Patent Description:
The present invention relates generally to wireless charging of batteries, including batteries in mobile computing devices, and more particularly to detection of foreign objects during a charging operation as defined in the claims.

Wireless charging systems have been deployed to enable certain types of devices to charge internal batteries without the use of a physical charging connection. Devices that can take advantage of wireless charging include mobile processing and/or communication devices. Standards, such as the Qi standard defined by the Wireless Power Consortium enable devices manufactured by a first supplier to be wirelessly charged using a charger manufactured by a second supplier. Standards for wireless charging are optimized for relatively simple configurations of devices and tend to provide basic charging capabilities.

Improvements in wireless charging capabilities are required to support continually increasing complexity of mobile devices and changing form factors. For example, there is a need for improved wireless transmission power control, including detection of foreign objects that may affect wireless transmission of power when placed on or near a charging device. <CIT> describes a power transmitting device with a power transmitting coil, a foreign object detector , a magnetic field detector, and a control device that receives information about a result of detection of a foreign object by the foreign object detector. The control device determines whether there is a foreign object or not based on the result of the detection of a foreign object performed by the foreign object detector during a timing period when the strength of the magnetic field is equal to or lower than a prescribed value. <CIT> discloses a wireless power transmitter in which a foreign object detector performs a foreign object detection test in response to a measured parameter for a test drive signal during the foreign object detection intervals.

Several aspects of wireless charging systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawing by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements").

The software may reside on a processor-readable storage medium. A processor-readable storage medium, which may also be referred to herein as a computer-readable medium may include, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., compact disk (CD), digital versatile disk (DVD)), a smart card, a flash memory device (e.g., card, stick, key drive), Near Field Communications (NFC) token, random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), a register, a removable disk, a carrier wave, a transmission line, and any other suitable medium for storing or transmitting software. The computer-readable medium may be resident in the processing system, external to the processing system, or distributed across multiple entities including the processing system. Computer-readable medium may be embodied in a computer-program product. By way of example, a computer-program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

Certain aspects of the present disclosure relate to systems, apparatus and methods applicable to wireless charging devices and techniques. In a wireless charging device, charging cells may be configured with one or more inductive coils to provide a charging surface that can charge one or more devices wirelessly. The location of a device to be charged may be detected through sensing techniques that associate location of the device to changes in a physical characteristic centered at a known location on the charging surface. Sensing of location may be implemented using capacitive, resistive, inductive, touch, pressure, load, strain, and/or another appropriate type of sensing.

In one aspect of the disclosure, an apparatus has a battery charging power source, a plurality of charging cells configured in a matrix, a first plurality of switches in which each switch is configured to couple a row of coils in the matrix to a first terminal of the battery charging power source, and a second plurality of switches in which each switch is configured to couple a column of coils in the matrix to a second terminal of the battery charging power source. Each charging cell in the plurality of charging cells may include one or more coils surrounding a power transfer area. The plurality of charging cells may be arranged adjacent to a charging surface of the wireless charging device without overlap of power transfer areas of the charging cells in the plurality of charging cells. Devices placed on the surface may receive power that is wirelessly transmitted through one or more of the charging cells.

In some instances, the apparatus may also be referred to as a charging surface. Power can be wirelessly transferred to a receiving device located anywhere on a surface of the apparatus. The devices can have an arbitrarily defined size and/or shape and may be placed without regard to any discrete placement locations enabled for charging. Multiple devices can be simultaneously charged on a single charging surface. The apparatus can track motion of one or more devices across the charging surface.

Certain aspects disclosed herein relate to improved wireless charging techniques. In various aspects of the disclosure, a method for operating a charging device includes providing a charging current to a resonant circuit when a receiving device is present on a surface of the wireless charging device, providing a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or to transitions of a current in the resonant circuit through a zero ampere level, providing a measurement slot by decreasing or terminating the charging current for a period of time, and determining whether an object other than the receiving device is present on a surface of the charging device based on measurements of samples of voltage or current captured based on timing provided by the zero-crossing signal, where the samples are captured during the measurement slot.

According to certain aspects disclosed herein, a charging device may provide a charging surface using charging cells that are deployed adjacent to the charging surface. In one example, the charging cells are deployed in one or more layers of the charging surface in accordance with a honeycomb packaging configuration. A charging cell may be implemented using one or more coils that can each induce a magnetic field along an axis that is substantially orthogonal to the charging surface adjacent to the coil. In this description, a charging cell may refer to an element having one or more coils where each coil is configured to produce an electromagnetic field that is additive with respect to the fields produced by other coils in the charging cell, the electromagnetic field producing a magnetic flux directed along or proximate to a common axis.

