CN106557724A - Fingerprint sensing circuit and control method - Google Patents
Fingerprint sensing circuit and control method Download PDFInfo
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- CN106557724A CN106557724A CN201510623011.XA CN201510623011A CN106557724A CN 106557724 A CN106557724 A CN 106557724A CN 201510623011 A CN201510623011 A CN 201510623011A CN 106557724 A CN106557724 A CN 106557724A
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- switch
- amplifier
- sensing circuit
- fingerprint sensing
- reference voltage
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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
Abstract
A kind of fingerprint sensing circuit and its control method, fingerprint sensing circuit include：Fingerprint detection electric capacity, one end couple the finger；Detecting electrode, couples the fingerprint detection electric capacity；Driving voltage interface, is suitable to for the driving voltage alternating of two kinds of level of height to be loaded onto the detecting electrode；Amplifier；The detecting electrode is coupled to the inverting input of the amplifier for first switch, being suitably selected for property；Reference voltage interface, is suitable to the normal phase input end being alternately input into the reference voltage of two kinds of level of height to the amplifier；Control unit, is suitable to generate control signal so that the amplifier exports the first output voltage and the second output voltage after the completion of a timing cycles；Subtraction circuit, be suitable to using the difference of first output voltage and second output voltage as the fingerprint sensing circuit output signal.Fingerprint sensing circuit has cut down low frequency common noise signal, improves the when fingerprint sensing sensitivity of output voltage noise.
Description
Technical field
The present invention relates to identity identification technical field, more particularly to a kind of fingerprint sensing circuit and control method.
Background technology
With society progress and science and technology development, Web bank, ecommerce, personal mail,
And social networkies etc. have brought increasing facility.While the basic function in these societies
Need password and data encryption to ensure safety.And fingerprint is used as biological property, due to uniqueness
Become the effective means of personal identification identification.Fingerprint recognition is advantageous in that for identity authentication：User
Just；Biological characteristicses are difficult to replicate, safer for technology of identification.
Such as Fig. 1, it is the structural representation of the fingerprint sensing circuit of prior art.Wherein, finger 1 is in sensing
Fingerprint detection electric capacity C1 is formed on electrode 2, C3 is finger direct-to-ground capacitance.Direct-to-ground capacitance C3 is long-range for finger
In fingerprint detection electric capacity C1.Fingerprint detection electric capacity C1, finger direct-to-ground capacitance C3 and electrode direct-to-ground capacitance
C2 couples the reverse input end of amplifier F, by the positive input input signal in amplifier F
Vin, drives fingerprint sensing circuit work, so as to the capacitance of fingerprint detection electric capacity C1 is converted to voltage
Value, realizes the detection of opponent's fingerprint valley and wrinkle ridge by the process to amplifier F output voltage Vout.
In the fingerprint sensing circuit of prior art, the noise signal low frequency common noise Vom meetings of external circuit
It is carried in fingerprint detection electric capacity C1.Now, the output voltage of fingerprint sensing circuit is
(Vin+Vom)(C1+C2)/C4.The signal to noise ratio of fingerprint sensing circuit is effective output voltage and output noise electricity
The ratio of pressure, low frequency common noise cause the output voltage signal to noise ratio of fingerprint sensing circuit not high.Meanwhile,
As the value of coupled capacitor C4 is minimum, the noise jamming of very little can all affect the output electricity of fingerprint sensing circuit
Pressure, reduces detection sensitivity of the fingerprint sensing circuit to fingerprint detection electric capacity C1.
The content of the invention
Present invention solves the technical problem that being the sensitivity for how improving fingerprint sensing circuit.
