PATENT DOCUMENT

Publication Number: US-11316383-B1
Application Number: US-202016925207-A
Country: US
Kind Code: B1

Title: Wireless power systems with foreign object detection

Abstract:
A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device during wireless power transmission periods. During alternating foreign object detection periods, the wireless power transmitting device gathers signals from the wireless power transmitting coil to detect foreign objects. Another wireless power transmitting device may transmit signals that can cause interference. To help reduce interference, the wireless power transmitting device gathers signals with a sensing coil that is separate from the wireless power transmitting coil and subtracts these signals from signals gathered with the wireless power transmitting coil. A signal quality metric may be used in adjusting the timing of the foreign object detection periods to help avoid interference from the other wireless power transmitting device.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device for transmitting wireless power to a wireless power receiving device in the presence of an additional wireless power transmitting device, comprising:
 wireless power transmitting circuitry having a wireless power transmitting coil configured to transmit wireless power signals to the wireless power receiving device; 
 a sensing coil; and 
 control circuitry configured to detect foreign objects using the wireless power transmitting coil while using the sensing coil to reduce interference from the additional wireless power transmitting device. 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein the wireless power transmitting coil has an interior region and wherein the sensing coil is located in the interior region. 
     
     
       3. The wireless power transmitting device of  claim 1  wherein the wireless power transmitting coil has an interior region and an exterior region and wherein the wireless power transmitting coil is located in the exterior region. 
     
     
       4. The wireless power transmitting device of  claim 1  wherein the control circuitry comprises a subtractor and wherein the control circuitry is configured to subtract interference received from the additional wireless power transmitting device using the sensing coil from a signal received from the wireless power transmitting coil during foreign object detection operations. 
     
     
       5. The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to measure a quality factor of the wireless power transmitting coil to detect foreign objects. 
     
     
       6. The wireless power transmitting device of  claim 5  wherein the wireless power transmitting circuitry is configured to transmit the wireless power signals during wireless power transmission periods that alternate with foreign object detection periods. 
     
     
       7. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to measure the quality factor of the wireless power transmitting coil during the foreign object detection periods. 
     
     
       8. The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to compare signals gathered during the foreign object detection periods using the wireless power transmitting coil to a basis function to produce a signal quality metric. 
     
     
       9. The wireless power transmitting device of  claim 8  wherein the control circuitry is configured to adjust relative timing between the foreign object detection periods and the wireless power transmission periods based on the signal quality metric to reduce interference between wireless power signals from the additional wireless power transmitting device and the measurements of the quality factor during the foreign object detection periods. 
     
     
       10. An electronic device, comprising:
 a housing; 
 wireless power transmitting circuitry in the housing, wherein the wireless power transmitting circuitry has a wireless power transmitting coil configured to transmit wireless power signals to a wireless power receiving device during wireless power transmission periods; 
 measurement circuitry configured to detect foreign objects using the wireless power transmitting coil during foreign object detection periods that alternate with the wireless power transmission periods; and 
 control circuitry that is configured to:
 analyze signals gathered by the measurement circuitry from the wireless power transmitting coil during the foreign object detection periods to produce a signal quality metric; and 
 adjust timing for the foreign object detection periods to reduce interference from an external wireless power transmitting device with the detection of the foreign objects during the foreign object detection periods. 
 
 
     
     
       11. The electronic device of  claim 10  further comprising a sensing coil separate from the wireless power transmitting coil, wherein the measurement circuitry measures signals in the sensing coil and uses the measured signals from the sensing coil to reduce the interference. 
     
     
       12. The electronic device of  claim 11  wherein the measurement circuitry includes a subtractor configured to subtract the measured signals from the sensing coil from the signals gathered from the wireless power transmitting coil. 
     
     
       13. The electronic device of  claim 12  wherein the control circuitry is configured to analyze signals from the wireless power transmitting coil and the sensing coil to determine relative gain and phase offset between the wireless power transmitting coil and the sensing coil. 
     
     
       14. The electronic device of  claim 13  wherein the subtractor is configured to use the relative gain and the phase offset in subtracting the measured signals. 
     
     
       15. The electronic device of  claim 11  wherein the sensing coil comprises a sensing coil selected from the group consisting of: a figure-eight sensing coil and a cloverleaf sensing coil. 
     
