PATENT DOCUMENT

Publication Number: US-10923955-B2
Application Number: US-201815868877-A
Country: US
Kind Code: B2

Title: Wireless power system with resonant circuit tuning

Abstract:
A wireless power system may use a wireless power transmitting device to transmit wireless power to a wireless power receiving device. The wireless power transmitting device may have an array of coils that extend under a wireless charging surface. Control circuitry may supply alternating-current control signals to inverters. The inverters are coupled to resonant circuits. Each resonant circuit includes a capacitor coupled to a respective one of the coils. During operation, wireless power signals are transmitted from the coils to the wireless power receiving device through the charging surface. The capacitor associated with each resonant circuit may potentially be individually selected to enhanced uniformity of the wireless power transmitting device. The array of coils may have multiple layers and the capacitors in each layer may have different respective values.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device configured to transmit wireless power to a wireless power receiving device through a charging surface, comprising:
 a plurality of wireless power transmitting coils of a common shape; 
 a capacitor coupled to each of the wireless power transmitting coils to form respective resonant circuits; 
 inverter circuitry coupled to the resonant circuits; and 
 control circuitry configured to use the inverter circuitry to transmit wireless power signals with at least one of the wireless power transmitting coils, wherein:
 the wireless power transmitting coils are arranged in a plurality of layers under the charging surface, and 
 the capacitors coupled to wireless power transmitting coils in different layers have different capacitances configured to produce a same open-circuit voltage at a rectifier output within the wireless power receiving device. 
 
 
     
     
       2. The wireless power transmitting device of  claim 1  wherein each of the wireless power transmitting coils has the same number of turns. 
     
     
       3. The wireless power transmitting device of  claim 2  wherein each of the wireless power transmitting coils has rotational symmetry. 
     
     
       4. The wireless power transmitting device of  claim 3  wherein the wireless power transmitting coils are circular or square. 
     
     
       5. The wireless power transmitting device of  claim 1  wherein at least two layers in the plurality of layers have a different number of wireless power transmitting coils. 
     
     
       6. The wireless power transmitting device of  claim 1  wherein the layers include first, second, and third layers and wherein the capacitors comprise:
 first capacitors of a first value coupled respectively to the wireless power transmitting coils of the first layer; 
 second capacitors of a second value that is different than the first value coupled respectively to the wireless power transmitting coils of the second layer; and 
 third capacitors of a third value that is different than the first and second values coupled respectively to the wireless power transmitting coils of the third layer. 
 
     
     
       7. The wireless power transmitting device of  claim 6  wherein each wireless power transmitting coil of the plurality of wireless power transmitting coils is positioned in one and only one layer of the plurality of layers of wireless power transmitting coils. 
     
     
       8. The wireless power transmitting device of  claim 6  wherein each of the coils has an outer diameter and wherein the outer diameters of the coils are equal. 
     
     
       9. The wireless power transmitting device of  claim 8  wherein each of the coils has an inner diameter and wherein the inner diameters of the coils are equal. 
     
     
       10. The wireless power transmitting device of  claim 9  wherein each of the wireless power transmitting coils has terminals located at a given angle with respect to a center of that wireless power transmitting coil and wherein the given angle is equal for at least some of the wireless power transmitting coils. 
     
     
       11. A wireless charging mat having a charging surface, wherein the wireless charging mat is configured to transmit wireless power to a wireless power receiving device through the charging surface, the wireless charging mat comprising:
 wireless power transmitting coils of a common shape; 
 capacitors coupled to the wireless power transmitting coils to form respective resonant circuits, wherein each capacitor has a different value individually optimized for magnetic coupling with a power receiving coil in the wireless power receiving device; 
 inverter circuits coupled respectively to the resonant circuits; and 
 control circuitry configured to use at least one of the inverter circuits and the resonant circuit coupled to that inverter circuit to transmit the wireless power. 
 
     
     
       12. The wireless charging mat of  claim 11  wherein the wireless power transmitting coils are arranged in at least first and second layers and wherein at least one of the wireless power transmitting coils in the first layer overlaps at least one of the wireless power transmitting coils in the second layer. 
     