To solve above-mentioned technical problem, the embodiment of the present invention provides a kind of fingerprint sensing circuit, the fingerprint
Sensing circuit includes：
Fingerprint detection electric capacity, one end couple the finger；
Detecting electrode, couples the fingerprint detection electric capacity；
Driving voltage interface, is suitable to for the driving voltage alternating of two kinds of level of height to be loaded onto the detection electricity
Pole；
Amplifier；
The detecting electrode is coupled to the inverting input of the amplifier for first switch, being suitably selected for property；
Reference voltage interface, is suitable to alternately be input into the amplifier reference voltage of two kinds of level of height
Normal phase input end；
Control unit, is suitable to generate control signal so that the amplifier is after the completion of a timing cycles
Export the first output voltage and the second output voltage；
Subtraction circuit, couples the outfan of the amplifier, is suitable to first output voltage and described
Output signal of the difference of the second output voltage as the fingerprint sensing circuit；
Wherein, the driving voltage is internal voltage driver.
Optionally, second switch, one end couple the positive input of the amplifier, the other end with it is described
The outfan of amplifier is connected；
Feedback capacity, one end couple the inverting input of the amplifier, the other end and the amplifier
Outfan is connected.
Optionally, described control unit couples the first switch, the second switch, driving electricity
Crimping mouth and the reference voltage interface.
Optionally, the driving voltage interface includes the 3rd switch and the 4th switch；The reference voltage connects
Mouth includes the 5th switch and the 6th switch；
The driving voltage of high level is loaded onto the detection electricity by the 3rd the being suitably selected for property of switch
Pole；The low level driving voltage is loaded onto the detecting electrode by the being suitably selected for property of the 4th switch；
The being suitably selected for property of 5th switch is input into the reference voltage of high level to the amplifier
Normal phase input end；6th the being suitably selected for property of switch is input into the low level reference voltage to described
The normal phase input end of amplifier.
Optionally, described control unit couples the first switch and the second switch；It is described to drive electricity
Pressure and the reference voltage are square-wave signal.
To solve above-mentioned technical problem, the embodiment of the invention also discloses a kind of control of fingerprint sensing circuit
Method, including：
In the first operative state, the driving voltage of two kinds of level of height is replaced by the driving voltage interface
The detecting electrode is loaded onto, the reference voltage interface is input into low level reference voltage to described to be put
The detecting electrode is coupled to the amplifier by the normal phase input end of big device, the first switch selectivity
Inverting input so that the amplifier exports the first output voltage；
In a second operative state, the driving voltage interface by height two kinds of level the driving voltage
Alternating is loaded onto the detecting electrode, and the reference voltage of high level is input into by the reference voltage interface
To the normal phase input end of the amplifier, the detecting electrode is coupled to institute by the first switch selectivity
State the inverting input of amplifier so that the amplifier exports the second output voltage.
Optionally, under first working condition, the first switch first disconnects and closing afterwards, and second opens
Pass closes first and then disconnect；The driving voltage interface includes the 3rd switch and the 4th switch, and the described 3rd opens
Pass closes first and then disconnect, and the 4th switch is set to normally closed；The reference voltage interface includes the 5th switch
Switch with the 6th, the 5th switch is set to normal off, the 6th switch is set to normally closed；
Under second working condition, the first switch first disconnects and closing afterwards, and second switch is first closed
After disconnect；It is described 3rd switch be set to it is normally closed, it is described 4th switch close first and then disconnect；Described 5th opens
Pass be set to it is normally closed, it is described 6th switch be set to normal off.
Optionally, the driving voltage interface includes the 3rd switch and the 4th switch；The reference voltage connects
Mouth includes the 5th switch and the 6th switch；3rd switch, the 4th switch, the 5th switch
It is set to the described 6th switch normally closed；
Under first working condition, the driving voltage interface accesses the driving electricity of two kinds of level of height
Pressure square-wave signal, the reference voltage interface access low level reference voltage square-wave signal；
Under second working condition, the driving voltage interface accesses the driving electricity of two kinds of level of height
Pressure square-wave signal, the reference voltage interface access the reference voltage square-wave signal of high level.
Optionally, the reference voltage square-wave signal cycle is the two of the driving voltage square-wave signal cycle
Times.
