CN110210349B - Fingerprint sensor and mobile terminal - Google Patents

Abstract

The application provides a fingerprint sensor and mobile terminal, wherein, this fingerprint sensor includes: the fingerprint calibration circuit comprises a fingerprint input circuit, a first switch, an adjusting circuit, an integrating circuit and a calibration circuit; the fingerprint input circuit is connected to a first end of the adjusting circuit through a first switch, and a second end of the adjusting circuit is respectively connected to the integrating circuit and the calibrating circuit; storing charges into the fingerprint input circuit and the parasitic capacitance in response to a touch operation of a user while the first switch is in an off state; when the first switch is in a closed state, charges stored in the fingerprint input circuit and the parasitic capacitor are transferred to the calibration circuit and the integration circuit, the integration circuit performs integration processing on the stored charges to generate an output signal, and the amount of the charges stored in the calibration circuit is equal to the variation of the charges stored in the parasitic capacitor in the process that the first switch is switched from an open state to a closed state. The fingerprint sensor can effectively improve the output dynamic range and improve the fingerprint identification accuracy.

Description

Fingerprint sensor and mobile terminal

Technical Field

The application relates to the technical field of fingerprint identification, in particular to a fingerprint sensor and a mobile terminal.

Background

The fingerprint is uneven lines formed on the surface of the finger, and has uniqueness, heredity and invariance. The fingerprint repetition rate is extremely low, so that the personal identity authentication can be completed by collecting the fingerprint through the fingerprint sensor. Currently, capacitive sensors can be used to identify fingerprints. The working principle of the capacitive fingerprint sensor is that when a finger is attached to a chip sensing area, a finger attaching surface and a sensing surface form a sensing capacitor. Because the finger plane has the valley and the ridge, the actual distances between the valley and the ridge and the touch sensing panel are different, the sizes of the formed capacitors are different, and the obtained data are also different. After data acquisition is finished, the acquired signals are processed through the fingerprint sensor, and finally acquired different numerical values are collected, so that the acquisition of fingerprints is finished, and fingerprint characteristics are obtained.

However, because the fingerprint sensor integration circuit has a problem of parasitic capacitance in the layout implementation process, a fixed base signal is introduced, the base signal is larger than the acquired effective signal, output saturation is caused after the integration amplification processing is completed, the output dynamic range is greatly reduced, and the output result is seriously distorted.

In view of the above problems, no effective solution has been proposed.

Disclosure of Invention

The embodiment of the application provides a fingerprint sensor and a mobile terminal, and aims to solve the problem that in the prior art, the output dynamic range of the fingerprint sensor is small, so that the output result is distorted.

The embodiment of the application provides a fingerprint sensor, includes: the fingerprint calibration circuit comprises a fingerprint input circuit, a first switch, an adjusting circuit, an integrating circuit and a calibration circuit; the fingerprint input circuit is connected to a first end of the adjusting circuit through a first switch, and a second end of the adjusting circuit is respectively connected to the integrating circuit and the calibrating circuit; storing charges into parasitic capacitances in the fingerprint input circuit and the fingerprint sensor in response to a touch operation by a user with the first switch in an off state; when the first switch is in the closed state, the charges stored in the fingerprint input circuit and the parasitic capacitor are transferred to the calibration circuit and the integration circuit, the integration circuit performs integration processing on the charges stored in the integration circuit to generate an output signal, and the charge amount of the charges stored in the calibration circuit is equal to the variation amount of the charges stored in the parasitic capacitor in the process of switching the first switch from the open state to the closed state.

In one embodiment, the calibration circuit includes a calibration capacitor, a second switch, and a third switch; the first end of the second switch is connected with the common-mode voltage, the second end of the second switch is connected with the first end of the third switch, and the second end of the third switch is grounded; the upper pole plate of the calibration capacitor is respectively connected with the second end of the adjusting circuit and the integrating circuit, and the lower pole plate of the calibration capacitor is respectively connected with the second end of the second switch and the first end of the third switch; wherein, in case the first switch is in the closed state, the second switch is in the open state and the third switch is in the closed state, and in case the first switch is in the open state, the second switch is in the closed state and the third switch is in the open state.

In one embodiment, a fingerprint input circuit includes a first metal layer forming a fingerprint capacitance with a user finger; the upper pole plate of the calibration capacitor is a second pole plate in a second metal layer, the lower pole plate of the calibration capacitor is a third pole plate in a third metal layer, wherein the first metal layer, the second metal layer and the third metal layer are sequentially arranged, the first metal layer is top metal, the second metal layer comprises at least one second pole plate, and the third metal layer comprises at least one third pole plate.