In some implementations, a charging cell includes coils that are stacked along a common axis and/or that overlap such that they contribute to an induced magnetic field substantially orthogonal to the charging surface. In some implementations, a charging cell includes coils that are arranged within a defined portion of the charging surface and that contribute to an induced magnetic field within the substantially orthogonal portion of the charging surface associated with the charging cell. In some implementations, charging cells may be configurable by providing an activating current to coils that are included in a dynamically defined charging cell. For example, in a charging device may include multiple stacks of coils deployed across the charging surface, the charging device may detect the location of a device to be charged and may select some combination of stacks of coils to provide a charging cell adjacent to the device to be charged. In some instances, a charging cell may include, or be characterized as a single coil. However, it should be appreciated that a charging cell may include multiple stacked coils and/or multiple adjacent coils or stacks of coils. The coils may be referred to herein as charging coils, wireless charging coils, transmitter coils, transmitting coils, power transmitting coils, power transmitter coils, or the like.

<FIG> illustrates an example of a charging cell <NUM> that may be deployed and/or configured to provide a charging surface of a charging device. As described herein, the charging surface may include an array of charging cells <NUM> provided on one or more substrates <NUM>. A circuit comprising one or more integrated circuits (ICs) and/or discrete electronic components may be provided on one or more of the substrates <NUM>. The circuit may include drivers and switches used to control currents provided to coils used to transmit power to a receiving device. The circuit may be configured as a processing circuit that includes one or more processors and/or one or more controllers that can be configured to perform certain functions disclosed herein. In some instances, some or all of the processing circuit may be provided external to the charging device. In some instances, a power supply or battery may be coupled to the charging device.

The charging cell <NUM> may be provided in close proximity to an outer surface area of the charging device, upon which one or more devices can be placed for charging. The charging device may include multiple instances of the charging cell <NUM>. In one example, the charging cell <NUM> has a substantially hexagonal shape that encloses one or more coils <NUM> constructed using conductors, wires or circuit board traces that can receive a current sufficient to produce an electromagnetic field in a power transfer area <NUM>. In various implementations, some coils <NUM> may have a shape that is substantially polygonal, including the hexagonal charging cell <NUM> illustrated in <FIG>. Other implementations provide coils <NUM> that have other shapes. The shape of the coils <NUM> may be determined at least in part by the capabilities or limitations of fabrication technology, and/or to optimize layout of the charging cells on a substrate <NUM> such as a printed circuit board substrate. Each coil <NUM> may be implemented using wires, printed circuit board traces and/or other connectors in a spiral configuration. Each charging cell <NUM> may span two or more layers separated by an insulator or substrate <NUM> such that coils <NUM> in different layers are centered around a common axis <NUM>.

<FIG> illustrates an arrangement of power transfer areas provided in a charging surface <NUM> of a charging device that employs multiple layers of charging cells configured in accordance with certain aspects disclosed herein. The illustrated charging surface is constructed from four layers of charging cells <NUM>, <NUM>, <NUM>, <NUM>. In <FIG>, each power transfer area provided by a charging cell in the first layer of charging cells <NUM> is marked "L1", each power transfer area provided by a charging cell in the second layer of charging cells <NUM> is marked "L2", each power transfer area provided by a charging cell in the third layer of charging cells <NUM> is marked "L3", and each power transfer area provided by a charging cell in the fourth layer of charging cells <NUM> is marked "L4".

<FIG> illustrates a wireless transmitter <NUM> that may be provided in a charger base station. A controller <NUM> may receive a feedback signal filtered or otherwise processed by a filter circuit <NUM>. The controller may control the operation of a driver circuit <NUM> that provides an alternating current (AC) signal to a resonant circuit <NUM> that includes a capacitor <NUM> and inductor <NUM>. The resonant circuit <NUM> may also be referred to herein as a tank circuit, an LC tank circuit and/or as an LC tank, and the voltage <NUM> measured at an LC node <NUM> of the resonant circuit <NUM> may be referred to as the tank voltage.

The wireless transmitter <NUM> may be used by a charging device to determine if a compatible device has been placed on a surface of the charging device. For example, the charging device may determine that a compatible device has been placed on the surface of the charging device by sending an intermittent test signal (active ping) through the wireless transmitter <NUM>, where the resonant circuit <NUM> may receive encoded signals when a compatible device responds to the test signal. The charging device may be configured to activate one or more coils in at least one charging cell after receiving a response signal defined by standard, convention, manufacturer or application. In some examples, the compatible device can respond to a ping by communicating received signal strength such that the charging device can find an optimal charging cell to be used for charging the compatible device.

Passive ping techniques may use the voltage and/or current measured or observed at the LC node <NUM> to identify the presence of a receiving coil in proximity to the charging pad of a device adapted in accordance with certain aspects disclosed herein. In many conventional wireless charger transmitters, circuits are provided to measure voltage at the LC node <NUM> or the current in the network. These voltages and currents may be monitored for power regulation purposes and/or to support communication between devices. In the example illustrated in <FIG>, voltage at the LC node <NUM> is monitored, although it is contemplated that current may additionally or alternatively be monitored to support passive ping. A response of the resonant circuit <NUM> to a passive ping (initial voltage V<NUM>) may be represented by the voltage (VLC) at the LC node <NUM>, such that: <MAT>.

