1 to 3, the electronic device 300 of the third preferred embodiment of the present invention includes a fingerprint detecting circuit (not shown). The fingerprint detecting circuit can be disposed inside the electronic device 300. The fingerprint detecting circuit can be the fingerprint detecting circuit of any of the above embodiments. In the present embodiment, the electronic device 300 will be described by taking a mobile phone as an example. It can be understood that in other embodiments, the electronic device 300 can also be an electronic device that requires fingerprint detection, such as a tablet computer, a notebook computer, a smart wearable device, an audio player, or a video player. The collection window 302 of the fingerprint sensor 502 is disposed on the front panel 304 of the electronic device 300 to facilitate collection of user fingerprints. Of course, the collection window 302 can also be disposed at other positions on the side and the back of the electronic device 300 according to other requirements. In summary, the electronic device 300 can improve the fingerprint detection effect. In the description of the present specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example", or "some examples", etc. Particular features, structures, materials or features described in the manner or examples are included in at least one embodiment or example of the invention. In the present specification, the schematic representation of the above terms does not necessarily mean the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defining "first" or "second" may include at least one of the features, either explicitly or implicitly. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless specifically defined otherwise. Any process or method description in the flowcharts or otherwise described herein can be understood as a module, segment or code representing code that includes one or more executable instructions for implementing the steps of a particular logical function or process. The scope of the preferred embodiments of the invention includes additional implementations, in which the functions may be performed in a substantially simultaneous manner or in the reverse order, depending on the order in which they are illustrated, This should be understood by those skilled in the art to which the embodiments of the present invention pertain. The logic and/or steps represented in the flowchart or otherwise described herein, for example, may be considered as an ordered list of executable instructions for implementing logical functions, and may be embodied in any computer readable medium, Used in conjunction with, or in conjunction with, an instruction execution system, apparatus, or device (eg, a computer-based system, a system including a processor, or other system that can fetch instructions and execute instructions from an instruction execution system, apparatus, or device) Or use with equipment. For the purposes of this specification, a "computer readable medium" can be any apparatus that can contain, store, communicate, propagate, or transport a program for use in an instruction execution system, apparatus, or device, or in conjunction with such an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of computer readable media include the following: electrical connections (electronic devices) having one or more wires, portable computer disk cartridges (magnetic devices), random access memory ( RAM), read-only memory (ROM), erasable editable read-only memory (EPROM or flash memory), fiber optic devices, and portable CD-ROM (CDROM). In addition, the computer readable medium may even be a paper or other suitable medium on which the program may be printed, as it may be optically scanned, for example by paper or other medium, followed by editing, interpretation or, if appropriate, other suitable The method is processed to obtain the program electronically and then stored in computer memory. It should be understood that portions of the invention may be implemented in hardware, software, firmware, or combinations thereof. In the above embodiments, multiple steps or methods may be implemented with software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one or combination of the following techniques well known in the art: having logic gates for implementing logic functions on data signals Discrete logic circuits, dedicated integrated circuits with suitable combinational logic gates, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), and more. A person skilled in the art can understand that all or part of the steps carried in the method of the above embodiment can be implemented by a program to instruct the related hardware, and the program can be stored in a computer readable storage medium. When executed, one or a combination of the steps of the method embodiments is included. In addition, each functional unit in each embodiment of the present invention may be integrated into one processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above integrated modules can be implemented in the form of hardware or in the form of software functional modules. The integrated module can also be stored in a computer readable storage medium if it is implemented as a software function module and sold or used as a standalone product. The storage medium mentioned above may be a read only memory, a magnetic sheet or a compact disc or the like. Although the embodiments of the present invention have been shown and described, it is understood that the above-described embodiments are illustrative and are not to be construed as limiting the scope of the invention. The embodiments are subject to variations, modifications, substitutions and variations.

