WO2016050035A1 - 指纹检测电路及其电容式指纹传感器、移动终端 - Google Patents

指纹检测电路及其电容式指纹传感器、移动终端 Download PDF

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WO2016050035A1
WO2016050035A1 PCT/CN2015/073823 CN2015073823W WO2016050035A1 WO 2016050035 A1 WO2016050035 A1 WO 2016050035A1 CN 2015073823 W CN2015073823 W CN 2015073823W WO 2016050035 A1 WO2016050035 A1 WO 2016050035A1
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Prior art keywords
fingerprint
amplifier
unit
detecting
capacitor
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PCT/CN2015/073823
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English (en)
French (fr)
Inventor
詹昶
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深圳市汇顶科技股份有限公司
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Application filed by 深圳市汇顶科技股份有限公司 filed Critical 深圳市汇顶科技股份有限公司
Priority to EP15846110.3A priority Critical patent/EP3203411B1/en
Priority to KR1020167023589A priority patent/KR102028243B1/ko
Publication of WO2016050035A1 publication Critical patent/WO2016050035A1/zh
Priority to US15/243,862 priority patent/US9904838B2/en

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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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/96—Touch switches
    • H03K17/962—Capacitive touch switches
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M2203/00—Aspects of automatic or semi-automatic exchanges
    • H04M2203/60—Aspects of automatic or semi-automatic exchanges related to security aspects in telephonic communication systems
    • H04M2203/6054—Biometric subscriber identification

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  • the present invention relates to the field of identity recognition technologies, and in particular, to a fingerprint detection circuit, a capacitive fingerprint sensor thereof, and a mobile terminal.
  • Fingerprints are an effective means of personal identification because of their uniqueness and stability.
  • Optical device image acquisition uses the principle of total reflection and uses CCD device to obtain fingerprint images. The effect is better, the device itself is wear-resistant but costly and bulky, and is not suitable for mobile terminals with high integration requirements.
  • Ultrasound imaging directly scans the dermal tissue, and the dirt or oil accumulated on the surface of the skin has little effect on the image, but the device cost is extremely high, and there is no mature product market at present.
  • the production of crystalline capacitive fingerprint sensors uses standard CMOS technology to obtain better image quality (which can be adjusted by software to improve the image quality of the gain) and is smaller in size and power consumption, and the cost is much lower than the other two sensors.
  • the crystal capacitive fingerprint sensor comprises a plurality of detecting units arranged in an array.
  • the fingerprint unit is equivalent to the anode of the capacitor, the skin of the finger becomes the other pole of the capacitor, and the texture of the finger is shallow (ie, the finger “ The peak distance and the valley are different from the actual distance of the detection unit, and the capacitance (or inductance) is also different.
  • the fingerprint depth of the finger can be detected to form a fingerprint image.
  • the fingerprint detection circuit commonly used in the fingerprint detection system is shown in FIG. 1.
  • the input signal VIN_1 from the finger and the cancellation signal VCAN from the high-precision signal source are simultaneously input to the fingerprint detection unit, and the detection unit In the output signal VPXL_1, the dotted line portion is the useful signal amplitude representing the fingerprint information, and the solid line portion is the base signal amplitude.
  • the problem with this method is that, first of all, the amplitude of the high-precision signal source output VCAN cannot follow the dynamically changing VIN_1 (this is because VIN_1 ⁇ VIN_n is determined by the coupling capacitance between the finger and the fingerprint detection unit. This capacitance is possible dynamic.
  • the main object of the present invention is to provide a fingerprint detecting circuit, a capacitive fingerprint sensor and a mobile terminal, which improve the elimination capability of the base signal and further improve the fingerprint recognition accuracy.
  • the present invention provides a fingerprint detecting circuit comprising a plurality of detecting units and summing units arranged in an array, the detecting unit comprising a first detecting unit and a second detecting unit, the first detecting unit and the Two detecting units are respectively connected to the summing unit, and the summing unit performs a summation operation on an output signal of each second detecting unit and an output signal of the first detecting unit to eliminate each second detecting unit
  • the base signal in the output signal yields a useful signal containing fingerprint information.
  • the second detecting unit is connected to a non-inverting input of the summing unit, and the first detecting unit is connected to an inverting input of the summing unit.
