WO2015135318A1 - 指纹检测电路和指纹检测装置 - Google Patents

指纹检测电路和指纹检测装置 Download PDF

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Publication number
WO2015135318A1
WO2015135318A1 PCT/CN2014/088392 CN2014088392W WO2015135318A1 WO 2015135318 A1 WO2015135318 A1 WO 2015135318A1 CN 2014088392 W CN2014088392 W CN 2014088392W WO 2015135318 A1 WO2015135318 A1 WO 2015135318A1
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Prior art keywords
fingerprint
circuit
signal
sensing unit
finger
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PCT/CN2014/088392
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English (en)
French (fr)
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詹昶
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深圳市汇顶科技股份有限公司
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Publication of WO2015135318A1 publication Critical patent/WO2015135318A1/zh

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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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  • the present invention relates to the field of fingerprint detection technologies, and in particular, to a fingerprint detection circuit and a fingerprint detection device having the fingerprint detection circuit.
  • the fingerprint detecting circuit is a core module for converting image information of "peak” and “valley” contained in the fingerprint into an electrical signal.
  • Chinese Patent No. 200710129193.0 discloses a fingerprint detecting circuit comprising an external electrode 10, a detecting unit 20, a resistor 30 and a signal generating source 40.
  • the external electrode 10 and the signal generating source 40 are respectively coupled to reference levels Vcmb and Vcma, and the detecting unit 20 is coupled to the signal generating source 40 through the resistor 30.
  • the detecting circuit further includes an output terminal OUT coupled between the detecting unit 20 and the resistor 30, and the output terminal OUT is connected to the determining circuit and the analog to digital converter.
  • Different detection units 20 and the surface of the finger 50 are equivalently configured to form a plurality of capacitance components having different capacitance values.
  • the resistor 30 and the capacitance component form a filter circuit, and thus at the output terminal OUT According to the reference signal provided by the signal generating source 40, different detection signals are generated corresponding to the difference between the resistance value of the resistor 30 and the capacitance value of the capacitor component, thereby implementing fingerprint detection.
  • the existing fingerprint detection circuit has higher circuit cost, poor circuit stability, and slower fingerprint detection speed.
  • the main object of the present invention is to provide a fingerprint detecting circuit and a fingerprint detecting device, aiming to reduce Low circuit cost, improved circuit stability and fingerprint detection speed.
  • the present invention provides a fingerprint detecting circuit comprising:
  • a signal generating circuit for generating an alternating current signal
  • a transmitting electrode for transmitting the alternating current signal to the finger
  • a sensing unit for collecting fingerprint information of a finger
  • a signal processing circuit configured to process the fingerprint information
  • the signal generating circuit is electrically connected to the transmitting electrode, the sensing unit is electrically connected to the signal processing circuit; a first capacitor is formed between the sensing unit and the finger, and the sensing unit and the GND are The second capacitor.
  • the signal generating circuit comprises a digital-to-analog converter, a driver and a DC booster, the driver being electrically connected to the digital-to-analog converter, the DC booster and the transmitting electrode, respectively, wherein the input of the driver An electrical connection is made to an output of the digital to analog converter, the output of the driver being electrically coupled to the transmitting electrode.
  • the signal generating circuit comprises a digital-to-analog converter and an LC resonant circuit, an input of the LC resonant circuit is electrically connected to an output of the digital-to-analog converter, an output of the LC resonant circuit and the The emitter electrode is electrically connected.
  • the signal processing circuit includes an amplifier and an analog to digital converter, the input of the amplifier being electrically coupled to the sensing unit, the output of the amplifier being electrically coupled to the input of the analog to digital converter.
  • the sensing unit comprises a plurality of sensing electrodes
  • the amplifier has a plurality of amplifiers, and each amplifier is electrically connected to a sensing electrode.
  • the emitter electrode and the sensing unit are integrated in a sensing chip.
  • the emitter electrode is a ring-shaped emitter electrode that surrounds the sensing unit.
  • the transmitting electrode directly contacts the finger or indirectly contacts the finger through an electrical conductor to transmit the alternating current signal.
