Sensor device

Abstract

This invention proposes a sensing device. The sensing device includes a biometric sensor comprising a substrate and a plurality of sensing electrodes located above the substrate. The sensing device also includes an amplifier electrically coupled to the biometric sensor and configured to provide an output signal based on a touch event received by the biometric sensor. The sensing device further includes interface circuitry located between the amplifier and the plurality of sensing electrodes.

Description

Technical Field

[0001] This disclosure relates generally to an in-glass biometric sensor, and more particularly, to a sensing device for an in-glass fingerprint sensor. Background Technology

[0002] Today, the convenience of mobile devices such as IC cards, smartphones, and laptops has brought us a better life, but it has also brought privacy threats. The more prevalent these mobile devices become, the more important personal security becomes. Therefore, the need for user authentication is becoming increasingly important. Some biometric features, such as fingerprints, palm prints, finger veins, iris scans, and voiceprints, are already widely used in user authentication. Due to their low cost, ease of integration, and high reliability, fingerprint sensors have seen widespread development. Summary of the Invention

[0003] The purpose of this invention is to provide a sensor device to solve at least one of the above-mentioned problems.

[0004] According to an embodiment of the present invention, an apparatus is provided. The sensing apparatus includes a biometric sensor comprising a substrate and a plurality of sensing electrodes located above the substrate. The sensing apparatus further includes an amplifier electrically coupled to the biometric sensor and configured to provide an output signal based on a touch event received by the biometric sensor. The sensing apparatus further includes an interface circuit located between the amplifier and the plurality of sensing electrodes.

[0005] In some embodiments, the biometric sensor is a touch biometric sensor.

[0006] In some embodiments, the biometric sensor includes a substrate made of glass, quartz, or silicon oxide.

[0007] In some embodiments, the sensor device further includes a display located below the biometric sensor, wherein the substrate is transparent to the light emitted by the display.

[0008] In some embodiments, the interface circuit includes a resistor.

[0009] In some embodiments, the amplifier includes a non-inverting terminal and an inverting terminal, wherein the resistor is connected in series to the inverting terminal.

[0010] In some embodiments, the amplifier includes a first stage coupled to a second stage via a coupling capacitor, the second stage defining a transconductance, wherein the resistor has a resistance greater than approximately 10 times the reciprocal of the transconductance.

[0011] In some embodiments, the interface circuit includes a current source connected between the biometric sensor and ground; an amplifying capacitor coupled between the current source and the amplifier; and a first switch coupled between the current source and the amplifying capacitor.

[0012] In some embodiments, the sensing device further includes a voltage buffer between at least one of the plurality of sensing electrodes and the current source.

[0013] In some embodiments, the first switch of the interface circuit is closed during a first sampling phase of a sensing step.

[0014] In some embodiments, the interface circuit further includes a second switch, wherein the second switch includes a first terminal connected to a node between the first switch and the amplifying capacitor.

[0015] In some embodiments, during a second sampling phase of the sensing step, the first switch is turned on while the second switch is closed.

[0016] In some embodiments, the sensor device further includes: a sensing control block configured to generate an initial sensing signal; and a signal transmission element electrically coupled to the sensing control block and configured to transmit a transmission sensing signal to a user based on the initial sensing signal according to the touch event.

[0017] In some embodiments, the signal transmission element includes an outer frame located above the biometric sensor and configured to contact the user during the touch event.

[0018] In some embodiments, the initial sensing signal has a plurality of sensing cycles, wherein each sensing cycle includes a first sampling cycle that alternates with a second sampling cycle, and wherein the initial sensing signal has a waveform that includes a rising edge and a falling edge corresponding to the start times of the first sampling cycle and the second sampling cycle, respectively.

[0019] In some embodiments, the sensing control block is configured to continuously generate a first sensing signal and a second sensing signal for the same part of the user during the first sampling period and the second sampling period, respectively.

[0020] In some embodiments, the sensor device further includes a processor configured to generate a processing signal by subtracting the second sensing signal from the first sensing signal.

[0021] In some embodiments, the sensor device further includes an analog-to-digital converter configured to convert the output signal into a digital signal.

[0022] The features and technical advantages of several embodiments have been broadly outlined above to provide a better understanding of the following detailed description of this disclosure. Additional features and advantages of this disclosure will be described below. It will be understood by those skilled in the art that the concepts and specific embodiments disclosed herein can be readily used as a basis for modifying or designing other structures and procedures to implement the same purposes as the embodiments introduced herein, without departing from the spirit and scope of this disclosure. Attached Figure Description

[0023] Details of one or more embodiments of this disclosure are set forth in the accompanying drawings and the following description. Other features and advantages of this disclosure will be apparent from the description, drawings, and claims. In the various views and illustrated embodiments, the same reference numerals are used to denote the same elements. Reference will now be made in detail to the exemplary embodiments shown in the accompanying drawings.

[0024] Figure 1 This is a cross-sectional view of a biometric sensor device according to some embodiments of the present disclosure.

[0025] Figure 2A and Figure 2B Various embodiments according to this disclosure Figure 1 A top view of the protective layer of the biometric sensor device shown.

[0026] Figure 3 This is a schematic block diagram of a sensing circuit according to various embodiments of the present disclosure.

[0027] Figure 4A This is a schematic block diagram of a sensing circuit according to various embodiments of the present disclosure.

[0028] Figure 4B This is a schematic block diagram of an amplifier according to various embodiments of the present disclosure.

[0029] Figure 5A and Figure 5B These are circuit diagrams of sensing circuits and amplifiers for sensing circuits according to various embodiments of the present disclosure.

[0030] Figure 5C and Figure 5D These are circuit diagrams of sensing circuits and amplifiers for sensing circuits according to various embodiments of the present disclosure.

[0031] Figure 6A This is a schematic block diagram of a sensing circuit according to various embodiments of the present disclosure.

[0032] Figure 6B This is a voltage waveform diagram of the interface circuit according to various embodiments of the present disclosure.

[0033] Figure 6CThis is a schematic block diagram of a sensing circuit according to various embodiments of the present disclosure.

[0034] Figure 6D This is a voltage waveform diagram of the interface circuit according to various embodiments of the present disclosure.

[0035] Figure 7 This is a schematic diagram of a signal model of a sensing circuit according to various embodiments of the present disclosure.

[0036] The attached figures are labeled as follows:

[0037] 100: Biometric sensor device

[0038] 101: Fingers

[0039] 110: First circuit board

[0040] 112: Biometric Sensor

[0041] 112A: First side

[0042] 112B: Second side

[0043] 113: Sensing Electrode

[0044] 114: Protective layer

[0045] 114C: Conductive layer

[0046] 114D: Insulation layer

[0047] 114E: Conductive layer

[0048] 116: Cover plate

[0049] 117: Conductive layer

[0050] 118: Molding materials

[0051] 120: Second circuit board

[0052] 122: Monitor

[0053] 124: Adhesive layer

[0054] 126: Electronic devices

[0055] 128: Bus

[0056] 130: Third circuit board

[0057] 132: Electronic devices

[0058] 134: Connector

[0059] 135: Bus

[0060] 136: Connection Port

[0061] 138: Electronic devices

[0062] 140: Conductive column

[0063] 142: Connector

[0064] 150: Outer frame

[0065] 300: Biometric sensor device

[0066] 302: Clock Pulse Generator

[0067] 304: Sensing Circuit

[0068] 305: Sensing Control Module

[0069] 306: Signal buffer block

[0070] 307: Receiver Control Module

[0071] 308: Signal transmission element

[0072] 312: Interface Circuit

[0073] 314: Amplifier Circuit

[0074] 316: Analog-to-digital converter

[0075] 322: Amplifier

[0076] 324: Switch

[0077] 400: Biometric sensor device

[0078] 412: Interface Circuit

[0079] 600: Sensing Circuit

[0080] 601: Sensing Circuit

[0081] 602: Voltage Buffer

[0082] 604: Current Source

[0083] 606: Switch

[0084] 612: Interface Circuit

[0085] 616: Switch

[0086] 622: Interface Circuit

[0087] 700: Sensing Circuit

[0088] C1: Capacitor

[0089] Ca: Amplifying capacitor

[0090] Cc: Coupling capacitor

[0091] Cfinger: Finger capacitor

[0092] Cf: Feedback capacitor

[0093] CL: Load capacitor

[0094] CM: Current Mirror

[0095] Cp: ​​Parasitic capacitor

[0096] Cs: Substrate capacitor

[0097] D1 off First signal offset

[0098] D2 off Second signal offset

[0099] Ix: Current load

[0100] Iy: Current load

[0101] I1: Current source

[0102] I2: Current source

[0103] M1: Transistor

[0104] M2: Transistor

[0105] M3: Transistor

[0106] M4: Transistor

[0107] M5: Transistor

[0108] M SF :transistor

[0109] N1: Output node

[0110] N2: Output node

[0111] Ri: Resistor

[0112] R1: Resistor

[0113] R2: Resistor

[0114] S1: Level 1

[0115] S2: Level Two

[0116] Sa: Output signal

[0117] Sb: Buffer sensing signal

[0118] Sc: Control signal

[0119] Sck: Clock pulse signal

[0120] Sd: Digital sensing signal

[0121] Sf: Buffered received sensing signal

[0122] Sh: Control signal

[0123] Si: Initial sensing signal

[0124] Sj: Initial sensing signal

[0125] Sp: Signal processing

[0126] Sr: Sensing signal

[0127] St: Transmitting sensing signals

[0128] Tm: Sensing period

[0129] Tn: Sensing period

[0130] Td1: Time Delay

[0131] Td2: Time Delay

[0132] Td3: Time Delay

[0133] Td4: Time Delay

[0134] Td5: Time Delay

[0135] Td6: Time Delay

[0136] Tr: Reset cycle

[0137] Ts: Sampling period

[0138] Tr1: Reset cycle

[0139] Tr2: Reset cycle

[0140] Ts1: First sampling period

[0141] Ts2: Second sampling period

[0142] V CM :Voltage

[0143] Vi+: Differential input terminal

[0144] Vi-: Differential input terminal

[0145] Vin: Voltage

[0146] +Vin: Positive polarity

[0147] -Vin: Negative polarity

[0148] Vout(N2): Output voltage

[0149] Vo1(N1): Output terminal

[0150] V CM,H :Voltage

[0151] V CM,L :Voltage

[0152] V SF,H :Voltage

[0153] V SF,L :Voltage

[0154] V SIG,H :Voltage

[0155] V SIG,L :Voltage

[0156] V Sa,H :Voltage

[0157] V Sa,M :Voltage

[0158] V Sa,L :Voltage

[0159] Vt: Amplified input voltage

[0160] Vx: Supply voltage

[0161] Vy: Supply voltage

[0162] Vz: Supply voltage

[0163] ΔV o Voltage difference Detailed Implementation

[0164] To facilitate understanding of this disclosure, detailed steps and structures are provided in the following description. It is apparent that implementation of this disclosure does not limit the specific details known to those skilled in the art. Furthermore, known structures and steps will not be repeated to avoid unnecessarily limiting this disclosure. Preferred embodiments of this disclosure will now be described in detail. However, in addition to the detailed description, this disclosure can be extensively implemented in other embodiments. The scope of this disclosure is not limited to the detailed description but is defined by the claims.

[0165] In addition, it should be understood that when a component is referred to as “connected” or “coupled” or “coupled to” another component, it can be directly connected to or coupled to the other component, or there can be an intermediate component.

[0166] While the numerical ranges and parameters described in this disclosure are approximate, the values ​​presented in specific examples are reported as precisely as possible. However, any numerical value inherently contains some error, which is necessarily caused by deviations common in individual test measurements. Furthermore, as used herein, the terms “about,” “substantial,” and “substantively” generally mean within 10%, 5%, 1%, or 0.5% of a given value or range. Alternatively, the terms “about,” “substantively,” and “substantively” mean within the acceptable standard error of the average value as considered by one of ordinary skill in the art. Except in operational / working examples, or unless expressly stated otherwise, all numerical ranges, quantities, values, and percentages disclosed herein, such as material quantity, duration, temperature, operating conditions, quantity ratios, etc., should be understood to be modified by the terms “about,” “substantively,” and “substantively” in all instances. Therefore, unless instructed to the contrary, the numerical parameters set forth in this disclosure and the appended claims may be approximate values ​​that vary as needed. Numerical parameters should be interpreted at least according to the number of significant figures in the report and by applying general rounding techniques. Ranges herein may be expressed as from one endpoint to another or between two endpoints. Unless otherwise stated, all ranges disclosed herein include the endpoints.

[0167] Figure 1 This is a cross-sectional view of a biometric sensor device 100 according to some embodiments of the present disclosure. In some embodiments, the biometric sensor device 100 is configured to sense biometric data and authenticate a user through the biometric data. The biometric sensor device 100 may be adapted to operate with electronic devices (not shown herein) (e.g., smartphones, personal computers, and personal digital assistants). Alternatively, the biometric sensor device 100 may be adapted to operate with personal items protected by physical keys or passwords (e.g., door locks, combination locks, ID cards, safes, etc.), so that the biometric sensor device 100 can be used to protect a user's personal information in place of keys or passwords. In this embodiment, the biometric sensor device 100 includes a fingerprint or palm print sensor, and the biometric feature is the user's fingerprint and / or palm print pattern.

[0168] The biometric sensor device 100 can be configured as a touch sensor device, wherein a stimulus source, such as a fingerprint, can be received by a sensing element during a touch event of the biometric sensor device 100. In some embodiments, the biometric sensor device 100 is adapted to operate in a non-touch sensing mode, wherein a sensing signal is transmitted to the user's finger or palm 101 and reflected back to the biometric sensor device 100. The reflected sensing signal may contain information about the user's fingerprint or palm print pattern, and can therefore be processed to verify the user's identity.

[0169] Reference Figure 1The biometric sensor device 100 includes a first circuit board 110, a second circuit board 120, a third circuit board 130, conductive pillars 140, and an outer frame 150. The biometric sensor device 100 also includes a biometric sensor 112, a protective layer 114, a cover plate 116, a display 122, and an adhesive layer 124.

[0170] In this embodiment, the display 122 is a self-emissive display. The display 122 is located above and electrically connected to the second circuit board 120. The display 122 may be formed of an organic light-emitting diode (OLED) panel or other suitable self-emissive display. As an example of an OLED display panel, the display 122 may include (but is not limited to) a substrate, an anode layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode layer, arranged in a stacked manner to emit light according to a bias voltage on the anode and cathode layers. The light from the display 122 can be transmitted through the adhesive layer 124, the biometric sensor 112, the protective layer 114, and the cover plate 116 to the user's finger or palm 101 above the cover plate 116. Throughout this disclosure, Figure 1 The symbol 101 shown can also represent the user's palm in the context of palmprint recognition. For the sake of brevity, the description of the user's palm will not be repeated.

[0171] A biometric sensor 112 is formed above the display 122. The biometric sensor 112 may include a fingerprint sensor configured to extract or sense fingerprint or palmprint data of a user's hand. In some embodiments, the biometric sensor 112 includes a first side 112A facing the user's finger or palm 101 and a second side 112B opposite to the first side 112A. The biometric sensor 112 includes a substrate made of a transparent material. In some embodiments, the substrate is transparent to light emitted by the display 122, such that the image of the display 122 is visible through the biometric sensor 112. In some embodiments, the light emitted by the display 122 contains wavelengths in the visible light range, for example, between approximately 300 nanometers and approximately 700 nanometers. In some embodiments, the substrate of the biometric sensor 112 is formed of silicon oxide and may be in the form of glass or quartz; therefore, the biometric sensor 112 is referred to herein as an "in-glass fingerprint sensor".

[0172] The biometric sensor 112 includes one or more sensing electrodes 113 on the surface of a first side 112A of the substrate of the biometric sensor 112. The sensing electrodes 113 may be arranged in an array. In some embodiments, the sensing electrodes 113 comprise a transparent conductive material, such as indium tungsten oxide (ITO), fluorine-doped tin oxide (FTO), or zinc oxide doped. In some embodiments, the biometric sensor 112 further includes sensing circuitry (not shown) surrounding and electrically connected to the sensing electrodes 113. The sensing circuitry may include one or more transistors configured to provide a sensing voltage based on a sensing capacitance or based on the sensing electrodes. In some embodiments, the sensing voltage is transmitted to a third circuit board 130 for further processing.

[0173] In some embodiments, adhesive layer 124 is used to bond biometric sensor 112 to display 122. Adhesive layer 124 may comprise optically clear adhesive (OCA), such as LOCA (liquid optically clear adhesive).

[0174] Cover plate 116 is located above biometric sensor 112. In some embodiments, cover plate 116 is transparent to the radiation spectrum of display 122, for example, in the range between approximately 400 nanometers and approximately 700 nanometers, such that the image of display 122 is visible to the user through cover plate 116. In some embodiments, cover plate 116 is made of glass or other suitable transparent material.

[0175] In some embodiments, a protective layer 114 is formed between the biometric sensor 112 and the cover plate 116, and is configured to protect the biometric sensor 112 or other features of the biometric sensor device 100 from damage caused by electrostatic discharge (ESD) effects. In some embodiments, the protective layer 114 is located over a first side 112A of the biometric sensor 112. Figure 2A A top view is shown of the protective layer 114 covering the biometric sensor 112, wherein Figure 1 The cross-sectional view is taken from Figure 2A The cross-section line AA. (Reference) Figure 1 and Figure 2A The biometric sensor 112 includes a plurality of sensing electrodes 113 configured to detect the coupling capacitance of a user's finger 101. In some embodiments, the sensing electrodes 113 are arranged to form a grid or array. In some embodiments, the sensing electrodes 113 are divided into driving electrodes that provide driving signals and receiving electrodes that receive sensing signals. The driving electrodes may be alternately arranged with the receiving electrodes.

