PATENT DOCUMENT

Publication Number: US-10998121-B2
Application Number: US-201715664154-A
Country: US
Kind Code: B2

Title: Capacitively balanced inductive charging coil

Abstract:
An inductor coil includes a wire which is wound in alternating layers such that the surface area of the wire in each winding viewed from above or below the coil is substantially equal in each half of the coil defined by a line bisecting the center point in each layer. The layers are also wound in a serpentine fashion to balance the capacitance between layers. The substantially equal surface area of wire in each half of a coil layer and in adjacent coil layers results in a balanced capacitance of the coil which, in turn, results in reduced common mode noise.

Claims:
What is claimed is: 
     
       1. An inductive coil, comprising:
 a wire wound in at least a first planar layer and a second planar layer adjacent to the first planar layer, the inductive coil comprising:
 a first half of the inductive coil; and 
 a second half of the inductive coil contiguous with the first half, 
 
 wherein the wire is wound such that a first plurality of windings of the wire form an inward spiral and a second plurality of windings of the wire form an outward spiral and wherein, within at least the first half of the inductive coil:
 each consecutive winding in the first plurality of windings occupies a different one of a plurality of planar layers such that consecutive windings in the first plurality of windings are disposed diagonally from each other when perceived from a cross-sectional perspective; 
 each consecutive winding in the second plurality of windings occupies a different one of the plurality of planar layers such that consecutive windings in the second plurality of windings are disposed diagonally from each other when perceived from the cross-sectional perspective; and 
 within each of the plurality of planar layers, windings in the first plurality of windings alternate with windings in the second plurality of windings. 
 
 
     
     
       2. The inductive coil of  claim 1 , wherein each of the first plurality of windings and each of the second plurality of windings is approximately circular. 
     
     
       3. The inductive coil of  claim 1 , wherein the wire crosses itself at an edge of the first and second halves. 
     
     
       4. The inductive coil of  claim 3 , wherein each of the first plurality of windings and each of the second plurality of windings has a symmetric geometric shape. 
     
     
       5. A portable electronic comprising:
 a housing; 
 an electronic componenet disposed within the housing; 
 an inductive coil disposed within the housing and coupled to the electronic component, the inductive coil comprising:
 a wire wound in at least a first planar layer and a second planar layer adjacent to the first planar layer, the inductive coil comprising:
 a first half of the inductive coil; and 
 a second half of the inductive coild contiguous with the first half, 
 
 wherein the wire is wound such that a first plurality of windings of the wire form an invward spiral and a second plurality of windings of the wire form an outward spiral and wherein, within at least the first half of the inductive coil:
 each consecutive winding in the first plurality of windings occupies a different one of a plurality of planar layers such that consecutive windings in the first plurality of windings are disposed diagonally from each other when preceived from a cross-sectional perspective; 
 each consecutive winding in the second plurality of windings occupies a different one of the plurality of planar layers such that consecutive windings in the second plurality of windings are disposed diagonally from each other when perceived from the cross-sectional perspective; and 
 within each of the plurality of planar layers, windings in the first plurality of windings alternate with windings in the second plurality of windings. 
 
 
 
     
     
       6. The portable electronic device of  claim 5 , wherein each of the first plurality of windings and each of the second plurality of windings is approximately circular. 
     
     
       7. The portable electronic device of  claim 5 , wherein the wire crosses itself at an edge of the first and second halves. 
     
     
       8. The portable electronic device of  claim 7 , wherein each of the first plurality of windings and each of the second plurality of windings has a symmetric geometric shape. 
     
