CN106557724B - Fingerprint sensing circuit and control method - Google Patents
Fingerprint sensing circuit and control method Download PDFInfo
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- CN106557724B CN106557724B CN201510623011.XA CN201510623011A CN106557724B CN 106557724 B CN106557724 B CN 106557724B CN 201510623011 A CN201510623011 A CN 201510623011A CN 106557724 B CN106557724 B CN 106557724B
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- G—PHYSICS
- G06—COMPUTING OR CALCULATING; 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
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Abstract
A kind of fingerprint sensing circuit and its control method, fingerprint sensing circuit include: fingerprint detection capacitor, and one end couples the finger；Detecting electrode couples the fingerprint detection capacitor；Driving voltage interface, suitable for the driving voltage of two kinds of level of height is alternately loaded onto the detecting electrode；Amplifier；The detecting electrode is coupled to the inverting input terminal of the amplifier by first switch, being suitably selected for property；Reference voltage interface, suitable for the reference voltage of two kinds of level of height to be alternately input to the normal phase input end of the amplifier；Control unit is suitable for generating 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, suitable for using the difference of first output voltage and second output voltage as the output signal of the fingerprint sensing circuit.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 methods.
Background technique
With the development of social progress and science and technology, Web bank, e-commerce, personal mail and social activity
Network etc. has brought more and more conveniences.The basic function in these societies needs password and data encryption simultaneously
Ensure safety.And fingerprint is as biological property, due to becoming the effective means of personal identification identification with uniqueness.Fingerprint is known
Not Yong Yu identity authentication be advantageous in that: it is easy to use；Biological characteristics are difficult to replicate, for identification Technical comparing safety.
It is the structural schematic diagram of the fingerprint sensing circuit of the prior art such as Fig. 1.Wherein, the shape on induction electrode 2 of finger 1
It is finger direct-to-ground capacitance at fingerprint detection capacitor C1, C3.Finger direct-to-ground capacitance C3 is much larger than fingerprint detection capacitor C1.Fingerprint detection
The reverse input end of capacitor C1, finger direct-to-ground capacitance C3 and electrode direct-to-ground capacitance C2 coupling amplifier F, by amplifier F's
Positive input input signal Vin, driving fingerprint sensing circuit work, so that the capacitance of fingerprint detection capacitor C1 be turned
It is changed to voltage value, the detection of opponent's fingerprint valley and wrinkle ridge is realized by the processing to amplifier F output voltage Vout.
In the fingerprint sensing circuit of the prior art, the noise signal low frequency common noise Vom of external circuit, which can be loaded, to be referred to
Line detects capacitor C1.At this point, the output voltage of fingerprint sensing circuit is (Vin+Vom) (C1+C2)/C4.Fingerprint sensing circuit
Signal-to-noise ratio is the ratio of effective output voltage and output noise voltage, and low frequency common noise leads to the output electricity of fingerprint sensing circuit
Press signal-to-noise ratio not high.Simultaneously as the value of coupled capacitor C4 is minimum, the noise jamming of very little can all influence fingerprint sensing circuit
Output voltage reduces fingerprint sensing circuit to the detection sensitivity of fingerprint detection capacitor C1.
Summary of the invention
Present invention solves the technical problem that being how to improve the sensitivity of fingerprint sensing circuit.
In order to solve the above technical problems, the embodiment of the present invention provides a kind of fingerprint sensing circuit, the fingerprint sensing circuit
Include:
Fingerprint detection capacitor, one end couple the finger；
Detecting electrode couples the fingerprint detection capacitor；
Driving voltage interface, suitable for the driving voltage of two kinds of level of height is alternately loaded onto the detecting electrode；
Amplifier；
The detecting electrode is coupled to the inverting input terminal of the amplifier by first switch, being suitably selected for property；
Reference voltage interface, the positive suitable for the reference voltage of two kinds of level of height is alternately input to the amplifier are defeated
Enter end；
Control unit is suitable for generating control signal, so that the amplifier exports first after the completion of a timing cycles
Output voltage and the second output voltage；
Subtraction circuit couples the output end of the amplifier, is suitable for first output voltage and second output
Output signal of the difference of 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, and the other end is defeated with the amplifier
Outlet is connected；
Feedback capacity, one end couple the inverting input terminal of the amplifier, the output end phase of the other end and the amplifier
Connection.