     
       16. The electronic device of  claim 10  wherein the control circuitry is further configured to adjust the timing for the foreign object detection periods to place the foreign object detection periods within power pause periods in which the external wireless power transmitting device is pausing wireless power transmission to detect foreign objects. 
     
     
       17. A wireless power transmitting device for transmitting wireless power to a wireless power receiving device, comprising:
 a housing; 
 wireless power transmitting circuitry in the housing, wherein the wireless power transmitting circuitry has a wireless power transmitting coil configured to transmit wireless power signals to the wireless power receiving device and wherein the wireless power transmitting coil has turns surrounding an interior region; 
 a sensing coil in the housing, wherein the sensing coil is located within the interior region of the wireless power transmitting coil; and 
 circuitry configured to detect foreign objects based on first signals from the wireless power transmitting coil and second signals from the sensing coil. 
 
     
     
       18. The wireless power transmitting device of  claim 17 , wherein the wireless power transmitting circuitry is configured to transmit the wireless power signals in the presence of an additional wireless power transmitting device and wherein the circuitry is configured to subtract the second signals gathered by the sensing coil from the first signals gathered by the wireless power transmitting coil to reduce interference from the additional wireless power transmitting device. 
     
     
       19. The wireless power transmitting device of  claim 18  wherein the sensing coil comprises a sensing coil selected from the group consisting of: a figure-eight coil and a cloverleaf coil. 
     
     
       20. The wireless power transmitting device of  claim 17  wherein the wireless power transmitting circuitry is configured to transmit the wireless power signals during wireless power transmission periods and wherein the circuitry is configured to use the wireless power transmitting coil and sensing coil to detect the foreign objects during foreign object detection periods that alternate with the wireless power transmission periods.

