WO2018058334A1 - 指纹辨识系统及电子装置 - Google Patents

指纹辨识系统及电子装置 Download PDF

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Publication number
WO2018058334A1
WO2018058334A1 PCT/CN2016/100451 CN2016100451W WO2018058334A1 WO 2018058334 A1 WO2018058334 A1 WO 2018058334A1 CN 2016100451 W CN2016100451 W CN 2016100451W WO 2018058334 A1 WO2018058334 A1 WO 2018058334A1
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WIPO (PCT)
Prior art keywords
circuit
output signal
layer
contact
coupled
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PCT/CN2016/100451
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English (en)
French (fr)
Inventor
赵国豪
杨孟达
Original Assignee
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 KR1020177029859A priority Critical patent/KR102052151B1/ko
Priority to PCT/CN2016/100451 priority patent/WO2018058334A1/zh
Priority to EP16898870.7A priority patent/EP3321849B1/en
Priority to CN201680001055.1A priority patent/CN106462758B/zh
Priority to US15/782,843 priority patent/US10474865B2/en
Publication of WO2018058334A1 publication Critical patent/WO2018058334A1/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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0416—Control or interface arrangements specially adapted for digitisers
    • G06F3/0418—Control or interface arrangements specially adapted for digitisers for error correction or compensation, e.g. based on parallax, calibration or alignment
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/044—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/044—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means
    • G06F3/0443—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means using a single layer of sensing electrodes
    • 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
    • G06V40/1329—Protecting the fingerprint sensor against damage caused by the finger
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2203/00—Indexing scheme relating to G06F3/00 - G06F3/048
    • G06F2203/041—Indexing scheme relating to G06F3/041 - G06F3/045
    • G06F2203/04107—Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds

Definitions

  • the invention relates to a fingerprint identification system and an electronic device, in particular to a fingerprint identification system and an electronic device capable of reducing the influence of parasitic capacitance.
  • a capacitive fingerprint identification system is a popular fingerprint identification method, which uses a contact layer to receive finger contact from a user and senses a change in capacitance of the contact layer to determine a fingerprint of the user. Finger Ridge or Finger Valley.
  • conventional techniques usually place a shielding layer under the contact layer during circuit layout to create a shielding effect to avoid interference of the contact layer under the shielding layer.
  • parasitic capacitance is generated between the contact layer and the shielding layer, and the capacitance value of the parasitic capacitance is often larger than that due to contact. The capacitance value of the generated contact capacitance affects the capacitance sensing circuit or the capacitive fingerprint identification system to determine the capacitance value of the contact capacitance, so that the accuracy of fingerprint identification is reduced.
  • the main object of the present invention is to provide a fingerprint identification system and an electronic device which can reduce the influence of parasitic capacitance and reduce the sensitivity to temperature and noise.
  • the present invention provides a fingerprint identification system including a plurality of first pixel circuits, wherein a first pixel circuit of the plurality of first pixel circuits forms a contact capacitance with a finger;
  • the measuring circuit is coupled to the first pixel circuit for sensing the contact capacitance and outputting a first output signal, wherein the first output signal comprises a large signal component and a small signal component, the small a second component of the at least one second pixel circuit coupled to the second pixel circuit a second output signal, wherein the second output signal is equal to the large signal component; and a differential amplifying circuit coupled to the first sensing circuit and the second sensing circuit for An amplitude difference between an output signal and the second output signal is amplified to produce an amplified output signal, wherein the amplified output signal is associated with the small signal component.
  • the second sensing circuit includes a contact layer coupled to a first driving circuit for receiving a first driving signal, the contact layer accepting contact of the finger; a first shielding layer, setting a second metal layer disposed under the first shielding layer, coupled to a second driving circuit for receiving a second driving signal, and a second metal layer disposed
  • the first metal layer is coupled to the second metal layer to receive a third driving signal; wherein the first metal The layer is coupled to the second sensing circuit.
  • the first driving circuit drives the contact layer to a positive voltage
  • the second driving circuit uses the first shielding layer, the first metal layer and the first Two metal layer Driving to the positive voltage
  • the first driving circuit provides the first voltage of the contact layer.
  • the second sensing circuit further includes a third metal layer having the same horizontal position as the second metal layer and spaced apart from the second metal layer, The third metal layer receives a fixed voltage.
  • the second sensing circuit further includes a second shielding layer having the same horizontal position as the first shielding layer and spaced apart from the first shielding layer, The second shield receives a fixed voltage.
  • the first sensing circuit includes a contact layer for receiving contact of the finger, the contact layer forms the contact capacitance with the finger, and the contact layer is coupled to a driving circuit and the a first sensing circuit; and a first shielding layer disposed under the contact layer.
  • the drive circuit drives the contact layer to a positive voltage.
  • the first sensing circuit further includes a second shielding layer having the same horizontal position as the first shielding layer and spaced apart from the first shielding layer, The second shield receives a fixed voltage.
  • the differential amplifying circuit is a programmable gain amplifier.
  • the present invention further provides an electronic device including an operation circuit, and a fingerprint identification system coupled to the operation circuit, the fingerprint identification system includes a plurality of first pixel circuits, and the plurality of first pixel circuits a first pixel circuit and a finger form a contact capacitance-first sensing circuit coupled to the first pixel circuit for sensing the contact capacitance and outputting a first output signal, wherein the first pixel An output signal includes a large signal component and a small signal component, wherein the small signal component is related to a change amount of the contact capacitance; at least one second pixel circuit; and a second sensing circuit coupled to the at least one a second pixel circuit for outputting a second output signal, wherein the second output signal is equal to the large signal component; and a differential amplifying circuit coupled to the first sense And the second sensing circuit is configured to use the first output signal and the second input A phase difference of the outgoing signal is amplified to produce an amplified output signal, wherein the amplified output signal is associated with the small
  • the fingerprint identification system and the electronic device provided by the invention use the dummy pixel circuit to generate a dummy output signal, thereby eliminating the effect of parasitic capacitance, thereby improving the accuracy and performance of the capacitive sensing or fingerprint identification.