Optionally, described control unit couples the first switch, the second switch, the driving voltage interface and institute
State reference voltage interface.
Optionally, the driving voltage interface includes third switch and the 4th switch；The reference voltage interface includes the
Five switches and the 6th switch；
The driving voltage of high level is loaded onto the detecting electrode by the being suitably selected for property of third switch；Described
The low level driving voltage is loaded onto the detecting electrode by four being suitably selected for property of switch；
The positive that the reference voltage of high level is input to the amplifier by the being suitably selected for property of the 5th switch is defeated
Enter end；6th the being suitably selected for property of switch inputs the positive that the low level reference voltage is input to the amplifier
End.
Optionally, described control unit couples the first switch and the second switch；The driving voltage and described
Reference voltage is square-wave signal.
In order to solve the above technical problems, the embodiment of the invention also discloses a kind of control method of fingerprint sensing circuit, packet
It includes:
In the first operative state, the driving voltage of two kinds of level of height is alternately loaded onto institute by the driving voltage interface
Detecting electrode is stated, low level reference voltage is input to the normal phase input end of the amplifier, institute by the reference voltage interface
The inverting input terminal that the detecting electrode is selectively coupled to the amplifier by first switch is stated, so that the amplifier exports
First output voltage；
In a second operative state, the driving voltage interface alternately loads the driving voltage of two kinds of level of height
To the detecting electrode, the positive that the reference voltage of high level is input to the amplifier by the reference voltage interface is defeated
Enter end, the detecting electrode is selectively coupled to the inverting input terminal of the amplifier by the first switch, so that described put
Big device exports the second output voltage.
Optionally, under first working condition, the first switch first disconnects to be closed afterwards, after second switch is first closed
It disconnects；The driving voltage interface includes third switch and the 4th switch, and the third switch closes first and then disconnect, and the described 4th
Switch is set to normally closed；The reference voltage interface includes the 5th switch and the 6th switch, and the 5th switch is set to normal off, described
6th switch is set to normally closed；
Under second working condition, the first switch first disconnects to be closed afterwards, and second switch closes first and then disconnect；Institute
State third switch be set to it is normally closed, it is described 4th switch close first and then disconnect；5th switch is set to normally closed, the 6th switch
It is set to normal off.
Optionally, the driving voltage interface includes third switch and the 4th switch；The reference voltage interface includes the
Five switches and the 6th switch；The third switch, the 4th switch, the 5th switch and the 6th switch are set to often
It closes；
Under first working condition, the driving voltage square wave letter of described driving voltage interface access two kinds of level of height
Number, the reference voltage interface accesses low level reference voltage square-wave signal；
Under second working condition, the driving voltage square wave letter of described driving voltage interface access two kinds of level of height
Number, the reference voltage square-wave signal of the reference voltage interface access high level.
Optionally, the reference voltage square-wave signal period is twice of the driving voltage square-wave signal period.
Optionally, after the completion of first working condition and second working condition, the subtraction circuit output signal
For 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 capacitor；C2 is the feedback capacity.
Compared with prior art, the technical solution of the embodiment of the present invention has the advantages that
Driving voltage and internal reference voltage are respectively set to the voltage of at least two level signals by the embodiment of the present invention,
By controlling the control of signal, driving voltage interface and reference voltage interface are selectively by the driving voltage with low and high level
Fingerprint sensing circuit is accessed with internal reference voltage, so that fingerprint sensing circuit output voltage has cut down noise signal low frequency
Common-mode voltage improves the output voltage signal-to-noise ratio of fingerprint sensing circuit, improves the sensitivity of fingerprint sensing circuit.
