U.S. patent application number 13/720835 was filed with the patent office on 2014-03-13 for adaptive impedance tuning in wireless power transmission.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM INCORPORATED. Invention is credited to Ernest T. Ozaki, Stanley S. Toncich, William H. Von Novak, Charles E. Wheatley.
Application Number | 20140070621 13/720835 |
Document ID | / |
Family ID | 42229293 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140070621 |
Kind Code |
A9 |
Von Novak; William H. ; et
al. |
March 13, 2014 |
ADAPTIVE IMPEDANCE TUNING IN WIRELESS POWER TRANSMISSION
Abstract
Exemplary embodiments are directed to wireless power. A wireless
power receiver includes a receive antenna for coupling with near
field radiation in a coupling-mode region generated by a transmit
antenna operating at a resonant frequency. The receive antenna
generates an RF signal when coupled to the near filed radiation and
a rectifier converts the RF signal to a DC input signal. A direct
current (DC)-to-DC converter coupled to the DC input signal
generates a DC output signal. A pulse modulator generate a
pulse-width modulation signal to the DC-to-DC converter to adjust a
DC impedance of the wireless power receiver by modifying a duty
cycle of the pulse-width modulation signal responsive to at least
one of a voltage of the DC input signal, a current of the DC input
signal, a voltage of the DC output signal, and a current of the DC
output signal.
Inventors: |
Von Novak; William H.; (San
Diego, CA) ; Wheatley; Charles E.; (San Diego,
CA) ; Toncich; Stanley S.; (San Diego, CA) ;
Ozaki; Ernest T.; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM INCORPORATED |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130113299 A1 |
May 9, 2013 |
|
|
Family ID: |
42229293 |
Appl. No.: |
13/720835 |
Filed: |
December 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12713123 |
Feb 25, 2010 |
8338991 |
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13720835 |
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61176468 |
May 7, 2009 |
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61162157 |
Mar 20, 2009 |
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Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H01F 38/14 20130101;
H02J 7/025 20130101; H02J 50/90 20160201; H04B 5/0037 20130101;
H02J 50/20 20160201; H04B 5/0093 20130101; H02J 50/70 20160201;
H02J 50/80 20160201; H02J 50/12 20160201; H02J 50/60 20160201; H02J
50/40 20160201 |
Class at
Publication: |
307/104 |
International
Class: |
H01F 38/14 20060101
H01F038/14 |
Claims
1. A wireless power receiver, comprising: a rectifier coupled to an
antenna that is configured to receive a wireless power signal, the
rectifier configured to convert the wireless power signal to a
direct current input signal, the direct current input signal having
voltage and current signals; a direct current-to-direct current
converter having an input impedance, the direct current-to-direct
current converter configured to generate a direct current output
signal based at least in part on the direct current input signal
and configured to adjust the input impedance based at least in part
on a control signal; and a circuit configured to adjust an
alternating current impedance of the wireless power receiver by
adjusting the control signal based at least in part on one of the
voltage signal or the current signal of the direct current input
signal.
2. The wireless power receiver of claim 1, wherein the direct
current-to-direct current converter is further configured to adjust
a power output of the direct current output signal based in part on
the voltage signal of the direct current input signal.
3. The wireless power receiver of claim 1, wherein the circuit
comprises a pulse modulator.
4. The wireless power receiver of claim 3, wherein the pulse
modulator is configured to adjust the control signal based at least
in part on one of a voltage of the direct current output signal and
a current of the direct current output signal.
5. The wireless power receiver of claim 1, wherein the circuit
comprises a comparator configured to generate the control signal
based in part on a comparison of the voltage signal of the direct
current input signal and a reference signal.
6. The wireless power receiver of claim 1, wherein the pulse
modulator comprises a processor configured to: receive the direct
current input signal; sample a value of the direct current input
signal; and adjust the alternating current impedance of the
wireless power receiver wherein adjusting comprises adjusting a
duty cycle of the control signal based in part on the sampled
value.
7. The wireless power receiver of claim 6, wherein the sampling
comprises sampling at least one of the voltage of the direct
current input signal, the current of the direct current input
signal, a voltage of the direct current output signal, or a current
of the direct current output signal.
