CN107704852A - Capacitive fingerprint sensor circuit and inductor - Google Patents

Capacitive fingerprint sensor circuit and inductor Download PDF

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Publication number
CN107704852A
CN107704852A CN201711156322.5A CN201711156322A CN107704852A CN 107704852 A CN107704852 A CN 107704852A CN 201711156322 A CN201711156322 A CN 201711156322A CN 107704852 A CN107704852 A CN 107704852A
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China
Prior art keywords
amplifier
input
feedback
sensor circuit
driving source
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CN201711156322.5A
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Chinese (zh)
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张均军
詹昶
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深圳市汇顶科技股份有限公司
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Priority to CN201410105847.6A priority Critical patent/CN104217193B/en
Priority to CN201711156322.5A priority patent/CN107704852A/en
Publication of CN107704852A publication Critical patent/CN107704852A/en
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    • GPHYSICS
    • G06COMPUTING; CALCULATING; COUNTING
    • G06KRECOGNITION OF DATA; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K9/00Methods or arrangements for reading or recognising printed or written characters or for recognising patterns, e.g. fingerprints
    • G06K9/00006Acquiring or recognising fingerprints or palmprints
    • G06K9/00013Image acquisition
    • G06K9/0002Image acquisition by non-optical methods, e.g. by ultrasonic or capacitive sensing

Abstract

The present invention is applied to fingerprint recognition field, provide a kind of capacitive fingerprint sensor circuit and inductor, sensor circuit includes cancellation module and feedback amplifier, the first input end of cancellation module is connected with the first external driving source, second input of cancellation module is connected by being pressed against the finger of second input with the second external driving source, the output end of cancellation module and the input of feedback amplifier connect, first external driving source and the signal of the second external driving source output are anti-phase each other, first external driving source is linked into the signal of cancellation module and the second external driving source is coupled to the signal generation counteracting of cancellation module, obtain the fingerprint induced signal related to fingerprint depth, the output end of feedback amplifier exports amplified fingerprint induced signal.The capacitive fingerprint sensor circuit and inductor of the embodiment of the present invention have been decayed the part unrelated with fingerprint by external driving source anti-phase each other and cancellation module, only amplify difference mode signal, improve the sensitivity of fingerprint sensing.

Description

Capacitive fingerprint sensor circuit and inductor

Technical field

The invention belongs to fingerprint recognition field, more particularly to a kind of capacitive fingerprint sensor circuit and inductor.

Background technology

The finger lines of people has depth difference, and convex place is referred to as " peak (ridge) ", and recessed place is referred to as " paddy (valley)”.Capacitance type fingerprint induction system is of different sizes using inductance capacitance corresponding to " peak " and " paddy " included on fingerprint, The amplitude of output signal also different principle, the image information at " peak " and " paddy " is converted under same AC signal excitation Corresponding electric signal.

To prevent from touching electrostatic damage of the process to fingerprint inductor repeatedly, and mechanical strength is improved, need to be in fingerprint sense Device surface is answered to place nonconducting thick dielectric layer (cover), so as to produce dielectric layer relevant capacitor (common mode part);Other fingerprint Depth is that fingerprint " peak " and " paddy " produce the electric capacity related to depth of lines, and both constitute finger to sensor sensing electrode Coupled capacitor (differential-mode portion).Prior art is as shown in figure 1, by charge amplifier by differential-mode portion and the summation of common mode part Directly amplify, differential-mode portion ratio very little shared in the summation, such differential-mode portion can be submerged in summation, it is not easy to point The difference of " peak " and " paddy " is discerned, i.e. the sensitivity of fingerprint inductor is relatively low.

The content of the invention

The purpose of the embodiment of the present invention is to provide a kind of capacitive fingerprint sensor circuit and inductor, it is intended to solves existing The problem of fingerprint inductor poor sensitivity.