[0176] In some embodiments, the protective layer 114 includes a conductive layer 114C and an insulating layer 114D surrounding the conductive layer 114C. In some embodiments, the conductive layer 114C is formed of a conductive material, such as copper, tungsten, aluminum, or other suitable conductive material. The insulating layer 114D serves to electrically insulate the conductive layer 114C from other conductive features of the biometric sensor device 100. The insulating layer 114D may be formed of a dielectric material, such as silicon oxide, silicon nitride, resin, epoxy resin, polymer, or other suitable material.

[0177] A conductive layer 114C is formed over the array of sensing electrodes 113 and configured to protect the sensing electrodes 113 from ESD damage. In this embodiment, the mesh pattern of the conductive layer 114C divides the electrodes of the sensing electrodes 113 into multiple electrode groups, each containing four electrodes in top view. However, this disclosure is not limited thereto. The mesh pattern of the conductive layer 114C may be configured to further divide the sensing electrodes 113 into electrode groups of various numbers of electrodes. In some embodiments, the thickness of the protective layer 114 in the z-direction is in the range of about 1 micrometer to about 3 micrometers, for example, 2 micrometers. In some embodiments, the thickness of the first circuit board 110 is substantially equal to the sum of the thicknesses of the biometric sensor 112, the protective layer 114, and the cover plate 116. In some embodiments, the thickness of the first circuit board 110 is substantially equal to the sum of the thicknesses of the biometric sensor 112, the protective layer 114, the cover plate 116, and the adhesive layer 124.

[0178] Figure 2B This is a top view of a protective layer 114 covering a biometric sensor 112 according to another embodiment. Figure 2B In the illustrated embodiment, the protective layer 114 comprises a conductive layer 114E and an insulating layer 114D. The conductive layer 114E is similar in many respects to the conductive layer 114C, except that the conductive layer 114E forms a mesh pattern that divides the array of sensing electrodes 113 into individual electrodes. In some embodiments, from a top view, each sensing electrode 113 is laterally surrounded by the mesh pattern of the conductive layer 114E.

[0179] Reference Figure 1A first circuit board 110, a second circuit board 120, and a third circuit board 130 are arranged parallel to each other along the xy-plane. A stack formed by a cover plate 116, a protective layer 114, a biometric sensor 112, an adhesive layer 124, and a display 122 is formed on the second circuit board 120 and extends through the first circuit board 110. The first circuit board 110, the second circuit board 120, and the third circuit board 130 are connected by conductive posts 140. The conductive posts 140 may be formed by screws, bolts, nails, or other conductive components and may extend through the first circuit board 110, the second circuit board 120, and the third circuit board 130 in the z-direction perpendicular to the xy-plane. In some embodiments, the thickness of the circuit boards 110, 120, or 130 in the z-direction is in the range of approximately 600 micrometers to approximately 1000 micrometers, for example, 700 micrometers. In some embodiments, each of the circuit boards 110, 120, and 130 includes an insulating material, such as a solder resist, configured to electrically insulate the conductive posts 140 from the conductive components of the circuit boards 110, 120, and 130. The conductive post 140 serves to secure circuit boards 110, 120, and 130. In some embodiments, the conductive post 140 is configured to provide an electronic signal, such as a sensing signal, between circuit boards 110 and 130. The electronic signal can be transmitted to a user's finger 101 and helps to establish an electric field between the user's finger 101 and the sensing electrode 113, thereby generating a coupling capacitance when the user's finger 101 is present.

[0180] The outer frame 150 is located above the first circuit board 110 and adjacent to the cover plate 116. In some embodiments, the outer frame 150 includes an upper cover portion that exposes the cover plate 116. The outer frame 150 may be formed of a rigid material to provide mechanical support for the first circuit board 110. A molding material 118 is provided between the cover plate 116 and the outer frame 150 to cover the cover plate 116. The molding material 118 may be formed of a material such as resin or epoxy. In some embodiments, the outer frame 150 is formed of a conductive material and configured to receive electronic signals from the circuit boards 110, 120, or 130 in response to a touch event. Although not shown separately herein, the outer frame 150 may include beveled portions surrounding the sidewalls of the cover plate 116, the protective layer 114, and the biometric sensor 112.

[0181] In some embodiments, the outer frame 150 includes a conductive material, such as a metallic material, electrically coupled to the conductive posts 140. The outer frame 150 faces the user's finger 101 and conducts current through the conductive posts 140. During operation, when the user's finger 101 touches the cover plate 116, the user's finger 101 also contacts the conductive outer frame 150. In this way, the finger 101 conducts current through the outer frame 150 to facilitate the fingerprint sensing process. In some embodiments, the first circuit board 110 includes a conductive layer exposed from the upper surface of the first circuit board 110. The conductive layer of the first circuit board 110 may face the outer frame 150 and the user's finger 101, wherein the conductive layer is configured to transmit electronic signals from the conductive posts 140 to the user's finger 101 during a touch event. In some other embodiments, the outer frame 150 is formed of a non-conductive material, such as glass, plastic, ceramic, etc., and the sensing signal is provided to the finger 101 in another manner.

[0182] A first circuit board 110 is configured to support an outer frame 150. In some embodiments, the first circuit board 110 is configured to secure and electrically connect a biometric sensor 112. The first circuit board 110 may be a printed circuit board (PCB), a metal-based printed circuit board (MCPCB), or a flexible printed circuit board (FPCB). The first circuit board 110 may include a peripheral region defining an opening located in a central portion, in which the biometric sensor 112 is embedded and laterally surrounded by the peripheral region of the first circuit board 110. In some embodiments, although not explicitly shown, the first circuit board 110 includes a bus, for example formed by conductive wiring or vias, electrically connecting the biometric sensor 112.

[0183] In some embodiments, the first circuit board 110 includes a conductive layer 117 formed on the upper surface of the first circuit board 110 and laterally surrounding the cover plate 116. The conductive layer 117 may be electrically coupled to the outer frame 150 and configured to transmit electronic signals through the outer frame 150 to the second circuit board 120 or the third circuit board 130 in response to a touch event.

[0184] The second circuit board 120 includes an upper surface on which the display 122 is located. In some embodiments, the second circuit board 120 is configured to electrically connect the display 122 to an external device. The second circuit board 120 may be a PCB, MCPCB, or FPCB. In some embodiments, the second circuit board 120 includes an electronic device 126 located on its lower surface opposite the upper surface of the second circuit board 120. The electronic device 126 may be a display driver configured to control the display functions of the display 122. In some embodiments, the second circuit board 120 includes a bus 128 to electrically connect the display 122 to the electronic device 126. The bus 128 may be a bus formed as a flexible printed circuit (FPC), or may include bonding wires or conductive vias extending through the second circuit board 120.

[0185] The third circuit board 130 is configured to electrically connect the first circuit board 110 and the second circuit board 120 to an external device. The third circuit board 130 may be a PCB, MCPCB, or FPCB. The third circuit board 130 includes an electronic device 132, a connector 134, and a connection port 136 located on its lower surface. The third circuit board 130 also includes an electronic device 138 and a connector 142 located on its upper surface opposite the lower surface of the third circuit board 130.

[0186] Electronic device 132 may be a processor, microcontroller, signal processing unit, etc., configured to control the sensing function of biometric sensor 112 and the display function of display 122. Third circuit board 130 is electrically connected to biometric sensor 112 via bus 135 (e.g., FPC or bonding wire) or connector 134 on third circuit board 130. Connector 134 may be a slot or pad for electrically coupling bus 135. Connector 134 may be a series connector or a parallel connector. In some embodiments, connection port 136 is a Universal Serial Bus (USB) port for electrically connecting third circuit board 130 to a device external to biometric sensor device 100.

[0187] In some embodiments, electronic device 138 is a sensor driver configured to enable the sensing function of biometric sensor 112. In some embodiments, electronic device 132 is configured to control biometric sensor 112 and display 122 via electronic devices 138 and 126, respectively. Electronic device 138 is electrically connected to biometric sensor 112 via bus 135 and connector 134, and optionally via conductive vias of third circuit board 130. In some embodiments, electronic device 138 is configured to generate sensing signals and transmit them to user's finger 101 via first circuit board 110 or frame 150.

[0188] Connector 142 can electrically connect the third circuit board 130 to the second circuit board 120. In some embodiments, connector 142 includes a bus, such as an FPC or bonding wire, and a slot for electrically coupling the second circuit board 120 to the third circuit board 130 to provide power or signals between the circuit boards 120 and 130. Connector 142 can be a series connector or a parallel connector.

