CN106778672B - Fingerprint detection circuit and fingerprint detection sensor - Google Patents
Fingerprint detection circuit and fingerprint detection sensor Download PDFInfo
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Abstract
The invention discloses a fingerprint detection circuit, which comprises at least two metal layers, a main control circuit, an external signal source, a first signal source, a second signal source, a third signal source and a plurality of fingerprint detection units, wherein the fingerprint detection units comprise a first switch, a second switch, a third switch and a charge amplifier, a fingerprint capacitor is formed between a finger and a top metal layer, the second signal source and the first signal source are added on the metal layer a and respectively form a first capacitor and a second capacitor with the top metal layer, a third capacitor is formed between the top metal layer and the ground, and a reference capacitor is formed between the top metal layer and the metal layer a; a fingerprint detection sensor is also disclosed, comprising the fingerprint detection circuit. The fingerprint detection circuit and the fingerprint detection sensor combine the active structure and the passive structure, so that the application design of the fingerprint detection circuit can be designed differently according to different requirements, and various costs of a fingerprint detection chip are saved.
Description
Technical Field
The invention relates to the field of fingerprint detection, in particular to a fingerprint detection circuit and a fingerprint detection sensor.
Background
The capacitive fingerprint sensor is used conveniently and rapidly, has high safety, and can realize safe payment, so that the capacitive fingerprint sensor is increasingly used in various electronic products, in particular various intelligent terminals.
The existing capacitive fingerprint detection device mainly has two detection modes, one is active and the other is passive. The active penetrating power is strong, but an additional control chip is needed, and the cost is relatively high compared with that of the passive type; while passive penetration is weak, it does not require an additional control chip and is therefore relatively low cost. To solve this problem, many companies design different chips for different situations, which results in a great increase in design cycle, cost, and stock cost after the measurement.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a fingerprint detection circuit compatible with an active working mode and a passive working mode, and correspondingly, a fingerprint detection sensor.
The technical scheme adopted by the invention is as follows: the fingerprint detection circuit comprises at least two metal layers, a main control circuit, an external signal source, a first signal source, a second signal source, a third signal source and a plurality of fingerprint detection units, wherein the fingerprint detection units comprise a first switch, a second switch, a third switch and a charge amplifier, and the main control circuit is used for outputting a first clock signal, a second clock signal and a third clock signal, respectively controlling the switching states of the first switch, the second switch and the third switch, and outputting an external analog signal, a first analog signal, a second analog signal and a third analog signal, which are used as the external signal source, the first signal source, the second signal source and the third signal source respectively;
the finger and the top metal form a fingerprint capacitor, the second signal source and the first signal source are added on the metal of the a layer and respectively form a first capacitor and a second capacitor with the metal of the top layer, the metal of the a layer is any metal below the metal of the top layer, a third capacitor is formed between the metal of the top layer and the ground, a reference capacitor is formed between the metal of the top layer and the metal of the a layer, the third signal source is connected with a positive input end of a charge amplifier through a third switch, the left side of the second switch is grounded, the right side of the second switch is connected with the positive input end of the charge amplifier, the inverting input end of the charge amplifier is connected with the top metal of the top layer, the inverting input end of the charge amplifier is connected with the left side of the first switch, the right side of the first switch is connected with the output end of the charge amplifier, the output end of the charge amplifier is connected with the metal of the a layer, and the output ends of the charge amplifiers are used as output signals of a fingerprint detection circuit.
Further, the fingerprint detection circuit further comprises a protective layer, the protective layer is arranged on the top metal, and the finger and the top metal form a fingerprint capacitor through the protective layer.
Further, the main control circuit comprises a control circuit and a digital-to-analog converter, the control circuit is used for controlling the switching states of the first switch, the second switch and the third switch and outputting external analog signals and controlling the digital-to-analog converter to output the first analog signal, the second analog signal and the third analog signal, the digital-to-analog converter is used for outputting the first analog signal, the second analog signal and the third analog signal, and the output end of the control circuit is connected with the input end of the digital-to-analog converter.
Further, the protective layer comprises a coating, glass or ceramic.