  • the fingerprint detecting circuit further includes a first amplifier, and the first amplifier amplifies a signal output by the summing unit.
  • the number of the first detecting units is one.
  • the detecting unit includes a second amplifier, a first capacitor, a second capacitor, and a third capacitor, the first capacitor is connected to the input signal of the finger at one end, and the inverting input of the other end is connected to the second amplifier.
  • An end connection; the second capacitor is coupled to the inverting input terminal and the positive phase of the second amplifier Between the input terminals; one end of the third capacitor is connected to the inverting input end of the second amplifier, and the other end is connected to the output end of the second amplifier; the non-inverting input terminal of the second amplifier is grounded.
  • the detecting unit includes a second amplifier, a first capacitor, a second capacitor, and a third capacitor, wherein the first capacitor and the second capacitor are both grounded at one end, and the other end is inverted with the second amplifier.
  • An input terminal is connected; one end of the third capacitor is connected to an inverting input end of the second amplifier, and the other end is connected to an output end of the second amplifier; and a positive phase input end of the second amplifier is connected to an input signal of a finger .
  • the summing unit includes a third amplifier, a non-inverting input of the third amplifier is coupled to an output of the second detecting unit, and an output of the inverting input and the first detecting unit End connection.
  • the summation unit further includes a first resistor, a second resistor, a third resistor, and a fourth resistor, wherein the first resistor is coupled to the output of the first detecting unit and the third amplifier Between the input terminals; the second resistor is coupled between the output of the second detecting unit and the non-inverting input of the third amplifier; a positive phase of one end of the third resistor and the third amplifier The input terminal is connected and the other end is grounded; one end of the fourth resistor is connected to the inverting input terminal of the third amplifier, and the other end is connected to the output end of the third amplifier.
  • the invention also discloses a capacitive fingerprint sensor, comprising a fingerprint detecting panel; a fingerprint detecting area located on the fingerprint detecting panel, wherein the fingerprint detecting area is provided with the fingerprint detecting circuit.
  • the present invention also discloses a mobile terminal comprising the above capacitive fingerprint sensor.
  • the fingerprint detecting circuit disclosed in the present invention selects at least one detecting unit as a canceling unit, and sums the output signals of the other detecting units and the output signals of the detecting unit to eliminate the base signal in the output signal of the detecting unit, and obtains the fingerprint Useful signal for information. Compared with the prior art, the elimination capability of the base signal is improved, and the fingerprint recognition accuracy is further improved.
  • the summing circuit has a simple structure, occupies a small chip area, and is easy to implement a low-power design.
  • FIG. 1 is a schematic diagram of a fingerprint detecting circuit of a capacitive fingerprint sensor in the prior art
  • FIG. 2 is a schematic diagram of a fingerprint detecting circuit of a capacitive fingerprint sensor according to an embodiment of the present invention
  • FIG. 3 is a schematic diagram of a detection unit of a capacitive fingerprint sensor according to an embodiment of the present invention
  • FIG. 4 is a schematic circuit diagram of a detecting unit of a capacitive fingerprint sensor according to an embodiment of the present invention.
  • FIG. 5 is a schematic circuit diagram of another detecting unit of a capacitive fingerprint sensor according to an embodiment of the present invention.
  • FIG. 6 is a schematic diagram of a fingerprint signal base amplitude of a capacitive fingerprint sensor according to an embodiment of the present invention
  • FIG. 7 is a schematic diagram of a summing unit circuit of a capacitive fingerprint sensor according to an embodiment of the present invention.
  • the capacitive fingerprint sensor includes a fingerprint detection panel, and is located in a fingerprint detection area on the fingerprint detection panel.
  • a fingerprint detection circuit is disposed in the fingerprint detection area.
  • FIG. 2 is a fingerprint according to the present invention.
  • a schematic diagram of a detection circuit comprising a plurality of detection units arranged in an array and a summing unit, a first amplifier A1. As shown in FIG.
  • one of the plurality of detecting units is arbitrarily selected (of course, a plurality of ones may be selected) as the first detecting unit, and the remaining detecting units are used as the second detecting unit, the first detecting unit and The output ends of the second detecting unit are all connected to the summing unit, and the summing unit sums the output signals of each second detecting unit and the output signals of the first detecting unit to eliminate the output signal of each second detecting unit.