  • FIG. 1 is a schematic diagram of a fingerprint identification system according to an embodiment of the present invention.
  • FIG. 2 is a waveform diagram of a plurality of clock signals according to an embodiment of the present invention.
  • FIG. 3 is a schematic diagram of a fingerprint identification system according to an embodiment of the present invention.
  • FIG. 4 is a top plan view of a fingerprint identification system according to an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of an electronic device according to an embodiment of the present invention.
  • the output signal of the pixel circuit is affected by the internal parasitic capacitance of the pixel circuit and the sensing circuit, so that the signal component of the output signal of the pixel circuit related to the change amount of the contact capacitance is not significant, and the output of the pixel circuit is not significant.
  • the signal is also affected by temperature and noise, which reduces the accuracy of fingerprint recognition. Therefore, in addition to the normal pixel circuit, the present invention further includes a dummy pixel circuit for generating a dummy output signal by using a dummy pixel circuit to cancel a signal component affected by parasitic capacitance, temperature, and noise in an output signal of a plurality of normal pixel circuits. And for a plurality of normal pixel circuits
  • the fingerprint signal component in the output signal is amplified and subsequently processed to determine the Finger Ridge or Finger Valley to increase fingerprint identification accuracy.
  • FIG. 1 is a schematic diagram of a fingerprint identification system 10 according to an embodiment of the present invention
  • FIG. 2 is a clock signal clk1 according to an embodiment of the present invention. Waveforms of clk2 and clk3.
  • FIG. 1 is a schematic diagram of a normal pixel circuit and a dummy pixel circuit of a plurality of normal pixel circuits in the fingerprint identification system 10.
  • the fingerprint identification system 10 includes a normal pixel circuit 11 and a dummy device.
  • the pixel circuit 12 a first sensing circuit 115, a second sensing circuit 125, and a differential amplifying circuit Amp.
  • Both the normal pixel circuit 11 and the dummy pixel circuit 12 can receive the contact of a finger FG, and form a contact capacitance Cf_1 and a contact capacitance Cf_2 with the finger FG, respectively.
  • the first sensing circuit 115 is coupled to the normal pixel circuit 11 for sensing the contact capacitance Cf_1 and outputting a first output signal Vo1.
  • the second sensing circuit 125 is coupled to the dummy pixel circuit 12 for outputting a The second output signal Vo2.
  • the first output signal Vo1 includes a large signal component And a small signal component ⁇ Vo1 (ie, the first output signal Vo1 can be expressed as ), where large signal components It may be an average value of the first output signal Vo1, and the small signal component ⁇ Vo1 is related to a change amount ⁇ Cf_1 of the contact capacitance Cf_1, which is a fingerprint signal used for fingerprint recognition.
  • the dummy pixel circuit 12 can be appropriately designed such that the second output signal Vo2 and the large signal component of the first output signal Vo1 are appropriately designed.
  • Equal ie, the second output signal Vo2 can be expressed as ).
  • the differential amplifying circuit Amp receives the first output signal Vo1 and the second output signal Vo2 for amplifying a phase difference (Vo1-Vo2) between the first output signal Vo1 and the second output signal Vo2 to generate an amplified output signal.
  • VO wherein the amplified output signal VO is only amplified for the phase difference value (Vo1-Vo2).
  • the differential amplifying circuit Amp is a Programmable Gain Amplifier (PGA).
  • the differential amplifier circuit Amp can be coupled to an analog-to-digital converter (ADC) and a back-end circuit (not shown in FIG. 1) for performing subsequent signal processing on the amplified output signal VO and determining
  • the normal pixel circuit 11 corresponds to a bee or a grain of the finger FG.
  • the first output signal Vo1 corresponding to the normal pixel circuit 11 is related to the contact capacitance Cf_1 corresponding to the normal pixel circuit 11, that is, the first output signal Vo1 contains the fingerprint signal (ie, the small signal component ⁇ Vo1).
  • the second output signal Vo2 corresponding to the dummy pixel circuit 12 is only used to cancel the signal component of the first output signal Vo1 which is affected by the parasitic capacitance, temperature and noise, and the second output signal Vo2 does not contain the fingerprint signal ( That is, the contact capacitance Cf_2 corresponding to the dummy pixel circuit 12 does not affect the second output signal Vo2).
  • the fingerprint identification system 10 amplifies the phase difference (Vo1-Vo2) between the first output signal Vo1 and the second output signal Vo2 by using the differential amplifying circuit Amp, that is, amplifying the fingerprint signal for subsequent signal processing.
  • the normal pixel circuit 11 includes a contact layer 110 , a shielding layer 112 , and a driving circuit 113 .
  • the contact layer 110 and the shielding layer 112 are metal layers in the integrated circuit layout, and the contact layer 110 It is a top metal layer for receiving the contact of the finger FG, the contact layer 110 forms a contact capacitance Cf_1 with the finger FG, and the shielding layer 112 can be the next metal layer of the top metal layer, that is, the shielding layer 112 layout Directly below the contact layer 100, a shielding effect is generated on the circuit below the shielding layer 112 to prevent the circuit below the shielding layer 112 from interfering with the contact layer 110, and the shielding layer 112 and the contact layer 110 form a parasitic capacitance Cp_1.
  • the contact layer 110 is coupled to the first sensing circuit 115.
  • the contact layer 110 and the shielding layer 112 are coupled to the driving circuit 113, and respectively receive the clock signals clk2 and cl
  • the clock signals clk2 and clk3 are at a high potential.
  • the driving circuit 113 drives the contact layer 110 and the shielding layer 112 to a positive voltage V DD ; in a sensing phase, The clock signal clk2 and the pulse signal clk3 are respectively a voltage V2 and a voltage V3.
