JP6651522B2 - Capacitive fingerprint sensing device with sensing element demodulation circuit configuration - Google Patents

Description

  The present invention relates to a capacitive fingerprint sensing system and a fingerprint pattern sensing method.

  Various types of biometric authentication systems are increasingly being used to enhance security and / or increase user convenience.

  In particular, fingerprint sensing systems are employed, for example, in home appliances due to their small form factor, high performance and user acceptance.

  Of the various available fingerprint sensing principles (such as capacitive, optical, thermal, etc.), capacitive sensing is the most commonly used, especially for size and power consumption. It is used for the application example which is a serious problem.

  Every capacitive fingerprint sensor provides a measure of the capacitance between each of a number of sensing structures and a finger resting on or across the surface of the fingerprint sensor.

  Some capacitive fingerprint sensors passively read the capacitance between the sensing structure and the finger. However, this requires a relatively large capacitance between the sensing structure and the finger. For this reason, such passive capacitance sensors generally comprise a very thin protective layer over the sensing structure. This makes such sensors somewhat sensitive to scratches and / or ESD (electrostatic discharge).

  U.S. Pat. No. 7,864,992 discloses a fingerprint sensing system in which a drive signal is injected into a finger by pulsing a conductive structure located in the vicinity of the sensor array and measuring the resulting change in charge carried by the sensing structure of the sensor array. Disclose.

  Such an active fingerprint sensing system generally allows measurement of the capacitance between a finger and each of the sensing structures with a significantly higher signal-to-noise ratio than the passive systems described above. Second, this allows the protective coating to be significantly thicker, so that more robust capacitive fingerprint sensors can be incorporated into items such as mobile phones that are subject to significant wear.

  However, there is still room for improvement. In particular, it would be desirable to further improve performance in terms of sensing fingerprints and / or signal-to-noise ratio through an even thicker protective coating.

  In view of the drawbacks of the prior art, including the above drawbacks, it is an object of the present invention to provide an improved capacitive fingerprint sensing device, and in particular, a capacitive fingerprint sensing device with improved sensing performance through a very thick protective coating. It is.

  Thus, according to a first aspect of the present invention, there is provided a capacitive fingerprint sensing system for sensing a fingerprint pattern of a finger. The capacitive fingerprint sensing system includes an excitation that provides an excitation signal indicative of a time-varying excitation potential that includes a cycling change from a first potential to a second potential with respect to the finger potential and back to the first potential. A signal supply circuitry, a plurality of sensing elements, each of which is a protective dielectric top layer to be contacted by a finger, and a conductive sensing structure disposed below the top layer, wherein the sensing structure comprises an excitation In a conductive sensing structure coupled to a signal supply circuitry and exhibiting a temporally varying sensing structure potential substantially following an excitation potential, a change in the excitation potential from a first potential to a second potential is a finger. A conductive sensing structure, connected to the sensing structure, which causes a change in the potential difference between the sensing structure and the change in the charge carried by the sensing structure due to the change in the potential difference between the finger and the sensing structure. A sensing circuit for supplying a sensing signal A demodulation circuitry coupled to the sensing circuitry for coupling the sensing signal to a demodulation signal related in timing to the excitation signal to provide a combined signal including a DC signal component indicative of a change in charge carried by the sensing structure; And readout circuitry coupled to each of the sensing elements for providing an indication of a fingerprint pattern based on a DC signal component from each of the sensing elements. .

  In the context of the present application, the term “potential” should be understood to mean “field strength at any point”.

  Therefore, the potential that changes over time is understood to mean a potential that has a magnitude that changes over time with respect to the reference potential. The temporally varying excitation potential may be provided, for example, as a pulse train having one pulse repetition frequency or a combination of various pulse repetition frequencies. Various pulses of such a pulse train may be, for example, rectangular wave pulses. Alternatively, the temporally varying excitation potential may be provided as a single sine wave or a combination of various sine waves.

  The sensing elements may be advantageously arranged in an array of rows and columns.

  Each sensing structure is a type of parallel plate capacitor that includes a sensing structure (sensing plate), a portion of the finger surface, and a protective coating (and between the portion of the finger surface and the protective coating depending on the location of the fingerprint pattern). May be advantageously provided in the form of a metal plate, as formed by any air which may be partially present in the air. The change in charge carried by the sensing structure resulting from the change in the potential difference between the finger and the sensing structure is an indication of the capacitance of the parallel plate capacitor, which in turn is the distance between the sensing structure and the finger surface. Is displayed.

  The protective coating may advantageously have a thickness of at least 20 μm and a high dielectric strength that protects the underlying structure of the fingerprint sensing device from wear and tear as well as from ESD. Even more advantageously, the protective coating may be at least 50 μm thick. In embodiments, the protective coating may be several hundred μm thick.

  Each sensing element may be controllable to perform a predetermined measurement sequence that spans a transition between different measurement states in a predetermined order. The measurement state may be defined by a particular combination of control signals supplied to circuitry included in the sensing element.

  The excitation signal supply circuitry may include a switching circuitry configured to switch between two or more different potentials on different lines. Alternatively or additionally, the excitation signal supply circuitry may include at least one signal source configured to provide a time-varying excitation potential.

  The excitation signal supply circuit configuration may be included in the fingerprint sensor component and, as a result, supply an excitation signal having an excitation potential that varies with respect to a reference potential of the fingerprint sensor component, for example, a sensor ground potential.

  Alternatively, the excitation signal supply circuitry is provided external to the fingerprint sensor component and is connected to the fingerprint sensor component to provide an excitation signal as a time-varying reference potential for the fingerprint sensor component. In this case, the excitation signal may represent an excitation potential that changes over time with respect to the device ground potential of the electronic device including the fingerprint sensing system. The external excitation signal supply circuit configuration may be controlled using a control signal generated by a timing circuit configuration included in the fingerprint sensor component.

  The time-varying sensing structure potential substantially follows the excitation potential when a change in the excitation potential results in a corresponding change in the sensing structure potential. The change in the sensing structure potential need not be exactly the same as the change in the excitation potential, but some delays may occur depending on the nature of the connection between the excitation signal supply circuitry and the sensing structure. In addition, there may be a potential shift between the excitation potential and the sensing structure potential, and some scaling may occur. However, the overall behavior of the excitation potential needs to be reflected in the sensing structure potential.

  The fact that the demodulated signal is timing related to the excitation signal means that the timing of the change from the first potential of the excitation signal to the second potential and / or the second potential to the first potential is the timing of the demodulated signal. It should be understood that this means that the timing of the potential change will be determined.

  In some embodiments, the demodulated signal may be a short pulse defining a sampling event. In other embodiments, the excitation signal itself may constitute the demodulated signal.

  The present invention, when speeding up the operation of the sensing elements, performs multiple reads from each sensing element during a single sensing event to obtain a measurement indicative of the local distance between the sensing element and the finger surface. It is based on the realization that it will be possible. This will, in turn, improve the sensing performance in terms of signal to noise ratio and common mode noise reduction, for example.

