CN207557976U - Fingerprint sensor and terminal device - Google Patents

Abstract

The embodiment of the present application provides a kind of fingerprint sensor and terminal device, the fingerprint sensor includes multiple integrating circuit and negative-feedback circuit, each integrating circuit includes a fingerprint capacitor, which is connected to multiple integrating circuit, forms feedback loop.The fingerprint sensor and terminal device of the embodiment of the present application can improve the SNR of fingerprint image on the basis of master control RAM resources are not increased.

Description

Fingerprint sensor and terminal device

Technical field

This application involves fingerprint detection field, and more particularly, to a kind of fingerprint sensor and terminal device.

Background technology

In capacitance type fingerprint circuit arrangement, two major class can be divided into according to the mode of stamp, mutual tolerance stamp and oneself appearance are beaten Code.Mutual tolerance stamp is low with the degree of dependence to parasitism, imbalance, and signal-to-noise ratio can be effectively improved by changing stamp voltage The features such as (Signal-to-Noise Ratio, SNR).But mutual tolerance stamp has a disadvantage, due to needing additional stamp electricity Road, and a large amount of energy dissipation is on finger during stamp, and therefore cost, the power consumption of mutual tolerance stamp scheme are relatively high It is many.

From stamp is held in order to obtain preferable performance, need to overcome parasitic and imbalance influence.A kind of existing way, just It is the image that a frame does not have finger to contact that prestores in master control random access memory (random access memory, RAM), Then the image that a frame has finger to contact is obtained again, is finally subtracted each other to obtain two field pictures and is eliminated parasitic, offset influence fingerprint Image.It is done so that there is a harm, since the pixel up to 10,000 of fingerprint image is even higher.Assuming that pixel has 10,000, And the quantized data of each pixel occupies 2 bytes, then two pictures at least need the RAM of 320kb, this consumes master control phase When big resource.

Utility model content

In view of this, the embodiment of the present application proposes a kind of fingerprint sensor and terminal device, can not increase master control The signal-to-noise ratio of fingerprint image is improved on the basis of RAM.

In a first aspect, providing a kind of fingerprint sensor, which includes multiple integrating circuit and negative-feedback electricity Road, each integrating circuit include a fingerprint capacitor, which is connected to multiple integrating circuit, forms negative feedback loop Road.

By introducing negative-feedback circuit so that the common mode input in multiple integrating circuit can be fixed as reset bias Voltage advantageously reduces the offset voltage of integrating circuit in fingerprint sensor, can be on the basis of master control RAM expenses are not increased Improve the SNR of fingerprint image.

Optionally, which is self-tolerant fingerprint sensor.

Optionally, the arrangement mode of multiple integrating circuit can be arrangement or other arrangement modes of M*N.

In a kind of possible design, which includes operational amplifier, zeroing capacitance, first switch, second Switch and third switch, one end of the zeroing capacitance is connected to the in-phase input end of the operational amplifier, and passes through this and first open Pass is connected with the output terminal of the integrating circuit；The output that the other end of the zeroing capacitance passes through the second switch and the integrating circuit End be connected, and pass through the third switch be connected with the inverting input of the operational amplifier, the output terminal of the operational amplifier and The feedback end of the integrating circuit is connected.

Optionally, which can also be a resistance, and a feedback loop is formed with integrating circuit.

Using operational amplifier as negative-feedback circuit, it can preferably stablize the common mode input of integrating circuit.

The offset voltage at operational amplifier both ends is obtained using zeroing capacitance, it is simple easy to implement.

Optionally, which can also be without reference to circuit, which can also connect fixed voltage work For reference voltage.

Introduce reference circuit provide bias voltage for operational amplifier, can expectation common mode input change when, It does not need to change circuit structure, it is only necessary to adjust the adjustable resistance in reference circuit, simple and flexible.

In a kind of possible design, which includes amplifying circuit, which includes input terminal, feedback end And output terminal, the feedback end are connected to the negative-feedback circuit.

In a kind of possible design, which includes the first metal-oxide-semiconductor and the second metal-oxide-semiconductor, the grid of first metal-oxide-semiconductor Pole is connected to the output terminal of the amplifying circuit, source electrode ground connection, and its drain electrode is connected to the output terminal of the amplifying circuit；This second The grid of metal-oxide-semiconductor is connected to the feedback end of the amplifying circuit by feedback switch, and drain electrode is connected to the leakage of first metal-oxide-semiconductor Pole, and its source electrode connection power end, and there is grid capacitance between the grid and source electrode of second metal-oxide-semiconductor.

In a kind of possible realization method, which further includes reset switch and integrating capacitor, the reset switch It is parallel with one another with integrating capacitor, and be connected between grid and the drain electrode of first metal-oxide-semiconductor.