     
       13. The wireless charging mat of  claim 11  wherein each of the coils has an outer diameter and wherein the outer diameters of the coils are within 5% of each other. 
     
     
       14. The wireless charging mat of  claim 11  wherein each of the coils has an inner diameter and wherein the inner diameters of the coils are within 5% of each other.

Description:
This application claims the benefit of provisional patent application No. 62/551,720, filed on Aug. 29, 2017, 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 charging mat wirelessly transmits power to a portable electronic device that is placed on the mat. The portable electronic device has a receiving coil and rectifier circuitry for receiving wireless alternating-current (AC) power from a coil in the wireless charging mat that is overlapped by the receiving coil. The rectifier converts the received AC power into direct-current (DC) power. 
     SUMMARY 
     A wireless power system may use a wireless power transmitting device to transmit wireless power to a wireless power receiving device. The wireless power transmitting device may have an array of coils under a wireless charging surface. Control circuitry may supply alternating-current control signals to inverters. The inverters are connected to resonant circuits. Each resonant circuit includes a capacitor connected to a respective one of the coils. During operation, wireless power signals are transmitted from the coils to the wireless power receiving device through the charging surface. 
     The capacitor associated with each resonant circuit may be individually selected to enhanced uniformity of the wireless power transmitting device or layers of the coils may have capacitors of different respective values. The coils in the array may all have the same shape. The coils in a layer may overlap one or more coils in other layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system that includes a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG. 2  is a circuit diagram of illustrative wireless power transmitting circuitry and illustrative wireless power receiving circuitry in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative wireless power transmitting device on which a wireless power receiving device has been placed in accordance with an embodiment. 
         FIG. 4  is a top view of an illustrative wireless power transmitting coil in accordance with an embodiment. 
         FIG. 5A  is a cross-sectional side view of an illustrative wireless power transmitting device with multiple layers of wireless power transmitting coils in accordance with an embodiment. 
         FIG. 5B  is a top view of an illustrative wireless power transmitting device with an array of 22 coils in three layers in accordance with an embodiment. 
         FIG. 5C  is a top view of an illustrative lower layer of eight coils for the wireless power transmitting device of  FIG. 5B  in accordance with an embodiment. 
         FIG. 5D  is a top view of an illustrative middle layer of seven coils for the wireless power transmitting device of  FIG. 5B  in accordance with an embodiment. 
         FIG. 5E  is a top view of an illustrative upper layer of seven coils for the wireless power transmitting device of  FIG. 5B  in accordance with an embodiment. 
         FIG. 6  is a diagram of illustrative test equipment for characterizing wireless power circuitry in accordance with an embodiment. 
         FIG. 7  is a flow chart of illustrative operations involved in selecting capacitor values for resonant circuits in a wireless power transmitting device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system has a wireless power transmitting device such as a wireless charging mat. The wireless power transmitting device wirelessly transmits power to a wireless power receiving device such as a wristwatch, 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. 
     The wireless power transmitting device has an array of wireless power transmitting coils arranged in multiple layers under a charging surface. During operation, the wireless power transmitting coils are used to transmit wireless power signals that are received by a wireless power receiving coil in the wireless power receiving device. Each wireless power transmitting coil may be connected to a respective capacitor in a resonant circuit. The inductances of the wireless power transmitting coils may vary as a function of position within the mat and distance from the wireless power receiving device. This can lead to potential variations in the resonant circuit behavior of the resonant circuits. By characterizing coil behavior with test equipment, capacitor values may be chosen for the resonant circuits that ensure uniform wireless charging performance across the charging surface. 
