Biometric identification device comprising an array of ultrasonic transducers and current reading circuits

Abstract

Biometric identification device comprising an array of ultrasonic transducers and current reading circuits. This description relates to a biometric identification device (100) comprising at least: - an array of ultrasonic transducers (104), each ultrasonic transducer comprising first and second electrodes (110, 112), the first electrodes (110) of the ultrasonic transducers in the same row of the array being electrically coupled to each other, and / or the second electrodes (112) of the ultrasonic transducers in the same column of the array being electrically coupled to each other; - current reading circuits intended to be delivered to the first and / or second electrodes, each reading circuit comprising at least one transimpedance amplifier. Figure for the abbreviation: Fig. 5

Description

Title of the invention: Biometric identification device comprising an array of ultrasonic transducers and current reading circuits Technical field

[0001] The present description relates to the field of biometric identification devices based on the capture and measurement of biometric information by ultrasonic transduction. Prior art

[0002] A biometric identification device makes it possible to verify or determine the identity of a user of the device based on a measurement of one or more of its biometric characteristics such as a fingerprint, the shape of the face, the pattern of the iris, the pattern of the retina, etc. The different techniques for carrying out measurements of one or other of these biometric characteristics each have advantages and disadvantages according to different criteria, including in particular: more or less significant error rate, ease or not of theft of the template with which the measurements are compared, possibility of detecting or not an imitation, proof or not of life, ease and comfort of use, size of the sensor required, energy consumption required, etc.

[0003] In the case of a biometric identification device provided with an array of ultrasonic transducers, the electrodes of the transducers are arranged in rows and columns common to the transducers, and are electrically coupled to analog front-end circuits, or AFEs. Each of the AFEs can form a circuit for reading the signals delivered on the electrodes of the transducers and can also implement different functions from the signals delivered on the electrodes of the transducers: amplification, filtering, analog-digital conversion, etc.

[0004] Given the row and column arrangement of the electrodes of the ultrasonic transducers, they form significant electrical capacitances electrically coupled at the input of the AFEs. These electrical capacitances absorb a large part of the currents delivered by the ultrasonic transducers. The sensitivity of the biometric identification device is therefore highly dependent on these capacitances, as well as on the frequency of the ultrasonic signals used. Summary of the invention

[0005] There is a need to propose a biometric identification device which does not have at least some of the drawbacks of existing solutions.

[0006] An embodiment overcomes all or part of the drawbacks of known solutions. and offers a biometric identification device comprising at least:

[0007] - an array of ultrasonic transducers, each of the ultrasonic transducers comprising first and second electrodes, the first electrodes of the ultrasonic transducers of the same row of the matrix being electrically coupled to each other, and / or the second electrodes of the ultrasonic transducers of the same column of the matrix being electrically coupled to each other;

[0008] - current reading circuits intended to be delivered to the first and / or second electrodes, each reading circuit comprising at least one transimpedance amplifier.

[0009] According to a particular embodiment, in each reading circuit, at least one output and at least one input of the transimpedance amplifier are electrically coupled to each other by a feedback resistor or by an electrical feedback capacitor.

[0010] According to a particular embodiment, in each reading circuit, the transimpedance amplifier is a low noise amplifier.

[0011] According to a particular embodiment, in each reading circuit, an output of the transimpedance amplifier is electrically coupled to an input of at least one second amplifier.

[0012] According to a particular embodiment, the current reading circuits intended to be delivered to the first electrodes are part of at least one first analog front-end circuit electrically coupled to at least one part of the first electrodes, and / or the current reading circuits intended to be delivered to the second electrodes are part of at least one second analog front-end circuit electrically coupled to at least one part of the second electrodes.

[0013] According to a particular embodiment, the device is such that:

[0014] - the first electrodes of ultrasonic transducers of the same line of the matrix are electrically coupled to the first analog front-end circuit or to one of the first analog front-end circuits, and / or

[0015] the second ultrasonic transducer electrodes of the same column of the matrix are electrically coupled to the second analog front-end circuit or to one of the second analog front-end circuits.

[0016] According to a particular embodiment, the device is such that:

[0017] - the first analog front-end circuit or at least one of the first front-end circuits analog comprises a first multiplexer whose inputs are electrically coupled to first electrodes of ultrasonic transducers belonging to different rows of the matrix, and / or

[0018] - the second analog front-end circuit or at least one of the second circuits analog front-ends have a second multiplexer whose inputs are electrically coupled to second electrodes of ultrasonic transducers belonging to different columns of the matrix.