  • Base The bottom signal obtains a useful signal containing fingerprint information, and then the signal output from the summation unit is amplified by the first amplifier A1.
  • FIG. 4 shows two specific circuits of the detection unit.
  • the detecting unit in FIG. 4 includes a second amplifier A2, a first capacitor Cs, a second capacitor Cp, and a third capacitor Cf, wherein Cs represents a coupling capacitance between the finger and the fingerprint detecting unit, and Cf is a feedback capacitor inside the detecting unit, Cp To detect the parasitic capacitance inside the unit.
  • Cs represents a coupling capacitance between the finger and the fingerprint detecting unit
  • Cf is a feedback capacitor inside the detecting unit, Cp
  • Cs To detect the parasitic capacitance inside the unit.
  • Cs is the minimum value Csmin
  • Cs is the maximum value Csmax.
  • the first capacitor Cs is connected to the input signal of the finger at one end, and the other end is connected to the inverting input terminal of the second amplifier A2.
  • the second capacitor Cp is coupled between the inverting input of the second amplifier A2 and the non-inverting input.
  • One end of the third capacitor Cf is connected to the inverting input terminal of the second amplifier A2, and the other end is connected to the output end of the second amplifier A2.
  • the non-inverting input of the second amplifier A2 is grounded.
  • the detecting unit in FIG. 5 includes a second amplifier A2, a first capacitor Cs, a second capacitor Cp, and a third capacitor Cf, wherein Cs represents a coupling capacitance between the finger and the fingerprint detecting unit, and Cf is a feedback capacitor inside the detecting unit, Cp To detect the parasitic capacitance inside the unit.
  • Cs represents a coupling capacitance between the finger and the fingerprint detecting unit
  • Cf is a feedback capacitor inside the detecting unit, Cp To detect the parasitic capacitance inside the unit.
  • Cs is the minimum value Csmin
  • Cs is the maximum value Csmax.
  • the first capacitor Cs and the second capacitor Cp are both grounded at one end, and the other end is connected to the inverting input terminal of the second amplifier A2.
  • One end of the third capacitor Cf is connected to the inverting input terminal of the second amplifier A2, and the other end is connected to the output end of the second amplifier A2.
  • the signal amplitude corresponding to the valley of the fingerprint is the substrate amplitude.
  • VIN_c is exactly the signal amplitude corresponding to the valley of the fingerprint.
  • VPXL_1 is connected to the non-inverting input of the summing unit
  • VCAN is connected to the negative phase input of the summing unit
  • the signal VOUT_1 after VSUM_1 is amplified by the first amplifier A1 can make the useful signal amplitude representing the fingerprint information as enlarged as possible.
  • the summation unit in the embodiment includes a third amplifier A3.
  • the non-inverting input terminal of the third amplifier A3 is connected to the output end of the second detecting unit, and the inverting input terminal and the first The output of the detection unit is connected.
  • the summation unit further includes a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4.
  • the first resistor R1 is connected to the output end of the first detecting unit and the inverting input terminal of the third amplifier A3. between.
  • the second resistor R2 is connected between the output of the second detecting unit and the non-inverting input of the third amplifier A3.
  • One end of the third resistor R3 is connected to the non-inverting input terminal of the third amplifier A3, and the other end is grounded.
  • the fourth resistor R4 has one end connected to the inverting input terminal of the third amplifier A3 and the other end connected to the output end of the third amplifier A3.
  • VCAN amplitude is a fixed value
  • transfer function of the circuit is:
  • the transfer function of the circuit is:
  • the VOUT_1 signal amplitude is all the useful fingerprint amplitude. (The substrate amplitude is reduced from 99% to 0% after elimination.)
  • the first amplifier A1 gain G2 can be set larger to obtain a larger useful fingerprint signal amplitude. Thereby improving the accuracy of fingerprint recognition.
  • the fingerprint detecting circuit disclosed in the present invention selects at least one detecting unit as a canceling unit, and sums the output signals of the other detecting units and the output signals of the detecting unit to eliminate the base signal in the output signal of the detecting unit, and obtains the fingerprint
  • the useful signal of the information improves the elimination ability of the base signal and further improves the fingerprint recognition accuracy.