Detailed description of the invention
Fig. 1 is fingerprint sensing circuit structural schematic diagram in the prior art；
Fig. 2 is a kind of fingerprint sensing circuit structural schematic diagram of the embodiment of the present invention；
Fig. 3 is another kind fingerprint sensing circuit structural schematic diagram of the embodiment of the present invention；
Fig. 4 is a kind of timing diagram of fingerprint sensing circuit operating mode of the embodiment of the present invention；
Fig. 5 is that a kind of a kind of equivalent circuit structure of fingerprint sensing circuit of the embodiment of the present invention in the first operative state shows
It is intended to；
Fig. 6 is that a kind of a kind of equivalent circuit structure of fingerprint sensing circuit of the embodiment of the present invention in a second operative state shows
It is intended to；
Fig. 7 is the timing diagram of another kind fingerprint sensing circuit operating mode of the embodiment of the present invention；
Fig. 8 is a kind of fingerprint sensing circuit structural schematic diagram of another embodiment of the present invention.
Specific embodiment
As described in the background art, in practical applications, the noise signal low frequency common noise Vom of external circuit can add
It is loaded in fingerprint detection capacitor C1.At this point, the output voltage of fingerprint sensing circuit is (Vin+Vom) (C1+C2)/C4.Due to coupling
The value of capacitor C4 is minimum, the noise jamming of very little can strong influence fingerprint sensing circuit output voltage, reduce fingerprint
Detection sensitivity of the sensing circuit to fingerprint detection capacitor C1；Meanwhile the signal-to-noise ratio of fingerprint sensing circuit is effective output voltage
With the ratio of output noise voltage, low frequency common noise causes the output voltage signal-to-noise ratio of fingerprint sensing circuit not high.
Driving voltage by being divided into the driving voltages of at least two level signals by the embodiment of the present invention, by internal reference electricity
Pressure is divided into the driving voltage of at least two level signals, selective by driving voltage and internal reference voltage by the way of switch
Fingerprint sensing circuit is accessed, so that fingerprint sensing circuit output voltage has cut down noise signal low frequency common voltage, thus
The output voltage signal-to-noise ratio for improving fingerprint sensing circuit, improves fingerprint sensing sensitivity.
To make the above purposes, features and advantages of the invention more obvious and understandable, with reference to the accompanying drawing to the present invention
Specific embodiment be described in detail.
Fig. 3 is a kind of fingerprint sensing circuit structural schematic diagram of the embodiment of the present invention, and the fingerprint sensing circuit includes:
Fingerprint detection capacitor C1, detecting electrode 2 (referring to figure 2. shown in), first switch T1, control unit 201, with reference to electricity
Crimp mouth 202, driving voltage interface 203 and subtraction circuit 204；
Wherein, the one end (shown in Fig. 2) fingerprint detection capacitor C1 connects finger 1, and the other end couples detecting electrode 2；Driving electricity
Crimping mouth 203 is suitable for driving voltage VD being loaded onto the fingerprint detection capacitor C1.
In the present embodiment, driving voltage VD is provided with two kinds of level signals of low and high level, and driving voltage interface 203 is suitable for will
The driving voltage VD of two kinds of level of the height is alternately loaded onto the fingerprint detection capacitor C1, and the driving voltage is that fingerprint passes
The internal voltage driver being arranged inside inductive circuit.
In specific implementation, the noise signal low frequency common noise Vom that external circuit generates is loaded in fingerprint detection capacitor C1.
It is understood that other than low frequency common noise Vom, it is total that there are also other high frequencies in actual application environment
Mode noise, electric current source noise, phase noise etc., the embodiment of the present invention are reduced low in the case where other described noises are constant
Interference of the frequency common-mode noise to fingerprint sensing circuit, should not be used as the limitation to the embodiment of the present invention.