[0019] According to a particular embodiment, the ultrasonic transducers are of the PMUT or CMUT type. Brief description of the drawings

[0020] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0021] - [Fig.l] and [Fig.2] schematically represent an identification device biometric according to a particular embodiment;

[0022] - [Fig.3] schematically represents an example of a matrix of transducers with ultrasound of a biometric identification device according to a particular embodiment;

[0023] - [Fig.4] schematically represents an example of the embodiment of a part of a biometric identification device according to a particular embodiment;

[0024] - [Fig.5] represents an example of embodiment of a reading circuit of a device biometric identification according to a particular embodiment. Description of the embodiments

[0025] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0026] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, various elements (ultrasonic transducer array, control circuit, data processing circuit, analog front-end circuits, reading circuits, etc.) and various steps implemented (image acquisition, processing of acquired images, details of calculations performed, etc.) are not detailed. Those skilled in the art will be able to implement these elements in detail from the functional description given here.

[0027] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0028] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures in a normal position of use.

[0029] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0030] Throughout the description, the terms "row" and "column" are used considering an arbitrary orientation given to the described biometric identification device, these terms being able to be interchanged depending on the orientation of the device.

[0031] A biometric identification device 100 according to a particular embodiment is described below in connection with FIGS. 1 to 5.

[0032] The device 100 is configured to implement biometric identification by performing measurements of biometric characteristics of a part of the body of the user of the device 100. In the described exemplary embodiment, this part of the user's body corresponds to one or more fingers of the user. Alternatively, other parts of the user's body may be used to perform the biometric identification by the device 100. Furthermore, in the described exemplary embodiment, the part of the user's body used to perform the biometric identification corresponds to a single finger of the user.

[0033] The device 100 comprises a capture surface 102 on which the finger of the user of the device 100 is intended to be placed during biometric identification.

[0034] The device 100 further comprises a matrix of ultrasonic transducers 104 configured to carry out, through the capture surface 102, an emission and a reception of ultrasonic signals during the measurements used to carry out an acquisition of image(s) from which a biometric identification of the user of the device 100 is possible. The number of ultrasonic transducers of the matrix 104 may depend on the dimensions of the capture surface 102, the dimensions of each ultrasonic transducer, the resolution of the measurements intended to be carried out by the device 100, etc. The matrix 104 may for example comprise transducers of the CMUT type (“Capacitive Micromachined Ultrasonic Transducer” in English, or capacitive micromachined ultrasonic transducer) or of the PMUT type (“Piezoelectric Micromachined Ultrasonic Transducer” in English, or piezoelectric micromachined ultrasonic transducer) or of another type.

[0035] According to an exemplary embodiment, the device 100 further comprises at least one control circuit 106 and at least one data processing circuit 108. In the schematic example shown in [Fig. 2], the control circuit 106 can be electrically coupled to the matrix of ultrasonic transducers 104 and thus be able to transmit to this matrix 104 signals controlling the emission of ultrasound for the measurements to be carried out, and also be able to receive electrical measurement signals transmitted by the matrix of ultrasonic transducers 104 following the reception of echoes of the emitted ultrasounds. The control circuit 106 can also be electrically coupled to the data processing circuit 108 in order to transmit to the data processing circuit 108 the measurement results obtained from the matrix of ultrasonic transducers 104.

[0036] In the described embodiment, the data processing circuit 108 may be configured to analyze and process the electrical response signals received by the control circuit 106 and sent by the ultrasonic transducer array 104. The processing circuit 108 may comprise, for example, at least one microprocessor coupled to at least one memory for processing the received data.

[0037] In the exemplary embodiment described, the device 100 can be configured to perform an acquisition of at least one surface image of the user's finger placed on the capture surface 102 and in contact therewith, that is to say an acquisition of at least one image of a fingerprint of the finger, formed of ridges and valleys present on the surface of the skin of the finger placed on the capture surface 102. In the device 100, the acquisition of a surface image of the user's finger placed on the capture surface 102 and in contact therewith is possible because the ultrasound emitted by the matrix 104 is reflected more strongly against the air present in the valleys of the finger than against the ridges.The difference between the signals received by the transducers of the matrix 104 which are reflected on the valleys and those which are reflected on the ridges can be used to reconstruct the image of the fingerprint of the user's finger present on the capture surface 102.