  • the invention also provides a fingerprint detecting device, comprising a fingerprint detecting circuit, the fingerprint detecting circuit comprising: a signal generating circuit for generating an alternating current signal; a transmitting electrode for transmitting the alternating current signal to a finger; and a sensing unit And acquiring signal information of the finger; the signal processing circuit is configured to process the fingerprint information; the signal generating circuit is electrically connected to the transmitting electrode, and the sensing The unit is electrically connected to the signal processing circuit; a first capacitor is disposed between the sensing unit and the finger, and a second capacitor is disposed between the sensing unit and the GND.
  • the invention provides a fingerprint detecting circuit, which couples an alternating current signal having a certain amplitude to a finger through a transmitting electrode, so that the alternating current signal passes through a first capacitor formed between the finger and the sensing unit and the sensing unit and the ground (GND)
  • the second capacitor formed between the two generates a voltage dividing signal, which is a fingerprint sensing signal, which is processed by the signal processing circuit to generate output data containing the fingerprint information, thereby realizing the detection of the fingerprint. Since the whole circuit adopts an open-loop structure, does not include any feedback loop, the circuit cost is low, and there is no loop stability problem, and the reliability is high; and the fingerprint detecting circuit of the present invention can use only one analog-to-digital converter at the earliest. By converting the time of the cycle, the image information of "peak” and “valley” can be converted into corresponding electrical signals, thus improving the speed of fingerprint detection.
  • FIG. 1 is a circuit diagram of a prior art fingerprint detecting circuit
  • FIG. 2 is a block diagram showing the structure of an embodiment of the fingerprint detecting circuit of the present invention.
  • FIG. 3 is an equivalent circuit diagram of the fingerprint detecting circuit of FIG. 2.
  • the fingerprint detecting circuit of the present invention is a capacitive voltage-dividing fingerprint detecting circuit, and uses the first capacitor C1 (or the sensing capacitor) corresponding to the “peak” and the “valley” included in the fingerprint to have different sizes, so the same AC signal excitation
  • the fingerprint detecting circuit includes a signal generating circuit 100, a transmitting electrode 200, a sensing unit 300, and a signal processing circuit 400, wherein the signal generating circuit 100 and the transmitting circuit
  • the electrode 200 is electrically connected, and the sensing unit 300 is electrically connected to the signal processing circuit 400.
  • the signal generating circuit 100 is configured to generate an alternating current signal; the transmitting electrode 200 is configured to transmit an alternating current signal to the finger 500, which may be in direct contact with the finger 500 or connected to a conductive body.
  • the inductive unit 300 is used to indirectly contact the finger 500; the sensing unit 300 is configured to collect the fingerprint information of the finger 500, that is, generate a voltage signal of a corresponding amplitude according to the fingerprint, and the surface thereof covers an insulating layer to isolate the finger 500 and the sensing unit 300; the signal processing circuit The 400 is configured to perform corresponding processing on the fingerprint information collected by the sensing unit 300, thereby converting the voltage signal into fingerprint data.
  • FIG. 2 A specific equivalent circuit diagram is shown in FIG. 2, which will be described in detail below with reference to FIG.
  • the signal generating circuit 100 includes a digital-to-analog converter 110, a driver 120, and a DC booster 130.
  • the driver 120 is electrically connected to the digital-to-analog converter 110, the DC booster 130, and the transmitting electrode 200, respectively, wherein the input and the number of the driver 120 are
  • the output of the mode converter 110 is electrically connected, and the output of the driver 120 is electrically connected to the transmitting electrode 200.
  • the AC signal source of the input driver 120 is the output voltage of the digital-to-analog converter 110, and the digital-to-analog converter 110 can output various AC waveforms according to different digital codes, such as a sine wave, a square wave, a triangle wave, and the like.
  • the operating power supply voltage of the driver 120 is provided by the DC booster 130.
  • the DC booster 130 boosts the low voltage power supply voltage in the system to a high voltage power supply voltage and outputs it to the driver 120 to increase the output of the driver 120 to the transmitting electrode 200.
  • the driver 120 and the DC booster 130 may also be replaced by an LC resonant circuit.
  • the input of the LC resonant circuit is electrically connected to the digital-to-analog converter 110.
  • the output of the LC resonant circuit and the transmitting electrode 200 are The LC resonant circuit increases the voltage amplitude of the AC signal input from the digital-to-analog converter 110 and outputs it to the transmitting electrode 200.
  • the emitter electrode 200 and the sensing unit 300 are integrated in a sensing chip.
  • the sensing unit 300 is composed of a plurality of arrayed sensing electrodes 310, and the transmitting electrode 200 is a ring-shaped transmitting electrode that surrounds the sensing unit 300.