     
       9. A wireless charging system, comprising:
 an inductive transmit coil configured to transmit wireless power, the inductive transmit coil comprising:
 a first wire wound in a plurality of turns in at least a first planar layer and a second planar layer adjacent to the first planar layer, the inductive transmit coil comprising:
 a first half of the inductive transmit coil; and 
 a second half of the inductive transmit coil contiguous with the first half, 
 
 wherein two consecutive turns of the first wire in the first half of the inductive transmit coil alternate between the first planar layer and the second planar layer; and 
 
 an inductive receive coil configured to receive the wireless power from the inductive transmit coil, the inductive receive coil comprising:
 a second wire wound in at least a third planar layer and a fourth planar layer adjacent to the third planar layer, the inductive receive coil comprising:
 a first half of the inductive receive coil; and 
 a second half of the inductive receive coil contiguous with the first half, 
 
 wherein the second wire is wound such that a first plurality of windings of the second wire form an inward spiral and a second plurality of windings of the second wire form an outward spiral and wherein, within at least the first half of the inductive receive coil:
 each consecutive winding in the first plurality of windings occupies a different one of the third planar layer or the fourth planar layer such that consecutive windings in the first plurality of windings are disposed diagonally from each other when perceived from a cross-sectional perspective; 
 each consecutive winding in the second plurality of windings occupies a different one of the third planar layer or the fourth planar layer such that consecutive windings in the second plurality of windings are disposed diagonally from each other when perceived from the cross-sectional perspective; and 
 within each of the third and fourth planar layers, windings in the first plurality of windings alternate with windings in the second plurality of windings. 
 
 
 
     
     
       10. The wireless charging system of  claim 9 , wherein the two consecutive turns of the first wire are disposed diagonally from each other when perceived from a cross-sectional perspective. 
     
     
       11. The wireless charging system of  claim 9 , wherein the two consecutive turns of the first wire are disposed directly vertically or horizontally from each other when perceived from a cross-sectional perspective. 
     
     
       12. The wireless charging system of  claim 9 , wherein each of the first plurality of windings of the second wire and each of the second plurality of windings of the second wire is approximately circular. 
     
     
       13. The wireless charging system of  claim 9 , wherein the first wire crosses itself at an edge of the first and second halves of the inductive transmit coil. 
     
     
       14. The wireless charging system of  claim 13 , wherein each of the plurality of turns of the first wire has a symmetric geometric shape. 
     
     
       15. The wireless charging system of  claim 9 , wherein the second wire crosses itself at an edge of the first and second halves of the inductive receive coil. 
     