In a kind of possible realization method, multiple integrating circuit includes multirow integrating circuit, and the negative-feedback circuit Corresponding to wherein a line integrating circuit.

Second aspect provides a kind of terminal device, the terminal device include as first aspect or first aspect is any can Select the fingerprint sensor that realization method is somebody's turn to do.

Based on above-mentioned technical proposal, by introducing negative-feedback circuit, the offset voltage of multiple integrating circuit can be reduced, It even eliminates, and then the SNR of fingerprint image can be improved on the basis of master control RAM resources are not take up.Namely do not need to be logical Acquisition two field pictures are crossed, and two field pictures are subtracted each other to overcome the imbalance of fingerprint sensor.And due to the negative-feedback Circuit is only operated in the reseting stage of integrating circuit, therefore does not also increase any power consumption substantially.

These aspects or other aspects of the application can more straightforward in the following description.

Description of the drawings

Fig. 1 shows the schematic block diagram of the fingerprint sensor of the embodiment of the present application.

Fig. 2 shows the circuit diagrams of the fingerprint sensor of the embodiment of the present application.

Fig. 3 shows the working timing figure of the fingerprint sensor of the embodiment of the present application.

Fig. 4 shows another circuit diagram of the fingerprint sensor of the embodiment of the present application.

Fig. 5 shows another circuit diagram of the fingerprint sensor of the embodiment of the present application.

Fig. 6 shows another circuit diagram of the fingerprint sensor of the embodiment of the present application.

Specific embodiment

Below in conjunction with the attached drawing in the embodiment of the present application, the technical solution in the embodiment of the present application is carried out clear, complete Site preparation describes.

Fingerprint sensor is the Primary Component for realizing fingerprint automatic collection.Earliest fingerprint identification technology is with optical finger print Optical recognition system based on sensor, the identification range are only limitted to the surface layer of skin, referred to as first generation fingerprint identification technology； The second generation fingerprint recognition system then developed then employs capacitive fingerprint sensing device technology, realizes identification range from epidermis To the conversion of corium, so as to substantially increase the safety of the accuracy rate of identification and system.

Capacitive fingerprint sensing device is of different sizes with capacitance that induction electrode is formed according to the wrinkle ridge of fingerprint and line paddy, comes Where judgement is where wrinkle ridge is line paddy；Its course of work is by the capacitive sensing electrode on each pixel It is pre-charged to a certain reference voltage.When finger is touched on semicoductor capacitor fingerprint sensor surface, finger print and picture A capacitor array can be formed between pixel array；Wherein, the capacitance of each fingerprint capacitor of capacitor array can with conductor it Between distance increase and become smaller because wrinkle ridge is raised, and line paddy is concave, according to capacitance and the relationship of distance, can be existed Wrinkle ridge and line paddy are respectively formed different capacitances.Then, it is discharged using discharge current, by reading what is be charged and discharged Capacitance difference obtains fingerprint image.

In simple terms, capacitive fingerprint sensing device includes many pixels (pixel) circuit, each pixel circuit can have One pixel electrode (i.e. induction plate) generates fingerprint capacitor come the lines with finger surface, and all pixels electrode forms one Pel array (such as 128*96 or 96*96).Wherein, distance difference is therefore between the wrinkle ridge of fingerprint and line paddy and pixel electrode The capacitance of the fingerprint capacitor of formation is different, can identify that pixel electrode position is line by detecting capacitance Ridge or line paddy can obtain fingerprint image according to the testing result of each pixel circuit.

Capacitive fingerprint sensing device can be divided into self-capacitance fingerprint sensor and mutual capacitance fingerprint again according to its testing principle Sensor.

In general, there are larger parasitism and imbalance, current self-capacitance fingerprint biographies for self-capacitance fingerprint sensor Sensor is then to be influenced caused by imbalance by sacrificing the resource of master control RAM to overcome, but increase master control RAM resources equally can band Carry out some other influences, and performance raising is not apparent enough.In view of this, a kind of next gram of new self-tolerant fingerprint sensor is needed Take foregoing circuit imbalance.

Fig. 1 shows a kind of schematic block diagram for fingerprint sensor 100 that the embodiment of the present application proposes.It as shown in Figure 1, should Fingerprint sensor 100 includes multiple integrating circuit 110 and negative-feedback circuit 120, which includes multiple integrating circuit And negative-feedback circuit, each integrating circuit include a fingerprint capacitor, which is connected to multiple integrating circuit, structure Into feedback loop.

It should be understood that fingerprint sensor 100 generally includes an integrating circuit array, it, should as a kind of preferred embodiment Integrating circuit array can be a square array, as M rows N is arranged；Alternatively, which can also use it His arrangement mode, the embodiment of the present application are not construed as limiting the arrangement mode of integrating circuit array.

