WO2022230030A1

WO2022230030A1 - Capacitive sensor system and current conveyor for capacitive sensor system

Info

Publication number: WO2022230030A1
Application number: PCT/JP2021/016687
Authority: WO
Inventors: Steve NOALL; Brent Quist
Original assignee: Alps Alpine Co., Ltd.
Priority date: 2021-04-26
Filing date: 2021-04-26
Publication date: 2022-11-03
Also published as: KR20230161519A; JP2024518295A; DE112021007594T5; CN117043726A

Abstract

A capacitive sensor system includes a capacitive sensor and a current conveyor coupled to an output of the capacitive sensor. The current conveyor includes an input side including first and second transistors coupled to in input voltage, an output side including third and fourth transistors coupled to the capacitive sensor, a first capacitor coupled between a gate and a source of the third transistor, and a second capacitor coupled between a gate and a source of the fourth transistor.

Description

CAPACITIVE SENSOR SYSTEM AND CURRENT CONVEYOR FOR CAPACITIVE SENSOR SYSTEM

The present disclosure relates to capacitive sensors, and more particularly to a current conveyor for a capacitive sensor.

The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

An electronic device may implement a capacitive sensor configured to sense contact between an object (e.g., a finger) and a surface, such as a surface of the electronic device, and generate a sensed signal indicative of the sensed contact. For example, a reference signal generator (e.g., a waveform generator) is configured to generate and output a control signal to the capacitive sensor. In some examples, the control signal is sinusoidal (i.e., the control signal is a sine wave). The sensed signal corresponds to changes in an amplitude and/or phase of the control signal based on whether an object is contacting the sensor. Accordingly, the presence or absence of an object contacting the sensor can be determined based on the amplitude or phase of the sensed signal (for example, see PTL 1).

[PTL 1]　　United States Patent No. 9,727,183

In such capacitive sensors as explained above, a current conveyer circuit including an operational amplifier and field-effect transistors (FETs) constituting a current mirror circuit detects an object (e.g., a finger) by measuring changes in charge that occur due to changes in capacitances caused by the object coming into contact with the capacitive sensor.

However, such capacitive sensors are prone to various electrical noises that result in transient voltage changes in the current conveyer circuit, and such transient voltage changes at the source terminals cause voltage changes across the gate and source terminals of the FETs in the current conveyer circuit. The gate-source voltage changes in turn result in changes in the current flowing through the FETs at the output side, which may make it difficult to preserve the current-mirror bias voltages inside the current conveyer circuit.

In view of the problems associated with the conventional capacitive sensors as explained above, it is an object of an embodiment of the present disclosure to provide a capacitive sensor system that can alleviate voltage changes across the gate and source terminals in response to transient voltage changes at the source terminals of the FETs in the current conveyer circuit, and maintain the current flowing through the FETs at the output side that would be otherwise changed by the gate-source voltage changes.

A capacitive sensor system includes a capacitive sensor and a current conveyor coupled to an output of the capacitive sensor. The current conveyor includes an input side including first and second transistors coupled to an input voltage, an output side including third and fourth transistors coupled to the capacitive sensor, a first capacitor coupled between a gate and a source of the third transistor, and a second capacitor coupled between a gate and a source of the fourth transistor.

In other features, the current conveyor is a second generation current conveyor. The current conveyor includes a first node coupled to a control signal, a second node coupled to the output of the capacitive sensor, and a third node outputting an output current based on the control signal and the output of the capacitive sensor. The output of the capacitive sensor is a sensed signal corresponding to the control signal as modified in accordance with at least one of contact with and proximity of an object. The control signal coupled to the first node is the input voltage of the current conveyor and the second node outputs a regulated voltage corresponding to the input voltage.

In other features, the current conveyor includes a current mirror circuit coupled to the output side, and wherein the third node is coupled to the current mirror circuit. The output side includes fifth, sixth, seventh, and eighth transistors, the current mirror circuit includes the seventh transistor and the eighth transistor, and the third node is coupled between the seventh transistor and the eighth transistor. Gates of the first transistor and the seventh transistor are coupled together. A fourth node between the first capacitor and the second capacitor is coupled to the second node. Gates of the first transistor and the third transistor are coupled together and gates of the second transistor and the fourth transistor are coupled together. A reference signal generator is configured to provide a control signal to the input side of the current conveyor. An offset control module coupled to the output side of the current conveyor.