     
       16. The wireless charging system of  claim 15 , wherein each of the plurality of windings of the second wire and each of the second plurality of windings of the second wire has a symmetric geometric shape.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional patent application of and claims the benefit to U.S. patent application Ser. No. 14/840,842, filed Aug. 31, 2015 entitled “Capacitively Balanced Inductive Charging Coil,” which is a nonprovisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 62/044,957, Sep. 2, 2014 entitled “Capacitively Balanced Inductive Changing Coil,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to inductive energy transfer and, more particularly, to an inductive coil design that may reduce noise in portable electronic devices. 
     BACKGROUND 
     Recent advances in portable computing have resulted in increased convenience for users of portable electronic devices. For example, mobile telephone, smart phones, computer tablets, and laptop computers allow a user to communicate while that user is mobile. That is, a user has the ability to travel freely while employing these electronic devices for communication and internet access including for navigational purposes. In addition to portable electronic devices, many other devices use battery power. For example, battery powered automobiles and golf carts are in widespread use. Lawn mowers or other rechargeable devices such as electric toothbrushes utilize rechargeable battery power. 
     The portable electronic devices referred to above operate on battery power which is what allows them to be mobile. That is, no power cords or other paraphernalia which might interfere with, or restrict, user movement are required. However, battery life may be a significant concern to a user in that it may limit the amount of time available for his or her mobility. Batteries require periodic recharging in order to maintain their power capabilities. Battery recharging requires power cords which may present certain limitations. Thus, the use of electric battery chargers, while suited for their intended purpose, may be limited in their usefulness and convenience. 
     One alternative battery charging technology that is being adopted is inductive charging using wireless chargers. Wireless transmission uses a magnetic field to transfer electricity allowing compatible devices to receive power through this induced current rather than using conductive wires and cords. Inductive charging is a method by which a magnetic field transfers electricity from an external charger to a mobile device such as a phone or laptop computer eliminating wired connection. Induction chargers typically use an induction coil to create an alternating electromagnetic field and a second induction coil in the portable device 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. 
     Under some circumstances, inductive charging can result in unwanted electromagnetic effects. A conventional coil winding may create unbalanced capacitance that can cause unwanted common mode noise on ground planes of portable electronic devices. “Common mode noise” is generally a form of coherent interference that affects two or more elements of an electromagnetic device in a highly coupled manner. This unwanted noise is especially troublesome for portable electronic devices that include touch sensors which require low noise on ground planes for optimal operation. The result is that use of touch sensors and screens may be significantly negatively impacted while the portable electronic device is being charged with an inductive charging device. Thus, in some cases the portable electronic device may be effectively inoperable during inductive battery charging. 
     SUMMARY 
     Embodiments described herein include improved coil constructions that can reduce unwanted capacitive losses and noise generated in the transmitter and receiver coils. The windings i.e., turns of the coil are oriented such that the surface area of wire on each half of the coil is approximately equal in order that the capacitive effects produced by the coils are balanced and noise is thus substantially reduced. The portable electronic device may be a transmitter device or a receiver device. 
     One embodiment may take the form of an inductive coil comprising: a length of electrically conductive wire forming at least one winding in a planar layer, the layer including a center point, the at least one winding comprising: a first half of the winding; and a second half of the winding contiguous with the first half; wherein the wire crosses itself at a an edge of the first and second halves. 
     Another embodiment may take the form of an inductive coil comprising: first and second adjacent coil layers formed from a single wire; wherein the first layer defines a plane bisected by a line through a center point of the plane, the line defining a first half and a second half of the at least one layer; the first layer comprises a plurality of windings made from a continuous length of wire that crosses itself; the wire forms a first winding of the at least one layer before crossing itself; and the wire forms a second winding of the at least one layer after crossing itself. 
     Still another embodiment may take the form of a portable electronic device comprising: 