In one embodiment, the calibration capacitor is a coupling capacitor between a second plate as an upper plate of the calibration capacitor and a third plate as a lower plate of the calibration capacitor, and the second plates of the second metal layer except the second plate as the upper plate of the calibration capacitor are connected to a common mode voltage.

In one embodiment, the fingerprint sensor further comprises: and a fourth metal layer disposed between the first metal layer and the second metal layer, the fourth metal layer being connected to the common mode voltage.

In one embodiment, a dielectric layer is disposed between one second plate of the second metal layer and one third plate of the third metal layer, so that the formed calibration capacitor is a MIM capacitor.

In one embodiment, the integrating circuit includes an integrating amplifier, an integrating capacitor, and a fourth switch; the negative input end of the integrating amplifier is respectively connected with the second end of the regulating circuit and the calibration circuit, and the positive input end of the integrating amplifier is connected with the common-mode voltage; the upper polar plate of the integrating capacitor is connected with the negative input end of the integrating amplifier, and the lower polar plate of the integrating capacitor is connected with the output end of the integrating amplifier; the first end of the fourth switch is connected with the upper pole plate of the integrating capacitor, and the second end of the fourth switch is connected with the lower pole plate of the integrating capacitor; wherein the fourth switch is in an open state when the first switch is in the closed state, and the fourth switch is in the closed state when the first switch is in the open state.

In one embodiment, the adjusting circuit comprises an adjusting capacitor and a fifth switch, wherein a first end of the fifth switch is connected with the common-mode voltage, and a second end of the fifth switch is connected with the fingerprint input circuit; an upper pole plate of the adjusting capacitor is connected with the second end of the fifth switch, and a lower pole plate of the adjusting capacitor is respectively connected with the integrating circuit and the calibrating circuit; the second end of the fifth switch is the first end of the adjusting circuit, the lower pole plate of the adjusting capacitor is the second end of the adjusting circuit, the fifth switch is in an off state under the condition that the first switch is in an on state, and the fifth switch is in an on state under the condition that the first switch is in the off state.

In one embodiment, the fingerprint input circuit includes a first metal layer and a sixth switch; the first end of the sixth switch is connected with the driving voltage, and the second end of the sixth switch is connected with the first metal layer; the first metal layer and a finger of a user form a fingerprint capacitor, and the first metal layer is connected with the first end of the adjusting circuit through a first switch; wherein the sixth switch is in an open state when the first switch is in the closed state, and the sixth switch is in a closed state when the first switch is in the open state.

The embodiment of the application also provides a mobile terminal which comprises the fingerprint sensor in any embodiment.

In an embodiment of the present application, there is provided a fingerprint sensor including a fingerprint input circuit, a first switch, an adjustment circuit, an integration circuit, and a calibration circuit, and a charge amount of a charge stored to the calibration circuit in a closed state of the first switch is equal to a variation amount of the charge stored in a parasitic capacitance during switching of the first switch from an open state to a closed state. Because the charge quantity of the charges stored in the calibration circuit is equal to the variation quantity of the charges stored in the parasitic capacitor, namely, the charge quantity transferred by the charges in the parasitic capacitor is completely transferred to the calibration capacitor in the process that the first switch is switched from off to on, the influence of the charges transferred by the parasitic capacitor on the integration circuit is counteracted, namely, the signals output by the parasitic capacitor to the integration circuit are invisible, the output dynamic range of the integration circuit is improved, and the accuracy of fingerprint identification is favorably improved. Meanwhile, the adjustment circuit is arranged, so that the sensitivity of the output signal changing along with the effective signal input by the fingerprint input circuit can be adjusted by adjusting the adjustment circuit, and the accuracy of fingerprint identification is further improved. By the technical scheme, the problems that an existing fingerprint sensor is small in output dynamic range and output results are distorted are solved, and the technical effects of effectively improving the output dynamic range and improving the fingerprint identification accuracy are achieved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application, are incorporated in and constitute a part of this application, and are not intended to limit the application. In the drawings:

FIG. 1 shows a schematic view of a fingerprint sensor in an embodiment of the present application;

FIG. 2 shows a circuit diagram of a fingerprint sensor in an embodiment of the present application;

fig. 3 is a schematic diagram illustrating a layout implementation of a fingerprint sensor in an embodiment of the present application;

fig. 4 shows a layout implementation diagram of a fingerprint sensor in an embodiment of the present application.

