Patent Description:
A basic wireless charging system may include a wireless power transmitter unit (PTU) and a wireless power receiving unit (PRU). For example, a PTU may include a transmit (Tx) coil and a PRU may include receive (Rx) coil. The Tx and Rx coils may be referred to as induction coils. In a typical induction charger, the Tx coil creates an alternating electromagnetic field and the Rx coil takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer. Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling.

In some cases, a PRU may be implemented in a computing device, such as a mobile computing device, that can be placed on a charging mat including a PTU. The wireless energy emitted by the PTU is subject to various industry standards and regulatory standards that limit the level of power that RF transmitters are allowed to emit. For example, organizations such as Alliance for Wireless Power (A4WP), and Wireless Power Consortium (WPC) among others define standards for interoperability such as the frequency of operation and other parameters that define magnitude of fields and power levels in wireless power systems. Such systems should also conform to regulatory standards for RF exposure as required by regulatory bodies such as the US Federal Communications Commission (FCC) and guidelines by the International Commission on Non-Ionizing Radiation (ICNIRP). <CIT>discloses a power loss detection method for regulating the transmitted power of a transmitter coil of a wireless charger. If a power loss is detected, the transmitted power may be reduced or switched off. Further, capacitance sensing elements for sensing a change of capacitance are disclosed. Capacitance sensing elements may be placed to detect a metallic object located in a predefined area by means of a deviation of a sensed capacitance value. If a capacitance is sensed, power may be deactivated. However, this arrangement is not able to distinguish between foreign objects and human/animal tissues. This drawback is overcome by an apparatus according to claim <NUM> and a method according to claim <NUM>.

The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the <NUM> series refer to features originally found in <FIG>; numbers in the <NUM> series refer to features originally found in <FIG>; and so on.

The present disclosure relates generally to techniques for wireless charging. More specifically, the techniques described herein provide a technique for controlling the power level of a transmitted wireless charging signal based on whether a person is in the vicinity of a wireless power transmitter. A system in accordance with the present techniques can use capacitively coupled proximity sensors that are incorporated close to the Tx coil to sense the presence of a human tissue in close proximity. If human tissue is detected, the fields radiated by the wireless power system are reduced to maintain conformance to regulatory requirements for RF exposure as specified by the regulatory bodies the FCC and guidelines by the ICNIRP. If human tissue is not detected, the fields radiated by the wireless power system can be increased to provide faster battery charging.

In some cases, the techniques discussed herein may be implemented using a wireless charging standard protocol, such as the specification provided by Alliance For Wireless Power (A4WP) version <NUM>, November <NUM>, <NUM>. A wireless power receiving (Rx) coil may be a component in a power receiving unit (PRU), while a wireless power transmission (Tx) coil may be a component in a power transmitting unit (PTU), as discussed in more detail below. However, the techniques described herein may be implemented using any other wireless charging standard protocol where applicable.

<FIG> is block diagram of a PTU to provide power to a PRU, wherein the PTU includes a presence detection circuit. A PTU <NUM> may be coupled to a PRU <NUM> via magnetic inductive coupling between resonators <NUM> and108, as indicated by the arrow <NUM>. The PRU <NUM> may be a component of a computing device <NUM> configured to receive charge by the inductive coupling <NUM>. The resonator <NUM> may be referred to herein as a Tx coil <NUM> of the PTU <NUM>. The resonator <NUM> may be referred to herein as an Rx coil <NUM> of the PRU <NUM>.

The PTU <NUM> may include a matching circuit <NUM> configured to match the amplified oscillation provided to the resonator <NUM> of the PTU <NUM>. The matching circuit <NUM> may include any suitable arrangement of electrical components such as capacitors, inductors, and other circuit elements that can be adjusted match the resonator <NUM> to the power amplifier <NUM>. The operation of the matching circuit <NUM> can generate a reactance shift to compensate for detuning of the magnetic inductive coupling <NUM>.

Other components of the PTU may include a power amplifier <NUM>, and oscillator <NUM>, a current sensor <NUM>, a Bluetooth Low Energy (BLE) module <NUM>, a controller <NUM>, direct current to direct current (DC2DC) converter <NUM>, and the like. The current sensor <NUM> may be an ampere meter, a volt meter, or any other sensor configured to sense load variations occurring due to inductive coupling between the PTU <NUM> and another object, such as the PRU <NUM>. The current sensor <NUM> may provide an indication of load change to the controller <NUM> of the PTU <NUM>. The controller <NUM> may power on the power amplifier <NUM> configured to receive direct current (DC) from the DC2DC converter <NUM>, and to amplify and oscillate the current. The oscillator <NUM> may be configured to oscillate the power provided at a given frequency.