Optionally, after the completion of first working condition and second working condition, the subtraction circuit
Output signal is Δ VOUT=(Δ VOUT1- Δ VOUT2) C1/C2；
Wherein, Δ VOUT is the subtraction circuit output signal；Δ VOUT1 is first output voltage；
Δ VOUT2 is second output voltage；C1 is the fingerprint detection electric capacity；C2 is the feedback capacity.
Compared with prior art, the technical scheme of the embodiment of the present invention has the advantages that：
Driving voltage and internal reference voltage are respectively set at least two level signals by the embodiment of the present invention
Voltage, by the control of control signal, driving voltage interface and reference voltage interface optionally will tools
The driving voltage and internal reference voltage for having low and high level accesses fingerprint sensing circuit, so that fingerprint is passed
Inductive circuit output voltage has cut down noise signal low frequency common voltage, improves the output of fingerprint sensing circuit
Voltage signal to noise ratio, improves the sensitivity of fingerprint sensing circuit.
Description of the drawings
Fig. 1 is fingerprint sensing circuit structural representation in prior art；
Fig. 2 is a kind of fingerprint sensing circuit structural representation of the embodiment of the present invention；
Fig. 3 is embodiment of the present invention another kind fingerprint sensing circuit structural representation；
Fig. 4 is a kind of sequential chart of fingerprint sensing circuit mode of operation of the embodiment of the present invention；
Fig. 5 is a kind of a kind of fingerprint sensing circuit of embodiment of the present invention equivalent electric in the first operative state
Line structure schematic diagram；
Fig. 6 is a kind of a kind of fingerprint sensing circuit of embodiment of the present invention equivalent electric in a second operative state
Line structure schematic diagram；
Fig. 7 is the sequential chart of embodiment of the present invention another kind fingerprint sensing circuit mode of operation；
Fig. 8 is a kind of fingerprint sensing circuit structural representation of another embodiment of the present invention.
Specific embodiment
As described in the background art, in actual applications, the noise signal low frequency common of external circuit is made an uproar
Sound Vom can be carried in fingerprint detection electric capacity C1.Now, the output voltage of fingerprint sensing circuit is
(Vin+Vom)(C1+C2)/C4.As the value of coupled capacitor C4 is minimum, the noise jamming of very little can be very big
Impact fingerprint sensing circuit output voltage, reduce fingerprint sensing circuit to fingerprint detection electric capacity C1's
Detection sensitivity；Meanwhile, the signal to noise ratio of fingerprint sensing circuit is effective output voltage and output noise voltage
Ratio, low frequency common noise causes the output voltage signal to noise ratio of fingerprint sensing circuit not high.
The embodiment of the present invention, will be interior by driving voltage to be divided into the driving voltage of at least two level signals
Portion's reference voltage is divided into the driving voltage of at least two level signals, and by the way of switch, selectivity will drive
Galvanic electricity is pressed and internal reference voltage accesses fingerprint sensing circuit, so that fingerprint sensing circuit output voltage
Cut down noise signal low frequency common voltage, thus improve the output voltage signal to noise ratio of fingerprint sensing circuit,
Improve fingerprint sensing sensitivity.
It is understandable to enable the above objects, features and advantages of the present invention to become apparent from, below in conjunction with the accompanying drawings
The specific embodiment of the present invention is described in detail.
Fig. 2 is a kind of fingerprint sensing circuit structural representation of the embodiment of the present invention, the fingerprint sensing circuit
Including：
Fingerprint detection electric capacity C1, detecting electrode 2, first switch T1, control unit 201, reference voltage
Interface 202, driving voltage interface 203 and subtraction circuit 204；
Wherein, fingerprint detection electric capacity C1 one end connection finger 1, other end coupling detecting electrode 2；Drive
Voltage interface 203 is suitable to for driving voltage VD to be loaded onto the fingerprint detection electric capacity C1.