     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 includes 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 determining power transmission levels, processing sensor data, processing user input, handling communications between devices  12  and  24  (e.g., sending and receiving in-band and out-of-band data), selecting wireless power transmitting coils, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be used to authorize components to use power and ensure that components do not exceed maximum allowable power consumption levels. 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 that includes power adapter circuitry), may be a wireless charging mat that is connected 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, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat may sometimes be described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wristwatch, a cellular telephone, a laptop computer, a tablet computer, or other electronic equipment. Power transmitting device  12  may be connected to a wall outlet (e.g., alternating current), may have a battery for supplying power, and/or may have another source of power. Power transmitting device  12  may have an AC-DC power converter such as 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  may use 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  60  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 coils  42 . Coils  42  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat). 
     As AC currents pass through one or more coils  42 , alternating-current electromagnetic fields (signals  44 ) are produced that are received by one or more corresponding coils such as coil  48  in power receiving device  24 . When the alternating-current electromagnetic fields are received by coil  48 , corresponding alternating-current currents are induced in coil  48 . Rectifier circuitry such as rectifier  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 coil  48  into DC voltage signals for powering device  24 . 
     The DC voltages produced by rectifier  50  can be used in powering 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  such as a display, touch sensor, communications circuits, audio components, sensors, and other components and these components may be powered by the DC voltages produced by rectifier  50  (and/or DC voltages produced by battery  58 ). 
     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 . 
     Wireless transceiver circuitry  40  uses one or more coils  42  to transmit in-band signals to wireless transceiver circuitry  46  that are received by wireless transceiver circuitry  46  using coil  48 . Any suitable modulation scheme may be used to support in-band communications between device  12  and device  24 . 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 is conveyed wirelessly from device  12  to device  24  during these FSK and ASK transmissions. 
     During wireless power transmission operations, circuitry  52  supplies AC drive signals to one or more coils  42  at a given power transmission frequency. The power transmission frequency may be, for example, a predetermined frequency of about 125 kHz, at least 80 kHz, at least 100 kHz, less than 500 kHz, less than 300 kHz, 50-200 kHz, or other suitable wireless power frequency. In some configurations, the power transmission frequency may be negotiated in communications between devices  12  and  24 . In other configurations, the power transmission frequency is fixed. 
     During wireless power transfer operations, while power transmitting circuitry  52  is driving AC signals into one or more of coils  42  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  uses FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  42  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     In-band communications between device  24  and device  12  uses ASK modulation and demodulation techniques. Wireless transceiver circuitry  46  transmits in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are connected to coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  42 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  42  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  42  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     Control circuitry  16  has external object measurement circuitry  41  (sometimes referred to as foreign object detection circuitry or external object detection circuitry) that detects external objects on a charging surface associated with 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 . Control circuitry  30  has measurement circuitry  43 . Measurement circuitry  41  and  43  may be used in making inductance measurements (e.g., measurements of the inductances of coils  42  and  48 ), input and output voltage measurements (e.g., a rectifier output voltage, and inverter input voltage, etc.), current measurements, capacitance measurements, and/or other measurements on the circuitry of system  8 . 
     Illustrative circuitry of the type that may be used for forming power transmitting circuitry  52  and power receiving circuitry  54  of  FIG. 1  is shown in  FIG. 2 . 