[0189] During a touch event, biometric sensor 112 is configured to sense the presence of a user's finger 101. Biometric sensor 112 and electronic device 132 are configured to authenticate the user by recognizing the user's fingerprint pattern. In some embodiments, display 122 is configured to generate an image containing instructions or recognition results, which can be displayed to the user via the in-glass biometric sensor 112. In some embodiments, display 122 is configured to display an image to the user based on sensing results generated by biometric sensor 112 associated with the user's biometrics. In some embodiments, display 122 is configured to display an image associated with the sensing results provided by biometric sensor 112 before, during, or after the fingerprint recognition process. Because the substrate and sensing electrodes 113 of biometric sensor 112 are made of a transparent material, the user can immediately see the image on display 122 during a touch event. No additional area is required for the individual biometric sensor 112 and display 122. Therefore, biometric sensor device 100 can provide display and fingerprint recognition functionality with a minimal device size.

[0190] In some embodiments, the biometric sensor device 100 can be used for blood oxygen detection applications by including a pulse oximeter (not shown separately), or simply an oximeter, disposed on a second circuit board 120. In some embodiments, the oximeter may additionally be disposed on the second circuit board 120 adjacent to the display 122. The pulse oximeter can be used as a self-illuminating device. In some embodiments, the pulse oximeter is configured to non-invasively measure the oxygen content in a user's blood by transmitting sensing light through the biometric sensor 112 and the cover plate 116 to the user's finger 101. In some embodiments, the sensing light of the pulse oximeter is in the range of red and infrared light. During a touch event, the biometric sensor device 100 is capable of substantially performing user authentication and blood oxygen concentration measurement simultaneously. In addition, due to the transparency of the substrate of the biometric sensor 112 and the sensing electrode 113, the sensing light of the pulse oximeter can be immediately transmitted to the user and reflected back to the pulse oximeter during a touch event. When viewed from above, no additional area is required to configure individual biometric sensors 112 and pulse oximeters. Therefore, the biometric sensor device 100 can provide blood oxygen concentration measurement and user authentication functions with a minimal device size.

[0191] Figure 3 This is a schematic block diagram of a sensing circuit according to various embodiments of the present disclosure. The sensing circuit 300 may be formed from the elements of the biometric sensor device 100 described above. (See reference...) Figure 3 The top sub-figure shows that the sensing circuit 300 includes a clock pulse generator 302, a sensing control block 304, a signal buffer block 306, and a signal transmission element 308. The sensing circuit 300 further includes a biometric sensor 112 and an electronic device 132 electrically connected to the sensing control block 304, as described in the reference above. Figure 1 The discussion has already taken place.

[0192] In some embodiments, a clock pulse generator 302 is included in a sensing control block 304, and electronic device 138 includes circuitry for implementing the clock pulse generator 302 and the sensing control block 304. In some embodiments, the biometric sensor device 100 includes more than one electronic device disposed on at least one of circuit boards 110, 120, or 130 for individually implementing the clock pulse generator 302 and the sensing control block 304. In some embodiments, a signal buffer block 306 is included in the sensing control block 304, and electronic device 138 includes circuitry for implementing the sensing control block 304 and the signal buffer block 306. In some embodiments, the biometric sensor device 100 includes more than one electronic device disposed on at least one of circuit boards 110, 120, or 130 for individually implementing the sensing control block 304 and the signal buffer block 306.

[0193] In some embodiments, the sensing control block 304 performs regular sensing steps with the aid of a clock pulse signal Sck generated by a clock pulse generator 302. The sensing control block 304 includes a transmitting sensing control module 305 and a receiving sensing control module 307. During the sensing steps, in response to an enable command provided by a user or authentication procedure, the transmitting sensing control module 305 is configured to receive the clock pulse signal Sck and generate an initial sensing signal Si and a control signal Sc. The transmitting sensing control module 305 can also transmit the initial sensing signal Si to the user's finger 101 via a signal buffer block 306 and a signal transmission element 308. In some embodiments, the transmitting sensing control module 305 is configured to send the initial sensing signal Si or the control signal Sc to the receiving sensing control module 307 to synchronize the received sensing signal with elements in the receiving sensing control module 307, such as switches. The initial sensing signal Si may resemble the control signal Sc in waveform or sampling frequency. In some other embodiments, the initial sensing signal Si has a different waveform from the control signal Sc but is still in phase with the control signal; for example, the initial sensing signal Si has a signal transition edge corresponding to the control signal Sc. In some embodiments, the signal edge of the initial sensing signal Si is synchronized with the signal edge of the control signal Sc. In some embodiments, the on-state or off-state of the initial sensing signal Si may be the same as or opposite to the on-state or off-state of the control signal Sc, respectively.

[0194] refer to Figure 3 The bottom subplot illustrates the signal waveforms of the initial sensing signal Si and the control signal Sc. In some embodiments, the initial sensing signal Si comprises a signal amplitude Vin with a sensing period Tm. The sensing period Tm comprises a reset period Tr and a sampling period Ts, and the duty cycle of the control signal Sc is expressed as Dc = Tr / Ts. Throughout this disclosure, the clock pulse generator 302 provides an initial sensing signal Si having a non-zero input voltage Vin in the on state and a substantially zero voltage (or contact level) in the off state. In some embodiments, the initial sensing signal Si provides a signal transition voltage +Vin with a rising edge, corresponding to or substantially aligned with the start time of the sampling period Ts. The signal polarity +Vin appearing at the rising edge of the initial sensing signal Si can be used as a sensing voltage, thus the sensing voltage can be generated during the sampling period Ts. The sensing voltage can have the same signal polarity as the signal transition voltage, such as a positive or negative voltage.

[0195] In some embodiments, the control signal Sc is configured to control the open or closed state of the switches in the receiving sensing control module 307. For example, during the reset cycle Tr, some switches are opened and some other switches are closed depending on the open state of the control signal Sc. Similarly, the switches that are open or closed during the reset cycle Tr are closed or opened depending on the open state of the control signal Sc during the sampling cycle.

[0196] In some embodiments, signal buffer block 306 is configured to buffer an initial sensing signal Si and generate a buffered sensing signal Sb. Signal buffer block 306 may also convert the voltage or current level of the initial sensing signal Si to another signal level to provide the drive capability required for the sensing step. In some embodiments, signal buffer block 306 includes at least one of a current amplifier and a level shifter, configured to generate the buffered sensing signal Sb based on the initial sensing signal Si.

[0197] In some embodiments, the signal transmission element 308 is configured to generate a transmission sensing signal St based on a buffer sensing signal Sb and transmit it to the user's finger 101. The signal transmission element 308 can transmit the buffer sensing signal Sb by contacting the finger 101 or in a non-contact manner. In some embodiments, in touch mode, the signal transmission element 308 includes a conductive layer 117 and / or a frame 150, through which the buffer sensing signal Sb is transmitted as the transmission sensing signal St. During a touch event, the finger 101 contacts the frame 150 or the conductive layer 117 on the first circuit board 110 (if there is no frame 150). Therefore, the finger 101 receives the current provided by the transmission sensing signal St for sensing.

[0198] Alternatively, in a non-touch mode, the signal transmission element 308 is configured to convert the sensing signal Sb from an electrical form into an optical form of a transmitted sensing signal St, and to transmit the optically modulated transmitted sensing signal St to the finger 101. In some embodiments, the signal transmission element 308 includes a laser diode for converting the electrical sensing signal Sb into an optical transmitted sensing signal St, and using the transmitted sensing signal St to illuminate the user's finger 101.

[0199] In some embodiments, during a touch event, finger 101 approaches or contacts biometric sensor 112 and receives a transmitted sensing signal St. A capacitance Cfinger is thus generated between finger 101 and biometric sensor 112. Throughout this disclosure, for ease of reference, the symbol used for a capacitor, such as Cfinger, may also refer to the capacitance of that capacitor. Sensing electrode 113 may generate a received sensing signal Sr, which is generated by the transmitted sensing signal St transmitted to finger 101 and the capacitance Cfinger according to the touch event.

[0200] In some embodiments, the receiving sensing control module 307 is configured to receive a receiving sensing signal Sr and generate a digital sensing signal Sd, which represents the sensing result provided by the sensing electrode 113 based on a touch event. The digital sensing signal Sd can be transmitted to the electronic device 132, where the individual digital sensing signals Sd detected by different sensing electrodes 113 at different locations of the finger 101 are processed to form a processing signal Sp representing a fingerprint image of the finger 101.

[0201] In some embodiments, the receiving sensing control module 307 includes interface circuitry 312, amplification circuitry 314, and an analog-to-digital converter (ADC) 316. In some embodiments, interface circuitry 312 interconnects biometric sensor 112 with amplification circuitry 314 and is configured to improve the amplification performance of amplification circuitry 314 for in-glass type biometric sensor 112. Interface circuitry 312 will be described in more detail in the following paragraphs.

[0202] In some embodiments, amplifier circuit 314 is configured to increase the quantization resolution of ADC 316 and reduce noise introduced during the sensing step. In some embodiments, amplifier circuit 314 includes an operational (OP) amplifier. In this embodiment, amplifier circuit 314 includes a voltage amplifier; however, other types of amplifiers, such as current amplifiers, transconductance amplifiers, or transimpedance amplifiers, are also possible. In some embodiments, amplifier circuit 314 includes a two-stage amplification design. In some embodiments, ADC 316 is configured to convert the analog value of the received sensing signal Sr into a digital signal in digital form, which is used as a digitized sensing signal Sd, to facilitate processing by electronic device 132. In some embodiments, ADC 316 includes a successive approximation register (SAR) ADC, a trigonometric integrator (ΔΣ) ADC, a dual-slope ADC, a pipelined ADC, a flash ADC, etc.

