Combined inductive and capacitive detection

Abstract

A combined detection circuit that includes the following: a first electrode that is coupled to a first terminal; a resonant circuit coupled between the first electrode and the first terminal; and a second electrode coupled to a second terminal, wherein: the first and second electrodes form a variable capacitance in a first mode when a transmitted signal from a signal generator coupled to the first terminal is smaller than the oscillation frequency of the resonant circuit. The first and second electrodes form a variable induction coil in a second mode when the transmitted signal from the generated signal coupled to the first terminal is equal to the oscillation frequency of the resonant circuit, and The second electrode is intended for receiving a first receive signal (RX signal) from the first electrode in the first mode and for receiving a second RX signal from the first electrode in the second mode.

Description

RELATED REGISTRATIONS

[0001] This application is an international application of US application No. 15 / 637,731, filed on June 29, 2017, which claims priority over preliminary US application No. 62 / 470,061, filed on March 10, 2017, and preliminary US application No. 62 / 470,044, filed on March 10, 2017, all of which are incorporated herein by reference in their entirety. AREA OF INVENTION

[0002] A touch sensor can be used to detect the presence and location of an object, or the proximity of an object, within the touch-sensitive area of ​​the sensor. For example, a touch detection circuit arrangement can detect the presence and location of a touch object near a touch sensor connected to a screen. There are several different types of touch sensors. These types can include resistive touch sensors, AOW touch sensors (AOW = surface acoustic wave), capacitive touch sensors, inductive touch detection, and so on. Different touch sensors can detect different types of objects. Furthermore, the disclosures in US 2013 / 0 106 769 A1 and US 2010 / 0 225 332 A1 may be helpful in understanding the present invention.US 2013 / 0 106 769 A1 describes a device comprising a capacitive touch sensor, which includes a first electrode and a second electrode, wherein the capacitive touch sensor is configured to operate in an inductive sensing mode and in a capacitive sensing mode, and a control unit. This control unit is configured, in the inductive sensing mode, to apply an alternating current signal to a first electrode of the capacitive touch sensor, to detect a signal indicating a magnetic field at the first electrode, wherein the signal is at least partially attributable to a magnetic field generated by an object, the magnetic field being generated at least partially in response to the application of the alternating current signal to the first electrode, and to determine the position of the object generating a magnetic field based on the signal indicating the magnetic field.US 2010 / 0225332A1 describes a proximity sensor comprising a resonant circuit, an amplitude measurement circuit, a control circuit, and a signal processing circuit. The resonant circuit has an LC resonant circuit and an oscillation control circuit configured to supply an electrical current to the LC resonant circuit to generate an oscillating voltage across it. The amplitude measurement circuit is configured to generate an amplitude signal equal to the amplitude of the oscillating voltage. The control circuit is configured to set the negative admittance of the oscillation control circuit to a critical value around which the LC resonant circuit can oscillate based on the amplitude signal.The signal processing circuit is configured to generate a distance signal based on a parameter associated with the negative conductivity, which corresponds to the distance between an object and the scanning coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The present revelation is illustrated by way of example and without limitation in the figures of the accompanying drawings, in which Fig. Figure 1 illustrates a detection circuit for self-capacity detection according to one embodiment. Fig. Figure 2A illustrates a device for capacitive and inductive detection according to one embodiment. Fig. 2B the detection unit, which is operated as a variable capacitor in a capacitance mode when a frequency of the TX signal is below or above an oscillation frequency, is illustrated according to one embodiment. Fig. 2C the detection unit, which is operated as a variable induction coil in an inductance mode when the phase of the TX signal has been shifted so that a resonant circuit is excited, is illustrated according to one embodiment. Fig. Figure 2D illustrates a circuit diagram of the device that performs capacitive and inductive full-wave detection according to one embodiment. Fig. Figure 2E illustrates the charge measurement circuit (CMC) of the device, which is configured for capacitive and inductive half-wave detection, according to one embodiment. Fig. 3 a detection unit in which the resonant circuit comprises a resistor, an induction coil, a capacitor, a second capacitor and a ground, according to one embodiment illustrated. Fig. 4A The detection unit, comprising a capacitor and an induction coil, is illustrated according to one embodiment. Fig. 4B the recording unit from Fig. 4A, which includes a flat coil, is illustrated according to one embodiment. Fig. 4C the acquisition unit from Fig. 4A, which comprises a flat coil with a small inner circumference, is illustrated according to one embodiment. Fig. 4D the capture unit from Fig. 4A, which includes a rectangular coil, is illustrated according to one embodiment. Fig. 4E the recording unit from Fig. 4A, which includes a multi-layer coil, is illustrated according to one embodiment. Fig. 4F the recording unit from Fig. 4A, comprising a primary coil and a secondary coil, is illustrated according to one embodiment. Fig. 4G the detection unit from Fig. 4A, comprising the primary coil 438 and the secondary coil, which are coplanar, is illustrated according to one embodiment. Fig. Figure 5 illustrates a detection circuit with a hybrid capacitive-inductive sensor according to one embodiment. Fig. 6A the recording unit from Fig. 5, which includes the first circuit arrangement with a capacitor and the second circuit arrangement with an induction coil, illustrated according to one embodiment. Fig. 6B the recording unit from Fig. 5, which includes the first circuit arrangement with the capacitor and the second circuit arrangement with the induction coil, a capacitor and a ground, illustrated according to one embodiment. Fig. Figure 6C illustrates the acquisition unit in which the GPIO is open and the GPIO is closed, according to one embodiment. Fig. 6D the capture unit from Fig. 5, which comprises a first circuit arrangement with a capacitor and the second circuit arrangement with the induction coil, a capacitor, an induction coil, a capacitor and a ground, illustrated according to an embodiment. Fig. Figure 7 illustrates a graph of an amplitude change associated with a digital representation of the RX signal according to one embodiment. Fig. Figure 8A illustrates a graph of a phase shift and demodulation of a TX signal for inductive detection according to one embodiment. Fig. Figure 8B illustrates a graph with a TX signal for capacitive sensing according to one embodiment. Fig. Figure 9 illustrates a graph showing the phase shift and demodulation of a resonant circuit output signal for inductive detection according to one embodiment. Fig. 10A a graph that passes through the CMC in Fig. 2A shows frequencies used for inductive detection according to one embodiment. Fig. 10B a graph of another frequency, which is measured by the CMC in Fig. 2A can be used for inductive detection, according to one embodiment. Fig. 10C a graph of another through the CMC in Fig. 2A shows the frequency used for inductive detection according to one embodiment. Fig. Figure 11 illustrates a flowchart of a method for determining the inductance of a detection unit according to a further embodiment. Fig. Figure 12 illustrates a flowchart of a method for applying signals to a first electrode and a second electrode according to a further embodiment. DETAILED DESCRIPTION

[0004] Many electronic devices include touch sensors (also referred to herein as sensing units or unit cells) through which the user can interact with the electronic devices. For example, ATMs, information kiosks, smartphones, vending machines, washing machines, televisions, computers, and refrigerators may include sensing units and a corresponding touch sensing circuitry. When an object touches or is near the sensing unit, the touch sensing circuitry can be used to register and record the presence and location of the object using the sensing unit.

[0005] Unlike buttons or other mechanical controls, sensing units can be more sensitive and respond differently to various types of touch, such as tapping, swiping, and pinching or pulling fingers apart. Different sensing units can also respond differently to different types of objects. Various techniques exist for measuring capacitance, inductance, or resistance; however, these techniques utilize different types of sensing units and different circuitry for measuring these values. For example, inductive sensing can be used to detect ferrous and non-ferrous metals, while capacitive sensing can be used to detect conductive ferrous and non-ferrous objects.Until now, a device for detecting different object types had to include different detection elements and different circuits for measuring these different object types. Integrating these different detection elements and circuit components may not be possible due to cost or the space available within the device, especially if the device has a small form factor.

[0006] Embodiments of the present disclosure describe a technology for combined inductive and capacitive sensing. The embodiments can provide a sensing unit that can be used to detect different types of objects, and a circuit arrangement for combined inductive and capacitive sensing that can be used to detect these different types of objects via inductive and capacitive sensing. In one embodiment, the sensing unit can be used not only for capacitive sensing in a first mode, but also for inductive sensing in a second mode.In one embodiment, the circuit arrangement for combined inductive and capacitive sensing (also referred to herein as the "touch sensing circuit arrangement" or "sensing circuit arrangement") uses a type of capacitive sensing circuit arrangement such that it can measure the inductance of the sensing element in a first mode (an inductive sensing mode) and the capacitance of the sensing element in a second mode (a capacitive sensing mode), as described in more detail herein. When the sensing circuit is operated in the capacitive sensing mode, the sensing circuit can use the sensing unit to detect objects using a capacitive sensing technique.When the detection circuit is operated in inductive detection mode, the detection circuit can detect ferrous and non-ferrous metal objects near the detection unit using inductive detection techniques.

[0007] In one embodiment, the sensing circuit arrangement comprises 1) a signal generator for outputting a first signal in a first mode and a second signal in a second mode via a first terminal; and 2) a charge-measuring circuit for receiving a third signal in the first mode and a fourth signal in the second mode at a second terminal. The third signal represents an inductance of a sensing unit coupled between the first terminal and the second terminal, and the fourth signal represents a capacitance of the sensing unit.

