CN107066960B - Signal processing circuit for fingerprint sensor - Google Patents
Signal processing circuit for fingerprint sensor Download PDFInfo
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- CN107066960B CN107066960B CN201710209368.2A CN201710209368A CN107066960B CN 107066960 B CN107066960 B CN 107066960B CN 201710209368 A CN201710209368 A CN 201710209368A CN 107066960 B CN107066960 B CN 107066960B
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Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/12—Fingerprints or palmprints
- G06V40/13—Sensors therefor
- G06V40/1306—Sensors therefor non-optical, e.g. ultrasonic or capacitive sensing
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
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- H03F2203/20—Indexing scheme relating to power amplifiers, e.g. Class B amplifiers, Class C amplifiers
- H03F2203/21—Indexing scheme relating to power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
- H03F2203/211—Indexing scheme relating to power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only using a combination of several amplifiers
- H03F2203/21136—An input signal of a power amplifier being on/off switched
Abstract
The invention discloses a signal processing circuit for a fingerprint sensor, which comprises: a first input circuit, a second input circuit, and a differential amplifier; the first input circuit is used for being electrically connected with the first fingerprint sensing module so as to provide a first sensing signal generated by the first fingerprint sensing module for the differential amplifier; the second input circuit is used for being electrically connected with the second fingerprint sensing module so as to provide a second sensing signal for the differential amplifier; the differential amplifier comprises a first input end, a second input end, a first signal processing unit electrically connected with the first input end, and a second signal processing unit electrically connected with the second input end; the first signal processing unit is coupled with the second signal processing unit so as to perform differential amplification processing on the first sensing signal and the second sensing signal, and the differential amplifier further comprises an output end for outputting the processed signals.
Description
Technical Field
The invention relates to the technical field of fingerprint sensing, in particular to a signal processing circuit for a fingerprint sensor.
Background
Currently, fingerprint sensors have been widely used in client devices with fingerprint recognition function, which may include, for example, mobile smartphones, computers (including notebook computers, desktop computers), tablet electronic devices, personal Digital Assistants (PDAs), smart wearable devices, or the like.
FIG. 1 is a schematic diagram of a capacitive fingerprint sensor in the prior art, wherein a coupling capacitor C is formed between a finger and a touch insulating layer of the fingerprint sensor when the finger contacts the touch insulating layer as shown in FIG. 1 finger Since the distances from the fingerprint ridges and the fingerprint valleys of the finger to the touch insulating layer are different, the coupling capacitance values formed between the respective portions of the finger and the touch insulating layer are also different. In order to identify the fingerprint information of each part of the finger, the touch insulating layer is typically divided into individual cells, which constitute an array of fingerprint sensing cells. The important function of the fingerprint sensor is to collect the fingerprintAnd the coupling capacitance value of each unit in the fingerprint sensing unit array is used for identifying fingerprint information corresponding to the unit according to the capacitance value.
Based on the application manner of the capacitive sensor, a signal processing manner based on charge transfer of the conventional capacitive fingerprint sensor is described below through fig. 2. As shown in fig. 2, the fingerprint sensor is in the reset mode during the phase of the clock PH1 (i.e., switch PH1 is on and switch PH2 is off in fig. 2). In the phase of the clock PH2 (i.e. switch PH2 is on and switch PH1 is off in fig. 2), the fingerprint sensor is in the sampling mode, and the voltage signal Vcharge is used to reduce or eliminate the fixed offset caused by the parasitic capacitance Cs between the touch insulating layer and the conductive layer in fig. 1. In order to enhance the capacitive load at the input of the differential amplifier AMP1, the capacitor C0 may be connected to the voltage signal Vcharge and the inverting input of AMP1, but due to the coupling capacitor C finger The value of Vcharge and the value of capacitor C0 are difficult to set due to the unfixed value, and the fixed offset caused by parasitic capacitance Cs cannot be completely eliminated due to the voltage signal Vcharge. In addition, in the phase of the clock PH2, noise generated by power supply or ground in certain frequency bands affects the reference voltage Vref, and under the action of the differential amplifier AMP1, the noise is transferred to the output voltage Vo1 of the AMP1, thereby affecting the sampling coupling capacitor C finger And the reference capacitance Cref, resulting in a degradation of the fingerprint image quality. The noise of the power supply or the ground is generally common mode noise like the influence of the parasitic capacitance Cs between the touch insulating layer and the conductive layer in fig. 1, but the parasitic capacitance Cs is a fixed value, and the common mode noise of the power supply or the ground has randomness. In order to avoid the influence of common mode noise on a power supply or the ground on the fingerprint identification sensor, it is important to provide an improved signal processing unit of the fingerprint identification sensor. Fig. 3 is a block diagram of a signal processing circuit of the fingerprint sensor based on the improvement of fig. 2 in the prior art. As shown in fig. 3, the improvement of fig. 3 with respect to fig. 2 is that the common mode voltage Vcom connected to the inverting input terminal of the differential amplifier AMP2 in fig. 2 is replaced with a fixed reference input circuit having the same structure as the fingerprint input circuit shown in fig. 2. In particular during the working process, the same as In this case, the reset mode or sampling mode of the fingerprint sensor may be controlled by the switches PH1 and PH 2. In the circuit structure shown in fig. 3, although the reference voltage Vref or other circuit blocks connected to the power supply or the ground still carry common mode noise and are amplified by the differential amplifiers AMP3 and AMP4, the same common mode noise exists in both the first input circuit and the second input circuit, and after the common mode signal of the differential amplifier AMP5 is suppressed, the influence of the common mode noise on the output result can be reduced or even eliminated. The reduction or elimination of the common mode noise effect described above is based only on the scenario where the fingerprint sensing module connected to the fingerprint input circuit has finger contact. If the fingerprint input circuit has no finger contact or insufficient finger contact, the common mode noise interference cannot be transferred to the input end of the differential amplifier AMP5 through the charge transfer structure, and even after the differential processing of the AMP5, the common mode noise cannot be eliminated or even reduced, and the effect is similar to that of the conventional signal processing manner shown in fig. 2.