The embodiment of the present invention is achieved in that a kind of capacitive fingerprint sensor circuit, including cancellation module and feedback amplify Device, the first input end of the cancellation module are connected with the first external driving source, and the second input of the cancellation module passes through The finger for being pressed against second input is connected with the second external driving source, and the output end of the cancellation module is put with the feedback The signal of the input connection of big device, the first external driving source and the second external driving source output is anti-phase each other, institute State that the first external driving source is sent to the signal of the cancellation module and the described second external driving source is coupled to the counteracting mould The signal of block produces counteracting, obtains the fingerprint induced signal related to fingerprint depth, the output end output of the feedback amplifier Amplified fingerprint induced signal.

Further, the cancellation module includes inductance capacitance and offsets electric capacity, and the input of the inductance capacitance is institute The second input of cancellation module is stated, the output end of the inductance capacitance is connected with the output end of the counteracting electric capacity, described to support The input that electric eliminating is held is the first input end of the cancellation module, the inductance capacitance and the tie point for offsetting electric capacity For the output end of the cancellation module.

Further, the second input of the cancellation module includes induction plate, between finger and the induction plate Isolated by dielectric layer, form the inductance capacitance, the first input end of the cancellation module, which includes, offsets pole plate, the sensing The counteracting electric capacity is formed between pole plate and the counteracting pole plate.

Further, the induction plate and the counteracting pole plate are formed by metal level.

Further, the feedback amplifier is current amplifier, and the current amplifier includes the first low noise amplifier And it is connected to the resistance between the input of first low noise amplifier and output end.

Further, the feedback amplifier is charge amplifier, and the charge amplifier includes the second low noise amplifier And it is connected to the feedback capacity between the input of second low noise amplifier and output end.

Further, the feedback amplifier also includes being connected to first low noise amplifier or second low noise Reset switch between the input and output end of amplifier.

Further, the capacitive fingerprint sensor circuit also includes driving amplifier and offsets amplifier, and the driving is put The input of big device is connected with external driving source, and the output end of the driving amplifier is defeated with being pressed against the cancellation module second Enter the finger connection at end;The input for offsetting amplifier is connected with the external driving source, described to offset the defeated of amplifier Go out end to be connected with the first input end of the cancellation module;The gain of the driving amplifier and the counteracting amplifier is anti-phase.

The present invention also proposes a kind of capacitive fingerprint inductor, and the capacitive fingerprint inductor includes multiple pixel cells, often The corresponding capacitive fingerprint sensor circuit of individual pixel cell, the capacitive fingerprint sensor circuit are any electric capacity as described above Fingerprint sensor circuit.

Further, the capacitive fingerprint inductor also includes driving amplifier and offsets amplifier, the drive amplification The input of device is connected with external driving source, and the output end of the driving amplifier is with being pressed against each capacitive fingerprint sensor circuit Cancellation module the second input finger connection, it is described offset amplifier input be connected with the external driving source, The output end for offsetting amplifier is connected with the first input end of the cancellation module of each capacitive fingerprint sensor circuit, the drive The gain of dynamic amplifier and the counteracting amplifier is anti-phase.

The part of the invention unrelated with fingerprint of having been decayed by external driving source anti-phase each other and cancellation module, only amplifies The difference mode signal related to fingerprint depth, therefore the amplifier of subsequent cascaded is not easy saturation, reduces the reality of fingerprint inductor Existing difficulty, improves the sensitivity of fingerprint inductor.Further, the gain of amplifier is offset by changing, is suitable for difference The dielectric layer of thickness and material, improve the compatibility of fingerprint sensor.Due to introducing the electricity of the stable induction plate of feedback amplifier Pressure, therefore signal processing is unrelated with the parasitic capacitance of induction electrode, improves system reliability, and the electric capacity in the present invention refers to Line sensor circuit is simple for structure, compatibility standard CMOS technology, and integrated cost is low.

Brief description of the drawings

Fig. 1 is the circuit diagram of the fingerprint inductor of prior art.

Fig. 2 is the circuit diagram for the capacitive fingerprint sensor circuit that the embodiment of the present invention one provides.

Fig. 3 is another circuit diagram for the capacitive fingerprint sensor circuit that the embodiment of the present invention one provides.