100, 200‧‧‧ fingerprint detection circuit
102, 202‧‧‧Signal Amplifier
104, 204‧‧‧ circuit capacitance
106, 206‧‧‧ Switching unit
108‧‧‧Power supply
110, 210‧‧‧Sampling and holding circuit
112, 212‧‧‧ Analog to Digital Converter
114, 214‧‧‧ finger capacitance
116, 218‧‧‧ signal generator
118, 216‧‧‧ reference voltage terminal
300‧‧‧Electronic devices
302‧‧‧ Collection window
304‧‧‧ front panel
500‧‧‧ fingers
502‧‧‧Finger sensor
504‧‧‧Border
506‧‧‧Finger sensing unit
508‧‧‧Two-dimensional inspection array
A1‧‧‧ first choice
A2‧‧‧ second choice
B1‧‧‧First power terminal
B2‧‧‧second power terminal
C1, D1‧‧‧ first connection
C2, D2‧‧‧ second connection
Capacitance value of Ci‧‧‧ circuit capacitor
Capacitance value of Cx‧‧‧ finger capacitor
Frequency of S‧‧‧ AC signals
S1‧‧‧ first switch
S2‧‧‧ second switch
Va‧‧‧Detection voltage
Vo‧‧‧ voltage
Vs‧‧‧ power supply voltage
Vt‧‧‧ excitation voltage

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments of the present invention in which: FIG. 1 is a schematic diagram of a fingerprint detection circuit in accordance with a preferred embodiment of the present invention; 2 is a schematic diagram of a fingerprint detecting circuit for collecting fingerprints according to a preferred embodiment of the present invention; FIG. 3 is another schematic diagram of a fingerprint detecting circuit according to a preferred embodiment of the present invention; and FIG. 4 is a preferred embodiment of the present invention. A schematic plan view of an electronic device.

100‧‧‧Fingerprint detection circuit

102‧‧‧Signal Amplifier

104‧‧‧Circuit capacitance

106‧‧‧Switch unit

108‧‧‧Power supply

110‧‧‧Sampling and holding circuit

112‧‧• Analog to Digital Converter

114‧‧‧ finger capacitance

116‧‧‧Signal Generator

118‧‧‧reference voltage terminal

A1‧‧‧ first choice

A2‧‧‧ second choice

B1‧‧‧First power terminal

B2‧‧‧second power terminal

C1‧‧‧ first connection

C2‧‧‧second connection

Capacitance value of Ci‧‧‧ circuit capacitor

Capacitance value of Cx‧‧‧ finger capacitor

Frequency of S‧‧‧ AC signals

S1‧‧‧ first switch

S2‧‧‧ second switch

Va‧‧‧Detection voltage

Vo‧‧‧ voltage

Vs‧‧‧ power supply voltage

Vt‧‧‧ excitation voltage

Claims (11)