It should also be understood that the data reading of usually integrating circuit array is with behavior unit, that is, institute is read each time State the image data of wherein a line integrating circuit output of integrating circuit array.

Optionally, in one embodiment, can be that a negative-feedback circuit is respectively configured in each integrating circuit, then Integrating circuit per a line can form feedback loop with respective negative-feedback circuit respectively in reseting stage simultaneously.It is preferred that Ground, in the present embodiment, or a negative-feedback circuit, i.e., described fingerprint sensor is configured in the integrating circuit per a line 100 are configured with M negative-feedback circuit, are connected respectively M row integrating circuit；When reading the defeated of certain a line integrating circuit When going out data, the row integrating circuit can be caused to be respectively at reseting stage, it is corresponding negative anti-with the row integrating circuit successively Current feed circuit forms feedback loop.In other alternate embodiments, or entire integrating circuit array configuration one is negative anti- Current feed circuit can successively be formed the negative-feedback circuit and each integrating circuit when each integrating circuit is in reseting stage Feedback loop.

In actual circuit design, the quantity of the negative-feedback circuit of the fingerprint sensor 100 can combine fingerprint sensing Requirement of the device to cost and acquisition speed implements, if the fingerprint sensor is higher to time requirement, but to cost It is of less demanding, can be the more negative-feedback circuit of integrating circuit array configuration；And if the fingerprint sensor is to cost requirement It is higher, it is of less demanding to acquisition speed, then can be the less negative-feedback circuit of integrator configuration.The embodiment of the present application to this not It forms and limits.

For ease of description, it is firstly introduced into a kind of circuit structure of the fingerprint sensor of the embodiment of the present application.Fig. 2 shows The schematic frame of any integrating circuit of the fingerprint sensor 200 of the embodiment of the present application and the circuit connection structure of negative-feedback circuit Figure.As shown in Fig. 2, the feedback end of the integrating circuit is connect with the negative-feedback circuit, the negative-feedback circuit can include Operational amplifier 214, zeroing capacitance 213, first switch 216, second switch 217 and third switch 218.The integrating circuit Output terminal by the second switch 217 with it is described zeroing capacitance 213 negative electrode plate be connected, also, the integrating circuit Output terminal also pass through the first switch 216 and the zeroing positive electrode plate of the capacitance 213 and operational amplifier 214 In-phase input end be connected；The negative electrode plate of the zeroing capacitance 213 passes through third switch 218 and the operational amplifier 214 inverting input is connected.On the other hand, the inverting input of the operational amplifier 214 is further also connected to ginseng Circuit is examined, for receiving the reset bias voltage that the reference circuit provides.The zeroing capacitance 213 can be used as offset correction Unit, for obtaining the offset voltage of the operational amplifier 214, the offset voltage is used to lose the integrating circuit Adjustment is just.In the embodiment shown in Figure 2, the reference circuit can include metal-oxide semiconductor (MOS) (metal oxide Semiconductor, MOS) pipe 215, the metal-oxide-semiconductor 215 can be specially N-type MOS transistor, and source electrode is grounded, and grid connects It is connected to drain electrode；Also, the drain electrode of the metal-oxide-semiconductor 215 is connected to constant-current source, and is connected with the negative-feedback circuit, for for The negative-feedback circuit provides the reset bias voltage.

It will be appreciated by those skilled in the art that capacitance is actually what is be made of two metal layers, positive and negative electrode is not necessarily distinguished Plate, therefore, the connection relation of the zeroing capacitance 213 described in Fig. 2 are used merely to schematically illustrate, this composition are not limited.

The integrating circuit includes amplifying circuit, integrating capacitor 209 and reset switch 201, and the amplifying circuit includes first 211 and second metal-oxide-semiconductor 210 of metal-oxide-semiconductor；Wherein, first metal-oxide-semiconductor 211 and second metal-oxide-semiconductor 210 can be respectively N-type MOS transistor and N-type MOS transistor.In a particular embodiment, the amplifying circuit can include input terminal, feedback end and defeated Outlet, the integrating capacitor 209 and the reset switch 201 are parallel with one another, and are connected to the input terminal of the amplifying circuit Between output terminal.The grid of first metal-oxide-semiconductor 211 is connected to the input terminal of the amplifying circuit, for receiving input electricity Vn, the source electrode ground connection of first metal-oxide-semiconductor 211 are pressed, and its drain electrode may be coupled to the output terminal of the amplifying circuit, for carrying For output voltage Vout.The grid of second metal-oxide-semiconductor 210 is connected to the anti-of the amplifier circuit by feedback switch 202 End is presented, the drain electrode that the drain electrode of second metal-oxide-semiconductor 210 is connected to first metal-oxide-semiconductor 211 (is attached to the amplifying circuit Output terminal), the source electrode of second metal-oxide-semiconductor 210 connection power end, and between the grid and source electrode of second metal-oxide-semiconductor 210 With grid capacitance 212.