Description:
This application claims the benefit of provisional patent application No. 62/946,044, filed Dec. 10, 2019, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless power transmitting device such as a charging mat wirelessly transmits power to a wireless power receiving device such as a portable electronic device. The portable electronic device has a coil and rectifier circuitry. The coil of the portable electronic device receives alternating-current wireless power signals from the wireless charging mat. The rectifier circuitry converts the received signals into direct-current power. 
     SUMMARY 
     A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may be a wireless charging mat or other device with a charging surface. The wireless power receiving device may be a portable electronic device receiving transmitted wireless power signals from the wireless power transmitting device while resting on the charging surface. During foreign object detection periods, the wireless power receiving device may make signal measurement to detect the presence of foreign objects such as coin or paperclips on the charging surface. 
     The wireless power transmitting device may transmit power in the vicinity of other wireless power equipment. For example, the wireless power transmitting device may transmit wireless power signals to a first wireless power receiving device while another wireless power transmitting device is transmitting its own wireless power signals to a second wireless power receiving device. The wireless power signals transmitted by the other wireless power transmitting device represent a potential source of wireless interference when attempting to detect foreign objects. 
     The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device during wireless power transmission periods. During alternating foreign object detection periods, the wireless power transmitting device gathers signals from wireless power transmitting coil to detect foreign objects. To help reduce interference created when other equipment is transmitting wireless power signals, the wireless power transmitting device gathers signals with a sensing coil that is separate from the wireless power transmitting coil and subtracts these signals from the signals gathered with the wireless power transmitting coil. A signal quality metric may also be used in adjusting the timing of the foreign object detection periods to help avoid interference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless power system in accordance with an embodiment. 
         FIG. 2  is a circuit diagram of an illustrative wireless power system with multiple wireless power transmitting devices in accordance with an embodiment. 
         FIG. 3  is a graph showing illustrative wireless signals involved in operating a wireless power system during wireless power transmission periods and foreign object detection periods in accordance with an embodiment. 
         FIG. 4  is a top view of an illustrative wireless power transmitting device with one or more wireless signal sensing coils in accordance with an embodiment. 
         FIGS. 5, 6, and 7  are diagrams of illustrative wireless power sensing coils in accordance with embodiments. 
         FIG. 8  is a diagram showing how adjacent transmitter noise can be removed from a wireless power transmitting coil signal during foreign object detection operations in accordance with an embodiment. 
         FIG. 9  is a flow chart of illustrative operations involved in using a wireless power transmission system in accordance with an embodiment. 
         FIG. 10  is a timing diagram for a pair of adjacent wireless power transmitting devices in accordance with an embodiment. 
         FIG. 11  is a flow chart of illustrative operations involved in using a wireless power transmission system that evaluates signal quality during foreign object detection periods in accordance with an embodiment. 
         FIG. 12  is a diagram of an illustrative circuit for measuring wireless signals during operation of a wireless power system in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system includes a wireless power transmitting device such as a wireless charging mat. The wireless power transmitting device wirelessly transmits power to one or more wireless power receiving devices. A wireless power receiving device may be a device such as a wrist watch, cellular telephone, tablet computer, laptop computer, or other electronic equipment. The wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     Wireless power is transmitted from the wireless power transmitting device to the wireless power receiving device using one or more wireless power transmitting coils. The wireless power receiving device has one or more wireless power receiving coils coupled to rectifier circuitry that converts received wireless power signals into direct-current power. 
     If a foreign object such as a paperclip, coin, or other metallic object is present near the wireless power transmitting coil, there may be a risk of eddy current generation in the foreign object that could reduce charging efficiency and/or elevate the temperature of the foreign object. To determine whether a foreign object such as a paperclip or coin is present in the vicinity of the wireless power transmitting device, the wireless power transmitting device can measure the quality factor of the wireless power transmitting coil and can determine whether the quality factor has been affected by the presence of a foreign object. By detecting whether foreign objects are present in this way, suitable action can be taken (e.g., power transfer operations may be halted when a foreign object is detected). To ensure that foreign objects are detected satisfactorily during foreign object detection operations, signal subtraction circuitry and/or other noise mitigation techniques can be used to help reduce wireless signal interference from nearby wireless power transmitting devices. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data to detect foreign objects and perform other tasks, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  30 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat or charging puck that includes power adapter circuitry), may be a wireless charging mat or puck that is coupled to a power adapter or other equipment by a cable, may be a portable device, may be equipment that has been incorporated into furniture, a vehicle, or other system, may be a removable battery case, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wrist watch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  uses power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  61  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more wireless power transmitting coils such as wireless power transmitting coils  36 . These coil drive signals cause coil(s)  36  to transmit wireless power. Coils  36  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat) or may be arranged to form a cluster of coils (e.g., in configurations in which device  12  is a wireless charging puck). In some arrangements, device  12  (e.g., a charging mat, puck, etc.) may have only a single coil. In other arrangements, a wireless charging device may have multiple coils (e.g., two or more coils, 5-10 coils, at least 10 coils, 10-30 coils, fewer than 35 coils, fewer than 25 coils, or other suitable number of coils). 
     As the AC currents pass through one or more coils  36 , alternating-current electromagnetic (e.g., magnetic) fields (wireless power signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil(s)  48  in power receiving device  24 . Device  24  may have a single coil  48 , at least two coils  48 , at least three coils  48 , at least four coils  48 , or other suitable number of coils  48 . When the alternating-current electromagnetic fields are received by coil(s)  48 , corresponding alternating-current currents are induced in coil(s)  48 . The AC signals that are used in transmitting wireless power may have any suitable frequency (e.g., 100-250 kHz, etc.). Rectifier circuitry such as rectifier circuitry  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from one or more coils  48  into DC voltage signals for powering device  24 . 
     The DC voltage produced by rectifier circuitry  50  (sometime referred to as rectifier output voltage Vrect) can be used in charging a battery such as battery  58  and can be used in powering other components in device  24 . For example, device  24  may include input-output devices  56 . Input-output devices  56  may include input devices for gathering user input and/or making environmental measurements and may include output devices for providing a user with output. As an example, input-output devices  56  may include a display for creating visual output, a speaker for presenting output as audio signals, light-emitting diode status indicator lights and other light-emitting components for emitting light that provides a user with status information and/or other information, haptic devices for generating vibrations and other haptic output, and/or other output devices. Input-output devices  56  may also include sensors for gathering input from a user and/or for making measurements of the surroundings of system  8 . Illustrative sensors that may be included in input-output devices  56  include three-dimensional sensors (e.g., three-dimensional image sensors such as structured light sensors that emit beams of light and that use two-dimensional digital image sensors to gather image data for three-dimensional images from light spots that are produced when a target is illuminated by the beams of light, binocular three-dimensional image sensors that gather three-dimensional images using two or more cameras in a binocular imaging arrangement, three-dimensional lidar (light detection and ranging) sensors, three-dimensional radio-frequency sensors, or other sensors that gather three-dimensional image data), cameras (e.g., infrared and/or visible cameras with respective infrared and/or visible digital image sensors and/or ultraviolet light cameras), gaze tracking sensors (e.g., a gaze tracking system based on an image sensor and, if desired, a light source that emits one or more beams of light that are tracked using the image sensor after reflecting from a user&#39;s eyes), touch sensors, buttons, capacitive proximity sensors, light-based (optical) proximity sensors such as infrared proximity sensors, other proximity sensors, force sensors, sensors such as contact sensors based on switches, gas sensors, pressure sensors, moisture sensors, magnetic sensors, audio sensors (microphones), ambient light sensors, optical sensors for making spectral measurements and other measurements on target objects (e.g., by emitting light and measuring reflected light), microphones for gathering voice commands and other audio input, distance sensors, motion, position, and/or orientation sensors that are configured to gather information on motion, position, and/or orientation (e.g., accelerometers, gyroscopes, compasses, and/or inertial measurement units that include all of these sensors or a subset of one or two of these sensors), sensors such as buttons that detect button press input, joysticks with sensors that detect joystick movement, keyboards, and/or other sensors. Device  12  may have one or more input-output devices  70  (e.g., input devices and/or output devices of the type described in connection with input-output devices  56 ). 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . In-band transmissions between devices  12  and  24  may be performed using coils  36  and  48 . With one illustrative configuration, frequency-shift keying (FSK) is used to convey in-band data from device  12  to device  24  and amplitude-shift keying (ASK) is used to convey in-band data from device  24  to device  12 . Power may be conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. 