  The inventor has determined that the desired information content of the sensing signal (the aforementioned change in charge carried by the sensing structure) is indicated by a DC signal or a signal close to the DC signal (a constant voltage with respect to the reference potential of the fingerprint sensing system). It is understood that by at least partially demodulating the sensing signal localized within the sensing element, a desired speed up of operation of the sensing element can be achieved without causing a corresponding increase in power consumption.

  By outputting from each sensing element a change in charge that the sensing structure takes as a DC signal component, there is no need to move the potential read line up and down with respect to the parasitic capacitance of the read line, and energy consumption per read event is reduced. It will be greatly reduced.

  Thus, in embodiments of the present invention, the readout frequency can be increased without a corresponding increase in energy consumption, and thus the sensing performance, and the multiple output signals can be interlocked using a filtering method known per se. By allowing more coupling, common mode noise can be reduced and the signal-to-noise ratio can be increased.

  This allows measurements through thicker dielectric coatings, such as control buttons or parts of covers of electronic devices such as cell phones. In addition, the energy consumption of the fingerprint sensor and / or the time required to acquire a fingerprint display (image) may be potentially reduced.

  In embodiments, the readout circuitry may be configured to provide a temporal average or sum of several reads of a particular sensing element or group of sensing elements. In other embodiments, the readout circuitry may be configured to receive the combined signals from multiple sensing elements (either sequentially or substantially simultaneously). This allows a spatial average to be formed, which may be useful, for example, for noise cancellation and / or gain control.

  In various embodiments of the fingerprint sensing system of the present invention, the sensing circuitry may advantageously include a charge amplifier. The charge amplifier has a first input connected to the sensing structure, a second input connected to the excitation signal supply circuitry, an output for providing a sense signal, and a first input connected to the output. And at least one amplifier stage between first and second inputs and the output. The charge amplifier is configured such that the potential at the first input substantially tracks the potential at the second input.

  The charge amplifier converts the charge at the first input to a voltage at the output. The gain of the charge amplifier is determined by the capacitance of the feedback capacitor.

  The charge amplifier is configured such that the potential at the first input (sometimes referred to as the negative input) substantially follows the potential at the second input (sometimes referred to as the positive input). That should be understood to mean that a change in the potential at the second input results in a substantially corresponding change in the potential at the first input. Depending on the actual configuration of the charge amplifier, the potential at the first input may be substantially the same as the potential at the second input, or between the second input and the first input. A substantially constant potential difference may occur. As an example, if the charge amplifier is configured as a one-stage amplifier, the potential difference will be the gate-source voltage of the sense transistor.

  The output of the charge amplifier does not need to be directly connected to the feedback capacitor, and an additional circuit configuration may be provided between the output and the feedback capacitor. This circuitry could be located outside the array of sensing elements.

  According to the embodiment, the demodulation circuit configuration may include a signal multiplication circuit configuration that multiplies the sensing signal together with the demodulation signal.

  By multiplying the sensing and demodulation signals, the change in charge carried by the sensing structure can be mathematically separated as a desired DC signal component, facilitating signal transport and processing in a fingerprint sensing system. Becomes possible.

  The signal multiplying circuit configuration may be any circuit configuration that can multiply both instantaneous voltages of two signals (a sensing signal and a demodulated signal) and generate an output signal at each instant.

  Examples of signal multiplying circuit configurations include different types of mixers, such as multiplier mixers or switching mixers.

  Alternatively, the correlated double sampling sampler may be mathematically considered as a signal multiplying circuit configuration for multiplying the demodulated signal having a negative pulse and a positive pulse together with the sensing signal.

  The demodulation circuit configuration may further include a low-pass filter that allows a DC signal component to pass while removing a frequency component whose frequency has been increased. Alternatively or additionally, a low-pass filter may be provided outside the sensing element for low-pass filtering the combined signal output by the sensing element. The low-pass filter may be included in the readout circuit configuration.

  In various embodiments, the read lines interconnecting the sensing element and the read circuitry are between adjacent read lines and between the read lines and other components of the fingerprint sensor component, such as ground terminals and / or supply voltage rails. It may operate as a low-pass filter because of the parasitic capacitance between them.

  Each sensing element is configured to provide a maximum output current of less than 10 μΑ so that the read lines and their associated parasitic capacitance can operate as a suitable low pass filter for the combined signal provided by the sensing element. May be done.

  For a typical CMOS design that produces an output parasitic capacitance of approximately 1-10 pF and a read frequency of approximately 10-100 MHz from each sensing element, if the maximum output current is less than 10 μΑ, then one One or more readout lines would be able to function as (part of) the low pass filter.

  As a result, the frequency component having a high frequency can be sufficiently attenuated between each sensing element and the read circuit configuration, and only the desired DC signal component substantially remains in the read circuit configuration. This simplifies fingerprint sensor design and lowers energy consumption.

  According to various embodiments, the amplifier stage included in the charge amplifier may include a sense transistor having a gate forming a first input. The sense transistor may be formed in a well of a semiconductor substrate, and an interface between the well and the substrate is configured to prevent a current from flowing between the well and the substrate. Further, the excitation signal supply circuit configuration is connected to the well, and the difference between the third potential and the fourth potential is substantially equal to the difference between the first potential and the second potential. Under the same condition, the potential of the well may be changed from the third potential to the fourth potential, thereby reducing the influence of the parasitic capacitance between the sensing structure and the well.

  The semiconductor substrate may advantageously be a doped semiconductor substrate, and the well may be part of a substrate doped with the opposite polarity to the semiconductor substrate (if the semiconductor substrate is p-doped, the well may be (The well may be p-doped if the semiconductor substrate is n-doped). This is one way to achieve an interface between the well and a substrate configured to prevent current flow between the well and the substrate. In particular, the well and the substrate may be maintained at such a potential that no current flows through a diode formed at the interface between the substrate and the well.

  Alternatively, an insulating layer may be provided between the substrate and the well, for example in the form of a thin layer of glass. Such an insulating layer would also prevent current from flowing between the well and the substrate.

  In an embodiment of the present invention, the effect of parasitic capacitance between the sensing structure of the fingerprint sensing device and the semiconductor structure is such that the excitation signal supply circuit is configured to change the potential of the well in which the sense transistor of the charge amplifier is formed. The provision of the configuration can greatly reduce the number of components. Thereby, the potential of the well, which is the semiconductor structure adjacent to the connection between the sensing structure and the sense transistor (the input stage of the charge amplifier), is controlled to follow the potential of the sensing structure, and the potential of the sensing structure and the finger is controlled. At least at the time associated with the measurement of the capacitance between, the potential difference between the well and the sensing structure can be kept substantially constant.

  According to various embodiments, the fingerprint sensing device may further include a shielding structure disposed between the sensing structure and the substrate. The excitation signal supply circuitry is further connected to the shielding structure, wherein a difference between the fifth potential and the sixth potential is substantially equal to the difference between the first potential and the second potential. In the state, the potential of the shielding structure may be changed from the fifth potential to the sixth potential.