  • the summation circuit has a simple structure, occupies a small chip area, and is easy to implement a low-power design.
  • the invention also discloses a mobile terminal, which comprises the above capacitive fingerprint sensor.
  • the fingerprint detecting circuit disclosed in the present invention selects at least one detecting unit as a canceling unit, and sums the output signals of the other detecting units and the output signals of the detecting unit to eliminate the base signal in the output signal of the detecting unit, and obtains the fingerprint Useful signal for information. Compared with the prior art, the elimination capability of the base signal is improved, and the fingerprint recognition accuracy is further improved.
  • the summing circuit has a simple structure, occupies a small chip area, and is easy to implement a low-power design.

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Abstract

本发明公开了一种指纹检测电路，包括阵列排列的多个检测单元，还包括求和单元，所述检测单元包括第一检测单元和第二检测单元，所述第一检测单元和第二检测单元分别与所述求和单元连接，所述求和单元将每个第二检测单元的输出信号与所述第一检测单元的输出信号进行求和运算以消除每个第二检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。本发明公开的指纹检测电路，选择至少一个检测单元作为抵消单元，将其他检测单元的输出信号与该检测单元的输出信号进行求和运算以消除检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。与现有技术相比，提高了基底信号的消除能力，进一步提高了指纹识别精度。

Description

指纹检测电路及其电容式指纹传感器、移动终端 技术领域
本发明涉及身份识别技术领域，尤其是涉及一种指纹检测电路及其电容式指纹传感器、移动终端。
背景技术
随着社会的进步和技术的发展，近年来，移动银行、手机钱包、网络购物等电子商务业务在智能移动设备上的应用日趋广泛。相对的，公众对于集成的电子元器件性能以及网络信息安全的要求也越来越高。指纹由于具有唯一性和稳定性而使其成为个人身份识别的一种有效手段。指纹传感器有很多种类型，目前主流的有三种类型：光学取像指纹传感器、晶体电容式(或者压感式)指纹传感器和超声波取像指纹传感器。光学设备取像是利用全反射原理并使用CCD器件来获取指纹图像，效果较好、器件本身耐磨损但成本高、体积大，不适用于集成度要求很高的移动终端上。超声波取像直接扫描真皮组织，积累在皮肤表面的赃物或油脂对获得图像影响不大，但器件成本极高，目前没有成熟的产品市场。晶体电容式指纹传感器生产采用标准CMOS技术，获取图像质量比较好(可以通过软件调整来改善增益的图像质量)且体积和功耗都比较小，成本相对于另两种传感器低廉很多。