8. The wireless power receiver of claim 1, wherein the circuit
comprises a processor configured to: receive the direct current
input signal; and sample a value of the direct current input
signal, wherein adjusting the control signal is based in part on
the sampled value from the direct current input signal to reduce a
power output on the direct current output signal to a power level
less than optimal and acceptable to a receiver device configured to
receive the direct current output signal.
9. The wireless power receiver of claim 1, wherein the direct
current-to-direct current converter comprises a buck converter or a
boost converter configured to receive the direct current input
signal, the control signal, and output the direct current output
signal.
10. The wireless power receiver of claim 1 wherein the circuit is
further configured to adjust a receive bandwidth of the wireless
power receiver based at least in part on the alternating current
impedance.
11. A method, comprising: receiving a wireless power signal at a
wireless power receiver; rectifying the wireless power signal to a
direct current input signal; converting the direct current input
signal to a direct current output signal; modifying an alternating
current impedance of the wireless power receiver by adjusting a
power output of the direct current output signal based in part on
the direct current input signal; and adjusting a receive bandwidth
of the wireless power receiver based at least in part on the
alternating current impedance.
12. The method of claim 11, wherein the modifying the alternating
current impedance of the wireless power receiver further comprises
adjusting the power output of the direct current output signal
based in part on one or more of a voltage of the direct current
input signal and a current of the direct current input signal.
13. The method of claim 11, wherein the modifying the alternating
current impedance of the wireless power receiver further comprises
adjusting the power output of the direct current output signal
based in part on one or more of a voltage of the direct current
input signal, a voltage of the direct current output signal, and a
current of the direct current output signal.
14. The method of claim 11, wherein the modifying the alternating
current impedance of the wireless power receiver further comprises
adjusting the power output of the direct current output signal
based in part on one or more of a voltage of the direct current
input signal, a current of the direct current input signal, a
voltage of the direct current output signal and a current of the
direct current output signal.
15. The method of claim 11, wherein modifying the alternating
current impedance of the wireless power receiver is based in part
on a comparison of the direct current input signal to a voltage
reference signal.
16. A wireless power receiver, comprising: means for receiving a
wireless power signal; means for rectifying the wireless power
signal to a direct current input signal; means for converting the
direct current input signal to a direct current output signal; and
means for modifying an alternating current impedance of the
wireless power receiver comprising a means for adjusting, based at
least in part on the direct current input signal, an input
impedance of the means for converting the direct current input
signal to a direct current output signal.
17. The wireless power receiver of claim 16, wherein the means for
modifying the alternating current impedance of the wireless power
receiver further comprises means for adjusting the power output of
the direct current output signal from the means for converting the
direct current input signal to a direct current output signal based
in part on one or more of a-voltage of the direct current input
signal and a current of the direct current input signal.
18. The wireless power receiver of claim 16, wherein the means for
modifying the alternating current impedance of the wireless power
receiver further comprises means for adjusting the power output of
the direct current output signal from the means for converting the
direct current input signal to a direct current output signal based
in part on one or more of a-voltage of the direct current input
signal, a voltage of the direct current output signal, and a
current of the direct current output signal.
19. The wireless power receiver of claim 16, wherein the means for
modifying the alternating current impedance of the wireless power
receiver further comprises means for adjusting the power output of
the direct current output signal from the means for converting the
direct current input signal to a direct current output signal based
in part on one or more of the direct current input signal, a
current of the direct current input signal, a voltage of the direct
current output signal and a current of the direct current output
signal.
20. The wireless power receiver of claim 16, further comprising
means for comparing the direct current input signal to a voltage
reference signal to determine a value, the means for modifying the
alternating current impedance of the wireless power receiver
configured to modify the alternating current impedance based in
part on the value.
21. The wireless power receiver of claim 16, further comprising
means for adjusting a receive bandwidth of the wireless power
receiver based at least in part on the alternating current
impedance.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] This application is a continuation of:
[0002] U.S. application Ser. No. 12/713,123 entitled "ADAPTIVE
IMPEDANCE TUNING IN WIRELESS POWER TRANSMISSION" filed on Feb. 25,
2010;
[0003] This application claims priority under 35 U.S.C.
.sctn.119(e) to: [0004] U.S. Provisional Patent Application
61/162,157 entitled "WIRELESS POWER IMPEDANCE CONTROL" filed on
Mar. 20, 2009; and [0005] U.S. Provisional Patent Application
61/176,468 entitled "DC-BASED ADAPTIVE TUNING" filed on May 7,
2009.