  • the first sensing circuit 115 outputs a first output signal Vo1, wherein the first output signal Vo1 is related to the contact capacitance Cf_1 and the parasitic capacitance Cp_1,
  • An output signal Vo1 can be expressed as Where A, B, and D are parameters related to the positive voltage V DD or the driving circuit and the voltage generated by it, It can represent an average of a plurality of contact capacitances formed by a plurality of pixel circuits. In addition, parameters A, B, and D are subject to changes in temperature or noise.
  • the dummy pixel circuit 12 includes a contact layer 120, a shielding layer 122, metal layers 124, 126, a driving circuit 121, and a driving circuit 123, a contact layer 120, a shielding layer 122, and a metal.
  • the layers 124, 126 are all metal layers in the layout of the integrated circuit, wherein the contact layer 120 is a top metal layer for receiving the contact of the finger FG, the contact layer 120 forms a contact capacitance Cf_2 with the finger FG, and the shielding layer 122 can be the top layer.
  • the next metal layer of the metal layer that is, the shielding layer 122 is disposed directly under the contact layer 120, for shielding the circuit below the shielding layer 122 to prevent the circuit below the shielding layer 122 from interfering with the contact layer 120.
  • the shielding layer 122 and the contact layer 120 form a parasitic capacitance Cp_2.
  • the metal layer 124 may be the next metal layer of the shielding layer 122 (ie, the metal layer 124 may be disposed/disposed under the shielding layer 122), and the metal layer 126 may be the next metal layer of the metal layer 124 (ie, metal)
  • the layer 126 can be disposed/disposed under the metal layer 124), and a parasitic capacitance Cp_3 is formed between the metal layer 124 and the metal layer 126.
  • the contact layer 120 is coupled to the driving circuit 121 to receive a clock signal clk1; the metal layer 124 is coupled to the driving circuit 123 to receive the clock signal clk2; the shielding layer 122 and the metal layer 126 are coupled to the driving circuit 123 for receiving Clock signal clk3.
  • the second sensing circuit 125 is coupled to the metal layer 124 .
  • the clock signal clk1 and the clock signal clk2 are generated by different circuits (that is, the driving circuit 121 that generates the clock signal clk1 and the driving circuit 123 that generates the clock signal clk2 are different circuits), which can further reduce the contact capacitance.
  • the clock signals clk1, clk2, and clk3 are at a high potential (positive voltage V DD ), at which time the driving circuit 121 drives the contact layer 120 to the positive voltage V DD , and the driving circuit 123
  • the shielding layer 122 and the metal layers 124 and 126 are driven to a positive voltage V DD ;
  • the clock signal clk1 and the clock signal clk2 and the pulse signal clk3 are respectively a voltage V1, a voltage V2 and a voltage V3.
  • the second sensing circuit 125 outputs the second output signal Vo2.
  • the driving circuit 121 provides the contact layer 120 voltage V1
  • the second sensing circuit 125 forms the voltage V2
  • the voltage V1 can be equal to the voltage V2
  • the instantaneous pulse signal clk1 and the clock signal clk2 can be signals having the same waveform.
  • the clock signal clk1 and the pulse signal clk2 are respectively used by different circuits.
  • the clock signal clk1 and the pulse signal clk2 are respectively generated by the driving circuit 121 and the driving circuit 123.
  • the contact layer 120 receives the clock signal clk1, that is, the driving circuit 121 is always applied to the contact layer 120 positive voltage V DD or voltage V1 (the contact layer 120 is not floating), and the second sensing circuit 125 is not connected. In the contact layer 120, therefore, the contact capacitance Cf_2 (and the parasitic capacitance Cp_2) does not affect the second output signal Vo2.
  • the dummy pixel circuit 12 can be appropriately designed such that That is, the large output signal of the second output signal Vo2 and the first output signal Vo1 equal
  • the back end circuit of the fingerprint identification system 10 can determine the normal pixel circuit 11 corresponding to the bee or grain of the finger FG according to the amplified output signal VO.
  • the parameters A, B, and D are affected by temperature or noise
  • the parameters E and F are also subjected to temperature or noise.
  • the impact changes. That is, with the differential amplifying circuit Amp, the signal component of the first output signal Vo1 that is affected by temperature or noise can be eliminated (the first output signal Vo1 minus the first The second output signal Vo2), and the differential amplifying circuit Amp is only amplified for the fingerprint signal related to the contact capacitance change amount ⁇ Cf_1 to increase the fingerprint identification accuracy of the fingerprint recognition system 10.
  • FIG. 3 is a schematic diagram of a fingerprint identification system 30 according to an embodiment of the present invention.
  • the fingerprint identification system 30 is similar to the fingerprint identification system 10, so the same components follow the same symbols.
  • a first pixel circuit 31 (normal pixel circuit) includes a shielding layer 112_1 and a shielding layer 112_2, and the shielding layer 112_1 and the shielding layer 112_2 are metal layers of the same layer in the integrated circuit layout (ie, The shielding layer 112_1 and the shielding layer 112_2 are spaced apart from each other and have the same horizontal position.
  • the shielding layer 112_1 is coupled to the driving circuit 113 to receive the clock signal clk3, and the shielding layer 112_2 receives a fixed voltage or ground, the shielding layer 112_1 and the shielding layer.
  • a second pixel circuit 32 includes a shielding layer 122_1, a shielding layer 122_2, a metal layer 126_1, and a metal layer 126_2.
  • the shielding layer 122_1 and the shielding layer 122_2 are metal layers of the same layer in the integrated circuit layout (ie, the shielding layer). 122_1 is spaced apart from the shielding layer 122_2 and has the same horizontal position.
  • the metal layer 126_1 and the metal layer 126_2 are metal layers of the same layer in the integrated circuit layout (ie, the metal layer 126_1 and the metal layer 126_2 are spaced apart from each other and have the same level.