Referring to Fig. 2, the integrating circuit further include fingerprint capacitor 207, substrate eliminate capacitance 208 and switch 203~ 207。

Wherein, the fingerprint capacitor 207 is specially finger surface when user presses the fingerprint sensor 100 by finger The capacitance formed with induction plate, it should be noted that the finger that the application mentions, which presses the fingerprint sensor 100, to be had Body refers to that finger is pressed on the cover board of 100 top of fingerprint sensor, such as the positive cover sheet of terminal device (i.e. main glass Glass cover board) the either ceramic cover plate of fingerprint module, glass cover-plate, sapphire cover board or coat, as a kind of reality of replacement Example is applied, the fingerprint sensor 100 can also be arranged below display screen (such as OLED display screen), and above-mentioned cover board can at this time To specifically refer to the display screen.

In a particular embodiment, the fingerprint sensor 100 can have induction arrays, and the induction arrays include multiple Induction plate (i.e. pixel electrodes), each induction plate correspond respectively to an integrating circuit.When finger presses the fingerprint During sensor 100, fingerprint capacitor 207, in other words, the induction plate are formed between finger surface meeting and the induction plate As one of pole plate of fingerprint capacitor 207, and another pole plate of finger surface as fingerprint capacitor 207, and finger with Cover board and other materials layer (such as plastic packaging layer of the fingerprint sensor 100) between induction plate is as fingerprint electricity Hold 207 dielectric layer.Since finger surface has the different texture of height, the i.e. wrinkle ridge of fingerprint and line paddy, therefore when finger is pressed When being pressed onto the fingerprint sensor 100, the wrinkle ridge of finger surface and line paddy are different from the distance of induction plate, lead to different zones Fingerprint capacitor 207 it is different, therefore can know that corresponding position corresponds to hand by detecting the stool and urine of the fingerprint capacitor 207 Finger watch can be obtained by detecting each fingerprint capacitor 207 by referring to the wrinkle ridge on surface or line paddy, the fingerprint sensor 100 The fingerprint image in face.

In circuit shown in Fig. 2, the positive electrode plate of the fingerprint capacitor 207 refers to corresponding induction plate, and institute The negative electrode plate for stating fingerprint capacitor 207 refers to finger surface, can be equivalent to and make grounding by human body.Fingerprint capacitor 207 are connected by the switch 203 with power vd D, and the input terminal of the amplifying circuit is connected to by the switch 204. Wherein, the switch 203 is equivalent to the charge switch of the fingerprint capacitor 207, can be to the fingerprint capacitor when being closed 207 carry out being charged such that the fingerprint capacitor 207 generates charge inducing, and the capacitance of charge inducing in the induction plate It is related to the capacitance size of the fingerprint capacitor 207.The switch 204 is equivalent to the discharge switch of the fingerprint capacitor 207, It can be by the electric charge transfer of the fingerprint capacitor 207 to the integrating capacitor 201, so as to obtain the input voltage when being closed Vn.It therefore, can be to the fingerprint capacitor by the way that the switch 203 and switch 204 is controlled to carry out periodically alternation switch 207 electric charge transfers for carrying out repeatedly charging and generating each charging to the integrating capacitor 201 and carry out Integral Processing, so as to Output voltage Vout is obtained in the output terminal of the amplifying circuit, the output voltage Vout is related to the fingerprint capacitor 207, It can be used for calculating the capacitance of the related fingerprint capacitor 207 of the integrating circuit.

The substrate eliminate capacitance 208 can be specifically the induction plate with the inside of the fingerprint sensor 100 its The parasitic capacitance that his line layer is formed, in circuit shown in Fig. 2, the substrate eliminates the positive electrode plate of capacitance 208 and described The positive electrode plate of fingerprint capacitor 207 can share the induction plate, and the substrate eliminates the negative electrode plate difference of capacitance 208 Supply voltage VDD and reference voltage Vdac are connected to by switch 205 and switch 206.The fingerprint sensor 100 is by described The disconnection of switch 205 and switch 206 and closure eliminate the substrate progress charge and discharge electric treatment of capacitance 208 to control, so as to real Basal signal Processing for removing now is carried out to fingerprint capacitor 207 each in the fingerprint sensor 100.