A current conveyor for a capacitive sensor system includes an input side coupled to an input voltage and including first and second transistors, an output side that provides an output voltage coupled to a capacitive sensor and an output current and including third and fourth transistors, a first capacitor coupled between a gate and a source of the third transistor, and a second capacitor coupled between a gate and a source of the fourth transistor.

In other features, the current conveyor is a second generation current conveyor. The first capacitor and the second capacitor are configured to function as a low pass filter. The current conveyor includes a first node coupled to the input voltage, a second node that outputs the output voltage, and a third node that outputs the output current. The third node is coupled to the current mirror circuit.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

According to an embodiment of the present disclosure, provided is a capacitive sensor system that can alleviate voltage changes across the gate and source terminals in response to transient voltage changes at the source terminals of the FETs in the current conveyer circuit, and maintain the current flowing through the FETs at the output side that would be otherwise changed by the gate-source voltage changes.

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is an example electronic device including a capacitive sensor; FIG. 2A is an example reference signal generator for a capacitive sensor; FIG. 2B is an example reference signal generator for a capacitive sensor; FIG. 3 is an example capacitive sensor system implementing current conveyor for a capacitive sensor according to the present disclosure; and FIG. 4 is an example current conveyor according to the present disclosure.

In the drawings, reference numbers may be reused to identify similar and/or identical elements.

A change in a signal supplied to a capacitive sensor (corresponding to a sensed signal) in response to a contact with an object is typically small relative to a supplied signal (i.e., a control or drive signal) and may be difficult to detect. Accordingly, different methods may be implemented to improve detection of the change. For example, a reference signal generator that provides the signal to the sensor may also supply a duplicate of the signal or a second reference signal generator can be provided to supply the duplicate of the signal. The duplicated signal is subtracted from the supplied signal and the result, which can be amplified to improve detection, corresponds to the sensed signal.

In some examples, the reference signal generator is a sinewave generator such as a Wien bridge oscillator. In other examples, the reference signal generator may be configured to supply a digital sine wave to a digital-to-analog converter (DAC) and the output of the DAC is filtered and/or amplified. In some examples, an offset control module is configured to generate an offset signal that is a duplicate of the sensed signal when there is no contact between an object and the capacitive sensor.

An electronic device including the capacitive sensor may include a regulator circuit (e.g., a voltage-controlled current mode regulator) coupled to an output of the capacitive sensor. The regulator circuit is configured to regulate an output voltage of the capacitive sensor (corresponding to the sensed signal) and generate an output current indicative of the sensed signal. In some examples, the regulator circuit is implemented as a current conveyor. A current conveyor according to the principles of the present disclosure includes a low-pass filter (LPF) coupled between an input voltage and the output current of the current conveyor. The LPF improves noise rejection of the current conveyor.

Referring now to FIG. 1, an example electronic device 100 including a sensor module 104 corresponding to a capacitive sensor is shown. A reference signal generator (e.g., a waveform generator) 108 supplies a reference or control signal (e.g., a square wave, a sinewave, etc.) 110 to the sensor module 104. The reference signal generator 108 may supply the control signal 110 to an offset control module 112 or an optional second reference signal generator 116 may provide a duplicate of the control signal 110 to the offset control module 112.

The sensor module 104 modifies the control signal 110 and generates a sensed signal 118 based on the control signal 110 and proximity or contact with a sensed object. In other words, the sensed signal 118 corresponds to the control signal 110 as modified in accordance with detection of (e.g., contact with and/or proximity of) an object. The sensed signal 118 is indicative of whether an object (e.g., a finger) is in contact with the sensor module 104. In some examples, the sensed signal 118 indicates a proximity of the object to the sensor module 104. The sensed signal 118 may differ (e.g., in amplitude and/or phase) from the control signal 110 regardless of whether an object is in contact with the sensor module 104.

In one example, the offset control module 112 is configured to generate an offset signal 120 that is a duplicate of the sensed signal 118 without contact between an object and the sensor module 104. In other words, the offset control module 112 is configured to modify the control signal 110 in the same manner as the sensor module 104 when there is no contact between an object and the sensor module 104 (and/or, in some examples, when the object is not sufficiently near the sensor module 104 to affect the sensed signal 118). As such, when there is no contact with an object, the sensed signal 118 and the offset signal 120 will be essentially the same (e.g., in magnitude, phase, and/or both magnitude and phase) and a difference between the sensed signal 118 and the offset signal 120 will approach zero. In other examples, the offset signal 120 may be configured to have an opposite polarity relative to the control signal 110 and may simply be summed with the sensed signal 118.