Fig. 4 is the structure chart for the capacitive fingerprint sensor circuit that the embodiment of the present invention one provides.

Fig. 5 is another structure chart for the capacitive fingerprint sensor circuit that the embodiment of the present invention one provides.

Fig. 6 is the circuit diagram for the capacitive fingerprint inductor that the embodiment of the present invention two provides.

Embodiment

In order to make the purpose , technical scheme and advantage of the present invention be clearer, it is right below in conjunction with drawings and Examples The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and It is not used in the restriction present invention.

Embodiment one

The embodiment of the present invention one proposes a kind of capacitive fingerprint sensor circuit.As shown in Fig. 2 the electric capacity of the embodiment of the present invention one Fingerprint sensor circuit includes cancellation module 10 and feedback amplifier 20, the first input end of cancellation module 10 and the first external driving Source VS1 connections, the second input of cancellation module 10 pass through the external driving source of finger and second that is pressed against second input VS2 connections, the output end of cancellation module 10 are connected with the input of feedback amplifier 20, the first external driving source VS1 and second The signal of external driving source VS2 outputs is anti-phase each other, and the first external driving source VS1 is sent to the signal and second of cancellation module 10 The signal that external driving source VS2 is coupled to cancellation module 10 produces counteracting, obtains the fingerprint induced signal related to fingerprint depth, The output end of feedback amplifier 20 exports amplified fingerprint induced signal.In the embodiment of the present invention one, feedback amplifier 20 can be current amplifier or charge amplifier, for convenience of explanation, be illustrated by taking charge amplifier 20 as an example.

The embodiment of the present invention one is operated by the counteracting of cancellation module 10, declined before finger coupled signal is amplified first Subtract the signal section unrelated with fingerprint, then amplify the small-signal part related to lines by charge amplifier 20, then it is defeated Go out to the other parts of fingerprint inductor to be amplified, the operation such as analog-to-digital conversion, image mosaic, extract effective fingerprint letter Breath, realizes the processing to fingerprint signal.

As shown in figure 3, cancellation module 10 includes inductance capacitance Cs and offsets electric capacity Cc.Inductance capacitance Cs input be to Second input of the module that disappears 10, inductance capacitance Cs output end are connected with offsetting electric capacity Cc output end, offset electric capacity Cc's Input is the first input end of cancellation module 10, and inductance capacitance Cs and the tie point for offsetting electric capacity Cc are the defeated of cancellation module 10 Go out end.

Charge amplifier 20 includes the second low noise amplifier (Low Noise Amplifier, LNA) 107 and is connected to Feedback capacity Cfb between the input and output end of second low noise amplifier 107.Charge amplifier 20, which may also include, to be connected to Reset switch SW between the input and output end of second low noise amplifier 107, for that will input and export in reseting stage Node voltage is set to bias voltage.

In the embodiment of the present invention one, capacitive fingerprint sensor circuit may also include driving amplifier 101 and offset amplifier 102, the input of driving amplifier 101 is connected with external driving source VS, and output end is with being pressed against the input of cancellation module 10 second The finger connection at end, the input for offsetting amplifier 102 are connected with external driving source VS, output end and the first of cancellation module 10 Input connects, and the gain of driving amplifier 101 and counteracting amplifier 102 is anti-phase.

The structure chart of capacitive fingerprint sensor circuit is as shown in figure 4, wherein comprising induction plate 201, offset pole plate 202 and anti- Pole plate 203 is presented, is isolated between finger and induction plate 201 by the dielectric layer 204 of insulation, when finger contacts or be pressed against fingerprint When on a certain pixel cell of inductor, inductance capacitance Cs is formed between finger and induction plate, induction plate 201 is with offsetting pole Formed between plate 202 and offset electric capacity Cc, fed back and feedback capacity Cfb is formed between pole plate 203 and induction plate 202.In order to improve The integrated level of circuit, induction plate 201, pole plate 202 and feedback pole plate 203 is offset using metal level composition.