     a housing; one or more electronic components within the housing; and an inductive coil including a length of electrically conductive wire formed into at least one winding in a planar layer, the layer including a center point in the planar layer, each winding including: a first portion comprising approximately one half of the winding as determined by a line through the center point parallel with the planar layer; and a second portion comprising another half of the winding in the planar layer opposite to the first portion; wherein the length of wire comprising the first portion is approximately equal to the length of wire comprising the second portion. 
     These and other embodiments will be appreciated upon reading the description in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  is a perspective view of a portable electronic device and a separate charging device; 
         FIG. 2  is a perspective view of a portable electronic device and a charging device shown with the devices inductively coupled; 
         FIG. 3  depicts a cross-sectional view of the portable electronic device taken along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  depicts a simplified block diagram of one example of an inductive charging system; 
         FIG. 5  is a simplified circuit diagram of an inductive charging system; 
         FIG. 6  is a top view of a spirally wound inductive coil; 
         FIG. 7  is a top view of a capacitively balanced inductive coil according to one embodiment; 
         FIG. 8  is a side sectional view of inductive charging and receiving coils according to one embodiment; and 
         FIG. 9  is a flow chart illustrating a method of manufacturing an inductive coil according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. For example, a suitable electronic device may be any portable or semi-portable electronic device that may receive energy inductively (“receiver device”), and a suitable docking device may be any portable or semi-portable docking station or charging device that may transmit energy inductively (“transmitter device”). 
     Embodiments described herein provide an inductive energy transfer system that transfers energy inductively from a transmitter device to a receiver device to charge a battery or to operate the receiver device. Additionally or alternatively, communication or control signals can be transmitted inductively between the transmitter and receiver devices. Thus, the terms energy, power, or signal(s) are meant to encompass transferring energy for wireless charging, transferring energy as communication and/or control signals, or both wireless charging and the transmission of communication and/or control signals. 
     Referring now to  FIG. 1 , there is shown a perspective view of one example of an inductive energy transfer system  11  in an unmated configuration. The illustrated embodiment shows a transmitter or charging device  12  that is configured to wirelessly pass energy to a receiver device, which may be a portable electronic device  13 . Although system  11 , as illustrated in  FIGS. 1 and 2 , depicts a watch as the portable electronic device, any electronic device may be configured for use with embodiments described herein. Sample electronic devices that may be configured to incorporate inductive charging as described herein include: tablet computing devices; mobile phones; computers; health monitors; wearable computing devices (e.g., glasses, a watch, clothing or the like); and so on. 
     In many embodiments, a wearable accessory, such as electronic device  13  as depicted in  FIG. 1 , may include a controller, processor, or other processing unit(s) coupled with or in communication with a memory, one or more communication interfaces, output devices such as displays and speakers, one or more sensors, such as biometric and imaging sensors, and one or more input devices such as buttons, dials, microphones, or touch-based interfaces. The communication interface(s) can provide electronic communications between the communications device and any external communication network, device or platform, such as but not limited to wireless interfaces, Bluetooth interfaces, Near Field Communication interfaces, infrared interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces. The wearable device may provide information regarding time, health, statuses of externally connected or communicating devices and/or software executing on such devices, messages, video, operating commands, and so forth (and may receive any of the foregoing from an external device), in addition to communications. 
     As stated above, electronic device  13  may include a controller or other electronic components. The controller may execute instructions and carry out operations associated with portable electronic devices as described herein. Using instructions (which may be retrieved from device memory), a controller may regulate the reception and manipulation of input and output data between components of the electronic device. The controller may be implemented in a computer chip or chips. Various architectures can be used for the controller such as microprocessors, application specific integrated circuits (ASICs) and so forth. The controller, together with an operating system, may execute computer code and manipulate data. The operating system may be a well-known system such as iOS, Windows, UNIX or a special purpose operating system or other systems as are known in the art. The controller may include memory capability to store the operating system and data. The controller may also include application software to implement various functions associated with the portable electronic device. 