In the present embodiment, driving voltage VD is provided with two kinds of level signals of low and high level, and driving voltage connects
Mouth 203 is suitable to for the driving voltage VD alternatings of two kinds of level of the height to be loaded onto the fingerprint detection electricity
Hold C1, the driving voltage is the internal voltage driver arranged inside fingerprint sensing circuit.
In being embodied as, the noise signal low frequency common noise Vom that external circuit is produced is carried in fingerprint inspection
Survey electric capacity C1.
It is understood that in actual applied environment, in addition to low frequency common noise Vom, also
Other high frequency common mode noises, electric current source noise, phase noise etc., the embodiment of the present invention be it is described other
In the case that noise is constant, interference of the low frequency common noise to fingerprint sensing circuit is reduced, it is right to should not be used as
The restriction of the embodiment of the present invention.
First switch T1, one end couple the fingerprint detection electric capacity C1, and the other end couples the amplification
The inverting input of device F.
The positive that reference voltage interface 202 is suitable to reference voltage REF is input into the amplifier F is input into
End.
In the present embodiment, reference voltage REF is provided with two kinds of level signals of low and high level, and reference voltage connects
Mouth 202 is suitable to alternately be input into the amplifier F's the reference voltage REF of two kinds of level of the height
Normal phase input end.
In the present embodiment, reference voltage REF is provided in the reference voltage inside fingerprint sensing circuit.
It should be noted that the reference voltage interface 202 can be switched including two, it is also possible to include
The reference electricity of one single-pole double-throw switch (SPDT), or any alternative connection two kinds of level of height
The element of pressure REF；The driving voltage interface 203 can be switched including two, it is also possible to including one
The driving voltage VD of single-pole double-throw switch (SPDT), or any alternative connection two kinds of level of height
Element；The embodiment of the present invention is without limitation.
Control unit 201, generates control signal, controls first switch T1, the second switch T2
State, control the driving voltage VD and be loaded onto the fingerprint detection electric capacity C1 and the reference voltage
REF is input into the state of the amplifier F so that the amplifier F is after the completion of a timing cycles
Export the first output voltage and the second output voltage.
Subtraction circuit 204, couples the outfan of the amplifier F, by first output voltage and described
Output signal Vout of the difference of the second output voltage as the fingerprint sensing circuit.
In the embodiment of the present invention, the subtraction circuit 204 can be realized by the way of analog circuit,
Can realize that the embodiment of the present invention is without limitation using Digital Logical Circuits.
One end of the second switch T2 couples first switch T1, the other end and the amplifier F
Outfan be connected；One end of feedback capacity C2 couples the inverting input of the amplifier F,
The other end couples the outfan of the amplifier F.
In the present embodiment, the control signal that control unit 201 is generated controls first switch T1, described
The state of second switch T2, control the driving voltage VD be loaded onto the fingerprint detection electric capacity C1 and
The reference voltage REF is input into the state of the amplifier F, according to the combination of the state, control
Unit 201 provides the work schedule of the fingerprint sensing circuit.
Fig. 3 is embodiment of the present invention another kind fingerprint sensing circuit structural representation, the fingerprint sensing electricity
Road includes：
Fingerprint detection electric capacity C1, feedback capacity C2, amplifier F, control unit 201, subtraction circuit 204,
First switch T1, second switch T2, the 3rd switch T3, the 4th switch T4, the 5th switch T5 and the
Six switch T6.
Wherein, fingerprint detection electric capacity C1 one end ground connection, other end coupling the 3rd switch T3, the 4th switch
T4 and first switch T1；The driving voltage VP of high level is added by the 3rd switch the being suitably selected for property of T3
The fingerprint detection electric capacity C1 is loaded onto, the 4th switch the being suitably selected for property of T4 drives electricity by low level
Pressure VN is loaded onto the fingerprint detection electric capacity C1.
In being embodied as, noise signal low frequency common voltage Vom is carried in fingerprint detection electric capacity C1.
In the present embodiment, first switch T1, one end couple the fingerprint detection electric capacity C1, the other end
Couple the inverting input of the amplifier F.