[0008] In a further embodiment, a sensing unit comprises a first terminal coupled to a first node, a first electrode coupled to the first node, a second terminal, and a second electrode coupled to the second terminal. The sensing unit also includes an inductive coil and a first capacitor. In a first mode (capacitive sensing mode), a first signal is received at the first terminal and a second signal is output via the second terminal. The second signal represents a capacitance of the sensing unit. In a second mode (inductive sensing mode), a third signal is received at the first terminal and a fourth signal is output from the second terminal. The fourth signal represents an inductance of the sensing unit.

[0009] Fig. Figure 1 illustrates a detection circuit 100 for self-capacitance measurement according to one embodiment. The detection circuit 100 can include a processor 119, a charge measurement circuit (CMC) 110, a general purpose input / output (GPIO) 112, and a detection capacitor (C). sense ) 114, a GPIO 116 and a modulator capacitor (C mod) 118. GPIO 112 and GPIO 116 can be connections of any type configured for coupling to external components, such as sensing units, and other external devices. In one example, GPIOs might be connections that are terminals of a circuit. The GPIOs can be coupled to pins, pads, solder bumps, or the like. In another example, the GPIOs might include special outputs, dedicated outputs / inputs, or the like. The GPIOs can be an internal trace routing mechanism for connecting pins or pads to a power source, ground, high-Z, an internal circuit arrangement (such as a sensing circuit arrangement), a pulse-width modulator (PWM), or the like.

[0010] In Fig. In step 1, GPIO 112 is coupled to a sensing element 114, which is a single electrode. The CMC 110 can measure the self-capacitance of the single electrode with respect to ground potential. Therefore, the sensing element 114 (C sense ) is represented as an external capacitor. The CMC 110 can use a modulator capacitor (C mod ) 118 to measure the capacity in the sensing element 114. In some embodiments, the C mod 118 an external capacitor coupled to GPIO 116, as in Fig. Figure 1 illustrates this. In one example, the CMC 110 might be a capacitive digital-to-analog converter (CDC). In another example, the CMC 110 might be a charge transfer circuit, a circuit designed for capacitive charge sensing, a capacitive sensing sigma-delta circuit (CSD circuit), or the like. The CSD circuit could include physical, electrical, and software components.

[0011] The CSD circuit may include an array of capacitive sensing elements (as sensing units) coupled to a sigma-delta modulator via an analog multiplexer, digital counting functions, and high-level software routines to compensate for environmental and physical changes in the sensing element. The physical component may include the physical sensing element itself, typically a conductor pattern produced on a printed circuit board (PCB) with an insulating cover, a flexible membrane, or a transparent top layer. In one embodiment, the physical component may also include a transparent conductor, such as indium tin oxide (ITO), deposited on a substrate, which may also be transparent. The electrical component can convert a charged capacitance into a measured signal.The electrical component may include an operational amplifier capable of outputting a bitstream that can be quantified by a counter circuit or a timer circuit. The software component may include detection and compensation software algorithms for converting a count value into a sensor element detection decision.

[0012] As in Fig. As illustrated in Figure 1, the CMC 110 can be connected to GPIO 112 and GPIO 116. In one example, GPIO 112 might be the first connection of the CMC 110 and GPIO 116 the second connection. These connections could be pins, pads, solder pads, or other mechanisms for connecting conductors of the various components. During operation, the CMC 110 can be detected using the sensing element 114 (C). sense) perform a charge measurement. For example, the CMC 110 can charge and discharge the electrode of the sensing unit to determine the capacitance of the sensing element 114 (C). senseThe CMC 110 can convert the measured capacitance into a total digital voltage value or a bitstream. In one embodiment, the CMC 110 may compare the charge measurement with a reference value to determine a difference between the charge measurement and the reference value. In one embodiment, the reference value may be a previous value measured by the charge measurement circuit 110. In another embodiment, the reference value may be a predefined value. The predefined value may be a standard reference value or a value derived from previously measured charge measurements accumulated over time. The difference value may indicate a difference between the charge measurement and the reference value. In one example, the CMC 110 may send the difference value to the processor 119.The processor 119 or the CMC 110 can determine whether the difference value exceeds a threshold. If the difference value exceeds the threshold, it indicates that an object is near the detection element 114 (C. sense ). If the difference value does not exceed the threshold, the difference value indicates that no object detectable via capacitive sensing is near C. sense 114 is.

[0013] Fig. Figure 2A illustrates a device 200 for capacitive and inductive sensing according to one embodiment. The device 200 can measure the capacitance and / or inductance of a sensing unit 225 as described herein. The device 200 comprises a charge measurement circuit 210 coupled to the sensing unit 225. In a capacitive sensing mode, the charge measurement circuit 210 can include a signal generator 229, which can generate an excitation signal (TX signal) that can be applied to the sensing unit 225 via a GPIO 226, and a receiver channel (in Fig. 2A (not illustrated), which can measure a received signal (RX signal) at GPIO 220. The RX signal is representative of a counter-capacitance of the sensing unit 225. In a further embodiment, the charge measurement circuit 210 can charge and discharge the sensing unit 225 via GPIO 220 to measure its own capacitance.

[0014] In inductive sensing mode, the charge sensing circuit 210 can phase-shift the TX signal relative to a reference signal to generate a phase-shifted signal to be applied to the sensing unit 225. For example, the charge sensing circuit 210 can output the TX signal to a smart input / output interface 230 (hereinafter referred to as "smart SST 230") and a pulse width modulator (PWM) 228 to generate a phase-shifted TX signal (e.g., a TX signal shifted by 90 degrees), as described herein. In another example, the smart SST 230 and / or the PWM 228 may shift / shift the phase of a signal. A second receive signal (RX signal) can be measured by the charge sensing circuit 210 via the GPIO 220. The second signal is representative of an inductance of the detection unit 225.

[0015] The charge measurement circuit 210 can use a modulator capacitor (Cmod ) 214 and another capacitor (C tank ) 218 ​​in capacitive sensing mode and / or inductive sensing mode, as described herein. The charge sensing circuit 210 may also include an analog-to-digital converter (ADC) for converting the analog capacitance and inductance readings of the sensing unit 225 into digital values. These digital values ​​can be output to a processor 219 for further digital signal processing for an application.

[0016] As in Fig. As illustrated in Figure 2A, the detection unit 225 can comprise a resonant circuit 224 and a pair of electrodes (a first electrode and a second electrode) forming a detection capacitor 222. Various embodiments of the detection unit 225, including the resonant circuit 224, are described with reference to the Fig. 2B-6D describes and illustrates this. In capacitive sensing mode, the CMC 210 can measure the counter-capacitance of the sensing unit 225, where the counter-capacitance exists between the first and second electrodes of the sensing capacitor 222. In inductive sensing mode, the CMC 210 can measure the inductance for inductive sensing as described herein. For example, the CMC 210 may measure the inductance of a sensing unit 225. The device 200 can include any number of sensing units 225. For example, the device 200 can include only one sensing unit 225 or multiple sensing units 225.

[0017] In one embodiment, the processor 219, the CMC 210, the C mod 214, the C tank218, the PWM 228 and / or the intelligent SST 230 of the device 200 possibly in the same integrated circuit that connects the GPIOs 226, 212, 220, 216, the sensing unit 225, the modulator capacitor (C mod ) 214 and the oscillating capacitor (C tank ) 218 ​​are coupled. Alternatively, the different components of device 200 may be implemented in several integrated circuits. The modulator capacitor (C mod ) 214 and the oscillating capacitor (C tank ) 218 ​​may be located at least partially outside the integrated circuit containing the charge measurement circuit 210.

[0018] As noted above, the CMC 210 can include a signal generator 229. The signal generator 229 can generate a transmit signal (TX signal) (also called an excitation signal). In one example, the TX signal might be a square wave. The intelligent SST 230 can be coupled to the CMC 210. The intelligent SST 230 might be a digital control unit of an I / O interface that is located outside of, or not coupled to, a microcontroller (MCU). The intelligent SST 230 can offload tasks from the MCU to provide configuration of SSTs.

[0019] In one embodiment, the PWM 228 may be coupled to the intelligent SST 230. In another embodiment, the PWM 228 may be directly coupled to the CMC 210. The PWM 228 can adjust the phase of the TX signal. For example, an input to the PWM 228 can be mixed with the TX signal to adjust the phase of the TX signal.

[0020] The phase of the TX signal can be shifted when the device 200 performs a measurement relative to an inductive sensing signal. Alternatively, other embodiments are possible in which the TX signal is shifted for measurements relative to a capacitive sensing signal. In one example, the signal generator 229 may generate a TX signal with a phase of 0 degrees relative to a reference signal. With a TX signal phase of 0 degrees, the CMC 210 can be operated in a capacitive sensing mode to perform measurements relative to a capacitive sensing signal, as discussed below. If the CMC 210 is operated in an inductive sensing mode to perform measurements relative to an inductive sensing signal, the TX signal phase can be shifted by 90 degrees, as discussed below.

[0021] GPIO 226 can include a driver for adjusting the amplitude of the TX signal. GPIO 226 might, for example, include a first switch 231 and a second switch 232. A switch could be a transistor, a gate, a component for making or breaking circuit connections, etc. In an example where GPIO 226 is connected to a power source via a closed first switch 231 and an open second switch 232, GPIO 226 can be set to high. In another example where GPIO 226 is connected to ground via a closed second switch 232 and an open first switch 231, GPIO 226 can be set to low. In yet another example where GPIO 226 is shorted to voltage and shorted to ground, both the first switch 231 and the second switch 232 are closed.In another example, where both switches 231 and 232 are open, GPIO 226 can be set to a high impedance (High-Z) and output the signal received by PWM 228. In one example, processor 119 or the intelligent SST 230 might control switches 231 and 232 via PWM 228.