晶体电容式指纹传感器包括阵列排布的多个检测单元，当手指触摸检测单元时，指纹单元相当于电容器的阳极，手指的皮肤变成了电容另一极，手指的纹路深浅(即手指的“峰”和“谷”)与检测单元的实际距离不同，电容(或电感)也不同，根据该原理可检测到手指的纹路深浅形成指纹图像。指纹检测系统中常用的指纹检测电路如图1所示，来自手指的输入信号VIN_1和来自高精度信号源的抵消信号VCAN同时输入到指纹检测单元，检测单元 的输出信号VPXL_1中，虚线部分为代表指纹信息的有用信号幅度，实线部分为基底信号幅度。这种方法的问题在于，首先，高精度信号源输出VCAN的幅度无法跟随可能动态变化的VIN_1(这是因为VIN_1～VIN_n由手指和指纹检测单元之间的耦合电容大小决定，这个电容是可能动态变化的)，所以VPXL_1的信号幅度中仍可能包含相当一部分的基底信号幅度，经过放大器之后的最终输出信号VOUT_1中也是一样。其次，假设在VIN_1固定的情况下，要获得理想的基底消除效果，对于高精度信号源的指标要求很高，在芯片内部实现相应的信号源会消耗更多的成本和功耗。
发明内容
本发明的主要目的在于提供一种指纹检测电路及其电容式指纹传感器、移动终端，提高了基底信号的消除能力，进一步提高了指纹识别精度。
为达以上目的，本发明提出一种指纹检测电路，包括阵列排列的多个检测单元和求和单元，所述检测单元包括第一检测单元和第二检测单元，所述第一检测单元和第二检测单元分别与所述求和单元连接，所述求和单元将每个第二检测单元的输出信号与所述第一检测单元的输出信号进行求和运算以消除每个第二检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。
一实施例中，所述第二检测单元与所述求和单元的正相输入端连接，所述第一检测单元与所述求和单元的反相输入端连接。
其中，所述的指纹检测电路还包括第一放大器，所述第一放大器对所述求和单元输出的信号进行放大。
优选地，所述第一检测单元的数量为一个。
一实施例中，所述检测单元包括第二放大器、第一电容、第二电容和第三电容，所述第一电容一端接手指的输入信号，另一端与所述第二放大器的反相输入端连接；所述第二电容连接在所述第二放大器的反相输入端和正相 输入端之间；所述第三电容一端连接所述第二放大器的反相输入端，另一端连接所述第二放大器的输出端；所述第二放大器的正相输入端接地。
一实施例中，所述检测单元包括第二放大器、第一电容、第二电容和第三电容，所述第一电容和第二电容均一端接地，另一端与所述第二放大器的反相输入端连接；所述第三电容一端连接所述第二放大器的反相输入端，另一端与所述第二放大器的输出端连接；所述第二放大器的正相输入端接手指的输入信号。
一实施例中，所述求和单元包括第三放大器，所述第三放大器的正相输入端与所述第二检测单元的输出端连接，反相输入端与所述第一检测单元的输出端连接。
其中，所述求和单元还包括第一电阻、第二电阻、第三电阻和第四电阻，所述第一电阻连接在所述第一检测单元的输出端和所述第三放大器的反相输入端之间；所述第二电阻连接在所述第二检测单元的输出端和所述第三放大器的正相输入端之间；所述第三电阻一端与所述第三放大器的正相输入端连接，另一端接地；所述第四电阻一端连接所述第三放大器的反相输入端，另一端与所述第三放大器的输出端连接。
同时，本发明还公开了一种电容式指纹传感器，包括指纹检测面板；位于指纹检测面板上的指纹检测区域，指纹检测区域内设有上述的指纹检测电路。
再者，本发明还公开了一种移动终端，包括上述的电容式指纹传感器。
本发明公开的指纹检测电路，选择至少一个检测单元作为抵消单元，将其他检测单元的输出信号与该检测单元的输出信号进行求和运算以消除检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。与现有技术相比，提高了基底信号的消除能力，进一步提高了指纹识别精度。
进一步地，与采用高精度信号源的指纹检测电路相比，求和电路结构简单，占用芯片面积小，且容易实现低功耗设计。
附图说明
图1是现有技术中电容式指纹传感器的指纹检测电路示意图；
图2为本发明实施例提供的一种电容式指纹传感器的指纹检测电路示意图；
图3为本发明实施例提供的电容式指纹传感器的检测单元分布示意图；
图4是本发明实施例提供的电容式指纹传感器的检测单元电路示意图；
图5是本发明实施例提供的电容式指纹传感器的另一种检测单元电路示意图；
图6是本发明实施例提供的电容式指纹传感器的指纹信号基底幅度示意图；
图7是本发明实施例提供的电容式指纹传感器的一种求和单元电路示意图。
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。