Detailed Description

The principles and spirit of the present application will be described with reference to a number of exemplary embodiments. It should be understood that these embodiments are given solely for the purpose of enabling those skilled in the art to better understand and to practice the present application, and are not intended to limit the scope of the present application in any way. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

As will be appreciated by one skilled in the art, embodiments of the present application may be embodied as a system, apparatus, device, method or computer program product. Accordingly, the present disclosure may be embodied in the form of: entirely hardware, entirely software (including firmware, resident software, micro-code, etc.), or a combination of hardware and software.

Considering that a fixed substrate signal is introduced into an integrating circuit by a parasitic capacitor in the existing fingerprint sensor, the substrate signal is larger than an acquired effective signal, output saturation is caused after integral amplification processing is finished, the dynamic range of output is greatly reduced, and the output result is seriously distorted. In view of this problem, it is considered that if the influence of the parasitic capacitance on the output signal can be eliminated, the output dynamic range can be increased, thereby improving the accuracy of fingerprint recognition. In this regard, the inventor thought that by introducing a calibration circuit, the charge transfer occurring in the parasitic circuit during the integration process is completely transferred to the calibration circuit, so that the influence of the parasitic capacitance on the integration circuit can be eliminated, and because there is a deviation in the manufacturing process, the implementation of the calibration capacitance can be improved to further increase the output dynamic range of the integration circuit.

An embodiment of the present application provides a fingerprint sensor, as shown in fig. 1, the fingerprint sensor 100 may include: a fingerprint input circuit 101, a first switch S1, anadjustment circuit 102, anintegration circuit 103, and acalibration circuit 104. The fingerprint input circuit 101 is connected to a first terminal of theadjustment circuit 102 via a first switch S1. A second terminal of the adjustingcircuit 102 is connected to the integratingcircuit 103 and thecalibration circuit 104, respectively.

The first switch S1 can be switched under the control of the firstclock signal CK 1. The first switch S1 is closed when the first clock signal is high, and the first switch S1 is open when the first clock signal is low. When a user performs touch operation, the finger of the user and a polar plate in the fingerprint input circuit form a fingerprint capacitor. With the first switch S1 in the off state, in response to a touch operation by the user, electric charges are stored into the fingerprint input circuit 101 and parasitic capacitances (not shown in fig. 1) in the fingerprint sensor. With the first switch S1 in the closed state, the charges stored in the fingerprint input circuit 101 and the parasitic capacitance are transferred to theadjustment circuit 102, thecalibration circuit 104, and theintegration circuit 103. Theintegration circuit 103 performs integration processing on the electric charge stored to theintegration circuit 103 to generate an output signal. The amount of charge stored to thecalibration circuit 104 is equal to the amount of change in the charge stored in the parasitic capacitance during the switching of the first switch from the open state to the closed state.

In the above embodiment, since the amount of charge stored in the calibration circuit is equal to the amount of change of charge stored in the parasitic capacitor, that is, the amount of charge transferred in the parasitic capacitor is completely transferred to the calibration capacitor in the process of switching the first switch from off to on, the influence of the charge transferred by the parasitic capacitor on the integration circuit is offset, that is, the signal output by the parasitic capacitor to the integration circuit is invisible, the output dynamic range of the integration circuit is improved, and the accuracy of fingerprint identification is improved. Meanwhile, the adjustment circuit is arranged, so that the sensitivity of the output signal changing along with the input signal input by the fingerprint input circuit can be adjusted by adjusting the adjustment circuit, and the accuracy of fingerprint identification is further improved.

Referring to fig. 2, a circuit diagram of a fingerprint sensor according to an embodiment of the present application is shown. As shown in fig. 2, in some embodiments of the present application, thecalibration circuit 204 includes a calibration capacitor Cc, a second switch S2, and a third switch S3. In fig. 2, a first terminal of the second switch S2 is connected to the common mode voltage Vcm, a second terminal of the second switch S2 is connected to a first terminal of the third switch S3, and a second terminal of the third switch S3 is grounded. The upper plate of the calibration capacitor Cc is connected to the second terminal of the adjustingcircuit 202 and theintegrating circuit 203, respectively, and the lower plate of the calibration capacitor Cc is connected to the second terminal of the second switch S2 and the first terminal of the third switch S3, respectively. That is, the calibration capacitor is connected to the common mode voltage Vcm through the second switch S2 and to ground through the third switch S3. With the first switch S1 in the closed state, the second switch S2 is in the open state and the third switch S3 is in the closed state, and with the first switch S1 in the open state, the second switch S2 is in the closed state and the third switch S3 is in the open state.