  This allows the sensing structure to benefit from other components that may be located beneath the sensing element, such as connection lines in the metal layer and / or connection lines formed in the semiconductor substrate and / or semiconductor circuitry. May be shielded. This will further reduce the effect of the parasitic capacitance of the sensing element.

  The fifth potential may be advantageously equal to the third (and / or first) potential described above, and the sixth potential may be advantageously equal to the fourth (and / or second) potential described above. Good. For example, the shielding structure (plate) may advantageously be conductively connected directly to the well.

  According to a first set of embodiments, the sense transistors may be NMOS or PMOS transistors and the wells may be p-wells or n-wells.

  According to a second set of embodiments, p-wells and / or n-wells may be formed in wells connected to the excitation signal supply circuitry. If at least one p-well and at least one n-well are formed in a well, this well may be called an iso well.

  Further, the well may be common to multiple sensing elements. By way of example, the well may be an iso well surrounding the n-well and p-well of some sensing elements. The excitation signal supply circuit configuration is connected to the iso well, connected to one (or a plurality of) iso wells formed inside the well, and one (or a plurality of) formed inside the iso well and the iso well. Is configured to change the voltage of the well.

  According to various embodiments, each of the sensing elements is a timing circuit configuration and is connected to the excitation signal supply circuit configuration to provide a first excitation control signal to the excitation signal supply circuit configuration, Causing a first change in the potential difference between the finger and the sensing structure at the excitation transition time of the excitation and providing a second excitation control signal to the excitation signal supply circuitry, and the finger at the second excitation transition time. Timing circuitry may be provided to cause a second change in potential difference between the sensing structure.

  According to various embodiments, further, each of the sensing elements is connected to a reset circuit configuration that is controllable to discharge a feedback capacitor, and a reset state and a feedback state where the feedback capacitor is discharged. A timing circuit for controlling the reset circuit configuration between a time when the capacitor is charged and a change in the charge carried by the sensing structure is enabled to be measured.

  By locally providing a timing circuit configuration within each sensing element or group of sensing elements, at least part of the timing control of the circuit configuration included in the sensing element or group of sensing elements is locally controlled by each sensing element or group of sensing elements. May be controlled.

  Thus, it can be said that the timing circuitry functions as a local state machine, which may be asynchronous or synchronous or a combination thereof.

  By localizing the timing of at least one (or more) of the most urgent transitions between measurement states, the time available for measurement can be increased (for any read frequency) and / or capacitive Or to facilitate the design of a fingerprint sensing device. By way of example, it may not be necessary to carefully route certain timing control signals to each sensing element, but timing may be initiated by an external signal that selects a particular sensing element or group of sensing elements. .

  Thus, such an embodiment of the present invention can increase the readout frequency, and thus improve the measurement performance, and further by allowing (eg, via filtering) the coupling of multiple output signals, Reducing common-mode noise and increasing the signal-to-noise ratio further facilitates the realization.

  The timing circuitry is configured to control the sensing element to transition from the first measurement state to the second measurement state at a transition time defined by a first event and a time delay for the first event. A delay element may be advantageously provided. The first delay element has an input for receiving a first signal defining a first event, and an output for providing a second signal defining a transition from a first measurement state to a second measurement state. And

  The first signal may be a time-varying voltage, and the first event may be defined by, for example, a rising or falling surface of the first signal.

  The first signal may be generated internally to the sensing element, or, according to various embodiments, generated externally to the sensing element and provided as a signal, which may be referred to as an activation signal or a selection signal, or the like. May be done.

  The second signal may be a delayed version of the first signal. However, it should be understood that transformations other than delay may be applied to the first signal to form the second signal. By way of example, the first signal may be additionally amplified and / or attenuated and / or inverted to form a second signal.

  The first delay element may advantageously comprise a semiconductor circuit configuration such as one or more logic gates.

  A capacitive fingerprint sensing system according to various embodiments of the present invention may be advantageously included in an electronic device. The electronic device is a processing circuit configuration, wherein the electronic device obtains a display of the fingerprint pattern from the fingerprint sensing device, authenticates the user based on the display, and performs at least one user request process only when the user is authenticated based on the display. May be further provided. The electronic device may be, for example, a portable communication device such as a mobile phone or tablet, a computer, or a wearable electronic component such as a watch or similar device.

  According to a second aspect of the present invention, there is provided a method for sensing a fingerprint pattern of a finger using a capacitive fingerprint sensing system including an excitation signal supply circuit configuration and a plurality of sensing elements. Each sensing element is connected to the sensing structure and a change in potential difference between the finger and the sensing structure. Providing a sensing signal indicative of a change in charge carried by the sensing structure due to the sensing circuitry. The method includes using an excitation signal supply circuitry to provide an excitation signal to a finger and / or a sensing structure to provide a time-varying potential difference between the finger and the sensing structure. Providing a demodulated signal that is timing related to the excitation signal by the system and combining the demodulated signal and the sense signal by the fingerprint sensing system to include a DC signal component indicative of a change in charge carried by the sensing structure. Supplying a fingerprint pattern based on DC signal components from each of the sensing elements using a readout circuit configuration external to the sensing elements.

  Effects obtained from the other embodiments of the present invention and the second aspect of the present invention are largely similar to those described above for the first aspect of the present invention.

  In summary, the present invention relates to a capacitive fingerprint sensing system comprising an excitation signal supply circuit configuration and a plurality of sensing elements. Each sensing element is a protective dielectric top layer and a conductive sensing structure coupled to the excitation signal, the sensing element exhibiting a change in charge carried by the sensing structure due to a change in potential difference between the finger and the sensing structure. A conductive sensing structure for providing a signal; and a DC signal component coupled to the sensing circuitry and coupled to the sensing signal and the demodulated signal timingly related to the excitation signal to indicate a change in charge carried by the sensing structure. And a demodulation circuit configuration for supplying a combined signal. The fingerprint sensing system further comprises readout circuitry connected to each of the sensing elements for providing an indication of the fingerprint pattern based on a DC signal component from each of the sensing elements.