  • the shielding layer 122_1 and the metal layer 126_1 are coupled to the driving circuit 113 to receive the clock signal clk3, the shielding layer 122_2 and the metal layer 126_2 receive a fixed voltage or ground, and the shielding layer 122_1 and the shielding layer 122_2 and the contact layer 120 are respectively formed.
  • a first output signal Vo1' corresponding to the first pixel circuit 31 can be expressed as Vo2
  • the dummy pixel circuit 12 can be appropriately designed such that the second output signal Vo2' and the large signal component of the first output signal Vo1' Equal (ie ), where large signal components Can be expressed as
  • the remaining operating principles of the fingerprint identification system 30 are the same as those of the fingerprint identification system 10, and will not be described herein.
  • the fingerprint identification system 30 can be regarded as dividing the shielding layer 112, the shielding layer 122 and the metal layer 126 in the fingerprint identification system 10 into two (ie, the shielding layer 112 is divided into shielding layers 112_1, 112_2, and the shielding layer 122 is divided.
  • the shielding layer 122_1, 122_2 is divided into the metal layers 126_1, 126_2), and the shielding layer 112, the shielding layer 122 and the metal layer 126 in the fingerprint identification system 10 can be divided into three, four or more.
  • the second output signal is exactly equal to the large signal component of the first output signal.
  • FIG. 4 is a schematic top view of the fingerprint identification system 40 according to the embodiment of the present invention.
  • the fingerprint identification system 40 includes an arrangement. An array of a plurality of normal pixel circuits 41 and a plurality of dummy pixel circuits 42 are shown in FIG. 4, and a plurality of dummy pixel circuits 42 are arranged in the array in a random manner.
  • the arrangement of the plurality of normal pixel circuits 41 and the plurality of dummy pixel circuits 42 is only one embodiment, and a plurality of dummy pixel circuits may be arranged around the array or arranged in the same manner. A row or column of an array, not limited to this.
  • FIG. 5 is a schematic diagram of an electronic device 50 according to an embodiment of the present invention.
  • the electronic device 50 can be a tablet computer or a smart phone.
  • the electronic device 50 includes an operation circuit 52 and a fingerprint identification.
  • the system 54 is coupled to the operation circuit 52, which can be implemented by the fingerprint identification system 10, the fingerprint identification system 30 or the fingerprint identification system 40.
  • the operation circuit 52 can include a processor and a storage device.
  • the storage device can be a read-only memory (ROM), a random access memory (RAM), a non-volatile memory (Non-Volatile Memory, for example, an electronic erasable rewritable only Electrically Erasable Programmable Read Only Memory (EEPROM) or a flash memory (Flash Memory).