Further, the active operation control time sequence of the fingerprint detection circuit is as follows:
the second clock signal is a low level signal; the third clock signal is a high level signal;
the first analog signal is a low level signal; when the first clock signal is at a low level, the voltage value of the second analog signal is a first voltage v1, and when the first clock signal is at a high level, the voltage value of the second analog signal is a second voltage v2; the third analog signal is a direct current signal;
the external signal source outputs an external analog signal to the finger, the external analog signal and the first clock signal are non-overlapping signals, the low-level voltage of the external analog signal is 0, and the high-level voltage of the external analog signal is an external analog voltage vtx.
Further, the fingerprint detection circuit further comprises an active control circuit, the external signal source is connected with the input end of the active control circuit, the output end of the active control circuit is connected with the ground of the fingerprint detection circuit, and the active control circuit is used for controlling the voltage of the ground of the fingerprint detection circuit according to an external analog signal.
Further, the active operation control time sequence of the fingerprint detection circuit is as follows:
the second clock signal is a low level signal; the third clock signal is a high level signal;
the first analog signal is a low level signal; when the first clock signal is at a low level, the voltage value of the second analog signal is a first voltage v1, and when the first clock signal is at a high level, the voltage value of the second analog signal is a second voltage v2; the third analog signal is a direct current signal;
the external signal source outputs an external analog signal to the active control circuit, the external analog signal and the first clock signal are non-overlapping signals, the low-level voltage of the external analog signal is 0, and the high-level voltage of the external analog signal is an external analog voltage vtx; the power supply voltage of the active control circuit is a first power supply voltage VDDH, and the output voltage of the active control circuit is a ground voltage VGND; when the low level voltage of the external analog signal is 0, the ground voltage VGND output by the active control circuit is 0, and the voltage of the ground of the fingerprint detection circuit is controlled to be 0; when the high-level voltage of the external analog signal is vtx, the ground voltage VGND output by the active control circuit is not 0, and the active control circuit controls the ground voltage of the fingerprint detection circuit to be the ground voltage VGND.
Further, the passive operation control time sequence of the fingerprint detection circuit is as follows:
the first clock signal and the second clock signal are the same clock signal, and the first clock signal and the third clock signal are non-overlapping clock signals;
when the first clock signal is at a high level, the voltage value of the second analog signal is a third voltage v3, and the voltage value of the first analog signal is a fifth voltage v5; when the first clock signal is at a low level, the voltage value of the second analog signal is a fourth voltage v4, and the voltage value of the first analog signal is a sixth voltage v6; the third analog signal is a low level signal or a high level signal.
Further, the output voltage of the output end of the charge amplifier is:
wherein VTX is the voltage value of the external analog signal, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
Further, the output voltage of the output end of the charge amplifier is:
wherein VDDHV is the voltage value of the first power supply voltage, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
Further, the output voltage of the output end of the charge amplifier is:
wherein Cfinger is the capacitance value of the fingerprint capacitor, C3 is the capacitance value of the third capacitor, C1 is the capacitance value of the first capacitor, C2 is the capacitance value of the second capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
The invention adopts another technical scheme that: a fingerprint detection sensor comprises the fingerprint detection circuit.
The beneficial effects of the invention are as follows: the fingerprint detection circuit comprises at least two metal layers, a main control circuit, an external signal source, a first signal source, a second signal source, a third signal source and a plurality of fingerprint detection units, wherein the fingerprint detection units comprise a first switch, a second switch, a third switch and a charge amplifier, fingerprint capacitance is formed between a finger and top metal, the second signal source and the first signal source are added on a metal layer a and respectively form a first capacitance and a second capacitance with the top metal, the metal layer a is any metal layer below the top metal layer, a third capacitance is formed between the top metal layer and the ground, a reference capacitance is formed between the top metal layer and the metal layer a, the third signal source is connected with a positive input end of the charge amplifier through the third switch, the left side of the second switch is grounded, the right side of the second switch is connected with the positive input end of the charge amplifier, the reverse phase input end of the charge amplifier is connected with the top metal layer, the right side of the first switch is connected with the output end of the charge amplifier, and the output end of the charge amplifier is connected with the metal layer a; the fingerprint detection circuit combines the active structure and the passive structure, so that the application design of the fingerprint detection circuit can be designed differently according to different requirements, and the main control circuit inputs different clock control signals to the finger and the fingerprint detection unit according to different design requirements, so that the fingerprint detection circuit can be packaged into an active or passive scheme, and various costs of designing, verifying, stock and the like of the fingerprint detection chip are greatly saved. In addition, the fingerprint detection sensor comprises a fingerprint detection circuit, and compared with the design of an active chip and a passive chip respectively, the fingerprint detection sensor has the advantages of short design period and low cost.