BACKGROUND
[0006] 1. Field
[0007] The present invention relates generally to wireless power
transfer, and more specifically to devices, systems, and methods
related to adaptively tuning impedance in a receiver device to
improve wireless power transfer.
[0008] 2. Background
[0009] Typically, each battery powered device such as a wireless
electronic device requires its own charger and power source, which
is usually an alternating current (AC) power outlet. Such a wired
configuration becomes unwieldy when many devices need charging.
[0010] Approaches are being developed that use over-the-air or
wireless power transmission between a transmitter and a receiver
coupled to the electronic device to be charged. Such approaches
generally fall into two categories. One is based on the coupling of
plane wave radiation (also called far-field radiation) between a
transmit antenna and a receive antenna on the device to be charged.
The receive antenna collects the radiated power and rectifies it
for charging the battery. Antennas are generally of resonant length
in order to improve the coupling efficiency. This approach suffers
from the fact that the power coupling falls off quickly with
distance between the antennas, so charging over reasonable
distances (e.g., less than 1 to 2 meters) becomes difficult.
Additionally, since the transmitting system radiates plane waves,
unintentional radiation can interfere with other systems if not
properly controlled through filtering.
[0011] Other approaches to wireless energy transmission techniques
are based on inductive coupling between a transmit antenna
embedded, for example, in a "charging" mat or surface and a receive
antenna (plus a rectifying circuit) embedded in the electronic
device to be charged. This approach has the disadvantage that the
spacing between transmit and receive antennas must be very close
(e.g., within millimeters). Though this approach does have the
capability to simultaneously charge multiple devices in the same
area, this area is typically very small and requires the user to
accurately locate the devices to a specific area.
[0012] Efficiency is of importance in a wireless power transfer
system due to the losses occurring in the course of wireless
transmission of power. Since wireless power transmission is often
less efficient than wired transfer, efficiency is of an even
greater concern in a wireless power transfer environment.
[0013] As a result, when attempting to provide power to one or more
wireless charging devices, there is a need for methods and
apparatuses for adapting to changes in coupling between a transmit
antenna and a receive antenna to optimize or otherwise adjust power
delivery to a receiver device coupled to the receive antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a simplified block diagram of a wireless power
transfer system.
[0015] FIG. 2 shows a simplified schematic diagram of a wireless
power transfer system.
[0016] FIG. 3 shows a schematic diagram of a loop antenna for use
in exemplary embodiments of the present invention.
[0017] FIG. 4 is a simplified block diagram of a transmitter, in
accordance with an exemplary embodiment of the present
invention.
[0018] FIG. 5 is a simplified block diagram of a receiver, in
accordance with an exemplary embodiment of the present
invention.
[0019] FIG. 6 shows a schematic of transmit circuitry and receive
circuitry showing coupling therebetween and an adjustable DC
load.
[0020] FIGS. 7A-7B show Smith charts illustrating change in input
impedance of a coupled coil pair responsive to a change in DC
impedance at the receiver device.
[0021] FIGS. 8A-8B show amplitude plots showing improved coupling
between a coupled coil pair responsive to a change in DC impedance
at the receiver device.
[0022] FIGS. 9A-9B show simplified schematics of receiver devices
illustrating exemplary embodiments for adjusting DC impedance at
the receiver device.
[0023] FIGS. 10A-10D show simplified schematics of receiver devices
illustrating exemplary embodiments for adjusting DC impedance at
the receiver device using a pulse-width modulation converter.
[0024] FIG. 11 illustrates various input and output parameters that
may be used when adjusting DC impedance at the receiver device
DETAILED DESCRIPTION
[0025] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments.
[0026] The detailed description set forth below in connection with
the appended drawings is intended as a description of exemplary
embodiments of the present invention and is not intended to
represent the only embodiments in which the present invention can
be practiced. The term "exemplary" used throughout this description
means "serving as an example, instance, or illustration," and
should not necessarily be construed as preferred or advantageous
over other exemplary embodiments. The detailed description includes
specific details for the purpose of providing a thorough
understanding of the exemplary embodiments of the invention. It
will be apparent to those skilled in the art that the exemplary
embodiments of the invention may be practiced without these
specific details. In some instances, well-known structures and
devices are shown in block diagram form in order to avoid obscuring
the novelty of the exemplary embodiments presented herein.