  • ROM read-only memory
  • RAM random access memory
  • Non-Volatile Memory for example, an electronic erasable rewritable only Electrically Erasable Programmable Read Only Memory (EEPROM) or a flash memory (Flash Memory).
  • the present invention utilizes a dummy pixel circuit to generate a dummy output signal to cancel a signal component affected by parasitic capacitance, temperature, and noise in an output signal of a normal pixel circuit, and performs a fingerprint signal in an output signal of a normal pixel circuit. Amplification and subsequent signal processing to increase fingerprint identification accuracy.

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  • General Engineering & Computer Science (AREA)
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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
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Abstract

一种指纹辨识系统，包括复数个第一像素电路；一第一感测电路，用来感测一接触电容并输出一第一输出信号，其中所述第一输出信号包含一大信号分量以及一小信号分量，所述小信号分量相关于所述接触电容的一变化量；至少一第二像素电路；一第二感测电路，用来输出一第二输出信号，其中所述第二输出信号与所述大信号分量相等；以及一差分放大电路，用来将所述第一输出信号与所述第二输出信号的一相差值放大，以产生一放大输出信号，其中所述放大输出信号相关于所述小信号分量。

Description

指纹辨识系统及电子装置 技术领域
本发明涉及一种指纹辨识系统及电子装置，尤其涉及一种可降低寄生电容影响的指纹辨识系统及电子装置。
背景技术
随着科技日新月异，移动电话、数字相机、平板计算机、笔记本电脑等越来越多携带型电子装置已经成为了人们生活中必备的工具。由于携带型电子装置通常供个人使用，而具有一定的隐私性，因此其内部储存的数据，例如电话簿、相片、个人信息等等为私人所有。一旦电子装置丢失，则这些数据可能被他人所利用，而造成不必要的损失。虽然目前已有利用密码保护的方式来避免电子装置为他人所使用，但密码容易泄露或遭到破解，具有较低的安全性。并且，用户需记住密码才能使用电子装置，若忘记密码，则会带给使用者许多不便。因此，目前发展出利用个人指纹辨识系统的方式来达到身份认证的目的，以提升数据安全性。
在习知技术中，电容式指纹辨识系统是相当受欢迎的一种指纹辨识方法，其系利用接触层接受来自使用者的手指接触，并感测接触层的电容变化，以判断使用者指纹的纹蜂(Finger Ridge)或纹谷(Finger Valley)。为了避免接触层受到来自其他电路的干扰，习知技术通常会在电路布局时在接触层下方布局一屏蔽层，以产生屏蔽效应，避免屏蔽层以下的电路对接触层产生干扰。然而，接触层与屏蔽层的间会产生寄生电容，而寄生电容的电容值往往大于因接触而 产生的接触电容的电容值，影响电容感测电路或电容式指纹辨识系统判断接触电容的电容值，以致于降低了指纹辨识的精准度。
发明内容
因此，本发明的主要目的即在于提供一种既可降低寄生电容影响又可降低对温度及噪声敏感度的指纹辨识系统及电子装置。
为了解决上述技术问题，本发明提供了一指纹辨识系统，其包括复数个第一像素电路，所述复数个第一像素电路中一第一像素电路与一手指形成一接触电容；一第一感测电路，耦接于所述第一像素电路，用来感测所述接触电容并输出一第一输出信号，其中所述第一输出信号包含一大信号分量以及一小信号分量，所述小信号分量相关于所述接触电容的一变化量；至少一第二像素电路；一第二感测电路，耦接于所述至少一第二像素电路中一第二像素电路，用来输出一第二输出信号，其中所述第二输出信号与所述大信号分量相等；以及一差分放大电路，耦接于所述第一感测电路及所述第二感测电路，用来将所述第一输出信号与所述第二输出信号的一相差值放大，以产生一放大输出信号，其中所述放大输出信号相关于所述小信号分量。
优选地，所述第二感测电路包含有一接触层，耦接于一第一驱动电路，以接收一第一驱动信号，所述接触层接受所述手指的接触；一第一屏蔽层，设置于所述接触层的下方；一第一金属层，设置于所述第一屏蔽层的下方，耦接于一第二驱动电路，以接收一第二驱动信号；以及一第二金属层，设置于所述第一金属层的下方；其中，所述第一屏蔽层与所述第二金属层耦接于所述第二驱动电路，以接收一第三驱动信号；其中，所述第一金属层耦接于所述第二感测电路。
优选地，于一驱动阶段中，所述第一驱动电路将所述接触层驱动至一正电压，所述第二驱动电路将所述第一屏蔽层、所述第一金属层及所述第二金属层 驱动至所述正电压；以及于一感测阶段中，所述第一驱动电路提供所述接触层一第一电压。
优选地，所述第二感测电路另包含一第三金属层，所述第三金属层与所述第二金属层具有相同的水平位置，且与所述第二金属层相互间隔，所述第三金属层接收一固定电压。
优选地，所述第二感测电路另包含一第二屏蔽层，所述第二屏蔽层与所述第一屏蔽层具有相同的水平位置，且与所述第一屏蔽层相互间隔，所述第二屏蔽层接收一固定电压。
优选地，所述第一感测电路包含有一接触层，用来接受所述手指的接触，所述接触层与所述手指形成所述接触电容，所述接触层耦接于一驱动电路以及所述第一感测电路；以及一第一屏蔽层，设置于所述接触层的下方。
优选地，于一驱动阶段中，所述驱动电路将所述接触层驱动至一正电压。
优选地，所述第一感测电路另包含一第二屏蔽层，所述第二屏蔽层与所述第一屏蔽层具有相同的水平位置，且与所述第一屏蔽层相互间隔，所述第二屏蔽层接收一固定电压。