Drawings
The following is a further description of embodiments of the invention, taken in conjunction with the accompanying drawings:
FIG. 1 is a schematic diagram of a fingerprint detection circuit according to an embodiment of the present invention;
FIG. 2 is a schematic circuit diagram of a fingerprint detection circuit according to an embodiment of the present invention;
FIG. 3 is a waveform diagram of an active operation control of a fingerprint detection circuit according to the present invention;
FIG. 4 is a schematic diagram of an active circuit of a fingerprint detection circuit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of an active circuit of a fingerprint detection circuit according to another embodiment of the present invention;
FIG. 6 is a circuit diagram of an active circuit of a fingerprint detection circuit according to another embodiment of the present invention;
FIG. 7 is a waveform diagram of a passive operation control of a fingerprint detection circuit according to the present invention;
FIG. 8 is a schematic diagram of a passive circuit of a fingerprint detection circuit according to an embodiment of the present invention.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other.
Referring to fig. 1 and fig. 2, fig. 1 is a schematic structural diagram of an embodiment of a fingerprint detection circuit in the present invention, fig. 2 is a schematic circuit diagram of an embodiment of a fingerprint detection circuit in the present invention, including at least two metal layers, a main control circuit 100, an external signal source, a first signal source, a second signal source, a third signal source, and a plurality of fingerprint detection units 200, the fingerprint detection units 200 forming a fingerprint detection array, the fingerprint detection units 200 including a first switch SW1, a second switch SW2, a third switch SW3, and a charge amplifier CA, the main control circuit 100 being configured to output a first clock signal S1, a second clock signal S2, and a third clock signal S3 for controlling a switching state of the first switch SW1, the second switch SW2, and the third switch SW3, respectively, and outputting an external analog signal VTX, a first analog signal VDAC1, a second analog signal VDAC2, and a third analog signal VDAC3 as the external signal source, the first signal source, the second signal source, and the third signal source, respectively;
the finger 300 and the top metal M_top form a fingerprint capacitor Cfinger, a second signal source and a first signal source are added on the a-th metal M_a and respectively form a first capacitor C1 and a second capacitor C2 with the top metal M_top, the a-th metal M_a is any metal below the top metal M_top, a third capacitor C3 is formed between the top metal M_top and the ground VSS, a reference capacitor Cref is formed between the top metal M_top and the a-th metal M_a, the third signal source is connected with a positive input end of a charge amplifier CA through a third switch SW3, the left side of the second switch SW2 is grounded, the right side of the second switch SW2 is connected with the positive input end of the charge amplifier CA, the reverse input end of the charge amplifier CA is connected with the left side of the first switch SW1, the right side of the first switch SW1 is connected with an output end of the charge amplifier CA, the output end of the charge amplifier CA is connected with the positive input ends of the charge amplifier CA, and the negative input ends of the charge amplifier CA are connected with the negative input ends of the charge amplifier CA, and the negative output ends of the fingerprint detection units are connected with the negative fingerprint detection units.
The invention is a fingerprint detection circuit integrated with active and passive, when the circuit works in an active mode, an external signal source is needed to be relied on, and the external signal source outputs an external analog signal VTX and is coupled to the detection circuit through a fingerprint capacitor Cfinger; for the same amplitude of an external analog signal VTX, different fingerprint capacitors Cfinger can obtain different output voltages VCA; when the capacitance detection circuit works in a passive mode, an external signal source is not needed, the fingerprint capacitor is equivalent to the ground, and different output voltages VCA are obtained by inputting different signals; therefore, by quantifying the value of VCA, the size of the fingerprint capacitor Cfinger is indirectly quantified, so that fingerprint detection is realized. The fingerprint detection circuit combines the active structure and the passive structure, so that the application design of the fingerprint detection circuit can be designed differently according to different requirements, and the main control circuit inputs different signals to the finger and the fingerprint detection unit according to different design requirements, so that the fingerprint detection circuit can be packaged into an active or passive scheme, and various costs of designing, verifying, stock and the like of the fingerprint detection chip are greatly saved. Referring to fig. 2, fig. 2 is a schematic circuit diagram of a fingerprint detection circuit according to an embodiment of the present invention, in which when the circuit is in an active mode, an external analog signal VTX output from an external signal source is applied to a finger, and in addition, the external signal source may be input into the fingerprint detection circuit by other means in the prior art.