[0022] In one embodiment, GPIO 226 may be coupled to the sensing capacitor 222 (first and second electrodes). The charge-measuring circuit 210 can apply a TX signal to GPIO 226, which is coupled to the sensing unit 225. The TX signal can energize the sensing capacitor 222. Energizing a circuit or component can refer to applying a voltage or current to the circuit or component. For example, applying a voltage of the TX signal to a first electrode of the sensing capacitor 222 induces an RX signal in a second electrode of the sensing capacitor 222. The voltage or current of the RX signal can be measured by the charge-measuring circuit 210 via GPIO 220. As noted above, the RX signal can be integrated by an analog-to-digital converter (ADC) when converting the RX signal into a digital value.The processor 219 can also process the digital signals as described herein.

[0023] To perform a countercapacitance measurement, the CMC 210 can measure a countercapacitance between a first electrode and a second electrode, wherein the countercapacitance between the first electrode and the second electrode can be represented as a sensing capacitor 222. The device 200 can also include two capacitors for integration. In one embodiment, the C mod 214 can be used for countercapacitance measurement. The current from the C mod 214 can go into the C tank 218 are integrated and the TX signal is demodulated. In one example, the C mod 214 is used for self-capacity measurement and the current in the C tank 218 can be integrated. For the purpose of recording counter-capacity, the C mod 214 and the C tank 218 can be used for capacity recording.

[0024] In another embodiment, the device 200 can include the resonant circuit 224 coupled between the GPIOs 226 and the detection capacitor 222. The resonant circuit 224 and the detection capacitor 222 can form a detection unit 225. The CMC 210 can apply the TX signal to the resonant circuit 224 via the GPIO 226 in order to excite the resonant circuit 224. Fig. Figures 3-6D illustrate different embodiments of the resonant circuit 224, as discussed below.

[0025] GPIO 220 can couple the TX signal sent from GPIO 226 via the resonant circuit 224 and / or the capacitor 222 to the CMC 210. The signal received at GPIO 220 can be referred to as the received signal (RX signal). The CMC 210 can compare the amplitude of the RX signal with a reference signal. A converter in the CMC 210 can convert the C modFor example, capacitor 214 can be used as an integrating capacitor. A charge can be added to or removed from the capacitor. For example, a current can be induced from one electrode by voltage fluctuations in the capacitor. The charge of the integrating capacitor can be converted into a digital value of a first count by a converter in the CMC 210. The charge measured on capacitor 222 is also converted into a digital value of a second count by the converter. The conversion of the measured charges into digital values ​​of counts functions as a capacitive-to-digital converter.

[0026] The first count is compared to the second count to determine the relative difference between the digital representations of the capacitance of capacitors 214 and 218 and capacitor 222. If the relative difference between the first and second counts exceeds a threshold, the difference between the counts indicates a change in the capacitance of capacitor 222. This change in capacitance can indicate the presence of an object near capacitor 222. For example, the difference between the counts can be represented as the difference in amplitude between the signals from GPIO 220 and an integrated signal from GPIOs 212 and 216.

[0027] In one example, where a relative difference between counts does not exceed a threshold, the relative difference might indicate that an object is not near Device 200. In another example, where a relative difference between counts does not exceed a threshold, Device 200 might not be configured to detect the type of object near Device 200. In one example, where Device 200 is configured to perform capacitive detection, Device 200 might not be able to detect ferrous or non-ferrous metal objects. In another example, where Device 200 is configured to perform inductive detection, Device 200 might not be able to detect capacitive objects. In one embodiment, one phase of the TX signal for performing capacitive detection might be 0 degrees.In another embodiment, the phase of the TX signal may be shifted to perform capacitive sensing. If the phase of the TX signal is shifted, the phase shift changes how a charge is coupled to the resonant circuit 224 and the capacitor 222. In one example, the resonant circuit 224 may not oscillate when used for capacitive sensing. If the resonant circuit 224 does not oscillate, the induction coil in the resonant circuit 224 cannot be excited. In another example, the resonant circuit 224, or the induction coil, may oscillate when used for inductive sensing. The TX signal may be phase-shifted, provided the corresponding RX signal can be demodulated at the CMC 210. In one example, the phase of the TX signal may be shifted by approximately 80 to 100 degrees.In another example, the phase of the TX signal may be shifted by at least 45 degrees. In yet another example, the phase of the TX signal may be shifted by approximately 90 degrees. With an even greater deviation from the 90-degree phase shift, the change in the amplitude of the RX signal at GPIO 220 may decrease. If the charge level decreases by the amount of the deviation from the 90-degree phase shift, the accuracy of the inductive detection may also decrease.

[0028] Processor 219 can be coupled to PWM 228. Processor 119 can configure PWM 228 to set a first phase for conductive detection or a second phase for inductive detection as the phase of the TX signal generated by CMC 210. Processor 119 can also configure CMC 210 for capacitive or inductive detection based on the TX signal phase. For example, CMC 210 might measure current as a charge for the TX signal at GPIO 220. CMC 219 might measure a charge change over time within the current. If CMC 210 is configured to measure current or voltage for capacitive detection, it can determine that an initial change in charge for a signal with a 0-degree phase shift indicates the presence of an object.If the CMC 210 is configured for current measurements for inductive detection, the CMC 210 can determine that a second change in charge for a signal with a 90-degree phase shift indicates the presence of an object near the capacitor 222. In one embodiment, the CMC 210, the intelligent SST 230, the processor 119, the PWM 228, the GPIO 226, the resonant circuit 224, the capacitor 222, the GPIO 533, the GPIO 216, the GPIO 220, the C. mod 214 and the C tank 218 on a single substrate, such as a single substrate with an integrated circuit or a common support substrate.

[0029] The CMC 210 may include a filter for filtering the signal received at GPIO 220. In one example, the filter may be an infinite impulse response (IIR) filter. In another example, the filter may be a decimation filter. In another example, the device 200 may be configured for capacitive sensing to receive user input and inductive sensing to receive non-user input. For example, the device 200 may be configured for capacitive sensing when receiving user input via a touchscreen and for inductive sensing when receiving input via a metal knob, an angle position sensor for control knobs, a door-open sensor, a drawer-open / closed sensor, a liquid level sensor, etc.

[0030] In an automotive embodiment, inductive sensing can be used to determine gearshift positions, and a capacitive sensor can be used for touchscreen force detection. The Device 200 can be integrated into a desktop computer, laptop computer, tablet computer, personal digital assistant (PDA), smartphone, satellite navigation device, portable media player, portable game console, kiosk computer, point-of-sale device, dishwasher, washing machine, liquid dispenser, control panel on a household or other device that includes a sensing unit, etc.

[0031] Fig. Figure 2B illustrates the detection unit 225, which operates as a variable capacitor in a capacitance mode when the frequency of the TX signal is below or above a resonant frequency, according to one embodiment. If the frequency of the TX signal received at the resonant circuit 224 differs from the resonant frequency of the resonant circuit 224 (for example, because it is below or above the resonant frequency), the resonant circuit 224 and the detection capacitor 222 can output a current for capacitance detection. The TX signal, for example, excites a current in an inductor of the resonant circuit 224. This can lead to an interaction of the inductor with an induced current at the object. The proximity of the object 237 can affect the inductance of the inductor. If the object 237 is connected to ground, a capacitance between the inductor and the object can further increase the overall parasitic coupling of the inductor to ground, and the capacitance is distributed.If a TX frequency is not at the oscillation frequency, the resonant circuit can be operated as a variable capacitor in a capacitance mode, and an RX signal can be passed through it to the CMC 210 so that the CMC 210 can perform a capacitance measurement.

[0032] Fig. Figure 2C illustrates the detection unit 225, which is operated as a variable induction coil in an inductance mode when the phase of the TX signal has been shifted to excite a resonant circuit, according to one embodiment. When the TX signal is approximately at the resonance frequency of the detection unit 225, as shown in graph 235, the resonant circuit 224 and the capacitor 222 can be operated as an inductive detection unit in an inductance mode. If the object 237 is connected to ground, the capacitance between the coil and the object 237 can further increase the parasitic coupling of the coil to ground, and the capacitance is distributed. This results in an interaction of the electric current in the coil with an induced current at the metal object. The proximity of the metal object can affect the inductance of the coil.If the frequency of the TX signal is at the oscillation frequency, the current can be maximized beyond that, making the resonant circuit relatively sensitive to inductance changes versus capacitance changes when operating in inductance mode.

[0033] Fig. Figure 2D illustrates a circuit diagram of the device 200, which performs capacitive and inductive full-wave detection, according to one embodiment. Some of the features in Fig. 2D corresponds to or resembles some of the features in the Fig. 1 and Fig. 2A, as indicated by the same reference numerals, unless explicitly described otherwise. The device 200 can perform full-wave detection using GPIOs 212, 216, 220 and 226, the resonant circuit 224, a CMC 216, a digital sequence controller 233, an intelligent SST 230 and / or a PWM 228.

[0034] The CMC 210 can transmit a TX signal (also known as CSD). _(designated as a sense signal). Device 200 can be operated in either capacitive sensing or inductive sensing mode. The digital sequence controller 233 can control the switches in the CMC 210 to configure the CMC 210 for capacitive or inductive sensing. While Device 200 is operating in capacitive sensing mode, PWM 228 may not be able to shift the phase of the TX signal sent to the sensing unit 225 via GPIO 226. While Device 200 is operating in inductive sensing mode, PWM 228 can shift the phase of the TX signal before it is sent to GPIO 226.