In the present embodiment, the normal phase input end coupling the 5th of the amplifier F switchs the switches of T5 and the 6th
T6；5th switch the being suitably selected for property of T5 is input into the reference voltage VREFP of high level to described puts
Big device F, the 6th switch the being suitably selected for property of T6 are input into low level reference voltage VREFN to institute
State amplifier F.
In the present embodiment, the reference voltage VREFP of the high level and low level reference voltage VREFN
The reference voltage being provided in inside stricture of vagina detection circuit.
In the present embodiment, one end of the second switch T2 couples first switch T1, the other end with
The outfan of the amplifier F is connected；One end of feedback capacity C2 couples the amplifier F's
Inverting input, the other end couple the outfan of the amplifier F.
The control signal that control unit 201 is generated so that the amplifier F is completed in a timing cycles
After export the first output voltage and the second output voltage；Subtraction circuit 204, couples the defeated of the amplifier F
Go out end, using the difference of first output voltage and second output voltage as fingerprint sensing electricity
Output signal VOUT on road.
In the present embodiment, the fingerprint sensing circuit is opened by clock signal control first switch T1, second
The state of T2, the 3rd switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch T6 is closed, and
According to the combinations of states of the switch, there is provided the mode of operation of the fingerprint sensing circuit.That is,
The corresponding corresponding clock signal of the mode of operation.
Fig. 4 is refer to, Fig. 4 is a kind of sequential chart of fingerprint sensing circuit mode of operation of the embodiment of the present invention.
In the present embodiment, the clock signal of the output of control unit 201 can be divided into two stages, the first rank
Section S1 and second stage S2.
In being embodied as, fingerprint sensing circuit working condition in the first stage under the sequencing contro of S1 is the
One working condition, amplifier export the first output voltage；Sequential of the fingerprint sensing circuit in second stage S2
Working condition under controlling be the second working condition, amplifier export the second output voltage.
Fig. 3 is referred in the lump, and in the present embodiment, in the first operative state, the 3rd switchs fingerprint sensing circuit
T3 and the 5th switch T5 be set to it is normally opened, the 6th switch T6 be set to it is normally closed.Fig. 5 is referred to, Fig. 5 is finger
A kind of equivalent circuit diagram of stricture of vagina sensing circuit first stage S1 in the operational mode, the driving voltage interface
The driving voltage VP of high level is accessed, internal reference voltage is configured to low level reference voltage VREFN,
Noise signal low frequency common voltage Vom is carried in fingerprint detection electric capacity C1.
With continued reference to Fig. 4, the timing cycles of first stage S1 include two stages, sample phase and
The transmission stage.Under sample phase sequencing contro, first switch T1 disconnects, the 3rd switch T3 and second
Switch T2 closures, the driving voltage VP and low frequency common of the fingerprint detection electric capacity C1 couplings high level
Voltage Vom.The driving voltage VP of high level is charged to fingerprint detection electric capacity C1, feedback capacity
The voltage of C2 resets, and the positive input of amplifier F accesses low level reference voltage VREFN.Adopt
After sample stage sequential terminates, driving voltage VP of the fingerprint detection electric capacity C1 both end voltages size for high level
Size, the output end voltage of amplifier F is low level reference voltage VREFN, i.e.,
VOUT1=VREFN.
Transmission stage of the fingerprint sensing circuit in the first working condition, first switch T1 closure, the 3rd switch
The switch T6 of T3 and the 6th disconnect, and the driving voltage VP of high level disconnects the connection with circuit.Amplifier F
Inverting input access detecting electrode C1 and low frequency common voltage Vom, the positive input of amplifier F
Access low level reference voltage VREFN.After transmission stage sequential terminates, according to law of conservation of charge,
The outfan output voltage of amplifier F is VOUT2=VREFN- (VP+Vom-VREFN) C1/C2.