本发明实施例中电容式指纹传感器包括指纹检测面板，位于指纹检测面板上的指纹检测区域，指纹检测区域内设有指纹检测电路，如图2所示，图2为本发明提出的一种指纹检测电路示意图，该指纹检测电路包括阵列排列的多个检测单元以及求和单元、第一放大器A1。如图3所示，本实施例中，从多个检测单元中任意选择其中一个(当然也可以选择多个)作为第一检测单元，剩余的检测单元作为第二检测单元，第一检测单元和第二检测单元的输出端均与求和单元连接，求和单元将每个第二检测单元的输出信号与第一检测单元的输出信号进行求和运算以消除每个第二检测单元的输出信号中的基 底信号，得到包含指纹信息的有用信号，然后由第一放大器A1对求和单元输出的信号进行放大。
图4和图5给出了检测单元的两种具体电路。图4中检测单元包括第二放大器A2、第一电容Cs、第二电容Cp和第三电容Cf，其中Cs代表手指和指纹检测单元之间的耦合电容，Cf为检测单元内部的反馈电容，Cp为检测单元内部的寄生电容。检测单元检测到指纹的谷时，Cs为最小值Csmin；检测单元检测到指纹的峰时，Cs为最大值Csmax。第一电容Cs一端接手指的输入信号，另一端与第二放大器A2的反相输入端连接。第二电容Cp连接在第二放大器A2的反相输入端和正相输入端之间。第三电容Cf一端连接第二放大器A2的反相输入端，另一端连接所述第二放大器A2的输出端。第二放大器A2的正相输入端接地。
图5中检测单元包括第二放大器A2、第一电容Cs、第二电容Cp和第三电容Cf，其中Cs代表手指和指纹检测单元之间的耦合电容，Cf为检测单元内部的反馈电容，Cp为检测单元内部的寄生电容。检测单元检测到指纹的谷时，Cs为最小值Csmin；检测单元检测到指纹的峰时，Cs为最大值Csmax。第一电容Cs和第二电容Cp均一端接地，另一端与第二放大器A2的反相输入端连接。第三电容Cf一端连接所述第二放大器A2的反相输入端，另一端与所述第二放大器A2的输出端连接。第二放大器A2的正相输入端接手指的输入信号。
请参阅图6所示，由于指纹的峰对应的信号幅度最大，而指纹的谷对应的信号幅度最小，可以认为指纹的谷对应的信号幅度即为基底幅度。为了简化描述，假设VIN_c正好为指纹的谷对应的信号幅度。VPXL_1连接到求和单元的正相输入端，VCAN连接到求和单元的负相输入端，求和单元的输出信号VSUM_1＝VPXL_1-VCAN，因此VSUM_1信号将只包含指纹信息的有用信号幅度，基底幅度被完全抵消掉。VSUM_1经过第一放大器A1放大之后的信号VOUT_1即可使代表指纹信息的有用信号幅度得到尽可能的放大。
请参阅图7所示，本实施例中求和单元包括第三放大器A3，第三放大器A3的正相输入端与所述第二检测单元的输出端连接，反相输入端与所述第一检测单元的输出端连接。
其中，求和单元还包括第一电阻R1、第二电阻R2、第三电阻R3和第四电阻R4，第一电阻R1连接在第一检测单元的输出端和第三放大器A3的反相输入端之间。第二电阻R2连接在第二检测单元的输出端和第三放大器A3的正相输入端之间。第三电阻R3一端与第三放大器A3的正相输入端连接，另一端接地。第四电阻R4一端连接第三放大器A3的反相输入端，另一端与第三放大器A3的输出端连接。
下面按照常规的电路参数给出本发明电容式指纹传感器的指纹检测系统的基底消除电路中的计算说明：
对于图1中的常用电路而言，VCAN幅度为固定值，电路的传递函数为：
VOUT_1＝G2*VPXL_1＝G2*G1*(k*VIN_1-VCAN)
假设各个参数的数值为：放大器增益G2＝10，检测单元增益G1＝5，耦合电容变化系数k＝1.01，手指信号幅度VIN_1＝1V(有用指纹幅度占比1％，即VSIG＝0.01V，VBS＝0.99V，VIN_1＝VSIG+VBS)，高精度信号源输出幅度VCAN＝0.99V，可算得VOUT_1＝G2*G1*(k*(VSIG+VBS)-VCAN)＝G2*G1*(1.01*VSIG+0.01VBS)＝50*1.01*VSIG+50*0.01*VBS＝0.505V+0.495V＝1V。其中指纹幅度为0.505V，基底幅度为0.495V。(经消除后基底幅度由99％降低至49.5％。)
对于图2本发明电容式指纹传感器的指纹检测系统的基底消除电路而言，电路的传递函数为：
VOUT_1＝G2*VSUM_1＝G2*(VPXL_1-VCAN)＝G2*G1*k*(VIN_1-VIN_c)