  • the sensing electrode 310 acquires fingerprint information by detecting fingerprints of the finger 500 to generate different detection values. More specifically, the different sensing electrodes 310 and the surface of the finger 500 are equivalently configured to have a plurality of different capacitance values. In the capacitor component, the detected value is the capacitance value of the capacitor component.
  • One of the electrodes of the capacitor component is composed of the sensing electrode 310, and the other electrode is composed of the surface of the finger 500 and the emitter electrode 200, and the insulating layer becomes The dielectric layer in the capacitor assembly.
  • the finger 500 When the finger 500 is pressed against the sensing chip, it is directly or indirectly contacted with the transmitting electrode 200, so that the transmitting electrode 200 couples the alternating current signal to the finger 500; while the finger 500 contacts the insulating layer on the surface of the sensing unit 300, covering the plurality of sensing electrodes 310, Under the excitation of the AC signal, a first capacitor C1 (or a sense capacitor) is formed between the surface of the finger 500 and the sensing electrode 310.
  • the capacitance value is inversely proportional to the distance between the upper and lower plates of the capacitor. Therefore, the first capacitor C1 corresponding to the “peak” and the “valley” in the fingerprint path is different in size.
  • the signal processing circuit 400 includes an amplifier 410 and an analog to digital converter 420.
  • the input of the amplifier 410 is electrically coupled to the sensing unit 300, and the output of the amplifier 410 is electrically coupled to the input of the analog to digital converter 420.
  • the number of amplifiers 410 is the same as the number of sensing electrodes 310.
  • Each amplifier 410 is electrically connected to a sensing electrode 310 (for simplicity, only one connection diagram of the sensing electrodes and one amplifier is shown in FIG. 2), and each sensing electrode 310 is A second capacitor C2 (or parasitic capacitance) exists between ground (GND), and the voltage difference between the first capacitor C1 and the second capacitor C2 on the finger 500 is the input of the amplifier 410.
  • the voltage is amplified by the amplifier 410 and output to the analog-to-digital converter 420.
  • the analog-to-digital converter 420 converts the received analog voltage signal into a digital signal and outputs it.
  • the output data is the detected fingerprint information. By using an analog-to-digital converter 420 of suitable accuracy, it is ensured that the output data contains sufficient gray scale information.
  • the output voltage of the amplifier 410 is calculated as:
  • the output voltage of the amplifier 410 can be calculated as:
  • V1-V2 68mV
  • the resolution voltage of the 8-level gradation corresponding to the voltage difference is:
  • the accuracy N of the analog-to-digital converter 420 can be calculated as 8-bit (8-bit). .
  • the fingerprint detecting circuit of the present invention couples an alternating current signal having a certain amplitude to the finger 500 through the transmitting electrode 200, so that the alternating current signal passes through the first capacitor C1 formed between the finger 500 and the sensing unit 300 and the sensing unit 300.
  • the second capacitor C2 formed between the ground generates a voltage dividing signal
  • the voltage division signal is a fingerprint sensing signal, which is processed by the signal processing circuit 400 to generate output data including fingerprint information, thereby realizing fingerprint detection. Since the whole circuit adopts an open-loop structure, does not include any feedback loop, the circuit cost is low, and there is no loop stability problem, and the reliability is high; and the fingerprint detecting circuit of the present invention can use only one analog-to-digital converter at the earliest. By converting the time of the cycle, the image information of "peak” and “valley” can be converted into corresponding electrical signals, so the fingerprint detection speed is fast.
  • the amplitude of the AC signal generated by the digital-to-analog converter 110 is relatively low, and the corresponding effective signal amplitude of the fingerprint sensing is relatively low.
  • the DC booster 130 is used to boost the voltage in the mobile terminal system and output to the driver 120, so that the AC signal generated by the digital-to-analog converter 110 passes through the driver 120 to form an AC signal having a sufficiently large amplitude, and finally by the amplifier 410.
  • the fingerprint sensing signal generated by the sensing unit 300 is amplified. Therefore, the output data includes the image gradation with sufficient precision to distinguish the fingerprint information, and has the voltage precision corresponding to the gradation of the 8-level image, so the fingerprint detection accuracy is high.