After the completion of one timing cycles of mode of operation first stage S1, fingerprint sensing circuit output voltage is
The difference of the output voltage of sample phase and output stage amplifier F, the i.e. output voltage of subtraction circuit
Δ VOUT=VOUT1-VOUT2=(VP+Vom-VREFN) C1/C2.The voltage of the fingerprint sensing circuit is moved
State scope is (VDACP+Vom-VREFN) C1/C2.
In the present embodiment, in the second working condition, first switch T1 and the 4th is switched fingerprint sensing circuit
T4 be set to it is normally opened, the 3rd switch T3 be set to it is normally closed.With reference to Fig. 6, Fig. 6 is fingerprint sensing circuit in work
Equivalent circuit diagram under pattern second stage S2 sequencing contro, driving voltage are low level driving voltage
VN, internal reference voltage are configured to the reference voltage VREFP of high level, noise signal low frequency common voltage
Vom is carried in fingerprint detection electric capacity C1.
With continued reference to Fig. 4, the sequential of second stage S2 includes two stages, sample phase and transmission stage,
Fig. 3 is referred in the lump, and under the sequencing contro of sample phase, the 5th switch T5 disconnects fingerprint sensing circuit,
The switch T6 closures of second switch T2 and the 6th, low level driving voltage VN is to fingerprint detection electric capacity C1
It is charged, the positive input of amplifier F couples the reference voltage VREFP of high level.Sample phase
After end, fingerprint detection electric capacity C1 voltage swings reach VN sizes, the outfan output electricity of amplifier F
Press the reference voltage for high level, i.e. VOUT1=VREFP.
In the present embodiment, fingerprint sensing circuit under the transmission stage sequencing contro of the second working condition,
Five switch T5 closures, the switch T6 of second switch T2 and the 6th disconnect, the normal phase input end coupling of amplifier F
Meet fingerprint detection electric capacity C1 and low frequency common voltage Vom, the voltage VN of fingerprint detection electric capacity C1 and low
Frequency common-mode voltage Vom accesses the inverting input of amplifier F, and the positive input coupling of amplifier F is high
The reference voltage VREFP of level.After the transmission stage terminates, according to law of conservation of charge, amplifier F's
Outfan output voltage is VOUT2=VREFP- (VN+Vom-VREFP) C1/C2.
After the completion of the second working condition, the output voltage of subtraction circuit is fingerprint sensing circuit
VOUT2=(VN+Vom-VREFP) C1/C2.
In the present embodiment, after the completion of the sequencing contro of mode of operation first stage S1 and second stage S2,
Output voltage of the output voltage of subtraction circuit as the fingerprint sensing circuit, i.e. output voltage is：
(VP+VREFP-VN-VREFN)C1/C2。
In being embodied as, the driving voltage VP of high level is set to supply voltage；Low level driving voltage
VN is set to ground voltage.The reference voltage VREFP of high level is set to supply voltage, but is amplified
Device structure influence is less than supply voltage；Low level reference voltage VREFN is set to ground connection, but is amplified
Device structure influence is higher than ground voltage.
In the present embodiment, the driving voltage VP of high level and low level driving voltage VN is internal drive
Voltage.
In the present embodiment, subtraction circuit is to amplifier S1 output voltages Δ VOUT1 and second in the first stage
Stage S2, output voltage Δ VOUT2 made the difference, relative to fingerprint sensing circuit output voltage of the prior art
(VP+Vom-VREFN) C1/C2, output electricity of the fingerprint sensing circuit under embodiment of the present invention mode of operation
Press as (VP+VREFP-VN-VREFN) C1/C2, noise signal low frequency common voltage Vom is cut out.
The output voltage signal to noise ratio increase of fingerprint sensing circuit, the sensitivity of fingerprint sensing and effectiveness are improved.
It is understood that the reference voltage interface 202 and driving voltage interface 203 in the embodiment of the present invention
The square-wave signal of rule change can also be accessed, wherein, the reference voltage signal cycle is drive voltage signal
The twice in cycle.