优选地，所述差分放大电路为一程控增益放大器。
本发明另提供了一种电子装置，包括一运作电路；以及一指纹辨识系统，耦接于所述运作电路，所述指纹辨识系统包含复数个第一像素电路，所述复数个第一像素电路中一第一像素电路与一手指形成一接触电容一第一感测电路，耦接于所述第一像素电路，用来感测所述接触电容并输出一第一输出信号，其中所述第一输出信号包含一大信号分量以及一小信号分量，所述小信号分量相关于所述接触电容的一变化量；至少一第二像素电路；一第二感测电路，耦接于所述至少一第二像素电路中一第二像素电路，用来输出一第二输出信号，其中所述第二输出信号与所述大信号分量相等；以及一差分放大电路，耦接于所述第一感测电路及所述第二感测电路，用来将所述第一输出信号与所述第二输 出信号的一相差值放大，以产生一放大输出信号，其中所述放大输出信号相关于所述小信号分量。
本发明提供的指纹辨识系统及电子装置，其利用虚设像素电路产生虚设输出信号，进而消除寄生电容的效应，以提升电容感测或指纹辨识的精准度及效能。
附图说明
图1为本发明实施例一指纹辨识系统的示意图。
图2为本发明实施例复数个时脉信号的波形图。
图3为本发明实施例一指纹辨识系统的示意图。
图4为本发明实施例一指纹辨识系统的俯视示意图。
图5为本发明实施例一电子装置的示意图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。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。
于传统指纹辨识系统中，像素电路的输出信号受到像素电路及感测电路内部寄生电容的影响，使得像素电路的输出信号中相关于接触电容变化量的信号成份并不显着，像素电路的输出信号亦受到温度和噪声的影响，而使指纹辨识的精准度下降。因此，本发明除了正常的像素电路之外，另包含虚设像素电路，利用虚设像素电路产生虚设输出信号，来抵消复数个正常像素电路的输出信号中受到寄生电容、温度及噪声影响的信号成份，并针对复数个正常像素电路的 输出信号中的指纹信号成份进行放大以及后续信号处理，以判断纹蜂(Finger Ridge)或纹谷(Finger Valley)，增加指纹辨识精准度。
关于正常像素电路及虚设像素电路的电路结构，请参考图1及图2，图1为本发明实施例一指纹辨识系统10的示意图，图2为本发明实施例时脉(Clock)信号clk1、clk2、clk3的波形图。为了方便说明，图1绘示指纹辨识系统10中复数个正常像素电路的一正常像素电路以及一虚设像素电路的示意图，如图1所示，指纹辨识系统10包含一正常像素电路11、一虚设像素电路12、一第一感测电路115、一第二感测电路125以及一差分放大电路Amp。正常像素电路11及虚设像素电路12皆可接受一手指FG的接触，并与手指FG分别形成一接触电容Cf_1及一接触电容Cf_2。第一感测电路115耦接于正常像素电路11，用来感测接触电容Cf_1并输出一第一输出信号Vo1，另外，第二感测电路125耦接于虚设像素电路12，用来输出一第二输出信号Vo2。其中，第一输出信号Vo1包含一大信号分量
Figure PCTCN2016100451-appb-000001
以及一小信号分量ΔVo1(即第一输出信号Vo1可表示为
Figure PCTCN2016100451-appb-000002
)，其中大信号分量
Figure PCTCN2016100451-appb-000003
可为第一输出信号Vo1的一平均值，而小信号分量ΔVo1相关于接触电容Cf_1的一变化量ΔCf_1，其为用来进行指纹辨识的指纹信号。需注意的是，虚设像素电路12可经适当设计，使得第二输出信号Vo2与第一输出信号Vo1的大信号分量
Figure PCTCN2016100451-appb-000004
相等(即第二输出信号Vo2可表示为
Figure PCTCN2016100451-appb-000005
)。差分放大电路Amp接收第一输出信号Vo1及第二输出信号Vo2，用来将第一输出信号Vo1与第二输出信号Vo2之间的一相差值(Vo1－Vo2)放大，以产生一放大输出信号VO，其中放大输出信号VO仅针对相差值(Vo1－Vo2)放大。于一实施例中，差分放大电路Amp为一程控增益放大器(Programmable Gain Amplifier，PGA)。差分放大电路Amp可耦接至一模拟数字转换器(Analog-to-Digital Converter，ADC)以及一后端电路(未绘示于图1)，以对放大输出信号VO进行后续信号处理，并判断正常像素电路11对应于手指FG的一纹蜂或一纹谷。
换句话说，对应于正常像素电路11的第一输出信号Vo1相关于正常像素电路11所对应的接触电容Cf_1，即第一输出信号Vo1包含指纹信号(即小信号分量ΔVo1)。另一方面，对应于虚设像素电路12的第二输出信号Vo2仅用来抵消第一输出信号Vo1中受到寄生电容、温度及噪声影响的信号成份，而第二输出信号Vo2并未包含指纹信号(即虚设像素电路12所对应的接触电容Cf_2并不会对第二输出信号Vo2造成影响)。指纹辨识系统10利用差分放大电路Amp将第一输出信号Vo1与第二输出信号Vo2之间的相差值(Vo1－Vo2)放大，即将指纹信号放大，以进行后续信号处理。
详细来说，如图1所示，正常像素电路11包含一接触层110、一屏蔽层112以及一驱动电路113，接触层110及屏蔽层112皆为集成电路布局中的金属层，接触层110为一顶层金属层(Top Metal)，用来接受手指FG的接触，接触层110与手指FG形成接触电容Cf_1，而屏蔽层112可为顶层金属层的下一层金属层，即屏蔽层112布局于接触层100的正下方，用来对屏蔽层112以下的电路产生屏蔽效应，以避免屏蔽层112以下的电路对接触层110产生干扰，屏蔽层112与接触层110形成寄生电容Cp_1。接触层110耦接于第一感测电路115，另外，接触层110及屏蔽层112皆耦接于驱动电路113，分别接收驱动电路113所产生的时脉信号clk2、clk3。
如图2所示，于驱动阶段中，时脉信号clk2、clk3为一高电位，此时驱动电路113将接触层110及屏蔽层112驱动至一正电压VDD；于一感测阶段中，时脉信号clk2及时脉信号clk3分别为一电压V2及一电压V3，此时第一感测电路115输出第一输出信号Vo1，其中第一输出信号Vo1与接触电容Cf_1及寄生电容Cp_1相关，第一输出信号Vo1可表示为
Figure PCTCN2016100451-appb-000006
Figure PCTCN2016100451-appb-000007
其中A、B、D为相关于正电压VDD或是驱动电路及其所产生电压的 参数，
Figure PCTCN2016100451-appb-000008
可代表复数个像素电路所形成的复数个接触电容的一平均值。另外，参数A、B、D会受到温度或噪声的影响而随之变化。