     It is desirable for power transmitting device  12  and power receiving device  24  to be able to communicate information such as received power, battery states of charge, and so forth, to control wireless power transfer. However, the above-described technology need not involve the transmission of personally identifiable information in order to function. Out of an abundance of caution, it is noted that to the extent that any implementation of this charging technology involves the use of personally identifiable information, implementers should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Control circuitry  16  has external object measurement circuitry  41  that may be used to detect external objects on the charging surface of the housing of device  12  (e.g., on the top of a charging mat or, if desired, to detect objects adjacent to the coupling surface of a charging puck). The housing of device  12  may have polymer walls, walls of other dielectric, metal structures, fabric, and/or other housing wall structures that enclose coils  36  and other circuitry of device  12 . The charging surface may be a planer outer surface of the upper housing wall of device  12 . Circuitry  41  can detect foreign objects such as coils, paper clips, and other metallic objects and can detect the presence of wireless power receiving devices  24  (e.g., circuitry  41  can detect the presence of one or more coils  48 ). During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  36  and/or on other coils such as optional foreign object detection coils in device  12  to determine whether any devices  24  are present on device  12 . 
     In an illustrative arrangement, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator that can create impulses so that impulse responses can be measured) and/or uses the transmission of wireless power signals from device  12  to energize the coils in system  8 . Circuitry  41  also includes circuits (e.g., analog-to-digital converter circuits, filters, analog combiners, digital processing circuitry, etc.) to measure the response of system  8 . 
     In an illustrative configuration, device  24  alternates between a wireless power transmission mode in which device  24  transmits wireless power signals and a foreign object detection mode in which device  24  measures the signals in coil(s)  36 . System  8  alternates between first periods (sometimes referred to as wireless power transmission periods) in which device  24  operates in the wireless power transmission mode and circuitry  52  transmits wireless power signals through coil(s)  36  and second periods (sometimes referred to as foreign object detection periods) in which device  24  operates in the foreign object detection mode and uses circuitry  41  to measure the signals on coil  36 . The signals measured on coils  36  during the foreign object detection periods can be analyzed to extract parameters (Q-factor, resonant frequency, etc.) that are indicative of whether foreign objects are present. 
     During the foreign object detection periods, the signal on coil(s)  36  exhibits a decaying resonance. The rate of decay (e.g., the decay envelope) can be measured to determine the quality factor Q (Q-factor) of coil(s)  36 . By monitoring for changes in Q (e.g., changes from a baseline level that are due to a foreign object) and/or by analyzing other parameters associated with the measured signal in coil(s)  36 , device  24  can determine whether a foreign object is present on the charging surface overlapping coil(s)  36  and can take appropriate action (e.g., by halting power transmission). 
     Illustrative wireless power circuitry of the type that may be used in system  8  is shown in  FIG. 2 . The wireless power circuitry of  FIG. 2  includes wireless power transmitter TX 1  and wireless power receiver RX 1 . During operation, wireless power signals  44  are transmitted by wireless power transmitting circuitry such as transmitter TX 1  and received by wireless power receiving circuitry such as receiver RX 1 . As shown in  FIG. 2 , transmitter TX 1  includes inverter circuitry  80 . Control circuitry supplies control signals to control input  82  of inverter circuitry  80 . Inverter circuitry  80  supplies corresponding alternating-current drive signals to coil  36 . Circuit components such as capacitor  70  may be coupled in series with coil  36  as shown in  FIG. 2 . When alternating-current current signals are supplied to coil  36 , corresponding alternating-current electromagnetic signals (wireless power signals  44 ) are transmitted to nearby coils such as illustrative coil  48  in receiver RX 1 . This induces a corresponding alternating-current (AC) current signal in coil  48 . Capacitors such as capacitors  72  may be coupled in series with coil  48 . Rectifier  50  receives the AC current from coil  48  and produces corresponding direct-current power (e.g., direct-current voltage Vrect) at output terminals  76 . This power may be used to power a load. 
     In some scenarios, more than one wireless power transmitting device may be used in system  8  at the same time. As shown in  FIG. 2 , for example, a device containing wireless power transmitting circuitry such as transmitter TX 2  may operate in the vicinity of devices  12  and  24  (e.g., within 20 cm, within 1 m, or other relatively close proximity of devices  12  and  24 ). For example, this device may supply wireless power signals  44 ′ to charge a battery in a wireless power receiving device containing wireless power receiving circuitry such as receiver RX 2 . The presence of transmitter TX 2  near to transmitter TX 1  can lead to a potential for wireless interference. 