[0027] The words "wireless power" is used herein to mean any form
of energy associated with electric fields, magnetic fields,
electromagnetic fields, or otherwise that is transmitted between
from a transmitter to a receiver without the use of physical
electromagnetic conductors.
[0028] FIG. 1 illustrates a wireless transmission or charging
system 100, in accordance with various exemplary embodiments of the
present invention. Input power 102 is provided to a transmitter 104
for generating a radiated field 106 for providing energy transfer.
A receiver 108 couples to the radiated field 106 and generates an
output power 110 for storing or consumption by a device (not shown)
coupled to the output power 110. Both the transmitter 104 and the
receiver 108 are separated by a distance 112. In one exemplary
embodiment, transmitter 104 and receiver 108 are configured
according to a mutual resonant relationship and when the resonant
frequency of receiver 108 and the resonant frequency of transmitter
104 are very close, transmission losses between the transmitter 104
and the receiver 108 are minimal when the receiver 108 is located
in the "near-field" of the radiated field 106.
[0029] Transmitter 104 further includes a transmit antenna 114 for
providing a means for energy transmission and receiver 108 further
includes a receive antenna 118 for providing a means for energy
reception. The transmit and receive antennas are sized according to
applications and devices to be associated therewith. As stated, an
efficient energy transfer occurs by coupling a large portion of the
energy in the near-field of the transmitting antenna to a receiving
antenna rather than propagating most of the energy in an
electromagnetic wave to the far field. When in this near-field a
coupling mode may be developed between the transmit antenna 114 and
the receive antenna 118. The area around the antennas 114 and 118
where this near-field coupling may occur is referred to herein as a
coupling-mode region.
[0030] FIG. 2 shows a simplified schematic diagram of a wireless
power transfer system. The transmitter 104 includes an oscillator
122, a power amplifier 124 and a filter and matching circuit 126.
The oscillator is configured to generate a desired frequency, which
may be adjusted in response to adjustment signal 123. The
oscillator signal may be amplified by the power amplifier 124 with
an amplification amount responsive to control signal 125. The
filter and matching circuit 126 may be included to filter out
harmonics or other unwanted frequencies and match the impedance of
the transmitter 104 to the transmit antenna 114.
[0031] The receiver 108 may include a matching circuit 132 and a
rectifier and switching circuit 134 to generate a DC power output
to charge a battery 136 as shown in FIG. 2 or power a device
coupled to the receiver (not shown). The matching circuit 132 may
be included to match the impedance of the receiver 108 to the
receive antenna 118. The receiver 108 and transmitter 104 may
communicate on a separate communication channel 119 (e.g.,
Bluetooth, zigbee, cellular, etc).
[0032] As illustrated in FIG. 3, antennas used in exemplary
embodiments may be configured as a "loop" antenna 150, which may
also be referred to herein as a "magnetic" antenna. Loop antennas
may be configured to include an air core or a physical core such as
a ferrite core. Air core loop antennas may be more tolerable to
extraneous physical devices placed in the vicinity of the core.
Furthermore, an air core loop antenna allows the placement of other
components within the core area. In addition, an air core loop may
more readily enable placement of the receive antenna 118 (FIG. 2)
within a plane of the transmit antenna 114 (FIG. 2) where the
coupled-mode region of the transmit antenna 114 (FIG. 2) may be
more powerful.
[0033] As stated, efficient transfer of energy between the
transmitter 104 and receiver 108 occurs during matched or nearly
matched resonance between the transmitter 104 and the receiver 108.
However, even when resonance between the transmitter 104 and
receiver 108 are not matched, energy may be transferred at a lower
efficiency. Transfer of energy occurs by coupling energy from the
near-field of the transmitting antenna to the receiving antenna
residing in the neighborhood where this near-field is established
rather than propagating the energy from the transmitting antenna
into free space.
[0034] The resonant frequency of the loop or magnetic antennas is
based on the inductance and capacitance. Inductance in a loop
antenna is generally simply the inductance created by the loop,
whereas, capacitance is generally added to the loop antenna's
inductance to create a resonant structure at a desired resonant
frequency. As a non-limiting example, capacitor 152 and capacitor
154 may be added to the antenna to create a resonant circuit that
generates resonant signal 156. Accordingly, for larger diameter
loop antennas, the size of capacitance needed to induce resonance
decreases as the diameter or inductance of the loop increases.