Accordingly, there is a need in the art for a signal processing circuit for a fingerprint sensor that eliminates common mode noise.
Disclosure of Invention
The invention aims to provide a signal processing circuit for a fingerprint sensor, which has a simple circuit structure and can effectively eliminate the influence of common mode noise.
The above object of the present invention can be achieved by the following technical solutions:
a signal processing circuit for a fingerprint sensor, comprising: a first input circuit, a second input circuit, and a differential amplifier;
the first input circuit is used for being electrically connected with a first fingerprint sensing module of the fingerprint sensor so as to provide a first sensing signal generated by the first fingerprint sensing module for the differential amplifier;
the second input circuit is used for being electrically connected with a second fingerprint sensing module of the fingerprint sensor so as to provide a second sensing signal generated by the second fingerprint sensing module for the differential amplifier; the first fingerprint sensing module and the second fingerprint sensing module are any two different sensing modules in a fingerprint sensing module array of the fingerprint sensor;
the differential amplifier comprises a first input end and a second input end which are opposite in polarity and are respectively electrically connected with the first input circuit and the second input circuit, a first signal processing unit which is electrically connected with the first input end, and a second signal processing unit which is electrically connected with the second input end; the first signal processing unit is coupled with the second signal processing unit so as to perform differential amplification processing on the first sensing signal and the second sensing signal, and the differential amplifier further comprises an output end for outputting the processed signals.
Further, the first signal processing unit and the second signal processing unit are provided with a row selection switch and a column selection switch, and when the row selection switch and the column selection switch of the first signal processing unit and the second signal processing unit are all conducted, the first signal processing unit and the second signal processing unit are coupled to generate the differential amplifier.
Further, the row selection switch and the column selection switch are controlled to be turned on or turned off by a digital circuit.
Further, the areas of the input transistors in the first signal processing unit and the second signal processing unit for amplifying the first sensing signal and the second sensing signal are not smaller than a first preset threshold.
Further, in the differential amplifier, the first signal processing unit and the second signal processing unit share a tail current source and an output load.
Further, the first signal processing unit and the second signal processing unit are provided with a common mode feedback loop, and the common mode feedback loop is used for controlling the tail current source so as to stabilize the common mode working voltage of the differential amplifier.
Further, the output terminal comprises a first output terminal for outputting a first output voltage and a second output terminal for outputting a second output voltage, the first output signal is used for determining fingerprint information corresponding to the first fingerprint sensing module, and the second output signal is used for determining fingerprint information corresponding to the second sensing module.
Further, the signal processing circuit further includes:
the first control module is used for starting the fingerprint sensor to work in a reset function;
and the second control module is used for starting the fingerprint sensor to work in the sampling function.
Further, the first fingerprint sensing module and the second fingerprint sensing module further comprise a touch insulating layer and a conductive layer which are mutually connected, and the conductive layer is connected with the first input end and the second input end; when the fingerprint sensor is set to a sampling mode, a finger or the conducting layer is applied with a voltage with a preset value, and when the finger touches the touch insulating layer, a coupling capacitance is generated between the finger and the conducting layer; the first fingerprint sensing module and the second fingerprint sensing module generate the first sensing signal and the second sensing signal matched with the coupling capacitance value based on the applied voltage respectively.
Further, when the fingerprint sensor is set to a reset mode, a fixed voltage is applied to the first input terminal and the second input terminal to adjust a circuit operating point of the differential amplifier.
Further, the first control module includes:
One end of the feedback capacitor is respectively connected with the first input end and the second input end, and the other end of the feedback capacitor is respectively connected with the output end;
the two first reset switches are respectively connected to two ends of the feedback capacitor;
one end of the second reset switch is connected with each other, and the other end of the second reset switch is connected with the first input end and the second input end respectively;
one end of the second reset switch is respectively connected with the first fingerprint sensing module and the second fingerprint sensing module, and the other end of the second reset switch is respectively grounded;
the first reset switch, the second reset switch and the third reset switch are consistent in connection or disconnection.
Further, the second control module includes:
and one end of the sampling switch is respectively connected with the first fingerprint sensing module and the second fingerprint sensing module, and the other end of the sampling switch is respectively connected with the first output end and the second input end.
Further, the first input circuit includes a first adder, where the first adder is electrically connected to the first fingerprint sensing module and a fingerprint sensing module adjacent to the first fingerprint sensing module, and is configured to perform summation calculation on the first sensing signal and a sensing signal generated by the fingerprint sensing module adjacent to the first fingerprint sensing module, so as to generate a first summation sensing signal;
Correspondingly, the second input circuit comprises a second adder, wherein the second adder is electrically connected with the second fingerprint sensing module and the fingerprint sensing module adjacent to the second fingerprint sensing module respectively and is used for carrying out summation calculation on the second sensing signal and the sensing signal generated by the fingerprint sensing module adjacent to the second fingerprint sensing module to generate a second summation sensing signal;
accordingly, the first signal processing unit and the second signal processing unit are coupled to perform differential amplification processing on the first summed sensing signal and the second summed sensing signal. A fingerprint sensor comprising the signal processing circuit of any one of claims 1-12, wherein the number of fingerprint sensing modules matches the number of signal processing units.
Further, the fingerprint sensor comprises a preset number of tail current sources and output loads, and the preset number is smaller than the number of the signal processing units.
An electronic device comprising a fingerprint sensor therein, the fingerprint sensor comprising the signal processing circuit of any one of claims 1-12.
Further, the electronic device has a function of quick charge.
Further, the electronic device includes any one of the following: mobile smartphones, notebook computers, desktop computers, tablet electronic devices, personal Digital Assistants (PDAs), smart wearable devices.