  • the invention also provides a fingerprint detecting device, comprising a fingerprint detecting circuit, the fingerprint detecting circuit comprising: a signal generating circuit for generating an alternating current signal; a transmitting electrode for transmitting the alternating current signal to the finger; and a sensing unit, Fingerprint information for collecting a finger; a signal processing circuit for processing the fingerprint information; the signal generating circuit is electrically connected to the transmitting electrode, the sensing unit is electrically connected to the signal processing circuit; and the sensing unit There is a first capacitor between the sensing unit and the GND, and a second capacitor is disposed between the sensing unit and the GND.
  • the fingerprint detecting circuit described in this embodiment is the fingerprint detecting circuit according to the above embodiment of the present invention, and details are not described herein again.
  • the fingerprint detecting device of the invention adopts the above-mentioned fingerprint detecting circuit, reduces the cost, improves the reliability, and improves the fingerprint detecting speed and the detecting precision.
  • the invention provides a fingerprint detecting circuit, which has a certain amplitude through the transmitting electrode
  • the flow signal is coupled to the finger such that the AC signal generates a voltage division signal through a second capacitance formed between the first capacitance formed between the finger and the sensing unit and the sensing unit and the ground (GND), and the voltage dividing signal is a fingerprint sensing
  • the signal is processed by the signal processing circuit to generate output data containing the fingerprint information, thereby realizing the detection of the fingerprint. Since the whole circuit adopts an open-loop structure, does not include any feedback loop, the circuit cost is low, and there is no loop stability problem, and the reliability is high; and the fingerprint detecting circuit of the present invention can use only one analog-to-digital converter at the earliest. By converting the time of the cycle, the image information of "peak” and “valley” can be converted into corresponding electrical signals, thus improving the speed of fingerprint detection.