[0035] GPIO 226 may be a driver that amplifies the TX signal or the phase-shifted TX signal when the amplitudes of these signals are below a certain amplitude threshold. The CMC 210 can send the TX signal via GPIO 226 to the resonant circuit 224 at node 251. The resonant circuit 224 may be a sensor, such as an RLC circuit or an electrode, which the CMC 210 can use for capacitance or inductance measurements, as discussed above. GPIO 220 can receive the RX signal from capacitor 222 and couple the RX signal to the CMC 210.

[0036] The CMC 210 can include an analog multiplexer (AMUX) 236, an equalizer 238, and a comparator 240. The AMUX 236 can combine or aggregate the signals from GPIO 212, GPIO 216, and GPIO 220 and send the combined signal to the equalizer 238. The equalizer 238 can balance the current sources of the CMC 210. The equalizer 238 may, for example, be coupled to the digital sequence controller 233 via a control line. The equalizer 238 can receive control signals from the PHI1 252 and PHI2 254 pins of the digital sequence controller 233 to balance the CMC 210.

[0037] The compensator 238 may also include a time-comparison circuit (not shown). The time-comparison circuit can couple positive and negative charges at the CMC 210 with the correct phase. The compensator 238 may also include a demodulator that determines the counts of the CMC 210. The compensator 238 adds to the resonant circuit 224, the Cmod 214, the C tank 218 and capacitor 222 add a charge. In one example, equalizer 238 adds a charge to C mod 214 and the C tank 218 possibly adds another charge, so that the charge level of the C mod 214 and of C tank 218 is back to how it was at the beginning.

[0038] A converter can convert the C modThe capacitor 214 is used as an integrating capacitor to store or integrate charge from multiple transfer operations. The charge is converted at the converter into a digital current value (RX) that is representative of the capacitance. The comparator 240 can compare the digital value with a threshold value to determine whether the amplitude of the RX signal has changed. The comparator 240 can compare a digital value representative of an amplitude of the RX signal from GPIO 220 with a digital value representative of an amplitude of the reference signal at the comparator 240 to determine a relative difference between the voltage amplitudes of the RX signal and the reference signal. If the difference between the amplitudes exceeds a threshold value, the difference may indicate the presence of an object near the capacitor 222.

[0039] The CMC 210 can combine measurements while the device is set to capacitive sensing, and it can take measurements while the device is set to inductive sensing. The CMC 210 can use the combined measurement information to differentiate between different object types. For example, the combined information can indicate whether an object is a plastic bottle or a metal can.

[0040] The digital sequence controller 233 can control the switches in the CMC 210 to configure the CMC 210 for capacitive or inductive sensing. The intelligent SST 230 can enable internal interconnection of the digital sequence controller 233 with the PWM 228 or a TX signal driver. The digital sequence controller 233 can send a trigger input to the PWM 228 via the intelligent SST 230 to cause the PWM 228 to shift a phase of the TX signal. In another embodiment, the intelligent SST 230 may be an external connector that routes the signal between the digital sequence controller and the PWM 228.

[0041] The PWM 228 can shift the phase of the TX signal to excite the components of the resonant circuit 224 for capacitive or inductive sensing. In one embodiment, the PWM 228 can maintain a 0-degree phase to excite the resonant circuit 224 for capacitive sensing. In another embodiment, the PWM 228 can shift the phase of the TX signal by 90 degrees to excite the resonant circuit 224 for inductive sensing.

[0042] In one example, the resistance R can s The resonant circuit 224 limits the current flow. In another example, the TX signal might be a sine wave and the resistance R s can define the amplitude of the sine wave. Capacitor 222 can couple the sine wave from resonant circuit 224 into CMC 210. In one example, the resistor R sIt may be a component of a GPIO and can be programmable. In another example, the GPIO could have a different control signal for generating the resistance.

[0043] In an example where the power consumption of the resonant circuit 224 is to be reduced, oscillation in the LC components of the resonant circuit 224 may not be maximized, and a relatively large resistance R is used. s The GPIO 220 can receive the sine wave from capacitor 222 and couple the RX signal to a capture channel of the CMC 210. The CMC 210 can convert the RX signal into a digital value.

[0044] In one embodiment, the CMC 210 may include a transducer for capacitive whole-wave detection. The 90-degree phase shift by the PWM 228 can enable demodulation of the sine wave by the transducer for capacitive whole-wave detection.

[0045] Fig. Figure 2E illustrates the CMC 210 of the device 200, configured for capacitive and inductive half-wave detection, according to one embodiment. Some of the features in Fig. 2E corresponds to or resembles some of the features in the Fig. 1 and 2A-2D, as indicated by the same reference numerals, unless explicitly described otherwise.

[0046] If the device 200 is configured for capacitive and inductive half-wave detection, GPIO 216 and C can be used. tank The 218 component in device 200 is omitted. The CMC 210 can include an analog multiplexer (AMUX) 242, an equalizer 244, and a comparator 246. The AMUX 242 can combine the signals from GPIO 212 and GPIO 220 and send the combined signal to the equalizer 244.

[0047] The compensator 244 can balance the current sources of the CMC 210. The compensator 244 may, for example, be coupled to the digital sequence controller 233 via a control line. The compensator 244 can send control signals to the digital sequence controller 233 to balance the CMC. The compensator 244 may also include a time comparison circuit. The compensator 244 may also include a demodulator that determines the digital values ​​of the CMC 210 and accumulates a charge for the resonant circuit 224, the C. mod 214 and capacitor 222.

[0048] The comparator 246 can compare a digital value for the RX signal from GPIO 220 with a digital representation of the amplitude of the comparator 246's reference signal to determine a difference between the amplitudes of the RX signal and the reference signal. If the difference exceeds a threshold, it may indicate the presence of an object near capacitor 222.

[0049] Fig. Figure 3 illustrates a detection unit 300 in which the resonant circuit 224 comprises a resistor 332, an induction coil 334, a capacitor 336, a second capacitor 338, and a ground 340, according to one embodiment. Some of the features in Fig. 3 correspond to or resemble some of the features in the Fig. 1 and 2A-2E, as indicated by the same reference numerals, unless explicitly described otherwise.

[0050] Resistor 332 can be connected between GPIO 226 and node 342. Inductor 334, capacitor 336, the second capacitor 338, and ground 340 can be components of a series circuit 344, which can be connected to node 342. In one example, capacitor 336 and / or the second capacitor 338 may be discrete components. In another example, capacitor 336 and / or the second capacitor 338 may represent capacitances formed between components. For example, capacitor 336 may represent a capacitance formed between inductor 334 and 340. The series circuit 344 can be connected between resistor 332 and capacitor 222. Capacitor 222 can be connected between node 342 and CMC 210.

[0051] In one embodiment, the series circuit 344 may include the induction coil 334, which is connected in series with the capacitor 336 (i.e., LC). The capacitor 336 may be connected to ground 340. In another embodiment, the series circuit 344 may include the induction coil 334, which is connected in parallel with the second capacitor 338 (i.e., L||C). The induction coil 334 and the second capacitor 338 may be connected to ground 340.

[0052] The combination of the induction coil 334 and the second capacitor 338 can be connected in series with the capacitor 336 (i.e., L||CC). The capacitor 336 can be connected to ground 340. The L||CC configuration can control the lowest and highest impedances of the resonant circuit 224. For example, the L||CC configuration may be used as an analog amplifier to control the frequency range between the lowest and highest impedances of the resonant circuit 224. The L||CC configuration can provide tuning for a resonant frequency of the detection circuit.

[0053] The components of the series circuit 344 or the resonant circuit 224 are not subject to any restrictions. The resonant circuit 224 may also include other components or have other configurations.

[0054] Fig. Figure 4A illustrates the detection unit 400, which comprises a capacitor 412 and an induction coil 416, according to one embodiment. The capacitor 412 and the induction coil 416 can be coupled to a processing circuit 418. When operating in an inductive detection mode, the processing circuit 418 can use the induction coil 416 to detect the presence of an object.

[0055] In inductance detection mode, capacitor 412 may serve as a ground for induction coil 416. In inductance detection mode, for example, a magnetic field can be generated at induction coil 416, and when a signal is applied to induction coil 416, the magnetic field induces a current in the induction coil 416. If an object comes near the magnetic field, the object can generate an eddy current acting in the opposite direction to the magnetic field.

[0056] When operating in capacitance detection mode, the processing circuit 418 can use the capacitor 412 to detect the presence of an object. The field lines 420 illustrate the capacitance between the induction coil 416 and the capacitor 412. In self-capacitance detection mode, capacitance can be measured across the induction coil 416. In reverse capacitance detection mode, capacitance can be measured between the induction coil 416 and the capacitor 412. For example, the induction coil 416 cannot be energized when an alternating current (AC) is applied to the detection unit 400 and then acts like a grounded metal.

[0057] In one embodiment, the capacitor 412 may be a parallel-plate capacitor located on a first side of a substrate. The capacitor 412 may be connected to ground. The induction coil 416 may be a spiral coil located on a second side of the substrate. In inductive mode, the capacitor 412 may be connected to ground and be passive. In capacitive mode, the ground of the induction coil 416 couples the capacitive field to detect an object.

[0058] Fig. Figure 4B illustrates the recording unit 401 from Fig. 4A, comprising a flat coil 422, according to one embodiment. Some of the features in Fig. 4B corresponds to or resembles some of the features in Fig. 4A, as indicated by the same reference numerals, unless explicitly described otherwise. The flat coil 422 can serve as the induction coil 416, for example, as a planar induction coil. The flat coil 422 can have a relatively large inner diameter compared to its outer diameter. Due to the smaller surface area of ​​the flat coil 422, this relatively large inner diameter can provide relatively low capacitive coupling with an object near the flat coil 422. The flat coil 422 can be coupled to a grounding plate 424. In one example, the grounding plate 424 can be located on the top or bottom of the flat coil.