Aspects of the present invention, including those described above, are described in further detail below with reference to the accompanying drawings, which illustrate exemplary embodiments of the present invention. here,
FIG. 1 is a schematic diagram of a mobile phone having a fingerprint sensing system. FIG. 2 is a schematic diagram of the fingerprint sensing system of FIG. FIG. 3 is a circuit diagram illustrating the configuration of the sensing element and the transfer of the sensing signal from the sensing element to the readout circuitry, and illustrates one example of the fingerprint sensing system of FIG. It is a schematic sectional drawing of a part. FIG. 4a is a schematic cross-sectional view of a portion of the fingerprint sensing system of FIG. 2 illustrating a first embodiment of the fingerprint sensing system of the present invention. FIG. 4B is a circuit diagram of an example of a demodulation circuit configuration used in the fingerprint sensing device of FIG. 4A. 5a-b are schematic diagrams of a sensing element included in a sensing system according to a second embodiment of the present invention. 5a-b are schematic diagrams of a sensing element included in a sensing system according to a second embodiment of the present invention. FIG. 6 is a schematic circuit diagram of a part of the sensing element shown in FIG. 5b, including a sensing circuit configuration and a demodulation circuit configuration. FIG. 7 is a timing diagram illustrating an example of a measurement sequence for the capacitive fingerprint sensing system of FIG. FIG. 8 is a schematic diagram of an example of a timing circuit configuration for controlling the timing of a measurement sequence executed by the sensing element of FIG. FIG. 9 is a circuit diagram of a delay element included in the timing circuit configuration of FIG. 10a-b are schematic diagrams of a third embodiment of the fingerprint sensing system of the present invention. 10a-b are schematic diagrams of a third embodiment of the fingerprint sensing system of the present invention. FIG. 11 is a schematic diagram of an embodiment in which the excitation signal supply circuit configuration is arranged and configured to raise or lower the reference potential of the fingerprint sensor element.

  In the detailed description, various embodiments of the fingerprint sensing device and the fingerprint sensing method according to the present invention will be mainly described with reference to the capacitive fingerprint sensing device. In this capacitive fingerprint sensing device, each sensing element comprises an excitation signal supply circuit configuration for supplying an excitation signal or a drive signal to the sensing structure. Further, the capacitive fingerprint sensing device is illustrated as a touch sensor sized and configured to obtain a fingerprint display from a stationary finger.

  Note that this does not limit the scope of the present invention in any way, for example, a change in the potential difference between the finger potential and the sensing structure potential may cause the fingerprint sensor component to fail relative to the reference potential of an electronic system including the fingerprint sensing system. It equally well includes a capacitive fingerprint sensing system that is instead provided by controlling a reference potential, such as a local ground level. Other sensor array configurations, such as so-called swipe sensors (or line sensors), for obtaining a fingerprint display from a moving finger are also within the scope of the present invention, as defined in the appended claims. Further, the touch sensor may have dimensions other than those illustrated in the accompanying drawings.

  FIG. 1 schematically shows an application example of a fingerprint sensing device according to an exemplary embodiment of the present invention in the form of a mobile phone 1 in which a fingerprint sensing device 2 is incorporated. The fingerprint sensing device 2 may be used, for example, to unlock the mobile phone 1 and / or authenticate a process performed using the mobile phone.

  FIG. 2 schematically shows a fingerprint sensing device 2 included in the mobile phone 1 of FIG. As shown in FIG. 2, the fingerprint sensing device 2 includes a sensor array 5, a power supply interface 6, and a communication interface 7. The sensor array 5 includes a large number of sensing elements 8 (only one sensing element is shown with a reference number to avoid cluttering the drawing). Each of the sensing elements 8 is controllable to sense a distance between a sensing structure (top plate) included in the sensing element 8 and a surface of a finger that contacts an upper surface of the sensor array 5.

The power supply interface 6 comprises a first contact pad 10a and a second contact pad 10b, here shown as adhesive pads, connecting the supply voltage V _supply to the fingerprint sensor 2.

  The communication interface 7 includes a number of adhesive pads that enable control of the fingerprint sensor 2 and obtain fingerprint data from the fingerprint sensor 2.

  FIG. 3 is a schematic cross-sectional view of a part of a fingerprint sensing system according to the prior art, taken along line A-A ′ of FIG. 2, wherein a finger 11 is placed on the upper surface of the sensor array 5. The fingerprint sensing system comprises a plurality of sensing elements 8, each sensing element 8 comprising a protective dielectric top layer 13, a conductive sensing structure here in the form of a metal plate 17 under the protection dielectric top layer 13, and a charge amplifier 18. And a selection circuit configuration, here functionally illustrated as a simple selection switch 21 enabling selection / activation of the sensing element 8, and an excitation for supplying an excitation signal to the finger as schematically illustrated in FIG. And a signal supply circuit configuration 19.

  Charge amplifier 18 has a first input (negative input) 25 connected to sensing structure 17, a second input (positive input) 26 connected to excitation signal supply circuitry 19, and an output 27. It comprises at least one amplifier stage, schematically shown here as an operational amplifier (op-amp) 24 having Furthermore, the charge amplifier 18 comprises a feedback capacitor 29 connected between the first input 25 and the output 27, and a reset circuit, functionally shown here as a switch 30, enabling control of the discharge of the feedback capacitor 29. And a configuration. Charge amplifier 18 may be reset by operating reset circuitry 30 so that feedback capacitor 29 discharges.

  As is common with op amps 24, the voltage at first input 25 tracks the voltage applied to second input 26. Depending on the particular amplifier configuration, the potential at the first input 25 is substantially the same as the potential at the second input 26, or the potential at the first input 25 and the potential at the second input 26. And there may be a substantially fixed offset between them.

  By providing the finger 11 with a time-varying potential, a time-varying potential difference is created between the sensing structure 17 and the finger 11.

As described below in more detail, by the potential difference of the change between the reference structure 17 and the finger 11, the sensing signal V _s is produced at the output 27 of the charge amplifier 18.

  When the indicated sensing element 8 is selected for sensing, the select switch 21 is closed and connects the output of the charge amplifier to the readout line 33. A read line 33, which may be a common read line for a row or column of the sensor array 5 of FIG. 2, is shown in FIG. As shown schematically in FIG. 3, an additional readout line for emitting a sense signal from another row / column of the sensor array 5 is also connected to the multiplexer 36.

The sensing signal V _s from the sensing element 8 is demodulated by a sample and hold circuitry 37 arranged outside the array of sensing elements. The output of the sample and hold circuitry 37 is connected to an analog to digital converter 38 that converts the analog DC voltage signal output by the sample and hold circuitry to a digital representation of the fingerprint pattern of the finger 11.

As shown schematically in Figure 3, there is a parasitic capacitance C _p between the read line 33 and the ground terminal. When transmitting along the read line 33 the sensing signal V _s, is required constant current to raise and lower the potential to parasitic capacitance C _p and drives the read line 33. This current is frequency dependent. Using a read frequency of approximately 1 MHz used in known capacitive fingerprint sensing devices, the sensing device is appropriately designed such that the parasitic capacitance of the read line is approximately 1 pF in power consumption. If so, it is considered acceptable. However, when the read frequency is greatly increased above about 20MHz, the power consumption by the parasitic capacitance C _p would be substantial.

  In various embodiments of the present invention, the read frequency can be increased without increasing the current consumption due to the parasitic capacitance of the read line 33.

  Here, a first embodiment of the fingerprint sensing system of the present invention will be described with reference to FIGS. 4A and 4B.

  The fingerprint sensing system of FIG. 4 a further comprises the point that the excitation signal supply circuit 19 is connected to the sensing structure 17, and that each sensing element comprises a demodulation circuit arrangement in the form of a demodulator 31 here and a demodulation signal supply circuit arrangement 32. It differs from that described with reference to FIG. 3 mainly in that it is provided.