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Abstract

本发明公开了一种指纹检测电路和指纹检测装置，所述指纹检测电路包括：信号发生电路，用于产生交流信号；发射电极，用于传递所述交流信号至手指；感应单元，用于釆集手指的指纹信息；信号处理电路，用于处理所述指纹信息；所述信号发生电路与所述发射电极电连接，所述感应单元与所述信号处理电路电连接。从而，通过发射电极将具有一定幅度的交流信号耦合至手指，使得该交流信号通过手指和感应单元之间形成的第一电容与感应单元和地之间形成的第二电容产生分压信号，其经信号处理电路处理后产生包含了指纹信息的输出数据，最终实现指纹的检测。由于整个电路釆用开环结构，不包含任何反馈环路，因此电路成本低，可靠性高，指纹检测速度快。

Description

指纹检测电路和指纹检测装置 技术领域
本发明涉及指纹检测技术领域，尤其是涉及一种指纹检测电路和具有该指纹检测电路的指纹检测装置。
背景技术
在指纹检测装置中，指纹检测电路是用于将指纹包含的“峰”和“谷”的图像信息转化为电信号的核心模块。中国专利200710129193.0披露了一种指纹检测电路，其包括外部电极10、检测单元20、电阻30和信号产生源40，外部电极10与信号产生源40分别耦接至参考电平Vcmb与Vcma，检测单元20通过电阻30耦接至信号产生源40，检测电路还包括一输出端OUT耦接于检测单元20与电阻30之间，输出端OUT连接判断电路和模数转换器。不同的检测单元20与手指50表面不同的纹路之间等效构成许多具有不同电容值的电容组件，对信号产生源40而言，电阻30以及电容组件则构成一个滤波电路，因此在输出端OUT上会根据信号产生源40所提供的参考信号，随着电阻30的电阻值与电容组件的电容值的不同而对应产生不同的检测信号，从而实现指纹检测。
然而，该技术方案存在以下缺陷：首先，由于电容组件的电容很小，要获得适当的截止频率就要求电阻30非常大，集成在芯片上会消耗很大的成本；其次，在检测单个指纹像素点时需要经历多个“比较器检测->输入信号调节”周期来确定最终的直流电平，检测精度越高要求的检测周期越长，导致了检测速度和检测精度这两个重要指标不可兼得；最后，该专利的信号产生源40与模数转换器构成了一个闭环回路，使得电路存在环路不稳定的风险。
综上所述，现有的指纹检测电路，电路成本较高，电路稳定性较差，指纹检测速度较慢。
发明内容
本发明的主要目的在于提供一种指纹检测电路和指纹检测装置，旨在降 低电路成本，提高电路稳定性和指纹检测速度。
为达以上目的，本发明提出一种指纹检测电路，包括：
信号发生电路，用于产生交流信号；
发射电极，用于传递所述交流信号至手指；
感应单元，用于采集手指的指纹信息；
信号处理电路，用于处理所述指纹信息；
所述信号发生电路与所述发射电极电连接，所述感应单元与所述信号处理电路电连接；所述感应单元与所述手指之间有第一电容，所述感应单元与GND之间有第二电容。
优选地，所述信号发生电路包括数模转换器、驱动器和直流升压器，所述驱动器分别与所述数模转换器、直流升压器和发射电极电连接，其中所述驱动器的输入端与所述数模转换器的输出端电连接，所述驱动器的输出端与所述发射电极电连接。
优选地，所述信号发生电路包括数模转换器和LC谐振电路，所述LC谐振电路的输入端与所述数模转换器的输出端电连接，所述LC谐振电路的输出端与所述发射电极电连接。
优选地，所述信号处理电路包括放大器和模数转换器，所述放大器的输入端与所述感应单元电连接，所述放大器的输出端与所述模数转换器的输入端电连接。
优选地，所述感应单元包括多个感应电极，所述放大器有多个，每一放大器电连接一感应电极。
优选地，所述发射电极和感应单元集成于一感应芯片。
优选地，所述发射电极为环形发射电极，其环绕于所述感应单元周围。
优选地，所述发射电极直接与手指接触或通过一导电体间接与手指接触来传递所述交流信号。
本发明同时提出一种指纹检测装置，包括一指纹检测电路，所述指纹检测电路包括：信号发生电路，用于产生交流信号；发射电极，用于传递所述交流信号至手指；感应单元，用于采集手指的指纹信息；信号处理电路，用于处理所述指纹信息；所述信号发生电路与所述发射电极电连接，所述感应 单元与所述信号处理电路电连接；所述感应单元与所述手指之间有第一电容，所述感应单元与GND之间有第二电容。
本发明所提供的一种指纹检测电路，通过发射电极将具有一定幅度的交流信号耦合至手指，使得该交流信号通过手指和感应单元之间形成的第一电容与感应单元和地(GND)之间形成的第二电容产生分压信号，该分压信号即为指纹感应信号，其经信号处理电路处理后产生包含了指纹信息的输出数据，实现了指纹的检测。由于整个电路采用开环结构，不包含任何反馈环路，电路成本低，且不存在环路稳定性问题，可靠性高；而且本发明的指纹检测电路最快可仅使用一个模数转换器的转换周期的时间，即可将“峰”和“谷”的图像信息转化为相应的电信号，因此提高了指纹检测速度。