The invention is implemented using a CMOS process, but the invention is not limited to CMOS processes, e.g. bipolars process, but can also be implemented. As shown in fig. 2, m_top and m_a are the top metal and the a-th metal of the CMOS process, respectively, and the top metal m_top is a sensing electrode, which is used as one plate of the fingerprint sensing capacitor, and forms a fingerprint capacitor Cfinger with the finger. 3 parasitic capacitances are generated between the top metal m_top and the a-th metal m_a, and are a first capacitance C1, a second capacitance C2 and a reference capacitance Cref, wherein the first capacitance C1 and the second capacitance C2 are used for adjusting the output range of the charge amplifier CA, and the first capacitance C1 is used for adjusting the output voltage range of the charge amplifier CA when active; the second capacitor C2 is used to regulate the output voltage range of the charge amplifier CA in the passive mode. The reference capacitance Cref is used to measure the fingerprint capacitance Cfinger. The metal M_a of the a-th layer can be the metal M_top-1 of the first layer under the top layer metal, the metal M_top-2 of the second layer under the top layer metal, or other metal layers according to design requirements.
As a further improvement of the technical solution, referring to fig. 2, fig. 2 is a schematic circuit diagram of a specific embodiment of a fingerprint detection circuit in the present invention, where the fingerprint detection circuit further includes a protection layer cover, the protection layer cover is disposed on the top metal m_top, and the finger 300 forms a fingerprint capacitor Cfinger with the top metal m_top through the protection layer cover. Further, the protective layer comprises a coating, glass or ceramic for protecting the chip from damage, and the protective layer cover can be directly adhered to the chip; after the finger 300 is pressed to the surface of the protective layer cover, the top metal m_top and the surface of the finger 300 form a fingerprint capacitor Cfinger.
As a further improvement of the technical solution, referring to fig. 1 and 2, fig. 1 is a schematic structural diagram of an embodiment of a fingerprint detection circuit in the present invention, fig. 2 is a schematic circuit diagram of an embodiment of a fingerprint detection circuit in the present invention, in this embodiment, a master circuit 100 includes a control circuit 101 and a digital-analog converter 102, the control circuit 101 is configured to control a switching state of a first switch SW1, a second switch SW2, a third switch SW3 and output an external analog signal VTX, and control the digital-analog converter 102 to output a first analog signal VDAC1, a second analog signal VDAC2 and a third analog signal VDAC3, the digital-analog converter 102 is configured to output a first analog signal VDAC1, a second analog signal VDAC2 and a third analog signal VDAC3, an output terminal of the control circuit 101 is connected to an input terminal of the digital-analog converter 102, and the control circuit 101 is configured to output a first clock signal S1, a second clock signal S2 and a third clock signal S3, which are configured to control the first switch SW1, the second switch SW2 and the third switch SW3, respectively. A digital-to-analog converter (Digital to analog converter, acronym: DAC) is a device that converts a digital signal into an analog signal (in the form of current, voltage, or charge). In many digital systems (e.g., computers), signals are stored and transmitted digitally, and digital-to-analog converters can convert such signals to analog signals so that they can be recognized by the outside world (human or other non-digital system).