As shown in <FIG>, an inductive coupling <NUM> may occur between the Tx coil <NUM> and the Rx coil <NUM>, and as a magnetic flux associated with the inductive coupling passes through the Rx coil <NUM> the computing device <NUM> may receive power. A rectifier <NUM> may receive voltage having an alternating current (AC) from the Rx coil <NUM> and may be configured to generate a rectified voltage (Vrect) having a direct current (DC). As illustrated in <FIG>, a DC2DC converter <NUM> may provide a DC output to a battery <NUM>.

The PRU <NUM> may also include a controller <NUM> configured to initiate a wireless broadcast having wireless handshake data. As discussed above, the wireless handshake broadcast may be carried out by a wireless data transmission component such as BLE module <NUM>.

The PTU <NUM> also includes one or more proximity sensors <NUM> for detecting the presence a person or animal in the vicinity of the resonator <NUM>. In some examples, the proximity sensors are capacitive. Capacitive proximity sensors can include adjacent conductive pads to which are applied an electrical charge. The presence of human tissue such as a person's hand near the proximity sensor <NUM> causes a change in the dielectric constant of the capacitor, which can be detected by the proximity sensor <NUM>. As an example, touching the proximity sensor <NUM> with a person's hand may be expected to result in approximately <NUM> pico Farads or change, placing the hand in close proximity to the proximity sensor <NUM> may be expected to result in approximately <NUM> pico Farad of change, while a <NUM> to <NUM> femto Farad change may still indicate some degree of proximity to the proximity sensor <NUM>. Any suitable number of proximity sensors may be used, including one, two, three, four, or more. If multiple proximity sensors <NUM> are used, the proximity sensors may be placed around the periphery of the resonator <NUM>.

The proximity sensors are coupled to the controller <NUM>. Based on the detection or non-detection of human or animal tissue, the controller <NUM> can determine the strength of wireless charging signal. For example, the controller may control the amplification level applied by the power amplifier <NUM>, which controls the magnitude of the current delivered to the resonator <NUM>. In embodiments with multiple proximity sensors <NUM>, the output of the proximity sensors <NUM> may be processed according to a voting algorithm. For example, depending on the design of a particular embodiment, the magnitude of the current delivered to the resonator <NUM> may be reduced if any single proximity sensor detects an object, or a majority of the proximity sensors detect an object, or all of the proximity sensors detect an object.

The proximity sensors are calibrated in the absence of any human tissue and at maximum load to obtain a baseline level that indicates non-presence of human tissue at maximum load. The load refers to the electrical effect on the resonator <NUM> due to the computing device <NUM>. A larger device, such as a tablet would be expected to have a higher load compared to a smaller device, such as a smart phone. Additionally, a threshold capacitance change, ΔCth, is defined such that any capacitance change above the baseline level greater than the threshold capacitance change, ΔCth, is used to indicate presence of human or animal tissue. The threshold capacitance change, ΔCth, can be determined based on empirical evaluation of detection thresholds of human subjects. Whenever the change in the detected capacitance is higher than the threshold capacitance change, ΔCth, the control logic sets a lower maximum current limit that can be driven into the resonator <NUM>. A reduced drive current into the resonator <NUM> helps to maintain the RF exposure below the regulatory specifications.

The block diagram of <FIG> is not intended to indicate that the PTU <NUM> and/or the PRU <NUM> are to include all of the components shown in <FIG>. Further, the PTU <NUM> and/or the PRU <NUM> may include any number of additional components not shown in <FIG>, depending on the details of the specific implementation.

<FIG> is block diagram of an example circuit that can be used to control the signal strength of a wireless charging signal based on the detection of presence. The circuit <NUM> of <FIG> includes the proximity sensor <NUM> coupled to a sensor monitor <NUM>. As shown in <FIG>, the proximity sensor <NUM> may be coupled to a voltage source. The sensor monitor <NUM> can include any suitable type of hardware or combination of hardware and programming. For example, the sensor monitor <NUM> may include logic circuits, microcontrollers, general purpose processors executing computer code, and the like. The sensor monitor <NUM> may be included as a component of the controller <NUM> shown in <FIG>, a sensor hub (not shown), or may be a separate component. The sensor monitor <NUM> receives a signal from the proximity sensor <NUM> that varies in response to the presence of objects in its vicinity. For example, in the case of a capacitive proximity sensor <NUM>, the proximity sensor <NUM> may generate an AC voltage signal wherein the magnitude and/or frequency of the signal changes in response to changing capacitance of the proximity sensor <NUM>. In some examples, the circuit <NUM> also includes a signal conditioning circuitry <NUM> coupled between the proximity sensor <NUM> and the sensor monitor <NUM>. The signal conditioning function <NUM> may be a low-pass filter to remove high frequency noise and thereby average out random spikes from the data.