According to certain aspects disclosed herein, coils in one or more charging cells may be selectively activated to provide an optimal electromagnetic field for charging a compatible device. In some instances, coils may be assigned to charging cells, and some charging cells may overlap other charging cells. In the latter instances, the optimal charging configuration may be selected at the charging cell level. In other instances, charging cells may be defined based on placement of a device to be charged on a surface of the charging device. In these other instances, the combination of coils activated for each charging event can vary. In some implementations, a charging device may include a driver circuit that can select one or more cells and/or one or more predefined charging cells for activation during a charging event.

One aspect of this disclosure relates to the use of a phase-modulated wireless charger <NUM>, an example of which is illustrated in <FIG>. A driver circuit <NUM> provides a charging current <NUM> to a resonant circuit <NUM> that includes a capacitor (Cp) and an inductor (Lp). The charging current <NUM> may be substantially the same as the current in the inductor (i.e., the Lp current), although some portion of the charging current <NUM> may be lost due to parasitic capacitance, or the like. The charging current <NUM> alternates at a frequency that may be closely matched to the resonant frequency of the resonant circuit <NUM> to improve efficiency of power transfer. In accordance with certain aspects of this disclosure, the level of power transferred through the resonant circuit <NUM> to a receiving device may be controlled through phase modulation of the charging current <NUM>.

The timing diagram <NUM> illustrates certain aspects of phase modulation as applied to the charging current <NUM> in certain implementations. Phase modulation enables fine control over the level of power delivery by the driver circuit <NUM>. The timing diagram <NUM> depicts three charging periods <NUM>, <NUM> and <NUM> in which power is delivered at different levels, as indicated by the varying amplitude of the charging current <NUM>.

Phase control is obtained using a zero-crossing detector <NUM> and a phase modulator <NUM> that responds to a phase control signal <NUM> provided by a controller or other processor. The zero-crossing detector <NUM> is used to provide timing information used by the phase modulator <NUM>. In one example, the zero-crossing detector <NUM> may compare polarity of a measurement signal <NUM> representing the current flowing to the resonant circuit <NUM> with polarity of a delayed version of the measurement signal <NUM>, whereby a difference in polarity is detected when a zero-crossing occurs in the measurement signal <NUM>. The zero-crossing detector <NUM> provides a zero-crossing signal <NUM> (ZC) that includes timing information identifying zero-crossings of the measurement signal <NUM>. In one example, the zero-crossing signal <NUM> includes an edge for each zero-crossing of the measurement signal <NUM>. Direction of transition of the edge may indicate positive-going or negative-going zero-crossings. In another example, the zero-crossing signal <NUM> includes a pulse for each zero-crossing of the measurement signal <NUM>.

The phase modulator <NUM> uses the zero-crossing signal <NUM> to generate a phase modulation signal <NUM>. The phase modulation signal <NUM> may change the phase of a modulated current that contributes to the charging current <NUM>. The phase of the modulated current with respect to the phase of the current in the resonant circuit can cause an increase or decrease in the charging current <NUM>. In the first charging period <NUM>, the phase modulation signal <NUM> is closely synchronized to the zero-crossing signal <NUM>, and the effect of the modulated current is additive over each cycle of the charging current <NUM>. In this example, the driver circuit <NUM> provides maximum power transfer through the resonant circuit <NUM>. In the second charging period <NUM>, the phase modulation signal <NUM> has a phase shift of <NUM>° with respect to the zero-crossing signal <NUM>, and the effect of the modulated current is additive and subtractive on alternating quarter cycles. In this example, the driver circuit <NUM> provides <NUM>% of the maximum available power through the resonant circuit <NUM>. In the third charging period <NUM>, the phase modulation signal <NUM> has a phase shift with respect to the zero-crossing signal <NUM> that increases from <NUM>° to <NUM>° in the last-depicted cycle <NUM>. The effect of the modulated current is negative over an increasing portion of each cycle of the charging current <NUM> and driver circuit <NUM> provides power through the resonant circuit <NUM> that decreases from <NUM>% of the maximum available power to no power transfer or minimal power transfer.

In certain implementations, the zero-crossing signal <NUM> is provided as a digital signal that provides the timing needed by the phase modulator <NUM> to add a phase-lead or phase-lag to the incoming zero-cross signal when indicated by the phase control signal <NUM>. In one example, the driver circuit <NUM> includes a half-bridge circuit. In one example, the phase control signal <NUM> is a multi-bit digital signal that indicates the amount of phase shift to be added to the zero-crossing signal <NUM> in order to directly affect the amount of power that flows in the resonant circuit <NUM> (i.e., Lp and Cp).

<FIG> illustrates an example of a PWM charger <NUM> and the timing diagrams <NUM>, <NUM> in <FIG> illustrate certain aspects of the operation of the PWM charger <NUM>. One aspect of this disclosure relates to the use of a pulse-width modulation (PWM) charging system to modulate a charging current <NUM> provided to a resonant circuit <NUM>. A driver circuit <NUM> provides a charging current <NUM> to a resonant circuit <NUM> that includes a capacitor (Cp) and an inductor (Lp). The charging current <NUM> may be substantially the same as the current in the inductor (i.e., the Lp current), although some portion of the charging current <NUM> may be lost due to parasitic capacitance, or the like. The charging current <NUM> alternates at a frequency that may be closely matched to the resonant frequency of the resonant circuit <NUM> to improve efficiency of power transfer. In accordance with certain aspects of this disclosure, the level of power transferred through the resonant circuit <NUM> to a receiving device may be controlled using PWM modulation to alter the charging current <NUM>.