For example, the second switch S2 may be switched under the control of the second clock signal CK2, and the third switch may be switched under the control of the first clock signal CK 1. The first clock signal CK1 and the second clock signal CK2 are inverted, i.e., the second clock signal CK2 is at a low level when the first clock signal CK1 is at a high level, and the second clock signal CK2 is at a high level when the first clock signal CK1 is at a low level. When the first clock signal CK1 is at a high level, the first switch S1 and the third switch S3 are closed, and the second switch S2 is opened. When the second clock signal CK2 is at a high level, the second switch S2 is closed, and the first switch S1 and the third switch S3 are opened.

Continuing with fig. 2, illustratively, the integratingcircuit 203 may include an integrating amplifier OP, an integrating capacitor Cref, and a fourth switch S4. The integrating amplifier OP comprises a negative input terminal, a positive input terminal and an output terminal. The negative input terminal of the integrating amplifier OP is connected to the second terminal of the adjustingcircuit 202 and thecalibration circuit 204, respectively, and the positive input terminal of the integrating amplifier OP is connected to the common-mode voltage Vcm. The upper polar plate of the integrating capacitor Cref is connected with the negative input end of the integrating amplifier OP, and the lower polar plate of the integrating capacitor Cref is connected with the output end of the integrating amplifier OP. A first terminal of the fourth switch S4 is connected to the upper plate of the integrating capacitor Cref, and a second terminal of the fourth switch S4 is connected to the lower plate of the integrating capacitor Cref. With the first switch S1 in the closed state, the fourth switch S4 is in the open state, and with the first switch S1 in the open state, the fourth switch S4 is in the closed state. The structure of the integration circuit in the above embodiment is only an example, and other structures may be adopted for the integration circuit, which is not limited in the present application.

For example, the fourth switch S4 may be switched under the control of the secondclock signal CK 2. The first clock signal CK1 and the second clock signal CK2 are inverted, i.e., the second clock signal CK2 is at a low level when the first clock signal CK1 is at a high level, and the second clock signal CK2 is at a high level when the first clock signal CK1 is at a low level. When the first clock signal CK1 is at a high level, the first switch S1 is closed and the fourth switch S4 is open. When the second clock signal CK2 is at a high level, the fourth switch S4 is closed and the first switch S1 is open.

With continued reference to fig. 2, theadjustment circuit 202 includes an adjustment capacitor C1 and a fifth switch S5. A first terminal of the fifth switch S5 is connected to the common mode voltage Vcm, and a second terminal of the fifth switch S5 is connected to thefingerprint input circuit 201. The upper plate of the adjusting capacitor C1 is connected to the second terminal of the fifth switch S5, and the lower plate of the adjusting capacitor C1 is connected to the integratingcircuit 203 and thecalibration circuit 204, respectively. The second terminal of the fifth switch S5 is the first terminal of the adjustingcircuit 202, and the bottom plate of the adjusting capacitor C1 is the second terminal of the adjustingcircuit 202. In the case where the first switch S1 is in the closed state, the fifth switch S5 is in the open state, and in the case where the first switch S1 is in the open state, the fifth switch S5 is in the closed state.

For example, the fifth switch S5 may be switched under the control of the secondclock signal CK 2. The first clock signal CK1 and the second clock signal CK2 are inverted, i.e., the second clock signal CK2 is at a low level when the first clock signal CK1 is at a high level, and the second clock signal CK2 is at a high level when the first clock signal CK1 is at a low level. When the first clock signal CK1 is at a high level, the first switch S1 is closed and the fifth switch S5 is open. When the second clock signal CK2 is at a high level, the fifth switch S5 is closed and the first switch S1 is open.

As shown in fig. 2, thefingerprint input circuit 201 includes a first metal layer and a sixth switch S6. A first terminal of the sixth switch S6 is connected to the driving voltage Vdrive, and a second terminal of the sixth switch S6 is connected to the first metal layer. The first metal layer forms a fingerprint capacitance Cf with the user' S finger, and the first metal layer is connected to the first terminal of the adjustingcircuit 202 via the first switch S1. In the case where the first switch S1 is in the closed state, the sixth switch S6 is in the open state, and in the case where the first switch S1 is in the open state, the sixth switch S6 is in the closed state.