It can be seen from the calculation formula of capacity plate antenna, inductance capacitance Cs capacitance and the dielectric constant of insulating materials are into just Than the distance between upper bottom crown is inversely proportional, therefore inductance capacitance Cs is of different sizes corresponding to the peak and valley of finger, induced electricity Two parts can be divided into by holding Cs:Common mode part (factor such as material, thickness to the dielectric layer 204 of insulation is related);Differential-mode portion (with The depth of fingerprint lines is related).The signal for being coupled to induction plate 201 also divides into common mode part and differential mode portion accordingly Point, and the capacitance difference of finger lines peak and valley is effective detected object of fingerprint sensor circuit.

In the embodiment of the present invention one, driving amplifier 101, finger, inductance capacitance Cs form coupled signal vias, and counteracting is put Big device 102, electric capacity Cc composition offseting signal paths are offset, both are connected to induction plate 201, are re-fed into the second low noise amplifier 107 carry out signal amplification.In finger the electricity related to finger lines is distinguished into the weaker coupled capacitor of fingerprint sensor circuit Hold, and retain the half-tone information of peak valley.

Specifically, when finger touches the surface of fingerprint sensor circuit, external driving source VS is through overdriven amplifier 101 It is loaded into after A1 times of amplification on finger, and induction plate 201 is coupled to by inductance capacitance Cs.Meanwhile external driving source VS warps Offset and be coupled to induction plate 201 by offsetting electric capacity Cc after amplifier 102 amplifies A2 times.After two Signal averagings, coupling The common mode part of signal is partially or completely counteracting, and differential-mode portion is sent into the negative input end of the second low noise amplifier 107.

Feedback capacity Cfb is connected between negative input end and the output of the second low noise amplifier 107, due to the second LNA The negative feedback of big device 107, the voltage of induction plate 201 keep constant, and inductance capacitance Cs and counteracting electric capacity Cc electric charge are asked Afterwards, it is transferred on feedback capacity Cfb, obtains output voltage VO UT.

Reset switch SW is connected between the input and output of the second low noise amplifier 107, reseting stage will input and Output node voltage is set to bias voltage VCM.

To further illustrate the negative function of the cancellation module 10 of the embodiment of the present invention one, the meter of relevant parameter is listed below Calculate.

The coupled capacitor of fingerprint to induction plate 201 is relevant with the pressing situation of dielectric layer and finger.If finger with The surface contact of fingerprint sensor circuit is close, then coupled capacitor depends primarily on the dielectric constant, thickness and sensing of dielectric layer The area of pole plate 201.If peak valley and the contact defective tightness of fingerprint sensor circuit, have the air related to pressing situation to be situated between Matter capacitive part.Assuming that inductance capacitance corresponding to the peak of finger is Csr, inductance capacitance corresponding to paddy is Csv, and both differences are Δ Cs, i.e. Csv=Csr+ Δs Cs.

The electric charge that external driving source VS is coupled to induction plate 201 by coupled signal vias is:Vs*A1*Cs.

Electric charge by offseting signal vias couple to induction electrode 201 is:Vs*A2*Cc.

Due to the presence of negative-feedback, the voltage of induction plate 201 keeps constant, and parasitic capacitance Cg electric charge is constant, is not involved in Signal amplification process.

After the completion of electric charge shifts between inductance capacitance Cs, counteracting electric capacity Cc and feedback capacity Cfb, output voltage is:

Vout=(VS*A1*Cs+VS*A2*Cc)/Cfb;

Output voltage is corresponding to peak:Voutr=(VS*A1*Csr+VS*A2*Cc)/Cfb;

Output voltage is corresponding to paddy:

Voutv=(VS*A1*Csv+VS*A2*Cc)/Cfb=(VS*A1*Csr+VS*A2*Cc)/Cfb+VS*A1* Δs Cs/ Cfb;