     As shown in  FIG. 2 , device  12  may have measurement circuitry  41  for monitoring signals on coil  36 . Circuitry  41  may, for example, measure the Q-factor of coil  36  (and, if desired, the frequency of signals in coil  36 ) during foreign object detection periods. In the presence of wireless power transmitting circuitry TX 2 , some of transmitted wireless power signals  44 ′ from coil  36  may be received by coil  36  and may create noise. To reduce the impact of this potential source of noise and thereby help ensure that coil signal measurements such as Q-factor measurements are made accurately, device  12  may have a separate sensing coil  86  that is used to measure signals  44 ′. Circuitry  41  can then use these measurements to remove the contribution of signals  44 ′ to the signals in coil  36  that are measured during the foreign object detection periods. 
     In addition to or instead of removing noise signals in this way, device  24  can evaluate the quality of the Q-factor measurements that are made during each foreign object detection period and can adjust the timing of the foreign object detection periods to help enhance measurement quality (e.g., foreign object detection period lengths, start times, and/or end times may be adjusted). Particularly in scenarios in which wireless power transmitting circuitry TX 2  is periodically pausing wireless power transmission (e.g., so that transmitter TX 2  can make its own foreign object detection measurements), there may be quiet periods (periods where signals  44 ′ are not being transmitted) in which noise is reduced. Device  24  can adjust the timing of the foreign object detection periods used by device  24  so as to align the foreign object detection periods with the quiet periods, thereby helping to enhance Q-factor measurement quality. 
       FIG. 3  is a graph in which an illustrative coil signal in coil  36  has been plotted as a function of time t. During wireless power transmission periods TN, wireless power transmitting circuitry TX 1  transmits wireless power signals  44  (e.g., the signal in coil  36  is relatively large and has a steady AC magnitude). Periodically, during foreign object detection periods TP, wireless power transmission by circuitry TX 1  is paused and measurement circuitry  41  is used to measure the signals in coil  36 . As shown in  FIG. 3 , because coil  36  is energized from the power applied during preceding period TN, circuitry TX 1  resonates during period TP (e.g., there is signal ringing in coil  36 ). By measuring signal resonating in coil  36  during each period TP, measurement circuitry  41  measures decay envelope  100  and thereby determines the value of Q. This Q-factor value and, if desired, information on the frequency of the coil signal during each period TP can be used to detect foreign objects. For example, the measured value of Q can be compared to a previously obtained baseline Q value. If a change in Q is detected (e.g., a change that is greater in magnitude than a predetermined threshold), device  12  can conclude that a foreign object is present and can take appropriate action (e.g., by halting wireless power transmission). 
     In the presence of a simultaneously transmitted wireless power signal such as wireless power signal  44 ′ from nearby wireless power transmitting circuitry TX 2 , there is a potential for signals  44 ′ to be received by coil  36  and create noise during foreign object detection periods TP. This can make it challenging to accurately measure Q and detect foreign objects. 
     By measuring signals  44 ′ with a sensing coil, device  12  can subtract signals  44 ′ from the signals being measured on coil  36 .  FIG. 4  is a top view of device  12  in an illustrative configuration in which device  12  has one or more sensing coils. The sensing coils may be located in areas such as wireless power transmitting coil interior region  104  (e.g., a location within the turns forming coil  36 ) and/or wireless power transmitting coil exterior region  106  (e.g., an exterior coil region located outside of the turns forming coil  36 ). The sensing coil and coil(s)  36  may be housed in a housing such as housing  102 . 
       FIGS. 5, 6, and 7  are illustrative sensing coils  86 . In the example of  FIG. 5 , coil  86  is formed from a single loop. Multi-turn loops may also be used in forming sensing coil  86 . In the example of  FIG. 6 , coil  86  is a figure-eight coil.  FIG. 7  shows how coil  86  may have a cloverleaf pattern. 
     In arrangements of the types shown in  FIGS. 6 and 7 , sensing coil  86  may be configured to exhibit zero output when placed within the interior of coil  36  in region  104  of  FIG. 4 . Consider, as an example, a scenario in which coil  36  has a figure-eight pattern of the type shown in  FIG. 6  and is placed in interior region  104  of coil  36  of device  12  of  FIG. 4 . In interior region  104 , the magnetic field B produced by coil  36  is roughly independent of angular orientation (e.g., all of the magnetic field is oriented in the positive Z direction or all is oriented in the negative Z direction depending on the phase of the AC magnetic field being emitted by coil  36  and all of the magnetic field is rotationally symmetric about the center of coil  36 ). As a result of the asymmetrical figure-eight pattern of sensing coil  86  of  FIG. 6 , the first half of the figure-eight of coil  86  will produce a positive voltage (e.g., when the magnetic field B in region  104  is positive) whereas the second half of the figure-eight of coil  86 , which has an opposing winding sense, will produce an equal and opposite negative voltage (when the magnetic field B in region  104  is positive). The contributions of the first and second halves of the figure-eight coil will likewise cancel when the magnetic field is negative. The cloverleaf pattern of  FIG. 7  is also configured to produce no output from the magnetic field produced by coil  36  when positioned within region  104 . 
