High sensitivity fingerprint sensor based on BCD techniquesTechnical field
The present invention relates to fingerprint identification technology field, is passed more particularly, to a kind of high sensitivity fingerprint based on BCD techniquesSensor.
Background technology
Existing major part fingerprint sensor produces a pumping signal using sensor, and one is installed by sensor peripheryA becket and finger to be collected contact the mode of the becket, this pumping signal are applied to finger surface to be collected, with realityNow the principle of finger electrode is driven to realize fingerprint collecting, as shown in Fig. 1 (a).The existing fingerprint using finger excitation principle passesIn sensor, in order to avoid groups of people are in fingerprint collecting, finger causes tingling sensation, the pulse excitation voltage max one on fingerAs be no more than 4V.
In addition, existing operative sensor realizes sensor height using high pressure activation signal driving fingerprint sensor substratePumping signal tingling sensation caused by finger surface, such as patent CN103376970A are penetrated and solve, as shown in Fig. 1 (b).ByThe state being excited by signal is in the substrate of sensor, therefore needs to be DC between the digital signal of sensor output and host computerIsolation processing.So, it is necessary to increase an interface conversion chip between sensor and host computer.Simultaneously as driving sensingThe substrate of device needs larger driving force, so, high-voltage signal is boosted by exterior DCDC chips and produced, and passes through interface conversionSubstrate high-voltage driven signal is formed after chip copped wave.
In becket incentive program, the power consumption of pumping signal generation circuit is larger.When pumping signal level on becketAfter 4V, for groups of people during fingerprint collecting, finger surface can experience a degree of shouting pain due to pumping signalSense.And the pumping signal less than 4V, the detectivity of the great limiting sensor of meeting.Due to needing peripheral metal ring, chipPackaging cost and encapsulation complexity it is generally higher.Becket is the larger conductive electrode of an area, can to its exterior orPerson is disturbed by its exterior.Meanwhile the sensor with becket is in an installation, when being bonded with system-level machine casing,The problem of in the presence of installation inconvenience.In bulk driven scheme, DCDC and high voltage interface chip it is system-level can consume it is higherPower consumption, increases the cost of system；Meanwhile system forms complicated, inconvenient debugging.
The content of the invention
The object of the present invention is to provide a kind of high sensitivity fingerprint sensor based on BCD techniques, without external metal ringExcitation, while not using DCDC and high voltage interface chip in applications, improves the collection sensitivity of fingerprint sensor.
To achieve these goals, the high sensitivity fingerprint sensor proposed by the present invention based on BCD techniques, including：Refer toLine collecting unit circuit, high-voltage pulse generation circuit and internal booster circuit.
The fingerprint collecting unit circuit, input terminal connection high-voltage pulse signal VH and digital analog converter DAC, output terminal connectConnect output circuit or rear class receives amplifying circuit；The high-voltage pulse generation circuit, output terminal connect the fingerprint collecting unitCircuit, is fingerprint collecting unit circuit output high pressure activation signal VH, for directly or indirectly driving the formation of finger print.InstituteInternal booster circuit is stated, output terminal is connected with high-voltage pulse generation circuit, and the low voltage for power supply to be provided is raised to higherVoltage, to high-voltage pulse generation circuit input high pressure Vout '.
Further, the fingerprint collecting unit circuit also includes the first pole plate and the second pole plate, first pole plate,Fringe field finger capacitance Cf is formed between two pole plates and finger surface.
Further, the fingerprint collecting unit circuit also includes amplifier, reference voltage and feedback capacity；The amplificationDevice includes normal phase input end, inverting input and output terminal；The reference voltage Vref is produced by front stage circuits, is input to describedThe normal phase input end of amplifier；One end of the feedback capacity Cfb is connected with the inverting input of the amplifier, the feedbackThe other end of capacitance is connected with the output terminal of the amplifier；The inverting input of the amplifier is also connected with the second pole plate；The output terminal of the amplifier exports the output signal Vout of the fingerprint collecting unit circuit.
Further, the digital analog converter DAC, produces suitable analog quantity, is coupled to by DC compensation capacitance CdcThe inverting input of the amplifier, for adjusting the direct current biasing of circuit.
Further, the amplifier is low-noise amplifier LNA.
Further, the high-voltage pulse generation circuit includes non-overlapping clock generation circuit, dynamic level carry circuitFirst, dynamic level carry circuit two, output insulated-gate field-effect crystal N pipes, output insulated-gate field-effect crystal P pipes.
