WO2015101349A1 - 电容指纹传感器 - Google Patents

电容指纹传感器 Download PDF

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Publication number
WO2015101349A1
WO2015101349A1 PCT/CN2015/070077 CN2015070077W WO2015101349A1 WO 2015101349 A1 WO2015101349 A1 WO 2015101349A1 CN 2015070077 W CN2015070077 W CN 2015070077W WO 2015101349 A1 WO2015101349 A1 WO 2015101349A1
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Prior art keywords
level
electrode
initialization switch
control signal
switch
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PCT/CN2015/070077
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English (en)
French (fr)
Inventor
李扬渊
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李扬渊
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Application filed by 李扬渊 filed Critical 李扬渊
Priority to US15/109,626 priority Critical patent/US9953200B2/en
Priority to KR1020167014591A priority patent/KR102010638B1/ko
Priority to EP15733234.7A priority patent/EP3093796B1/en
Publication of WO2015101349A1 publication Critical patent/WO2015101349A1/zh
Priority to US15/918,766 priority patent/US10289890B2/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

Definitions

  • the present invention relates to a capacitive sensor, and more particularly to a capacitive fingerprint sensor that can form an array to image a fingerprint.
  • capacitive fingerprint sensor technology routes are based on prototypes of macro-capacitance sensor circuits.
  • the technical rule in the sensor field determines that the capacitive sensor is a combination of the circuit and the sensor equation.
  • the circuit scale and implementation process determine the range and tolerance range of each parameter in the sensor equation.
  • capacitive fingerprint sensors, as an array sensor are also sensitive to mismatch between cells, which is difficult to control for microscale electronic components relative to macroscale electronic components.
  • the array sensor is generally designed as a single channel, and each unit is time-multiplexed with the measurement circuit.
  • the important method of improving the signal gain in the sensor design is greatly limited in the design of the array sensor, and it is not even feasible for the single-channel array sensor with many points.
  • a novel 'C-V-T is disclosed in CN201210403271.2) 'Type capacitive distance sensor.
  • the specific implementation method is: measuring the surface of the conductor (target electrode) with the fingerprint, measuring capacitance (target capacitance) formed by coupling with the capacitance measuring plate (sensing electrode); measuring the surface of the conductor (target electrode) to different array units
  • the distance between the capacitance measuring plates (sensing electrodes) is large or small, and the measuring capacitance (target capacitance) formed by the coupling is also different in size; the capacitive coupling plate (driving electrode) is controlled by the programmable level generator.
  • Level driver drive, so that the potential of the capacitance measuring plate (sensing electrode) rises, and the degree of rise differs depending on the size of the parallel measuring capacitance (target capacitance); the reference capacitor (integrated capacitor) is first filled with charge and then rises to the level After the capacitor measurement plate (sensing electrode) discharge, the discharge level is different due to the difference in potential of the capacitance measuring plate (sensing electrode); the repeated discharge causes the potential of the reference capacitor (integrated capacitor) to continuously decrease, due to the different rate of decline, Programming level generator 2 (Reference level) The threshold level generated by the time is different, so that the comparator outputs the inversion at different times; the number of discharges corresponding to the time when the comparator outputs the inversion is the output of the capacitive distance sensor.
  • the sensor's measurement function is 'S-C-V-T ', that is, the distance from the fingerprint to the sensing electrode is an independent variable, and the time-to-count value is used as a function value, and the measurement function has the advantage of anti-drift and linearization. Combined with the natural advantages of this sensor technology solution in improving resolution and suppressing thermal noise, the final performance is greatly improved. According to the flow test, the technical level is higher than that under the same process conditions. The world's leading level in 2012, but lower than the global leading level in 2013, the technical level of Touch ID loaded by iPhone5S.
  • the present invention provides a "C-Q-T" type capacitive sensor circuit including a “C-Q” converter and a “Q-T” converter.
  • the purpose of imaging the fingerprint is to perform fingerprint recognition, which is concerned with the spatial difference of the fingerprint ridge line and the valley line; the spatial difference quantity is first converted into a fingerprint as the target capacitance Cg formed by the coupling of the target electrode Pg and the sensing electrode Ps.
  • the difference between the capacitance values is converted into a difference in the amount of charge on the sensing electrode Ps by the "CQ” converter; the "QT” converter sequentially transfers the charge on the sensing electrode Ps to the integrating capacitor Ct, so that the integrating capacitor Ct is charged.
  • the difference in charge amount is converted into a difference in charge/discharge rate; since the charge/discharge rate is different, the potential Vt of Ct changes from the initial level to the number of charge/discharge times through the threshold level Vref3; using a comparator pair When Vt and Vref3 are compared, the number of charge transfer times corresponding to the time at which the edge of the jump occurs at the comparator output is the capacitance quantized value.
  • the capacitive fingerprint sensor provided by the invention outputs a transition edge at the output of the comparator, is acquired by the corresponding readout circuit, and is converted into the number of charge transfer times.
  • the edge time readout circuit disclosed in "Edge Time Readout Circuit" (publication number CN201210405080.X) filed by Chengdu Microarray Electronics Co., Ltd. in 2012 can be used for this purpose.
  • the "C-Q" converter includes a target electrode Pg (fingerprint), a sensing electrode Ps, a driving electrode Pd, a level driver 1, a level driver 2, an initialization switch 1, and a reference level 1.
  • the capacitance coupling between the sensing electrode Ps and the target electrode Pg is referred to as a target capacitance Cg; the capacitance coupling between the sensing electrode Ps and the driving electrode Pd is referred to as a driving capacitance Cd; and the sensing electrode Ps is coupled to a background circuit (eg, The substrate-coupled capacitor is called the background capacitor Cb.
  • the background capacitor Cb and the driving capacitor Cd are located inside the sensor and in parallel, to simplify the description, the background capacitor Cb is regarded as a part of the driving capacitor Cd, and the Cd is The voltage is recorded as a weighted average of the respective voltages of Cb and Cd based on the capacitance value; the initialization switch 1 port 1 and the sensing electrode Ps are connected; the level driver 1 and the target electrode Pg are connected; the level driver 2 and the driving electrode Pd are connected The reference level 1 output initialization level Vref1 is connected to the initialization switch 1 port 2.