[0038] The device 100 may also be configured to carry out other types of acquisition, for example an acquisition of volume images of the finger placed on the capture surface 102 of the device 100 and in contact with it, and from which it is possible to determine, by processing these volume images, an overall volume image of the microvasculature of this finger, that is to say an image capture of the micro-blood vessels present under the skin of the finger of the user of the device 100.

[0039] An exemplary embodiment of the ultrasonic transducer array 104 is shown schematically in [Fig. 3]. In this example, each of the transducers of the array 104 comprises a first electrode 110 and a second electrode 112. In addition, in this example, the first electrodes 110 of the transducers arranged on the same row of the array 104 are electrically coupled to each other. Furthermore, in the example of [Fig. 3], the first electrodes 110 of the transducers arranged on the same line of the matrix 104 are formed by the same portion of electrically conductive material extending in a direction parallel to the X axis visible in [Fig.3]. Alternatively, it is possible for the first electrodes 110 to be arranged in a configuration different from that shown in [Fig.3].

[0040] In the example described, the second electrodes 112 of the transducers arranged on the same column of the matrix 104 are electrically coupled to each other. Furthermore, in the example of [Fig. 3], the second electrodes 112 of the transducers arranged on the same column of the matrix 104 are formed by the same portion of electrically conductive material extending in a direction parallel to the Y axis visible in [Fig. 3]. Alternatively, it is possible for the second electrodes 112 to be arranged in a configuration different from that shown in [Fig. 3].

[0041] In the example described, the matrix 104 is such that the first electrodes 110 are arranged between the second electrodes 112 and the capture surface 102. In other words, the first electrodes 110 of the ultrasonic transducers of the matrix 104 are arranged on the side of the capture surface 102 of the device 100.

[0042] In the example of [Fig. 3], each ultrasonic transducer of the matrix 104 also comprises a transduction element 114 arranged between the first and second electrodes 110, 112 of the transducer. The material(s) of this transduction element depend on the technology used to produce the matrix 104, this transduction element 114 corresponding for example to a portion of piezoelectric material in the case of PMUT type transducers.

[0043] The device 100 further comprises one or more first analog front-end circuits 116, or first AFEs, electrically coupled to the first electrodes 110, and one or more second analog front-end circuits 118, or second AFEs, electrically coupled to the second electrodes 112. Each of the AFEs 116, 118 can implement different functions from the signals delivered on the electrodes 110, 112 of the transducers: amplification, filtering, analog-digital conversion, etc. The AFEs 116, 118 may also serve to bias the transducers of the array 104 by applying suitable electrical potentials to the electrodes 110, 112 of the transducers of the array 104. In [Fig.4], two first AFEs 116 and a second AFE 118 electrically coupled to the electrodes 110, 112 of the array 104 are shown.

[0044] The first and second AFE(s) 116, 118 comprise current reading circuits intended to be delivered to the first and second electrodes 110, 112, each of these reading circuits comprising at least one transimpedance amplifier. Each transimpedance amplifier, corresponding for example to a low noise amplifier, or LNA (Low Noise Amplifier) ​​is configured to convert an output current of the ultrasonic transducers, for example obtained on at least one electrode of the transducers electrically coupled to the AFE to which the amplifier belongs, into an output voltage. In the example of [Fig.4], the output voltages delivered by the AFEs 116, 118 are called Voutu VOut2 and VOut3-

[0045] In the example described, the first electrodes 110 of the transducers arranged on the same row of the matrix 104 are electrically coupled to the first AFE 116 (when the device 100 comprises a single first AFE 116) or to one of the first AFEs 116 of the device 100. In addition, in this example, the second electrodes 112 of the transducers arranged on the same column of the matrix 104 are electrically coupled to the second AFE 118 (when the device 100 comprises a single second AFE 118) or to one of the second AFEs 118 of the device 100.

[0046] In a particular configuration, it is possible for first electrodes 110 of transducers arranged on different lines of the matrix 104 to be electrically coupled to the same first AFE 116. In this case, this first AFE 116, or each of these first AFE 116, may comprise a first multiplexer (not visible in FIGS. 1 to 5) whose inputs are electrically coupled to these first electrodes 110. When the device 100 comprises a single first AFE 116, this single first AFE 116 may comprise a first multiplexer whose inputs are electrically coupled to the first electrodes 110 of all the transducers of the matrix 104.