Conversely, when there is contact between an object and the sensor module 104, the offset signal 120 and the sensed signal 118 will be different. A regulator circuit 124 outputs and amplifies a difference between the offset signal 120 and the sensed signal 118. An output signal 128 (e.g., an output current) of the regulator circuit 124 indicative of the sensed signal 118 may then be processed to detect contact between the sensor module 104 and an object. For example, contact may be determined based on whether an amplitude and/or a phase of the output signal 128 exceeds a respective threshold. In some examples, the sensed signal 118 may be indicative of a proximity of the object to the sensor module 104 regardless of whether the object is in direct contact with the sensor module 104. In these examples, the sensed signal 118 may be further indicative of a distance between the object and the sensor module 104.

The regulator circuit 124 is further configured to regulate a voltage provided to the sensor module 104 (e.g., a voltage of the control signal 110). For example, the regulator circuit 124 may be a voltage-controlled current mode regulator implemented as a current conveyor. The current conveyor according to the principles of the present disclosure includes an LPF coupled between an input voltage (e.g., the voltage of the control signal 110) and the output current of the current conveyor to improve noise rejection as described below in more detail.

In some examples, the reference signal generator 108 implements a Wien bridge oscillator, which may be difficult to tune and/or to modulate amplitude. In other examples, the reference signal generator 108 may generate a digital sinewave that is subsequently converted to an analog sinewave. For example, as shown in FIGS. 2A and 2B, the reference signal generator 108 may include a digital sinewave generator 200. In FIG. 2A, an analog DAC 204 converts the digital sinewave to an analog signal, which is then filtered and amplified (or, in some examples, attenuated) using an LPF 208 having gain control capabilities. For example, an amplitude control signal is provided to the LPF 208 to control the gain. The LPF 208 may be a first order filter to reduce cost or, in some examples, may be a second, third, or higher order filter. In other examples, a band pass filter may be used.

Conversely, in FIG. 2B, a multiplier 212 is provided between the digital sinewave generator 200 and the analog DAC 204. The amplitude control signal is provided to the multiplier 212 to control the gain. The output of the multiplier (corresponding to the amplified digital sinewave) is provided to the analog DAC 204. The analog signal output by the analog DAC 204 is filtered using an LPF 216 without gain control.

Referring now to FIG. 3, an example capacitive sensor system 300 (e.g., a capacitive sensor system 300 for the electronic device 100) including a sensor module 304 (e.g., a capacitive sensor) and implementing a regulator circuit 308 according to the present disclosure is shown. A reference signal generator 312 outputs a reference or control signal 316 (e.g., a modulated waveform such as a square wave, an analog sinewave, a digital waveform such as a digital sinewave that is converted to an analog sinewave, etc.). The control signal 316 is supplied to the sensor module 304 via the regulator circuit 308 and, in some examples, to an offset control module 320. The offset control module 320 is configured to generate an offset signal 324 based on the control signal 316. The offset signal 324 is provided to the regulator circuit 308.

The sensor module 304 corresponds to a capacitive sensor (e.g., a capacitive touch circuit) including one or more parasitic capacitances (e.g., parasitic capacitance Crg) that modify an amplitude and phase of the control signal 316 provided to the regulator circuit 308. In some examples, the control signal 316 is connected to the one or more sensing electrodes through a capacitance Crs. When an object (e.g., a finger 332) approaches (i.e., becomes within a proximity of) and/or contacts the one or more sensing electrodes of the sensor module 304, a capacitance 336 of the finger 332 further modifies the amplitude and phase of a sensed signal 340 that is based on the control signal 316. Accordingly, the sensor module 304 generates, as an output voltage, the sensed signal 340 indicative of whether an object such as the finger 332 is in contact with the sensor module 304 or, in some examples, a proximity of the finger 332 to the sensor module 304. More specifically, the sensed signal 340 is modified in accordance with the detected capacitance 336.

The regulator circuit 308 detects and outputs an indication of the sensed signal 340. In some examples, the regulator circuit 308 detects and outputs a difference between the sensed signal 340 and the offset signal 324. For example, the offset control module 320 is configured such that the sensed signal 340 and the offset signal 324 (i.e., respective amplitudes and phases of the sensed signal 340 and the offset signal 324) are the same when there is no contact between the sensor module 304 (e.g., the one or more sensing electrodes) and an object such as the finger 332. In some examples, the offset control module 320 is configured to adjust a phase and an amplitude of the offset signal 324 such that the output of the regulator circuit 308 (e.g., an output signal 344, corresponding to an output current) becomes substantially zero when there is no contact between the sensor module 304 (the one or more sensing electrodes) and the object.