假设各个参数的数值为：第一放大器A1增益G2＝10，检测单元增益G1＝5,耦合电容变化系数k＝1.01，手指信号幅度VIN_1＝1V(有用指纹幅度占比1％，即VSIG＝0.01V，VBS＝0.99V，VIN_1＝VSIG+VBS)。可算得
VOUT_1＝G2*G1*k*(VIN_1-VIN_c)＝0.505V
VOUT_1信号幅度全部为有用指纹幅度。(经消除后基底幅度由99％降低至0％。)
在第一放大器A1的输出电压幅度一定的情况下，在本发明的指纹检测系统的基底消除电路中，可以将第一放大器A1增益G2设置得更大，以获取更大的有用指纹信号幅度，从而提高指纹识别精度。
本发明公开的指纹检测电路，选择至少一个检测单元作为抵消单元，将其他检测单元的输出信号与该检测单元的输出信号进行求和运算以消除检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号，提高了基底信号的消除能力，进一步提高了指纹识别精度。相比现有采用高精度信号源的抵消电路，求和电路结构简单，占用芯片面积小，且容易实现低功耗设计。
同时，本发明还公开了一种移动终端，包括上述的电容式指纹传感器。
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
本发明公开的指纹检测电路，选择至少一个检测单元作为抵消单元，将其他检测单元的输出信号与该检测单元的输出信号进行求和运算以消除检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。与现有技术相比，提高了基底信号的消除能力，进一步提高了指纹识别精度。
进一步地，与采用高精度信号源的指纹检测电路相比，求和电路结构简单，占用芯片面积小，且容易实现低功耗设计。

Claims (10)

  1. 一种指纹检测电路，包括阵列排列的多个检测单元，还包括求和单元，所述检测单元包括第一检测单元和第二检测单元，所述第一检测单元和第二检测单元分别与所述求和单元连接，所述求和单元将每个第二检测单元的输出信号与所述第一检测单元的输出信号进行求和运算以消除每个第二检测单元的输出信号中的基底信号，得到包含指纹信息的有用信号。
  2. 根据权利要求1所述的指纹检测电路，其中，所述第二检测单元与所述求和单元的正相输入端连接，所述第一检测单元与所述求和单元的反相输入端连接。
  3. 根据权利要求1所述的指纹检测电路，其中，还包括第一放大器，所述第一放大器对所述求和单元输出的信号进行放大。
  4. 根据权利要求1所述的指纹检测电路，其中，所述第一检测单元的数量为一个。
  5. 根据权利要求1所述的指纹检测电路，其中，所述检测单元包括第二放大器、第一电容、第二电容和第三电容，所述第一电容一端接手指的输入信号，另一端与所述第二放大器的反相输入端连接；所述第二电容连接在所述第二放大器的反相输入端和正相输入端之间；所述第三电容一端连接所述第二放大器的反相输入端，另一端连接所述第二放大器的输出端；所述第二放大器的正相输入端接地。
  6. 根据权利要求1所述的指纹检测电路，其中，所述检测单元包括第二放大器、第一电容、第二电容和第三电容，所述第一电容和第二电容均一端接地，另一端与所述第二放大器的反相输入端连接；所述第三电容一端连接所述第二放大器的反相输入端，另一端与所述第二放大器的输出端连接；所述第二放大器的正相输入端接手指的输入信号。
  7. 根据权利要求2所述的指纹检测电路，其中，所述求和单元包括第三 放大器，所述第三放大器的正相输入端与所述第二检测单元的输出端连接，反相输入端与所述第一检测单元的输出端连接。
  8. 根据权利要求7所述的指纹检测电路，其中，所述求和单元还包括第一电阻、第二电阻、第三电阻和第四电阻，所述第一电阻连接在所述第一检测单元的输出端和所述第三放大器的反相输入端之间；所述第二电阻连接在所述第二检测单元的输出端和所述第三放大器的正相输入端之间；所述第三电阻一端与所述第三放大器的正相输入端连接，另一端接地；所述第四电阻一端连接所述第三放大器的反相输入端，另一端与所述第三放大器的输出端连接。
  9. 一种电容式指纹传感器，包括指纹检测面板；位于指纹检测面板上的指纹检测区域，指纹检测区域内设有权利要求1-8任一项所述的指纹检测电路。
  10. 一种移动终端，包括权利要求9所述的电容式指纹传感器。
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