[0059] Fig. Figure 4C illustrates the 402 acquisition unit. Fig. 4A, comprising a flat coil 426 with a small inner circumference, according to one embodiment. Some of the features in Fig. 4C correspond to or resemble some of the features in Fig. 4A, as indicated by the same reference numerals, unless explicitly described otherwise. The flat coil 426 can serve as the induction coil 416. The flat coil 426 may have a relatively small inner diameter compared to its outer diameter. This relatively small inner diameter, compared to the outer diameter of the flat coil 426, can provide a relatively high capacitive coupling with an object near the flat coil 426 due to the larger surface area of ​​the flat coil 426.

[0060] Fig. 4D illustrates the capture unit 403 from Fig. 4A, comprising a rectangular coil 428, according to one embodiment. Some of the features in Fig. 4D corresponds to or resembles some of the features in Fig. 4A, as indicated by the same reference numerals, unless explicitly described otherwise. The rectangular coil 428 can serve as the induction coil 416. The rectangular coil 428 can have a relatively small inner area compared to its outer diameter. Due to the larger surface area of ​​the rectangular coil 428, this relatively small inner area, compared to the outer surface of the flat coil 426, can provide a relatively high capacitive coupling with an object near the rectangular coil 428.

[0061] Fig. Figure 4E illustrates the recording unit 404 from Fig. 4A, comprising a multilayer coil 430, according to one embodiment. Some of the features in Fig. 4E correspond to or resemble some of the features in the Fig. 2 and Fig. 4A, as indicated by the same reference numerals, unless explicitly described otherwise. The multilayer coil 430 can comprise a first coil 432 and a second coil 434. The first coil 432 can be positioned above the second coil 434 along a Z-axis. In one example, where the sensing unit 400 is used for capacitance sensing, the coil 432 can be used for coupling with the capacitor 412. In another example, where the device 200 is used for inductance sensing, the coil 432 and the coil 434 can be used for inductive coupling.

[0062] Fig. Figure 4F illustrates the recording unit 405 from Fig. 4A, comprising a primary coil 438 and a secondary coil 440, according to one embodiment. Some of the features in Fig. 4F correspond to or resemble some of the features in Fig. 4A, as indicated by the same reference numerals, unless explicitly described otherwise. The outer circumference of the secondary coil 440 may be smaller than the inner circumference of the primary coil 438. The secondary coil 440 may be coplanar and lie within the inner circumference of the primary coil 438.

[0063] Fig. 4G illustrates the 406 acquisition unit. Fig. 4A, comprising the primary coil 438 and the secondary coil 440, which are coplanar, according to one embodiment. Some of the features in Fig. 4G corresponds to or resembles some of the features in the Fig. 2, Fig. 4A and Fig. 4H, as indicated by the same reference symbols, unless explicitly described otherwise. The outer circumference of the secondary coil 440 may be approximately equal to the outer circumference of the primary coil 438. The secondary coil 440 may be coplanar to the primary coil 438 and lie adjacent to it. The implementations in the Fig. 4A-4G are not subject to any restrictions. The 400 detection unit can, for example, include a spiral coil, a solenoid, a delta coil, an extended coil, etc.

[0064] Fig. Figure 5 illustrates a detection circuit 500 with a hybrid capacitive-inductive sensor according to one embodiment. Some of the features in Fig. 5 correspond to or resemble some of the features in the Fig. 1 and 2A-2E, as indicated by the same reference numerals, unless explicitly described otherwise.

[0065] The sensing circuit 500 can include the PWM 228, the GPIO 226, and a sensing unit 540. The sensing unit 540 can include at least one of the following: a resistor 511, a first LC circuit 512, a GPIO 514, a second LC circuit 516, a capacitor 518, a ground 520, a capacitor 522, the GPIO 533, the GPIO 220, or the CMC 210. The first LC circuit 512, the second GPIO 514, the second LC circuit 516, the GPIO 533, and the GPIO 220 can be configured to provide different configurations of the sensing circuit 500 for capacitive and inductive sensing.

[0066] The CMC 210 can include a signal generator. The signal generator can generate a TX signal. In one example, the TX signal might be a square wave. An initial phase of the TX signal generated by the signal generator can be relative to a reference signal at the CMC 210. The phase shifter of the PWM 228 can control the phase of the TX signal. The CMC 210 can use the sensing unit 540 for capacitive sensing when there is no phase shift. The CMC 210 can use the sensing unit 540 for inductive sensing when there is a phase shift.

[0067] GPIO 226 can be a driver for adjusting the amplitude of the TX signal. GPIO 226 can be coupled to resistor 511. The TX signal can be sent as an RX signal to the CMC 210 via resistor 511, a first circuit assembly 528, a second circuit assembly 530, capacitor 522, GPIO 220, and / or GPIO 533. The TX signal can energize resistor 511, a first circuit assembly 528, a second circuit assembly 530, capacitor 522, GPIO 220, and / or GPIO 533.

[0068] In one embodiment, the resistor 511 may be coupled to a node 524. In another embodiment, a first circuit arrangement 528 may be coupled to the node 524. The LC circuit 512 and the GPIO 514 may be components of the first circuit arrangement 528. The GPIO 514 may include a ground or be coupled to a ground. The LC circuit 512 and the GPIO 514 may be connected in series. The first circuit arrangement 528 may be in series with the resistor 511.

[0069] In another embodiment, the resistor 511 or the first circuit arrangement 528 can be coupled in parallel to a node 526. The second LC circuit 516 and the capacitor 518, for example, may be components of a second circuit arrangement 530 that is coupled to the node 526. The capacitor 518 may also be coupled to ground. The second LC circuit 516 and the capacitor 518 may be connected in series. In one embodiment, the second circuit arrangement 528 may be in series with the resistor 511. In another embodiment, the second circuit arrangement 528 may be connected in parallel to the first circuit arrangement 528.

[0070] Resistor 511, the first circuit assembly 528, and / or the second circuit assembly 530 can be connected to a node 532. Capacitor 522 can be connected in series with resistor 511, the first circuit assembly 528, and / or the second circuit assembly 528 to node 532. GPIO 220 can be connected in series with capacitor 522 and CMC 210. In one embodiment, GPIO 533 may be connected to node 532 and in parallel with capacitor 522 and GPIO 220. GPIO 533 may also be connected to CMC.

[0071] When the TX signal is sent via resistor 511, the first circuit assembly 528 and / or the second circuit assembly 528, and capacitor 522, the resulting signal can be called the RX signal. GPIO 220 and / or GPIO 533 can couple the RX signal received from GPIO 226 via resistor 511, the first circuit assembly 528, and / or the second circuit assembly 528 into the CMC 210. The CMC 210 can compare the digital value corresponding to the RX signal with a digital value of a reference signal to determine whether there is a relative difference between the amplitude of the RX signal and the amplitude of the reference signal that exceeds a threshold value. If the relative difference between the representative amplitudes of the RX signal and the reference signal exceeds the threshold, the difference may indicate the presence of an object near the device 200.

[0072] In one example, where the difference between the RX signal and the reference signal does not exceed the threshold, the difference might indicate that no object is near the sensing circuit 500, such as the LC circuit 512 or the LC circuit 516. In another example, where the difference between the RX signal and the reference signal does not exceed the threshold, the sensing circuit 500 might not be configured to detect the type of object near the device 200 and might not indicate that an object is near the sensing circuit 500. In an example where the sensing circuit 500 is configured to perform capacitive sensing, the sensing circuit 500 might detect conductive ferrous or non-ferrous objects.In another example, where the detection circuit 500 is configured to perform inductive detection, the detection circuit 500 can potentially detect conductive objects at a given potential. The detection circuit 500 can use the first circuit arrangement 528 and / or 530 to perform inductive detection and the capacitor 522 to perform capacitive detection. The components of the first circuit arrangement 528 and 530, respectively, are not subject to any restrictions. Fig. Figures 6A-6D illustrate different implementations of the 528 and 530 resonant circuits and the 533 and 220 GPIOs, as discussed below.

[0073] Fig. Figure 6A illustrates a detection circuit 600, which includes the detection unit 540. Fig. 5, comprising the first circuit arrangement 528 with a capacitor 640 and the second circuit arrangement 530 with an induction coil 642, according to one embodiment. In one embodiment, the sensing circuit can be described as a two-sensor hybrid sensing circuit, which can be configured for inductive or capacitive sensing. Some of the features in Fig. 6A corresponds to or resembles some of the features in Fig. 5, as indicated by the same reference numerals, unless explicitly described otherwise. The resistor 511 and the first circuit assembly 528 can be connected in series and / or to node 524. Node 524 can be connected to node 526. The second circuit assembly 530 can be connected to node 526. The second circuit assembly 530 can also be connected in parallel to the first circuit assembly 528. The induction coil 642 of the first circuit assembly 530 may be a first electrode. The first circuit assembly 528 and the second circuit assembly 530 can be connected to a common operating ground (AC ground).

[0074] Capacitor 518 can be connected between node 526 and GPIO 220. GPIO 220 can be connected to CMC 210. CMC 210 can be connected to resonant circuit 646 via a switch 645. When switch 645 is open, the connection between resonant circuit 646 and CMC 210 is broken. When switch 645 is closed, resonant circuit 646 can be connected to CMC 210. In one embodiment, resonant circuit 646 is a second electrode.