In <FIG>, the resonator is shown as Tx coil <NUM> The current driven out of the power amplifier <NUM> and into the Tx coil controls the radiated electric and magnetic fields. In the presence of a human tissue, the proximity sensor <NUM> may issue an interrupt PS serv_req signal to the sensor monitor <NUM>, which then senses the capacitance change, for example, by polling the output of the signal conditioning circuitry <NUM> that processes the output of the proximity sensor <NUM>. The SAR_sensor_OK signal is a signal to determine any malfunctioning in the proximity sensor <NUM>. As shown in <FIG>, the SAR_sensor_OK signal may be input to a logic circuit such an AND gate <NUM> in combination with a PA_enable signal received from another component of the PTU <NUM>, such as the controller <NUM>. In this way, the SAR_sensor_OK signal gates the PA_enable signal driving the power amplifier, and the Tx coil can be disabled or enabled only at reduced power if the proximity sensor <NUM> is not functioning properly.

In the presence of human tissue, the change in capacitance detected by the proximity sensor <NUM> will likely be higher than the threshold capacitance ΔCth that is calibrated to a value that is prevailing in the absence of human tissue at maximum load. This helps to ensure that the change in capacitance detected by the proximity sensor <NUM> is only due to the presence of a human tissue and not due to the increased load of a larger receiving device like a notebook instead of a phone. Whenever the change in the detected capacitance is higher than a threshold, ΔCth, the control logic sets a lower maximum current limit that can be driven into the Tx coil. A reduced drive current into the Tx coil helps in maintaining the RF exposure below the regulatory limits. In some examples, the maximum current limit is controlled by controlling the current fed to the input of the power amplfiier, PA_in. In the example shown in <FIG>, the maximum current limit is controlled by controlling the gain of the power amplifier <NUM>.

<FIG> is block diagram of another example circuit that can be used to control the signal strength of a wireless charging signal based on the detection of presence. The example circuit of <FIG> operates similarly to the example circuit shown in <FIG>, and includes proximity sensor <NUM>, the signal conditioning circuitry <NUM> and the sensor monitor <NUM>. However, in this example, the sensor monitor <NUM> controls the output of the current from transmitter coil <NUM> by controlling the gain of the power amplifier <NUM>.

In the presence of a human tissue, the proximity sensor <NUM> may issue an interrupt PS_serv_req signal to the sensor monitor <NUM>, which then senses the capacitance change. The degree of the capacitance change may then be used to determine a gain level of the power amplifier <NUM>. The sensor monitor <NUM> sends a corresponding gain signal to the gain adjust circuitry <NUM>. The PA_enable signal received from another component of the PTU <NUM> is also fed to the gain adjust circuitry <NUM>. The output of the gain adjust circuitry <NUM> is sent to the gain control input of the power amplifier <NUM>.

<FIG> is a process flow diagram showing an example of a method to control a wireless charging transmitter. The method <NUM> may be performed by the PTU <NUM> shown in <FIG>. The logic for performing the processed described below may be embodied in hardware, such as logic circuitry or one or more processors configured to execute instructions stored in a non-transitory, computer-readable medium. The method may begin at block <NUM>.

At block <NUM>, the output signal of the proximity sensor is received. At block <NUM>, the received signal is processed to compute the sensed capacitance change, ΔC. The capacitance change, ΔC, can be computed by monitoring the accumulated charge over the duration of sensing, Δt, wherein the accumulated charge is the integrated instantaneous current over the duration of sensing, as shown in the following equations: <MAT> In the above equation, V is normalized reference voltage.

At block <NUM>, the change in capacitance, ΔC, is computed for a particular time period, Δt, which is the duration of time from the start of the sensing operation. At the beginning of the method Δt is zero, and Δt is reset each time the proximity sensor is triggered leading to a current reduction operation.

At block <NUM>, the change in capacitance, ΔC, is compared to the threshold capacitance change, ΔCth, that was computed during the calibration of the PTU <NUM>. If the change in capacitance is less than the threshold, the process flow returns to block <NUM> and the process can be repeated. The process may be repeated periodically while the PTU <NUM> is operable.

If the change in capacitance is greater than the threshold, the process flow advances to block <NUM>. At block <NUM>, the setting of maximum current allowed to be delivered to the Tx coil is reduced. In some examples, reducing the maximum allowed current to the Tx coil may mean turning off the current to the Tx coil. In some examples, reducing the current to the Tx coil may mean reducing the current below a pre-specified level, such as a level specified by an industry standard or regulation. In some examples, the reduction of the max current level may be proportional to the degree of change in the capacitance. After the current to the Tx coil is reduced, the process flow may return to block <NUM>.