  • the control logic timing of the "C-Q" converter is:
  • Step 1-1 the level driver 1 outputs a level V11 to the target electrode Pg; the level driver 2 outputs a level V21 to the driving electrode Pd;
  • Step 1-2 closing the initialization switch 1, connecting the sensing electrode Ps to the reference level 1;
  • Step 1-3 disconnecting the initialization switch 1;
  • Step 1-4 the level driver 1 outputs a level V12 to the target electrode Pg; the level driver 2 outputs a level V22 to the driving electrode Pd;
  • Step 1-5 return to step 1-1.
  • the potential of the sensing electrode Ps is the initialization level Vref1; in step 1-4, since the sensing electrode Pg is in the floating state, the potential change of the target electrode Pg and the driving electrode Pd couples the charge into the transmission.
  • Equation (1) can be converted to:
  • Vs-Vref1 ( ⁇ V1*Cg + ⁇ V2*Cd) / (Cd+Cg) (3)
  • Vs ( ⁇ V1*Cg + ⁇ V2*Cd) / (Cd+Cg) + Vref1 (4)
  • the "Q-T” converter includes an integrating capacitor Ct, an initialization switch 2, a reference level 2, a charge transfer switch, a comparator, and a third reference level.
  • the integrating capacitor Ct is connected to the initialization switch 2 port 1, the charge transfer switch port 2, the comparator input terminal 1; the reference level 2 output initialization level Vref2 is connected to the initialization switch port 2; the charge transfer switch port 1 and "CQ"
  • the sensing electrode Pg in the converter is connected; the third reference level output threshold level Vref3 is connected to the comparator input 2.
  • the control logic timing of the "Q-T" converter is:
  • Step 2-1 closing the initialization switch 2, connecting the integration capacitor Ct to the reference level 2;
  • Step 2-2 disconnecting the initialization switch 2;
  • Step 2-3 if the "C-Q" converter is in steps 1-4, then lock the "C-Q” converter in steps 1-4;
  • Step 2-4 closing the charge transfer switch
  • Step 2-5 disconnecting the charge transfer switch
  • Step 2-6 unlocking the "C-V" converter
  • Steps 2-7 if the "C-Q" converter leaves step 1-4, return to step 2-3.
  • the comparator input terminal 1 is connected to the integration capacitor Ct, and the comparator input terminal 2 is connected to the third reference level to compare the potential Vt of the integration capacitor Ct with the threshold level Vref3 of the third reference level output, and output a comparison result.
  • the output of the "QT” converter it is also the output of the "CQT” sensor.
  • the time information T carried by the sensor output is the integral result of the charge transfer iterative process.
  • T(Cg) has no strong solution, and the weak solution expression has no value for analysis. It can only be analyzed by indirect expression.
  • the level of the integral capacitor Ct be Vt; Vt gradually change from Vref2 to Vs, and T(Cg) takes the length of the interval in which Vt'(Cg) is integrated into T at ⁇ (Vs-Vref2), where ⁇ 1;
  • a certain quantization bit length does not increase T(Cg) without limit to increase T'(Cg), so the relative value of T'(Cg)/T(Cg) should be increased.
  • Vt'(Cg) to T(Cg) are monotonically decreasing functions
  • Vt''(Cg) to T' (Cg) is also a monotonic reduction function
  • Vt''(Cg)/Vt'(Cg) can be used instead of T'(Cg)/T(Cg) for sensitivity analysis.
  • Vt' (Vs-Vt)*(Cd+Cg) / (Ct+Cd+Cg) (6)
  • Vt'(Cg) ( ( ⁇ V2+Vref1-Vt)*Cd + ( ⁇ V1+Vref1-Vt)*Cg ) / (Ct+Cd+Cg) (7)
  • Vt''(Cg) (( ⁇ V1+Vref1-Vt)*Ct + ( ⁇ V1- ⁇ V2)*Cd ) / (Ct+Cd+Cg) ⁇ 2 (8)
  • Vs–Vref2 ( ⁇ V1*Cg+ ⁇ V2*Cd) / (Cd+Cg) + Vref1 – Vref2 (9)
  • the influence of ⁇ V2 on ⁇ V1 is much smaller, even if ⁇ V2 is always equal to 0, the sensitivity of the sensor is also reduced.
  • the invention thus allows the level driver 2 to be implemented to be level connected to the sensor. This is the essential difference between the "C-Q" type and the "C-V” type: if you put CN201210403271.2
  • the programmable level generator 1 of the disclosed circuit corresponding to the level driver 2 of the present invention is also implemented to be level connected to the sensor, and the "C-V" portion will always output the ground level.
  • the capacitive fingerprint sensor provided by the invention is used to form an array to image a fingerprint, and a plurality of "CQ" converters are used to time-multiplex a "QT” converter in a single channel grouping, when multi-channel grouping Multiple sets of single-channel "CQT" sensor arrays work side by side in parallel.
  • FIG. 1 is a schematic diagram of a circuit of a capacitive fingerprint sensor provided by the present invention
  • FIG. 2 is a diagram of a switch control signal and a level control signal provided by the present invention
  • FIG. 3 is a comparison diagram of a family of integrated capacitance potential curves and a threshold level provided by the present invention
  • Figure 4 is a first embodiment of the level driver 1 provided by the present invention.
  • FIG. 5 is a second embodiment of the level driver 1 provided by the present invention.
  • Figure 6 is a third embodiment of the level driver 1 provided by the present invention.
  • Figure 7 is a first embodiment of the level driver 2 provided by the present invention.
  • Figure 8 is a second embodiment of the level driver 2 provided by the present invention.
  • Figure 9 is a schematic diagram of a group of capacitive fingerprint sensors provided by the present invention.
  • Figure 10 is a schematic diagram of a capacitive fingerprint sensor group provided by the present invention.
  • FIG. 11 is a schematic diagram of a group of capacitive fingerprint sensor groups provided by the present invention.
  • the circuit provided by the present invention includes a target electrode 1, a sensing electrode 2, a driving electrode 3, a first level driver 4, a second level driver 5, a first initialization switch 6, and a first reference.