As described in Figure 2, the switch 203 and the switch 205 break under the control of first switch control signal ck1 Open and close are closed, and the switch 204 and the switch 206 are turned off and closed under the control of second switch control signal ck2 It closes.Wherein, the first switch control signal ck1 and second control signal ck2 is in the integration of the fingerprint sensor 100 Circuit is low level signal when being in reseting stage, therefore in the reseting stage, and the switch 203~206 is in breaking Open state；And be two-phase disjoint signals both when the integrating circuit is in integration phase, i.e., described first switch control Signal ck1 and the second control signal ck2 are being switched in the integration phase mutual reverse phase described in the integration phase 203 and 205 alternate conducting with the switch 204 and 206.

On the other hand, the reset switch 201 and the feedback switch 202 are in the control of the first reseting controling signal rst Under turn off and be closed, the first switch 216 and the third switch 218 the second reseting controling signal crst control Under turn off and be closed, and the second switch 217 is turned off and is closed under the control of third reseting controling signal, Described in third reseting controling signal and the first reseting controling signal rst and the second reseting controling signal crst phases It closes, for example it is specifically as follows-crst＆rst, as shown in Fig. 2, in other words, the on off state of the second switch 217 is from original It is also assumed that being controlled by the first reseting controling signal rst and the second reseting controling signal crst from reason System.The fingerprint sensor 100 controls the reset switch 201, the feedback switch by above-mentioned reseting controling signal 202nd, the first switch 216, the second switch 217 and third switch 218 are turned off and are closed according to default sequential It closes, is divided into first stage and second stage so as to fulfill by the reseting stage of the integrating circuit, wherein the first stage is Offset voltage obtains the stage, and the second stage is practical reseting stage.

Below in conjunction with the sequence diagram in Fig. 3, the operation principle of circuit shown in Fig. 2 is described in detail.As shown in figure 3, One timing cycles of the integrating circuit can be divided into integrating circuit reseting stage and integrating circuit integration phase, wherein, institute First stage (offset voltage obtains the stage) and second stage (practical reset rank can be divided into again by stating integrating circuit reseting stage Section).

Specifically, rst=1, crst=1, ck1=0, the ck2=0 in the first stage of reseting stage, i.e. Fig. 3, this When Fig. 2 described in integral restrictor 201, the feedback switch 202, the first switch 216 and the third switch 218 be closed, And the second switch 217 disconnects, and the operational amplifier 214 powers on.The operational amplifier 214 and the amplifying circuit The first metal-oxide-semiconductor 211 and the second metal-oxide-semiconductor 210 formed negative feedback loop, and the reference circuit provide reset bias voltage lead to It crosses 218 pairs of the third switch zeroing capacitances 213 to charge, the equivalent circuit diagram of the first stage can be such as Fig. 4 It is shown.When the end of the first period, according to the empty short principle in operational amplifier both ends, the operational amplifier 214 it is same mutually defeated The voltage Vf for entering end should be equal with the voltage Vr of inverting input, and since the inverting input is switched by the third 218 are connected with the negative electrode plate of the zeroing capacitance 213, therefore the voltage Va of the negative electrode plate of the zeroing capacitance 213 is equal to The voltage Vr of the inverting input, then the offset voltage Vf-Vr at 214 both ends of operational amplifier can be by Vf-Va tables Show namely the voltage at 213 both ends of the zeroing capacitance is just the offset voltage at 214 both ends of operational amplifier.Therefore, Ke Yitong Cross the offset voltage that the zeroing capacitance 213 obtains the operational amplifier 214.

Rst=1, crst=0, ck1=0, ck2=0 in the second stage of reseting stage, i.e. Fig. 3, at this time in Fig. 2 The reset switch 201, the feedback switch 202 and the second switch 217 are closed, the first switch 216 and described Three switches 218 disconnect, at this time the first metal-oxide-semiconductor of the operational amplifier 214, the zeroing capacitance 213 and the amplifying circuit 211 and second metal-oxide-semiconductor 210 form feedback loop, the equivalent circuit diagram of the second stage can be as shown in Figure 5.From last The offset voltage Vf-Vr that stage can obtain the operational amplifier 214 is the voltage at 213 both ends of the zeroing capacitance, therefore, In second stage, Va=Vr=Vout=Vn, wherein, Vout represents the output voltage of the integrating circuit, and described in Vn represents The input voltage of the common mode input of integrating circuit namely the amplifying circuit.Therefore, for each integrating circuit, Its reseting stage can form feedback loop as shown in Figure 2 with the negative-feedback circuit, thus by the input common mode Voltage Vn is fixed to the reset bias voltage Vr that the reference circuit provides, therefore in the integrating circuit in reseting stage, The imbalance of the first metal-oxide-semiconductor 211 and the second metal-oxide-semiconductor 210 of the amplifying circuit can be eliminated.