  The state in which the finger 11 is "grounded" is shown schematically in FIG. 4a. It should be understood that finger "ground" may be different from sensor ground. As an example, the finger may be at the ground potential of an electronic device that includes a capacitive fingerprint sensing system. Alternatively, the body can be considered to have an electrical "mass" that is so large that the potential of the finger remains substantially constant as the potential of the reference structure 17 changes.

The demodulation signal supply circuit configuration 32 is connected to the excitation signal supply circuit configuration 19 and supplies a demodulation signal based on the excitation signal output by the excitation signal supply circuit configuration. Demodulated signal is associated with the excitation signal with respect to timing, associated with respect to the timing to the sensing signal V _s output by thus charge amplifier 18.

  The demodulator 31 is connected to the output 27 of the charge amplifier 18 and the demodulated signal supply circuitry 32 to couple the sensed signal to the demodulated signal and to determine the magnitude of the potential difference between the potential of the finger 11 and the potential of the sensing structure 17. The sensing structure 17 emits a combined signal that includes a DC signal component indicative of the above-described changes in the charge carried by the overlapping changes due to the overlapping changes.

In some embodiments, it may not require any demodulation signal supply circuitry 32, the excitation signal may be supplied directly to the demodulator 31 for coupling the sensing signal V _s. In other embodiments, the demodulated signal supply circuitry may generate one or several demodulated signals having a timing relationship to the excitation signal. An example of a demodulation signal supply circuit configuration 32 in the form of a timing circuit configuration for generating a sampling control signal for a demodulator in the form of a double sampler will be described below with reference to FIGS. 5a, 5b, 6, 6, 7 and 8. This will be further described below.

  Depending on the configuration of the sensing element 8 and the waveform of the excitation signal, the demodulator 31 may be implemented in various ways known to those skilled in the art. In principle, any suitable mixer or demodulator developed for AM demodulation may be adapted for use in the sensing element of the fingerprint sensing system according to the invention.

FIG. 4b shows a first input 35 for receiving the sensing signal V _s , a second input 37 for receiving the excitation signal from the excitation signal supply circuitry 19, and the change in charge carried by the sensing structure 17 and thus the sensing. FIG. 3 is a circuit diagram of a simple demodulation circuit arrangement (mixer) 31 having an output 38 that produces a combined signal including a DC signal component indicating the (electrical) distance between the structure 17 and the finger 11.

  5a and 5b schematically show a sensing element 8 included in a capacitive fingerprint sensing system 2 according to a second embodiment of the present invention.

  Referring first to FIG. 5a, one sensing element 8 from the sensor array 5 of FIG. 2 is shown, along with the surrounding elements. One (or more) sensing element 8 for sensing capacitive coupling between the sensing structure and the finger 31 receives activation signals from the row selection circuit configuration and the column selection circuit configuration. And may be selected using the Such activation signals are shown in FIG. 5a as R-ACT and C-ACT.

  Referring to FIG. 5b, each sensing element 8 of the capacitive fingerprint sensing system 2 includes a sensing circuitry 50 (such as the charge amplifier 18, excitation signal supply circuitry 19 and demodulator 31 of FIG. 4) and a timing circuitry. 51.

  The sensing circuitry 50 is connected to the sensing structure (plate) 17 and measures the change in the charge carried by the sensing structure 17 due to the change in the potential difference between the finger 11 and the sensing structure 17. This measurement is performed by executing a measurement sequence that includes a transition through a series of measurement states. One example of the measurement sequence is described in more detail below with reference to FIGS. The sensing circuitry 50 has an output that emits the above combined signal provided by the demodulator to the readout line 33.

  Timing circuitry 51 is connected to sensing circuitry 50 and controls at least one timing of the measurement state.

  The timing circuitry 51 may receive one or several control signals that trigger the measuring operation of the sensing element 8, as schematically illustrated in FIG. 5b. As an example, the row activation signal R-ACT and the column activation signal C-ACT described above may be received by the timing circuitry 51. Thereafter, timing circuitry 51 may independently supply various timing control signals to charge measurement circuitry 50, as schematically indicated by the arrows in FIG. 5b.

  Through this local control of at least one timing of the measurement states involved in the measurement sequence, the timing of the transitions between the measurement states is controlled more precisely and / or uniformly, so that the time between the transitions is further reduced. This has the effect of increasing the measurement frequency.

  An example of the sensing circuitry 50 of FIG. 5b is shown in more detail in FIG. The control signals (start signal ACT, reset signal RST, drive control signal DRV, first sampling control signal S1 and second sampling control signal S2) generated by the timing circuit configuration 51 are shown by arrows in FIG.

  The sensing circuitry 50 of FIG. 6 includes the charge amplifier 18, an excitation signal supply circuitry represented here by the controllable power supply 19, and a demodulator in the form of a sample and hold circuitry 74.

  As described above for sensing element 8 of FIG. 3, the charge amplifier of sensing circuitry 50 of FIG. 6 includes a negative input 25, a positive input 26, an output 27, a feedback capacitor 29, and an amplifier 24.

  Negative input 25 is connected to sensing structure (plate) 17 and output 27 is connected to sample and hold circuitry 74 included in sensing element 8.

  Feedback capacitor 29 is connected between negative input 25 and output 27 and defines the amplification of charge amplifier 18. The sensing element 8 further comprises a reset switch 30 in parallel with the feedback capacitor 29.

  The positive input 26 is connected to the controllable power supply 19 rather than being directly grounded or connected to another reference potential.

  The sample and hold circuit configuration 74 includes a first sampling capacitor 75, a first sampling switch 76 and a first output 77, a second sampling capacitor 79, a second sampling switch 80, and a second output 81.

  Differential amplifier 82 has a positive input connected to first output 77 and a negative input connected to second output 81 of sample and hold circuitry 74. The output of the differential amplifier 82 is connected to the read line 33.

  FIG. 7 illustrates an exemplary measurement sequence for the sensing element 8 of FIG. By locally controlling the transitions between the measurement states in the measurement sequence within the sensing element 8, the measurement sequence illustrated in FIG. 7 or another suitable measurement sequence can be performed much faster, and even faster. Since reading and / or multiple readings from each sensing element are possible, measurement performance will be improved.

  Referring to FIG. 7, the timing diagram shown in the figure is, from top to bottom, a start signal ACT, a drive (excitation) control signal DRV, a reset signal RST, a first sampling control signal S1, and a second sampling control signal S1. A sampling control signal S2 is provided.

Below the timing diagram, the sequence of measurement states S ₀ -S ₉ that together form the above measurement sequence is schematically shown.

  To activate the sensing element 8 of FIG. 6, a row select signal and a column select signal indicative of the sense element 8 may typically be provided. In the simplified and schematic timing diagram of FIG. 7, such a selection signal is represented by a single activation signal ACT.