[0203] Figure 4A This is a schematic block diagram of a sensing circuit 400 according to various embodiments of the present disclosure. The sensing circuit 400 can be considered as one implementation of the sensing circuit 300. Reference Figure 4A The interface circuit 412 includes a resistive element Ri, and the amplifier circuit 314 includes an amplifier 322, a feedback capacitor Cf, and a switch 324. The amplifier 322 is connected in parallel to the feedback capacitor Cf and the switch 324.

[0204] like Figure 4AAs shown, amplifier 322 includes an inverting terminal (-) and a non-inverting terminal (+), wherein the non-inverting terminal is connected to a supply voltage Vz. In some embodiments, the supply voltage Vz is predetermined to be Vdd / 2. In addition, the inverting terminal is coupled to a resistive element Ri. Amplifier 322 also includes an output terminal to provide an output signal Sa as an amplified sensing signal.

[0205] In the first stage of the sensing step, during the reset period Tr of the sensing period Tm, switch 324 is closed, configuring amplifier 322 in reset mode and forcing it to its initial state with unit gain. In the second stage of the sensing step, during the sampling period Ts of the sensing period Tm, switch 324 is opened, configuring amplifier in amplification mode and generating output signal Sa by amplifying the received sensing signal Sr. The timing of switch 324 can be synchronized or in phase with the control signal Sc; for example, the open and closed states of switch 324 correspond to the open and closed states of control signal Sc, respectively.

[0206] A resistive element Ri is electrically coupled between the biometric sensor 112 and the amplifier 322 of the amplifier circuit 314. The resistive element Ri can be a resistor. In some embodiments, the resistive element Ri is formed by a semiconductor processing process in a metallization layer above a substrate for forming a receiving sensing control module 307 or a sensing control block 304, and is electrically coupled to the sensing electrode 113 and the amplifier 322. The resistive element Ri can include a diffused resistor, an ion-implanted resistor, a thin-film resistor, a polysilicon resistor, etc. In some embodiments, the resistive element Ri is a separate resistor external to the biometric sensor 112 or the amplifier 322; for example, the resistive element Ri is disposed on a circuit board 110, 120, or 130, and is electrically coupled to the sensing electrode 113 and the amplifier 322 via various bonding techniques (e.g., wire bonding) through the circuit board 110, 120, or 130.

[0207] The resistance of resistor Ri (also denoted as Ri herein) is appropriately determined to enhance the stability of amplifier 322. As described above, biometric sensor 112 comprises a substrate formed of a dielectric material such as glass, quartz, or silicon oxide. While a biometric sensor 112 with a dielectric substrate can offer advantages, such as reduced processing costs, the dielectric properties of the substrate of biometric sensor 112 may cause substrate capacitance Cs to be electrically coupled to amplifier circuit 314. Substrate capacitance Cs can cause stability problems for amplifier 322, thereby significantly affecting the operating bandwidth or operating current of amplifier 322.

[0208] Figure 4B This is a schematic block diagram of amplifier 322 according to various embodiments of the present disclosure. Figure 4BAs shown, amplifier 322 includes a first stage S1 and a second stage S2 coupled to the first stage S1 via a coupling capacitor Cc. Figure 4B The implementation of the two-stage amplifier shown is for illustrative purposes only. Other types of amplifiers 322 are also within the scope of this disclosure.

[0209] Reference Figure 4B The first stage S1 includes a pair of input transistors M1 and M2, wherein the gate terminals of the input transistors M1 and M2 are configured as a pair of differential input terminals Vi- and Vi+, corresponding to the inverting input (-) and non-inverting input (+) pairs of amplifier 322, respectively. Figure 4A As shown. Each of the input transistors M1 and M2 includes a drain terminal coupled to the current mirror CM and a source terminal coupled to the current load Ix.

[0210] In some embodiments, the current mirror circuit CM includes a pair of transistors M4 and M5, wherein the source terminals of transistors M4 and M5 are coupled to a supply voltage Vx, such as Vdd, and the drain terminals of transistors M4 and M5 are coupled to the drain terminals of input transistors M1 and M2, respectively. The gate terminals of transistors M4 and M5 are electrically coupled together and also electrically coupled to the drain terminal of transistor M4.

[0211] A current load Ix is coupled between the supply voltage Vy (i.e., ground potential) and the source terminals of the input transistors M1 and M2. In some embodiments, the current load Ix comprises a current source.

[0212] During operation, the first stage S1 is configured to provide differential gains Vi+ and Vi- at ​​the output node N1 between the drain terminals of transistor M5 and transistor M2, based on the differential input voltage supplied to the input terminals.

[0213] The second stage S2 includes transistor M3, whose gate terminal is coupled to the output node N1 of the first stage S1, its source terminal is coupled to the supply voltage Vx, such as Vdd, and its drain terminal is coupled to the current load Iy. The second stage S2 includes an output node N2 coupled between transistor M3 and the current load Iy. Output node N2 corresponds to... Figure 4A The output terminal of the amplifier 322 shown is used to provide an amplified sensing signal Sa.

[0214] A current load Iy is coupled between the supply voltage Vy (i.e., ground potential) and transistor M3. In some embodiments, the current load Iy comprises a current source. A coupling capacitor is coupled between the output node N1 of the first stage S1 and the output node N2 of the second stage S2.

[0215] During operation, the second stage S2 is configured as a Class A, Class B, or Class AB amplifier and provides an amplified voltage at the output node N2 based on the intermediate voltage provided at node N1 of the first stage S1.

[0216] In some embodiments, transistors M1, M2, and M3 comprise metal-oxide-semiconductor (MOS) transistors, such as N-type MOS (NMOS) transistors or P-type MOS (PMOS) transistors. In some embodiments, input transistors M1 and M2 have the same conductivity type, such as N-type or P-type. Figure 4B The current mirror CM and current loads Ix and Iy of amplifier 322 shown are for illustrative purposes only, and other types of current mirrors and current loads are also within the scope of this disclosure.

[0217] In some embodiments, the output node N1 of the first stage S1 has an effective resistor (or equivalent, a resistance) R1 and an effective parasitic capacitor (or equivalent, a capacitance) C1. In some embodiments, the input transistors M1 or M2 include a transconductance gm1, which is determined by the bias current (e.g., provided by the current load Ix) and the dimensions of the respective channel regions of the input transistors M1 or M2 (e.g., the channel length, channel width, etc. of the input transistors M1 or M2). In some embodiments, the output node N2 of the second stage S2 has an effective resistor (or equivalent, a resistance) R2 and an effective parasitic capacitor (or equivalent, a capacitance) Cp. In some embodiments, the transistor M3 includes a transconductance gm2, which is determined by the bias current (e.g., provided by the current load Iy) and the dimensions of the channel regions of the transistor M3 (e.g., the channel length, channel width, etc. of the transistor M3).

[0218] Figure 5A and Figure 5B These are circuit diagrams of amplifier circuit 314 and amplifier 322 according to various embodiments of the present disclosure. Figure 5A and Figure 5B The amplifier circuit 314 and amplifier 322 shown represent respectively Figure 4A and Figure 4B The circuit diagram of amplifier 322 shown in the diagram under small-signal analysis does not include the effect of interface circuit 412 (i.e., resistor element Ri and ADC316), in order to illustrate... Figure 4B The performance of the independent amplifier 322 shown.

[0219] During the small-signal analysis of the reset phase, the inverting terminal (-) is disconnected from the feedback loop. Furthermore, since amplifier 322 is configured to amplify the input voltage Vt during the reset cycle Tr, switch 324 is closed. Assuming the receiving sensing control module 307 does not... Figure 4AThe interface circuit 412 in the amplifier 322 is used as the inverting terminal (-) of the amplifier 322, which is directly coupled to the sensing electrode 113 of the biometric sensor 112 or the conductive interconnect circuit between the biometric sensor 112 and the receiving sensing control module 307. Based on the assumption that the interface circuit 412 is absent and the total resistance between the biometric sensor 112 and the amplifier circuit 314 is negligible, under small-signal analysis, the feedback loop caused by the amplifier 322 can be represented as a parasitic capacitor Cp and a substrate capacitor Cs connected in parallel at the output node N2 (also labeled "Vout") of the amplifier 322.

[0220] like Figure 5B As shown, in terms of the two-stage operational amplifier structure and small-signal analysis, amplifier 322 includes a first stage, which is composed of a current source I1 connected in parallel with a resistor R1 and a capacitor C1 at the output node N1 of the first stage S1. The first stage S1 provides an output terminal Vo1 at the output node N1, and the current source I1 is represented as I1 = -gm1·Vt.