Fig. 7 is the sequential chart of embodiment of the present invention another kind fingerprint sensing circuit mode of operation.
In the embodiment of the present invention, the 3rd switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch
T6 is set to normally closed, and reference voltage interface 202 arranges the reference voltage for accessing square-wave signal, and driving voltage connects
Mouth 203 accesses the driving voltage of square-wave signals.
It is understood that in due to the embodiment of the present invention, the 3rd switch T3, the 4th switch T4, the 5th
Switch T5 and the 6th switch T6 be set to it is normally closed, therefore can also be not provided with the 3rd switch T3, the 4th switch
T4, the 5th switch T5 and the 6th switch T6, using arbitrary enforceable conducting element, access square wave letter
Number driving voltage and reference voltage.
Fig. 7 is refer to, the clock signal of the output of control unit 201 can be divided into two stages, first stage
S1 and second stage S2.Working condition of the fingerprint sensing circuit in the first stage under the sequencing contro of S1 be
First working condition, amplifier export the first output voltage；Fingerprint sensing circuit second stage S2 when
Sequence control under working condition be the second working condition, amplifier export the second output voltage.
Fig. 5 and Fig. 6, Fig. 5 are referred in the lump under fingerprint sensing circuit first stage S1 sequencing contro
Equivalent circuit diagram is planted, Fig. 6 is equivalent circuit diagram of the fingerprint sensing circuit under second stage S2 sequencing contro.
Specific implementation method refers to previous embodiment, and here is omitted.
In the present embodiment, after the completion of the sequencing contro of timing control signal, subtraction circuit exists to amplifier
First stage S1 output voltage Δ VOUT1 and second stage S2 output voltage Δ VOUT2 make the difference, relative to
Fingerprint sensing circuit output voltage (VP+Vom-VREFN) C1/C2 of the prior art, fingerprint sensing circuit
Output voltage under embodiment of the present invention mode of operation is (VP+VREFP-VN-VREFN) C1/C2, is made an uproar
Acoustical signal low frequency common voltage Vom is cut out.The output voltage signal to noise ratio increase of fingerprint sensing circuit,
The sensitivity of fingerprint sensing and effectiveness are improved.
Fig. 8 is a kind of fingerprint sensing circuit structural representation of another embodiment of the present invention.
In the present embodiment, in the present embodiment, the driving voltage VP and low level driving voltage of high level
VN is external drive voltage.User's finger is by contacting outer electrode (not shown) by external drive voltage
It is carried in fingerprint detection electric capacity C1.
Specific embodiment refers to preceding aspect embodiments, and here is omitted.
Although present disclosure is as above, the present invention is not limited to this.Any those skilled in the art,
Without departing from the spirit and scope of the present invention, can make various changes or modifications, therefore the guarantor of the present invention
Shield scope should be defined by claim limited range.
Claims (10)
1. a kind of fingerprint sensing circuit, it is characterised in that include：
Fingerprint detection electric capacity, one end couple the finger；
Detecting electrode, couples the fingerprint detection electric capacity；
Driving voltage interface, is suitable to for the driving voltage alternating of two kinds of level of height to be loaded onto the detecting electrode；
Amplifier；
The detecting electrode is coupled to the inverting input of the amplifier for first switch, being suitably selected for property；
Reference voltage interface, is suitable to alternately be input into the amplifier reference voltage of two kinds of level of height
Normal phase input end；
Control unit, is suitable to generate control signal so that the amplifier is defeated after the completion of a timing cycles
Go out the first output voltage and the second output voltage；
Subtraction circuit, couples the outfan of the amplifier, is suitable to first output voltage and described the
Output signal of the difference of two output voltages as the fingerprint sensing circuit；
Wherein, the driving voltage is internal voltage driver.
2. fingerprint sensing circuit according to claim 1, it is characterised in that also include：
Second switch, one end couple the reverse input end of the amplifier, and the other end is defeated with the amplifier
Go out end to be connected；
Feedback capacity, one end couple the inverting input of the amplifier, and the other end is defeated with the amplifier
Go out end to be connected.