In the integration phase of the integrating circuit, i.e. rst=0, crst=0, the reset switch 201, described anti-at this time Feedback switch 202, the first switch 216, the second switch 217 and third switch 218 all disconnect, the 2nd MOS The grid voltage of pipe 210 can be maintained by grid capacitance 212, therefore second metal-oxide-semiconductor 210 can be equivalent to a constant current Source provides load for first metal-oxide-semiconductor 211.Also, the first switch control in the integration phase of the integrating circuit, Fig. 3 The alternation switch of signal ck1 and second switch signal ck2 processed.Specifically, as ck1=1, ck2=0,203 Hes of the switch 205 are closed, and the switch 206 and 204 disconnects, and the positive electrode plate of the fingerprint capacitor 207 and the substrate eliminate electricity at this time The negative electrode plate for holding 208 is charged to supply voltage VDD.Work as ck1=0, during clk2=1, the switch 203 and 205 disconnects, and The switch 206 and 204 is closed, and the positive electrode plate of the fingerprint capacitor 207, which is connected to, at this time is connected to the defeated of the amplifying circuit Enter end, therefore the charge of the fingerprint capacitor 207 is transferred to the integrating capacitor 209 and carries out an Integral Processing, so as to shape Into the input voltage Vn (common mode input of i.e. described integrating circuit) of the amplifying circuit, at the same time the substrate elimination The negative electrode plate of capacitance 208 is charged to reference voltage Vdac, therefore, can obtain the output of each integrating circuit single integration Voltage increment is：

Wherein, Ci represents the capacitance of the integrating capacitor 209, and Cc represents that the substrate eliminates the capacitance of capacitance 208, Cf represents the capacitance of the fingerprint capacitor 207；VDD and Vdac represent respectively the supply voltage that the integrating circuit receives and Reference voltage, Vr represent the reset bias voltage that the reference circuit provides.The value of Ci, Cc, VDD, Vdac and Vr are all Know, and for the integrating circuit array of M*N, Ci, Cc, VDD, Vdac and Vr of each integrating circuit are phases With, then the output voltage increment Delta Vout is just only related with fingerprint capacitor Cf, as long as measuring the output voltage increment Δ Vout can calculate the capacitance of fingerprint capacitor Cf, and further get the data of fingerprint image.

It is possible to further which the output voltage Vout of the fingerprint sensor 100 is input to a processing unit, the processing Unit measures the voltage value of output voltage Vout and calculates the capacitance of corresponding fingerprint capacitor Cf.

Fig. 4 and Fig. 5 shows that an integrating circuit in the M*N integrating circuit arrays of the embodiment of the present application is respectively at product Divide the equivalent circuit diagram under the first stage and second stage of reseting stage.Specifically, as shown in figure 4, in the integral reset stage First stage, the reset switch 201 of integrating circuit is closed, therefore institute under the control of the first reseting controling signal rst Integrating capacitor 209 is stated by 201 short circuit of reset switch；And the first switch control signal ck1 and second switch control letter Number ck2 is low level, therefore the switch 203~206 is all off, and the fingerprint capacitor 207 and the substrate eliminate electricity Hold 208 not work.The operational amplifier 214 forms negative with the first metal-oxide-semiconductor 211 of the amplifying circuit and the second metal-oxide-semiconductor 210 Backfeed loop, according to the description of front, the offset voltage Vf-Vr of the operational amplifier 314 is 213 both ends of the zeroing capacitance Voltage, i.e. Vf-Vr=Vf-Va.

As shown in figure 5, in the second stage in integral reset stage, the reset switch 201 of the integrating circuit is described Closed state is maintained under the control of one reseting controling signal rst, therefore the integrating capacitor 209 is still short-circuited；The switch 203~206 maintain off-state in the case where the first switch controls the control of signal ck1 and second switch control signal ck2, because This fingerprint capacitor 207 and the substrate eliminate capacitance 208 and still do not work.The operational amplifier 214, the zeroing electricity The first metal-oxide-semiconductor 211 and the second metal-oxide-semiconductor 210 of appearance 213 and the amplifying circuit form negative feedback loop, the grid capacitance 212 For keeping grid voltage of second metal-oxide-semiconductor 210 in integration phase.The output terminal of the integrating circuit and the zeroing The negative electrode plate of capacitance 213 is connected directly, and since the reset switch 201 is closed, the output voltage of the integrating circuit Vout is equal with the input common mode voltage Vn of the amplifying circuit, and the negative of the zeroing capacitance 213 is understood from the first stage Electrode plate voltage Va is equal to the voltage Vr of the inverting input of the operational amplifier 214, therefore, it is known that Va=Vf=Vout= Vn, since the voltage of the inverting input of the operational amplifier 214 is the reset bias voltage Vr that the reference circuit provides, It is a fixed value, therefore, the input common mode voltage Vn of the amplifying circuit is fixed to the reset bias voltage Vr.It is right For each integrating circuit of the fingerprint sensor 100, when in reseting stage, all with the negative-feedback circuit structure Into feedback loop, for integrating circuit array, by introducing negative-feedback circuit, can be incited somebody to action in the integral reset stage The common mode input Vn of each integrating circuit is fixed as reset bias voltage, so as to be conducive to eliminate integrating circuit array Offset voltage.