[0075] When the detection circuit 600 is configured for inductive detection, the first circuit arrangement 528 and the second circuit arrangement 530 can be connected to the CMC 210 via the capacitor 518. The CMC 210 and GPIO 226 can be configured for inductive detection mode. For example, a metal object near the detection circuit 600, such as the capacitor 640 connected in parallel to the induction coil 642, might affect the amplitude and phase of the LC circuit arrangement comprising the first circuit arrangement 528 and the induction coil 642, which can be detected by the CMC 210. In the inductive detection configuration, the CMC 210 can detect the relative change in the amplitude of the RX signal.

[0076] In an embodiment where the detection circuit 600 is configured for inductive detection, the connection between the resonant circuit 646 and the CMC 210 can be interrupted by the switch 645. The resonant circuit 646 may, for example, be an electrode, and the switch 645 can set the electrode connection either to ground or to high-Z. The CMC 210 and GPIO 226 can be configured for inductive detection. Using the RX signal received at GPIO 220, the CMC 210 can detect ferrous or non-ferrous metal objects that change the amplitude of the RX signal.

[0077] In another embodiment, the second circuit arrangement 530 may be a flat, circular electrode. In another embodiment, the resonant circuit 646 may be a spiral electrode. The shape of the electrodes is not subject to any restrictions. For example, the electrodes may also have a shape that provides a threshold for capacitive coupling between the induction coil 642 and the resonant circuit 646 for capacitive detection.

[0078] Fig. Figure 6B illustrates an embodiment of a single-sensor hybrid sensing circuit of the sensing unit 540 from Fig. 5, comprising the first circuit arrangement 528 with the capacitor 640 and the second circuit arrangement 530 with the induction coil 642, a capacitor 648 and a ground 650, according to one embodiment. In alternative embodiments, the single-sensor hybrid sensing circuit can be used for capacitive sensing (in Fig. 6B) and inductive detection (in Fig. 6C) be configured. Some of the features in Fig. 6B correspond to or resemble some of the features in the Fig. 5 and Fig. 6A, as indicated by the same reference numerals, unless explicitly described otherwise.

[0079] Resistor 511 and the first circuit assembly 528 can be connected in series at node 524. Node 524 can be connected to node 526. The second circuit assembly 530 can be connected to node 526. The second circuit assembly 530 can include induction coil 642, capacitor 648, and ground 650, connected in series.

[0080] The second circuit arrangement 530 can also be connected in parallel to the first circuit arrangement 528. In one embodiment, the second circuit arrangement 530 can be connected in series with the first circuit arrangement 528 (in Fig. (Figure 6B not shown). Capacitor 518 can be connected between node 526 and GPIO 220. In one example, GPIO 220 might be a switch with an open and a closed position. When the switch is closed, capacitor 518 is connected to CMC 210. When the switch is open, the connection between capacitor 518 and CMC 210 is broken. GPIO 651 can also be a switch. When GPIO 651 is closed, CMC 210 can be directly connected to node 526. When GPIO 651 is open, the connection between CMC 210 and node 526 can be broken. In one embodiment, the first circuit arrangement 528 and the second circuit arrangement 530 can be connected to CMC 210 via coupling capacitor 518, and GPIO 651 can be open.

[0081] If the sensing unit 540 is configured for capacitance sensing, capacitor 518 can be bridged with GPIO 220. Switch 656 disconnects the connection to the circuit arrangement for inductive sensing, so that it no longer receives the TX signal, and sets the inactive connection to GPIO 226 to high-Z. Switch 658 disconnects the ground connection to the sensing circuit 500 and sets the inactive ground connection to high-Z. In this configuration, the CMC 210 may be configured for intrinsic capacitance sensing (CSD), with the induction coil 642 being configured as the intrinsic capacitance electrode. An object located near the induction coil 642 may change its intrinsic capacitance, which can be detected by the CMC 210 operating in the CSD configuration.

[0082] Fig. Figure 6C illustrates the acquisition unit 540, in which GPIO 651 is open and GPIO 220 is closed, according to one embodiment. The embodiment in Fig. 6C can be used in the single-sensor hybrid sensing circuit in Fig. It resembles the 6B, but is configured for inductive detection. Some of the features in Fig. 6C correspond to or resemble some of the features in the Fig. 5, Fig. 6A and Fig. 6B, as indicated by the same reference numerals, unless explicitly described otherwise. The resistor 511 and the first circuit assembly 528 may be connected in series through the node 524. The first circuit assembly 528 may be the capacitor 640. The node 524 may be connected to the node 526. The second circuit assembly 530 may be connected to the node 526. The second circuit assembly 530 may include the induction coil 642. The first circuit assembly 528 and the second circuit assembly 530 may be connected in parallel and connected to an AC ground. In an alternative embodiment, the first circuit assembly 528 and the second circuit assembly 530 may be connected in series.

[0083] Capacitor 518 can be connected to node 526 and GPIO 220. In one example, GPIO 220 might be a switch with an open and a closed position. When the switch is in the closed position, capacitor 518 is connected to CMC 210. When the switch is in the open position, the connection between capacitor 518 and CMC 210 is broken. GPIO 651 can also be a switch. When GPIO 651 is closed, CMC 210 can be connected directly to node 526. When GPIO 651 is open, the connection between CMC 210 and node 526 can be broken, or CMC 210 can be connected to node 526 via GPIO 220.

[0084] In an embodiment where the detection unit 540 is configured for inductive detection, the induction coil 642 can be connected to the CMC 210 via GPIO 220. GPIO 651 can be left open. The CMC 210 and GPIO 226 can be configured for inductive detection. Using the RX signal received at GPIO 220, the CMC 210 can detect ferrous or non-ferrous metal objects that change the amplitude of the RX signal.

[0085] Fig. Figure 6D illustrates the 540 acquisition unit. Fig. 5, comprising a first circuit arrangement 528 with a capacitor 514 and the second circuit arrangement 530 with the induction coil 642, a capacitor 662, an induction coil 664, a capacitor 666 and a ground 668, according to one embodiment. The embodiment in Fig. 6D can be used in Fig. The two-sensor hybrid sensing circuit shown in Figure 6A is similar, but is configured for capacitive sensing. Some of the features in Fig. 6D corresponds to or resembles some of the features in the Fig. 1, Fig. 2, Fig. 5, Fig. 6A, Fig. 6B and Fig. 6C, as indicated by the same reference numerals, unless explicitly stated otherwise.

[0086] GPIO 226 can be connected to a switch 660. When switch 660 is in the closed position, GPIO 226 is connected to resistor 511. When switch 660 is open, the connection between GPIO 226 and GPIO 226 is broken. Resistor 511 and the first circuit assembly 528 can be connected in series via node 524. The first circuit assembly 528 can be GPIO 514.

[0087] Node 524 can be connected to node 526. The second circuit arrangement 530 can be connected to node 526. The second circuit arrangement 530 can also be connected in parallel to the first circuit arrangement 528. The induction coil 642 and the capacitor 640 can be connected to an AC ground. The second circuit arrangement 530 can include the induction coil 642, the capacitor 662, the induction coil 664, the capacitor 666, and ground 668. The induction coil 642 can be connected in series with the capacitor 662. The capacitor 662 can be connected in series with the resonant circuit 646. The induction coil 664 can be connected in series with the capacitor 666. The capacitor 666 can be connected in series with ground 668.

[0088] Capacitor 518 can be connected between node 526 and GPIO 220. GPIO 220 can be connected to CMC 210. When GPIO 220 is in the open position, the connection between capacitor 518 and CMC 210 is broken. When GPIO 220 is in the closed position, the capacitor is connected to CMC 210.

[0089] In an embodiment where the sensing unit 540 is configured for capacitance sensing, the connection between the resonant circuit 642 and the CMC 210 can be interrupted via GPIO 220, and the third resonant circuit 642 can be connected to the CMC 210 via capacitor 662 and resonant circuit 646. For example, GPIO 220 can set the third resonant circuit 642 to ground or high-Z. Switch 660 can interrupt the connection to GPIO 226 so that the sensing unit 540 does not receive the TX signal. Switch 660 can set the connection for the TX signal to ground or high-Z.

[0090] In an embodiment where the CMC 210 is configured for self-capacitance detection, the third resonant circuit 642 can be connected to a ground and configured as a second electrode for coupling with the resonant circuit 646. The CMC 210 can use the received RX signal to detect conductive objects that can alter a capacitive field between the third resonant circuit and the resonant circuit 646.

[0091] Fig. Figure 7 illustrates a graph 700 of an amplitude change 720 associated with a digital representation of the RX signal 712 according to one embodiment. The graph 700 shows a digital representation of the RX signal 712, which is output from the CMC 210. Fig. 2A is received. The resonant circuit 224 and the capacitor 222 are made of Fig. 2A can receive a TX signal at period 714 and can be excited by the TX signal.

[0092] At period 714, line 710 shows no relative change between the amplitudes of the RX signal and the reference signal. The lack of a relative change may indicate that when performing capacitive sensing for the non-phase-shifted signal, as discussed above, no object may be detected by the CMC 210. At period 716, the PWM 228 may shift the phase of the TX signal by approximately 90 degrees. At period 716, line 710 shows a relative change between the amplitudes of the RX signal and the reference signal. This relative change may indicate that when performing inductive sensing using the phase-shifted signal, as discussed above, an object may be detected by the CMC 210. In one embodiment, the peaks 722 of the RX signal 712 may represent a period during which an object is placed near the device 200.