A fingerprint detecting circuit for transmitting an excitation signal to a finger to collect a finger capacitance, wherein the fingerprint detecting circuit comprises a signal amplifier, a circuit capacitor and a switch unit; and a negative input end of the signal amplifier is connected to the finger a capacitor, a forward input of the signal amplifier is connected to a reference voltage terminal, and the signal amplifier outputs a voltage from an output end of the signal amplifier according to a capacitance value of the finger capacitor; the switch unit is respectively connected to a negative input terminal of the signal amplifier The output of the signal amplifier is connected to control the capacitance of the circuit between the negative input terminal of the signal amplifier and the output end of the signal amplifier, so that the relationship between the voltage and the capacitance value of the finger capacitor is nonlinear. . The fingerprint detecting circuit of claim 1, wherein the reference voltage terminal is a ground end, and the fingerprint detecting circuit further comprises a power source; the power source is connected to the circuit capacitor through the switch unit, and the switch unit is used by the switch unit The power supply is controlled to charge the circuit capacitor and the circuit capacitor is disconnected from the power source. The fingerprint detecting circuit of claim 2, wherein the switch unit comprises a first switch and a second switch; the first switch includes a first selection end, a first power end, and a first connection end, The first selection end is connected to one end of the circuit capacitor, the first power end is connected to the first pole of the power source, and the first connection end is connected to the negative input end of the signal amplifier; the second switch includes a second selection end, a second power terminal and a second terminal, the second terminal is connected to the other end of the circuit capacitor, the second power terminal is connected to the second pole of the power source, and the second terminal is connected to the output end of the signal amplifier; The first selection end is connected to the first connection end and disconnected from the first power supply end, and the second selection end is connected to the second connection end and disconnected from the second power supply end, so that the circuit is capacitively connected to the signal amplifier Between the negative input terminal and the output of the signal amplifier, and disconnecting the circuit capacitor from the power source; or the first selection terminal is connected to the first And disconnect the power source terminal is connected to the first terminal, the second selection terminal connected to the second power supply terminal and the second connecting terminal is disconnected, so that the power supply circuit for charging the capacitor. The fingerprint detecting circuit according to claim 2, wherein the capacitance value of the finger capacitor is determined by the following formula: Vo=(Vc-Vt*Cx/Ci), wherein Vo is the voltage, and Vt is The voltage amplitude of the excitation signal, Cx is the capacitance value of the finger capacitance, Ci is the capacitance value of the circuit capacitor, and Vc is the voltage across the capacitance of the circuit. The fingerprint detecting circuit of claim 1, wherein the fingerprint detecting circuit further comprises a power source, the reference voltage terminal is an output end of the power source, and the switch unit is connected in parallel with the circuit capacitor; Opening the capacitor between the negative input of the signal amplifier and the output of the signal amplifier; the switching unit is closed such that the circuit capacitor is not connected to the negative input of the signal amplifier and the output of the signal amplifier Between the ends. The fingerprint detecting circuit according to claim 5, wherein the capacitance value of the finger capacitance is determined by the following formula: Vo=(Vs−Vt*Cx/Ci), wherein Vo is the voltage, and Vt is The voltage amplitude of the excitation signal, Cx is the capacitance value of the finger capacitor, Ci is the capacitance value of the circuit capacitor, and Vs is the voltage of the power source. The fingerprint detecting circuit of claim 1, wherein the fingerprint detecting circuit further comprises a sample and hold circuit and an analog to digital converter, wherein the sample and hold circuit is connected to the output end of the signal amplifier and the analog to digital conversion Between the devices. An electronic device includes a fingerprint detecting circuit for transmitting an excitation signal to a finger to collect a finger capacitance, wherein the fingerprint detecting circuit comprises a signal amplifier, a circuit capacitor and a switching unit; and a negative input of the signal amplifier The finger is connected to the finger capacitor, and the forward input end of the signal amplifier is connected to the reference voltage end, and the signal amplifier outputs a voltage from the output end of the signal amplifier according to the capacitance value of the finger capacitor; the switch unit is respectively negative with the signal amplifier Connecting the input end to the output end of the signal amplifier for controlling the capacitance of the circuit to be connected between the negative input terminal of the signal amplifier and the output end of the signal amplifier such that the voltage is related to the capacitance value of the finger capacitor It is a nonlinear relationship. The electronic device of claim 8, wherein the reference voltage terminal is a ground end, the fingerprint detecting circuit further comprises a power source; the power source is connected to the circuit capacitor through the switch unit, and the switch unit is used for The power supply is controlled to charge the circuit capacitor and control the circuit capacitance to be disconnected from the power source. The electronic device of claim 8, wherein the fingerprint detecting circuit further comprises a power source, the reference voltage terminal is an output end of the power source, and the switch unit is connected in parallel with the circuit capacitor; the switch unit is disconnected Having the circuit capacitively coupled between a negative input of the signal amplifier and an output of the signal amplifier; the switch unit is closed such that the circuit capacitance is not connected at a negative input of the signal amplifier and an output of the signal amplifier between. The electronic device of claim 8, wherein the fingerprint detecting circuit further comprises a sample and hold circuit and an analog to digital converter, the sample and hold circuit being connected to the output end of the signal amplifier and the analog to digital converter between.