The signal processing circuit for the fingerprint sensor can utilize the signal processing units in the fingerprint sensor to couple any two signal processing units into the differential amplifier, the differential amplifier has a certain gain, weak sensing signals can be amplified, and common mode noise brought by a power supply or ground in the circuit can be weakened or eliminated. For capacitive sensors, the offset effects of parasitic capacitance Cs between the touch insulating layer and the conductive layer may also be reduced or eliminated. In addition, compared with the signal processing circuit structure in the prior art, the two input circuits connected to the input ends of the differential amplifier are connected to the fingerprint sensing module, and whether the finger contacts or not fully contacts the finger contacts have no great influence on eliminating common mode noise or offset and the like of the differential amplifier.
Drawings
FIG. 1 is a schematic diagram of a prior art capacitive fingerprint sensor;
FIG. 2 is a schematic diagram of a conventional charge conversion-based signal processing circuit of a capacitive fingerprint sensor;
FIG. 3 is a schematic diagram of a signal processing circuit of the prior art fingerprint sensor based on the improvement of FIG. 2;
fig. 4 is a schematic block diagram of a signal processing circuit provided in the present application;
FIG. 5 is a schematic diagram of a circuit configuration of the signal processing circuit provided in the present application;
FIG. 6 is a schematic diagram of the circuit configuration of the fingerprint sensor of FIG. 5 in PH2 phase;
FIG. 7 is a schematic diagram of a circuit configuration of the fingerprint sensor shown in FIG. 5 in a PH1 phase;
FIG. 8 is a schematic diagram of another circuit configuration of the signal processing circuit provided herein;
fig. 9 is a schematic circuit diagram of a signal processing unit provided in the present application;
FIG. 10 is a schematic diagram of one embodiment of a differential amplifier provided herein;
fig. 11 is a schematic diagram of another circuit structure of the signal processing circuit provided in the present application.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and the specific embodiments, it should be understood that these embodiments are only for illustrating the present invention and not for limiting the scope of the present invention, and various modifications of equivalent forms of the present invention will fall within the scope of the appended claims of the present application after reading the present invention.
In the following, a technical environment of the technical solution of the present application is described, and at present, many client devices such as smart phones may support a high-voltage and/or high-current charging mode, and one advantage of the high-voltage and/or high-current charging mode is that fast charging can be achieved. When the client device is charged in a high-voltage and/or high-current charging mode, the power supply of the charger or noise on the ground easily interferes with the power supply and the ground of the client device, so that the normal working state of the fingerprint sensor is affected. In a typical application environment, a charger of a mobile phone of a user is in a high-voltage charging mode and is also provided with a fingerprint sensor, when the mobile phone is charged, and when the user uses the fingerprint to perform operations such as unlocking and payment of a mobile phone interface, the mobile phone cannot identify the fingerprint, so that the user cannot complete the operations such as unlocking and payment of the mobile phone interface.
Based on the technical environment, the signal processing circuit for the fingerprint sensor can remove noise interference caused by high-voltage and/or high-current charging when the client device with the fingerprint sensor is charged with high voltage and/or high current, so that the client device can perform fingerprint identification even when the client device is charged with high voltage and/or high current, and normal use of the fingerprint identification function of the client device is ensured.
Referring to fig. 4, the technical scheme of the present application is specifically described below. As shown in fig. 4, the signal processing circuit for a fingerprint sensor provided in the embodiment of the present application may include: a first input circuit 402, a second input circuit 404, and a differential amplifier 405.
The first input circuit 402 is configured to be electrically connected to the first fingerprint sensing module 401 of the fingerprint sensor, so as to provide the first sensing signal generated by the first fingerprint sensing module 401 to the differential amplifier 405.
The second input circuit 404 is configured to be electrically connected to the second fingerprint sensing module 403 of the fingerprint sensor, so as to provide the second sensing signal generated by the second fingerprint sensing module 403 to the differential amplifier 405; the first fingerprint sensing module 401 and the second fingerprint sensing module 403 are any two different sensing modules in the fingerprint sensing module array 408 of the fingerprint sensor.
The differential amplifier 405 includes a first input terminal and a second input terminal which have opposite polarities and are electrically connected to the first input circuit 402 and the second input circuit 404, a first signal processing unit 406 electrically connected to the first input terminal, and a second signal processing unit 407 electrically connected to the second input terminal; the first signal processing unit 406 and the second signal processing unit 407 are coupled to perform differential amplification processing on the first sensing signal and the second sensing signal, and the differential amplifier 405 further includes an output terminal for outputting the processed signals.
In this embodiment, the fingerprint sensing module array 408 may include a plurality of sensing modules, for example, the fingerprint sensing module array may include a plurality of sensing modules with a number of specifications of 64×64, 128×128, 50×50, 120×60, etc. In one embodiment of the present application, the sensing module may have a finger contact surface, which may include, for example, the touch insulation layer shown in fig. 1. When a finger contacts the finger contact surface, a certain physical quantity change is generated between the finger and the finger contact surface. For example, if the fingerprint sensor is a capacitive sensor, when a finger touches the finger contact surface, a change in coupling capacitance occurs between the finger and the finger contact surface. If the fingerprint sensor is an optical sensor, light and shade changes are generated between the finger and the contact surface of the finger. Based on this, the sensing module may be used to collect the physical quantity change and convert the physical quantity change into a sensing signal, which may comprise, for example, a voltage signal that is easy to process. Whereas the first fingerprint sensing module 401 and the second fingerprint sensing module 403 in the present application are any two different sensing modules in the fingerprint sensing module array 408 of the fingerprint sensor.
In this embodiment, the first input circuit 402 and the second input circuit 404 have a signal transmission function, one end of each of which is electrically connected to the first fingerprint sensing module 401 and the second fingerprint sensing module 403, and the other end of each of which is connected to the positive input terminal and the negative input terminal of the differential amplifier 405. Specifically, the first sensing signal generated by the first fingerprint sensing module 401 and the second sensing signal generated by the second fingerprint sensing module 403 are provided to the differential amplifier 405.