  • the sensing electrode 2 which is one or more electrodes, is connected to the first port of the first initialization switch 6, and is connected to the first port of the charge transfer switch 7;
  • the target electrode 1 is a measurement target surface, is connected to the first level driver 4, is located above the sensing electrode 2, has a dielectric layer between the sensing electrode 2, and forms a target capacitor 21 between the target electrode 1 and the sensing electrode 2. ;
  • a first level driver 4 connected to the target electrode 1;
  • a second level driver 5 connected to the driving electrode 3;
  • a first initialization switch 6 the first port of which is connected to the sensing electrode 2, and the second port of which is connected to the first reference level 7;
  • the integrating capacitor 8 is one or more shunt capacitors connected to the first port of the second initialization switch 9, connected to the second port of the charge transfer switch 7, and connected to the first input end of the voltage comparator 11;
  • a second initialization switch 9 having a first port connected to the integrating capacitor 8 and a second port connected to the second reference level 10;
  • a charge transfer switch 11 having a first port connected to the sensing electrode 2 and a second port connected to the integrating capacitor 8;
  • Comparator 12 the first input end of which is connected to the integrating capacitor 8, the second input end of which is connected to the third reference level 13, and the output end is the output of the sensor;
  • a third reference level 13 is coupled to the second input of comparator 12.
  • Figure 2 provides the timing relationship between the switch control signal and the level control signal:
  • Step 1 closing the first initialization switch 6, turning off the charge transfer switch 11, turning off the second initialization switch 9, the first level control signal 413 is low, and the second level control signal 523 is low;
  • Step 2 closing the second initialization switch 9;
  • Step 3 disconnecting the second initialization switch 9;
  • Step 4 disconnecting the first initialization switch 6;
  • Step 5 the first level control signal 413 is high, and the second level control signal 523 is high;
  • Step 6 closing the charge transfer switch 11;
  • Step 7 disconnecting the charge transfer switch 11;
  • Step 8 the first level control signal 413 is low, and the second level control signal 523 is low;
  • Step 9 closing the first initialization switch 6
  • Step 10 return to step 4.
  • Figure 3 provides a comparison of the family of potential variations of the integrating capacitor 4 and the third reference level 13.
  • the different values of the target capacitor 23 are such that the potential change curve of the integral capacitor 4 falls on different curves in the family of graphs, and the intersection of the intersection with the third reference level 13 on the time axis is different; the comparator 12 pairs the two Compare and flip at the intersection of the graph to output the edge of the transition.
  • Figure 4 provides an embodiment 1 of a first level driver 4 comprising an input level V11 411, an input level V12 412, a first level control signal 413, a first level selector 414, and a resistor 415.
  • the input level V11 411 is connected to the first input of the first level selector 414, and the input level is V12.
  • 412 is coupled to the second input of the first level selector 414
  • the first level control signal 413 is coupled to the first level selector 414 control terminal
  • the output of the first level selector 414 is coupled to the first port of the resistor 415
  • the second port of the resistor 415 is connected to the target electrode 1. among them:
  • the first level selector 414 outputs a first input level when the first level control signal 413 is low and a second input level when the level control signal 413 is high.
  • Figure 5 provides an embodiment 2 of the first level driver 4, including an input level V11 411, an input level V12 412, a first level control signal 413, a first level selector 414, and a capacitor 416.
  • the input level V11 411 is connected to the first input of the first level selector 414, and the input level is V12.
  • 412 is connected to the second input end of the first level selector 414
  • the first level control signal 413 is connected to the control terminal of the first level selector 414
  • the output end of the first level selector 414 is connected to the first electrode of the capacitor 416.
  • the second electrode of the capacitor 416 is connected to the target electrode 1. among them:
  • the first level selector 414 outputs a first input level when the first level control signal 413 is low and a second input level when the level control signal 413 is high.
  • Figure 6 provides an embodiment 3 of a first level driver 4 comprising a first level control signal 413, an inverter 417, a signal converter 418, a drive circuit 419, and a sensor ground level input 420.
  • the first level control signal 413 is connected to the input of the inverter 417, the output of the inverter 417 is connected to the input of the signal converter 418, the output of the signal converter 418 is connected to the control terminal of the driving circuit 419, and the output of the driving circuit 419 is connected to the sensor.
  • Level input terminal 420; target electrode 1 is floating or grounded. among them:
  • a signal converter 418 is configured to convert an input signal from a sensor ground level domain to a system ground level domain
  • Driver circuit 419 is used to amplify the input level and provide drive capability at the output.
  • Figure 7 provides an embodiment 1 of a second level driver 5 comprising an input level V21 521, an input level V22 522, a second level control signal 523, a second level selector 524.
  • the input level V21 521 is connected to the first input of the second level selector 524, and the input level is V22.
  • 522 is coupled to the second input of the second level selector 524, the second level control signal 523 is coupled to the second level selector 524 control terminal, and the second level selector 524 output is coupled to the drive electrode 3. among them:
  • the second level selector 524 outputs a first input level when the second level control signal 523 is low and a second input level when the level control signal 523 is high.
  • FIG. 8 provides an embodiment 2 of the second level driver 5, including an input level V21 521. Input level V21 The drive electrode 3 is connected to 521.
  • Figure 9 provides a schematic diagram of the capacitive fingerprint sensor grouping.
  • the target electrode 1, the sensing electrode 2, the driving electrode 3, the first level driver 4, the second level driver 5, the first initialization switch 6, and the first reference level 7 are used as the first unit circuit 111; 8.
  • the second initialization switch 9, the second reference level 10, the charge transfer switch 11, the comparator 12, and the third reference level 13 are used as the first multiplexing circuit. 112; the first unit circuit 111 is connected to the first port 1 of the first check switch group 113; the second port of the first check switch group 113 is connected to the first bus 114; the first bus 114 is connected to the first multiplexing circuit 112. among them:
  • the first check switch group 113 is a one-dimensional or two-dimensional switch group, and at most one switch is closed at any time;
  • Figure 10 provides a schematic diagram of the capacitive fingerprint sensor grouping.