For example, the sixth switch S6 may be switched under the control of the secondclock signal CK 2. The first clock signal CK1 and the second clock signal CK2 are inverted, i.e., the second clock signal CK2 is at a low level when the first clock signal CK1 is at a high level, and the second clock signal CK2 is at a high level when the first clock signal CK1 is at a low level. When the first clock signal CK1 is high, the first switch S1 is closed and the sixth switch S6 is open. When the second clock signal CK2 is at a high level, the sixth switch S6 is closed and the first switch S1 is open.

With continued reference to fig. 2, the parasitic capacitances, including the first parasitic capacitance Cp, are schematically illustrated in fig. 2₁And a second parasitic capacitance Cp₂。

The working principle of the fingerprint sensor is explained below in connection with the fingerprint sensor in fig. 2:

in fig. 2, the first switch S1 and the third switch S3 of the fingerprint sensor perform switching operations under the control of the first clock signal CK1, and the first switch S1 and the third switch S3 are in a closed state when the first clock signal CK1 is at a high level, and the first switch S1 and the third switch S3 are in an open state when the first clock signal CK1 is at a low level. The second switch S2, the fourth switch S4, the fifth switch S5, and the sixth switch S6 in the fingerprint sensor perform switching operations under the control of the second clock signal CK2, the second switch S2, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are in a closed state when the second clock signal CK2 is at a high level, and the second switch S2, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are in an open state when the second clock signal CK2 is at a low level. One integration processing period of the fingerprint sensor includes a first phase when the first clock signal CK1 is at a low level while the second clock signal CK2 is at a high level, and a second phase when the first clock signal CK1 is at a high level while the second clock signal CK2 is at a low level.

In the first stage, the second switch S2, the fourth switch S4, the fifth switch S5, and the sixth switch S6 are in a closed state, while the first switch S1 and the third switch S3 are in an open state. The sixth switch S6 is closed, the first metal layer is connected with the driving voltage Vdrive, the fingerprint contact capacitor Cf is charged, and the charge amount stored in the fingerprint capacitor Cf is Cf · Vdrive; first parasitic capacitance Cp₁Is connected with a driving voltage Vdrive to the first parasitic capacitance Cp₁Charging is performed, the first parasitic capacitance Cp₁The amount of stored charge is Cp₁Vdrive. The fifth switch S5 is closed, the upper and lower plates of the adjusting capacitor C1 are connected with the common mode voltage Vcm, the amount of the stored electric charge on the adjusting capacitor C1 is zero, and the second parasitic capacitor Cp₂Is connected to the common mode voltage Vcm, for the second parasitic capacitance Cp₂Charging is performed, the second parasitic capacitance Cp₂The amount of stored charge is Cp₂Vcm. And the second switch S2 is closed, the upper and lower plates of the calibration capacitor Cc are both connected with the common-mode voltage Vcm, and the stored charge amount of the calibration capacitor Cc is zero. The fourth switch S4 is closed and the integration circuit is reset.

In the second stage, the first switch S1 and the third switch S3 are in a closed state, while the second switch S2, the fourth switch S4, the fifth switch S5 and the sixth switch S6 are in an open state. First switch S1 and third switch S3 are closed, meaningFringe capacitance, first parasitic capacitance Cp₁And a second parasitic capacitance Cp₂The charge on is transferred to the adjustment capacitor C1, the calibration capacitor Cc and the integration capacitor Cref. The potential at the first metal layer of the fingerprint capacitor Cf is set to be Vx, and the Vx can be solved through a charge conservation law. First parasitic capacitance Cp₁The stored charge being Cp₁Vx, second parasitic capacitance Cp₂The stored charge being Cp₂Vx. The charge stored on the capacitor C1 is adjusted to be (Vx-Vcm) · C1, meanwhile, the integrating capacitor Cref participates in the charge transfer, and the charge stored on the integrating capacitor Cref is (Vcm-Vout) · Cref. The lower plate of the calibration capacitor is grounded, and the charge amount stored in the calibration capacitor Cc is Vcm & Cc.