It should be understood that be to provide reset bias voltage for negative-feedback circuit by reference circuit in Fig. 2, Fig. 4 and Fig. 5, therefore, Adjustable resistance can be set and by adjusting the size of the adjustable resistance in reference circuit, to obtain desired reset bias electricity Pressure, without replacing circuit.Alternatively, which can also be directly connected to fixed voltage realization to operation amplifier The elimination of the offset voltage of device.

Optionally, the input of each integrating circuit can also be total to by the embodiment of the present application using other negative-feedback circuits Mode voltage Vn is stabilized to a fixed value, as shown in fig. 6, the negative-feedback circuit can include a resistance 216, the integration electricity Road can be the same with Fig. 2, and mainly including amplifying circuit, integrating capacitor 209 and reset switch 201, the amplifying circuit has the One metal-oxide-semiconductor 211 and the second metal-oxide-semiconductor 210.The integrating circuit further includes fingerprint capacitor 207, substrate eliminates capacitance 208, integration electricity Hold 209 and switch 203~206, reseting stage be in integrating circuit, is i.e. reset switch 201 in Fig. 6 is closed, and integration is electric Output voltage Vout and the common mode input Vn of amplifying circuit on road be it is equal, therefore, can by feedback resistance 216 come Stablize the output voltage Vout of integrating circuit namely stablize the common mode input Vn of amplifying circuit.If each integration electricity of access Feedback resistance value in road is identical, is similarly also possible to realize the input of each integrating circuit in integrating circuit array Common-mode voltage Vn is fixed to same value.It should be understood that similar with the operation principle of Fig. 2, the negative-feedback circuit is only multiple in integration The work of position stage, when in integration phase, which can disconnect with the integrating circuit.

The defects of generally, due to operational amplifier itself, that is to say, that there are voltages between operational amplifier input both ends Difference, i.e. offset voltage, the precision when operational amplifier is used to realize negative-feedback may be not high enough, therefore the present embodiment uses Special circuit designs the offset voltage to eliminate the operational amplifier both ends.For example, as shown in Fig. 2, Fig. 3 and Fig. 5, can pass through It is described to return to zero capacitance 213 to obtain the offset voltage at 214 both ends of operational amplifier, that is to say, that in the embodiment of the present application Offset correction unit can include zeroing capacitance, but the embodiment of the present application is without being limited thereto.It should also be understood that the embodiment of the present application provides The circuit structure of any of the above-described kind of fingerprint sensor be used merely to schematically illustrate, the embodiment of the present application includes but not limited to This.

Therefore, the fingerprint sensor of the embodiment of the present application by introducing negative-feedback circuit in the integral reset stage, can incite somebody to action The offset voltage of N*M integrating circuit reduces, and even eliminates, and then can be carried on the basis of master control RAM resources are not take up The SNR of high fingerprint image.Namely it does not need to by obtaining two field pictures, and two field pictures are subtracted each other to overcome self-tolerant The imbalance of fingerprint sensor.And since the negative-feedback circuit is only operated in the reseting stage of integrating circuit, therefore substantially also not Increase any power consumption.

The embodiment of the present application additionally provides a kind of terminal device, and the terminal device includes display screen, rear cover and the application Any fingerprint sensor that embodiment provides.Wherein, the display screen can be touching display screen, be set positioned at the terminal Standby front, the rear cover are located at the back side of the terminal device.The fingerprint sensor can be arranged on the terminal device Front or the back side.For example, the display screen includes cover sheet (i.e. main glass cover-plate), and the cover sheet is neighbouring The position of display area offers through-hole, alternatively, the rear cover can offer through-hole in presumptive area.The fingerprint sensor It can be arranged on the through-hole that the cover sheet or rear cover open up and its surface can be provided with fingerprint by cover clamp (such as glass Glass cover board, ceramic cover plate, sapphire cover board etc.) or it is formed with coat.Alternatively, the fingerprint sensor can be hidden in institute State the cover sheet either lower section (without opening up through-hole) of the rear cover and cover sheet or the rear cover are in the finger Line sensor region carries out reduction processing so that the cover sheet thickness in this region is less than the thickness in other regions, if will Fingerprint sensor is hidden in below the rear cover, it is preferable that the rear cover uses nonmetallic materials, such as ceramic rear cover or glass Glass rear cover, in order to avoid fingerprint inductive signal is caused to shield or be interfered.In other alternate embodiments, the fingerprint sensor is straight It connects and is arranged on the lower section of the display screen so as to form the lower dactylotype of screen.