Voutc=(VS*A1*Csr+VS*A2*Cc)/Cfb is recorded, is common mode part;Voutd=VS*A1* Δ Cs/Cfb, For differential-mode portion.The gray scale being only concerned due to finger print information between peak valley, therefore by adjusting A2 so that A2*Cc=-A1*Csr (it can thus be appreciated that A1 and A2 symbol is on the contrary, the gain of i.e. driving amplifier 101 and counteracting amplifier 102 is anti-phase, into counteracting mould The signal of the first input end of block 10 and the second input is anti-phase each other), it can decay or even eliminate Voutc, while not reduce Voutd。

Assuming that the relative dielectric constant of the insulating materials used is 10, thickness 300um, finger and fingerprint sensor circuit Contact may be assumed that, for capacity plate antenna, area corresponding to single pixel point is 50um*50um, according to the calculation formula of capacity plate antenna, Inductance capacitance size is:Cs≈0.74fF.

Assuming that Csr=1fF, Csv=0.95fF, Δ Cs=-0.05fF, Cfb=10fF, Cc=10fF;VS=1V, A1= 10.If operated without offsetting, the amplitude of the output signal of the second low noise amplifier 107 is:Voutr=Voutc=1V, Voutv=Voutc+Voutd=950mV.If the follow up amplifier of capacitive fingerprint sensor circuit is (with the second low noise amplifier 107 VOUT ends are connected) working power be 2V, common-mode point VCM=1V, then amplitude output signal is reachable after gain is set to 1 times To 0~2V, there is saturation in amplifier, and useful signal is that the amplitude of difference mode signal can not amplify.

If the gain A 2=-1 of amplifier 102 is offset in setting, by the partially complete counteracting of common mode, then the second low noise is amplified The amplitude of the output signal of device 107 is:Voutr=Voutc=0, Voutv=Voutc+Voutd=-50mV.Capacitive fingerprint senses The follow up amplifier gain of circuit can be set to sufficiently large (such as 15 times), and occur without saturation.Useful signal is the width of difference mode signal Degree is exaggerated 15 times, so as to improve the sensitivity of lines identification.

It was found from above-mentioned analysis process, a counteracting operation to work well, change A1/A2, meet condition:A1*Csr =-A2*Cc.Because Csr is relevant with the material and thickness of medium, therefore by changing A2 size, it is suitable for different media Layer.

As shown in figure 5, also available current amplifier replaces the charge amplifier 20 in above-described embodiment, to complete identical Function.Current amplifier includes the first low noise amplifier 107 and is connected to input and the output of the first low noise amplifier 107 Resistance Rfb between end, it may also include the reset switch between the input for being connected to the first low noise amplifier 107 and output end SW。

In summary, the capacitive fingerprint sensor circuit of the embodiment of the present invention one, operated by offsetting, improve fingerprint sensing It is convenient subsequently to be amplified while circuit sensitivity, improve subsequent treatment precision.Further, amplification is offset by changing The gain of device, the dielectric layer of different-thickness and material is suitable for, improves the compatibility of fingerprint sensor.Due to introducing feedback amplification The voltage of the stable induction plate of device, therefore signal processing is unrelated with the parasitic capacitance of induction electrode, and it is reliable to improve system Property.Circuit structure of the embodiment of the present invention is succinct, compatibility standard CMOS technology, and integrated cost is low.

Embodiment two

In order to reach enough resolution ratio DPI (dots per inch), the available area of capacitive fingerprint sensor circuit compared with It is small, the corresponding capacitive fingerprint sensor circuit of a pixel cell, and driving amplifier and counteracting amplifier then can be by multiple pictures Plain units shared.Therefore, the embodiment of the present invention two proposes a kind of capacitive fingerprint inductor, as shown in fig. 6, the embodiment of the present invention two Capacitive fingerprint inductor include multiple pixel cells, the corresponding capacitive fingerprint sensor circuit of each pixel cell.Also include Driving amplifier 401 and counteracting amplifier 402, the input of driving amplifier 401 are connected with external driving source VS, and output end is led to The finger connection of the second input of the cancellation module 40 for being pressed against each capacitive fingerprint sensor circuit is crossed, offsets amplifier 402 Input be connected with external driving source VS, the first input of the cancellation module 40 of output end and each capacitive fingerprint sensor circuit End connection, the gain of driving amplifier 401 and counteracting amplifier 402 are anti-phase.