As a further improvement of the technical solution, referring to fig. 1, 2, 3 and 4, fig. 1 is a schematic structural diagram of an embodiment of a fingerprint detection circuit according to the present invention, fig. 2 is a schematic circuit diagram of an embodiment of a fingerprint detection circuit according to the present invention, fig. 3 is an active operation control waveform diagram of an embodiment of a fingerprint detection circuit according to the present invention, and fig. 4 is a schematic diagram of an embodiment of an active circuit of a fingerprint detection circuit according to the present invention, wherein an external signal source is required to output an external analog signal VTX when the fingerprint detection circuit is in an active operation mode, in this embodiment, the external analog signal VTX is output to a finger 300; preferably, the capacitance values of the reference capacitor Cref and the first capacitor C1 belong to the same magnitude, the capacitance values of the reference capacitor Cref and the first capacitor C1 may be equal or equivalent, and belong to the same magnitude, and the capacitance values of the reference capacitor Cref and the first capacitor C1 are not greatly different, for example, the capacitance value of the reference capacitor Cref is 3FF, and the capacitance value of the first capacitor C1 is 4FF; the active operation control time sequence of the fingerprint detection circuit specifically comprises the following steps:
the second clock signal S1 is a low level signal, i.e., sw2=0; the third clock signal S3 is a high level signal, i.e., sw3=1; the first analog signal VDAC1 is a low level signal; the second analog signal VDAC2 is a square wave signal, when the first clock signal S1 is at a low level, the voltage value of the second analog signal VDAC2 is a first voltage V1, when the first clock signal S1 is at a high level, the voltage value of the second analog signal VDAC2 is a second voltage V2, V1 and V2 in fig. 3 are relative values, and V1 may be greater than V2; the third analog signal VDAC3 is a direct current signal; the voltage of the third analog signal VDAC3 is controlled by the main control circuit only by keeping the voltage of the third analog signal VDAC3 unchanged; the external analog signal VTX and the first clock signal S1 are non-overlapping signals, the low level voltage of the external analog signal VTX is 0, and the high level voltage of the external analog signal VTX is the external analog voltage VTX.
Referring to fig. 3 and 4, sw1=1, the charge on the reference capacitor Cref is no longer stored after the discharge is completed; when sw1=0, the external analog signal VTX rises to VTX. When the fingerprint detection circuit is controlled according to the waveform of fig. 3, the left end of the fingerprint capacitor Cfinger is charged to VTX, the required charge amount is q1=vtx×cfinger, and these charge amounts are from the first capacitor C1 and the reference capacitor Cref, wherein the first capacitor C1 provides a charge amount of q2= (v 2-v 1) ×c1, and the reference capacitor Cref provides a charge amount of q3= (VCA-VDAC 3) ×cref. According to the law of conservation of charge, q1=q2+q3, the value of the output voltage VCA of the charge amplifier CA can be calculated, namely:
as can be seen from the above equation, the second analog signal VDAC2 and the first capacitor C1 are used to adjust the range of the output voltage VCA, so that the output voltage VCA is better quantized by the following analog-to-digital converter. Wherein VTX is the voltage value of the external analog signal, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
As a further improvement of the technical solution, referring to fig. 5 and 6, fig. 5 is a schematic structural diagram of another embodiment of an active circuit of a fingerprint detection circuit according to the present invention, fig. 6 is a schematic circuit diagram of another embodiment of an active circuit of a fingerprint detection circuit according to the present invention, the fingerprint detection circuit further includes an active control circuit, an external signal source is connected to an input terminal of the active control circuit, an output terminal of the active control circuit is connected to a ground of the fingerprint detection circuit, and is used for controlling a voltage of the ground of the fingerprint detection circuit according to an external analog signal, thereby, the fingerprint detection circuit processes to realize the active circuit by adding an active control circuit in addition to the external analog signal to the active circuit, in this embodiment, the active control circuit is realized by adopting an active control chip, in fig. 6, an output terminal of the active control chip is connected to a ground VSS of the fingerprint detection circuit, in this embodiment, an output terminal of the active control chip is schematically connected to a ground terminal of a third capacitor, which indicates that the output terminal of the active control chip is connected to the ground of the fingerprint detection circuit, and an amplifier of the active control chip is also connected to the ground of the active control chip.