The first switch T1, one end couple the fingerprint detection capacitor C1, and the other end couples the reverse phase of the amplifier F
Input terminal.
Reference voltage interface 202 is suitable for for reference voltage REF being input to the normal phase input end of the amplifier F.
In the present embodiment, reference voltage REF is provided with two kinds of level signals of low and high level, and reference voltage interface 202 is suitable for
The reference voltage REF of two kinds of level of the height is alternately input to the normal phase input end of the amplifier F.
In the present embodiment, reference voltage REF is the reference voltage being arranged in inside fingerprint sensing circuit.
It should be noted that the reference voltage interface 202 may include two switches, it also may include that a hilted broadsword is double
Throw switch is also possible to the element of any alternative reference voltage REF for connecting described two kinds of level of height；The driving electricity
Crimping mouth 203 may include two switches, also may include a single-pole double-throw switch (SPDT), be also possible to any alternative connection
The element of the driving voltage VD of two kinds of level of the height；The embodiment of the present invention is without limitation.
Control unit 201 generates control signal, controls the state of the first switch T1, the second switch T2, controls
The driving voltage VD is loaded onto the fingerprint detection capacitor C1 and the reference voltage REF is input to the shape of the amplifier F
State, so that the amplifier F exports the first output voltage and the second output voltage after the completion of a timing cycles.
Subtraction circuit 204 couples the output end of the amplifier F, by first output voltage and second output
Output signal Vout of the difference of 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 also use number
Word logic circuit realizes that the embodiment of the present invention is without limitation.
One end of the second switch T2 couples the first switch T1, the output end phase of the other end and the amplifier F
Connection；One end of the feedback capacity C2 couples the inverting input terminal of the amplifier F, and the other end couples the amplifier F's
Output end.
In the present embodiment, the control signal that control unit 201 generates controls the first switch T1, the second switch T2
State, control the driving voltage VD be loaded onto the fingerprint detection capacitor C1 and reference voltage REF be input to it is described
The state of amplifier F, according to the combination of the state, control unit 201 provides the working sequence of the fingerprint sensing circuit.
Fig. 3 is another kind fingerprint sensing circuit structural schematic diagram of the embodiment of the present invention, and the fingerprint sensing circuit includes:
Fingerprint detection capacitor C1, feedback capacity C2, amplifier F, control unit 201, subtraction circuit 204, first switch T1,
Second switch T2, third switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch T6.
Wherein, the one end fingerprint detection capacitor C1 is grounded, and the other end couples third switch T3, the 4th switch T4 and first switch
T1；The driving voltage VP of high level is loaded onto the fingerprint detection capacitor C1 by the being suitably selected for property of third switch T3, described
Low level driving voltage VN is loaded onto the fingerprint detection capacitor C1 by the 4th being suitably selected for property of switch T4.
In specific implementation, noise signal low frequency common voltage Vom is loaded in fingerprint detection capacitor C1.
In the present embodiment, the first switch T1, one end couples the fingerprint detection capacitor C1, puts described in other end coupling
The inverting input terminal of big device F.
In the present embodiment, the normal phase input end of the amplifier F couples the 5th switch T5 and the 6th switch T6；Described 5th
The reference voltage VREFP of high level is input to the amplifier F by being suitably selected for property of switch T5, and the 6th switch T6 is suitable for choosing
Low level reference voltage VREFN is input to the amplifier F by selecting property.
In the present embodiment, the reference voltage VREFP of the high level and low level reference voltage VREFN are arranged in line
Reference voltage inside detection circuit.
In the present embodiment, one end of the second switch T2 couples the first switch T1, the other end and the amplifier F
Output end be connected；One end of the feedback capacity C2 couples the inverting input terminal of the amplifier F, described in other end coupling
The output end of amplifier F.
The control signal that control unit 201 generates, so that the amplifier F exports first after the completion of a timing cycles
Output voltage and the second output voltage；Subtraction circuit 204 couples the output end of the amplifier F, by first output voltage
Output signal VOUT with the difference of second output voltage as the fingerprint sensing circuit.