附图说明
图1是现有技术的指纹检测电路的电路图；
图2是本发明的指纹检测电路一实施例的结构框图；
图3是图2中的指纹检测电路的等效电路图。
本发明目的的实现、功能特点及优点将结合实施例，参照附图做进一步说明。
具体实施方式
应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
本发明的指纹检测电路，为电容分压式指纹检测电路，利用指纹上包含的“峰”和“谷”对应的第一电容C1(或称感应电容)大小不同，所以在同样的交流信号激励下输出信号的幅度也不同的原理，将“峰”和“谷”的图像信息转化为相应的电信号。
参见图1、图2，提出本发明的指纹检测电路一实施例，所述指纹检测电路包括信号发生电路100、发射电极200、感应单元300和信号处理电路400，其中，信号发生电路100与发射电极200电连接，感应单元300与信号处理电路400电连接。信号发生电路100用于产生交流信号；发射电极200用于传递交流信号至手指500，其可以直接与手指500接触，或连接一导电体后通 过该导电体间接与手指500接触；感应单元300用于采集手指500的指纹信息，即根据指纹产生相应幅度的电压信号，其表面覆盖一绝缘层以隔绝手指500和感应单元300；信号处理电路400用于对感应单元300采集到的指纹信息进行相应的处理，从而将电压信号转换为指纹数据。具体的等效电路图如图2所示，以下结合图2进行详细说明。
信号发生电路100包括数模转换器110、驱动器120和直流升压器130，驱动器120分别与数模转换器110、直流升压器130和发射电极200电连接，其中驱动器120的输入端与数模转换器110的输出端电连接，驱动器120的输出端与发射电极200电连接。输入驱动器120的交流信号源为数模转换器110的输出电压，数模转换器110可根据不同的数字编码输出各种交流波形，如正弦波、方波、三角波等。驱动器120的工作电源电压由直流升压器130提供，直流升压器130将系统中的低压电源电压升高为高压电源电压后输出给驱动器120，以增大驱动器120输出至发射电极200的交流信号的电压幅值。在某些实施例中，所述驱动器120与直流升压器130也可以由LC谐振电路代替，LC谐振电路的输入端与数模转换器110电连接，LC谐振电路的输出端与发射电极200电连接，从而LC谐振电路将数模转换器110输入的交流信号的电压幅值增大后输出至发射电极200。
发射电极200和感应单元300集成于一感应芯片。感应单元300由多个阵列排布的感应电极310构成，发射电极200为环形发射电极，其环绕于感应单元300周围。所述感应电极310通过检测手指500的指纹而产生不同的检测值而获取指纹信息，更明确地说，不同的感应电极310与手指500表面不同的纹路之间等效构成许多具有不同电容值的电容组件，该检测值即为电容组件的电容值，该电容组件的其中一个电极由感应电极310构成，而另一个电极则由手指500的表面与发射电极200等效构成，且绝缘层即成为电容组件中的介电层。手指500按压于感应芯片时，直接或间接的与发射电极200接触，以使发射电极200将交流信号耦合至手指500；同时手指500接触感应单元300表面的绝缘层，覆盖多个感应电极310，在交流信号的激励下，手指500表面与感应电极310之间形成第一电容C1(或称感应电容)，根据平板电容的计算公式可知，电容值与电容上下极板之间的距离成反比，因此手指纹路中“峰”和“谷”对应的第一电容C1大小不同。
信号处理电路400包括放大器410和模数转换器420，放大器410的输入端与感应单元300电连接，放大器410的输出端与模数转换器420的输入端电连接。放大器410的数量与感应电极310的数量相同，每一放大器410电连接一感应电极310(为简化起见，图2中仅显示了一个感应电极与一个放大器的连接示意图)，每个感应电极310与地(Ground，GND)之间都存在一个第二电容C2(或称寄生电容)，手指500上的交流信号经过第一电容C1与第二电容C2之间的分压电压即为放大器410的输入电压，放大器410将输入电压放大后输出至模数转换器420，再由模数转换器420将接收到的模拟电压信号转换为数字信号后输出，输出的数据即检测到的指纹信息。通过采用合适精度的模数转换器420，可确保输出的数据包含足够的灰度信息。
下面按照常规的电路参数给出本发明的指纹检测电路中的相关参数计算：
假设感应电极310与指纹的“峰”形成的第一电容C1最大为1fF，第二电容C2为20fF，驱动器120输出的交流信号的电压幅值为10V，放大器410的放大倍数为3倍，可算得放大器410的输出电压为：
V1＝10V*[1fF/(1fF+20fF)]*3＝1.428V
假设感应电极310与指纹的“谷”形成的第一电容C1最小为0.95fF，其它参数不变(即其它参数与指纹的“峰”相同)，可算得放大器410的输出电压为：
V2＝10V*[0.95fF/(0.95fF+20fF)]*3＝1.36V
因此指纹的“峰”和“谷”之间的输出电压差值为：
V1-V2＝68mV