     Because sensing coil arrangements such as the arrangements of  FIGS. 6 and 7  nominally produce no output as a result of the magnetic field produced by coil  36 , this type of sensing coil arrangement can exhibit good sensitivity when measuring magnetic fields from sources such as transmitter TX 2  that are off center with respect to coil  36 . Unlike circuitry TX 1 , which produces magnetic fields that are centered on region  104  and induce cancelling voltages in different portions of sensing antenna  86 , transmitter TX 2  tends to produce magnetic fields that are stronger on one side of coil  86  (the side nearest transmitter TX 2 ) than the other (the side farthest from transmitter TX 2 ). Accordingly, sensing coil arrangements such as the arrangements of  FIGS. 6 and 7  may be used to help enhance sensitivity to measurements of noise from circuitry TX 2  while decreasing sensitivity to signals from transmitter TX 1 . If desired, other coil designs can be used (e.g., sensing coil  86  may have one or more turns in a single loop as shown in  FIG. 5 , etc.). 
     The signals from circuitry TX 2  that are gathered with sensing coil  86  can be removed from the signals in coil  36  using measurement circuitry  41 . For example, analog and/or digital signal subtraction circuitry can be used to remove the noise component of the signals in coil  36  (e.g., the TX 2  signals measured with coil  86 ). Illustrative circuitry for removing adjacent transmitter noise from the measured signal in coil  36  during foreign object detection periods is shown in  FIG. 8 . As shown in  FIG. 8 , circuitry  41  may include subtractor  110 . The gain G (e.g., the relative weight assigned to the positive and negative inputs of subtractor  110 ) and the relative phase offset Φ imposed on the positive and negative inputs can be established based on settings obtained during learning operations (e.g. setup operations in which relative coil sensitivity and phase shift measurements are made). After setting up gain G and phase offset Φ, subtractor  100  can subtract signals from circuitry TX 2  that are received on sensing coil  86  (e.g., noise signals) from the signal present on coil  36  during foreign object detection periods TP. The resulting output of subtractor  110  may be digitized by analog-to-digital converter  112  and further processed (e.g., to extract decay envelop  100  of  FIG. 3  and thereby measure Q, to measure the resonant frequency, or to obtain other parameters during foreign object detection periods TP). By removing interference produced by transmitter TX 2  during the foreign object detection periods, the accuracy of the Q measurements (or other measurements) made by circuitry  41  can be enhanced. 
       FIG. 9  is a flow chart of illustrative operations involved in using system  8  in a configuration in which noise signals are subtracted from the measurements made on coil  36  during foreign object detection. 
     During the operations of block  114 , system  8  is operated in a learning mode. During this mode, device  12  temporarily turns off wireless power transmitting circuitry in device  12  (e.g., transmitter TX 1  is turned off), so that the signals from transmitter TX 2  can be measured in isolation. While transmitter TX 1  is off, device  12  (e.g., control circuitry such as measurement circuitry  41 ) measures the signals from transmitter TX 2  that are being received by sensing coil  86  and the signals from transmitter TX 2  that are being received by coil  36 . The relative strength (magnitude) of these signals and the relative phase between these signals can then be determined. For example, device  12  may determine that the received TX 2  signal on coil  36  is twice as strong as the received signal on coil  86  and that there is a 10° phase shift between these signals. Based on these measured attributes, device  12  can then establish corresponding compensating settings for gain G (e.g., a gain setting of 2 to compensate for the factor of two difference between the sensitivities of coils  86  and  36 ) and phase offset Φ (e.g., a phase offset of 10°). The phase offset and gain settings can be applied to subtractor  110 . 
     During the operations of block  116 , device  12  alternates between wireless power transmission periods TN in which wireless power is transmitted by the wireless power transmitting circuitry of device  12  (transmitter TX 1 ) and foreign object detection periods TP in which wireless power delivery by transmitter TX 1  is paused. During the foreign object detection periods, circuitry  41  measures the signals detected by coils  36  and  86 . Subtractor  110  uses the established gain setting G and phase offset setting Φ to subtract interference (noise) due to signals  44 ′ from transmitter TX 2  from the measured signal on coil  36 . The signal on coil  36  can therefore be accurately measured to determine decay envelope  100  (and optionally the frequency of signal resonance) and Q-factor for coil  36 . The measured value of Q-factor may be compared to a baseline value (e.g., a running average, default value, a value determined during initial setup operation, and/or other baseline Q-factor value). If the magnitude of the deviation between the measured value of Q and the baseline value of Q is below a threshold amount, device  12  can conclude that no foreign object is present and power delivery can resume during a subsequent wireless power transmission period TN. If, however, Q deviates from the baseline by more than the threshold amount, device  12  can conclude that a foreign object is present and suitable action can be taken. For example, wireless power transmission may be halted at block  118 . 