The signal processing units in this embodiment may have a one-to-one correspondence with the sensing modules in the fingerprint sensing module array 408, and the first signal processing unit 406 and the second signal processing unit 407 may respectively correspond to the first fingerprint sensing module 401 and the second fingerprint sensing module 403. The first signal processing unit 406 and the second signal processing unit 407 may be coupled to the differential amplifier 405. The differential amplifier 405 is configured to perform differential amplification processing on the first sensing signal and the second sensing signal, and output a signal after the processing. Specifically, the differential amplifier 405 has a certain gain, so that a weak sensing signal can be amplified, and in addition, compared with the differential amplifier single-ended input structure shown in fig. 3, the first input circuit 402 and the second input circuit 404 in this embodiment are connected to the positive and negative ends of the differential amplifier 405 at the same time to form a double-ended input structure, so that for a capacitive sensor, not only the offset effect caused by the parasitic capacitance Cs between the touch insulating layer and the conductive layer can be reduced or eliminated, but also the common mode noise caused by the power supply or ground in the circuit can be reduced or eliminated. Meanwhile, the first input circuit 402 and the second input circuit 404 are both input circuits connected to the fingerprint sensing module, and whether the finger contacts or not fully contacts the finger contacts has no great influence on eliminating common mode noise or offset and the like of the differential amplifier 405.
The signal processing circuit for the fingerprint sensor can utilize the signal processing units in the fingerprint sensor to couple any two signal processing units into the differential amplifier, the differential amplifier has a certain gain, weak sensing signals can be amplified, and common mode noise brought by a power supply or ground in the circuit can be weakened or eliminated. For capacitive sensors, the offset effects of parasitic capacitance Cs between the touch insulating layer and the conductive layer may also be reduced or eliminated. In addition, compared with the signal processing circuit structure in the prior art, the two input circuits connected to the input ends of the differential amplifier are connected to the fingerprint sensing module, and whether the finger contacts or not fully contacts the finger contacts have no great influence on eliminating common mode noise or offset and the like of the differential amplifier.
In a specific example, the fingerprint sensor is thus constructed as a capacitive fingerprint sensor, for clarity of illustration, but it will be understood by those skilled in the art that the fingerprint sensor of the present scheme may be any sensor that senses. The signal processing circuit provided by the application is described below through a signal trend flow of the capacitive fingerprint sensor.
A fingerprint sensor has an array of 64 x 64 fingerprint sensing modules, each having a finger contact surface for a user's finger to contact. When a finger touches the finger contact surface, a change in coupling capacitance is generated between the finger and the finger contact surface. The sensing module collects the coupling capacitance and converts the coupling capacitance into a sensing signal that is easy to process, which may include, for example, a voltage signal, a current signal, and the like.
Correspondingly, the fingerprint sensor is provided with 64 multiplied by 64 signal processing units which are in one-to-one correspondence with the 64 multiplied by 64 fingerprint sensing modules, and the output data processed by each signal processing unit is the fingerprint information acquired by the fingerprint sensing module corresponding to the output data. As described above, common mode noise may interfere with the fingerprint interference module, the input circuit, the signal processing unit, and the like through power or ground. In order to reduce or even remove the common mode noise, since each signal processing unit has the same structure, any two of the 64×64 signal processing units can be coupled into a differential amplifier, and the differential amplifier can amplify weak sensing signals, suppress common mode noise and eliminate offset effects.
In another specific example, the charger of the mobile phone of the user is in a high-voltage charging mode and is further provided with a fingerprint sensor, and as described in the above technical environment, when the mobile phone is charged, and the user uses the fingerprint to perform operations such as unlocking and payment of the mobile phone interface, the mobile phone cannot be found to identify the fingerprint, so that the user cannot open the mobile phone interface or use the fingerprint to perform payment.
Based on the technical environment, the signal processing circuit for the fingerprint sensor arranged in the mobile phone of the user can start the fingerprint sensor in the mobile phone when the finger touches the key of the mobile phone, so that the fingerprint sensor starts to collect fingerprint information of the user. The mobile phone key corresponds to the finger contact surface of the fingerprint sensing module, when the finger touches the mobile phone key, a coupling capacitance is generated between the finger and a metal sheet (i.e. a conductive layer in fig. 1) below the mobile phone key, and at this time, the signal processing circuit can collect the coupling capacitance and convert the coupling capacitance into a voltage signal or a current signal and then transmit the voltage signal or the current signal to a differential amplifier in the mobile phone. The differential amplifier is formed by coupling any two signal processing units, and can amplify weak sensing signals, inhibit common mode noise and eliminate offset influence.
Therefore, even when the mobile phone is charged rapidly, the signal processing unit can perform fingerprint identification, so that the influence of common mode noise caused by the rapid charging is weakened, the accuracy of fingerprint identification imaging is improved, the normal use of the fingerprint identification function of the mobile phone is ensured, and the accuracy of mobile phone processing and the experience of a user on the mobile phone are further improved.
In one embodiment of the present application, as shown in fig. 4, the output terminals may include a first output terminal for outputting a first output voltage, where the first output signal may be used to determine fingerprint information corresponding to the first fingerprint sensing module 401, and a second output terminal for outputting a second output voltage, where the second output signal may be used to determine fingerprint information corresponding to the second fingerprint sensing module 403.