The timing diagrams <NUM>, <NUM> illustrate certain aspects of PWM as applied to the charging current <NUM> in certain implementations. PWM enables fine control over the level of power delivery by the driver circuit <NUM>, although the timing diagrams <NUM>, <NUM> depict a limited number of charging periods <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> in which power is delivered at different levels, as indicated by the varying amplitude of the charging current <NUM>.

The power provided in the charging current <NUM> may be controlled using a zero-crossing detector <NUM> and a PWM circuit <NUM> that responds to a control signal <NUM> provided by a controller or other processor. The zero-crossing detector <NUM> is used to provide timing information used by the PWM circuit <NUM>. In one example, the zero-crossing detector <NUM> may compare the polarity of a measurement signal <NUM> representing the current flowing to the resonant circuit <NUM> with the polarity of a delayed version of the measurement signal <NUM>, whereby a difference in polarity is detected when a zero-crossing occurs in the measurement signal <NUM>. The zero-crossing detector <NUM> provides a zero-crossing signal <NUM> (ZC) that includes timing information identifying zero-crossings of the measurement signal <NUM>. In one example, the zero-crossing signal <NUM> includes an edge for each zero-crossing of the measurement signal <NUM>. Direction of transition of the edge may indicate positive-going or negative-going zero-crossings. In another example, the zero-crossing signal <NUM> includes a pulse for each zero-crossing of the measurement signal <NUM>.

The PWM circuit <NUM> uses the zero-crossing signal <NUM> to generate a PWM signal <NUM>. The PWM signal <NUM> may control the contribution of energy to the charging current <NUM>. In one example, pulses in the PWM signal <NUM> are used to gate a current that is provided to a power inverter circuit that produces an alternating output used to provide the charging current <NUM>.

In the first charging period <NUM>, <NUM>, the PWM signal <NUM> includes pulses that match the duration of a half-cycle of the charging current <NUM>, and provides a charging current <NUM> with maximum (<NUM>%) power. In this example, the driver circuit <NUM> provides maximum power transfer through the resonant circuit <NUM>. In the second charging period <NUM>, <NUM>, the PWM signal <NUM> includes pulses that have a duration of approximately half the duration of a half-cycle of the charging current <NUM>, and the resultant charging current <NUM> with provides <NUM>% of the maximum available power when provided to the resonant circuit <NUM>. In the third charging period <NUM>, <NUM>, the PWM signal <NUM> includes pulses that decrease, initially having a duration of approximately half the duration of a half-cycle of the charging current <NUM>, and decreasing to almost an absence of a pulse. The driver circuit <NUM> provides power through the resonant circuit <NUM> that decreases from <NUM>% of the maximum available power to no power transfer or minimal power transfer.

The timing of the pulses in the PWM signal <NUM> may be selected based on the method of generating the charging current <NUM> used in the driver circuit <NUM>. In the example illustrated by the first timing diagram <NUM> of <FIG>, each pulse is initiated at a zero crossing and has a duration that may be determined by the width control signal <NUM>. The width control signal <NUM> may be provided as a multi-bit digital signal that configures a programmable delay circuit or selects an out of a delay line to provide a delay that determines the duration of a pulse in the width control signal <NUM>.

In the example illustrated by the second timing diagram <NUM> of <FIG>, each pulse in the PWM signal <NUM> is centered on the mid-point of a corresponding pulse in the zero-crossing signal <NUM>. In other words, the center of each pulse is midway between zero crossings of the measurement signal <NUM>. The duration of these pulses may be determined by the width control signal <NUM>. The width control signal <NUM> may be provided as a multi-bit digital signal that configures a programmable delay circuit or selects an output of a delay line to provide a delay that determines the duration of a pulse in the width control signal <NUM>. The location of the pulses may be configured using counters, delay lines, lookup tables and/or other circuits. Centering the pulses in the PWM signal <NUM> between zero crossings of the measurement signal <NUM> can lower distortion of the AC signal in the charging current <NUM>.

In some implementations, resonant pulse width modulation may use a detected zero-crossing as a temporal reference to initiate a PWM drive cycle. In one example, a timer may be started to control the width of the pulse. In another example, a delay circuit may be used to control the width of the pulse. The charging current <NUM> flowing in the resonant circuit <NUM> is controlled by the width of the pulse.

In some implementations, PWM may be used to control the charging current <NUM> flowing in the resonant circuit <NUM> without zero-crossing synchronization. Accordingly, a current measurement circuit and a zero-crossing detector <NUM> may not be necessary, provided other information is known, including the values of Lp and Cp, for example.