Furthermore, as the diameter of the loop or magnetic antenna
increases, the efficient energy transfer area of the near-field
increases. Of course, other resonant circuits are possible. As
another non-limiting example, a capacitor may be placed in parallel
between the two terminals of the loop antenna. In addition, those
of ordinary skill in the art will recognize that for transmit
antennas the resonant signal 156 may be an input to the loop
antenna 150.
[0035] Exemplary embodiments of the invention include coupling
power between two antennas that are in the near-fields of each
other. As stated, the near-field is an area around the antenna in
which electromagnetic fields exist but may not propagate or radiate
away from the antenna. They are typically confined to a volume that
is near the physical volume of the antenna. In the exemplary
embodiments of the invention, magnetic type antennas such as single
and multi-turn loop antennas are used for both transmit (Tx) and
receive (Rx) antenna systems since magnetic near-field amplitudes
tend to be higher for magnetic type antennas in comparison to the
electric near-fields of an electric-type antenna (e.g., a small
dipole). This allows for potentially higher coupling between the
pair. Furthermore, "electric" antennas (e.g., dipoles and
monopoles) or a combination of magnetic and electric antennas is
also contemplated.
[0036] The Tx antenna can be operated at a frequency that is low
enough and with an antenna size that is large enough to achieve
good coupling (e.g., >-4 dB) to a small receive antenna at
significantly larger distances than allowed by far field and
inductive approaches mentioned earlier. If the transmit antenna is
sized correctly, high coupling levels (e.g., -1 to -4 dB) can be
achieved when the receive antenna on a host device is placed within
a coupling-mode region (i.e., in the near-field) of the driven
transmit loop antenna.
[0037] FIG. 4 is a simplified block diagram of a transmitter 200,
in accordance with an exemplary embodiment of the present
invention. The transmitter 200 includes transmit circuitry 202 and
a transmit antenna 204. Generally, transmit circuitry 202 provides
RF power to the transmit antenna 204 by providing an oscillating
signal resulting in generation of near-field energy about the
transmit antenna 204. By way of example, transmitter 200 may
operate at the 13.56 MHz ISM band.
[0038] Exemplary transmit circuitry 202 includes a fixed impedance
matching circuit 206 for matching the impedance of the transmit
circuitry 202 (e.g., 50 ohms) to the transmit antenna 204 and a low
pass filter (LPF) 208 configured to reduce harmonic emissions to
levels to prevent self-jamming of devices coupled to receivers 108
(FIG. 1). Other exemplary embodiments for the matching circuit may
include inductors and transformers. Other exemplary embodiments for
the low pass filter may include different filter topologies,
including but not limited to, notch filters that attenuate specific
frequencies while passing others and may include an adaptive
impedance match, that can be varied based on measurable transmit
metrics, such as output power to the antenna or DC current draw by
the power amplifier. Transmit circuitry 202 further includes a
power amplifier 210 configured to drive an RF signal as determined
by an oscillator 212 (also referred to herein as a signal
generator). The transmit circuitry may be comprised of discrete
devices or circuits, or alternately, may be comprised of an
integrated assembly. An exemplary RF power output from transmit
antenna 204 may be on the order of 2.5 to 8.0 Watts.
[0039] Transmit circuitry 202 further includes a controller 214 for
enabling the oscillator 212 during transmit phases (or duty cycles)
for specific receivers, for adjusting the frequency of the
oscillator, for adjusting the output power level, for implementing
a communication protocol for interacting with neighboring devices
through their attached receivers. The controller 214 is also for
determining impedance changes at the transmit antenna 204 due to
changes in the coupling-mode region due to receivers placed
therein.
[0040] The transmit circuitry 202 may further include a load
sensing circuit 216 for detecting the presence or absence of active
receivers in the vicinity of the near-field generated by transmit
antenna 204. By way of example, a load sensing circuit 216 monitors
the current flowing to the power amplifier 210, which is affected
by the presence or absence of active receivers in the vicinity of
the near-field generated by transmit antenna 204. Detection of
changes to the loading on the power amplifier 210 are monitored by
controller 214 for use in determining whether to enable the
oscillator 212 for transmitting energy to communicate with an
active receiver.