First parasitic capacitance Cp from the first stage to the second stage₁And a second parasitic capacitance Cp₂The amount of change in charge on is: cp₁(Vrive-Vx) + Cp2 (Vcm-Vx). In the second stage, the amount of charge stored on the calibration capacitor Cc is Vcm · Cc. By setting Cc.Vcm equal to Cp₁·(Vdrive-Vx)+Cp₂V. (Vcm-Vx), parasitic Cp₁And Cp₂The amount of charge above will be transferred to Cc entirely, thereby canceling the parasitic first parasitic capacitance Cp₁And a second parasitic capacitance Cp₂The influence on the output signal of the integrating circuit ensures that the parasitic capacitance can not see the signal output by the integrating circuit, thereby improving the output dynamic range of the integrating circuit and being beneficial to improving the accuracy of fingerprint identification.

In order to reduce the dynamic effect of adjusting the integrating capacitance Cref on the integrating circuit, the circuit sensitivity can be adjusted by fixing the integrating capacitance Cref and introducing an adjusting capacitance C1. The sensitivity of the output signal changing along with the fingerprint capacitance is adjusted by adjusting the capacitance of the adjusting capacitor C1, so that the identification precision of the fingerprint sensor is further improved.

Specifically, after introducing the adjustment capacitance C1, in a first phase: in an ideal state (the calibration capacitor completely eliminates the influence of the parasitic capacitor, namely, no parasitic capacitor exists and no calibration capacitor Cc exists), the switch S6 is closed, the first metal layer is connected with the Vdrive potential, the charge quantity stored on the fingerprint contact capacitor Cf is Cf.Vdrive, the switch S5 is closed, the upper plate of the adjusting capacitor C1 is connected with the Vcm potential, and the charge quantity stored on the adjusting capacitor C1 is zero; in the second stage: the switch S1 is closed, the charge stored on the fingerprint contact capacitor Cf is shared with the adjusting capacitor C1, and assuming that the lower plate potential of the fingerprint contact capacitor is Vx, the amount of charge stored on the fingerprint capacitor Cf is Cf · Vx, the amount of charge stored on the adjusting capacitor C1 is (Vx-Vcm) · C1, and meanwhile, the integrating capacitor Cref participates in the transfer of charge, and according to the charge conservation theorem, it can be obtained:

(Vx-Vcm)·C1+Cf·Vx＝Cf·Vdrive；

(Vx-Vcm)·C1＝(Vcm-Vout)·Cref；

vx and Vout can be obtained as follows:

where Vout is the output voltage of the integrating circuit, ideally, the output voltage is only related to the fingerprint input capacitance Cf, and is not affected by parasitic capacitance. By fixing the integrating capacitance Cref and introducing the adjusting capacitance C1, the dynamic influence of the adjusting integrating capacitance Cref on the integrating circuit can be reduced, so that the sensitivity of the fingerprint sensor can be adjusted by adjusting the adjusting capacitance C1.

Due to errors in the manufacturing process, in order to further improve the output dynamic range of the capacitive fingerprint sensor, the implementation of the capacitive fingerprint sensor is improved, and the implementation of the calibration capacitor in the fingerprint sensor is described below with reference to fig. 3 and 4.

As shown in fig. 3, a schematic diagram of a layout implementation of a fingerprint sensor in an embodiment of the present application is shown. In FIG. 3, plate M_NThe first metal layer in the fingerprint capacitor Cf, the upper plate of the calibration capacitor Cc is the second metal layer M_N-1A lower plate of the calibration capacitor Cc is a third metal layer M_N-2A calibration capacitor Cc is formed between the second and third platesThe coupling capacitance therebetween. First metal layer M_NIs a top metal, a first metal layer M_NA second metal layer M_N-1And a third metal layer M_N-2Sequentially arranged, a second metal layer M_N-1Comprises at least one second electrode plate, a third metal layer M_N-2Comprising at least one third plate. Further, as shown in fig. 3, the upper plate of the adjusting capacitor C1 may be the second metal layer M_N-1The lower plate of the adjusting capacitor C1 may be the third metal layer M_N-2The other third plate. Second metal layer M_N-1Wherein the other second plates except the second plate as the upper plates of the calibration capacitor and the adjustment capacitor are connected with a common mode voltage.

In the fingerprint sensor in the above embodiment, the calibration capacitor is formed by the second pole plate and the third pole plate in the second metal layer and the third metal layer which are sequentially arranged with the first metal layer, so that under the condition of process errors, because the error directions of the second metal layer and the third metal layer are the same, the influence of the process on the calibration capacitor is small, the effect of eliminating the influence of parasitic capacitance is good, and the output dynamic range can be better improved. Furthermore, the rest second plates in the second metal layer are connected with the common-mode voltage, so that the influence of the signal processing circuit on the first metal layer can be isolated, and the distortion caused by the influence of a dynamic circuit is further avoided.