Therefore, terminal device provided by the embodiments of the present application introduces one by the integral reset stage in fingerprint sensor The offset voltage of N*M integrating circuit can be reduced, even eliminated, and then can be not take up leading by a negative-feedback circuit The SNR of fingerprint image is improved on the basis of control RAM resources.

Those of ordinary skill in the art may realize that each exemplary lists described with reference to the embodiments described herein Member and circuit can be realized with the combination of electronic hardware or computer software and electronic hardware.These functions are actually with hard Part or software mode perform, specific application and design constraint depending on technical solution.Professional technician can be with Described function is realized using distinct methods to each specific application, but this realization is it is not considered that beyond this Shen Range please.

In several embodiments provided herein, it should be understood that disclosed circuit, branch and unit, it can be with It realizes by another way.For example, branch described above is schematical, for example, the division of the unit, only one Kind of division of logic function, can there is an other dividing mode in actual implementation, for example, multiple units or component can combine or It is desirably integrated into a branch or some features can be ignored or does not perform.

If the integrated unit is realized in the form of SFU software functional unit and is independent product sale or uses When, it can be stored in a computer read/write memory medium.Based on such understanding, the technical solution of the application is substantially The part to contribute in other words to the prior art or the part of the technical solution can be embodied in the form of software product Come, which is stored in a storage medium, is used including some instructions so that a computer equipment (can To be personal computer, server or the network equipment etc.) perform all or part of each embodiment the method for the application Step.And aforementioned storage medium includes：It is USB flash disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random Access various Jie that can store program code such as memory (Random Access Memory, RAM), magnetic disc or CD Matter.

The specific embodiment of the above, only the application, but the protection domain of the application is not limited thereto, it is any In the technical scope that those familiar with the art discloses in the application, change or replacement can be readily occurred in, should all be contained It covers within the protection domain of the application.Therefore, the protection domain of the application should be subject to the scope of the claims.

Claims (6)

1. a kind of fingerprint sensor, which is characterized in that the fingerprint sensor includes multiple integrating circuit and negative-feedback circuit, often A integrating circuit includes a fingerprint capacitor, and the negative-feedback circuit is connected to the multiple integrating circuit, forms negative feedback loop Road, the integrating circuit include amplifying circuit, and the amplifying circuit includes input terminal, feedback end and output terminal, the negative-feedback Circuit includes operational amplifier, zeroing capacitance, first switch, second switch and third switch, and one end of the zeroing capacitance connects The in-phase input end of the operational amplifier is connected to, and is connected by the first switch with the output terminal of the integrating circuit； The other end of the zeroing capacitance is connected, and pass through the third by the second switch with the output terminal of the integrating circuit Switch is connected with the inverting input of the operational amplifier, and the output terminal of the operational amplifier is anti-with the integrating circuit Feedback end is connected.

2. fingerprint sensor according to claim 1, which is characterized in that the fingerprint sensor further includes reference circuit, The reference circuit is connected with the negative-feedback circuit.

3. fingerprint sensor according to claim 1, which is characterized in that the amplifying circuit includes the first metal-oxide-semiconductor and the Two metal-oxide-semiconductors, the grid of first metal-oxide-semiconductor are connected to the output terminal of the amplifying circuit, source electrode ground connection, and its drain electrode connection To the output terminal of the amplifying circuit；The grid of second metal-oxide-semiconductor is connected to the anti-of the amplifying circuit by feedback switch End is presented, drain electrode is connected to the drain electrode of first metal-oxide-semiconductor, and its source electrode connection power end, and the grid of second metal-oxide-semiconductor There is grid capacitance between source electrode.

4. fingerprint sensor according to claim 3, which is characterized in that the integrating circuit further includes reset switch and product Divide capacitance, the reset switch and integrating capacitor are parallel with one another, and are connected between grid and the drain electrode of first metal-oxide-semiconductor.

5. fingerprint sensor according to any one of claim 1 to 4, which is characterized in that the multiple integrating circuit packet Multirow integrating circuit is included, and the negative-feedback circuit corresponds to wherein a line integrating circuit.

6. a kind of terminal device, which is characterized in that the terminal device is included such as any one of claim 1 to claim 5 The fingerprint sensor.