<FIG> illustrates an example of a wireless charging system <NUM> that employs a class-D wireless transmitter <NUM> provided in accordance with certain aspects disclosed herein. The timing diagram <NUM> in <FIG> illustrates certain aspects of the operation of the class-D wireless transmitter <NUM>. The class-D wireless transmitter <NUM> includes a class-D amplifier that operates as a switching amplifier. The class-D wireless transmitter <NUM> generates a first signal that switches between voltage rails at a first frequency. The first signal is modulated by a second lower-frequency signal. In the illustrated example, the first signal is pulse-width modulated to obtain a PWM signal <NUM>.

The PWM signal <NUM> is provided to a driver circuit <NUM> that generates a charging current to drive a resonant circuit <NUM> that includes an LC tank circuit including a capacitor (Cp) and an inductor (Lp). The charging current may be substantially the same as the current in the inductor (i.e., the Lp current <NUM>). The resonant circuit <NUM> operates as a low-pass filter that converts the high frequency PWM signal <NUM> to obtain an amplified version of the modulating signal, which may be a sine wave. The PWM controller <NUM> may be operated to control the peak amplitude of the Lp current <NUM> using cumulative scaling in order to control the power transmitted to a wireless receiver <NUM>. For example, wider pulses in the PWM signal <NUM> may correspond to peaks in the Lp current <NUM> amplitude.

The power provided by the driver circuit <NUM> may be controlled using a zero-crossing detector <NUM> and the PWM controller <NUM>, which may respond to a control signal <NUM> provided by a controller or other processor. The PWM controller <NUM> receives a sinusoidal signal from a reference source <NUM> that provides a carrier signal that can be PWM modulated. The zero-crossing detector <NUM> is used to provide timing information used by the PWM controller <NUM>. In one example, the zero-crossing detector <NUM> may compare the polarity of a measurement signal <NUM> representing the current flowing to the resonant circuit <NUM> with the polarity of a delayed version of the measurement signal <NUM>, whereby a difference in polarity is detected when a zero-crossing occurs in the measurement signal <NUM>. The zero-crossing detector <NUM> provides a zero-crossing signal <NUM> (ZCS) that includes timing information identifying zero-crossings of the measurement signal <NUM>. In one example, the zero-crossing signal <NUM> includes an edge for each zero-crossing of the measurement signal <NUM>. Direction of transition of the edge may indicate positive-going or negative-going zero-crossings. In another example, the zero-crossing signal <NUM> includes a pulse for each zero-crossing of the measurement signal <NUM>. The PWM controller <NUM> may use the zero-crossing signal <NUM> to generate a PWM signal <NUM>, in which the PWM signal <NUM> is in phase alignment with the Lp current <NUM>.

Slotted foreign object detection may be used to detect a foreign object (FO) on the surface of a wireless charging device. A driver circuit in the wireless charging device is periodically turned off for a short period of time, which may be referred to as a slot, during which the energy in a resonant circuit driven by the driver circuit is allowed to decay. The Q factor of the resonant circuit can be determined by measuring the rate of decay. A high sample rate is typically required to accurately measure the AC waveform in the tank circuit without aliasing or artifacts that may spoil the measurement accuracy of the Q factor. The sample rate can be a factor of ten to twenty times the frequency of the current in the resonant circuit, and generally requires the use of a fast and expensive analog-to-digital converter (ADC).

In certain aspects of the disclosure, a zero-crossing detector is used to provide timing information that permits a low-cost ADC to reliably obtain an accurate measurement of the voltage at the same point in each cycle of the AC waveform in the resonant circuit, during a slot provided for foreign object detection. Zero crossing slotted foreign object detection can be used to detect the zero crossing of the voltage and/or the current in the resonant circuit. The detection of the zero crossing starts a hold-off timer that triggers a sample and hold circuit in the ADC. In one example, the hold-off timer triggers the sample and hold circuit after a quarter cycle of the AC waveform in the resonant circuit. In this example, the ADC reads a sample taken at the peak of the AC wave. A sample frequency that is less than the fundamental frequency of the AC waveform can be used.

<FIG> includes timing diagrams <NUM>, <NUM> that illustrate certain aspects of a zero-crossing, slotted foreign object detection. A measurement slot <NUM>, <NUM> is provided between periods <NUM>, <NUM> or <NUM>, <NUM> of normal charging operation. The first timing diagram <NUM> relates to an example of a signal <NUM> representing energy, voltage or current in the resonant circuit when no foreign object is present, and the slow decay <NUM> in the signal <NUM> corresponds to a resonant circuit with a high Q factor. The second timing diagram <NUM> relates to an example of a signal <NUM> representing energy, voltage or current in the resonant circuit when a foreign object <NUM> (see <FIG>) is present, and the decay <NUM> corresponds to a resonant circuit with a low Q factor. A zero-crossing, slotted foreign object detection technique according to certain aspects of the disclosure uses sample points <NUM>, <NUM> identified based on detected zero crossings identified by a zero-crossing signal <NUM>, <NUM>.