In the present embodiment, the fingerprint sensing circuit controls first switch T1, second switch T2, third by clock signal
The state of switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch T6, and according to the combinations of states of the switch, it provides
The operating mode of the fingerprint sensing circuit.That is, the operating mode corresponds to corresponding clock signal.
Referring to FIG. 4, Fig. 4 is a kind of timing diagram of fingerprint sensing circuit operating mode of the embodiment of the present invention.
In the present embodiment, the clock signal that control unit 201 exports can be divided into two stages, first stage S1 and second
Stage S2.
In specific implementation, the working condition under the timing control of S1 is the first work shape to fingerprint sensing circuit in the first stage
State, amplifier export the first output voltage；Working condition of the fingerprint sensing circuit under the timing control of second stage S2 is the
Two working conditions, amplifier export the second output voltage.
Refer to Fig. 3 together, in the present embodiment, fingerprint sensing circuit in the first operative state, third switch T3 and the 5th
Switch T5 is set to normally opened, and the 6th switch T6 is set to normally closed.It can refer to Fig. 5, Fig. 5 is fingerprint sensing circuit in the operational mode first
A kind of equivalent circuit diagram of stage S1, the driving voltage VP of the driving voltage interface access high level, internal reference voltage are matched
It is set to low level reference voltage VREFN, noise signal low frequency common voltage Vom is loaded in fingerprint detection capacitor C1.
With continued reference to Fig. 4, a timing cycles of first stage S1 include two stages, sample phase and transmission stage.
Under sample phase timing control, first switch T1 is disconnected, third switch T3 and second switch T2 closure, the fingerprint detection electricity
Hold the driving voltage VP and low frequency common voltage Vom of C1 coupling high level.The driving voltage VP of high level is to fingerprint detection capacitor
C1 charges, and the voltage of feedback capacity C2 is reset, and the positive input of amplifier F accesses low level reference voltage VREFN.
After sample phase timing, fingerprint detection capacitor C1 both end voltage size is the driving voltage VP size of high level, amplifier F
Output end voltage be low level reference voltage VREFN, i.e. VOUT1=VREFN.
Fingerprint sensing circuit is in the transmission stage of the first working condition, first switch T1 closure, third switch T3 and the 6th
Switch T6 is disconnected, and the driving voltage VP of high level disconnects the connection with circuit.The inverting input terminal of amplifier F accesses detecting electrode
The positive input of C1 and low frequency common voltage Vom, amplifier F access low level reference voltage VREFN.Transmission stage timing
After, according to law of conservation of charge, the output end output voltage of amplifier F is VOUT2=VREFN- (VP+Vom-VREFN)
C1/C2。
After the completion of a timing cycles of operating mode first stage S1, fingerprint sensing circuit output voltage is sample phase
With the difference of the output voltage of output stage amplifier F, i.e. the output voltage Δ VOUT=VOUT1-VOUT2=(VP+ of subtraction circuit
Vom-VREFN)C1/C2.The voltage dynamic range of the fingerprint sensing circuit is (VDACP+Vom-VREFN) C1/C2.
In the present embodiment, in the second working condition, first switch T1 and the 4th switch T4 are set to often fingerprint sensing circuit
It opens, third switch T3 is set to normally closed.It is fingerprint sensing circuit under operating mode second stage S2 timing control with reference to Fig. 6, Fig. 6
Equivalent circuit diagram, driving voltage is low level driving voltage VN, and internal reference voltage is configured to the reference voltage of high level
VREFP, noise signal low frequency common voltage Vom are loaded in fingerprint detection capacitor C1.