The first output signal and the second output signal in this embodiment may be directly used to determine fingerprint information corresponding to the first fingerprint sensing module 401 and the second fingerprint sensing module 403. For example, when the first output signal and the second output signal are both voltage values, determining that the fingerprint information of the first fingerprint sensing module 401 is a fingerprint valley when the first output signal is within a first preset voltage value range; when the voltage is within the second preset voltage range, the fingerprint information of the first fingerprint sensing module 401 is determined to be a fingerprint ridge, and the fingerprint can be imaged according to the fingerprint information. The specific processing of the first output signal and the second output signal may be implemented in the data reading circuit shown in fig. 4. For example, the data reading circuit may include a programmable gain amplifier, an analog-to-digital converter, and the like. Compared with the prior art in which Vo1 and Vo2 generated by the signal processing circuit shown in fig. 3 cannot be used to directly determine fingerprint information due to the existence of common mode noise interference, the signal processing structure in this embodiment only needs a first-stage differential amplifier, i.e. can amplify the sensing signal, and weaken or even eliminate common mode noise and offset.
In one embodiment of the present application, as shown in fig. 4, the signal processing circuit may further include:
the first control module is used for starting the fingerprint sensor to work in a reset function;
and the second control module is used for starting the fingerprint sensor to work in the sampling function.
In this embodiment, the reset mode is mainly used for resetting parameters of the fingerprint sensor, and the sampling mode is mainly used for collecting fingerprint information. And switching the two working modes of the fingerprint sensor is completed through the first control module and the second control module.
In one embodiment of the present application, fig. 5 is a schematic structural diagram of one embodiment of a signal processing circuit provided in the present application, as shown in fig. 5, where the first control module may include:
the two feedback capacitors Cref are respectively connected between the first input end and the first output end, and between the second input end and the second output end;
the two first reset switches PH1-1, the first reset switches PH1-1 are respectively connected with two ends of the feedback capacitor Cref;
one end of the second reset switch PH1-2 is connected with each other, and the other end of the second reset switch PH1-2 is connected with the first input end and the second input end respectively;
One end of the third reset switch PH1-3 is respectively connected with the first fingerprint sensing module 401 and the second fingerprint sensing module 403, and the other end is respectively grounded;
the first reset switch PH1-1, the second reset switch PH1-2 and the third reset switch PH1-3 are consistent in connection or disconnection.
In another embodiment of the present application, the second control module may include:
and one end of the sampling switch PH2 is respectively connected with the first fingerprint sensing module 401 and the second fingerprint sensing module 403, and the other end is respectively connected with the first output end and the second input end.
In the application, the sampling mode of the fingerprint sensor can be controlled through four groups of switches, wherein three groups of reset switches are respectively a first reset switch PH1-1, a second reset switch PH1-2 and a third reset switch PH1-3, and a group of sampling switches PH2. The first reset switch PH1-1, the second reset switch PH1-2, and the third reset switch PH1-3 may be controlled by the same control signal, so as to ensure the consistency of the on or off of the three sets of switches. When three groups of reset switches are on and one group of sampling switches are off, the fingerprint sensor is in a reset mode, and the reset mode is mainly used for resetting information of the fingerprint sensor; conversely, when three sets of reset switches are turned off and one set of sampling switches are turned on, the fingerprint sensor is in a sampling mode, and the sampling mode is mainly used for collecting fingerprint information.
When a finger touches the finger contact surface of the fingerprint sensing module, the fingerprint sensor or equipment where the fingerprint sensor is located can sense the contact of the mobile phone, and at the moment, the four groups of switches can be controlled by clock signals with fixed frequency, so that the fingerprint sensor is switched between a reset mode and a sampling mode.
In one embodiment of the present application, the first fingerprint sensing module 401 and the second fingerprint sensing module 403 further comprise a touch insulating layer and a conductive layer connected to each other, and the conductive layer is connected to the first input end and the second input end; when the fingerprint sensor is in a sampling mode, the sampling switch PH2 is turned on, the first reset switch PH1-1, the second reset switch PH1-2 and the third reset switch PH1-3 are turned off, a voltage with a preset value is applied to a finger, and when the finger touches the touch insulating layer, a coupling capacitance is generated between the finger and the conductive layer (refer to figure 1); the first fingerprint sensing module 401 and the second fingerprint sensing module 403 generate the first sensing signal and the second sensing signal matched to the coupling capacitance value based on the applied voltage, respectively.
In this embodiment, the first fingerprint sensing module 401 and the second fingerprint sensing module 403 further include a touch insulating layer and a conductive layer that are connected to each other. The touch insulating layer may include, for example, the touch insulating layer shown in fig. 1, and the touch insulating layer may include a dielectric material of a type such as barium titanate, oxide, nitride, carbide, glass, ceramic, thin film of sapphire, or the like in a polyimide matrix. The conductive layer may include, for example, a conductive material such as a metal layer. When a finger touches the touch insulating layer, a coupling capacitance is formed between the finger and the conductive layer.
Fig. 6 is a schematic circuit diagram of the fingerprint sensor of fig. 5 in a phase PH2, and the driving voltage Vdriver of fig. 5 may be a square wave signal having a fixed frequency, and a period of the square wave signal corresponds to a clock period of the switching signals PH1-1, PH1-2, PH1-3 and PH 2. When the switch signals PH1-1, PH1-2, PH1-3 are on and PH2 is off, the signal processing circuit is in a reset mode, and correspondingly, the driving voltage Vdriver provides a low level 0; when the switching signals PH1-1, PH1-2, PH1-3 are turned off and PH2 is turned on, the signal processing circuit is in a sampling mode, and correspondingly, the driving voltage Vdriver provides a high level Vhigh. The driving voltage Vdriver may apply a high level Vhigh to the finger through a conductive means such as a metal ring, and the high level Vhigh may generate the first sensing signal and the second sensing signal matched with the coupling capacitance value at one end of the conductive layer through a coupling capacitance formed by the finger and the conductive layer due to a conductive function of the human body.
In one embodiment of the present application, when the fingerprint sensor is in the reset mode, the sampling switch PH2 is turned off, the first reset switch PH1-1, the second reset switch PH1-2, and the third reset switch PH1-3 are turned on, and a fixed voltage is applied to the first input terminal and the second input terminal to adjust the circuit operating point of the differential amplifier 405.