<FIG> illustrates an example of a wireless charging system <NUM> that employs zero-crossing detection to obtain measurements <NUM> at one or more points in each cycle of current or voltage in a resonant circuit <NUM>. In one example, the measurements may be used for slotted foreign object detection in accordance with certain aspects disclosed herein. The wireless charging system <NUM> includes a driver circuit <NUM> that generates a charging current to drive a resonant circuit <NUM> that includes an LC tank circuit including a capacitor (Cp) and an inductor (Lp). The charging current may be substantially the same as the current in the inductor. In some implementations, a voltage measurement signal <NUM> representative of the voltage across the resonant circuit <NUM> is provided to a first zero-crossing detector <NUM>. The first zero-crossing detector <NUM> produces a zero-voltage signal (ZVS <NUM>) as an output that indicates the timing of zero-crossings of the voltage across the resonant circuit <NUM>. In some implementations, a current measurement signal <NUM> representative of the current in the resonant circuit <NUM> is provided to a second zero-crossing detector <NUM>. The second zero-crossing detector <NUM> produces a zero-current signal (ZCS <NUM>) as an output that indicates the timing of zero-crossings of the current in the resonant circuit <NUM>.

A capture timing circuit <NUM> may be used to track zero crossings and determine or manage the sample and hold circuit <NUM>. In one example, the capture timing circuit <NUM> may include or use a hold-off timer <NUM> that can locate the peak amplitude of the voltage or current across the resonant circuit <NUM> that occurs after period of time corresponding to a half cycle of the resonant circuit <NUM>. In other examples, the capture timing circuit <NUM> may include or use a hold-off timer <NUM> that can locate one or more points of the voltage or current across the resonant circuit <NUM>. The sample and hold circuit <NUM> provides an output digitized by the ADC <NUM> to obtain a measurement <NUM>. The measurement <NUM> may be used to track the rate of decay of the energy in the resonant circuit <NUM>.

The measurements obtained using the zero-crossing detection techniques illustrated in <FIG> may be used for Amplitude Shift Keying (ASK) demodulation. ASK modulation is commonly used to carry messages defined by the Qi protocol, which is used for wirelessly interconnecting a power transmitter to a power receiver. The Qi protocol permits the power receiver to control the power transmitter wirelessly. The measurements <NUM> obtained at one or more points in each cycle of current or voltage in a resonant circuit <NUM> may be used for ASK demodulation. One or more zero-crossing detectors <NUM>, <NUM> provide reference timing for sampling voltage or current associated with the resonant circuit <NUM>. Sampled data can be used to extract the ASK data that is modulated on the carrier power signal by the receiving device.

Data can be extracted from signals that have much higher frequencies than the sampling frequency when zero cross detection is used to provide timing for sampling. In some instances, sampling can be performed at the fundamental frequency of the current or voltage associated with the resonant circuit <NUM>, or at double the frequency of the current or voltage associated with the resonant circuit <NUM>. Conventional sampling circuits operate at ten times the fundamental frequency of the current or voltage associated with the resonant circuit <NUM> or more to avoid aliasing and other distortion artifacts.

In one example, ASK demodulation is performed using measurements of voltage captured using timing provided by the ZVS <NUM> that is output by the first zero-crossing detector <NUM> to time the trigger of a sample and hold circuit <NUM>. In another example, ASK demodulation is performed using measurements of current captured using timing provided by the ZCS <NUM> that is output by the second zero-crossing detector <NUM> to time the trigger of a sample and hold circuit <NUM>. ASK demodulation can be performed using a single sample taken at the peak of a cycle of voltage or current. Zero-crossing ASK demodulation can reject any communications channels that may be in the same domain, provided the phase and/or frequency of the interfering carrier is different from the target carrier.

<FIG> and <FIG> illustrate of certain aspects of a wireless charging system <NUM> that employs zero-crossing detection to support phase-based ASK demodulation. Referring to the timing diagram <NUM> of <FIG>, zero-crossing phase demodulation includes detecting the phase difference between zero-volt crossings of the voltage <NUM> and the current <NUM> in the resonant circuit <NUM>. Phase shifts between the voltage <NUM> and the current <NUM> may correspond to different modulation levels <NUM> when the power receiving device <NUM> uses ASK modulation to encode data through load or resonance shift. A digital phase detector <NUM> can determine the phase difference between a current zero-crossing signal (ZCS <NUM>) and a voltage zero-crossing signal (ZVS <NUM>) provided by corresponding zero-crossing detector circuits <NUM>, <NUM> respectively. Phase differences can be measured at one or more points in each cycle of current or voltage in a resonant circuit <NUM>. The wireless charging system <NUM> includes a driver circuit <NUM> that generates a charging current <NUM> to drive the resonant circuit <NUM>, which includes a capacitor (Cp) and an inductor (Lp). The charging current <NUM> may be substantially the same as the current in the inductor. In some implementations, a voltage measurement signal <NUM> representative of the voltage across the resonant circuit <NUM> is provided to a first zero-crossing detector <NUM>. The first zero-crossing detector <NUM> produces the current zero-crossing signal <NUM> at an output indicating the timing of zero-crossings of the voltage across the resonant circuit <NUM>. A current measurement signal <NUM> representative of the current in the resonant circuit <NUM> is provided to a second zero-crossing detector <NUM>. The second zero-crossing detector <NUM> produces the current zero-crossing signal <NUM> at an output indicating the timing of zero-crossings of the current in the resonant circuit <NUM>.