With continued reference to Fig. 4, the timing of second stage S2 includes two stages, sample phase and transmission stage, is referred to together
Fig. 3, under the timing control of sample phase, the 5th switch T5 is disconnected fingerprint sensing circuit, second switch T2 and the 6th switch T6
Closure, low level driving voltage VN charge to fingerprint detection capacitor C1, and the positive input of amplifier F couples high level
Reference voltage VREFP.After sample phase, fingerprint detection capacitor C1 voltage swing reaches VN size, the output of amplifier F
Holding output voltage is the reference voltage of high level, i.e. VOUT1=VREFP.
In the present embodiment, fingerprint sensing circuit is under the transmission stage timing control of the second working condition, the 5th switch T5
Closure, second switch T2 and the 6th switch T6 are disconnected, and the normal phase input end coupling fingerprint detection capacitor C1 and low frequency of amplifier F is total
The inverting input terminal of voltage VN and low frequency common voltage Vom access the amplifier F of mode voltage Vom, fingerprint detection capacitor C1, amplification
The reference voltage VREFP of the positive input coupling high level of device F.After the transmission stage, according to law of conservation of charge, amplification
The output end output voltage of device F is VOUT2=VREFP- (VN+Vom-VREFP) C1/C2.
For fingerprint sensing circuit after the completion of the second working condition, the output voltage of subtraction circuit is VOUT2=(VN+Vom-
VREFP)C1/C2。
In the present embodiment, after the completion of the timing control of operating mode first stage S1 and second stage S2, subtraction circuit
Output voltage of the output voltage as the fingerprint sensing circuit, i.e. output voltage are as follows: (VP+VREFP-VN-VREFN) C1/C2.
In specific implementation, the driving voltage VP of high level is set as supply voltage；Low level driving voltage VN is set as
Ground voltage.The reference voltage VREFP of high level is set as supply voltage, but is influenced to be less than supply voltage by amplifier architecture；
Low level reference voltage VREFN is set as being grounded, but is influenced to be higher than ground voltage by amplifier architecture.
In the present embodiment, the driving voltage VP of high level and low level driving voltage VN are internal voltage driver.
In the present embodiment, S1 output voltage Δ VOUT1 and second stage S2 are defeated in the first stage to amplifier for subtraction circuit
Voltage Δ VOUT2 makes the difference out, compared with the existing technology in fingerprint sensing circuit output voltage (VP+Vom-VREFN) C1/C2,
Output voltage of the fingerprint sensing circuit under operating mode of the embodiment of the present invention is (VP+VREFP-VN-VREFN) C1/C2, noise
Signal low frequency common voltage Vom is cut out.The output voltage signal-to-noise ratio of fingerprint sensing circuit increases, the sensitivity of fingerprint sensing
It is improved with validity.
It is understood that the reference voltage interface 202 and driving voltage interface 203 in the embodiment of the present invention can also connect
Enter the square-wave signal of rule variation, wherein the reference voltage signal period is twice of drive voltage signal period.
Fig. 7 is the timing diagram of another kind fingerprint sensing circuit operating mode of the embodiment of the present invention.
In the embodiment of the present invention, third switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch T6 be set to it is normally closed,
The reference voltage of the setting access square-wave signal of reference voltage interface 202, driving voltage interface 203 access the driving electricity of square-wave signal
Pressure.
It is understood that due in the embodiment of the present invention, third switch T3, the 4th switch T4, the 5th switch T5 and
Six switch T6 be set to it is normally closed, therefore can also be not provided with third switch T3, the 4th switch T4, the 5th switch T5 and the 6th switch
T6 accesses the driving voltage and reference voltage of square-wave signal using any enforceable conducting element.
Referring to FIG. 7, the clock signal that control unit 201 exports can be divided into two stages, first stage S1 and second
Stage S2.The working condition under the timing control of S1 is the first working condition to fingerprint sensing circuit in the first stage, and amplifier is defeated
First output voltage out；Working condition of the fingerprint sensing circuit under the timing control of second stage S2 is the second working condition,
Amplifier exports the second output voltage.