[0041] Transmit antenna 204 may be implemented as an antenna strip
with the thickness, width and metal type selected to keep resistive
losses low. In a conventional implementation, the transmit antenna
204 can generally be configured for association with a larger
structure such as a table, mat, lamp or other less portable
configuration. Accordingly, the transmit antenna 204 generally will
not need "turns" in order to be of a practical dimension. An
exemplary implementation of a transmit antenna 204 may be
"electrically small" (i.e., fraction of the wavelength) and tuned
to resonate at lower usable frequencies by using capacitors to
define the resonant frequency. In an exemplary application where
the transmit antenna 204 may be larger in diameter, or length of
side if a square loop, (e.g., 0.50 meters) relative to the receive
antenna, the transmit antenna 204 will not necessarily need a large
number of turns to obtain a reasonable capacitance in order to
resonate the transmitting antenna at the desired frequency.
[0042] The transmitter 200 may gather and track information about
the whereabouts and status of receiver devices that may be
associated with the transmitter 200. Thus, the transmitter
circuitry 202 may include a presence detector 280, an enclosed
detector 290, or a combination thereof, connected to the controller
214 (also referred to as a processor herein). The controller 214
may adjust an amount of power delivered by the amplifier 210 in
response to presence signals from the presence detector 280 and the
enclosed detector 290. The transmitter may receive power through a
number of power sources, such as, for example, an AC-DC converter
(not shown) to convert conventional AC power present in a building,
a DC-DC converter (not shown) to convert a conventional DC power
source to a voltage suitable for the transmitter 200, or directly
from a conventional DC power source (not shown).
[0043] As a non-limiting example, the presence detector 280 may be
a motion detector utilized to sense the initial presence of a
device to be charged that is inserted into the coverage area of the
transmitter. After detection, the transmitter may be turned on and
the RF power received by the device may be used to toggle a switch
on the receiver device in a pre-determined manner, which in turn
results in changes to the driving point impedance of the
transmitter.
[0044] As another non-limiting example, the presence detector 280
may be a detector capable of detecting a human, for example, by
infrared detection, motion detection, or other suitable means. In
some exemplary embodiments, there may be regulations limiting the
amount of power that a transmit antenna may transmit at a specific
frequency. In some cases, these regulations are meant to protect
humans from electromagnetic radiation. However, there may be
environments where transmit antennas are placed in areas not
occupied by humans, or occupied infrequently by humans, such as,
for example, garages, factory floors, shops, and the like. If these
environments are free from humans, it may be permissible to
increase the power output of the transmit antennas above the normal
power restrictions regulations. In other words, the controller 214
may adjust the power output of the transmit antenna 204 to a
regulatory level or lower in response to human presence and adjust
the power output of the transmit antenna 204 to a level above the
regulatory level when a human is outside a regulatory distance from
the electromagnetic field of the transmit antenna 204. Furthermore,
the presence detector 280 may be a detector capable of detecting
objects placed in the region of the transmit antenna. This may be
useful to reduce or stop power output when objects that are not
meant to receive wireless power and may be damaged by magnetic
fields are placed near the transmit antenna.
[0045] As a non-limiting example, the enclosed detector 290 (may
also be referred to herein as an enclosed compartment detector or
an enclosed space detector) may be a device such as a sense switch
for determining when an enclosure is in a closed or open state.
When a transmitter is in an enclosure that is in an enclosed state,
a power level of the transmitter may be increased.
[0046] In exemplary embodiments, a method by which the transmitter
200 does not remain on indefinitely may be used. In this case, the
transmitter 200 may be programmed to shut off after a
user-determined amount of time. This feature prevents the
transmitter 200, notably the power amplifier 210, from running long
after the wireless devices in its perimeter are fully charged. This
event may be due to the failure of the circuit to detect the signal
sent from either the repeater or the receive coil that a device is
fully charged. To prevent the transmitter 200 from automatically
shutting down if another device is placed in its perimeter, the
transmitter 200 automatic shut off feature may be activated only
after a set period of lack of motion detected in its perimeter. The
user may be able to determine the inactivity time interval, and
change it as desired. As a non-limiting example, the time interval
may be longer than that needed to fully charge a specific type of
wireless device under the assumption of the device being initially
fully discharged.
[0047] FIG. 5 is a simplified block diagram of a receiver 300, in
accordance with an exemplary embodiment of the present invention.
