U.S. patent application number 14/840842 was filed with the patent office on 2016-03-03 for capacitively balanced inductive charging coil.
The applicant listed for this patent is Apple Inc.. Invention is credited to Makiko K. Brzezinski, Christopher S. Graham, Karl Ruben F. Larsson, Yehonatan Perez.
Application Number | 20160064137 14/840842 |
Document ID | / |
Family ID | 54150659 |
Filed Date | 2016-03-03 |
United States Patent
Application |
20160064137 |
Kind Code |
A1 |
Perez; Yehonatan ; et
al. |
March 3, 2016 |
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.
Inventors: |
Perez; Yehonatan;
(Cupertino, CA) ; Brzezinski; Makiko K.;
(Cupertino, CA) ; Larsson; Karl Ruben F.;
(Cupertino, CA) ; Graham; Christopher S.;
(Cupertino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
54150659 |
Appl. No.: |
14/840842 |
Filed: |
August 31, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62044957 |
Sep 2, 2014 |
|
|
|
Current U.S.
Class: |
336/90 ; 29/605;
336/223 |
Current CPC
Class: |
H04B 5/0081 20130101;
H02J 7/00034 20200101; H01F 38/14 20130101; H02J 50/10 20160201;
H01F 27/2823 20130101; H01F 41/098 20160101; H04B 5/0037 20130101;
H04B 5/0031 20130101; H02J 7/025 20130101 |
International
Class: |
H01F 27/28 20060101
H01F027/28; H01F 41/06 20060101 H01F041/06; H01F 27/02 20060101
H01F027/02 |
Claims
1. 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 an edge of the first and second halves.
2. The inductive coil of claim 1 wherein the winding is
approximately circular.
3. The inductive coil of claim 1 wherein the winding is a symmetric
geometric shape.
4. The inductive coil according to claim 1 further comprising at
least one additional coil formed by the wire.
5. The inductive coil according to claim 4 wherein the at least one
additional coil is a spirally wound coil.
6. The inductive coil according to claim 1, further including: at
least one adjacent planar layer; wherein both of the layers include
a plurality of windings made from a continuous length of the wire;
and the wire from the first half crosses the wire from the second
half.
7. 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.
8. The inductive coil according to claim 7, wherein: The second
layer comprises: a first half; and a second half; wherein: a
surface area of the wire comprising the first portion is
approximately equal to a surface area of the wire comprising the
second portion; and the wire crosses itself between windings.
9. The inductive coil according to claim 7 wherein the coil layers
are approximately circular.
10. The inductive coil according to claim 7 wherein the coil layers
include a symmetric geometric shape.
11. The inductive coil according to claim 7 wherein the at least
one of the coil layers is a conventional spirally wound coil.
12. A portable electronic device comprising: a housing; electronic
components associated with the housing; 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 the 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.
13. The portable electronic device according to claim 12 wherein
the winding is approximately circular.
14. The portable electronic device according to claim 12 further
including at least one additional coil.
15. The portable electronic device according to claim 14 wherein
the at least one additional coil is a conventional spirally wound
coil.
16. The portable electronic device according to claim 12 further
including: at least one adjacent planar layer; wherein: both of the
layers include a plurality of windings made from a continuous
length of wire, the wire from the first half crossing the wire from
the second half and forming a first half of a winding in the
adjacent layer.
17. A method for forming an inductive coil comprising the steps of:
operating a rotating mandrel; wrapping a wire length on the
mandrel; translating the wire in conjunction with the step of
wrapping to alternate the wire in adjacent layers; and forming the
wrapped wire into an inductive coil.
18. The method of claim 17 wherein the step of translating
includes: winding the wire into a first half of a first winding
layer; winding the wire into a second half of a second winding
layer; winding the wire thence into a first half of the first
winding layer; wherein the wire alternates between layers in a
serpentine manner.
19. The method of claim 17 wherein the step of translating includes
alternating approximately each half of a wire winding such that the
length of wire comprising a first half portion of the winding is
approximately equal to the length of wire comprising a second half
portion of the winding.
20. The method of claim 17 wherein the step of translating includes
forming a conventional spiral wound winding in at least one
adjacent layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a nonprovisional patent application of
and claims the benefit to U.S. Provisional Patent Application No.
62/044,957, Sep. 2, 2014 and titled "Capacitively Balanced
Inductive Changing Coil," the disclosure of which is hereby
incorporated herein by reference in its entirety.
FIELD
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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
[0007] Embodiments described herein include improved coil
constructions that can reduce unwanted capacitive losses and noise
generated in the transmitter and receiver coils. The windings 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.
[0008] 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.
[0009] 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.
[0010] Still another embodiment may take the form of a portable
electronic device comprising: [0011] 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.
[0012] These and other embodiments will be appreciated upon reading
the description in its entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] 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:
[0014] FIG. 1 is a perspective view of a portable electronic device
and a separate charging device;
[0015] FIG. 2 is a perspective view of a portable electronic device
and a charging device shown with the devices inductively
coupled;
[0016] FIG. 3 depicts a cross-sectional view of the portable
electronic device taken along line 3-3 in FIG. 2;
[0017] FIG. 4 depicts a simplified block diagram of one example of
an inductive charging system;
[0018] FIG. 5 is a simplified circuit diagram of an inductive
charging system;
[0019] FIG. 6 is a top view of a spirally wound inductive coil;
[0020] FIG. 7 is a top view of a capacitively balanced inductive
coil according to one embodiment;
[0021] FIG. 8 is a side sectional view of inductive charging and
receiving coils according to one embodiment; and
[0022] FIG. 9 is a flow chart illustrating a method of
manufacturing an inductive coil according to one embodiment.
DETAILED DESCRIPTION
[0023] 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").
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] Coil geometry in inductive charging systems can generate
parasitic or unwanted capacitance, as represented by capacitors 24a
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.
[0039] 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' 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.
[0040] 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 24a may be larger
than the capacitance represented by capacitor 24b. 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.
[0041] 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.
[0042] 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.
[0043] 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., 2.pi.rh, 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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 24a and 24b 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.
[0048] 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.
[0049] 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 24a between coil layer 48 and layer 50 is typically
lower than a capacitance 24b 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,
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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 24a, 24b.
[0054] 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.
[0055] 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.
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