In the process of manufacturing, each metal layer needs to be polished and smoothed, and during polishing, the purpose of planarization is achieved by mechanical membrane removal, but due to the problem that the stress of the middle area and the stress of the peripheral area are not uniform, the thickness of the metal layer has slight difference, so that in order to further reduce the influence of process errors, as shown in fig. 4, a layout implementation schematic diagram of the fingerprint sensor in an embodiment of the present application is shown. In FIG. 4, plate M_NThe first metal layer in the fingerprint capacitor Cf, the upper plate of the calibration capacitor Cc is the second metal layer M_N-2A lower plate of the calibration capacitor Cc is a third metal layer M_N-3A third plate of the first plate. First metal layer M_NIs a top layerMetal, first metal layer M_NA second metal layer M_N-1And a third metal layer M_N-2Sequentially arranged, a second metal layer M_N-2Comprises at least one second electrode plate, a third metal layer M_N-3Comprising at least one third plate. As shown in fig. 4, the fingerprint sensor further includes: is arranged on the first metal layer M_NAnd a second metal layer M_N-2Fourth metal layer M in between_N-1Fourth metal layer M_N-1Connected to a common mode voltage Vcm.

In the fingerprint sensor in the above embodiment, the fourth metal layer is disposed between the first metal layer and the second metal layer, when the sixth switch is turned off, the first metal layer is connected to the driving voltage, and the fourth metal layer is connected to the common-mode voltage.

With continued reference to fig. 4, in one embodiment, a dielectric layer may be disposed between one second plate of the second metal layer and one third plate of the third metal layer, such that the calibration capacitor Cc formed is a MIM capacitor.

Compared with the method of calibrating the capacitor through the coupling capacitor between the plates, the fingerprint sensor in the above embodiment can further reduce the influence introduced by part of the process manufacturing process through the method of calibrating the capacitor through fixing the MIM capacitor, thereby improving the output dynamic range of the circuit.

It is understood that the implementation manner of calibrating the capacitor includes, but is not limited to, the above manners, and various capacitor implementations, such as MOM capacitor, interdigital capacitor, etc., may also be combined according to the selected process, which is not limited by the present invention.

The embodiment of the application also provides a mobile terminal, which comprises the fingerprint image acquisition device in any embodiment. The electronic device may comprise any one of the following: a mobile smart phone, a computer (including a laptop computer and a desktop computer), a tablet electronic device, a Personal Digital Assistant (PDA), a smart wearable device, and the like, which are not limited herein.

It will be apparent to those skilled in the art that the modules or steps of the embodiments of the present application described above may be implemented by a general purpose computing device, they may be centralized on a single computing device or distributed across a network of multiple computing devices, and alternatively, they may be implemented by program code executable by a computing device, such that they may be stored in a storage device and executed by a computing device, and in some cases, the steps shown or described may be performed in an order different from that described herein, or they may be separately fabricated into individual integrated circuit modules, or multiple ones of them may be fabricated into a single integrated circuit module. Thus, embodiments of the present application are not limited to any specific combination of hardware and software.

It is to be understood that the above description is intended to be illustrative, and not restrictive. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the application should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the pending claims along with the full scope of equivalents to which such claims are entitled.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and it will be apparent to those skilled in the art that various modifications and variations can be made in the embodiment of the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (10)

1. A fingerprint sensor is characterized by comprising a fingerprint input circuit, a first switch, a sixth switch, an adjusting circuit, an integrating circuit and a calibrating circuit; wherein,

the fingerprint input circuit is connected to a first end of the adjusting circuit through the first switch and is connected to a driving voltage through the sixth switch, a second end of the adjusting circuit is connected to one end of the calibrating circuit and is connected to the integrating circuit, and a third end of the adjusting circuit is connected to a common-mode voltage;

a first parasitic capacitor exists between the first switch and the fingerprint input circuit, a second parasitic capacitor exists between the first switch and the adjusting circuit, and the calibration circuit comprises a calibration capacitor;

a duty cycle of the fingerprint sensor comprises at least a first phase and a second phase:

in the first stage, the first switch is controlled to be in an off state, the sixth switch is controlled to be closed, a driving voltage is communicated with the fingerprint input circuit in response to touch operation of a user, charges are stored in the fingerprint input circuit and the first parasitic capacitor, and the common mode voltage stores charges in the second parasitic capacitor;