The receiver 300 includes receive circuitry 302 and a receive
antenna 304. Receiver 300 further couples to device 350 for
providing received power thereto. It should be noted that receiver
300 is illustrated as being external to device 350 but may be
integrated into device 350. Generally, energy is propagated
wirelessly to receive antenna 304 and then coupled through receive
circuitry 302 to device 350.
[0048] The receive antenna 304 is tuned to resonate at the same
frequency, or near the same frequency, as transmit antenna 204
(FIG. 4). Receive antenna 304 may be similarly dimensioned with
transmit antenna 204 or may be differently sized based upon the
dimensions of the associated device 350. By way of example, device
350 may be a portable electronic device having diametric or length
dimension smaller that the diameter of length of transmit antenna
204. In such an example, receive antenna 304 may be implemented as
a multi-turn antenna in order to reduce the capacitance value of a
tuning capacitor (not shown) and increase the receive antenna's
impedance. By way of example, receive antenna 304 may be placed
around the substantial circumference of device 350 in order to
maximize the antenna diameter and reduce the number of loop turns
(i.e., windings) of the receive antenna and the inter-winding
capacitance.
[0049] Receive circuitry 302 provides an impedance match to the
receive antenna 304. Receive circuitry 302 includes power
conversion circuitry 306 for converting a received RF energy source
into charging power for use by device 350. Power conversion
circuitry 306 includes an RF-to-DC converter 308 and may also in
include a DC-to-DC converter 310. RF-to-DC converter 308 rectifies
the RF energy signal received at receive antenna 304 into a
non-alternating power while DC-to-DC converter 310 converts the
rectified RF energy signal into an energy potential (e.g., voltage)
that is compatible with device 350. Various RF-to-DC converters are
contemplated, including partial and full rectifiers, regulators,
bridges, doublers, as well as linear and switching converters.
[0050] Receive circuitry 302 may further include switching
circuitry 312 for connecting receive antenna 304 to the power
conversion circuitry 306 or alternatively for disconnecting the
power conversion circuitry 306. Disconnecting receive antenna 304
from power conversion circuitry 306 not only suspends charging of
device 350, but also changes the "load" as "seen" by the
transmitter 200 (FIG. 2), which can be used to "cloak" the receiver
from the transmitter.
[0051] As disclosed above, transmitter 200 includes load sensing
circuit 216 which detects fluctuations in the bias current provided
to transmitter power amplifier 210. Accordingly, transmitter 200
has a mechanism for determining when receivers are present in the
transmitter's near-field.
[0052] When multiple receivers 300 are present in a transmitter's
near-field, it may be desirable to time-multiplex the loading and
unloading of one or more receivers to enable other receivers to
more efficiently couple to the transmitter. A receiver may also be
cloaked in order to eliminate coupling to other nearby receivers or
to reduce loading on nearby transmitters. This "unloading" of a
receiver is also known herein as a "cloaking." Furthermore, this
switching between unloading and loading controlled by receiver 300
and detected by transmitter 200 provides a communication mechanism
from receiver 300 to transmitter 200 as is explained more fully
below. Additionally, a protocol can be associated with the
switching which enables the sending of a message from receiver 300
to transmitter 200. By way of example, a switching speed may be on
the order of 100 .mu.sec.
[0053] In an exemplary embodiment, communication between the
transmitter and the receiver refers to a device sensing and
charging control mechanism, rather than conventional two-way
communication. In other words, the transmitter uses on/off keying
of the transmitted signal to adjust whether energy is available in
the near-field. The receivers interpret these changes in energy as
a message from the transmitter. From the receiver side, the
receiver uses tuning and de-tuning of the receive antenna to adjust
how much power is being accepted from the near-field. The
transmitter can detect this difference in power used from the
near-field and interpret these changes as a message from the
receiver.
[0054] Receive circuitry 302 may further include signaling detector
and beacon circuitry 314 used to identify received energy
fluctuations, which may correspond to informational signaling from
the transmitter to the receiver. Furthermore, signaling and beacon
circuitry 314 may also be used to detect the transmission of a
reduced RF signal energy (i.e., a beacon signal) and to rectify the
reduced RF signal energy into a nominal power for awakening either
un-powered or power-depleted circuits within receive circuitry 302
in order to configure receive circuitry 302 for wireless
charging.
[0055] Receive circuitry 302 further includes processor 316 for
coordinating the processes of receiver 300 described herein
including the control of switching circuitry 312 described herein.