Fig. 5 and Fig. 6 is referred to together, and Fig. 5 is a kind of equivalent circuit under fingerprint sensing circuit first stage S1 timing control
Figure, Fig. 6 are equivalent circuit diagram of the fingerprint sensing circuit under second stage S2 timing control.
Specific implementation method can refer to previous embodiment, and details are not described herein again.
In the present embodiment, after the completion of the timing control of timing control signal, subtraction circuit to amplifier in the first stage
S1 output voltage Δ VOUT1 and second stage S2 output voltage Δ VOUT2 make the difference, compared with the existing technology in fingerprint sensing electricity
Road output voltage (VP+Vom-VREFN) C1/C2, output voltage of the fingerprint sensing circuit under operating mode of the embodiment of the present invention
It is cut out for (VP+VREFP-VN-VREFN) C1/C2, noise signal low frequency common voltage Vom.The output of fingerprint sensing circuit
Voltage signal-to-noise ratio increases, and the sensitivity of fingerprint sensing and validity are improved.
Fig. 8 is a kind of fingerprint sensing circuit structural schematic diagram of another embodiment of the present invention.
In the present embodiment, in the present embodiment, the driving voltage VP of high level and low level driving voltage VN are external drive
Dynamic voltage.User's finger is loaded external drive voltage in fingerprint detection capacitor C1 by contact external electrode (not shown).
Specific embodiment can refer to preceding aspect embodiments, and details are not described herein again.
Although present disclosure is as above, present invention is not limited to this.Anyone skilled in the art are not departing from this
It in the spirit and scope of invention, can make various changes or modifications, therefore protection scope of the present invention should be with claim institute
Subject to the range of restriction.
Claims (10)
1. a kind of fingerprint sensing circuit characterized by comprising
Fingerprint detection capacitor, one end couple finger；
Detecting electrode couples the fingerprint detection capacitor；
Driving voltage interface, suitable for the driving voltage of two kinds of level of height is alternately loaded onto the detecting electrode；
Amplifier；
The detecting electrode is coupled to the inverting input terminal of the amplifier by first switch, being suitably selected for property；
Reference voltage interface, the positive suitable for the reference voltage of two kinds of level of height is alternately input to the amplifier input
End；
Control unit is suitable for generating control signal, so that the amplifier exports the first output after the completion of a timing cycles
Voltage and the second output voltage, described control unit couple the driving voltage interface and the reference voltage interface；
Subtraction circuit couples the output end of the amplifier, is suitable for first output voltage and second output voltage
Output signal of the difference as the fingerprint sensing circuit；
Wherein, the driving voltage is internal voltage driver.
2. fingerprint sensing circuit according to claim 1, which is characterized in that further include:
Second switch, one end couple the reverse input end of the amplifier, and the other end is connected with the output end of the amplifier；
Feedback capacity, one end couple the inverting input terminal of the amplifier, and the other end is connected with the output end of the amplifier.
3. fingerprint sensing circuit according to claim 2, which is characterized in that described control unit couples the first switch
With the second switch.
4. fingerprint sensing circuit according to claim 3, which is characterized in that the driving voltage interface includes third switch
With 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 third 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 input to the normal phase input end of the amplifier by the being suitably selected for property of the 5th switch；
The low level reference voltage is input to the normal phase input end of the amplifier by the being suitably selected for property of the 6th switch.
5. fingerprint sensing circuit according to claim 2, which is characterized in that described control unit couples the first switch
With the second switch；The driving voltage and the reference voltage are square-wave signal.
6. according to the control method of the described in any item fingerprint sensing circuits of claim 2-3 characterized by comprising
In the first operative state, the driving voltage of two kinds of level of height is alternately loaded onto the inspection by the driving voltage interface
Electrode is surveyed, low level reference voltage is input to the normal phase input end of the amplifier by the reference voltage interface, and described the
The detecting electrode is coupled to the inverting input terminal of the amplifier by one switch selectivity, so that amplifier output first
Output voltage；
In a second operative state, the driving voltage of two kinds of level of height is alternately loaded onto institute by the driving voltage interface
Detecting electrode is stated, the reference voltage interface inputs the positive that the reference voltage of high level is input to the amplifier
End, the detecting electrode is selectively coupled to the inverting input terminal of the amplifier by the first switch, so that the amplification
Device exports the second output voltage.