     Electronic device  13  includes a housing  14  to enclose electronic, mechanical and structural components of electronic device  13 . Similarly, housing  15  may enclose electronic components of charging device  12 . In some embodiments electronic device  13  may have a larger lateral cross section than that of the charging device  12 , although such a configuration is not required. In other examples, charging device  12  may have a larger lateral cross section than that of the receiver device. In still further examples, the cross sections of the charging device and the receiving device may be substantially the same. In other embodiments, charging device  12  can be adapted to be inserted into a charging port (not shown) in the receiving device. 
     In the illustrated embodiment, charging device  12  may be connected to a power source by a cord or connector  16 . For example, charging device  12  can receive power from a wall outlet, or from another electronic device through a connector, such as a USB connector. Additionally or alternatively, charging device  12  may be battery operated. Similarly, although the illustrated embodiment is shown with the connector  16  coupled to the housing of charging device  12 , connector  16  may be electromagnetically connected by any suitable means. Connector  16  may be removable and may include a connector that is sized to fit within an aperture or receptacle opening within housing  15  of charger device  12 . 
     Electronic device  13  may include a first interface surface  17  that may interface with, align or otherwise contact a second interface surface  18  of charging device  12 . While shown as substantially rounded (e.g., convex and concave, respectively), interfaces  17 ,  18  may be rectangular, triangular, or have any other suitable shape in three dimensions or in cross-section. In some embodiments the shape of the interface surfaces  17 , 18  may facilitate alignment of the electronic device  13  and charging device  12 . For example and as shown, the second interface surface  18  of charging device  12  may be configured to have a particular shape that mates with a complementary shape of electronic device  13  as shown in  FIG. 2 . In the current example, second interface surface  18  may include a concave shape that follows a selected curve of first interface surface  17 . That is, first interface surface  17  of electronic device  13  may include a convex shape following the same or substantially similar curve as the concave shape of the second interface surface  18 . 
     Charging device  12  and electronic device  13  can be positioned with respect to each other using one or more alignment mechanisms, as shown in  FIG. 3 . As one example, one or more magnetic devices  60 ,  61  may be included in charging device  12  and/or electronic device  13  and used to align the devices. In another embodiment, one or more actuators in the charging device  12  and/or electronic device  13  can be used to move one or both the devices with respect to one another to facilitate alignment. In another embodiment, alignment features, such as protrusions and corresponding indentations in the housings  14 ,  15  of the charging device  12  and/or electronic device  13 , may be used to align the charging device  12  and/or electronic device  13 . 
       FIG. 3  depicts a side cross-sectional view of the inductive energy transfer system taken along line  3 - 3  in  FIG. 2 . As discussed earlier, both charging device  12  and electronic device  13  can include electronic, mechanical, and/or structural components. The illustrated embodiment of  FIG. 3  omits many electronic, mechanical, and structural components for ease of illustration. 
       FIG. 3  shows one example inductive energy transfer system in a mated and aligned configuration. Electronic device  13  includes one or more receiver coils  19  having one or more windings. Likewise, charging device  12  includes one or more transmitter coils  21  having one or more windings. Transmitter coil  21  may transmit energy to receiving coil  19  in electronic device  13 . Receiver coil  19  may receive energy from the charging device  12  and may use the received energy to perform or coordinate one or more functions of the electronic device  13 , and/or to replenish the charge of a battery (not shown) within electronic device  13 . The receiver coil  19  and transmitter coil  21  may have any number of rows, columns, windings, and so on. 
     The transmitter and receiver coils can be implemented with any suitable type of inductor and each coil can have any of a number of shapes and dimensions. As will be further discussed with respect to specific embodiments, transmitter coils  21  and receiver coils  19  can have the same number of windings or a different number of windings. Typically, the transmitter  19  and receiver  21  coils are surrounded by an enclosure to direct the magnetic flux in a desired direction (e.g., toward the other coil). The enclosures are omitted in  FIG. 3  for ease of illustration. 
       FIG. 4  is a schematic diagram illustrating one simplified example of an inductive charging system configuration. As shown, a charging device  12  includes power unit and control circuitry  23 . Transmitting coil  21  generates a magnetic field  20 . A mobile device includes a battery pack  10  which includes a battery  25  and associated control circuitry  26 . Receiving coil  19  captures magnetic field  20  from charging device  12 . Receiving coil  19  has an electrical current induced therein when receiving coil  19  is positioned adjacent to transmitting coil  21  and battery charging device  12  is energized. 