  • the target electrode 1, the sensing electrode 2, the driving electrode 3, the first level driver 4, the second level driver 5, the first initialization switch 6, the first reference level 7, and the charge transfer switch 11 are used as the second unit circuit 121; the integration capacitor 8, the second initialization switch 9, the second reference level 10, the comparator 12, the third reference level 13 as the second multiplexing circuit 122; the second unit circuit 121 is connected to the second selection switch group
  • the first port of 123; the second port of the second check switch group 123 is connected to the second bus 124; the second bus 124 is connected to the second multiplexing circuit 122. among them:
  • the second check switch group 124 is a one- or two-dimensional switch group that closes at most one switch at any time.
  • Figure 11 provides a schematic diagram of the capacitive fingerprint sensor grouping.
  • the target electrode 1, the sensing electrode 2, the driving electrode 3, the first level driver 4, the second level driver 5, the first initialization switch 6, the first reference level 7, and the charge transfer switch 11 are used as the third unit circuit
  • the integration capacitor 8, the second initialization switch 9, and the second reference level 10 are used as the primary multiplexing circuit 132; the comparator 12 and the third reference level 13 are used as the secondary multiplexing circuit 133; and the third unit circuit 131 is connected to the first port of the primary switching switch group 134; the second port of the primary switching switch group 134 is connected to the third bus 135; the third bus 135 is connected to the primary multiplexing circuit 132; and the primary multiplexing circuit 132 is connected.
  • the first port of the secondary check switch group 136; the second port of the secondary check switch group 136 is connected to the fourth bus 137; and the fourth bus 137 is connected to the second multiplexing circuit 133. among them:
  • the first-level check switch group 134 is a plurality of sets of one-dimensional switch groups, and each group closes at most one switch at any time;
  • the secondary switching switch group 136 is a one-dimensional switch group, and at most one switch is closed at any time;
  • the secondary multiplexing circuit 133 may include a plurality of comparators 12 and a third reference level 13 pairing, the third reference level output levels of the different pairs being different.

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Abstract

基于电容值与电容电极间距离成反比的物理原理，可以通过测量物体表面到传感器表面电极阵列之间的耦合电容，来对物体表面空间结构成像，例如对指纹脊线谷线凹凸不平的空间特征成像。使用"C-Q-T"型电容指纹传感器，先将指纹与传感电极的耦合电容差异转换为电荷量差异，然后将电荷量差异转换为时间量差异，并输出携带该时间量差异的边沿信号。将指纹传感器成组为阵列，并对该边沿时间信号进行读出和数据组合，可对指纹成像。

Description

电容指纹传感器
本申请要求了申请日为2014年01月06日，申请号为201410004072.3，发明名称为“电容指纹传感器”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