[0221] like Figure 5B As shown, the second stage S2 is coupled to the first stage S1 via a coupling capacitor Cc. In small-signal analysis, the second stage S2 consists of a current source I2 connected in parallel with a resistor R2 and a load capacitor CL. The capacitance of the load capacitor CL can be expressed as the sum of the capacitances of the substrate capacitor Cs and the parasitic capacitor Cp, i.e., CL = Cs + Cp. The current source I2 is expressed as I2 = gm²·Vo1. The second stage S2 provides the output voltage Vout of the amplifier 322's output signal Sa.

[0222] according to Figure 5B From the small-signal analysis circuit diagram shown, the voltage gain of amplifier 322 can be derived as follows:

[0223]

[0224] In the above equation (1), the frequency response of the voltage gain Vout / Vt contains two poles ω. p1 and ω p2 In some embodiments, the conditions listed in procedure (2) are satisfied:

[0225] gm2 >> 1 / R2 and C p <<C s (2)

[0226] Using the conditions given in equation (2) to simplify equation (1), the two poles ω can be obtained. p1 and ω p2 The approximate value is represented as follows:

[0227]

[0228] From the above analysis, it can be seen that the second pole ω determines the stability of amplifier 322. p2 The stability of amplifier 322 is determined by the transconductance gm2 and the capacitances of the substrate capacitor Cs and the parasitic capacitor Cp. The capacitance of the substrate capacitor Cs is typically greater than that of the parasitic capacitor Cp, for example, at least 10 times greater. As a result, the stability of amplifier 322 is affected by the second pole ω. p2 The frequency of [something] is reduced and significantly limited.

[0229] Figure 5C and Figure 5D These are circuit diagrams of amplifier circuit 314 and amplifier 322 according to various embodiments of this disclosure. Different from... Figure 5A and Figure 5B The circuit diagram shown is as follows. Figure 5C and Figure 5D The amplifier circuit 314 and amplifier 322 shown illustrate the operation during the reset phase. Figure 4A and Figure 4B As shown, this is a small-signal analysis of amplifier 322, which includes interface circuitry 412 (i.e., resistive element Ri). Figure 5C As shown, the resulting feedback loop can be represented as a parasitic capacitor Cp connected in parallel with a resistor Ri at the output node Vout or N2, while the resistor Ri is connected in series with the substrate capacitor Cs.

[0230] like Figure 5D As shown, in terms of the two-stage operational amplifier structure and small-signal analysis, the first stage S1 of amplifier 322 is represented as a current source I1, which is connected in parallel with resistor R1 and capacitor C1 at the output node Vo1 or N1 of the first stage S1. The current source I1 is represented as I1 = -gm1·Vt.

[0231] The second stage S2 is represented as current source I2. When the resistive element Ri is connected in series with the substrate capacitor Cs, the current source I2 is connected in parallel with resistor R2, parasitic capacitor Cp, and resistive element Ri at the output node Vout or N2. The current source I2 is represented as I2 = gm2·Vo1.

[0232] according to Figure 5D The voltage gain of amplifier 322 in the circuit diagram shown can be expressed as follows:

[0233]

[0234] In the above equation (4), the frequency response of the voltage gain Vout / Vt contains a zero ω. z and the three poles ω p1 ω p2 and ω p3.

[0235] In some embodiments, the conditions given in equation (2) are satisfied. Using the conditions given in equation (2) to simplify equation (4) yields an approximate representation of the three poles shown in the following equation (5):

[0236]

[0237] In some embodiments, the bandwidth of amplifier 322 is determined by the second pole ω. p2 The decision is determined not only by the substrate capacitor Cs, but also by the resistance of the resistive element Ri in the interface circuit 412. In some embodiments, the resistance Ri is chosen to be much greater than the reciprocal of the transconductance gm2, i.e., Ri >> 1 / gm2. Therefore, the second pole ω of equation (5) p2 It can be further simplified as shown in the following procedure (6):

[0238]

[0239]

[0240] By substituting the square procedure (6) into the square procedure (4), the zero point ω z Approximate value and second pole ω p2 The approximations are canceled out, resulting in the following formula (8):

[0241]

[0242] In some embodiments, the resistance of the resistive element Ri is much greater than the reciprocal of the transconductance gm2, for example, the reciprocal of the transconductance gm2 is greater than about 10 times, greater than about 20 times, greater than about 50 times, or greater than about 100 times.

[0243] Based on the formula (8), it is clear that the third pole ω determines the stability of amplifier 322. p3 Most of the capacitance is determined solely by the parasitic capacitor Cp, rather than the substrate capacitor Cs. As described above, the substrate capacitor Cs typically has a capacitance at least 10 times greater than that of the capacitor Cp. As a result, this can be disclosed by comparing formula (3) and formula (7). Figure 5C The third pole ω of amplifier 322 shown in the figure (with resistor Ri present) p3 Significantly greater than Figure 5A The second pole of amplifier 322 is shown in the diagram (without resistor Ri), where the capacitance of the substrate capacitor Cs is much larger than that of the parasitic capacitor Cp. This significantly improves the stability and operating frequency of amplifier 322 without sacrificing its performance.

[0244] In some embodiments, to increase the stability of amplifier 322, the second pole ω can be further increased even in the absence of the proposed interface circuit 412. p2 It can be clearly seen from equation (3) that increasing the second transconductance gm2 can also proportionally increase the second pole ω. p2 However, this arrangement means that the bias current of the current source in the second stage S2 of amplifier 322 must be increased, which inevitably requires greater power consumption and heat generation in the second stage S2. In contrast, the proposed interface circuit 412 can help to effectively improve the second pole ω. p2 This does not increase the bias current level of the second stage S2. As a result, the performance and power efficiency of amplifier 322 can be improved in an efficient manner.

[0245] Figure 6A This is a schematic block diagram of a sensing circuit 600 according to various embodiments of the present disclosure. The sensing circuit 600 is similar in many respects to... Figure 4A The sensing circuit 400 is shown in the diagram; therefore, for the sake of brevity, the description of these features of the sensing circuit 600 will not be repeated. The sensing circuit 600 differs from the sensing circuit 400 in that the biometric sensor device 100 further includes a voltage buffer 602 located between the biometric sensor 112 and the sensing control block 304. Additionally, the receiving sensing control module 307 of the sensing circuit 400 includes an interface circuit 612, which includes a current source 604, a switch 606, and an amplifying capacitor Ca. The amplifying capacitor Ca is disposed between the switch 606 and the inverting terminal (-) of the amplifier 322, and is connected in series with the feedback capacitor Cf and the switch 324.

[0246] In some embodiments, voltage buffer 602 includes a source follower or a common-drain MOS transistor Msf, wherein voltage buffer 602 includes a gate terminal coupled to the sensing electrode 113 of biometric sensor 112, a drain terminal coupled to a supply voltage Vx, such as Vdd, and a source terminal coupled to interface circuit 612. The source terminal of voltage buffer 602 provides a buffered receive signal Vsf based on the received sensing signal Sr. Although Figure 6B Only one voltage buffer 602 is shown for the entire array of sensing electrodes 113. In some embodiments, the biometric sensor 112 may include multiple voltage buffers 602 at the output of each row or column of the array of sensing electrodes 113, or at the output of each sensing electrode 113.

[0247] In some embodiments, current source 604 is coupled between the input terminal of receiving control module 307 and ground potential to provide a low-resistance output for biometric sensor 112. In this way, the effect of the insignificant capacitance of substrate capacitor Cs can be effectively mitigated or ignored by current source 604.

[0248] Figure 6B Voltage waveforms of the interface circuit 612 according to various embodiments of the present disclosure are shown. During the sensing step, a control signal Sc or an initial sensing signal Si is transmitted to the receiving control module 307 to control the states of switches 324 and 606.

[0249] In some embodiments, reference Figure 6A and Figure 6B The proposed sensing step requires two phases (cycles), comprising a reset cycle Tr and a sampling cycle Ts. In the first phase of the sensing step, the reset phase with the reset cycle Tr, the control signal Sc is set to a logic-high state with amplitude Vin, causing switch 324 to close. Therefore, the feedback capacitor Cf is bypassed. In some embodiments, switch 606 is closed during the reset phase. In some embodiments, the received sensing signal Sr is set to an initial state, for example, at a low voltage V. SIG,L And it is independent of touch events. The voltage V at the source terminal of voltage buffer 602 SF Provide buffer voltage V SF,L In some embodiments, the voltage V SF,L With voltage V SIG,L The difference between them follows V SF,L =V SIG,L The relationship is -Vgs, where the voltage Vgs is the turn-on voltage Vgs of the voltage buffer 602 and is greater than 0 volts. In some embodiments, the output signal Sa of the amplifier 322 is set to the voltage Vgs during the reset phase in the feedback mode of the amplifier 322. CM V out,1 =V CM In some embodiments, the voltage V CM It is predetermined to be, for example, Vdd / 2. In some embodiments, the voltage V CM It can be greater than or less than the voltage V SF,L or V SIG,L As a result, a voltage difference will be generated at the two terminals of the amplifying capacitor Ca.