in the second phase, the first switch is controlled to be in a closed state, the sixth switch is controlled to be opened, and charges stored in the fingerprint input circuit and the first parasitic capacitor and the second parasitic capacitor are transferred to the calibration capacitor and the integrating circuit, wherein the charge amount stored in the calibration capacitor is equal to the change amount of the charges stored in the first parasitic capacitor and the second parasitic capacitor in the second phase relative to the charges stored in the first parasitic capacitor and the second parasitic capacitor in the first phase, so that only the electrical parameters in the fingerprint input circuit and the adjusting circuit influence the output of the integrating circuit in the second phase.

2. The fingerprint sensor of claim 1, wherein the calibration circuit comprises a calibration capacitor, a second switch, and a third switch; wherein,

the first end of the second switch is connected with common-mode voltage, the second end of the second switch is connected with the first end of the third switch, and the second end of the third switch is grounded;

the upper pole plate of the calibration capacitor is respectively connected with the second end of the adjusting circuit and the integrating circuit, and the lower pole plate of the calibration capacitor is respectively connected with the second end of the second switch and the first end of the third switch;

wherein, with the first switch in a closed state, the second switch is in an open state and the third switch is in a closed state, and with the first switch in an open state, the second switch is in a closed state and the third switch is in an open state.

3. The fingerprint sensor of claim 2, wherein the fingerprint input circuit comprises a first metal layer that forms a fingerprint capacitance with a user's finger;

the upper pole plate of the calibration capacitor is a second pole plate in a second metal layer, the lower pole plate of the calibration capacitor is a third pole plate in a third metal layer, the first metal layer, the second metal layer and the third metal layer are sequentially arranged, the first metal layer is top metal, the second metal layer comprises at least one second pole plate, and the third metal layer comprises at least one third pole plate.

4. The fingerprint sensor of claim 3, wherein the calibration capacitor is a coupling capacitor between the second plate as the upper plate and the third plate as the lower plate, and the second plates of the second metal layer other than the second plate as the upper plate of the calibration capacitor are connected to a common mode voltage.

5. The fingerprint sensor of claim 3, further comprising:

a fourth metal layer disposed between the first metal layer and the second metal layer, the fourth metal layer being connected to a common mode voltage.

6. The fingerprint sensor of claim 3, wherein a dielectric layer is disposed between the upper plate and the lower plate of the calibration capacitor, such that the calibration capacitor formed is a MIM capacitor.

7. The fingerprint sensor of claim 1, wherein the integration circuit comprises an integrating amplifier, an integrating capacitor, and a fourth switch; wherein,

the integrating amplifier comprises a negative input end, a positive input end and an output end, the negative input end of the integrating amplifier is respectively connected with the second end of the regulating circuit and the calibration circuit, and the positive input end of the integrating amplifier is connected with common-mode voltage;

the upper polar plate of the integrating capacitor is connected with the negative input end of the integrating amplifier, and the lower polar plate of the integrating capacitor is connected with the output end of the integrating amplifier;

the first end of the fourth switch is connected with the upper pole plate of the integrating capacitor, and the second end of the fourth switch is connected with the lower pole plate of the integrating capacitor;

wherein the fourth switch is in an open state if the first switch is in a closed state, and the fourth switch is in a closed state if the first switch is in an open state.

8. The fingerprint sensor of claim 1, wherein the adjustment circuit includes an adjustment capacitor and a fifth switch, wherein,

a first end of the fifth switch is connected with a common-mode voltage, and a second end of the fifth switch is connected with the fingerprint input circuit;

an upper pole plate of the adjusting capacitor is connected with a second end of the fifth switch, and a lower pole plate of the adjusting capacitor is respectively connected with the integrating circuit and the calibrating circuit;

the second end of the fifth switch is the first end of the adjusting circuit, the lower plate of the adjusting capacitor is the second end of the adjusting circuit, the fifth switch is in an open state when the first switch is in a closed state, and the fifth switch is in a closed state when the first switch is in an open state.

9. The fingerprint sensor of claim 1, wherein the fingerprint input circuit comprises a first metal layer forming a fingerprint capacitance with a user's finger, the first metal layer being connected to the first terminal of the adjustment circuit via the first switch, the first metal layer being connected to a driving voltage via the sixth switch.

10. A mobile terminal, characterized in that it comprises a fingerprint sensor according to any one of claims 1-9.

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