In other words, the offset control module 320 is configured to adjust the phase and the amplitude of the offset signal 324 such that the phase and the amplitude of the offset signal 324 respectively coincide with a phase and an amplitude of the sensed signal 340 when the sensing electrodes of the sensor module 304 do not sense the proximity of or contact with an object. For example, the parasitic capacitances Crs and Crg modify the amplitude and phase of the control signal 316. The offset control module 320 adjusts the amplitude and the phase of the offset signal 324 to compensate for the changes to the control signal 316 caused by the parasitic capacitances Crs and Crg. The output of the regulator circuit 308 (i.e., the output signal 344) indicates whether there is contact between the sensor module 304 and the finger 332 or, in some examples, a proximity of the finger 332 to the sensor module 304 based on a comparison between the sensed signal 340 and the offset signal 324.

The regulator circuit 308 receives the control signal 316 (e.g., as an input voltage of the regulator circuit 308) from the reference signal generator 312. The regulator circuit 308 is configured to regulate a voltage coupled to the sensor module 304 (e.g., a voltage of the control signal 316). In some examples, the voltage coupled to the sensor module 304 corresponds to a voltage coupled to an optional sensor input/output (I/O) pad 348 that is further coupled to an output of the sensor module 304. Accordingly, the sensed signal 340 corresponds to an output voltage of the regulator circuit 308 that is generated based on the control signal 316 and is further modified by the detected capacitance 336. The regulator circuit 308 generates the output signal 344 (e.g., the output current) indicative of the sensed signal 340.

Referring now to FIG. 4, the regulator circuit 308 is shown in more detail. The regulator circuit 308 includes a current conveyor 400, such as a second generation current conveyor (CCII). The current conveyor 400 includes an input side 404 and an output side 408 each coupled between a supply voltage (e.g., VDD) and a reference potential (e.g., a ground terminal). The input side 404 includes first and second transistors 412 and 416 (e.g., field effect transistors (FETs) and current sources (e.g., adjustable current sources) 420 and 424. For example only, the

current sources

420 and 424 may be implemented with transistors. Respective gates and sources of the first and

second transistors

412 and 416 are coupled together. The current source 420 is coupled between the supply voltage and the first transistor 412. The current source 424 is coupled between the second transistor 416 and ground.

The output side 408 includes third, fourth, fifth, and sixth transistors (e.g., FETs) 428, 432, 436, and 440. A gate of the third transistor 428 is coupled to a gate of the first transistor 412. A gate of the fourth transistor 432 is coupled to a gate of the second transistor 416. Third transistor 428 and the fourth transistor 432 are coupled to the sensor module 304. The fifth transistor 436 is coupled between the supply voltage and the third transistor 428. The sixth transistor 440 is coupled between the fourth transistor 432 and ground.

A first node 444 between the first transistor 412 and the second transistor 416 functions as an input voltage node (e.g., a Y node) of the current conveyor 400. The first node 444 receives an input voltage, such as an input voltage corresponding to the control signal 316 from the reference signal generator 312. The first and

second transistors

412 and 416 are coupled to the input voltage via the node 444 and maintain a bias voltage reference based on the input voltage received at the first node 444. Conversely, a second node 448 between the third transistor 428 and the fourth transistor 432 functions as an output voltage node (e.g., an X node) of the current conveyor 400. More specifically, gate voltages of the first and

second transistors

412 and 416 control gate voltages of the third and

fourth transistors

428 and 432 such that the voltage at the second node 448 is equal to the input voltage received at the first node 444. In this manner, the second node 448 outputs a regulated output voltage corresponding to the input voltage received at the first node 444.

An output of the sensor module 304 is coupled to the output voltage of the second node 448. Accordingly, the voltage provided to the sensor module 304 corresponds to the output voltage of the second node 448, which in turn corresponds to the input voltage provided to the first node 444. As the detected capacitance 336 changes, the third and

fourth transistors

428 and 432 together supply a current required to maintain the output voltage at the second node 448. In other words, as the detected capacitance 336 changes, an amount of current required to maintain the output voltage of the second node 448 at the same input voltage as the first node 444 also changes. In this manner, a summed current of the third and

fourth transistors

428 and 432 is an output current corresponding to the sensed signal 340.