The operation principle of high-voltage pulse generation circuit is：Circuit input signal be low voltage high level V0, low levelFor 0V, by non-overlapping clock generation circuit and dynamic level generation circuit one, one group of non-overlapping clock is generated, while by pulseHigh level lifting to V1, the control sequential as output N pipes；By dynamic level carry circuit two, by the high level of pulseV1 liftings are to V2, the control sequential as output P pipes；By controlling the switch of output N pipes and P pipes, output and input signalThe output high pressure Vout " that high level with sequential is V2, low level is 0V.The signal is input to the input of fingerprint collecting unit circuitEnd, is high-voltage pulse signal VH.Described V0, V1 are actually needed by circuit and determined, the size of high level V2 is determined by Vout '.
Further, the internal booster circuit is charge pump.
The beneficial effect of this patent：
1. sensor circuit described in this patent, can save the pumping signal and metal of the generation of prior art fingerprint sensorRing, avoids finger from directly contacting electric signal.So as to save the power consumption of pumping signal generation circuit；Avoid in fingerprint collecting mistakeCheng Zhong, pumping signal tingling sensation caused by finger surface；Due to eliminating peripheral metal ring, reduce chip package cost andThe complexity of installation；Improve the antijamming capability of chip.
2. this patent pumping signal puts on chip internal by being produced inside circuit, therefore driving voltage can reach 20VHigh pressure above, while will not cause tingling sensation to collection finger, can effectively improve the detectivity of sensor.
3. the implementation of this patent, is ensureing the high sensitivity of original sensor and is not causing the premise of tingling sensation to fingerUnder, the exterior DCDC chips and interface conversion chip for generating high pressure can be removed, so as to effectively reduce fingerprint collecting modulePower consumption, saves the volume and cost of module, while system is simplified, improves the reliability of system.
Brief description of the drawings
Fig. 1 (a) uses the fingerprint collecting unit circuit of finger excitation in the prior art；
Fig. 1 (b) fingerprint sensor bulk driven schemes in the prior art；
Fig. 2 is the fingerprint collecting unit circuit based on fringe field finger capacitance and high-voltage pulse of the embodiment of the present invention；
Fig. 3 is the high-voltage pulse generation circuit of the embodiment of the present invention；
Fig. 4 is the charge pump booster circuit of the embodiment of the present invention.
Embodiment
To make the object, technical solutions and advantages of the present invention clearer, below in conjunction with the accompanying drawings come illustrate the present invention it is excellentEmbodiment is selected, this patent is retouched in detail by taking the capacitive fingerprint sensing device formed by capacitance type sensing element arrays as an exampleState, wherein, capacitance type sensing element arrays include two and more than two fingerprint collecting units.Fig. 2 is the embodiment of the present inventionThe fingerprint collecting unit circuit based on fringe field finger capacitance and high-voltage pulse.Fig. 3 is the high-tension pulse of the embodiment of the present inventionRush generation circuit.Fig. 4 is the charge pump booster circuit of the embodiment of the present invention.
High sensitivity fingerprint sensor proposed by the present invention based on BCD techniques, including：Fingerprint collecting unit circuit 100,High-voltage pulse generation circuit 200 and internal booster circuit.
Fingerprint collecting unit circuit 100, input terminal connection high-voltage pulse signal VH and digital analog converter 101, output terminal connectConnect output circuit or rear class receives amplifying circuit 102；High-voltage pulse generation circuit 200, output terminal connection fingerprint collecting unit electricityRoad 100, exports high-voltage pulse signal VH, for directly or indirectly driving the shape of finger print for fingerprint collecting unit circuit 100Into.Internal booster circuit, output terminal are connected with high-voltage pulse generation circuit 200, and the low voltage for power supply to be provided is raised toHigh voltage, high pressure Vout ' is inputted to high-voltage pulse generation circuit 200.
Fingerprint collecting unit circuit 100 is also comprising the first pole plate 103, the second pole plate 104, amplifier 105, reference voltageVref and feedback capacity Cfb.
Wherein, high-voltage pulse signal VH includes but not limited to 16V, 20V, below by taking high-voltage value 20V as an example.
Wherein, fringe field finger capacitance Cf is formed between the first pole plate 103, the second pole plate 104 and finger surface 106；First pole plate 103 and the top-level metallic that the second pole plate 104 is chip, chip surface dielectric layer material include but not limited to chip listThe common vehicle materials such as face passivation layer, PI, molding material, coating materials or ceramic cover plate.