[0250] In the second stage of the sensing step, namely the sampling stage with a sampling period Ts, the control signal Sc is set to a logic-low state, with an amplitude lower than the voltage Vin, for example, 0 volts, which causes switch 324 to open. Simultaneously, switch 606 remains closed. Based on the touch event, the sensing electrode 113 senses the voltage change caused by the presence of capacitance Cfinger and transmits this voltage change to the received sensing signal Sr. Therefore, the voltage of the received sensing signal Sr increases to reach a high voltage V. SIG,H The rising edge of the received sensing signal Sr lags behind the falling edge of the control signal Sc by a time delay Td1. The time delay Td1 is due to the propagation or processing delay of the initial sensing signal Si and the received sensing signal Sr between the transmission sensing control module 305, the signal buffer block 306, the signal transmission element 308, and the sensing electrode 113. In some embodiments, the time delay Td1 is introduced to ensure the correct switching time of the switch 324 and the proper operation of the amplifier 322. Voltage V SIG,H The amplitude varies depending on the different sensing capacitances Cfinger, and therefore can vary according to different finger heights or different positions of the finger 101 during the same touch event. As a result, the voltage V of the buffered received sensing signal Sf... SF According to the increased voltage V SIG,H Increase to high voltage V SF,H Voltage V SF,H and V SIG,H Follow V SF,H =V SIG,H The relationship between –Vgs and the voltage difference is expressed as ΔV SIG =V SIG,H -V SIG,L A time delay Td2 is observed between the rising edge of the buffered received sensing signal Sf and the falling edge of the initial sensing signal Si. Due to the propagation delay of the voltage buffer 602, the time delay Td2 may be greater than the time lag Td1. In some embodiments, due to the presence of the feedback capacitor Cf and the increase in the received sensing signal Sr, the output signal Sa of amplifier 322 is driven to a low voltage as follows:

[0251] V out,2 =V CM -(V SF,H -V SF,L (C) a / C f (9) During the detection phase, the voltage difference ΔV o =V out,2 -V out,1 The following program represents:

[0252]

[0253] According to the procedure (10), Figure 6A The amplification effect of the amplifier 322 shown can be determined by the interface circuit 612, i.e., the capacitance ratio of the amplifying capacitor Ca to the feedback capacitor Cf, and is independent of the substrate capacitor Cs. In some embodiments, the amplifying capacitor Ca is determined to have a capacitance greater than that of the feedback capacitor Cf, for example, it can be a capacitance in the range of 1 to 10 times that of the feedback capacitor Cf. Figure 6A The interface circuit 612 shown can effectively reduce the capacitive effect of the substrate capacitor Cs and improve the sensing process.

[0254] Figure 6C This is a schematic block diagram of a sensing circuit 601 according to various embodiments of the present disclosure. The sensing circuit 601 is similar in many respects to... Figure 6A The sensing circuit 600 is shown; therefore, for the sake of brevity, the description of these features of the sensing circuit 600 will not be repeated. The difference between sensing circuit 601 and sensing circuit 600 is that sensing circuit 601 includes interface circuit 622, instead of... Figure 6A Interface circuit 612 is shown. Comparing interface circuit 612 and interface circuit 622, interface circuit 622 further includes a switch 616 having a first terminal connected to a node between switch 606 and amplifying capacitor Ca, and a second terminal connected to a supply voltage Vz, for example, Vdd / 2. In some embodiments, switch 606 is also connected to the non-inverting terminal (+) of amplifier 322. In some embodiments, the non-inverting terminal (+) of amplifier 322 is connected to the supply voltage Vz.

[0255] Figure 6D Voltage waveforms of the interface circuit 622 according to various embodiments of the present disclosure are shown. During the sensing step, a control signal Sc or an initial sensing signal Si is transmitted to the receiving control module 307 to control the state of switch 324, while additional control signals Sk and Sh are generated to control switches 616 and 606, respectively. In some embodiments, the control signal Sh is in phase with the control signal Sc, while the control signal Sk is out of phase with the control signal Sc.

[0256] In some embodiments, reference Figure 6C and Figure 6D The proposed sensing process requires four stages (cycles), including two reset cycles, referred to as reset cycles Tr1 and Tr2, and two sampling cycles Ts, referred to as sampling cycles Ts1 and Ts2. In some embodiments, in each reset cycle Tr1, Tr2 and sampling cycle Ts1, Ts2, the on / off states of switches 324 and 606 are opposite to the on / off states of switch 616.

[0257] In the first stage of the sensing step, namely the reset stage with a reset period Trl, the initial sensing signal Si and the control signal Sh are set to a logic high state with amplitude Vin, which closes switches 324 and 606. Therefore, the feedback capacitor Cf is bypassed. Simultaneously, the control signal Sk is set to a logic low state, which opens switch 616. In some embodiments, the received sensing signal Sr is set to an initial state, such as a low voltage V. SIG,L The buffered received sensing signal Sf has a buffered voltage V at the source terminal of the voltage buffer 602. SF,L In some embodiments, the voltage V SF,L Via V SF,L =V SIG,L -Vgs and voltage V SIG,L Relatedly, in some embodiments, during the reset phase, the output signal Sa of amplifier 322 is set to the intermediate voltage V. Sa,M For example, Vdd / 2. As a result, a voltage difference will be generated between the two terminals of the amplifying capacitor Ca.

[0258] In the second phase, i.e., the first sampling phase, with a first sampling period Tsl, control signals Sc and Sh are set to a logic low state with an amplitude lower than the voltage Vin, for example, 0 volts, which causes the corresponding switches 324 and 606 to open. Conversely, control signal Sk is set to a logic high state, which causes switch 616 to close. A time delay Td3 is formed between the rising edge of control signal Sk and the falling edge of control signal Sc, and a time delay Td4 is formed between the falling edge of control signal Sh and the falling edge of control signal Sc. In some embodiments, time delay Td3 is greater than time delay Td4. In some embodiments, time delay Td4 is substantially greater than zero. In some embodiments, time delays Td3 and Td4 are introduced to ensure the correct switching sequence of switches 324, 606, and 616 and the proper operation of amplifier 322.

[0259] In some embodiments, during the second phase, the received signal Sr is configured in the initial phase and is independent of any touch event; therefore, the voltages of the received sensing signal Sr and the buffered sensing signal Sf are maintained at voltage V, respectively. SIG,L and V SF,L After switch 616 is closed, the output voltage of amplifier 322 undergoes a transition period and is driven to the first output voltage as follows:

[0260] V out,1 =V Sa,M +(V SF,L -V Sa,M (Ca / Cf) (11)

[0261] In the third stage of the sensing step, namely the reset stage with a reset period Tr2, switches 324 and 606 close in a manner similar to the reset period Tr1. Otherwise, switch 616 is open. A time delay Td5 is formed between the falling edge of control signal Sk and the rising edge of control signal Sc, and a time delay Td6 is formed between the rising edge of control signal Sh and the rising edge of control signal Sc. In some embodiments, time delay Td5 is greater than time delay Td6. In some embodiments, time delay Td6 is substantially equal to, greater than, or less than zero. In some embodiments, time delays Td5 and Td6 are introduced to ensure the correct switching sequence of switches 616, 606, and 324 and the proper operation of amplifier 322.

[0262] In the third stage, the sensing electrode 113 senses the touch event, and therefore receives the sensing signal Sr, which is driven to a high voltage V according to the touch event. SIG,H The source terminal of voltage buffer 602 provides the buffer voltage V. SF,H V SF,H =V SIG,H -Vgs. In addition, due to the closing of switch 324, the output signal Sa of amplifier 322 recovers to the intermediate voltage V. Sa,M .

[0263] In the fourth stage of the sensing step, namely the second sampling stage with a sampling period Ts2, control signals Sc and Sh are set to a logic low state with an amplitude lower than the voltage Vin, for example, 0 volts, which causes the corresponding switches 324 and 606 to open. Simultaneously, control signal Sk is set to a logic high state, which causes switch 616 to close. After switch 616 closes, the output voltage of amplifier 322 undergoes a transition period and is driven to a second output voltage as follows:

[0264] V out,2 =V Sa,M +(V SF,H -V Sa,M (Ca / Cf) (12)

[0265] During the detection phase, the voltage difference ΔV o =V out,2 -V out,1 This can be represented by the following procedure:

[0266]

[0267] In the above equation (13), the voltage difference is expressed as ΔV SIG =V SIG,H -V SIG,L .

[0268] According to the procedure (13), Figure 6C The amplification effect of the amplifier 322 shown can be determined by the interface circuit 622, that is, through appropriately controlled switches 324, 606, and 616, the capacitance ratio between the amplifying capacitor Ca and the feedback capacitor Cf is independent of the substrate capacitor Cs. In some embodiments, the amplifying capacitor Ca is determined to contain a capacitance greater than that of the feedback capacitor Cf, for example, in the range of 1 to 10 times the capacitance of the feedback capacitor Cf. Figure 6C The interface circuit 622 shown can effectively reduce the capacitive effect of the substrate capacitor Cs and improve the sensing process.