In t ₁ the first time, the sensing element 8 is activated by a low-to-high transition of the activation signal ACT. This may extend, for example, to the activation of the amplifier 39. At substantially the same point in time as time t ₁ , the drive (excitation) control signal DRV provided by the timing circuitry 51 to the excitation signal supply circuitry 19 is controlled from low to high.

Thus, at time t ₁ , a transition from the “pause” state S ₀ of the measurement sequence to the first measurement state S ₁ is seen.

When an excitation signal is applied to the sensing structure 17, the charge carried by the sensing structure 17 will change. After a lapse of a certain period of time at which the output of the charge amplifier can be stabilized, a reset signal RST is supplied at time t ₂ to close the reset switch 30, thereby discharging the feedback capacitor and causing the output of the charge amplifier 18 to output. The reference of the potential at 27 is the potential of the sensing structure (plate) 17.

By providing the first rising edge of the reset signal transitions from the first measurement state S ₁ to the second measurement state S ₂ (reset state).

The reset switch 30 is released (permitted to be opened again) at time t ₃ , thereby transiting to the third measurement state S ₃ (measurement ready state).

At time t ₄ , a transition to the fourth measurement state S ₄ is recognized. Here, the sample-and-hold circuit 41 is controlled so that the first sampling control signal S1 changes from low to high, and the sensing signal at the output 27 of the charge amplifier 18 is sampled.

At time t _5, the transition to the fifth measurement state S ₅ is observed, the first sampling control signal S1 is changed from high to low.

Next, at time t ₆ , the drive signal DRV changes from high to low, changing the potential difference between the finger 11 and the sensing structure 17. This is because, as shown schematically in Figure 7 is also a transition to a sixth measurement state S _6.

At time t _7, the transition to the seventh measurement state S ₇ is observed. Here, the second sampling control signal S2 changes from low to high, and controls the sample and hold circuit 74 to sample the sensing signal at the output 27 of the charge amplifier 18 twice.

At time t ₈ , there is a transition to the eighth measurement state S ₈ where the second sampling control signal S2 changes from high to low.

Finally, at time t _9, the transition to the ninth measurement state S ₉ can be seen. Here, the sensing element 8 is stopped and the drive signal DRV changes from low to high again. Ninth measurement state S ₉ is the same as the "dormant" state S ₀ of the initial.

  The charge measurement circuit configuration 50 includes the various control signals (the start signal ACT, the reset signal RST, the drive control signal DRV, the first sampling control signal S1, and the second sampling signal) as schematically indicated by arrows in FIG. The control signal S2) is controlled to execute the measurement sequence described above with reference to FIG. If the measurement sequence described with reference to FIG. 4 is being performed, the potential difference between the first output 77 and the second output 81 of the sample and hold circuit 74 will be between the sensing structure 17 and the finger 11. Will be shown. This potential difference is provided to the output line 33 via the differential amplifier 82.

  In the above exemplary embodiment, the demodulation circuitry is formed by the sample and hold circuit 74, and the DC signal component indicative of the change in charge couples the sense signal at the output 27 of the charge amplifier 18 to the sampling control signals S1 and S2. Provided by that. The sampling control signal is timing related to the excitation signal and is generated by a demodulation signal supply circuit configuration in the form of a timing circuit 51.

  Note that the circuit diagram of FIG. 6 is simplified in order to facilitate the description of the embodiment of the present invention. As an example, the level shift at the output of the sensing element 8 has been omitted. However, performing a level shift is easy for those skilled in the art. Further, a simple example of a level shifter is described below with reference to FIG.

  With reference to FIG. 8, an exemplary configuration of the timing circuit 51 of FIG. 5b will now be described. As shown in FIG. 6B, the timing circuit 51 includes a first AND gate 83, a first delay element 84, a second delay element 85, a second AND gate 86, a first inverter 87, a third delay The element 88, the fourth delay element 89, the third AND gate 90, the second inverter 91, the fifth delay element 92, the sixth delay element 93, the fourth AND gate 94, the third inverter 95, A seventh delay element 96, an eighth delay element 97, a fifth AND gate 98, and a fourth inverter 99 are provided.

  As schematically shown in FIG. 8, the row activation signal R-ACT and the column activation signal C-ACT are input to a first logical AND gate 83. Referring also to FIG. 6, the output of the first AND gate 83 is supplied to the amplifier 24 of the sensing circuit arrangement 50 as the above-mentioned activation signal ACT, and is supplied to the input of the first delay element 84, The signal is supplied to an AND gate 94. The output of the first delay element 84 is supplied to a second AND gate 86, and is supplied to the input of the second delay element 85. The output of the second delay element 85 is supplied to the second AND gate 86 via the first inverter 87 and to the input of the third delay element 88. The output of the third delay element 88 is supplied to the input of the third AND gate 90 and is supplied to the input of the fourth delay element 89. The output of the fourth delay element 89 is supplied to the third AND gate 90 via the second inverter 91, and is supplied to the input of the fifth delay element 92. The output of the fifth delay element 92 is provided to the input of a sixth delay element 93. The output of the sixth delay element 93 is supplied to the fourth AND gate 94 via the third inverter 95, and is supplied to the input of the seventh delay element 96. The output of the seventh delay element 96 is provided to the input of an eighth delay element 97 and the input of a fifth AND gate 98. Finally, the output of the eighth delay element 97 is provided via a fourth inverter 99 to the input of a fifth AND gate 98.

When the sensing element 8 comprising the sensing circuit arrangement 50 of FIG. 6 and the timing circuit 51 of FIG. 8 is selected by setting both the row activation signal R-ACT and the column activation signal C-ACT high, the activation for the sensing element 8 is performed. The signal ACT goes high (at time t ₁ in FIG. 7). The output from the first AND gate 83 passes through a first delay element 84 and is delayed by a first time delay ΔT ₁ to provide a first delayed version of the activation signal ACT to a second AND gate 86. I do.

The first time delay ΔT ₁ corresponds to t ₂ -t ₁ in FIG. 7 and defines the duration of the first measurement state S ₁ .

  Also, the output from the first delay element 84 is provided to the input of the second delay element 85 and is delayed to provide a second delayed version of the activation signal ACT.

  A second delayed version of the activation signal ACT is provided via a first inverter 87 to the input of a second AND gate 86, providing a reset control signal RST at the output of the second AND gate 86.

The second time delay ΔΤ ₂ corresponds to t ₃ -t ₂ in FIG. 7 and defines the duration of the second measurement state S ₂ (here the reset control signal RST is high).

  The rest of the timing circuit 51 operates in the same way, with the delay elements being configured such that the control signals shown in the timing diagram of FIG. 7 are achieved.

Therefore, the third time delay ΔΤ ₃ corresponds to t ₄ -t ₃ in FIG. 7 and defines the duration of the third measurement state S ₃ . The fourth time delay ΔΤ ₄ corresponds to t ₅ -t ₄ in FIG. 7 and defines the duration of the fourth measurement state S _{4 and the} like.