【技术领域】
本发明涉及一种电容传感器，尤其涉及一种可组成阵列对指纹进行成像的电容指纹传感器。
【背景技术】
通过测量指纹脊线谷线和平面传感电极阵列单元间形成耦合电容的大小差异来对指纹进行成像的技术，最早见于专利 US4353056 A （ Simens, 1980 ）。 30 多年来，基于测量耦合电容来对指纹进行成像的传感器技术不断被提出，涉足该领域的著名企业曾有 Simens, AT&T Bell, Philips, Toshiba, ST, NEC, Motorola, Sharp, Intel, Epson 等，风险企业不计其数。
绝大部分电容指纹传感器技术路线基于宏观电容传感器电路原型来建立。但是，传感器领域的技术规律决定了，电容传感器是电路与传感器方程的结合体，电路尺度和实现工艺决定了传感器方程中各参变量的取值范围和公差范围。大部分可使用宏观尺度电子元器件组成的技术方案，当替换为微尺度电子元器件，其灵敏度、噪声特性将发生恶化。进一步，电容指纹传感器，作为一种阵列传感器，还对单元间失配敏感，而这正是微尺度电子元器件相对于宏观尺度电子元器件难以控制的。同时，由于测量电路往往尺寸较大，导致阵列传感器一般设计为单通道，各单元分时复用测量电路。为保证一定的图像帧率，延长采样时间这个传感器设计中重要的提高信号增益的方法在阵列传感器设计中受到很大局限，对于点数较多的单通道阵列传感器甚至不可行。
这些技术条件制约导致只有极少数技术路线有走向商用化的潜力；不符合客观规律要求的技术路线则走向消亡。到 2013 年，有一定应用规模的电容指纹传感器共有 3 个技术类别：射频响应型，测量射频反射信号的幅度，代表为美国 Authentec （ US5828773 A ）， 2012 年被 Apple 公司收购，最主要应用为 Apple 公司的 iPhone5S ；瞬态响应型，测量瞬态耦合的电平，代表为瑞典 Fingerprint Cards （ US 20080069413 A1 ），最主要应用为中国国有银行柜员系统；电荷转移型，代表为台湾 Egistec （ US7099497 B2 ），最主要应用为 Lenovo 公司的 ideaPad 。其中前两者被业界称为主动式，后一者被称为被动式，其共同特征是：将电容量转换为电压量以进行测量。从传感器的分类来看，这归类为' C-V '型传感器。
近年来，在千万像素级 CMOS 光电传感器领域，为适应越来越大的图像点数要求，从单通道向多通道发展。所谓多通道阵列传感器，实际上就是多个独立的单通道阵列传感器在空间上的组合。考虑到实际电路布局的限制，由于测量电路从一个变成多个，必须大幅度减小测量尺寸。' V-T '型 ADC 是一种新型的模数转换器，相对于直接型 ADC ，其优点是在同等幅度分辨率要求下电路尺寸大大减小，其缺点是需要更长的采样保持时间。多通道 CMOS 传感器往往采用' V-T '转换器，并在通道数、采样保持时间、电路尺寸三者之间权衡，以确定最佳的设计方案。
成都微阵列电子有限责任公司于 2012 年申请的发明专利《电容式距离传感器》（公开号 CN201210403271.2 ）中披露了一种新颖的' C-V-T '型电容式距离传感器。具体实现方法是，以指纹被测导体表面（目标电极），其与电容测量极板（传感电极）耦合形成的测量电容（目标电容）；被测导体表面（目标电极）到不同阵列单元的电容测量极板（传感电极）的距离有大有小，耦合形成的测量电容（目标电容）亦大小不同；电容耦合极板（驱动电极）受可编程电平生成器 1 （电平驱动器）驱动，使电容测量极板（传感电极）电位上升，上升程度因并联的测量电容（目标电容）大小不同而不同；参考电容（积分电容）先充满电荷然后向电平上升后的电容测量极板（传感电极）放电，因电容测量极板（传感电极）电位不同而放电程度不同；重复放电使参考电容（积分电容）电位持续下降，由于下降速率不同，通过可编程电平生成器 2 （参考电平）生成的阈值电平的时间不同，从而使比较器在不同时刻输出翻转；该比较器输出翻转的时间对应的放电次数即为电容式距离传感器的输出。
将该传感器的测量函数视为' S-C-V-T '，即，以指纹到传感电极的距离为自变量，以该时间向计数值作为的函数值，则该测量函数具备抗漂移、线性化的优势。结合该传感器技术方案在提高分辨率、抑制热噪声方面具备的天然优势，大大提高了最终性能表现。经流片验证，在同等工艺条件下技术水平高于 2012 年全球领先水平，但低于 2013 年全球领先水平，即 iPhone5S 所装载的 Touch ID 的技术水平。
由于 Apple 公司等企业对指纹传感器技术研发和应用的大力推动，消费电子市场对电容式指纹传感器技术提出了巨大的需求和更高的技术要求。本专利发明人对 CN201210403271.2 所披露的技术方案进行发展提高，建立并分析传感器灵敏度方程，一方面引入增大灵敏度的项和对应的电路，另一方面则对部分电路提出一般化的模型以及作出简化。
【发明内容】
本发明的目的是提供一种电容指纹传感器，与CN201210403271.2中披露的电容式距离传感器相比，灵敏度有大幅度的提高。
为达到上述目的，本发明提供了一种“C-Q-T”型电容传感器电路，包括“C-Q”转换器和“Q-T”转换器。对指纹进行成像的目的是进行指纹识别，所关心的是指纹脊线和谷线的空间差异；该空间差分量首先转换为指纹作为目标电极Pg和传感电极Ps耦合形成的目标电容Cg大小的差分；电容值差分通过“C-Q”转换器转换为传感电极Ps上电荷量的差分；“Q-T”转换器将传感电极Ps上的电荷逐次转移到积分电容Ct中，使积分电容Ct被充/放电，电荷量的差分被转换成充/放电速率的差分；由于充/放电速率不同，Ct的电位Vt从初始化电平变化到通过阈值电平Vref3的充/放电次数不同；使用比较器对Vt和Vref3进行比较，则比较器输出端发生跳变边沿的时间所对应的电荷转移次数即为电容量化值。本发明所提供的电容指纹传感器在比较器输出端输出跳变边沿，由相应的读出电路进行获取，并转换为电荷转移次数。成都微阵列电子有限责任公司2012年申请的《边沿时间读出电路》（公开号CN201210405080.X）中披露的边沿时间读出电路即可用于该途。
“C-Q”转换器包括：目标电极Pg（指纹）、传感电极Ps、驱动电极Pd、电平驱动器1、电平驱动器2、初始化开关1、参考电平1。将传感电极Ps和目标电极Pg之间耦合的电容称为目标电容Cg；将传感电极Ps与驱动电极Pd之间耦合的电容称为驱动电容Cd；将传感电极Ps与背景电路（例如衬底）耦合的电容称为背景电容Cb，由于背景电容Cb和驱动电容Cd同位于传感器内部且为并联关系，为简化表述，将背景电容Cb看作驱动电容Cd的一部分，并将Cd上的电压记为为Cb和Cd各自电压基于电容值的加权平均；初始化开关1端口1和传感电极Ps相连接；电平驱动器1和目标电极Pg相连接；电平驱动器2和驱动电极Pd相连接；参考电平1输出初始化电平Vref1，与初始化开关1端口2相连接。“C-Q”转换器的控制逻辑时序为：