     Transmitting coil  21 , is energized by applying a current thereto, which creates magnetic flux lines  20  that allow receiving coil  19  to receive voltage when in sufficient proximity to the transmitting coil. Voltage received in receiving coil  19  may induce current therein, which may charge battery  25  after being rectified in control circuitry  26 . As discussed above, charging coil  21  and receiving coil  19  should be in sufficiently close proximity to enable charging coil  21  to induce the electrical current in receiving coil  19  through magnetic flux  20 . 
     Referring to  FIG. 5 , a schematic of the circuitry associated with the inductive charging system is shown. Charging device  12  typically includes power input  16 . Charger device  12  typically includes control circuitry  23 , which may be a switching power supply to boost voltage and/or frequency of current on the charger coil  21 . A/C current conducted through coil  21  may create magnetic flux lines  20  that will allow receiving coil in the vicinity to receive voltage and that voltage may induce current in receiving coil  19 . In certain embodiments, receiving coil  19  may be of sufficient size to accept induced voltage from charging coil  21  at a voltage level and frequency sufficient to allow it to charge a battery  25  and still power other functions of the electronic device. The current induced in receiving coil  19  may be rectified by control circuitry  26  prior to be provided to battery  25 . 
     Coil geometry in inductive charging systems can generate parasitic or unwanted capacitance, as represented by capacitors  24   a  and  b . These capacitors are shown in phantom because they do not exist in actuality, but represent a parasitic capacitive effect produced by coils  19  and  21  as will be discussed herein. 
     Any two adjacent conductors with a resulting potential difference existing between them can be considered a capacitor. Capacitance is inversely proportional to distance such that a greater separation results in less capacitance so that conductors in close proximity generally may have higher capacitance between them. This stray capacitance is typically small unless the conductors are close together, cover a large area, or both. For example, stray capacitance may exist between the parts of an inductor winding simply because of the conductive wires&#39; proximity to each other. When a potential difference exists across the windings of an inductor, the coils may act like the plates of a capacitor and store charge. 
     In the embodiment shown in  FIG. 5 , parasitic capacitances may be generated by coils  19  and  21 . Further, if the coils are conventionally wound, the parasitic capacitances may be unbalanced. That is, the capacitance represented by capacitor  24   a  may be larger than the capacitance represented by capacitor  24   b . This unbalanced capacitance can generate unwanted noise in the receiving device  13 , which may interfere with the operation of various features and functions of portable electronic device  13  such as capacitive touch sensing, biometric sensing, force sensing and other functionalities. 
     The presence of parasitic capacitance introduces interference (e.g., noise) in portable electronic device  13 . That is, the parasitic stray capacitance may cause large voltage swings which interfere with the capacitive sensing functions because these functions use ground reference. The stray capacitance may cause a ground differential between the transceiver  12  and receiver  13  portions of the inductive charging function thereby changing the ground reference for the capacitive sensing function. 
     A top view of a conventional wire winding coil  27  for an inductive charging device is shown in  FIG. 6 , although the distance between windings of the coil is increased to simplify viewing and comprehension of the figure. A single length of wire  28  is spirally wound in conventional inductive coil  27  such that the radius of each winding of wire  28  increases from center point  30 . In  FIG. 6 , lines  34 - 34  and  35 - 35  extend though center point  30  of coil  27 , which generally lies in a plane. A winding is defined as one revolution of wire  28 , beginning and ending at the intersection of a bisecting radius extending from a center point of coil  27 , such as one half of line  34 - 34  of any other line passing through the center of the coil. For example, wire  28  intersects line  34  at a given point on the line. A single coil winding starts at the point of intersection, continues around the coil and through the line  34 , and ends where wire  28  intersects that same line  34  for the third time. 
     An electrical current is conducted through wire  28  as indicated by the + and − signs  31  and  32 , respectively. (It should be appreciated that the direction of current flow may vary from embodiment to embodiment or during operation and so is not fixed.) Wire  28  has a cross sectional surface dimension  33  taken through a center point of the wire. The length of wire times the half the wire width  33  times 2 pi (e.g., 2πrh, where r is a wire radius and h is the wire length) yields a surface area of the wire, so a longer wire length has a greater surface area. The wire surface area generally is proportional to the capacitance of the wire, so the greater the surface area, the greater the capacitance. 