  The timing circuit 51 is a simplified example illustrating the operating principle of the combination of a delay element and a logic gate that locally controls the timing of the measurement state of the charge measurement circuit configuration included in the sensing element. . The timing circuitry may include additional or other circuitry for signal shaping and / or timing, etc., depending on the actual implementation. Those skilled in the art will be able to design a suitable implementation of the timing circuit without undue burden based on the description herein.

  It should be noted that, depending on the particular embodiment, fewer or additional timing control signals may be provided independently from timing circuitry 51 to sensing circuitry 50.

  FIG. 9 illustrates an illustrative example of a delay element 100 that may be included in the timing circuitry 51 of FIG.

  The delay element 100 includes a first CMOS inverter 101 and a second CMOS inverter 102 connected in series. Since the time delay of the delay element depends on the dimension setting of the components included in the delay element 100, it can be set when designing the delay element. If it is desired to further increase the delay time, additional CMOS inverters can be connected in series.

  Here, a third embodiment of the fingerprint sensing system 2 of FIG. 2 will be described with reference to FIGS. 10A and 10B. The embodiment of FIGS. 10a and 10b is intended to eliminate or at least greatly reduce the effect of the parasitic capacitance of the sensing element 8, thus facilitating the operation of the sensing element 8 at high frequencies.

  FIG. 10a shows an embodiment of the sensing element 8 of FIG. 2 formed on a doped semiconductor substrate, partially in a schematic configuration diagram and partially in a schematic circuit diagram. The protective dielectric layer 13, the sensing plate 17, the shielding plate 65, and the reference plate 66 are schematically shown in an exploded perspective view, while the charge amplifier 18 is shown in a transistor level circuit diagram.

  As shown in FIG. 10 a, this simple example of charge amplifier 18 includes a sense transistor 68, a cascode transistor 69, a reset circuit configuration in the form of a reset transistor 30, and a bias current source 71. The sense transistor 68, the cascode transistor 69, and the reset transistor 30 are all formed in the same well 73 (n-well, p-well, or iso-well).

The same schematic configuration is also shown at a more abstract level in FIG. 10b to aid in understanding the components and connections of FIG. 10a. Here, the transistor circuit arrangement of FIG. 10a comprises a negative input 25 connected to the sensing plate 17 and a positive input 26 connected to an excitation signal supply circuit 19, here in the form of a pulse generator, is replaced with a general symbol representing charge amplifier having an output 27 for emitting a sensing signal V _s indicating the changes occurring to the electric charge is sensed plate 17 tinged due to a change in potential difference between the 11 and the sensing plate 17 . As described above, the change in the potential difference between the finger 11 and the sensing plate 17 is caused by a change in the potential applied by the pulse generator 19 to the sensing plate 17 via the charge amplifier. The feedback capacitor formed by the sense plate 17 and the reference plate 66 is connected between the negative input 25 and the output 27 of the charge amplifier. The general functionality of a charge amplifier is well known to those skilled in the art. FIG. 10 b schematically shows the well 73 connected to the excitation signal supply circuit configuration 19.

  Returning to FIG. 10a, it can be seen that the gate of the sense transistor 68 comprises the negative input 25 of the charge amplifier and the source of the sense transistor 68 comprises the positive input 26 of the charge amplifier. The positive input 26 of the charge amplifier is connected to the shielding plate 65, and thus to the well 73 in which the sense transistor 68 is formed, and to the pulse generator 19.

  The sensing element 8 further includes a drive transistor 75, a drive control switch 76, and a reset control switch 77. The drive control switch 76 is controllable between a first state in which the gate of the drive transistor 75 is connected to the pulse generator 19 and a second state in which the gate of the drive transistor 75 is connected to the sensor ground. When the drive control switch 76 is in its first state, the drive transistor 75 will be energized and will connect the sensing structure 17 directly to the pulse generator 19. If the drive control switch is in its second state, drive transistor 75 will be in a de-energized state. Thus, in the latter case, there will not be a direct connection between the sensing structure 17 and the pulse generator 19 via the driving transistor 75. As shown in FIG. 10A, the driving transistor 75 is formed in the well 73. The bias current source 71 can be installed inside the sensing element or outside the sensor array 5.

  Similarly, the reset control switch 77 detects the first state in which the reset transistor 30 is in the non-conductive state and a potential difference occurs between the sensing plate 17 and the feedback plate 66, and the reset state in which the reset transistor 30 is in the conductive state. Control is possible between the potential of the plate 17 and a second state in which the potential of the feedback plate 66 is equal.

  Referring to FIG. 10a, the sensing element 8 further comprises a simple level shifter and a demodulation circuit configuration 31 in the form of a sampler as described above with reference to FIG.

  The level shifter comprises a transistor 105, a first register 106, and a second register 107, first converting the sensed signal at the output 27 of the charge amplifier into a current, which is then referenced to a sensor ground, here. It operates by returning to a voltage that does.

Through the configuration of the sensing element 8 of FIG. 10a, the effects of the internal parasitic capacitances C _p1 and C _p3 are eliminated or at least greatly reduced. Further, driving adjacent sensing structures will eliminate or at least greatly reduce the effects of parasitic capacitance between adjacent sensing plates.

  In the above exemplary embodiment of the present invention, the excitation signal supply circuitry 19 is illustrated as being included in a fingerprint sensing component. In the embodiments including the above embodiments, the excitation signal supply circuit configuration 19 included in the fingerprint sensing system is provided alternately outside the fingerprint sensor component, and the first signal supply circuit configuration 19 with respect to the potential of the finger 11 is used. The fingerprint sensor component (sensor ground) may be arranged and configured to raise and lower the reference potential of the fingerprint sensor component (sensor ground) between the potential and the second potential.

  This alternative of arranging the excitation signal supply circuitry 19 outside the fingerprint sensor component will now be briefly described with reference to FIG. FIG. 11 schematically shows a fingerprint sensing system 2 comprising a fingerprint sensor 4, a processing circuitry 125, here in the form of a microprocessor, and a power supply circuitry 126.

  The fingerprint sensor 4 includes the sensor array 5, the power supply interface 6, and the communication interface 7, as described above with reference to FIG. The communication interface 7 may be provided, for example, in the form of an SPI interface (serial peripheral device interface).

  The microprocessor 125 may acquire the fingerprint data from the fingerprint sensor 4 and process the fingerprint data according to the request of the application. By way of example, microprocessor 125 may execute a fingerprint verification (confirmation and / or identification) algorithm.

The power supply circuit configuration 126 includes a sensor power supply 127 configured to output a supply voltage V _supply and an excitation signal supply that modulates a low potential side of the sensor power supply 127 with respect to a reference potential DGND of the electronic device 1 including the fingerprint sensing system 2. And a circuit configuration (here, a rectangular wave pulse generator 19).

  The pulse generator may generate any other suitable pulse shape, such as a sine wave or sawtooth signal, as an alternative to a square wave signal.