The current conveyor 400 further includes seventh and

eighth transistors

452 and 456. Gates of the seventh and

eighth transistors

452 and 456 are coupled to respective gates of the fifth and

sixth transistors

436 and 440. The seventh transistor 452 and the eighth transistor 456 form a current mirror circuit. For example, the fifth and

sixth transistors

436 and 440 provide a gate voltage that is indicative of a current-to-voltage relationship to be replicated by the current mirror circuit formed by the seventh and

eighth transistors

452 and 456. In other words, the gate voltages applied by the fifth and

sixth transistors

436 and 440 to the seventh and

eighth transistors

452 and 456, respectively, cause the seventh and

eighth transistors

452 and 456 to mirror the current of the fifth and

sixth transistors

436 and 440.

Accordingly, a third node 460 is coupled to the current mirror circuit between the seventh transistor 452 and the eighth transistor 456 and functions as an output current node (e.g., a Z node) of the current conveyor 400. In other words, the third node 460 outputs the output signal 344 of the regulator circuit 308, which corresponds to the output current that indicates whether there is contact between the sensor module 304 and the finger 332 or, in some examples, a proximity of the finger 332 to the sensor module 304. In some examples, the third node 460 is coupled to an offset current (e.g., the offset signal 324) and the output signal 344 corresponds to a sum of the output current and the offset current. For example, the offset current is configured to have an opposite polarity relative to a current of the control signal 316. The output signal 344 is provided to an output signal path (e.g., an output signal path of the capacitive sensor system 300).

The current conveyor 400 according to the present disclosure includes a dedicated low pass filter 464 coupled between the input voltage (i.e., the first node 446) and the output current (i.e., the third node 460) to improve the noise rejection performance of the current conveyor 400. For example, the low pass filter 464 lowers a low pass cutoff frequency of the current conveyor 400 and filters high frequency voltages in the input voltage from the output current. In other words, the low pass filter 464 prevents high frequency voltages in the input voltage from being translated into high frequency currents in the output current at the third node 460.

For example, the low pass filter 464 includes first and

second capacitors

468 and 472 coupled between gates of the third and

fourth transistors

428 and 432. Capacitance values of the first and

second capacitors

468 and 472 may be selected in accordance with a desired low pass cutoff frequency of the current conveyor 400. For example, as respective capacitances of the first and

second capacitors

468 and 472 increase, the low pass cutoff frequency of the current conveyor 400 decreases.

A fourth node 476 between the first and

second capacitors

468 and 472 is coupled to the second node 448 between the third and

fourth transistors

428 and 432. In other words, the first capacitor 468 is connected between a gate and source of the third transistor 428 and the second capacitor 472 is connected between a gate and source of the fourth transistor 432. When a voltage transient occurs at the second node 448, a portion of the corresponding voltage change transfers through the first and

second capacitors

468 and 472 to the gates of the third and

fourth transistors

428 and 432. Accordingly, gate-source voltage changes at the third and

fourth transistors

428 and 432 in response to the transient voltages are reduced. In this manner, by reducing the change in the gate-source voltages at the third and

fourth transistors

428 and 432, changes in the current through the third and fourth transistors 428 and 432 (and, therefore, the output current at the third node 460) in response to the transient voltages are also reduced.

In some examples, the low pass filter 464 includes first and second resistors R1 and R2. The first resistor R1 is coupled between the first capacitor 468 and the gate and the source of the first transistor 412. The second resistor R2 is coupled between the second capacitor 472 and the gate and the source of the second transistor 416. The first and second resistors R1 and R2 further adjust the low pass cutoff frequency of the current conveyor 400. For example, increasing the resistances of the first and second resistors R1 and R2 decreases the low pass cutoff frequency of the current conveyor 400.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "next to," "on top of," "above," "below," and "disposed." Unless explicitly described as being "direct," when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean "at least one of A, at least one of B, and at least one of C."

In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

In this application, including the definitions below, the term "module" or the term "controller" may be replaced with the term "circuit." The term "module" may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules.

The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language), XML (extensible markup language), or JSON (JavaScript Object Notation) (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective C, Swift, Haskell, Go, SQL, R, Lisp, Java (registered trademark), Fortran, Perl, Pascal, Curl, OCaml, Javascript (registered trademark), HTML5 (Hypertext Markup Language 5th revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash (registered trademark), Visual Basic (registered trademark), Lua, MATLAB, SIMULINK, and Python (registered trademark).