与该电压差值对应的8级灰度的分辨率电压为：
VLSB＝68mV/8＝8.5mV；
假设模数转换器420的参考电压Vref＝2V，则根据公式：VLSB＝Vref/2N(其中N代表精度等级)可算得对模数转换器420的精度N要求为8-bit(8位)。
据此，本发明的指纹检测电路，通过发射电极200将具有一定幅度的交流信号耦合至手指500，使得该交流信号通过手指500和感应单元300之间形成的第一电容C1与感应单元300和地之间形成的第二电容C2产生分压信号， 该分压信号即为指纹感应信号，其经信号处理电路400处理后产生包含了指纹信息的输出数据，实现了指纹的检测。由于整个电路采用开环结构，不包含任何反馈环路，电路成本低，且不存在环路稳定性问题，可靠性高；而且本发明的指纹检测电路最快可仅使用一个模数转换器的转换周期的时间，即可将“峰”和“谷”的图像信息转化为相应的电信号，因此指纹检测速度快。
同时，鉴于移动终端系统中常用的电源电压较低(通常为2.8V)，致使数模转换器110产生交流信号的幅度较低，相应的会导致产生的指纹感应的有效信号幅度较低，本发明中采用直流升压器130将移动终端系统中的电压升高后输出至驱动器120，使得数模转换器110产生的交流信号通过驱动器120之后形成幅度足够大的交流信号，最后再由放大器410将感应单元300产生的指纹感应信号进行放大处理。从而，使得输出数据包含了精度足够的图像灰度以分辨指纹信息，具备对应8级图像灰度的电压精度，因此指纹检测精度较高。
本发明同时提出一种指纹检测装置，包括一指纹检测电路，所述指纹检测电路包括包括：信号发生电路，用于产生交流信号；发射电极，用于传递所述交流信号至手指；感应单元，用于采集手指的指纹信息；信号处理电路，用于处理所述指纹信息；所述信号发生电路与所述发射电极电连接，所述感应单元与所述信号处理电路电连接；所述感应单元与所述手指之间有第一电容，所述感应单元与GND之间有第二电容。本实施例中所描述的指纹检测电路为本发明中上述实施例所涉及的指纹检测电路，在此不再赘述。
本发明的指纹检测装置，采用了上述指纹检测电路后，降低了成本，提高了可靠性，同时提高了指纹检测速度和检测精度。
应当理解的是，以上仅为本发明的优选实施例，不能因此限制本发明的专利范围，凡是利用本发明说明书及附图内容所作的等效结构或等效流程变换，或直接或间接运用在其他相关的技术领域，均同理包括在本发明的专利保护范围内。
工业实用性
本发明所提供的一种指纹检测电路，通过发射电极将具有一定幅度的交 流信号耦合至手指，使得该交流信号通过手指和感应单元之间形成的第一电容与感应单元和地(GND)之间形成的第二电容产生分压信号，该分压信号即为指纹感应信号，其经信号处理电路处理后产生包含了指纹信息的输出数据，实现了指纹的检测。由于整个电路采用开环结构，不包含任何反馈环路，电路成本低，且不存在环路稳定性问题，可靠性高；而且本发明的指纹检测电路最快可仅使用一个模数转换器的转换周期的时间，即可将“峰”和“谷”的图像信息转化为相应的电信号，因此提高了指纹检测速度。

Claims (10)

  1. 一种指纹检测电路，包括：
    信号发生电路，用于产生交流信号；
    发射电极，用于传递所述交流信号至手指；
    感应单元，用于采集手指的指纹信息；
    信号处理电路，用于处理所述指纹信息；
    所述信号发生电路与所述发射电极电连接，所述感应单元与所述信号处理电路电连接；所述感应单元与所述手指之间有第一电容，所述感应单元与GND之间有第二电容。
  2. 根据权利要求1所述的指纹检测电路，其中，所述信号发生电路包括数模转换器、驱动器和直流升压器，所述驱动器分别与所述数模转换器、直流升压器和发射电极电连接，其中所述驱动器的输入端与所述数模转换器的输出端电连接，所述驱动器的输出端与所述发射电极电连接。
  3. 根据权利要求1所述的指纹检测电路，其中，所述信号发生电路包括数模转换器和LC谐振电路，所述LC谐振电路的输入端与所述数模转换器的输出端电连接，所述LC谐振电路的输出端与所述发射电极电连接。
  4. 根据权利要求1-3任一项所述的指纹检测电路，其中，所述信号处理电路包括放大器和模数转换器，所述放大器的输入端与所述感应单元电连接，所述放大器的输出端与所述模数转换器的输入端电连接。
  5. 根据权利要求4所述的指纹检测电路，其中，所述感应单元包括多个感应电极，所述放大器有多个，每一放大器电连接一感应电极。
  6. 根据权利要求1-3任一项所述的指纹检测电路，其中，所述发射电极和感应单元集成于一感应芯片。
  7. 根据权利要求6所述的指纹检测电路，其中，所述发射电极为环形发射电极，其环绕于所述感应单元周围。
  8. 根据权利要求6所述的指纹检测电路，其中，所述感应单元由多个阵列排布的感应电极构成。
  9. 根据权利要求1-3任一项所述的指纹检测电路，其中，所述发射电极直接与手指接触或通过一导电体间接与手指接触来传递所述交流信号。
  10. 一种指纹检测装置，包括如权利要求1-9任一项所述的指纹检测电路。
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