     When viewed along line  34 - 34 , the right side  35  of coil  27  includes more wire surface area than on left side  36 . This is primarily due to the increased length of the wire in outer winding  37 , as opposed to the smaller corresponding winding of the opposing side. That is, the length of wire  28  in each half of a winding increases as the radial distance from center  30  increases. Similarly, when viewed along line  38 - 38 , lower half  39  of coil  27  contains more wire than upper half  41  and thus the surface area of wire  28  is greater. Such imbalance exists from each half of coil  27  no matter whether along lines  34 - 34  or  35 - 35  or along any other axis bisecting center point  29 . This imbalance in wire length, and thus surface area, is inherent in the geometry of a spirally wound coil because of the increasing radius of a winding as it extends from the center point. Accordingly, many spiral-wound inductive coils may have one side with a greater capacitance than the other, which in turn may inject noise across the inductive coupling and into an electronic device. This noise, as previously mentioned, may deleteriously impact the operation and accuracy of various sensors, including capacitive sensors, in the electronic device and/or charging device. 
     Referring to  FIG. 7 , one embodiment of a coil  42  is shown in which wire  28  is wound so as to substantially equalize the surface area of wire  28  included on each half of the coil  42 . Again, it should be appreciated that the distance between windings of the coil is exaggerated to simplify viewing and comprehension of the figure. As with coil  27 , coil  42  consists of a single length of wire wound in one or more windings to form the coil. In this embodiment, however, wire  28  may be wound such that each winding of the coil is substantially circular and presents substantially the same surface area on each side of a line bisecting the center  29  (when viewed from above, e.g., in the orientation of  FIG. 7 ). This equalization of surface area is accomplished by winding wire  28  to pass over or under itself to form the other half of the winding. As shown at points  43  and  44  wire  28  passes over and under itself to form coil  42  with substantially circular and balanced windings. 
     In this embodiment, a line  45  drawn through center  30  of coil  42  results in the upper half  46  and lower half  47  of coil  42  containing approximately the same length of wire  28 . Thus, the capacitance generated by each half of coil  42  is equalized and parasitic capacitance resulting from imbalance between the halves is substantially eliminated. While the embodiment shown in  FIG. 7  includes wire  28  passing over itself at every winding turn (a “crossing”), for ease of manufacture and in other embodiments one or more conventional spiral windings may be interspersed with the circular windings described in this embodiment. Thus, in some embodiments, only every second, third, fourth, or so on winding may include a crossing. That is, conventional spiral wound windings (for example, as shown in  FIG. 6 ) may be alternated or interspersed with the winding shown in  FIG. 7  to provide a balanced or near-balanced capacitance. 
     These alternate embodiments may also reduce stray capacitance in a coil and thus reduce common mode noise. Referring to  FIG. 5 , the capacitance represented by capacitors  24   a  and  24   b  is substantially equalized in these embodiments thus reducing or eliminating unwanted common mode noise. These embodiments may result in improved manufacturability and a reduction in the size of the resultant coil. While coil  42  in  FIG. 7  is shown substantially circular it may be any symmetric geometry such as a square provided the surface area of wire  28  on adjacent halves of a winding, when viewed from above, are approximately equal. 
     Referring to  FIG. 8 , in another embodiment, a side view of a receiver coil  19  and transceiver coil  21  is shown, again with the distance between adjacent wires exaggerated. In conventional inductive coils, two layers of windings may be adjacent as shown in  FIG. 8  and there may be parasitic capacitance generated between those windings. In the embodiment shown in  FIG. 8 , coil  19  includes two winding layers  48  and  49 . Transceiver coil  21  also includes two winding layers  50  and  51 . In multiple layer coils such as the embodiment shown in  FIG. 8 , parasitic capacitance may also be generated between layers of a single transmit or receive coil, or between layers of the two coils. 
     For example, in some cases there may be parasitic capacitances between coil layers  48  and  49  of the receive coil  19 , between layers  50  and  51  of the transmit coil  21 , between layer  48  of the receive coil and layer  51  of the transmit coil, between layer  48  of the receive coil and layer  50  of the transmit coil, between layer  49  of the transmit coil and layer  50  of the receive coil, and between layer  49  of the receive coil and layer  51  of the transmit coil. By way of comparison, the capacitance between nearer pairs of layers is lower than the capacitance between further pairs of layers. Thus, any given layer has a higher parasitic capacitance with a nearer coil than it does with a further coil, presuming all characteristics of the layers are equal. So, for example, a capacitance  24   a  between coil layer  48  and layer  50  is typically lower than a capacitance  24   b  between coil layer  49  and layer  50 . This leads to an unbalanced capacitance between layers of the inductive transmit and receive coils and results in the generation of common mode noise which, as discussed above, may deleteriously affect certain functions of the portable electronic device. In the foregoing example, 