     As shown in  FIG. 2 , power transmitting circuitry  52  may include drive circuitry such as inverters  60  coupled to respective resonant circuits RC 1  . . . RCN. Each resonant circuit may include a wireless power transmitting coil  42  and capacitor  70 . In resonant circuits RC 1  . . . RCN, coils  42  may have respective inductances Ltx 1  . . . Ltxn and capacitors  70  may have respective capacitances Ctx 1  . . . Ctxn. Coils  42  may all have a common shape, but the values of Ltx 1  . . . Ltxn may differ due to differing distances to coil  48  of device  24 . 
     Inverters  60  have metal-oxide-semiconductor transistors or other suitable transistors that are modulated by AC control signals from control circuitry  16  ( FIG. 1 ) that are received on respective control signal inputs  62 . The attributes of each AC control signal (e.g., duty cycle, etc.) may be adjusted dynamically during power transmission to control the amount of power being transmitted by power transmitting coils  42 . 
     When transmitting wireless power, control circuitry  16  ( FIG. 1 ) selects one or more appropriate coils  42  to use in transmitting signals  44  to coil  48  (e.g., control circuitry  16  supplies control signals to the inputs  62  of the inverters  60  connected to the selected coils to produce signals  44 ). Coil  48  and capacitor  74  (of capacitance Crx) form a resonant circuit in circuitry  54  that receives signals  44 . Receiver  50  rectifies the received signals and provides direct-current output power at output  68 . 
     A top view of an illustrative configuration for device  12  in which device  12  has an array of coils  42  is shown in  FIG. 3 . Device  12  may, in general, have any suitable number of coils  42  (e.g., 22 coils, at least 5 coils, at least 10 coils, at least 15 coils, fewer than 30 coils, fewer than 50 coils, etc.). Coils  42  may be arranged in rows and columns and may or may not partially overlap each other. Device  12  may have a planar housing surface that covers coils  42  (sometimes referred to as a charging surface). One or more wireless power receiving devices such as device  24  may be positioned on the charging surface as shown in  FIG. 3  to receive wireless power from coils  42 . Coils  42  may be circular or may have other suitable shapes (e.g., coils  42  may be square, may have hexagonal shapes, may have other shapes having rotational symmetry, etc.). In the illustrative configuration of  FIG. 3 , coils  42  are circular and are formed from multiple wire turns (e.g., multiple turns formed from metal traces, bare wire, insulated wire, wire monofilaments, multifilament wire, etc.) surrounding respective coil centers CP. 
     To enhance spatial freedom, the wireless power transmitting coils of device  12  may be identical or nearly identical to each other (e.g., coils  42  may all have a common shape). For example, each of coils  42  may have a configuration of the type shown in  FIG. 4 . As shown in  FIG. 4 , each coil  42  may be characterized by a number of circular turns (wire loops) of wire  42 W about coil center  42  (e.g., 10-200, less than 300, less than 100, at least 5, at least 25, or other suitable number of turns). The number of turn of wire in each of coils  42  in device  12  may be identical or may vary by less than 10% between coils, less than 5% between coils, less than 2% between coils, etc. (as examples). Coils  42  may also all share a common inner diameter ID (e.g., the value of inner diameter ID may exhibit a coil-to-coil variation of less than 5%, less than 2%, or other suitable value) and/or may all share a common outer diameter OD (e.g., outer diameter OD may exhibit a coil-to-coil variation of less than 5%, less than 2%, or other suitable amount). Each coil  42  may have terminals  42 T and, to enhance manufacturability, each pair of terminals  42 T or at least some of these pairs of terminals may be located with the same angular orientation (angle) relative to coil center CP (e.g., the 12:00 position in the example of  FIG. 4 ). Coils  42  that have the same number of turns, inner diameter, outer diameter, terminal location, etc. (e.g., coils  42  that have the same shape) may be organized in multiple layers and may include coils that overlap each other (e.g., coils in one layer that overlap coils in one or more other layers). 