Fig. 7 is a schematic circuit diagram of the fingerprint sensor shown in fig. 5 in the PH1 phase, and as shown in fig. 7, the positive input terminal and the negative input terminal of the differential amplifier 405 are shorted when the fingerprint sensor is in the reset mode. In this embodiment, a fixed voltage Vcom may be connected to the input end of the differential amplifier 405, where the fixed voltage Vcom is used to adjust a circuit operating point of the look-up amplifier, so that the fingerprint sensor can quickly enter a stable state when switching from a reset mode to a sampling mode.
In another embodiment of the present application, fig. 8 is a schematic structural diagram of an embodiment of a signal processing circuit provided in the present application, as shown in fig. 8, where the first control module may include:
And the feedback capacitors Cref are respectively connected between the first input end and the first output end, and between the second input end and the second output end.
The two first reset switches PH1-1 are respectively connected to two ends of the feedback capacitor Cref.
And one ends of the second reset switches PH1-2 are connected with each other, and the other ends of the second reset switches PH1-2 are respectively connected with the first input end and the second input end.
And one ends of the third reset switches PH1-3 are respectively connected with the first fingerprint sensing module 401 and the second fingerprint sensing module 403, and the other ends of the third reset switches PH1-3 are respectively connected with reference voltages.
The first reset switch PH1-1, the second reset switch PH1-2 and the third reset switch PH1-3 are consistent in connection or disconnection.
In another embodiment of the present application, the second control module may include:
and one end of the sampling switch PH2 is respectively connected with the first fingerprint sensing module 401 and the second fingerprint sensing module 403, and the other end is respectively connected with the first output end and the second input end.
In this embodiment, in the reset mode, the switching signals PH1-1, PH1-2, PH1-3 are turned on and PH2 is turned off, and at this time, the reference voltage charges the capacitor Cin1, so that one end of the capacitor Cin1 has a voltage value with a certain value. In the sampling mode, the switching signals PH1-1, PH1-2 and PH1-3 are turned off and PH2 is turned on, and at this time, the voltage value on the capacitor Cin1 applies a voltage on the conductive layer, so that when a finger touches the touch insulating layer, a coupling capacitor can be generated between the finger and the conductive layer, and the coupling capacitor is contained in Cin 1; the first fingerprint sensing module 401 and the second fingerprint sensing module 403 generate the first sensing signal and the second sensing signal matched to the coupling capacitance value based on the applied voltage, respectively.
In one embodiment of the present application, the first signal processing unit 406 and the second signal processing unit 407 may have a row selection switch and a column selection switch, and when the row selection switch and the column selection switch of the first signal processing unit 406 and the second signal processing unit 407 are turned on, the first signal processing unit 406 and the second signal processing unit 407 are coupled to generate the differential amplifier 405.
In this embodiment, the main function of the single first signal processing unit 406 and the single second signal processing unit 407 is to amplify weak first sensing signals and weak second sensing signals. After the first signal processing unit 406 and the second signal processing unit 407 are coupled into the differential amplifier 405, the differential amplifier 405 may amplify not only the sensing signal but also reduce or eliminate common mode noise and offset. As shown in fig. 9, the present application provides a circuit structure of a signal processing unit with a simple structure, in which MOS1 is an input transistor, and is mainly used for receiving a sensing signal and amplifying the sensing signal, MOS2 is a row selection switch, MOS3 is a column selection switch, and after voltages greater than a preset threshold are applied to input ends (i.e., gates) of MOS2 and MOS3, both MOS2 and MOS3 are turned on, and at this time, the corresponding signal processing unit is selected. Of course, the implementation of the row selection switch and the column selection switch is not limited to the MOS transistor, and may be, for example, a transistor, etc., which is not limited herein.
Based on this, in one embodiment of the present application, the row selection switch, the column selection switch may be turned on or off by digital circuit control.
In this embodiment, the digital circuit may control the on or off of the row selection switch and the column selection switch, and since the digital circuit control mode has small noise and high speed compared with the analog circuit control mode, the noise in the switching process may be reduced, and the fingerprint information processing efficiency may be improved.
In an embodiment of the present application, an area of the input transistors for amplifying the first sensing signal and the second sensing signal in the first signal processing unit 406 and the second signal processing unit 407 may be not smaller than a first preset threshold.
In this embodiment, as can be seen by comparing fig. 4 and fig. 3, the signal processing circuit structure in the present application is relatively much simpler, and particularly, in the subsequent integrated circuit layout design, the circuit occupied chip area is also much reduced, so that on one hand, the current sheet cost can be reduced, and on the other hand, a margin is left for optimizing the size design of a part of transistors. In this embodiment, the sizes of the input transistors (e.g., the transistor MOS1 in fig. 9) in the first signal processing unit 406 and the second signal processing unit 407 may be increased so that the area of the input transistor is not smaller than the first preset threshold. In the field of analog ICs, the increase of the area of the input transistor can not only reduce the imbalance of the integrated circuit process, but also greatly reduce the influence of noise. Therefore, on the basis of simple structure of the signal processing circuit provided by the application, the size of the input tube is increased, and the influence of process mismatch and noise is reduced.
In one embodiment of the present application, in the differential amplifier 405, the first signal processing unit 406 and the second signal processing unit 407 may share a tail current source and an output load.
Fig. 10 is a schematic diagram of an embodiment of a differential amplifier 405 provided in the present application, as shown in fig. 10, where the first signal processing unit 406 and the second signal processing unit 407 may share a tail current source and an output load. In this embodiment, the tail current source and the output load may be implemented by MOS transistors, or may be implemented by transistors, etc., which is not limited herein. As described above, the number of modules in the fingerprint sensing module array is large, and correspondingly, the number of signal processing units is also large, and if each signal processing unit is connected to a separate tail current and output load, the chip area cost is extremely consumed. The common tail current or output load can greatly reduce the chip design cost.