[0093] At interval 718, the PWM 228 can shift the phase of the TX signal back to approximately 0 degrees. At interval 718, line 710 shows no relative change between the amplitude of the RX signal and the amplitude of the reference signal. This lack of relative change may indicate that when performing capacitive sensing using the non-phase-shifted signal, as discussed above, the CMC 210 might not detect an object.

[0094] In one embodiment, the PWM 228 can alternately send a TX signal with a phase of 0 degrees and a phase-shifted TX signal. The timing settings of the CMC 210 can be synchronized such that the phases of the TX signal are alternately switched; thus, the CMC 210 can be configured to perform sequential capacitive and inductive sensing.

[0095] In another embodiment, the device 200 can switch between capacitive and inductive sensing depending on the application for which it is being used. For example, the device 200 may have a power-saving mode that uses capacitive sensing for an on / off button. Once the device is switched on, it can switch to using inductive sensing to receive user input.

[0096] In another embodiment, the device can perform 200 measurements for capacitive detection until the signal-to-noise ratio of the RX signal, namely an input charge (Vtank*Cc), exceeds a signal-to-noise ratio threshold. If the signal-to-noise ratio exceeds the threshold, the processor 119 can Fig. 2A switches the PWM 228 and the CMC 210 to inductive sensing. If the device 200 is performing inductive sensing and the signal-to-noise ratio of the TX signal exceeds the signal-to-noise ratio threshold, the processor 119 can analogously switch the PWM 228 and the CMC 210 to capacitive sensing.

[0097] In one embodiment, the signal-to-noise ratio threshold may vary depending on the size or type of object for which the Device 200 is configured to detect. For example, if the object is relatively small, the signal-to-noise ratio threshold may be increased to allow sufficient time for capacitive or inductive detection by the Device 200. More time may be required because the TX signal may be noisier, and calculating averages from various capacitive or inductive measurements by the CMC 210 to determine the presence of the object may take longer. Measurements for relatively smaller objects may take longer than for relatively large objects because the amount of coupling between the relatively small objects and the Device 200 is smaller.

[0098] Fig. Figure 8A illustrates a graph 800 of a phase shift and demodulation of a TX signal 810 for inductive detection according to one embodiment. As discussed above, the resonant circuit 224 can be made of Fig. 2B receives the TX signal 810 from node 250 of GPIO 226, which excites the components of the resonant circuit 224. For inductive detection, the PWM 228 shifts Fig. 2A the TX signal in phase.

[0099] In graph 800 for inductive detection, the TX signal 810 may be phase-shifted by approximately 90 degrees. The Vamp signal 812 may indicate a voltage change across an inductor of the resonant circuit 224 and across capacitor 222. The Vamp signal 812 can be received at GPIO 220. The Vamp signal 812 may be a sinusoidal oscillation, as the inductor may not respond instantly to a change between the high and low voltage of the TX signal 810. In one example, the PWM 228 may shift the TX signal in phase by 90 degrees with respect to the demodulation clock signals PHI1 814 and PHI2 816. The demodulation clock signals PHI1 814 and PHI2 816 are possibly internal signals that are fed from PHI1 252 and PHI2 254 of the digital sequence controller 233 to the demodulator of the CMC 210. Fig. 2A are supplied. In one embodiment, there may be a dead zone between the PHI1 814 and the PHI2 816. The dead zone may be an interval of a signal domain or signal band in which no action takes place. In another embodiment, the PHI1 814 and the PHI2 816 may control the switches of the CMC 210 from the Fig. 2A-6D.

[0100] The phase-shifted TX signal can be phase-shifted such that the peak of the sine wave vamp signal 818 occurs 90° after a rising edge of the initial TX signal. The phase-shifted TX signal can be fully integrated by the CMC 210. The CMC 210's demodulator can convert the signals 820 received by the CMC 210 from GPIOs 212, 216, and / or 220 to generate an aggregated signal 822 with the same phase. For example, the CMC 210 can combine the positive and negative components of the signals from GPIOs 212, 216, and 220 to obtain signal 822. Since in this example the CMC 210 pushes and pulls charge from the resonant circuit 224, the CMC 210 can aggregate the signals over time and integrate them together to obtain a V integrate-Signal 824 is generated. By aggregating and integrating the signals, the amount of charge applied to the resonant circuit 224 can be increased. The CMC 210 can also convert signal 822 into a digital signal using an analog-to-digital converter (ADC).

[0101] The V integrate Signal 824 can be a useful voltage illustrating the accumulation of a signal voltage. In one example, digital values ​​from the converter can be accumulated using a counter, and these digital values ​​can be sent from terminal 256 of comparator 240. Each cycle is integrated and converted, and the integration capacitors are set to a value (V). ref ), at which the integration capacitors have started to be reset. The CMC 210 can use the digital values ​​to apply a signal to the resonant circuit 224 to excite the components of the resonant circuit 224 for inductive detection.

[0102] Fig. Figure 8B illustrates a graph 802 with a TX signal 810 for capacitive sensing according to one embodiment. The TX signal 810 may not be phase-shifted with respect to the demodulation clock signals PHI1 814 and PHI2 816. The demodulation clock signals PHI1 814 and PHI2 816 may be internal signals that are fed from PHI1 252 and PHI2 254 of the digital sequence controller 233 into the demodulator of the CMC 210. Fig. 2A can be fed in. V ref 826 is the voltage from the signal of capacitor 218 at point 255 in Fig. Viewed from a 2D perspective. V ref 828 is the voltage from the signal of capacitor 214 at point 257 in Fig. Viewed from a 2D perspective. V ref 830 is the voltage from the signal of GPIO 220 at point 259 in Fig. Viewed from a 2D perspective. A count duration of 832 is representative of V. ref 826, V ref 828, and V ref 830 can indicate whether an object is near a detection unit.

[0103] In one example, digital values ​​from the converter are accumulated using a counter, and the digital values ​​can be sent from terminal 256 of comparator 240. Each cycle is integrated and converted into a digital value, for which the V DD at point 261 in Fig. The CMC 210 uses 2D technology. It can determine whether an object is near the detection unit using digital values. For example, the CMC 210 can determine that an object is near the detection unit if a counter duration of the digital values ​​changes.

[0104] Fig. Figure 9 illustrates a graph 900 showing the phase shift and demodulation of a resonant circuit output signal for inductive detection according to one embodiment. Some of the features in Fig. 9 correspond to or resemble some of the features in Fig. 8, as indicated by the same reference symbols, unless explicitly described otherwise. Signal 912 shows that PHI1 814 and PHI2 816 form a demodulation clock signal 912, which is fed into the demodulator of the CMC 210. Fig. 2A is supplied and can be combined. Signal 912 can control the switches of the CMC 210 from the Fig. Control 2A-6D.

[0105] In one embodiment, a charge in an AMUX of the CMC 210 can be transduced below a reference voltage (V) during the PHI2 clock phase of the demodulation clock signal 912. ref HI) increase. During the PHI1 clock phase, the digital sequence control 233 can be switched off. Fig. 2A den C tank 218 unloaded again to such an extent that V ref The voltage falls below HI. During the high phase of the demodulation clock signal 912, the voltage in the AMUX can rise above V. ref Increase the -HI voltage. During the PHI2 clock phase, the digital sequence controller 233 charges the C mod 214 out Fig. 2A up to the reference voltage.

[0106] Fig. Figure 10A shows a graph 1000 generated by the CMC 210. Fig. 2A Frequencies used for inductive detection according to one embodiment. An electrode can be used for inductive detection. The detection range of an electrode can depend on the type of object detected and on the size and shape of the electrode. Ferrous metals such as iron and steel, for example, can enable a greater detection range, while non-ferrous metals such as aluminum and copper can reduce the detection range of the electrode by up to 60 percent.

[0107] In one embodiment, selecting the size and shape of an electrode may involve determining an approximate inner diameter / outer diameter ratio of the electrode, determining an inductance factor (AL) for the electrode as a function of inner diameter, outer diameter, thickness, conductor width and spacing, number of turns and layers, and the layout of the electrode layers. The size and shape of an electrode may vary depending on its application. For example, the electrode may be a flat coil or a disc coil. If the electrode is used for capacitive sensing, a high potential may be applied to an outer terminal of the electrode rather than its central or inner terminal surface.The ratio of the electrode's inner diameter (D_inner) to its outer diameter (D_outer) can be based on the size of the detected object and the detection distance between the electrode and the object. For example, a D_inner / D_outer ratio of approximately 0.25 might be used for objects located relatively close to the electrode. Conversely, a D_inner / D_outer ratio of approximately 0.6 might be used for objects located relatively far from the electrode.

[0108] In another embodiment, selecting the electrode size may also include determining the capacitive coil coupling between the electrode's windings and layers, as well as between ground and a target object. The electrode's inductance and resistance can then be analyzed to select an electrode size with an optimal frequency response.

[0109] The operating frequency is optimal when the signal difference between an object and no object is greatest, and when the digital values ​​change by the greatest amount. For example, a resonant circuit can be excited by a TX signal at a specific resonant frequency. In another example, this resonant circuit frequency might be 1 / 2 * π * LC. In yet another example, the further the frequency is from the resonant frequency, the greater the potential signal difference. In yet another example, a series resistor in the resonant circuit 224 can be used in Fig. 2A can be changed so that the magnitude of the signal difference becomes larger or smaller.

[0110] Graph 1000 shows the amplitude of a reference signal 1012 and the amplitude of the RX signal 1010. The greatest difference between the amplitude of the reference signal 1012 and the amplitude of the RX signal 1010 occurs at points 1014 and 1016, thus indicating the largest difference in the digital values. The amplitude differences indicate that the optimal frequency is approximately 600 kilohertz (kHz) or 1000 kHz.