步骤1-1，电平驱动器1输出电平V11至目标电极Pg；电平驱动器2输出电平V21至驱动电极Pd；
步骤1-2，闭合初始化开关1，将传感电极Ps连接参考电平1；
步骤1-3，断开初始化开关1；
步骤1-4，电平驱动器1输出电平V12至目标电极Pg；电平驱动器2输出电平V22至驱动电极Pd；
步骤1-5，回到步骤1-1。
在步骤1-2中，传感电极Ps的电位为初始化电平Vref1；在步骤1-4中，由于传感电极Pg处于悬空状态，目标电极Pg和驱动电极Pd的电位变化将电荷耦合入传感电极Pg；定义步骤1-4时刻传感电极Ps的电位为Vs，根据电荷守恒，有：
(Vref1-V11)*Cg + (Vref1-V21)*Cd = (Vs-V12)*Cg + (Vs-V22)*Cd (1)
式(1)可转换为：
(Vs-Vref1)*(Cd+Cg) = (V12-V11)*Cg + (V22-V21)*Cd (2)
定义ΔV1=V12-V11，ΔV2=V22-V21
Vs-Vref1 = (ΔV1*Cg + ΔV2*Cd) / (Cd+Cg) (3)
为方便代入，转换为Vs的表达形式：
Vs = (ΔV1*Cg + ΔV2*Cd) / (Cd+Cg) + Vref1 (4)
“Q-T”转换器包括：积分电容Ct、初始化开关2、参考电平2、电荷转移开关、比较器、第三参考电平。积分电容Ct与初始化开关2端口1、电荷转移开关端口2、比较器输入端1相连接；参考电平2输出初始化电平Vref2，与初始化开关端口2相连接；电荷转移开关端口1和“C-Q”转换器中的传感电极Pg相连接；第三参考电平输出阈值电平Vref3，与比较器输入端2相连接。“Q-T”转换器的控制逻辑时序为：
步骤2-1，闭合初始化开关2，将积分电容Ct连接参考电平2；
步骤2-2，断开初始化开关2；
步骤2-3，如果“C-Q”转换器处于步骤1-4，则锁定“C-Q”转换器在步骤1-4；
步骤2-4，闭合电荷转移开关；
步骤2-5，断开电荷转移开关；
步骤2-6，解除对“C-V”转换器的锁定；
步骤2-7，如果“C-Q”转换器离开步骤1-4，回到步骤2-3。
比较器输入端1连接积分电容Ct，比较器输入端2连接第三参考电平，以将积分电容Ct的电位Vt与第三参考电平输出的阈值电平Vref3进行比较，并输出比较结果，作为“Q-T”转换器的输出，亦“C-Q-T”传感器的输出。
传感器输出所携带的时间信息T是电荷转移迭代过程的积分结果，T(Cg)不存在强解，而弱解表达式没有进行分析的价值，只能通过间接表达式进行分析。令积分电容Ct的电平为Vt；Vt从Vref2逐渐变化至Vs，T(Cg)取使Vt’(Cg)在T上积分为δ(Vs-Vref2)的区间长度，其中δ<1；对于一定的量化位长，并不能无限制的增大T(Cg)来提高T’(Cg)，所以应提高T’(Cg)/T(Cg)的相对值。由于Vt’(Cg)到T(Cg)的映射的弱解的最高阶项为指数下降函数，所以Vt’(Cg)到T(Cg)是单调减函数，Vt’’(Cg)到T’(Cg)也是单调减函数；可以使用Vt’’(Cg)/Vt’(Cg)来替代T’(Cg)/T(Cg)以进行灵敏度分析。
令积分电容Ct由Vt经一次电荷转移变为Vt+Vt’，由于电荷守恒：
(Vt+Vt’) * (Ct+Cd+Cg ) = Vt*Ct + Vs*(Cd+Cg) (5)
转换为：
Vt’ = (Vs-Vt)*(Cd+Cg) / (Ct+Cd+Cg) (6)
式(4)代入式(6)，得：
Vt’(Cg) = ( (ΔV2+Vref1-Vt)*Cd + (ΔV1+Vref1-Vt)*Cg ) / (Ct+Cd+Cg) (7)
对Cg求导，并化简为：
Vt’’(Cg) = ( (ΔV1+Vref1-Vt)*Ct + (ΔV1-ΔV2)*Cd ) / (Ct+Cd+Cg)^2 (8)
从式(7)和式(8)中能判断单个参变量的增减对Vt’(Cg)和Vt’’(Cg)的影响力的方向和阶数；同时还要兼顾对Vs-Vref2的影响，使其保持在合适的范围以使T(Cg)的取值区间为所期望
Vs–Vref2 = (ΔV1*Cg+ΔV2*Cd) / (Cd+Cg) + Vref1 – Vref2 (9)
结合对式(7)、(8)、(9)的分析，并综合考虑微型电子元器件特性、工艺平台特性以及各种设计约束，可以得到最优化的电路设计方案。与电路构造有关的方程特性如下：
一般有Ct>>Cd，对于目标电容极小的情形还有Cd>>Cg；ΔV1在式(8)中影响分子主要项（基于Ct>>Cd），在式(7)和式(9)中则影响分子的次要项，所以增大ΔV1对传感器灵敏度的提高是显著的。本发明和CN201210403271.2所述技术方案相比，最重要的技术进步就是引入了电平驱动器1来从目标电极Pg向传感电极Ps耦合电荷。与ΔV1==0的情形相比，式(8)约被提高到了(ΔV1+Vref1-Vt) / (Vref1-Vt)倍。
式(7) 、(8)、(9)中只出现了ΔV1和ΔV2，与V11、V12、V21和V22的绝对值无关。所以电平驱动器1和目标电极Pg之间，以及电平驱动器2和驱动电极Pd之间，可以用电容隔离直流只传递交流分量。特别的，使目标电极Pg获得ΔV1交流分量，可以通过向传感器地电平耦合与ΔV1反向的交流电平分量来达到同样的效果。
结合式(7) 、(8)、(9)综合分析，ΔV2相对于ΔV1的影响力小得多，即使ΔV2恒等于0，导致传感器灵敏度的下降也微乎其微。所以本发明允许将电平驱动器2实现为与传感器地电平连接。这正是“C-Q”型和“C-V”型的本质区别：如果把CN201210403271.2 所披露的电路中与本发明电平驱动2相对应的可编程电平生成器1也实现为与传感器地电平连接，则“C-V”部分将始终输出地电平。
通过建立和分析传感器方程，发明人提出了“C-Q-T”型电容指纹传感器的电路技术方案和实施范围。本发明所提供的电容指纹传感器用于组成阵列以对指纹进行成像，在单通道成组时使用多个“C-Q”转换器分时复用一个“Q-T”转换器，在多通道成组时将多组单通道“C-Q-T”传感器阵列并排并行工作。
【附图说明】
图1是本发明提供的电容指纹传感器电路原理图；
图2是本发明提供的开关控制信号和电平控制信号图；
图3是本发明提供的积分电容电位曲线族与阈值电平对比图；
图4是本发明提供的电平驱动器1的实施例1；
图5是本发明提供的电平驱动器1的实施例2；
图6是本发明提供的电平驱动器1的实施例3；
图7是本发明提供的电平驱动器2的实施例1；
图8是本发明提供的电平驱动器2的实施例2；
图9是本发明提供的电容指纹传感器成组原理图1；
图10是本发明提供的电容指纹传感器成组原理图2；
图11是本发明提供的电容指纹传感器成组原理图3。