100　　ELECTRONIC DEVICE
104　　SENSOR MODULE
108　　REFERENCE SIGNAL GENERATOR
110　　CONTROL SIGNAL
112　　OFFSET CONTROL MODULE
116　　OPTIONAL SECOND REFERENCE SIGNAL GENERATOR　　|
118　　SENSED SIGNAL
120　　OFFSET SIGNAL
124　　REGULATOR CIRCUIT
128　　OUTPUT SIGNAL
200　　DIGITAL SINEWAVE GENERATOR
208　　LPF　　
212　　MULTIPLIER
216　　LPF
300　　CAPACITIVE SENSOR SYSTEM
304　　SENSOR MODULE
308　　REGULATOR CIRCUIT
312　　REFERENCE SIGNAL GENERATOR
316　　CONTROL SIGNAL
320　　OFFSET CONTROL MODULE
324　　OFFSET SIGNAL
332　　FINGER
336　　CAPACITANCE
340　　SENSED SIGNAL
344　　OUTPUT SIGNAL
400　　CURRENT CONVEYOR
404　　INPUT SIDE
408　　OUTPUT SIDE
412　　FIRST TRANSISTOR
416　　SECOND TRANSISTOR
420　　CURRENT SOURCE
424　　CURRENT SOURCE
428, 432, 436, 440　　THIRD, FOURTH, FIFTH, AND SIXTH TRANSISTORS
444　　FIRST NODE
448　　SECOND NODE　　
452　　SEVENTH TRANSISTOR
456　　EIGHTH TRANSISTOR
460　　THIRD NODE
464　　LOW PASS FILTER
468　　FIRST CAPACITOR
472　　SECOND CAPACITOR
476　　FOURTH NODE　　
Crs, Crg　　PARASITIC CAPACITANCES
R1　　FIRST RESISTOR
R2　　SECOND RESISTOR

Claims

　　　　A capacitive sensor system, comprising:
　　　　a capacitive sensor; and
　　　　a current conveyor coupled to an output of the capacitive sensor, wherein the current conveyor includes
　　　　an input side including first and second transistors coupled to an input voltage,
　　　　an output side including third and fourth transistors coupled to the capacitive sensor,
　　　　a first capacitor coupled between a gate and a source of the third transistor, and
　　　　a second capacitor coupled between a gate and a source of the fourth transistor.
　　　　The capacitive sensor system of claim 1, wherein the current conveyor is a second generation current conveyor.
　　　　The capacitive sensor system of claim 1, wherein the current conveyor includes a first node coupled to a control signal, a second node coupled to the output of the capacitive sensor, and a third node outputting an output current based on the control signal and the output of the capacitive sensor.
　　　　The capacitive sensor system of claim 3, wherein the output of the capacitive sensor is a sensed signal corresponding to the control signal as modified in accordance with at least one of contact with and proximity of an object.
　　　　The capacitive sensor system of claim 4, wherein the control signal coupled to the first node is the input voltage of the current conveyor and the second node outputs a regulated voltage corresponding to the input voltage.
　　　　The capacitive sensor system of claim 5, wherein the current conveyor includes a current mirror circuit coupled to the output side, and wherein the third node is coupled to the current mirror circuit.
　　　　The capacitive sensor system of claim 6, wherein the output side includes fifth, sixth, seventh, and eighth transistors, the current mirror circuit includes the seventh transistor and the eighth transistor, and the third node is coupled between the seventh transistor and the eighth transistor.
　　　　The capacitive sensor system of claim 7, wherein gates of the first transistor and the seventh transistor are coupled together.
　　　　The capacitive sensor system of claim 3, wherein a fourth node between the first capacitor and the second capacitor is coupled to the second node.
　　　　The capacitive sensor system of claim 1, wherein gates of the first transistor and the third transistor are coupled together and gates of the second transistor and the fourth transistor are coupled together.
　　　　The capacitive sensor system of claim 1, further comprising a reference signal generator configured to provide a control signal to the input side of the current conveyor.
　　　　The capacitive sensor system of claim 11, further comprising an offset control module coupled to the output side of the current conveyor.
　　　　A current conveyor for a capacitive sensor system, the current conveyor comprising:
an input side including first and second transistors coupled to an input voltage;
　　　　an output side including third and fourth transistors, wherein the output side provides an output voltage and an output current, and wherein the output voltage is coupled to a capacitive sensor;
　　　　a first capacitor coupled between a gate and a source of the third transistor; and
　　　　a second capacitor coupled between a gate and a source of the fourth transistor.
　　　　The current conveyor of claim 13, wherein the first capacitor and the second capacitor are configured to function as a low pass filter.
　　　　The current conveyor of claim 14, wherein the current conveyor includes a first node coupled to the input voltage, a second node that outputs the output voltage, and a third node that outputs the output current.