  The sensor power supply 127 may be provided in the form of a constant voltage source such as a battery specialized for supplying power to the fingerprint sensor 4. Alternatively, the sensor power supply 127 may include a separation circuit configuration that at least partially separates the power supply from the fingerprint sensor 4.

The fingerprint sensing system 2 optionally includes an isolation circuit 129 that provides galvanic isolation or level shifting between the sensor array 5 and the microprocessor 125, as schematically illustrated by a box with a dotted border. May be included. By using the isolation circuit configuration 129, the microprocessor 125 can operate _{independently} of changing the reference potential _VL of the sensor array 5 with respect to the device ground (DGND).

  Isolation circuitry 129 can be implemented in many different ways known to those skilled in the art. By way of example, the isolation circuitry 129 may be implemented using components such as optocouplers, coils and / or capacitors. Although shown here as separate circuitry, it will be appreciated that the isolation circuitry 129 may be integral with the fingerprint sensor 4 or the microprocessor 125.

  Those skilled in the art understand that the present invention is in no way limited to the preferred embodiment described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

  In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other device may perform the functions of several features recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid state medium provided with or as a part of other hardware, but may also be stored on the Internet or via a wired or wireless electrical device. The distribution may be performed in another form such as through a communication system. Any reference signs in the claims shall not be construed as limiting the scope.

Claims (14)

A capacitive fingerprint sensing system for sensing a fingerprint pattern of a finger, wherein the capacitive fingerprint sensing system comprises:
An excitation signal supply circuit configuration that supplies an excitation signal indicating an excitation potential that changes with time, including a cyclic change returning from the first potential to the second potential with respect to the finger potential, and returning to the first potential,
A plurality of sensing elements, each of which is a protective dielectric top layer with which the finger contacts,
A conductive sensing structure disposed beneath said protective dielectric top layer, wherein the sensing structure is coupled to the excitation signal supply circuit arrangement, the sensing structure potential varying the perform additional follow in time to the excitation potential The conductive sensing structure shown, wherein each change in the excitation potential from the first potential to the second potential results in a change in a potential difference between the finger and the sensing structure;
A sensing circuit arrangement connected to the sensing structure for providing a sensing signal indicative of a change in charge carried by the sensing structure due to the change in the potential difference between the finger and the sensing structure;
Connected to the sensing circuitry, the sensing signal, and a demodulated signal timing related to the excitation signal in such a way that the timing of the change in potential of the excitation signal determines the timing of the change in potential of the demodulation signal. And a demodulation circuit arrangement for providing a combined signal comprising a DC signal component indicative of said change in charge carried by said sensing structure;
A plurality of sensing elements, including:
A readout circuitry connected to each of the sensing elements for providing an indication of the fingerprint pattern based on the DC signal component from each of the sensing elements;
A capacitive fingerprint sensing system comprising: The sensing circuit configuration includes:
A charge amplifier,
A first input connected to the sensing structure;
A second input connected to the excitation signal supply circuitry;
An output for providing the sensing signal;
A feedback capacitor connected between the first input and the output;
At least one amplifier stage between the first and second inputs and the output;
A charge amplifier comprising:
The charge amplifier is configured so that the potential at the first input is additionally follow the potential at the second input,
The capacitive fingerprint sensing system according to claim 1.   3. The capacitive fingerprint sensing system according to claim 1, wherein the demodulation circuit configuration includes a signal multiplication circuit configuration that multiplies the sensing signal together with the demodulation signal. 4.   4. The capacitive fingerprint according to claim 1, wherein the demodulation circuit configuration further includes a low-pass filter that allows the DC signal component to pass while removing a frequency component having a high frequency. 5. Sensing system.   The capacitive fingerprint sensing system according to any of the preceding claims, wherein each of the sensing elements is configured to provide a maximum output current of less than 10 μΑ.   6. The capacitive fingerprint sensing system according to claim 1, wherein the capacitive fingerprint sensing system includes a fingerprint sensor component including the plurality of sensing elements and the readout circuit configuration. 7.   7. The capacitive fingerprint sensing system of claim 6, wherein said fingerprint sensor component further comprises said excitation signal supply circuitry.   The excitation signal supply circuit configuration is disposed separately from the fingerprint sensor component, and supplies the excitation signal to a reference potential input of the fingerprint sensor component to set a reference potential for the fingerprint sensor component to the potential of the finger. 7. The capacitive fingerprint sensing system of claim 6, wherein the capacitive fingerprint sensing system is connected to the fingerprint sensor component for changing relative thereto. The amplifier stage included in the charge amplifier includes a sense transistor having a gate constituting the first input,
The sense transistor is formed in a well of a semiconductor substrate, and an interface between the well and the substrate is configured to prevent a current from flowing between the well and the substrate.
The excitation signal supply circuit configuration is connected to the well, changes the potential of the well from a third potential to a fourth potential, and the difference between the third potential and the fourth potential is the difference and equal properly between the first potential and said second potential, thereby to reduce the influence of parasitic capacitance between said sensing structure well,
The capacitive fingerprint sensing system according to claim 2 . Further comprising a shielding plate disposed between the sensing structure and the substrate,
The excitation signal supply circuit configuration is further connected to the shield plate, and configured to change the potential of the shield plate from a fifth potential to a sixth potential, wherein the fifth potential and the sixth potential correct equal the difference between the difference between said first potential and said second potential between,
The capacitive fingerprint sensing system according to claim 9. Each of the sensing elements is
A timing circuit configuration connected to the excitation signal supply circuit configuration,
Providing a first excitation control signal to the excitation signal supply circuitry to cause a first change in the potential difference at a first excitation transition time;
Supplying a second excitation control signal to the excitation signal supply circuitry to cause a second change in the potential difference at a second excitation transition time;
Timing circuit configuration,
The capacitive fingerprint sensing system according to any one of the preceding claims, comprising: Each of the sensing elements is
A reset circuit configuration that can be controlled to discharge the feedback capacitor,
Between a reset state, in which the feedback capacitor is discharged, connected to the reset circuitry, and a measurement ready state, in which the feedback capacitor is charged and the change in charge carried by the sensing structure is enabled. A timing circuit configuration for controlling the reset circuit configuration;
The capacitive fingerprint sensing system according to any one of claims 1 to 11, further comprising: The timing circuitry controls the sensing element to transition from a first measurement state to a second measurement state at a transition time defined by a first event and a time delay for the first event. Comprising a first delay element,
The first delay element provides an input for receiving a first signal defining the first event and a second signal defining the transition from a first measurement state to a second measurement state. Having an output and
A capacitive fingerprint sensing system according to claim 11 or claim 12. An electronic device,
14. A capacitive fingerprint sensing system according to any one of the preceding claims,
A processing circuit configuration,
Obtaining the indication of the fingerprint pattern from the capacitive fingerprint sensing system ;
Authenticate the user based on the display,
Perform at least one user request process only when the user is authenticated based on the display,
A processing circuit configuration configured as
An electronic device comprising:

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