[0047] Similarly, it is possible for second electrodes 112 of transducers arranged on different columns of the matrix 104 to be electrically coupled to the same second AFE 118. In this case, this second AFE 118, or each of these second AFE 118, may comprise a second multiplexer (not visible in FIGS. 1 to 5) whose inputs are electrically coupled to these second electrodes 112. When the device 100 comprises a single second AFE 118, this single second AFE 118 may comprise a second multiplexer whose inputs are electrically coupled to the second electrodes 112 of all the transducers of the matrix 104.

[0048] When one or more of the AFEs 116, 118 comprises a multiplexer whose inputs are electrically coupled to the electrodes 110 of different rows or to the electrodes 112 of different columns, the reading circuit(s) of this or these AFEs can be configured to sequentially read the currents delivered on the electrodes of the different rows or columns electrically coupled to the inputs of this multiplexer.

[0049] [Fig. 5] schematically represents an example of a transimpedance amplifier 120 of a current reading circuit intended to be delivered to first or second electrodes 110, 112 of at least one same row or column of ultrasonic transducers of the device 100. This amplifier 120 makes for example part of one of the AFE 116, 118 visible in [Fig.4].

[0050] In [Fig. 5], the row(s) of first electrodes, or the column(s) of second electrodes, electrically coupled to the input of the amplifier 120 are modeled according to an equivalent electrical diagram comprising a self-inductor 122, a first capacitor 124 and a resistor 126, these three components being electrically coupled together in series. This electrical diagram also includes a second electrical capacitor 128 electrically coupled in parallel with the three components 122, 124, 126. The value of this second electrical capacitor is for example of the order of 150 pF. A current source 130 is electrically coupled in parallel with the first capacitor 124 and symbolically represents the measurement current Is delivered to the electrodes modeled by this equivalent electrical diagram and intended to be read by the amplifier 120.

[0051] In [Fig. 5], the electrodes modeled by the components 122 to 128 are also electrically coupled to a first electrode of a third electrical capacitance 134, the second electrode of which is electrically coupled to the reference electrical potential of the device 100. The value of the third electrical capacitance 134 is for example equal to approximately 50 pF. A first input of the amplifier 120 is electrically coupled to the components 122 to 128 and to the first electrode of the third electrical capacitance 134 through a fourth electrical capacitance 136. A second input of the amplifier 120 is electrically coupled to the reference electrical potential of the device 100 through a fifth electrical capacitance 138. The electrical capacitances 134, 136 and 138 model the electrical connection between the amplifier 120 and the electrodes of the transducers of the matrix 104 to which the amplifier is connected.

[0052] In the example of [Fig.5], the output of the amplifier 120 is looped back to the input of the amplifier 120 by a feedback resistor 140 whose value is for example of the order of 1 kOhm. Alternatively, the resistor 140 can be replaced by an electrical feedback capacitor.

[0053] Because the reading of the signals delivered by the transducer matrix 104 corresponds to a current reading, the detection sensitivity is weakly dependent on the line capacitance Ciine formed at the input of the amplifier 120. The value of the line capacitance Ciine is for example of the order of 200 pF. Furthermore, in the configuration described above, the voltage V obtained at the output of the amplifier 120 is such that V = R*IS, with R corresponding to the value of the feedback resistor 140.

[0054] The use of transimpedance amplifiers for reading the signals delivered by the transducers of the matrix 104 makes it possible to present a low input impedance with respect to the matrix 104, for example of the order of ten Ohms. Thus, thanks to this type of amplifiers in the circuits for reading the signals delivered by the matrix 104, the entire current Is is sent to the input of the amplifier 120. In addition, with such an amplifier used to read the output signals of the transducers of the matrix 104, the signal-to-noise ratio obtained can be assimilated to the value of the ratio l / (Ciine*2*pi*fO), with fO corresponding to the frequency of the signals delivered by the transducers of the matrix 104.

[0055] In a particular configuration, it is possible for the output of the amplifier 120 to be coupled to the input of at least one other amplifier, for example a programmable gain amplifier, which makes it possible to increase the amplification gain obtained when that of the amplifier 120 alone is not sufficient. For example, when the required gain-bandwidth product is between 1 and 2 GHz, the use of one or more additional amplifiers coupled to the output of the amplifier 120 makes it possible to reduce the constraint concerning the required amplification gain.

[0056] The device 100 is configured to implement a biometric identification of the user of the device 100. This biometric identification can be carried out by implementing the steps described in a non-detailed manner below.