     In some scenarios, the wireless power transmitting device that includes transmitter TX 2  implements a foreign object detection scheme in which wireless power transmissions are periodically paused (e.g., so that foreign objects can be detected by measuring the Q-factor of the wireless power transmitting coil in transmitter TX 2 ). Wireless power pause periods associated with transmitter TX 2  may be misaligned with respect to the foreign object detection periods TP of transmitter TX 1 . As shown in  FIG. 10 , for example, device  12  may use transmitter TX 1  to transmit power in periods TN and may pause wireless power transmission during foreign object detection periods TP. Another wireless power transmitting device may use transmitter TX 2  to alternate between a) wireless power transmission periods TN′ in which transmitter TX 2  transmits wireless power signals  44 ′ that may interfere with the foreign object detection measurements made by device  12  during periods TP and b) foreign object detection periods (sometimes referred to as power pause periods) TP′ in which signals  44 ′ are not present and do not interfere with the foreign object detection measurements made by device  12 . 
     To help enhance measurement accuracy by device  12  during foreign object detection periods TP, device  12  can evaluate the quality of the foreign object detection measurements being made by device  12 . Device  12  can then adjust the timing of periods TP (e.g., start and end times for each period TP) so that these periods tend to coincide with low-noise time periods such as periods TP′. 
     A flow chart of illustrative operations involved in using system  8  in a configuration in which device  12  evaluates the quality of foreign object detection measurements so that the timing of foreign object detection measurements can be adjusted to enhance measurement quality is shown in  FIG. 11 . 
     During the operations of block  11 , the control circuitry of device  12  operates device  12  with default settings. For example, device  12  may initially be configured so that periods TP of about 100 microseconds (e.g., at least 10 microseconds, at least 50 microseconds, less than 1000 microseconds, less than 500 microseconds, etc.) alternate with periods TN of at least 10 ms, at least 100 ms, at least 1 s, at least 10 s, less than 20 s, less than 2 s, less than 200 ms, less than 20 ms, or less than 2 s (as examples). 
     During the operations of block  122 , device  12  makes foreign object detection measurements (e.g., Q-factor measurements and comparisons) in periods TP. Device  12  also determines the quality of these measurements. For example, because the expected signal during periods TP follows the function e −αt (sin(2πft)), this function can be used as a basis function in a least-squares curve fitting process. If the fit between the basis function and the measured signal on coil  36  during period TP is poor, signal quality metric QM will be relatively low, indicating that the quality of the signal on coil  36  is low because noise is present. If, however, the fit between the basis function and the measured signal on coil  36  during period TP is good, quality metric QM will be relatively high, indicating that the quality of the signal on coil  36  is high due to the absence of interference. Quality metric QM may be determined in this way whether or not sensing coil  86  is present and is being used to measure noise for subtraction from the signal on coil  36 . 
     If the measured Q factor from step  122  deviates by more than a threshold amount from the baseline Q factor, a foreign object is likely present and appropriate action can be taken by device  12  at block  126  (e.g., power transmission can be halted). Otherwise operations may continue at block  124 . 
     Because the quality measurement QM indicates whether noise is present or is not present, the value of QM may be used by device  12  to search for a satisfactory timing relationship between periods TP and periods TP′ that helps to reduce interference. As an example, during the operations of block  124 , device  12  can slightly increment the start time for periods TP. Device  12  can then evaluate QM and can compare the present value of QM to the previous value of QM. If QM decreases, device  12  can decrement the start time. If it is determined, however, that QM has increased due to the increase in the start time, device  12  can further increase the start time for periods TP in an attempt to further increase QM. By adjusting the timing of periods TP back and forth in this way (e.g., by using the measured value of QM as feedback when making dynamic adjustments to the timing of the foreign object detection periods TP), device  12  can ensure that the foreign object detection operations of block  122  are performed when noise from interference (e.g., signals  44 ′ from circuitry TX 2 ) is relatively low. This approach can be used when device  12  has one or more sensing coils  86  and subtracts sensed interference from the signal in coil(s)  36  and/or can be used when device  12  does not have any sensing coils  86  and only has one or more wireless power transmission coils  36  (see, e.g.,  FIG. 12 , which shows how measurement circuitry  41  may include analog-to-digital converter circuitry  112  that measures the signal in coil  36  without subtracting the signal in sensing coil  86  using subtractor  110  of  FIG. 8 ). 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20200709
Publication Date: 20220426
Grant Date: 20220426
Priority Date: 20191210
Inventors: TERRY, STEPHEN C.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/80", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/73", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 81259829