Amplifier 105 includes normal phase input end, inverting input and output terminal；Reference voltage Vref is produced by front stage circuitsIt is raw, it is input to the normal phase input end of amplifier 105；One end of the feedback capacity Cfb and the inverting input phase of amplifier 105Even, the other end of the feedback capacity Cfb is connected with the output terminal of amplifier 105, feedback capacity Cfb by the second pole plate 104 andThe parasitic capacitance of lower metal is formed, and capacitance size is in the 10fF orders of magnitude；The inverting input of amplifier 105 also with the second polePlate 104 is connected；The output signal Vout of the output terminal output fingerprint collecting unit circuit 100 of amplifier 105.Put in the present embodimentBig device 105 is low-noise amplifier LNA.
DAC is digital analog converter 101 in Fig. 2, produces suitable analog quantity, is coupled to by DC compensation capacitance Cdc and putThe inverting input of big device 105, for adjusting the direct current biasing of circuit.DC compensation capacitance Cdc is by the second pole plate 4 and lower floorThe parasitic capacitance of metal is formed, and capacitance size is in the 1fF orders of magnitude.
The output circuit or rear class that Output Circuit circuits are LNA in Fig. 2 receive amplifying circuit 105.In the fingerprintIn collecting unit circuit, using the first pole plate 103 of high-voltage pulse driving finger capacitance, pass through amplifier 105 and feedback capacityCfb, element circuit output terminal is mirrored to by high-voltage pulse signal VH and fringe field finger capacitance Cf.
Fig. 3 is the high-voltage pulse generation circuit of the embodiment of the present invention.High-voltage pulse generation circuit 200 includes non-overlapping clockGeneration circuit 201, dynamic level carry circuit 1, dynamic level carry circuit 2 203, output insulated-gate field-effect crystal NPipe 204, output insulated-gate field-effect crystal P pipes 205.Change Pump circuits are charge pump circuit 206 in Fig. 3.
Assuming that the input signal of circuit is high level 1.8V, the pulse signal of low level 0V, is produced by non-overlapping clockCircuit 201 and dynamic level generation circuit 1, generate one group of non-overlapping clock, while the high level of pulse is lifted to phaseTo high voltage, such as 3V, in this, as the control sequential of output N pipes 204.By the use of the pulse signal that high level is 3V as defeatedEnter signal, by the dynamic level carry circuit 2 203 of 3V to 20V, obtain the pulse signal that high level is 20V, in this, asExport the control sequential of P pipes 205.By controlling the switch of output N pipes 204 and P pipes 205, realize with input signal at the same timeThe high level of sequence is 20V high pressures, and low level is the output signal of 0V.The signal is input to fingerprint collecting unit circuit 100 and inputsEnd, is high-voltage pulse signal VH.
In the present embodiment, internal booster circuit is charge pump.Fig. 4 is the charge pump booster circuit of the embodiment of the present invention.AdoptCharge pump capacitor with the non-overlapping clock of two-phase and step by step, after n+1 clock cycle (n is capacitance number), circuit can be withThe low voltage that power supply is provided is raised to high voltage Vout ', such as 1.8V input voltages are increased to 20V outputs.The high pressureVout ' is input to high-voltage pulse generation circuit 200, the high-pressure section power supply as high-voltage pulse generation circuit.
This patent uses BCD techniques, and on piece is produced by internal booster circuit integration realization high pressure, then passes through high-voltage pulseGeneration circuit 200, produces a high-voltage pulse.A fringe field capacitance can be formed between two pole plates in array elementCf.Finger surface is nearer from pole plate, and the field effect between two pole plates is weaker, and Cf is smaller, on the contrary then anti-.Using the high-voltage pulseThe first pole plate of finger capacitance is driven, by amplifier 105 and Cfb feedback capacities, high-voltage pulse signal and Cf are mirrored to listFirst circuit output end, element circuit output voltage Vout, according to principle of charge conservation,
Wherein, Vout is the output signal of the fingerprint collecting unit circuit, and VH is the high-voltage pulse signal, and Cf is sideEdge electric field finger capacitance, Cfb are feedback capacity.
Know that element circuit output voltage Vout and Cf is positively correlated from formula (1), illustrate the corresponding Vout of fingerprint ridgeSmall, the corresponding Vout of fingerprint valley is big.After obtaining the Vout of circuit output, changed by the amplification of late-class circuit and ADC, circuitFinger print information may finally be converted into fixed bit digital output.
The detailed description and the accompanying drawings of the embodiment of the present invention are only intended to the explanation present invention, rather than limitation by claim andThe scope of the present invention that its equivalent defines.