[0057] First of all, the device 100 carries out an acquisition of at least one surface image of the finger 101 present on the capture surface 102, this acquisition comprising for example the emission of a series of ultrasonic signals in the form of pulses by the matrix 104, then the reception of the echoes by the matrix 104 and the processing of the responses obtained to obtain the surface image of the finger 101, that is to say the image of the fingerprint of the finger 101. The acquisition of the surface image of the finger 101 may also include the implementation of other steps not detailed here: filtering of the response signal obtained, envelope detection, logarithmic compression, etc. The data relating to the acquired image are for example stored in a memory of the device 100 or in an external memory of the device 100 for example connected to the device 100 by a communication link.

[0058] From the previously acquired surface image, the data processing circuit 108 can determine or extract minutiae from the fingerprint 101 obtained on this image. This determination of minutiae can be carried out by one or more image processing algorithms not described in detail here and known to those skilled in the art. Each of the minutiae extracted from the surface image can be characterized (type of minutiae, position in the plane of the surface image, orientation of the minutiae, orientation relative to the other minutiae, etc.).

[0059] The characteristics of the minutiae can then be compared with expected characteristics of minutiae, for example previously determined during a preliminary step of user enrollment, to confirm or not the identity of the user. This comparison may include a score calculation whose value depends on the correlations between, on the one hand, the characteristics of the previously determined minutiae and, on the other hand, the expected characteristics of minutiae to confirm or not the identity of the user. The score obtained can then be compared with a threshold value in order to evaluate the correspondence between the biometric measurement carried out and the expected biometric data, and thus confirm or not the identity of the user.

[0060] These steps related to biometric identification are known to those skilled in the art and are not described in detail in the present description.

[0061] The device 100 can be configured to implement other functions, such as for example a capture of volume images to determine a microvasculature of the finger 101 and implement a detection of the living (via a detection of blood circulation in the microvasculature of the finger 101) and / or a complementary biometric identification from the characteristics of the determined microvasculature.

[0062] Various configurations of the device 100 have been described. Those skilled in the art will understand that certain features of these various configurations could be combined, and other variations will occur to those skilled in the art.

[0063] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. Biometric identification device (100) comprising at least: - a matrix of ultrasonic transducers (104), each of the ultrasonic transducers comprising first and second electrodes (110, 112), the first electrodes (110) of the ultrasonic transducers of the same row of the matrix (104) being electrically coupled to each other, and / or the second electrodes (112) of the ultrasonic transducers of the same column of the matrix (104) being electrically coupled to each other; - current reading circuits intended to be delivered to the first and / or second electrodes (110, 112), each reading circuit comprising at least one transimpedance amplifier (120).

2. The biometric identification device (100) of claim 1, wherein in each reading circuit at least one output and at least one input of the transimpedance amplifier (120) are electrically coupled to each other by a feedback resistor (140) or by a feedback electrical capacitance.

3. A biometric identification device (100) according to one of the preceding claims, wherein, in each reading circuit, the transimpedance amplifier (120) is a low noise amplifier.

4. A biometric identification device (100) according to one of the preceding claims, wherein, in each reading circuit, an output of the transimpedance amplifier (120) is electrically coupled to an input of at least one second amplifier.

5. Biometric identification device (100) according to one of the preceding claims, wherein the current reading circuits intended to be delivered on the first electrodes (110) are part of at least one first analog front-end circuit (116) electrically coupled to at least a portion of the first electrodes (110), and / or wherein the current reading circuits intended to be delivered on the second electrodes (112) are part of at least one second analog front-end circuit (118) electrically coupled to at least a portion of the second electrodes (112).

6. Biometric identification device (100) according to claim 5, wherein: - the first electrodes (110) of ultrasonic transducers of the same row of the matrix (104) are electrically coupled electrically to the first analog front-end circuit (116) or to one of the first analog front-end circuits (116), and / or - the second electrodes (112) of ultrasonic transducers of the same column of the matrix (104) are electrically coupled to the second analog front-end circuit (118) or to one of the second analog front-end circuits (118).

7. Biometric identification device (100) according to claim 6, wherein: - the first analog front-end circuit (116) or at least one of the first analog front-end circuits (116) comprises a first multiplexer whose inputs are electrically coupled to first electrodes (110) of ultrasonic transducers belonging to different rows of the matrix (104), and / or - the second analog front-end circuit (118) or at least one of the second analog front-end circuits (118) comprises a second multiplexer whose inputs are electrically coupled to second electrodes (112) of ultrasonic transducers belonging to different columns of the matrix (104).

8. Biometric identification device (100) according to one of the preceding claims, wherein the ultrasonic transducers are of the PMUT or CMUT type.

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