The phase detector circuit <NUM> provides a signal representative of the phase difference between the ZCS <NUM> and the ZVS <NUM> to an ASK demodulator <NUM>.

<FIG> illustrates an example of a hardware implementation for an apparatus <NUM> that may be incorporated in a charging device or in a receiving device that enables a battery to be wirelessly charged. In some examples, the apparatus <NUM> may perform one or more functions disclosed herein. In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements as disclosed herein may be implemented using a processing circuit <NUM>. The processing circuit <NUM> may include one or more processors <NUM> that are controlled by some combination of hardware and software modules. Examples of processors <NUM> include microprocessors, microcontrollers, digital signal processors (DSPs), SoCs, ASICs, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, sequencers, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. The one or more processors <NUM> may include specialized processors that perform specific functions, and that may be configured, augmented or controlled by one of the software modules <NUM>. The one or more processors <NUM> may be configured through a combination of software modules <NUM> loaded during initialization, and further configured by loading or unloading one or more software modules <NUM> during operation.

In the illustrated example, the processing circuit <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing circuit <NUM> and the overall design constraints. The bus <NUM> links together various circuits including the one or more processors <NUM>, and storage <NUM>. Storage <NUM> may include memory devices and mass storage devices, and may be referred to herein as computer-readable media and/or processor-readable media. The storage <NUM> may include transitory storage media and/or non-transitory storage media.

The bus <NUM> may also link various other circuits such as timing sources, timers, peripherals, voltage regulators, and power management circuits. A bus interface <NUM> may provide an interface between the bus <NUM> and one or more transceivers <NUM>. In one example, a transceiver <NUM> may be provided to enable the apparatus <NUM> to communicate with a charging or receiving device in accordance with a standardsdefined protocol. Depending upon the nature of the apparatus <NUM>, a user interface <NUM> (e.g., keypad, display, speaker, microphone, joystick) may also be provided, and may be communicatively coupled to the bus <NUM> directly or through the bus interface <NUM>.

One or more processors <NUM> in the processing circuit <NUM> may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, algorithms, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside in computer-readable form in the storage <NUM> or in an external computer-readable medium. The external computer-readable medium and/or storage <NUM> may include a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a "flash drive," a card, a stick, or a key drive), RAM, ROM, a programmable read-only memory (PROM), an erasable PROM (EPROM) including EEPROM, a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium and/or storage <NUM> may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. Computer-readable medium and/or the storage <NUM> may reside in the processing circuit <NUM>, in the processor <NUM>, external to the processing circuit <NUM>, or be distributed across multiple entities including the processing circuit <NUM>. The computer-readable medium and/or storage <NUM> may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

The storage <NUM> may maintain and/or organize software in loadable code segments, modules, applications, programs, etc., which may be referred to herein as software modules <NUM>. Each of the software modules <NUM> may include instructions and data that, when installed or loaded on the processing circuit <NUM> and executed by the one or more processors <NUM>, contribute to a run-time image <NUM> that controls the operation of the one or more processors <NUM>. When executed, certain instructions may cause the processing circuit <NUM> to perform functions in accordance with certain methods, algorithms and processes described herein.

Some of the software modules <NUM> may be loaded during initialization of the processing circuit <NUM>, and these software modules <NUM> may configure the processing circuit <NUM> to enable performance of the various functions disclosed herein. For example, some software modules <NUM> may configure internal devices and/or logic circuits <NUM> of the processor <NUM>, and may manage access to external devices such as a transceiver <NUM>, the bus interface <NUM>, the user interface <NUM>, timers, mathematical coprocessors, and so on. The software modules <NUM> may include a control program and/or an operating system that interacts with interrupt handlers and device drivers, and that controls access to various resources provided by the processing circuit <NUM>. The resources may include memory, processing time, access to a transceiver <NUM>, the user interface <NUM>, and so on.

In one implementation, the apparatus <NUM> includes or operates as a wireless charging apparatus that has a battery charging power source coupled to a charging circuit, a plurality of charging cells and a controller, which may be included in one or more processors <NUM>. The plurality of charging cells may be configured to provide a charging surface. At least one transmitting coil may be configured to direct an electromagnetic field through a charge transfer area of each charging cell. The apparatus <NUM> may include a resonant circuit comprising a transmitting coil, a driver circuit configured to provide a charging current to the resonant circuit, and a zero-crossing detector configured to provide a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or corresponding to transitions of a current in the resonant circuit through a zero ampere level. The controller may be configured to cause the driver circuit to provide the charging current to the resonant circuit when a receiving device is present on a surface of the charging device, provide a measurement slot by causing the driver circuit to decrease or terminate the charging current for a period of time, and determine whether an object other than the receiving device is present on a surface of the charging device based on measurements of samples of voltage or current captured based on timing provided by the zero-crossing signal. The samples may be captured during the measurement slot.