[0269] Figure 7 This is a schematic diagram of a signal model of a sensing circuit 700 according to an embodiment of the present disclosure. The sensing circuit 700 is similar to the sensing circuit 300 in many respects; therefore, for the sake of brevity, descriptions of these features of the sensing circuit 700 will not be repeated. The sensing circuit 700 simulates the sensing circuit 300 under noise or interference, wherein one or more signal bias sources are introduced into the signal processing path in the receiving sensing control module 307.

[0270] In some embodiments, a first signal offset D1 is seen at the output node Vout of the amplifier circuit 314. off For example, the output terminal of operational amplifier 322. First signal offset D1 off The ideal output signal Va can be applied to amplifier circuit 314. Due to non-ideal effects of the analog front-end circuitry of amplifier circuit 314, such as the analog front-end circuitry in amplifier 322, a first signal offset D1 may occur. off .

[0271] In some other embodiments, a second signal offset D2 is seen at the output terminal of the ADC316. off Second signal offset D2 off The ideal digitized sensing signal Sd can be applied to the ADC316. Due to the non-ideal effects of the ADC316's analog front-end circuitry, a signal offset D2 may occur. off .

[0272] In this disclosure, a novel detection method is proposed to eliminate the signal offset D1 contained in the sensing circuit 300 or 700. off Or D2 off .

[0273] In some embodiments, the sensing control block 304 performs sensing steps with the aid of a modified initial sensing signal Sj, which is generated by the transmitting sensing control module 305 based on the clock pulse generator 302. Please refer to... Figure 7The bottom sub-figure shows the signal waveforms of the modified initial sensing signal Sj and the control signal Sc. In some embodiments, the sensing step of the sensing circuit 700, under the timing control of the modified initial sensing signal Sj and the control signal Sc, includes a timed repetitive sampling operation. (See reference...) Figure 4A and Figure 7 The modified initial sensing signal Sj differs from the initial sensing signal Si in that, for a single sensing electrode 113, the modified initial sensing signal Sj has a sensing period Tn, which is twice the sensing period Tm of the sensing circuit 300. Each sensing period Tn is formed by two reset periods Tr1 and Tr2 and two sampling periods Ts1 or Ts2 alternating with the reset periods Tr1 and Tr2, wherein the modified initial sensing signal Sj contains a rising edge +Vin and a falling edge -Vin at the beginning of the first sampling period Ts1 and the second sampling period Ts2, respectively. The first sampling period Ts1 and the second sampling period Ts2 are also referred to as the first sampling phase and the second sampling phase of the sensing step, respectively. The modified initial sensing signal Sj contains a waveform that is substantially zero voltage during the reset periods Tr1 and Tr2, a setting similar to that used in the initial sensing signal Si.

[0274] refer to Figure 3 and Figure 7 Under the assumption of no bias voltage, the sensing step of sensing circuit 300 requires one sensing period Tm for a single sensing electrode 113. In contrast, the sensing step of sensing circuit 700 requires one sensing period Tn to complete a single sensing step of the same location of finger 101. Therefore, the first sampling phase and the second sampling phase result in two consecutive sampling periods Ts1 and Ts2 for the same sensing location of finger 101. In some embodiments, the start times of the first sampling period Ts1 and the second sampling period Ts2 correspond to or substantially align to the rising edge +Vin and falling edge -Vin of the modified initial sensing signal Sj, respectively, at which time the sensing electrode 113 is configured to generate a sensing signal Sr with an amplitude associated with the sensing finger capacitor Cfinger. The signal polarity of the sensing signal Sr depends on the signal switching polarity, i.e., the rising edge or falling edge of the initial sensing signal Sj at the start of the respective sampling periods Ts1 or Ts2.

[0275] In some embodiments, the electronic device 132 is configured to receive a first sensing signal P1 and a second sensing signal P2 at the same location during a first sampling phase and a second sampling phase, respectively, as shown below:

[0276] P1=(V in *C finger / C p +D1 off )*G adc +D2off (14)

[0277] P2=(-V in *C finger / C p +D1 off )*G adc +D2 off (15)

[0278] In the above equations (14) and (15), the signal gain of the ADC316 is represented by the symbol G. adc At the beginning of the first sampling period Ts1, the first sensing signal P1 is obtained based on the positive polarity (i.e., +Vin) of the initial sensing signal Sj, and at the beginning of the second sampling period Ts2, the second sensing signal P2 is obtained based on the negative polarity (i.e., -Vin) of the initial sensing signal Sj. Subtracting equation (15) from equation (14), the final processing signal Sp of the detection stage is shown in the figure below:

[0279] Sp=(P1-P2) / 2=V in *C finger / C p *G adc (16)

[0280] As shown in the processing results of the procedure (16), it is clear that for the same sensing point, the proposed two-stage sensing steps can effectively eliminate the offset D1 caused by the first signal. off Or the second signal offset D2 off The generated signal bias voltage. The signal detection performance of sensing circuit 300 or 700 can be used as a reference. Figure 7 The proposed bias elimination scheme is used to improve upon this.

[0281] In some embodiments, the performance of the proposed scheme associated with the sampling period Ts can be further improved by including a longer sampling period Ts to reduce random noise. For example, refer to Figure 7 The sensing steps, performed in procedures (14)-(16) within a single sensing cycle Tn, can be extended to multiple sensing cycles Tn to extract more than one (e.g., an integer K between 2 and 10) processed signal Sp. These processed signals Sp are generated individually for the same part of finger 101 and can be combined, for example by averaging, to reduce inherent random noise. Therefore, the signal-to-noise ratio of the averaged processed signal can be increased by a factor of the square root of K compared to the single processed signal Sp obtained in procedure (16).

[0282] While this disclosure has shown and described one or more embodiments, equivalent changes and modifications will occur to those skilled in the art upon reading and understanding this specification and the accompanying drawings. This disclosure encompasses all such modifications and variations and is limited only by the scope of the following claims.

Claims

1. A sensing device comprising: A biometric sensor, comprising: A substrate; and Multiple sensing electrodes are located above the substrate; An amplifier electrically coupled to the biometric sensor and configured to provide an output signal based on a touch event received by the biometric sensor; and An interface circuit is located between the amplifier and the plurality of sensing electrodes. The interface circuit includes a resistor, and the amplifier includes a first stage coupled to a second stage via a coupling capacitor. The second stage defines a transconductance, and the resistor has a resistance greater than 10 times the reciprocal of the transconductance.

2. The sensor device of claim 1, wherein the biometric sensor is a touch-sensitive biometric sensor.

3. The sensor device of claim 1, wherein the biometric sensor comprises a substrate made of glass, quartz or silicon oxide.

4. The sensor device of claim 1, wherein the device further comprises a display located below the biometric sensor, wherein the substrate is transparent to light emitted by the display.

5. The sensor device of claim 1, wherein the amplifier includes a non-inverting terminal and an inverting terminal, wherein the resistor is connected in series to the inverting terminal.

6. The sensor device of claim 1, wherein the interface circuit comprises: A current source is connected to the biometric sensor and the ground terminal; An amplifying capacitor coupled to the current source and the amplifier; and A first switch is coupled to the current source and the amplifying capacitor.

7. The sensing device of claim 6, further comprising a voltage buffer located between at least one of the plurality of sensing electrodes and the current source.

8. The sensor device of claim 6, wherein the first switch of the interface circuit is closed during a first sampling phase of a sensing step.

9. The sensor device of claim 8, wherein the interface circuit further includes a second switch, wherein the second switch includes a first terminal connected to a node located between the first switch and the amplifying capacitor.

10. The sensor device of claim 9, wherein during a second sampling phase of the sensing step, the first switch is turned on and the second switch is turned off.

11. The sensor device of claim 1, further comprising: A sensing control block configured to generate an initial sensing signal; and A signal transmission element electrically coupled to the sensing control block and configured to transmit a transmission sensing signal to a user based on the initial sensing signal according to the touch event.

12. The sensor device of claim 11, wherein the signal transmission element includes an outer frame located above the biometric sensor and configured to contact the user during the touch event.

13. The sensor device of claim 11, wherein the initial sensing signal has a plurality of sensing cycles, wherein each plurality of sensing cycles includes a first sampling cycle that alternates with a second sampling cycle, wherein the initial sensing signal has a waveform including a rising edge and a falling edge, corresponding to the start time of the first sampling cycle and the second sampling cycle, respectively.

14. The sensor device of claim 13, wherein the sensing control block is configured to continuously generate a first sensing signal and a second sensing signal for the same location of the user during the first sampling period and the second sampling period.

15. The sensor device of claim 14, further comprising a processor configured to generate a processing signal by subtracting the second sensing signal from the first sensing signal.

16. The sensor device of claim 1, further comprising an analog-to-digital converter configured to convert the output signal into a digital signal.

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