[0111] Fig. Figure 10B shows a graph of another frequency generated by the CMC 210. Fig. 2A can be used for inductive detection, according to one embodiment. Graph 1020 shows the amplitude of a reference signal 1024 and the amplitude of the TX signal 1022. The greatest difference between the amplitude of the reference signal 1024 and the amplitude of the TX signal 1022 is at point 1026. The amplitude differences indicate that the optimal frequency is approximately 1000 kHz.

[0112] Fig. 10C shows a graph 1030 of another one through the CMC 210 from Fig. 2A for inductive detection, frequency used according to one embodiment. Graph 1030 shows the amplitude of a reference signal 1034 and the amplitude of the TX signal 1032. The greatest difference between the amplitude of the reference signal 1034 and the amplitude of the TX signal 1032 is at point 1036. The amplitude differences indicate that the optimal frequency is approximately 1000 kHz.

[0113] Fig. Figure 11 illustrates a flowchart of a method 1100 for determining the inductance or capacitance of a detection unit according to one embodiment. The method 1100 can be performed by processing logic that includes hardware (e.g., a circuit arrangement, dedicated logic, programmable logic, microcode, etc.), software (e.g., instructions executed in a processing element), or a combination thereof. The method 1100 can be performed wholly or partially by the device 200.

[0114] Procedure 1100 begins at block 1110, where a signal generator produces a first signal and a third signal. Procedure 1100 continues at block 1120, where the PWM shifts the phase of the first signal to obtain the third signal. In one example, the PWM might shift the phase of the third signal by approximately 90 degrees relative to the phase of a reference signal. Procedure 1100 continues at block 1130, where the first signal excites a sensing unit. Procedure 1100 continues at block 1140, where a charge-measuring circuit measures a second signal in a sensing unit when the first signal is applied to the sensing unit by the signal generator. The second signal might be representative of a capacitance of the sensing unit. Procedure 1100 continues at block 1150, where the third signal excites the sensing unit.Method 1100 continues at block 1160 by having the charge measurement circuit measure a fourth signal in a detection unit when the third signal is applied to the detection unit by the signal generator. The fourth signal can be representative of an inductance of the detection unit.

[0115] Fig. Figure 12 illustrates a flowchart of a method 1200 for applying signals to a first electrode and a second electrode according to a further embodiment. The method 1200 can be carried out by processing logic that includes hardware (e.g., a circuit arrangement, dedicated logic, programmable logic, microcode, etc.), software (e.g., instructions executed in a processing element), or a combination thereof. The method 1200 can be carried out in whole or in part by the device 200.

[0116] Method 1200 begins at block 1210 by applying a first signal to a first electrode in a first mode. Method 1200 continues at block 1220 by receiving a second signal at a second electrode in response to the application of the first signal to the first electrode. The second signal may indicate capacitance between the first and second electrodes. Method 1200 continues at block 1230 by applying a third signal to an inductive coil in a second mode. Method 1200 continues at block 1240 by receiving a fourth signal at the inductive coil in response to the third signal. The fourth signal indicates inductance of the inductive coil. The fourth signal may indicate inductance of the second electrode.Procedure 1200 continues at block 1240, where a CMC determines whether an object is near the first electrode, the second electrode, or the inductive coil. In one example, the CMC might determine that a capacitive object is near the first or second electrode when the second signal changes. The change in the second signal indicates a change between the capacitance of the first electrode and the capacitance of the second electrode. In another example, the CMC might determine that a ferrous metal object or a non-ferrous metal object is near the inductive coil when the fourth signal changes. The change in the fourth signal could indicate a change in the inductance of the inductive coil.

[0117] Embodiments of the present invention comprise various processes described herein. These processes can be carried out by hardware components, software, firmware, or a combination thereof.

[0118] The operations of the procedures herein are shown and described in a specific order; however, the order of operations of each procedure can be changed so that some operations may be performed in reverse order or so that some operations may be performed at least partially concurrently with other operations. In a further embodiment, instructions or sub-operations of different types of operations may be performed with interruptions and / or alternately. The terms "first," "second," "third," "fourth," etc., as used herein, serve as designations to distinguish different elements and are not necessarily ordinal numbers corresponding to their numerical designation.

[0119] The above description presents numerous specific details, such as examples of concrete systems, components, processes, etc., to facilitate an understanding of various embodiments of the present invention. However, it is obvious to those skilled in the art that at least some embodiments of the present invention can be practically implemented even without these specific details. In other cases, well-known components and processes are not described in detail or are presented in a simple block diagram form to avoid unnecessarily complicating the understanding of the present embodiments. Therefore, the specific details presented are merely exemplary. Certain embodiments may deviate from these exemplary details but may nevertheless be considered to fall within the scope of protection of the present invention.

Claims

[1] A combined detection circuit comprising the following: a first electrode that is coupled to a first terminal; a resonant circuit coupled between the first electrode and the first terminal; and a second electrode coupled to a second terminal, wherein: the first and second electrodes form a variable capacitance in a first mode when a transmitted signal from a signal generator coupled to the first terminal is smaller than the oscillation frequency of the resonant circuit. The first and second electrodes form a variable induction coil in a second mode when the transmitted signal from the generated signal coupled to the first terminal is equal to the oscillation frequency of the resonant circuit, and The second electrode is intended for receiving a first receive signal (RX signal) from the first electrode in the first mode and for receiving a second RX signal from the first electrode in the second mode. [2] Combined detection circuit according to claim 1, wherein the variable capacitance is a counter-capacitance formed between the first and the second electrode. [3] Combined detection circuit according to claim 1, wherein the first electrode forms an inductive coil. [4] Combined detection circuit according to claim 3, wherein a magnetic field is generated on the inductive coil in response to the transmitted signal in the second mode. [5] Combined detection circuit according to claim 4, wherein an object in the vicinity of the inductive coil induces an eddy current which is directed opposite to the magnetic field, wherein the eddy current changes an inductance of the variable inductive coil which is represented by the second RX signal. [6] Combined detection circuit according to claim 3, which further includes a capacitor coupled in series with the inductive coil. [7] Combined detection circuit according to claim 3, wherein the signal generator is a pulse with modulator (PWM). [8] Combined sensing circuit according to claim 7, wherein the charge sensing circuit is configured to output a value representative of a capacitance between the first and second electrodes in the first mode, and is configured to output a value representative of an inductance between the first and second electrodes in the second mode. [9] Combined detection circuit according to claim 7, wherein the charge measurement circuit has a first configuration in the first mode and a second configuration in the second mode. [10] Combined detection circuit according to claim 1, wherein the TX signal includes: a first TX signal in a first mode; and a second TX signal in the second mode, wherein the second TX signal is shifted approximately 90 degrees relative to a phase of the first TX signal. [11] A resonant circuit comprising the following: an induction coil coupled to a first terminal of a measuring instrument, the first terminal of the measuring instrument being designed to receive a transmitted signal from a signal generator; and an electrode near the induction coil to receive an initial received signal in response to the transmitted signal, if the transmitted signal frequency is lower than the oscillation frequency of the resonant circuit, and to receive a second received signal in response to the transmitted signal, if the transmitted signal frequency is equal to the oscillation frequency of the resonant circuit. [12] Resonant circuit according to claim 11, wherein the first received signal indicates a capacitance of the resonant circuit and wherein the second received signal indicates an inductance of the resonant circuit. [13] Resonant circuit according to claim 12, wherein the capacitance is an intrinsic capacitance of the induction coil. [14] Resonant circuit according to claim 13, wherein the capacitance is a counter-capacitance formed between the induction coil and the electrode. [15] Resonant circuit according to claim 11, wherein the first induction coil is a solenoid and the electrode is a flat coil. [16] Resonant circuit according to claim 12, wherein an inductance of the induction coil can be changed by an object in the vicinity of the induction coil. [17] A procedure that includes the following: Generating a first transmit signal (TX signal) by a first signal generator; Applying the TX signal to a first electrode of a detection unit in a first mode; Receiving a first receive signal (RX signal) at a second electrode of the acquisition unit in response to the application of the TX signal to the first electrode; Measuring the first RX signal by a measuring circuit at the second electrode in the first mode, where the first RX signal indicates a capacitance between the first electrode and the second electrode; Generating a second TX signal using a second signal generator, where the second TX signal is an alternating current signal (AC signal); Applying the second TX signal to the first electrode of the acquisition unit in a second mode; Receiving a second RX signal at the second electrode of the detection unit in response to the second RX signal, wherein the detection unit is designed to operate as a variable capacitor in the first mode when a first frequency of the first TX is below or above a resonant frequency of the resonant circuit, and wherein the detection unit is designed to operate as a variable inductor in the second mode when a second frequency of the second TX signal is at the resonant frequency of the resonant circuit in order to excite the resonant circuit; and Measuring the second TX signal by the measuring circuit at the second electrode in the second mode, wherein the second TX signal indicates an inductance of the variable induction coil, where the first electrode and the second electrode are common to the first mode and the second mode. [18] Method according to claim 17, further comprising determining that a capacitive object is near the first electrode or the second electrode when the first RX signal changes, wherein a change in the first RX signal indicates a change in the capacitance between the first electrode and the second electrode. [19] Method according to claim 17, further comprising determining that an iron metal object or a non-ferrous metal object is near the inductive coil electrode when the second RX signal changes, wherein a change in the second RX signal indicates a change in the inductance at the induction coil. [20] Method according to claim 17, wherein the second TX signal is phase-shifted by 90 degrees relative to the first TX signal.

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