7. the control method of fingerprint sensing circuit according to claim 6, which is characterized in that in first working condition
Under, the first switch first disconnects to be closed afterwards, and second switch closes first and then disconnect；The driving voltage interface includes third switch
With the 4th switch, the third switch closes first and then disconnect, and the 4th switch is set to normally closed；The reference voltage interface includes
5th switch and the 6th switch, the 5th switch are set to normal off, and the 6th switch is set to normally closed；
Under second working condition, the first switch first disconnects to be closed afterwards, and second switch closes first and then disconnect；Described
Three switch be set to it is normally closed, it is described 4th switch close first and then disconnect；It is described 5th switch 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, which is characterized in that the driving voltage interface packet
Include third switch and the 4th switch；The reference voltage interface includes the 5th switch and the 6th switch；The third switchs, is described
4th switch, the 5th switch and the 6th switch are set to normally closed；
Under first working condition, the driving voltage square-wave signal of driving voltage interface access two kinds of level of height,
The reference voltage interface accesses low level reference voltage square-wave signal；
Under second working condition, the driving voltage square-wave signal of driving voltage interface access two kinds of level of height,
The reference voltage square-wave signal of the reference voltage interface access high level.
9. the control method of fingerprint sensing circuit according to claim 8, which is characterized in that the reference voltage square wave letter
Number period is twice of the driving voltage square-wave signal period.
10. according to the control method of the described in any item fingerprint sensing circuits of claim 7- 9, which is characterized in that described first
After the completion of 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 described
Second output voltage；C1 is the fingerprint detection capacitor；C2 is the feedback capacity.
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| CN105373776A (en) * | 2015-10-28 | 2016-03-02 | 深圳市汇顶科技股份有限公司 | Pixel module and fingerprint recognition system |
| WO2019090528A1 (en) * | 2017-11-08 | 2019-05-16 | 深圳市汇顶科技股份有限公司 | Capacitance detection device, touch device and terminal device |
| CN110096931B (en) * | 2018-01-31 | 2023-07-04 | 敦泰电子有限公司 | Sensor unit, fingerprint identification method, fingerprint identification chip and electronic equipment |
| CN112149462A (en) * | 2019-06-27 | 2020-12-29 | 深圳芯启航科技有限公司 | Capacitive fingerprint sensing circuit and capacitive fingerprint sensing device |
| CN110874586B (en) | 2019-11-29 | 2023-06-30 | 厦门天马微电子有限公司 | Display panel and display device |
| CN113785300B (en) * | 2020-04-10 | 2024-07-26 | 京东方科技集团股份有限公司 | Fingerprint identification detection circuit, control method thereof and fingerprint identification control chip |
| US11222933B2 (en) * | 2020-04-28 | 2022-01-11 | Himax Technologies Limited | Display panel equipped with function of detecting an object, and method for detecting an object on a display panel |
| CN113257184B (en) | 2021-05-10 | 2022-10-25 | 京东方科技集团股份有限公司 | Sampling circuit, driving method, pixel sampling circuit and display device |
| CN113920551B (en) * | 2021-09-30 | 2023-02-07 | 深圳市汇顶科技股份有限公司 | Ultrasonic image sensor and related electronic device |
| WO2023050291A1 (en) | 2021-09-30 | 2023-04-06 | 深圳市汇顶科技股份有限公司 | Ultrasonic image sensor and related electronic device |
| CN114627514B (en) * | 2022-02-28 | 2024-12-03 | 敦泰电子（深圳）有限公司 | Fingerprint detection amplifier circuit and fingerprint recognition device |
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