In one example, the zero volt level corresponds to a current amplitude midway between maximum and minimum amplitudes of an AC measured in the resonant circuit. The zero volt level may correspond to a voltage level midway between maximum and minimum amplitudes of an AC voltage measured across the resonant circuit.

In one example, the controller is further configured to determine that the object other than the receiving device is present on the surface of the charging device based on a rate of decrease in voltage or current measured using the samples of voltage or current. In one example, the controller is further configured to determine that the object other than the receiving device is present on the surface of the charging device based on a rate of decrease of energy stored in the resonant circuit. The energy stored in the resonant circuit may be indicated by the samples of voltage or current.

In one example, the controller is further configured to determine that the object other than the receiving device is present on the surface of the charging device based on a Q factor of the resonant circuit. The Q factor of the resonant circuit may be indicated by a plurality of the samples of voltage or current.

In certain examples, apparatus <NUM> may include a sample and hold circuit configured to sample the voltage or current in the resonant circuit after a delay following each of a plurality of edges in the zero-crossing signal to obtain the samples of voltage or current. The delay may be calculated to cause sampling of the voltage or current when the voltage or current has a maximum amplitude.

In some implementations, the storage <NUM> maintains instructions and information where the instructions are configured to cause the one or more processors <NUM> to provide a charging current to a resonant circuit when a receiving device is present on a surface of the wireless charging device, provide a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or to transitions of a current in the resonant circuit through a zero ampere level, provide a measurement slot by decreasing or terminating the charging current for a period of time, and determine whether an object other than the receiving device is present on a surface of the charging device based on measurements of samples of voltage or current captured based on timing provided by the zero-crossing signal. The samples may be captured during the measurement slot.

In one example, the zero volt level corresponds to a current amplitude midway between maximum and minimum amplitudes of an AC current measured in the resonant circuit. In another example, the zero volt level corresponds to a voltage level midway between maximum and minimum amplitudes of an AC voltage measured across the resonant circuit. In some instances, it may be determined that the object other than the receiving device is present on the surface of the charging device based on a rate of decrease in voltage or current measured using the samples of voltage or current.

In some instances, it may be determined that the object other than the receiving device is present on the surface of the charging device based on a rate of decrease of energy stored in the resonant circuit. The energy stored in the resonant circuit may be indicated by the samples of voltage and/or current.

In some instances, it may be determined that the object other than the receiving device is present on the surface of the charging device based on a Q factor of the resonant circuit. The Q factor of the resonant circuit may be indicated by a plurality of the samples of voltage or current.

In certain examples, the voltage or current in the resonant circuit may be sampled after a delay following each of a plurality of edges in the zero-crossing signal to obtain the samples of voltage or current. The delay may be calculated to cause sampling of the voltage or current when the voltage or current has a maximum amplitude.

<FIG> is a flowchart <NUM> illustrating a method for operating a charging device in accordance with certain aspects of this disclosure. The method may be performed by a controller in the charging device. At block <NUM>, the controller may provide a charging current to a resonant circuit when a receiving device is present on a surface of the wireless charging device. At block <NUM>, the controller may provide a zero-crossing signal that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level or to transitions of a current in the resonant circuit through a zero ampere level. At block <NUM>, the controller may provide a measurement slot by decreasing or terminating the charging current for a period of time. At block <NUM>, the controller may determine whether an object other than the receiving device is present on a surface of the charging device based on measurements of samples of voltage or current captured based on timing provided by the zero-crossing signal. The samples may be captured during the measurement slot.

In one example, the zero volt level corresponds to a current amplitude midway between maximum and minimum amplitudes of an AC current measured in the resonant circuit. In another example, the zero volt level corresponds to a voltage level midway between maximum and minimum amplitudes of an AC voltage measured across the resonant circuit.

In some instances, it may be determined that the object other than the receiving device is present on the surface of the charging device based on a rate of decrease in voltage or current measured using the samples of voltage or current.

Claim 1:
A method for operating a wireless charging device comprising the steps of:
providing a charging current to a resonant circuit (<NUM>) when a receiving device is present on a surface of the wireless charging device (<NUM>);
providing a zero-crossing signal (<NUM>) that includes edges corresponding to transitions of a voltage measured across the resonant circuit through a zero volt level (<NUM>, <NUM>) or to transitions of a current in the resonant circuit through a zero ampere level; characterized in that it comprises:
providing a measurement slot (<NUM>, <NUM>) by decreasing or terminating the charging current for a period of time;
sampling the voltage or current (<NUM>, <NUM>) in the resonant circuit after a delay (<NUM>) following each of a plurality of edges in the zero-crossing signal (<NUM>) to obtain samples of voltage or current; and
determining whether an object (<NUM>) other than the receiving device is present on a surface of the wireless charging device based on measurements (<NUM>) of the samples of voltage or current captured based on timing provided by the zero-crossing signal (<NUM>), wherein the samples of voltage or current are captured during the measurement slot (<NUM>).