Further, in this embodiment, during the signal output process, only N differential amplifiers, that is, 2N fingerprint sensing modules, may output fingerprint information at a time, for example, N is 8, 10, 16, etc. Thus, the area of the chip can be further reduced without affecting fingerprint imaging.
In one embodiment of the present application, the first signal processing unit 406 and the second signal processing unit 407 have a common mode feedback loop therein, and the common mode feedback loop is used to control the tail current source to stabilize the common mode operating voltage of the differential amplifier 405.
In this embodiment, the tail current source determines the stability of the common mode operating voltage of the differential amplifier 405, so that in order to keep the tail current source stable, a common mode feedback loop may be set in the first signal processing unit 406 and the second signal processing unit 407 to control the tail current source, thereby further stabilizing the common mode operating voltage of the differential amplifier 405.
In one embodiment of the present application, the first input circuit may include a first adder, where the first adder is electrically connected to the first fingerprint sensing module and a fingerprint sensing module adjacent to the first fingerprint sensing module, and is configured to perform summation calculation on the first sensing signal and a sensing signal generated by the fingerprint sensing module adjacent to the first fingerprint sensing module, so as to generate a first summed sensing signal;
correspondingly, the second input circuit may include a second adder, where the second adder is electrically connected to the second fingerprint sensing module and a fingerprint sensing module adjacent to the second fingerprint sensing module, and is configured to perform summation calculation on the second sensing signal and a sensing signal generated by the fingerprint sensing module adjacent to the second fingerprint sensing module, to generate a second summed sensing signal;
Accordingly, the first signal processing unit and the second signal processing unit are coupled to perform differential amplification processing on the first summed sensing signal and the second summed sensing signal.
In this embodiment, before the differential processing is performed on the first sensing signal and the second sensing signal, the average processing may be performed on the sensing signals generated by the first sensing signal, the second sensing signal and the adjacent sensing modules thereof, so as to improve the data consistency of the sensing signals. Referring specifically to the schematic diagram shown in fig. 11, in the fingerprint sensing module array 408, the fingerprint sensing module (m, n) is located in the mth row and the nth column of the fingerprint sensing module array 408, if it is assumed that the first sensing signal generated by the fingerprint sensing module (m, n) is finger (m, n), the sensing signals generated by the fingerprint sensing module (m, n+1) and the fingerprint sensing module (m+1, n) adjacent to the fingerprint sensing module (m, n) are finger (m, n+1), finger (m+1, n+1), and finger (m+1, n), respectively, then the first summation sensing signal generated after the summation calculation is finger (m, n) +finger (m+1, n+1). Correspondingly, the processing manner of the second input circuit is the same as that of the first input circuit, and will not be described herein. Thereafter, the generated first and second summation sensing signals may be input to the first and second signal processing units, respectively, to perform differential amplification processing on the first and second summation sensing signals.
It should be noted that, in the process of performing the summation calculation, the sensing signals generated by all or part of the adjacent fingerprint sensing modules of the first fingerprint sensing module may be calculated, which is not limited herein.
In this embodiment, before differential amplification, the sensing signal generated by the fingerprint sensing module and the sensing signal generated by the fingerprint sensing module adjacent to the sensing signal are subjected to average processing, so that the data consistency of the sensing signal can be enhanced, and the precision of fingerprint imaging can be improved.
Based on the above signal processing circuit for a fingerprint sensor, another aspect of the present application further provides a fingerprint sensor, where the fingerprint sensor may include the signal processing circuit according to any one of the above embodiments, and the number of fingerprint sensing modules is matched with the number of signal processing units.
Further, the fingerprint sensor may include a preset number of tail current sources and output loads, where the preset number is smaller than the number of the signal processing units.
In another aspect, the present application further provides an electronic device, where the electronic device may include a fingerprint sensor, where the fingerprint sensor includes the signal processing circuit according to any one of the foregoing embodiments.
Further, the electronic device can also have a rapid charging function.
Further, the electronic device may include any one of the following: mobile smartphones, computers (including notebook computers, desktop computers), tablet electronic devices, personal Digital Assistants (PDAs), smart wearable devices, etc., the application is not limited herein.
The foregoing embodiments in the present specification are all described in a progressive manner, and the same and similar parts of the embodiments are mutually referred to, and each embodiment is mainly described in a different manner from other embodiments.
The foregoing description of the embodiments of the present invention is merely illustrative, and the present invention is not limited to the embodiments described above. Any person skilled in the art can make any modification and variation in form and detail of the embodiments without departing from the spirit and scope of the present disclosure, but the scope of the present disclosure is still subject to the scope of the appended claims.
Claims (18)
1. A signal processing circuit for a fingerprint sensor, comprising: a first input circuit, a second input circuit, and a differential amplifier;
the first input circuit is used for being electrically connected with a first fingerprint sensing module of the fingerprint sensor so as to provide a first sensing signal generated by the first fingerprint sensing module for the differential amplifier;
the second input circuit is used for being electrically connected with a second fingerprint sensing module of the fingerprint sensor so as to provide a second sensing signal generated by the second fingerprint sensing module for the differential amplifier; the first fingerprint sensing module and the second fingerprint sensing module are any two different sensing modules in a fingerprint sensing module array of the fingerprint sensor;
the differential amplifier comprises a first input end and a second input end which are opposite in polarity and are respectively electrically connected with the first input circuit and the second input circuit, a first signal processing unit which is electrically connected with the first input end, and a second signal processing unit which is electrically connected with the second input end; the first signal processing unit is coupled with the second signal processing unit so as to perform differential amplification processing on the first sensing signal and the second sensing signal, and the differential amplifier further comprises an output end for outputting the processed signals.