     As discussed above, capacitance may be related to both the surface area of the conductor and the distance between conductors. In the embodiment described in  FIG. 8 , the single length of wire  28  forming coil  19  alternates in a serpentine fashion within adjacent winding layers  48  and  49 . The same is true for the wire  28  forming winding layers  50  and  51  of transceiver coil  21 . For ease of reference, adjacent windings are shown with + and / symbols while the order in which the windings are formed by a wire (e.g., the path of the wire) is shown by the series of arrows. That is, the arrows show the order in which windings are formed by the wire. 
     This alternating winding may substantially or fully balance the capacitance between winding layers  48  and  49  and between layers  50  and  51  to substantially reduce common mode noise between those layers and between all other combinations of layers in the transmit and receive coils. The same is true for embodiments having more or fewer layers and more or fewer windings. 
     While the continuous length of wire  28  is shown alternating between layers  48  and  49  in the direction of arrows  52 , in another embodiment and as shown by arrows  53 , wire  28  may form windings in a stair-step pattern alternating between layers, and then between adjacent windings. As a non-limiting example, the wire may alternate vertically from adjacent coil layer  50  to coil layer  51 , then horizontally in layer  51  between adjacent windings, then back horizontally to layer  50 . This pattern may also help in balancing capacitance between layers and/or coils. 
     As discussed with respect to  FIG. 7 , windings of continuous length of wire  28  alternate in each half winding such that the length of wire in each winding is approximately equal on each half of a winding. In another embodiment, the winding embodiment of  FIG. 7  may be combined with the winding embodiments of  FIG. 8  for coils containing multiple winding layers such as  48 / 49  and  50 / 51  shown in  FIG. 8 . In effect, by constructing a coil in accordance with combining the embodiments shown in  FIGS. 7 and 8 , stray capacitance is reduced or eliminated because capacitance within and between coils is balanced or near-balanced, thereby substantially eliminating parasitic capacitances  24   a ,  24   b.    
     Referring to  FIG. 9 , a flow chart illustrating a method for manufacturing one embodiment of a coil  19  or  21  is shown. In step  54 , a rotating mandrel is utilized. An electrically conductive wire length is wrapped on the mandrel in step  55 . This wrapping may include wrapping the continuous wire length such that in each half winding the wire passes over itself to form substantially circular windings as described with respect to  FIG. 7 . In step  56  the wire is translated in conjunction with the step of wrapping to alternate the continuous wire length in alternate windings for a multiple winding layer coil. In this step  56 , the embodiments described with respect to both  FIGS. 7 and 8  may be achieved. That is the continuous length of wire  28  may be translated over or under itself within a winding as described with respect to  FIG. 7  and/or the continuous length of wire  28  may be alternately interwoven in adjacent layers  48 / 49  or  50 / 51  as described with respect to  FIG. 8 . Alternately, either step  55  or step  56  can be eliminated to form a coil winding in accordance with either embodiment of  FIG. 7  or  FIG. 8 . That is, if step  55  is eliminated, then a multiple winding layer coil may be produced but the continuous wire length is not alternated in each half winding as described with respect to  FIG. 7 . If step  56  is eliminated, then a single winding layer coil may be produced with the continuous wire length alternating in each half winding. In any of the above embodiments, in step  57  the wrapped wire is formed into an inductive coil structure to be incorporated into a portable electronic device. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. For example, while transceiver coil  21  and receiver coil  19  have been described as in a generally circular shape, it should be expressly understood that embodiments disclosed herein may be employed with coils of other geometric shapes. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170731
Publication Date: 20210504
Grant Date: 20210504
Priority Date: 20140902
Inventors: PEREZ, YEHONATAN
BRZEZINSKI, MAKIKO K.
LARSSON, KARL RUBEN F.
GRAHAM, Christopher S.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/00034", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/263", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/2823", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2823", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F41/098", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00034", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/098", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/0031", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B5/0081", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/0037", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/098", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2823", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B5/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/72", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2823", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/72", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/79", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54150659