Further, referring to fig. 3 and fig. 6, fig. 3 is a waveform diagram of an active operation control of a fingerprint detection circuit according to the present invention, and fig. 6 is a circuit schematic diagram of another embodiment of an active circuit of a fingerprint detection circuit according to the present invention, where the capacitance values of the reference capacitor Cref and the first capacitor C1 are the same magnitude; the active operation control time sequence of the fingerprint detection circuit is as follows:
the second clock signal S1 is a low level signal, i.e., sw2=0; the third clock signal S3 is a high level signal, i.e., sw3=1; the first analog signal VDAC1 is a low level signal; the second analog signal VDAC2 is a square wave signal, when the first clock signal S1 is at a low level, the voltage value of the second analog signal VDAC2 is a first voltage V1, when the first clock signal S1 is at a high level, the voltage value of the second analog signal VDAC2 is a second voltage V2, V1 and V2 in fig. 3 are relative values, and V1 may be greater than V2; the third analog signal VDAC3 is a direct current signal; the voltage of the third analog signal VDAC3 is controlled by the main control circuit only by keeping the voltage of the third analog signal VDAC3 unchanged; in this embodiment, the external signal source outputs an external analog signal VTX to the active control chip, the external analog signal VTX and the first clock signal S1 are non-overlapping signals, the low level voltage of the external analog signal VTX is 0, and the high level voltage of the external analog signal VTX is an external analog voltage VTX; the power supply voltage of the active control chip is the first power supply voltage VDDH, and the output voltage of the active control chip is the ground voltage VGND; when the low level voltage of the external analog signal VTX is 0, the ground voltage VGND output by the active control chip is 0, and the voltage of the ground of the fingerprint detection circuit is controlled to be 0; when the high-level voltage of the external analog signal VTX is VTX, the ground voltage VGND output by the active control chip is not 0, and the active control chip controls the ground voltage of the fingerprint detection circuit to be the ground voltage VGND. Further, the output voltage of the output terminal of the charge amplifier is:
wherein VDDHV is the voltage value of the first power supply voltage, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
As a further improvement of the technical solution, referring to fig. 7 and 8, fig. 7 is a waveform diagram of a passive operation control of a fingerprint detection circuit according to the present invention, and fig. 8 is a schematic diagram of a specific embodiment of a passive circuit of a fingerprint detection circuit according to the present invention, in which the circuit does not need to input an external analog signal, in this embodiment, preferably, the capacitance values of the reference capacitor Cref and the first capacitor C1 are the same magnitude, and the capacitance values of the second capacitor C2 and the third capacitor C3 are the same magnitude, and in this embodiment, the capacitance values of the second capacitor C2 and the third capacitor C3 are set to be about several tens of femtofarads; the specific passive operation control time sequence of the fingerprint detection circuit is as follows:
the first clock signal S1 and the second clock signal S2 are the same clock signal, and the first clock signal S1 and the third clock signal S3 are non-overlapping clock signals;
the first analog signal VDAC1 and the second analog signal VDAC2 are square wave signals, when the first clock signal S1 is at a high level, the voltage value of the second analog signal VDAC2 is a third voltage v3, and the voltage value of the first analog signal VDAC1 is a fifth voltage v5; when the first clock signal S1 is at a low level, the voltage value of the second analog signal VDAC2 is the fourth voltage V4, the voltage value of the first analog signal VDAC1 is the sixth voltage V6, V3 and V4 are relative values in fig. 7, V3 may be greater than V4, V5 and V6 are relative values in fig. 7, and V5 may be greater than V6; the third analog signal VDAC3 is a low level signal or a high level signal, and similarly, the third analog signal VDAC3 is a direct current signal; the third analog signal VDAC3 only needs to have a constant voltage.
Referring to fig. 7 and 8, when sw1=1, the charge on the reference capacitor Cref is no longer stored after the discharge is completed, and the voltages of the three nodes, i.e., the point a, the point B and the charge amplifier VCA are all 0; when sw3=1, point a becomes VDAC3 and point B also becomes VDAC3 due to the action of the charge amplifier CA, so that the fingerprint capacitance Cfinger is charged from 0 to VDAC3.
In the above operation, the right end of the fingerprint capacitor Cfinger is charged to VDAC3, the required charge amount is q1=vdac3×cfinger, the upper end of the third capacitor C3 is also charged to VDAC3, the required charge amount is q2=vdac3×cp, and Q1 and Q2 are both from the first capacitor C1, the second capacitor C2 and the reference capacitor Cref, wherein the first capacitor C1 provides the charge amount of q3= (v 4-v 3) ×c1, the second capacitor C2 provides the charge amount of q4= (v 6-v 5) ×c2, and the reference capacitor Cref provides the charge amount of q5= (VCA-VDAC 3) ×cref. According to the law of conservation of charge, q1+q2=q3+q4+q5, the value of the output voltage VCA of the charge amplifier CA can be calculated, namely:
as can be seen from the above equation, the first analog signal VDAC1, the second analog signal VDAC2, the first capacitor C1 and the second capacitor C2 are used to adjust the range of the output voltage VCA, so that the output voltage VCA is better quantized by the following ADC. Wherein Cfinger is the capacitance value of the fingerprint capacitor, C3 is the capacitance value of the third capacitor, C1 is the capacitance value of the first capacitor, C2 is the capacitance value of the second capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
The fingerprint detection sensor comprises the fingerprint detection circuit, and can realize an active mode and a passive mode by only designing one chip, so that the fingerprint detection sensor has short design period and low cost.