The method <NUM> should not be interpreted as meaning that the blocks are necessarily performed in the order shown. Furthermore, fewer or greater actions can be included in the method <NUM> depending on the design considerations of a particular implementation.

<FIG> is a process flow diagram showing another example of a method to control a wireless charging transmitter. The method <NUM> may be performed by the PTU <NUM> shown in <FIG>. The logic for performing the processed described below may be embodied in hardware, such as logic circuitry or one or more processors configured to execute instructions stored in a non-transitory, computer-readable medium.

The method may begin at block <NUM> and proceed similarly to the method <NUM>. At the start of the method <NUM>, Δt equals zero. At block <NUM>, the output signal of the proximity sensor is received. At block <NUM>, the received signal is used processed to compute the sensed capacitance. At block <NUM>, the change in capacitance, ΔC, is computed for a particular time period, Δt. At block <NUM>, the change in capacitance, ΔC, is compared to the threshold capacitance change, ΔCth, that was computed during the calibration of the PTU <NUM>.

If the change in capacitance is greater than the threshold capacitance change, ΔCth, the process flow advances to block <NUM>. At block <NUM>, a timer is started and the process flow advances to block <NUM>. At block <NUM>, a determination is made regarding whether the time elapsed since the start of the timer is greater than a threshold time. If the elapsed time is not greater than the threshold time, the process flow returns to block <NUM> and the process repeats.

If the elapsed time is greater than the threshold time, the process flow advances to block <NUM>. At block <NUM>, the current to the Tx coil is reduced. As mentioned above, reducing the current to the Tx coil may mean turning off the current to the Tx coil, reducing the current below a pre-specified level, and/or reducing the max current level in proportional to the degree of change in the capacitance. After the setting for max current to the Tx coil is reduced, the process flow may advance to block <NUM>. At block <NUM>, the timer is reset. The process flow then returns to block <NUM> and the process repeats.

Returning to block <NUM>, if the change in capacitance is less than the threshold, the process flow advances to block <NUM>. At block <NUM>, a timer is started and the process flow advances to block <NUM>. At block <NUM>, a determination is made regarding whether the time elapsed since the start of the timer is greater than a threshold time. If the elapsed time is not greater than the threshold time, the process flow returns to block <NUM> and the process repeats.

If the elapsed time is greater than the threshold time, the process flow advances to block <NUM>. At block <NUM>, the current to the Tx coil is increased. Increasing the current to the Tx coil may mean turning on the current to the Tx coil, increasing the current above a pre-specified level, and/or increasing the max current level in proportional to the degree of change in the capacitance. After the setting for max current to the Tx coil is increased, the process flow may advance to block <NUM>. At block <NUM>, the timer is reset. The process flow then returns to block <NUM> and the process repeats.

Not all components, features, structures, characteristics, etc. described and illustrated herein need be included in a particular aspect or aspects. If the specification states a component, feature, structure, or characteristic "may", "might", "can" or "could" be included, for example, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to "a" or "an" element, that does not mean there is only one of the element.

It is to be noted that, although some aspects have been described in reference to particular implementations, other implementations are possible according to some aspects.

It is to be understood that specifics in the aforementioned examples may be used anywhere in one or more aspects. For instance, all optional features of the computing device described above may also be implemented with respect to either of the methods or the computer-readable medium described herein. Furthermore, although flow diagrams and/or state diagrams may have been used herein to describe aspects, the techniques are not limited to those diagrams or to corresponding descriptions herein.

Claim 1:
An apparatus for proximity sensing in a wireless power transmitter, comprising:
a transmitter coil (<NUM>) configured to generate a magnetic field;
a controller (<NUM>) coupled to the transmitter coil (<NUM>) and configured to provide power to the transmitter coil (<NUM>), in response to load variations occurring due to inductive coupling with another object; and
a capacitive proximity sensor (<NUM>) coupled to the controller (<NUM>);
wherein the proximity sensor (<NUM>) is configured such that it is calibrated in the absence of any human or animal tissue and at maximum load to obtain a baseline level that indicates the non-presence of human or animal tissue at maximum load to define a threshold capacitance change above the baseline level; and
wherein the controller (<NUM>) is further configured to reduce a maximum current that can be driven into the transmitter coil (<NUM>), in response to the capacitive proximity sensor (<NUM>) detecting that a change in capacitance is higher than the threshold capacitance change above the baseline level, said threshold capacitance change indicating presence of human or animal tissue.