2. The signal processing circuit of claim 1, wherein the first signal processing unit and the second signal processing unit have row select switches and column select switches, and wherein the first signal processing unit and the second signal processing unit are coupled to generate the differential amplifier when the row select switches and the column select switches of the first signal processing unit and the second signal processing unit are all turned on.
3. The signal processing circuit of claim 2, wherein the row select switch and the column select switch are turned on or off by digital circuitry.
4. The signal processing circuit of claim 1, wherein an area of an input transistor in the first signal processing unit, the second signal processing unit for amplifying the first sensing signal and the second sensing signal is not less than a first preset threshold.
5. The signal processing circuit of claim 1, wherein in the differential amplifier, the first signal processing unit and the second signal processing unit share a tail current source and an output load.
6. The signal processing circuit of claim 5, wherein the first signal processing unit and the second signal processing unit have a common mode feedback loop therein for controlling the tail current source to stabilize a common mode operating voltage of the differential amplifier.
7. The signal processing circuit of claim 1, wherein the output comprises a first output for outputting a first output signal for determining fingerprint information corresponding to the first fingerprint sensing module and a second output for outputting a second output signal for determining fingerprint information corresponding to the second fingerprint sensing module.
8. The signal processing circuit of claim 1, wherein the signal processing circuit further comprises:
the first control module is used for starting the fingerprint sensor to work in a reset function;
and the second control module is used for starting the fingerprint sensor to work in the sampling function.
9. The signal processing circuit of claim 1 or 8, wherein the first fingerprint sensing module, the second fingerprint sensing module further comprise a touch insulating layer and a conductive layer connected to each other, the conductive layer being connected to the first input terminal, the second input terminal; when the fingerprint sensor is set to a sampling mode, a finger or the conducting layer is applied with a voltage with a preset value, and when the finger touches the touch insulating layer, a coupling capacitance is generated between the finger and the conducting layer; the first fingerprint sensing module and the second fingerprint sensing module generate the first sensing signal and the second sensing signal matched with the coupling capacitance value based on the applied voltage respectively.
10. A signal processing circuit according to claim 1 or 3, wherein a fixed voltage is applied to the first input terminal and the second input terminal to adjust the circuit operating point of the differential amplifier when the fingerprint sensor is set to a reset mode.
11. The signal processing circuit of claim 8, wherein the first control module comprises:
one end of the feedback capacitor is respectively connected with the first input end and the second input end, and the other end of the feedback capacitor is respectively connected with the output end;
the two first reset switches are respectively connected to two ends of the feedback capacitor;
one end of the second reset switch is connected with each other, and the other end of the second reset switch is connected with the first input end and the second input end respectively;
one end of the second reset switch is respectively connected with the first fingerprint sensing module and the second fingerprint sensing module, and the other end of the second reset switch is respectively grounded;
the first reset switch, the second reset switch and the third reset switch are consistent in connection or disconnection.
12. The signal processing circuit of claim 8, wherein the second control module comprises:
And one end of the sampling switch is respectively connected with the first fingerprint sensing module and the second fingerprint sensing module, and the other end of the sampling switch is respectively connected with the first output end and the second input end.
13. The signal processing circuit of claim 1, wherein the signal processing circuit comprises a logic circuit,
the first input circuit comprises a first adder, wherein the first adder is electrically connected with the first fingerprint sensing module and a fingerprint sensing module adjacent to the first fingerprint sensing module respectively and is used for carrying out summation calculation on the first sensing signal and the sensing signal generated by the fingerprint sensing module adjacent to the first fingerprint sensing module to generate a first summation sensing signal;
correspondingly, the second input circuit comprises a second adder, wherein the second adder is electrically connected with the second fingerprint sensing module and the fingerprint sensing module adjacent to the second fingerprint sensing module respectively and is used for carrying out summation calculation on the second sensing signal and the sensing signal generated by the fingerprint sensing module adjacent to the second fingerprint sensing module to generate a second summation sensing signal;
accordingly, the first signal processing unit and the second signal processing unit are coupled to perform differential amplification processing on the first summed sensing signal and the second summed sensing signal.
14. A fingerprint sensor, characterized in that it comprises the signal processing circuit of any of claims 1-12, wherein the number of fingerprint sensing modules matches the number of signal processing units.
15. The fingerprint sensor of claim 14, wherein the fingerprint sensor includes a predetermined number of tail current sources, output loads, the predetermined number being less than the number of signal processing units.
16. An electronic device comprising a fingerprint sensor, wherein the fingerprint sensor comprises the signal processing circuit of any one of claims 1-13.
17. The electronic device of claim 16, wherein the electronic device has a fast charge function.
18. The electronic device of claim 16 or 17, wherein the electronic device comprises any one of: mobile smartphones, notebook computers, desktop computers, tablet electronic devices, personal Digital Assistants (PDAs), smart wearable devices.
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| CN108596060B (en) * | 2018-04-12 | 2021-10-15 | 上海思立微电子科技有限公司 | Fingerprint image processing method, fingerprint identification device and electronic equipment |
| CN110869939A (en) * | 2018-06-25 | 2020-03-06 | 华为技术有限公司 | Fingerprint acquisition method and electronic equipment |
| CN109376715B (en) * | 2018-12-13 | 2020-11-20 | 厦门天马微电子有限公司 | Array substrate and display panel |
| CN110147718A (en) * | 2019-04-08 | 2019-08-20 | 杭州士兰微电子股份有限公司 | Sensor module and its pixel circuit and signal processing method |
| US11055508B2 (en) | 2019-08-29 | 2021-07-06 | Himax Technologies Limited | Display panel applicable to reducing noise coupling and enhancing sensing signal in optical fingerprint sensor thereof with aid of switch arrangement, and associated electronic device |
| TW202201210A (en) * | 2020-06-26 | 2022-01-01 | 瑞典商指紋卡公司 | Optical fingerprint sensing system with common mode compensation |
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