While the preferred embodiment of the present invention has been described in detail, the present invention is not limited to the embodiments, and those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are included in the scope of the present invention as defined in the appended claims.
Claims (12)
1. The fingerprint detection circuit is characterized by comprising at least two layers of metal layers, a main control circuit, an external signal source, a first signal source, a second signal source, a third signal source and a plurality of fingerprint detection units, wherein the fingerprint detection units comprise a first switch, a second switch, a third switch and a charge amplifier, the main control circuit is used for outputting a first clock signal, a second clock signal and a third clock signal, respectively controlling the switching states of the first switch, the second switch and the third switch, and outputting an external analog signal, a first analog signal, a second analog signal and a third analog signal, respectively serving as the external signal source, the first signal source, the second signal source and the third signal source;
the finger and the top metal form a fingerprint capacitor, the second signal source and the first signal source are added on the metal of the a layer and respectively form a first capacitor and a second capacitor with the metal of the top layer, the metal of the a layer is any metal below the metal of the top layer, a third capacitor is formed between the metal of the top layer and the ground, a reference capacitor is formed between the metal of the top layer and the metal of the a layer, the third signal source is connected with a positive input end of a charge amplifier through a third switch, the left side of the second switch is grounded, the right side of the second switch is connected with the positive input end of the charge amplifier, the inverting input end of the charge amplifier is connected with the top metal of the top layer, the inverting input end of the charge amplifier is connected with the left side of the first switch, the right side of the first switch is connected with the output end of the charge amplifier, the output end of the charge amplifier is connected with the metal of the a layer, and the output ends of the charge amplifiers are used as output signals of a fingerprint detection circuit.
2. The fingerprint detection circuit of claim 1 further comprising a protective layer disposed over the top metal, the finger forming a fingerprint capacitance with the top metal through the protective layer.
3. The fingerprint detection circuit of claim 1 wherein the master control circuit comprises a control circuit and a digital-to-analog converter, the control circuit is configured to control the switching states of the first switch, the second switch, the third switch and output external analog signals and to control the digital-to-analog converter to output the first analog signal, the second analog signal, and the third analog signal, and the digital-to-analog converter is configured to output the first analog signal, the second analog signal, and the third analog signal, and an output of the control circuit is coupled to an input of the digital-to-analog converter.
4. The fingerprint detection circuit of claim 2 wherein the protective layer comprises a coating, glass, or ceramic.
5. The fingerprint detection circuit according to any one of claims 1 to 4 wherein the active operation control timing of the fingerprint detection circuit is:
the second clock signal is a low level signal; the third clock signal is a high level signal;
the first analog signal is a low level signal; when the first clock signal is at a low level, the voltage value of the second analog signal is a first voltage v1, and when the first clock signal is at a high level, the voltage value of the second analog signal is a second voltage v2; the third analog signal is a direct current signal;
the external signal source outputs an external analog signal to the finger, the external analog signal and the first clock signal are non-overlapping signals, the low-level voltage of the external analog signal is 0, and the high-level voltage of the external analog signal is an external analog voltage vtx.
6. The fingerprint detection circuit according to any one of claims 1 to 4 further comprising an active control circuit, the external signal source being connected to an input of the active control circuit, an output of the active control circuit being connected to a ground of the fingerprint detection circuit for controlling a voltage of the ground of the fingerprint detection circuit in dependence on an external analog signal.
7. The fingerprint detection circuit of claim 6 wherein the active operation control timing of the fingerprint detection circuit is:
the second clock signal is a low level signal; the third clock signal is a high level signal;
the first analog signal is a low level signal; when the first clock signal is at a low level, the voltage value of the second analog signal is a first voltage v1, and when the first clock signal is at a high level, the voltage value of the second analog signal is a second voltage v2; the third analog signal is a direct current signal;
the external signal source outputs an external analog signal to the active control circuit, the external analog signal and the first clock signal are non-overlapping signals, the low-level voltage of the external analog signal is 0, and the high-level voltage of the external analog signal is an external analog voltage vtx; the power supply voltage of the active control circuit is a first power supply voltage VDDH, and the output voltage of the active control circuit is a ground voltage VGND; when the low level voltage of the external analog signal is 0, the ground voltage VGND output by the active control circuit is 0, and the voltage of the ground of the fingerprint detection circuit is controlled to be 0; when the high-level voltage of the external analog signal is vtx, the ground voltage VGND output by the active control circuit is not 0, and the active control circuit controls the ground voltage of the fingerprint detection circuit to be the ground voltage VGND.