另一方面，如图1所示，虚设像素电路12包含一接触层120、一屏蔽层122、金属层124、126、一驱动电路121以及一驱动电路123，接触层120、屏蔽层122及金属层124、126皆为集成电路布局中的金属层，其中接触层120为一顶层金属层，用来接受手指FG的接触，接触层120与手指FG形成接触电容Cf_2，而屏蔽层122可为顶层金属层的下一层金属层，即屏蔽层122布局于接触层120的正下方，用来对屏蔽层122以下的电路产生屏蔽效应，以避免屏蔽层122以下的电路对接触层120产生干扰，屏蔽层122与接触层120形成一寄生电容Cp_2。另外，金属层124可为屏蔽层122的下一层金属层(即金属层124可布局/设置于屏蔽层122下方)，而金属层126可为金属层124的下一层金属层(即金属层126可布局/设置于金属层124下方)，金属层124与金属层126之间形成有一寄生电容Cp_3。接触层120耦接于驱动电路121，以接收一时脉信号clk1；金属层124耦接于驱动电路123，以接收时脉信号clk2；屏蔽层122及金属层126耦接于驱动电路123，以接收时脉信号clk3。另外，第二感测电路125耦接于金属层124。需注意的是，时脉信号clk1与时脉信号clk2为不同电路所产生(即产生时脉信号clk1的驱动电路121与产生时脉信号clk2的驱动电路123为不同电路)，可进一步降低接触电容Cf_2(及寄生电容Cp_2)对第二输出信号Vo2的影响。
如图2所示，于驱动阶段中，时脉信号clk1、clk2、clk3为高电位(正电压VDD)，此时驱动电路121将接触层120驱动至正电压VDD，而驱动电路123将屏蔽层122及金属层124、126驱动至正电压VDD；于感测阶段中，时脉信号clk1、时脉信号clk2及时脉信号clk3分别为一电压V1、电压V2及电压V3，此时第二感测电路125输出第二输出信号Vo2，此外，驱动电路121提供接触 层120电压V1，第二感测电路125形成电压V2，并提供屏蔽层122及金属层126电压V3。需注意的是，就波形而言，电压V1可与电压V2相等，即时脉信号clk1与时脉信号clk2可为具有相同波形的信号，然而，时脉信号clk1及时脉信号clk2分别由不同电路所产生，以指纹辨识系统10为例，时脉信号clk1及时脉信号clk2分别由驱动电路121及驱动电路123所产生。
需注意的是，接触层120接收时脉信号clk1，即驱动电路121始终施加于接触层120正电压VDD或电压V1(接触层120并非浮接)，且第二感测电路125并未连接于接触层120，因此，接触电容Cf_2(及寄生电容Cp_2)并不会对第二输出信号Vo2造成影响。第二输出信号Vo2可表示为Vo2＝E*Cp_3+F，其中E、F为相关于正电压VDD或驱动电路的参数，参数E、F也会受到温度或噪声的影响而随之变化。
另外，虚设像素电路12可经适当设计，使得
Figure PCTCN2016100451-appb-000009
Figure PCTCN2016100451-appb-000010
即第二输出信号Vo2与第一输出信号Vo1的大信号分量
Figure PCTCN2016100451-appb-000011
相等
Figure PCTCN2016100451-appb-000012
如此一来，差分放大电路Amp可仅针对指纹信号(即小信号分量ΔVo1，其中ΔVo1＝Vo1－Vo2＝A*ΔCf_1)放大，也就是说，放大输出信号VO可表示为VO＝Av*(Vo1－Vo2)＝Av*ΔVo1，其中Av代表差分放大电路Amp的一增益。如此一来，指纹辨识系统10的后端电路即可根据放大输出信号VO，判断正常像素电路11对应于手指FG的纹蜂或纹谷。
需注意的是，于第一输出信号Vo1中，参数A、B、D会受到温度或噪声的影响而随之变化，然而于第二输出信号Vo2中，参数E、F也会受到温度或噪声的影响而随之变化。也就是说，利用差分放大电路Amp，第一输出信号Vo1中受到温度或噪声的影响的信号成份可被消除(第一输出信号Vo1减去第 二输出信号Vo2)，而差分放大电路Amp仅针对相关于接触电容变化量ΔCf_1的指纹信号进行放大，以增加指纹辨识系统10的指纹辨识精准度。
由上述可知，指纹辨识系统10除了正常像素电路(正常像素电路11)之外，另包含虚设像素电路(虚设像素电路12)，利用虚设像素电路(虚设像素电路12)产生虚设输出信号(第二输出信号Vo2)，来抵消复数个正常像素电路的输出信号中受到寄生电容、温度及噪声影响的信号成份，并针对复数个正常像素电路的输出信号中的指纹信号成份(小信号分量ΔVo1，ΔVo1＝A*ΔCf_1)进行放大以及后续信号处理，以判断手指FG的纹蜂或纹谷。
需注意的是，前述实施例是用以说明本发明之概念，本领域具通常知识者当可据以做不同之修饰，而不限于此。举例来说，请参考图3，图3为本发明实施例一指纹辨识系统30的示意图，指纹辨识系统30与指纹辨识系统10相似，故相同组件沿用相同符号。与指纹辨识系统10不同的是，一第一像素电路31(正常像素电路)包含一屏蔽层112_1以及一屏蔽层112_2，屏蔽层112_1及屏蔽层112_2为集成电路布局中同一层的金属层(即屏蔽层112_1与屏蔽层112_2相互间隔，且具有相同的水平位置)，屏蔽层112_1耦接于驱动电路113以接收时脉信号clk3，屏蔽层112_2接收一固定电压或接地，屏蔽层112_1及屏蔽层112_2与接触层110分别形成一寄生电容Cp_11及一寄生电容Cp_12。另外，一第二像素电路32包含一屏蔽层122_1、一屏蔽层122_2、一金属层126_1以及一金属层126_2，屏蔽层122_1及屏蔽层122_2为集成电路布局中同一层的金属层(即屏蔽层122_1与屏蔽层122_2相互间隔，且具有相同的水平位置)，金属层126_1及金属层126_2为集成电路布局中同一层的金属层(即金属层126_1与金属层126_2相互间隔，且具有相同的水平位置)，屏蔽层122_1及金属层126_1耦接于驱动电路113以接收时脉信号clk3，屏蔽层122_2及金属层126_2接收一固定电压或接地，屏蔽层122_1及屏蔽层122_2与接触层120 分别形成一寄生电容Cp_21及一寄生电容Cp_22，金属层126_1及金属层126_2与金属层124分别形成一寄生电容Cp_31及一寄生电容Cp_32。对应于第一像素电路31的一第一输出信号Vo1’可表示为
Figure PCTCN2016100451-appb-000013
Figure PCTCN2016100451-appb-000014
对应于第二像素电路32的一第二输出信号Vo2’可表示为Vo2’＝E1*Cp_31+E2*Cp_32+F，同样的，参数B1、B2、E1、E2皆会受到温度或噪声的影响而随之变化。虚设像素电路12可经适当设计，使得第二输出信号Vo2’与第一输出信号Vo1’的大信号分量