3. fingerprint sensing circuit according to claim 2, it is characterised in that described control unit couples institute
State first switch, the second switch, the driving voltage interface and the reference voltage interface.
4. fingerprint sensing circuit according to claim 3, it is characterised in that the driving voltage interface bag
Include the 3rd switch and the 4th switch；The reference voltage interface includes the 5th switch and the 6th switch；
The driving voltage of high level is loaded onto the detecting electrode by the being suitably selected for property of the 3rd switch；
The low level driving voltage is loaded onto the detecting electrode by the being suitably selected for property of the 4th switch；
The reference voltage of high level is just input into the amplifier by the being suitably selected for property of the 5th switch
Phase input；6th the being suitably selected for property of switch is input into the low level reference voltage to described
The normal phase input end of amplifier.
5. fingerprint sensing circuit according to claim 2, it is characterised in that described control unit couples institute
State first switch and the second switch；The driving voltage and the reference voltage are square-wave signal.
6. the control method of the fingerprint sensing circuit according to any one of claim 1-3, it is characterised in that
Including：
In the first operative state, the driving voltage of two kinds of level of height is alternately added by the driving voltage interface
The detecting electrode is loaded onto, the reference voltage interface is input into low level reference voltage to described to be put
The detecting electrode is coupled to the amplification by the normal phase input end of big device, the first switch selectivity
The inverting input of device so that the amplifier exports the first output voltage；
In a second operative state, the driving voltage of two kinds of level of height is handed over by the driving voltage interface
For the detecting electrode is loaded onto, the reference voltage of high level is input into by the reference voltage interface
To the normal phase input end of the amplifier, the detecting electrode is coupled to by the first switch selectivity
The inverting input of the amplifier so that the amplifier exports the second output voltage.
7. the control method of fingerprint sensing circuit according to claim 6, it is characterised in that described
Under one working condition, the first switch first disconnects and closing afterwards, and second switch closes first and then disconnect；Institute
Stating driving voltage interface includes the 3rd switch and the 4th switch, and the 3rd switch closes first and then disconnect,
4th switch is set to normally closed；The reference voltage interface includes the 5th switch and the 6th switch, institute
State the 5th switch and be set to normal off, the 6th switch is set to normally closed；
Under second working condition, the first switch first disconnects and closing afterwards, after second switch is first closed
Disconnect；It is described 3rd switch be set to it is normally closed, it is described 4th switch close first and then disconnect；Described 5th opens
Pass be set to it is normally closed, it is described 6th switch be set to normal off.
8. the control method of fingerprint sensing circuit according to claim 6, it is characterised in that the driving
Voltage interface includes the 3rd switch and the 4th switch；The reference voltage interface includes the 5th switch and the
Six switches；3rd switch, the 4th switch, the 5th switch and the 6th switch are put
For normally closed；
Under first working condition, the driving voltage interface accesses the driving voltage of two kinds of level of height
Square-wave signal, the reference voltage interface access low level reference voltage square-wave signal；
Under second working condition, the driving voltage interface accesses the driving voltage of two kinds of level of height
Square-wave signal, the reference voltage interface access the reference voltage square-wave signal of high level.
9. the control method of fingerprint sensing circuit according to claim 8, it is characterised in that the reference
The voltage square wave signal cycle is the twice in the driving voltage square-wave signal cycle.
10. the control method of the fingerprint sensing circuit according to any one of claim 7-9, it is characterised in that
After the completion of first working condition and second working condition, the subtraction circuit output signal is
Δ VOUT=(Δ VOUT1- Δ VOUT2) C1/C2；
Wherein, Δ VOUT is the subtraction circuit output signal；Δ VOUT1 is first output voltage；
Δ VOUT2 is second output voltage；C1 is the fingerprint detection electric capacity；C2 is the feedback electricity
Hold.
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