【具体实施方式】
如图1所示，本发明所提供的电路，包括目标电极1、传感电极2、驱动电极3、第一电平驱动器4、第二电平驱动器5、第一初始化开关6、第一参考电平7、积分电容8、第二初始化开关9、第二参考电平10、电荷转移开关11、比较器12、第三参考电平13。其中：
传感电极2，为一个或多个电极，与第一初始化开关6的第一端口连接，与电荷转移开关7的第一端口连接；
目标电极1，为测量目标表面，与第一电平驱动器4连接，位于传感电极2上方，与传感电极2之间有介质层，目标电极1与传感电极2之间形成目标电容21；
驱动电极3，为一个或多个电极，与第二电平驱动器5连接，位于传感电极2下方，与传感电极2之间有介质层，驱动电极3与传感电极2之间形成驱动电容23；
第一电平驱动器4，与目标电极1连接；
第二电平驱动器5，与驱动电极3连接；
第一初始化开关6，其第一端口与传感电极2连接，其第二端口与第一参考电平7连接；
第一参考电平7，与第一初始化开关6的第二端口连接；
积分电容8，为1个或多个并联电容器，与第二初始化开关9的第一端口连接，与电荷转移开关7的第二端口接，与电压比较器11的第一输入端连接；
第二初始化开关9，其第一端口与积分电容8连接，其第二端口与第二参考电平10连接；
第二参考电平10，与第二初始化开关9的第二端口连接；
电荷转移开关11，其第一端口与传感电极2连接，其第二端口与积分电容8连接；
比较器12，其第一输入端与积分电容8连接，其第二输入端与第三参考电平13连接，输出端是传感器的输出；
第三参考电平13，与比较器12的第二输入端连接。
图2提供了开关控制信号和电平控制信号间的时序关系：
步骤1，闭合第一初始化开关6，断开电荷转移开关11，断开第二初始化开关9，第一电平控制信号413为低，第二电平控制信号523为低；
步骤2，闭合第二初始化开关9；
步骤3，断开第二初始化开关9；
步骤4，断开第一初始化开关6；
步骤5，第一电平控制信号413为高，第二电平控制信号523为高；
步骤6，闭合电荷转移开关11；
步骤7，断开电荷转移开关11；
步骤8，第一电平控制信号413为低，第二电平控制信号523为低；
步骤9，闭合第一初始化开关6；
步骤10，回到步骤4。
图3提供了积分电容4电位变化曲线族和第三参考电平13的对比图。目标电容23的不同取值，使积分电容4电位变化曲线落在图示曲线族中不同的曲线上，与第三参考电平13的交点在时间轴上的投影不同；比较器12对两者进行比较，并在图示交点时刻翻转，输出跳变边沿。
图4提供了第一电平驱动器4的实施例1，包括输入电平V11 411，输入电平V12 412，第一电平控制信号413，第一电平选择器414，电阻器415。输入电平V11 411连接第一电平选择器414的第一输入端，输入电平V12 412连接第一电平选择器414的第二输入端，第一电平控制信号413连接第一电平选择器414控制端，第一电平选择器414输出端连接电阻器415的第一端口，电阻器415的第二端口连接目标电极1。其中：
第一电平选择器414在第一电平控制信号413为低时输出第一输入端电平，在电平控制信号413为高时输出第二输入端电平。
图5提供了第一电平驱动器4的实施例2，包括输入电平V11 411，输入电平V12 412，第一电平控制信号413，第一电平选择器414，电容器416。输入电平V11 411连接第一电平选择器414的第一输入端，输入电平V12 412连接第一电平选择器414的第二输入端，第一电平控制信号413连接第一电平选择器414控制端，第一电平选择器414输出端连接电容器416的第一电极，电容器416的第二电极连接目标电极1。其中：
第一电平选择器414在第一电平控制信号413为低时输出第一输入端电平，在电平控制信号413为高时输出第二输入端电平。
图6提供了第一电平驱动器4的实施例3，包括第一电平控制信号413、反向器417、信号转换器418、驱动电路419、传感器地电平输入端420。第一电平控制信号413连接反向器417输入端，反向器417输出端连接信号转换器418输入端，信号转换器418输出端连接驱动电路419控制端，驱动电路419输出端连接传感器地电平输入端420；目标电极1悬空或接地。其中：
信号转换器418用于将输入信号从传感器地电平域转换到系统地电平域；
驱动电路419用于将输入端电平放大并在输出端提供驱动能力。
图7提供了第二电平驱动器5的实施例1，包括输入电平V21 521，输入电平V22 522，第二电平控制信号523，第二电平选择器524。输入电平V21 521连接第二电平选择器524的第一输入端，输入电平V22 522连接第二电平选择器524的第二输入端，第二电平控制信号523连接第二电平选择器524控制端，第二电平选择器524输出端连接驱动电极3。其中：
第二电平选择器524在第二电平控制信号523为低时输出第一输入端电平，在电平控制信号523为高时输出第二输入端电平。
图8提供了第二电平驱动器5的实施例2，包括输入电平V21 521。输入电平V21 521连接驱动电极3。
图9提供了电容指纹传感器成组原理图1。将目标电极1、传感电极2、驱动电极3、第一电平驱动器4、第二电平驱动器5、第一初始化开关6、第一参考电平7作为第一单元电路111；将积分电容8、第二初始化开关9、第二参考电平10、电荷转移开关11、比较器12、第三参考电平13作为第一复用电路 112；第一单元电路111连接第一复选开关组113的第一端口1；第一复选开关组113的第二端口连接第一总线114；第一总线114连接第一复用电路 112。其中：
第一复选开关组113为一维或二维开关组，在任意时刻至多闭合1个开关；
图10提供了电容指纹传感器成组原理图2。将目标电极1、传感电极2、驱动电极3、第一电平驱动器4、第二电平驱动器5、第一初始化开关6、第一参考电平7、电荷转移开关11作为第二单元电路121；将积分电容8、第二初始化开关9、第二参考电平10、比较器12、第三参考电平13作为第二复用电路122；第二单元电路121连接第二复选开关组123的第一端口；第二复选开关组123的第二端口连接第二总线124；第二总线124连接第二复用电路122。其中：
第二复选开关组124为一维或二维开关组，在任意时刻至多闭合1个开关。
图11提供了电容指纹传感器成组原理图3。将目标电极1、传感电极2、驱动电极3、第一电平驱动器4、第二电平驱动器5、第一初始化开关6、第一参考电平7、电荷转移开关11作为第三单元电路131；将积分电容8、第二初始化开关9、第二参考电平10作为一级复用电路132；将比较器12、第三参考电平13作为二级复用电路133；第三单元电路131连接一级复选开关组134的第一端口；一级复选开关组134的第二端口连接第三总线135；第三总线135连接一级复用电路132；一级复用电路132连接二级复选开关组136的第一端口；二级复选开关组136的第二端口连接第四总线137；第四总线137连接二级复用电路133。其中：