     As shown in  FIG. 5A , device  12  may have a housing  78  (e.g., a housing formed from plastic or other materials with a planar upper surface such as charging surface  12 C) that encloses multiple layers of coils  42 . In the illustrative example of  FIG. 5A , device  12  has three layers of coils  42 : first (upper) layer  80 , second (middle) layer  82 , and third (lower) layer  84 . Middle layer  82  may include coils such as illustrative middle layer coil  42 ′. Lower layer  84  may include coils such as illustrative lower layer coil  42 ″. Despite being constructed identically, the inductances of coils  42  may vary depending on their location within device  12  (e.g., due to different distances between each coil  42  and coil  48  when coil  48  is aligned with that coil). As a result, a coil in middle layer  82  such as coil  42 ′ will exhibit a peak inductance value (when the center CP of coil  42 ′ is aligned with center CP′ of coil  48 ) that is less than the peak inductance value exhibited when coil  48  is aligned with a coil  42  in upper layer  80 . Unless care is taken, the differing inductance values for the coils will cause the different resonant circuits RC 1  . . . RCN of wireless power transmitting circuitry  52  to perform differently and the performance of device  12  will not be uniform across charging surface  12 C. 
       FIGS. 5B, 5C, 5D, and 5E  are diagrams of an illustrative wireless power transmitting device such as a charging mat having 22 coils in three layers. 
       FIG. 5B  is a top view of wireless power transmitting device  12  in an illustrative configuration in which there are 22 coils  42  (mounted above printed circuit board  77 , which has openings  79  to accommodate terminal wires in terminals  42 T) that partially overlap each other and that are arranged in three different layers. 
       FIG. 5C  is a top view of an illustrative configuration for lower layer  84  having eight coils  42  in wireless power transmitting device  12  of  FIG. 5B .  FIG. 5D  is a top view of an illustrative configuration for middle layer  82  having seven coils  42  for wireless power transmitting device  12  of  FIG. 5B .  FIG. 5E  is a top view of an illustrative configuration for upper layer  80  having seven coils for wireless power transmitting device  12  of  FIG. 5B . In this example, lower layer  84  has 8 coils, middle layer  82  has 7 coils, and upper layer  80  has 7 coils. In general, each layer may have any suitable number of coils (e.g., at least 2 coils, at least 5 coils, fewer than 9 coils, fewer than 14 coils, 6-9 coils, etc.). Device  12  may have one layer of coils  42 , at least two layers of coils  42 , at least three layers of coils  42 , at least four layers of coils  42 , fewer than five layers of coils  42 , 4-6 layers of coils, etc. 
     To enhance uniformity, capacitors  70  or at least the set of capacitors in each layer of coils  42  may each have a different respective value (e.g., these capacitors may have different rated capacitor values, not just incidentally different values arising from the normal manufacturing variations associated with capacitors having the same rated value). During manufacturing, satisfactory values for capacitance Ctx in each resonant circuit may be established using equipment of the type shown in  FIG. 6 . In the illustrative system of  FIG. 6  (e.g., a test system used during manufacturing characterization of wireless power transmission), test equipment  90  has probes connected to coil  42  and coil  48 . Coil  42  may form part of device  12  (e.g., a representative test device or other representative hardware) and may be connected to inverter  60  and capacitor Ctx in wireless power transmitting circuitry  52  of device  12 . Coil  48  may form part of device  24  (e.g., a representative test device or other representative hardware) and may be connected to rectifier  50  and capacitor Crx. 
     During characterization measurements, test equipment  90  may apply voltage Vin to the input of inverter  60  and measure the resulting direct-current output Vo of rectifier  50 . Test equipment  90  may also make additional measurements (e.g., measurements of the inductance of coil  42 , the inductance of coil  48 , etc.) and can use these measurements to determine magnetic coupling coefficient k. 
     The location of coil  48  may be adjusted while measuring k and other parameters in this way with test equipment  90 . In particular, coil  48  may be placed in various lateral locations across charging surface  12 C (e.g., various locations in the X-Y plane of  FIG. 5A ) while measuring coupling coefficient k. The value of k can be maximized by aligning coil  48  with a coil of interest such as illustrative coil  42 ′ in  FIG. 5A . After placing coil  48  in a known coupling coefficient relationship with coil  42  (e.g., by maximizing k or by achieving another desired known k value), test equipment  90  can characterize the performance of wireless power transmitting circuitry  52  and wireless power receiving circuitry  54  (e.g., by measuring Vo, the inductance of coil  42 , and the inductance of coil  48 ). The value of Vin that is applied to the inverter  60  that is connected to coil  42  is known by test equipment  90 . Using this information, equation 1 or equation 2 may be used to determine a satisfactory capacitance value (Ctx) to use for the capacitor  70  that is coupled to the coil  42  that is being characterized (or to use for the capacitors  70  coupled to all of the coils in the same layer as coil  42 ).
 