Figure PCTCN2016100451-appb-000015
相等(即
Figure PCTCN2016100451-appb-000016
)，其中大信号分量
Figure PCTCN2016100451-appb-000017
可表示为
Figure PCTCN2016100451-appb-000018
Figure PCTCN2016100451-appb-000019
指纹辨识系统30其余操作原理与指纹辨识系统10相同，于此不再赘述。
需注意的是，指纹辨识系统30可视为将指纹辨识系统10中的屏蔽层112、屏蔽层122及金属层126分割为二(即屏蔽层112分割成屏蔽层112_1、112_2，屏蔽层122分割成屏蔽层122_1、122_2，金属层126分割成金属层126_1、126_2)，而不在此限，指纹辨识系统10中的屏蔽层112、屏蔽层122及金属层126可分割为三、四或更多部份，使得第二输出信号精准地等于第一输出信号的大信号分量。
另外，本发明的指纹辨识系统中于正常像素电路及虚设像素电路并未有所限，请参考图4，图4为本发明实施例一指纹辨识系统40的俯视示意图，指纹辨识系统40包含排列成一数组的复数个正常像素电路41以及复数个虚设像素电路42，如图4所示，而复数个虚设像素电路42可以随机的方式排列于所述数组。需注意的是，图4所绘示复数个正常像素电路41以及复数个虚设像素电路42的排列方式仅为一实施方式，复数个虚设像素电路可排列于所述数组的周围，或排列于所述数组的一行或一列，而不在此限。
另外，本发明的指纹辨识系统可应用于一电子装置中。请参考图5，图5为本发明实施例一电子装置50的示意图，电子装置50可为一平板电脑或一智能手机，如图5所示，电子装置50包含一运作电路52以及一指纹辨识系统54，指纹辨识系统54耦接于运作电路52，其可由指纹辨识系统10、指纹辨识系统30或指纹辨识系统40来实现，另外，运作电路52可包含一处理器(Processor)及一储存装置，储存装置可为只读内存(Read-Only Memory，ROM)、随机存取存储(Random-Access Memory，RAM)、非挥发性内存(Non-Volatile Memory，例如，一电子抹除式可复写只读内存器(Electrically Erasable Programmable Read Only Memory,EEPROM)或一快闪存储(Flash Memory))。
综上所述，本发明利用虚设像素电路产生虚设输出信号，来抵消正常像素电路的输出信号中受到寄生电容、温度及噪声影响的信号成份，并针对正常像素电路的输出信号中的指纹信号进行放大以及后续信号处理，以增加指纹辨识精准度。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种指纹辨识系统，其特征在于，所述指纹辨识系统包括：
    复数个第一像素电路，所述复数个第一像素电路中一第一像素电路与一手指形成一接触电容；
    一第一感测电路，耦接于所述第一像素电路，用来感测所述接触电容并输出一第一输出信号，其中所述第一输出信号包含一大信号分量以及一小信号分量，所述小信号分量相关于所述接触电容的一变化量；
    至少一第二像素电路；
    一第二感测电路，耦接于所述至少一第二像素电路中一第二像素电路，用来输出一第二输出信号，其中所述第二输出信号与所述大信号分量相等；以及
    一差分放大电路，耦接于所述第一感测电路及所述第二感测电路，用来将所述第一输出信号与所述第二输出信号的一相差值放大，以产生一放大输出信号，其中所述放大输出信号相关于所述小信号分量。
  2. 如权利要求1所述的指纹辨识系统，其特征在于，所述第二像素电路包含有：
    一接触层，耦接于一第一驱动电路，以接收一第一驱动信号，所述接触层接受所述手指的接触；
    一第一屏蔽层，设置于所述接触层的下方；
    一第一金属层，设置于所述第一屏蔽层的下方，耦接于一第二驱动电路，以接收一第二驱动信号；以及
    一第二金属层，设置于所述第一金属层的下方；
    其中，所述第一屏蔽层与所述第二金属层耦接于所述第二驱动电路，以接收一第三驱动信号；
    其中，所述第一金属层耦接于所述第二感测电路。
  3. 如权利要求2所述的指纹辨识系统，其特征在于，于一驱动阶段中，所述第一驱动电路将所述接触层驱动至一正电压，所述第二驱动电路将所述第一屏蔽层、所述第一金属层及所述第二金属层驱动至所述正电压；以及于一感测阶段中，所述第一驱动电路提供所述接触层一第一电压。
  4. 如权利要求2所述的指纹辨识系统，其特征在于，所述第二像素电路另包含一第三金属层，所述第三金属层与所述第二金属层具有相同的水平位置，且与所述第二金属层相互间隔，所述第三金属层接收一固定电压。
  5. 如权利要求2所述的指纹辨识系统，其特征在于，所述第二像素电路另包含一第二屏蔽层，所述第二屏蔽层与所述第一屏蔽层具有相同的水平位置，且与所述第一屏蔽层相互间隔，所述第二屏蔽层接收一固定电压。
  6. 如权利要求1-5任一项所述的指纹辨识系统，其特征在于，所述第一像素电路包含有：
    一接触层，用来接受所述手指的接触，所述接触层与所述手指形成所述接触电容，所述接触层耦接于一驱动电路以及所述第一感测电路；以及
    一第一屏蔽层，设置于所述接触层的下方。
  7. 如权利要求6所述的指纹辨识系统，其特征在于，于一驱动阶段中，所述驱动电路将所述接触层驱动至一正电压。
  8. 如权利要求6所述的指纹辨识系统，其特征在于，所述第一像素电路另包含一第二屏蔽层，所述第二屏蔽层与所述第一屏蔽层具有相同的水平位置，且与所述第一屏蔽层相互间隔，所述第二屏蔽层接收一固定电压。
  9. 如权利要求1-8任一项所述的指纹辨识系统，其特征在于，所述差分放大电路为一程控增益放大器。
  10. 一种电子装置，其特征在于，所述电子装置包括：
    一运作电路；以及
    一指纹辨识系统，耦接于所述运作电路，所述指纹辨识系统包含有：
    复数个第一像素电路，所述复数个第一像素电路中一第一像素电路与一手指形成一接触电容；
    一第一感测电路，耦接于所述第一像素电路，用来感测所述接触电容并输出一第一输出信号，其中所述第一输出信号包含一大信号分量以及一小信号分量，所述小信号分量相关于所述接触电容的一变化量；
    至少一第二像素电路；
    一第二感测电路，耦接于所述至少一第二像素电路中一第二像素电路，用来输出一第二输出信号，其中所述第二输出信号与所述大信号分量相等；以及
    一差分放大电路，耦接于所述第一感测电路及所述第二感测电路，用来将所述第一输出信号与所述第二输出信号的一相差值放大，以产生一放大输出信号，其中所述放大输出信号相关于所述小信号分量。
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