一级复选开关组134为多组一维开关组，每组在任意时刻至多闭合1个开关；
二级复选开关组136为一维开关组，在任意时刻至多闭合1个开关；
二级复用电路133可包括多个比较器12和第三参考电平13配对，不同配对的第三参考电平输出电平不同。
本发明并非狭义地限制于上述实施例，而包括了说明书中基于理论推导所指出的电路实现形式的所有组合；在不超出本发明的精神与权利要求书范围的情况下，所做的种种变化实施，仍属于本发明的范围。

Claims (14)

  1. 一种电容指纹传感器，由目标电极、传感电极、驱动电极、第一电平驱动器、第二电平驱动器、第一初始化开关、第一参考电平、积分电容、第二初始化开关 、第二参考电平、电荷转移开关、比较器、第三参考电平构成，其特征在于：
    传感电极，为一个或多个电极，与初始化开关1的第一端口连接，与电荷转移开关的第一端口连接；
    目标电极，为测量目标表面，与第一电平驱动器连接，位于传感电极上方，与传感电极之间有介质层，目标电极与传感电极之间形成目标电容；
    驱动电极，为一个或多个电极，与第二电平驱动器连接，位于传感电极下方，与传感电极之间有介质层，驱动电极与传感电极之间形成驱动电容；
    第一电平驱动器，与第一电平控制信号连接，与目标电极连接；
    第二电平驱动器，与第二电平控制信号连接，与驱动电极连接；
    第一初始化开关，其第一端口与传感电极连接，其第二端口与第一参考电平连接；
    第一参考电平，与第一初始化开关的第二端口连接；
    积分电容，为1个或多个并联电容器，与第二初始化开关的第一端口连接，与电荷转移开关的第二端口连接，与电压比较器的第一输入端连接；
    第二初始化开关 ，其第一端口与积分电容连接，其第二端口与第二参考电平2连接；
    第二参考电平，与第二初始化开关的第二端口连接；
    电荷转移开关，其第一端口与传感电极连接，其第二端口与积分电容连接；
    比较器，其第一输入端与积分电容连接，其第二输入端与第三参考电平连接，输出端是传感器的输出；
    第三参考电平，与比较器的第二输入端连接。
  2. 如权利要求1所述电容指纹传感器，其特征在于，所述电平驱动器1在第一电平控制信号为低时通过电阻器向目标电极输出电平V11，在第一电平控制信号为高时通过电阻器向目标电极输出电平V12。
  3. 如权利要求2所述电容指纹传感器，其特征在于，所述第一电平驱动器在第一电平控制信号为低时向电容器输出电平V11，在第一电平控制信号为高时向电容器输出电平V12，电容器向目标电极耦合输出V11和V12的交流分量。
  4. 如权利要求3所述电容指纹传感器，其特征在于，所述第一电平驱动器向传感器地电平输出端输出与V11和V12交流分量反相的交流电平。
  5. 如权利要求1所述电容指纹传感器，其特征在于，所述第二电平驱动器在第二电平控制信号为低时向驱动电极输出电平V21，在第二电平控制信号为高时向驱动电极输出电平V22。
  6. 如权利要求5所述电容指纹传感器，其特征在于，所述第二电平驱动器向驱动电极输出电平V21。
  7. 如权利要求1所述电容指纹传感器，其特征在于，第一初始化开关、第二初始化开关 、电荷转移开关、第一电平控制信号、第二电平控制信号的控制时序为：
    步骤1，闭合第一初始化开关，断开电荷转移开关，断开第二初始化开关 ，第一电平控制信号为低，第二电平控制信号为低；
    步骤2，闭合第二初始化开关 ；
    步骤3，断开第二初始化开关 ；
    步骤4，断开第一初始化开关；
    步骤5，第一电平控制信号为高，第二电平控制信号为高；
    步骤6，闭合电荷转移开关；
    步骤7，断开电荷转移开关；
    步骤8，第一电平控制信号为低，第二电平控制信号为低；
    步骤9，闭合第一初始化开关；
    步骤10，回到步骤4。
  8. 如权利要求7所述电容指纹传感器，其特征在于，其控制时序包括由步骤1-3组成的初始化阶段和步骤4-10组成的电荷转移阶段。
  9. 如权利要求8所述电容指纹传感器，其特征在于，在电荷转移阶段，所述积分电容的电位发生单向变化。
  10. 如权利要求9所述电容指纹传感器，其特征在于，所述积分电容的电位的单向变化，当从高于第三参考电平变到低于第三参考电平，或从低于第三参考电平变到高于第三参考电平，将导致所述比较器输出端翻转，产生传感器输出。
  11. 如权利要求1所述电容指纹传感器，其特征在于，组成阵列时，以目标电极、传感电极、驱动电极、第一电平驱动器、第二电平驱动器、第一初始化开关、第一参考电平组成单元电路，以积分电容、第二初始化开关 、第二参考电平、电荷转移开关、比较器、第三参考电平组成复用电路。
  12. 如权利要求1所述电容指纹传感器，其特征在于，组成阵列时，以目标电极、传感电极、驱动电极、第一电平驱动器、第二电平驱动器、第一初始化开关、第一参考电平、电荷转移开关组成单元电路，以积分电容、第二初始化开关 、第二参考电平、比较器、第三参考电平组成复用电路。
  13. 如权利要求12所述电容指纹传感器，其特征在于，组成阵列时，以目标电极、传感电极、驱动电极、第一电平驱动器、第二电平驱动器、第一初始化开关、第一参考电平、电荷转移开关组成单元电路，以积分电容、第二初始化开关 、第二参考电平组成一级复用电路，以比较器、第三参考电平组成二级复用电路。
  14. 如权利要求13所述电容指纹传感器，其特征在于，所述二级复用电路包括一个或多个比较器、参考电平的配对，且当包括多个比较器、参考电平的配对时，不同配对的第三参考电平输出电平不同。
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TWI531979B (zh) 2016-05-01
CN103714330B (zh) 2017-12-19
KR20160087389A (ko) 2016-07-21
US10289890B2 (en) 2019-05-14
EP3093796B1 (en) 2022-05-11
US20180225496A1 (en) 2018-08-09
KR102010638B1 (ko) 2019-10-21
CN103714330A (zh) 2014-04-09
US20160328592A1 (en) 2016-11-10
EP3093796A1 (en) 2016-11-16
TW201528154A (zh) 2015-07-16
US9953200B2 (en) 2018-04-24

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