8. The fingerprint detection circuit according to any one of claims 1 to 4 wherein the passive operation control timing of the fingerprint detection circuit is:
the first clock signal and the second clock signal are the same clock signal, and the first clock signal and the third clock signal are non-overlapping clock signals;
when the first clock signal is at a high level, the voltage value of the second analog signal is a third voltage v3, and the voltage value of the first analog signal is a fifth voltage v5; when the first clock signal is at a low level, the voltage value of the second analog signal is a fourth voltage v4, and the voltage value of the first analog signal is a sixth voltage v6; the third analog signal is a low level signal or a high level signal.
9. The fingerprint detection circuit of claim 5 wherein the output voltage at the output of the charge amplifier is:
wherein VTX is the voltage value of the external analog signal, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
10. The fingerprint detection circuit of claim 7 wherein the output voltage at the output of the charge amplifier is:
wherein VDDHV is the voltage value of the first power supply voltage, cfinger is the capacitance value of the fingerprint capacitor, C1 is the capacitance value of the first capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
11. The fingerprint detection circuit of claim 8 wherein the output voltage at the output of the charge amplifier is:
wherein Cfinger is the capacitance value of the fingerprint capacitor, C3 is the capacitance value of the third capacitor, C1 is the capacitance value of the first capacitor, C2 is the capacitance value of the second capacitor, cref is the capacitance value of the reference capacitor, and VDAC3 is the voltage value of the third analog signal.
12. A fingerprint detection sensor comprising a fingerprint detection circuit according to any one of claims 1 to 11.
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| CN110084082B (en) * | 2018-01-26 | 2022-07-12 | 比亚迪半导体股份有限公司 | Electronic equipment, fingerprint identification device and finger touch detection circuit thereof |
| CN108664955B (en) * | 2018-06-14 | 2024-01-12 | 上海思立微电子科技有限公司 | Fingerprint identification device |
| WO2022109999A1 (en) * | 2020-11-27 | 2022-06-02 | 敦泰电子（深圳）有限公司 | Capacitive fingerprint recognition system, electronic device and fingerprint recognition method |
| CN112416043B (en) * | 2020-11-27 | 2025-06-20 | 敦泰电子（深圳）有限公司 | Negative pressure generating circuit and chip |
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| CN105138986A (en) * | 2015-08-25 | 2015-12-09 | 敦泰电子有限公司 | Fingerprint detection circuit, fingerprint detection device and touch panel |
| CN105447438A (en) * | 2015-02-13 | 2016-03-30 | 比亚迪股份有限公司 | Fingerprint detection circuit and electronic device |
| CN105512650A (en) * | 2016-01-26 | 2016-04-20 | 湖南融创微电子有限公司 | Capacitive fingerprint detection circuit, sensor and device |
| CN205247408U (en) * | 2015-12-07 | 2016-05-18 | 湖南融创微电子有限公司 | Fingerprint detection circuit and fingerprint sensor |
| CN205540784U (en) * | 2016-01-26 | 2016-08-31 | 湖南融创微电子有限公司 | Capacitanc fingerprint detection circuit, sensor and equipment |
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| CN105447438A (en) * | 2015-02-13 | 2016-03-30 | 比亚迪股份有限公司 | Fingerprint detection circuit and electronic device |
| CN105138986A (en) * | 2015-08-25 | 2015-12-09 | 敦泰电子有限公司 | Fingerprint detection circuit, fingerprint detection device and touch panel |
| CN205247408U (en) * | 2015-12-07 | 2016-05-18 | 湖南融创微电子有限公司 | Fingerprint detection circuit and fingerprint sensor |
| CN105512650A (en) * | 2016-01-26 | 2016-04-20 | 湖南融创微电子有限公司 | Capacitive fingerprint detection circuit, sensor and device |
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