ω o =1/( LtxCtx ) 1/2   (1)
 
 Vo≈ωk ( Lrx ) 1/2   V in/[ω( Ltx ) 1/2 −(1/ω Ctx ( Ltx ) 1/2 )]  (2)
 
     In equation 1, ω o  is the resonant frequency of the resonant circuit (set at 60-70% of the wireless power transfer frequency, which is the frequency of the AC drive signals supplied to the inverter circuitry of wireless power transmitting circuitry  52 ) and Ltx is the inductance of coil  42  that is measured at the peak-k (or other known k) location of coil  48 . When using equation 1 to determine Ctx for each coil  42  (or at least each different layer of coils  42 ), Ctx values are selected based on achieving the same resonant frequency for each coil. 
     In equation 2, Vo is the measured output voltage from rectifier  50 , k is the peak-k value (or other known k value) associated with coil  42  and coil  48 , Lrx is the measured inductance (at peak k or other known k) of coil  48 , Ltx is the measured inductance of coil  42 , and Vin is the known direct-current voltage value of the input voltage to inverter  60 . When using equation 2 to determine the values of Ctx for device  12 , Ctx values are chosen for each coil  42  (or layers of coils  42 ) so that use of each coil  42  produces the same open-circuit output voltage Vo at the output of rectifier  50 . 
     There is often metal present in device  24  that overlaps coils  42 , leading to a parasitic resistance in the resonant circuit (LC circuit) in circuitry  52 . During operation of device  12  (e.g., when estimating coupling coefficient k for each coil  42  to aid in coil selection), the parasitic resistance can be a source of inaccuracy. In configurations for device  12  in which the values of Ctx are chosen using an equation such as equation 1 or equation 2 (e.g., if Ctx is tuned separately for each associated coil  42  or each layer of coils  42 ), the magnitude of the parasitic resistance is reduced and accuracy in the estimation of coupling coefficient k by device  12  is enhanced. Individual (coil-specific) or layer-specific capacitor tuning also helps enhance the uniformity of the wireless power signal output of device  12  across charging surface  12 C. 
       FIG. 7  is a flow chart of illustrative operations involved in using test equipment  90  of  FIG. 6  to ensure that device  12  is manufactured with satisfactory capacitor values for capacitors  70  in resonant circuits RC 1  . . . RCN of wireless power transmitting circuitry  52 . 
     During the operations of block  91 , a device  24  (or representative hardware) containing coil  48  is positioned on charging surface  12 C of device  12  so that coil  48  is placed in a known magnetic coupling relationship with a given one of coils  42  in device  12  (or representative hardware with an array of coils  42 ). With one illustrative scenario, coil  48  is moved in the X-Y plane of charging surface  12 C until coil  48  and given coil under test (e.g., coil  42 ′ in the example of  FIG. 5A ) exhibit a peak value of coupling coefficient k (e.g., when coil center CP′ of coil  48  is aligned with coil center CP of coil  42 ′). With another illustrative scenario, coil  48  is moved into a position in which coil  48  and coil  42  exhibit a predetermined value of coupling coefficient k (e.g., k=0.7). 
     During the operations of block  92 , test equipment  90  gathers inductance measurements (e.g., Ltx and Lrx) and gathers a measurement of Vo from device  24 . This information and information on the known AC drive frequency and known input voltage Vin may be used during the operations of block  94  (e.g., with equation 1 or equation 2) to determine a value of Ctx to use in the resonant circuit associated with the given coil  42 . 
     After the current coil under test has been characterized and a corresponding value of Ctx identified, additional coils  42  can be characterized in the same way, as indicated by line  96 . Once all desired coils  42  have been characterized and corresponding capacitor values Ctx 1  . . . Ctxn have been determined, devices  12  can be manufactured in which resonant circuits RC 1  . . . RCN incorporate capacitors  70  of respective capacitances Ctx 1  . . . Ctxn (e.g., devices  12  can be formed during the operations of block  98 ). Individual capacitance values can be used in each resonant circuit, or all resonant circuits in each coil layer of a multilayer coil array can be provided with respective capacitance values selected based on equations 1 or 2. For example, in a three-layer coil array (see, e.g., layers  80 ,  82 , and  84 ), respective first, second, and third capacitor values can be chosen for the capacitors  70  respectively in the first, second, and third layers. Within each layer, the capacitor value that is used may, for example, be an average value of the individual capacitor values produced using equation 1 or equation 2 for the resonant circuits in that layer. 
     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: 20180111
Publication Date: 20210216
Grant Date: 20210216
Priority Date: 20170829
Inventors: LIU, NAN
DAYAL, ROHAN
QIU, WEIHONG
MOUSSAOUI, ZAKI
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/402", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 65435723