The structure and operation principle of the capacitive fingerprint sensor circuit and the capacitive fingerprint sensor circuit shown in Fig. 2 to Fig. 3 Similar, here is omitted.

Capacitive fingerprint sensor circuit is the elementary cell of capacitance-typed fingerprint sensor, and finger is by dielectric layer by drive signal It is coupled to induction electrode 301, while drive signal is sent into induction electrode 301 also by built-in counteracting electric capacity Cc, so as to decay Or the public coupled signal unrelated with fingerprint is eliminated, then amplify residual signal and be output to subsequent process circuit.

The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present invention All any modification, equivalent and improvement made within refreshing and principle etc., should be included in the scope of the protection.

Claims (10)

1. a kind of capacitive fingerprint sensor circuit, it is characterised in that including feedback amplifier, offset pole plate and induction plate;It is described Induction plate is used to form inductance capacitance with finger, and the counteracting pole plate is formed with the induction plate offsets electric capacity, and described Induction plate is connected to the input of the feedback amplifier;The input that capacitance connection is offset in the feedback amplifier And first between driving source, wherein, the first drive signal that first driving source provides is capacitively coupled to by the counteracting The induction plate;The second drive signal that second driving source provides is coupled to the induction plate by the inductance capacitance, And the signal for first drive signal being coupled to the induction plate is offset to obtain fingerprint induced signal, the feedback Amplifier is used to after being amplified the fingerprint induced signal export.
2. capacitive fingerprint sensing circuit as claimed in claim 1, it is characterised in that also include feedback pole plate, the feedback pole Plate is used to form feedback capacity with the induction plate, and the feedback capacity is connected to the input of the feedback amplifier and defeated Go out between end.
3. capacitive fingerprint sensor circuit as claimed in claim 2, it is characterised in that the induction plate, the counteracting pole plate It is metal level with the feedback pole plate.
4. capacitive fingerprint sensor circuit as claimed in claim 3, it is characterised in that the counteracting pole plate and the feedback pole plate It is disposed side by side on the lower section of the induction plate.
5. capacitive fingerprint sensing circuit as claimed in claim 2, it is characterised in that also opened including reset switch, the reset Close and the feedback capacity is connected in parallel between input and the output end of the feedback amplifier.
6. capacitive fingerprint sensor circuit as claimed in claim 1, it is characterised in that the feedback amplifier is current amplifier Or charge amplifier.
7. capacitive fingerprint sensor circuit as claimed in claim 1, it is characterised in that the feedback amplifier includes homophase input End, inverting input and output end, wherein the inductance capacitance and the counteracting electric capacity are connected to institute by the induction plate The inverting input of feedback amplifier is stated, and the in-phase input end of the feedback amplifier is used to receive reference signal, it is described defeated Go out end to be used to export the fingerprint induced signal.
8. the capacitive fingerprint sensor circuit as any one of claim 1 to 7, it is characterised in that first driving source The first drive signal provided and the second drive signal that second driving source provides are mutually anti-phase.
9. capacitive fingerprint sensor circuit as claimed in claim 8, it is characterised in that first driving source, which includes offsetting, amplifies Device, second driving source include driving amplifier, the input for offsetting amplifier and the driving amplifier with it is same External driving source is connected, and the gain of the driving amplifier and the counteracting amplifier is anti-phase.
10. a kind of capacitive fingerprint inductor, it is characterised in that including multiple pixel cells, each pixel cell includes one respectively Individual capacitive fingerprint sensor circuit, the capacitive fingerprint sensor circuit are the capacitive fingerprint sense any one of claim 1 to 9 Answer circuit.
CN201711156322.5A 2014-03-20 2014-03-20 Capacitive fingerprint sensor circuit and inductor CN107704852A (en)

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CN201410105847.6A CN104217193B (en) 2014-03-20 2014-03-20 Capacitive fingerprint sensor circuit and inductor
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