Cloaking of receiver 300 may also occur upon the occurrence of
other events including detection of an external wired charging
source (e.g., wall/USB power) providing charging power to device
350. Processor 316, in addition to controlling the cloaking of the
receiver, may also monitor beacon circuitry 314 to determine a
beacon state and extract messages sent from the transmitter.
Processor 316 may also adjust DC-to-DC converter 310 for improved
performance.
[0056] In some exemplary embodiments, the receive circuitry 320 may
signal a power requirement to a transmitter in the form of, for
example, desired power level, maximum power level, desired current
level, maximum current level, desired voltage level, and maximum
voltage level. Based on these levels, and the actual amount of
power received from the transmitter, the processor 316 may adjust
the operation of the DC-DC-to-DC converter 310 to regulate its
output in the form of adjusting the current level, adjusting the
voltage level, or a combination thereof.
[0057] Exemplary embodiments of the present invention are directed
to circuits and adjustment mechanisms that allows for adjustment of
a load impedance terminating the receive antenna of the receiver
device in a way that can compensate for changes in coupling effects
between transmit antennas and receive antennas.
[0058] Current solutions for adjusting load impedances are based on
use of RF components. These include tuners based on switchable
fixed capacitors and inductors, voltage variable capacitors (e.g.,
ferro-electric, Micro-Electro-Mechanical Systems (MEMS), and
varactor diodes). The switchable fixed capacitors and inductors
approach may have too much ohmic loss to be practical for a
charging system. Variable tuners based on ferro-electric devices
and MEMs voltage variable capacitors may not be commercially viable
at this time. Tuners based on varactor diodes may not be able to
handle the RF powers anticipated in wireless power
applications.
[0059] As described above, wireless charging systems typically
include a transmit antenna (i.e., transmit coupling coil), which
transmits RF energy to one or more receive antennas (i.e., receive
coupling coils) embedded in receiver devices to be charged or
otherwise supplied with power. The received energy is rectified,
conditioned, and delivered to the device's battery or other
operating circuitry. It is typical that these antennas are operated
at low frequencies where they are electrically small in order to
couple magnetically rather than radiate power.
[0060] These small antennas can achieve better coupling efficiency
when the two coils are resonant; that is when both are tuned to the
frequency used to transfer the power from one antenna to the other.
Unfortunately, while efficient power transfer is an important
aspect of any wireless power transfer scheme, a byproduct of using
small and resonantly coupled antennas is that the resulting
bandwidth is sometimes quite small, making the antennas susceptible
to detuning and possible dramatic loss in efficiency. Another
problem of using small, loosely coupled resonant antennas is that
the mutual coupling between the two antennas will vary as the
receive antenna is moved around relative to the transmit antenna
(e.g., at a different place on a charging pad), or when multiple
devices to be charged are placed within close proximity to each
other on the charging pad. These placement changes will vary
coupling between the transmit and receive coils and result in a
variation in the impedance seen at the transmit antenna, resulting
in less efficient power transfer between the transmit and receive
antennas in the charging system. Many of these issues can be
corrected, or at least reduced to a large extent by varying the RF
load resistance that is presented to the receive antenna.
[0061] In varying the RF load resistance in order to affect a
change in the impedance seen by the transmit amplifier, it is well
known that this impedance seen by the source can vary resistively,
reactively, or a combination thereof, depending on the matching
circuits used at the transmit and receive antennas. To maximize the
efficiency of the system, it is best to vary only the real value
(i.e., resistive value) and hold the reactive value of this input
impedance as constant as possible. While it is possible to
compensate for reactive changes, this may greatly increase the
complexity of the overall system. It can be shown that there is one
matching circuit that can meet a goal of maximum power transfer
over any range in resistive load variations. That matching circuit
may be a tuned (resonant) transformer, which is simply an extension
of the resonant transmit and receive antennas used to transfer the
power. The use of this form of matching circuit is assumed in the
following discussions.
[0062] FIG. 6 shows a schematic of transmit circuitry and receive
circuitry showing coupling therebetween and an adjustable DC load
450. As shown in FIG. 6, a charging system 405 can be characterized
by a coupled coil transformer model 430 where the transmitter
electronics are connected to a primary coil 432 (i.e., a transmit
antenna) and the rectifier/regulator electronics on the receiver
side are connected to a secondary coil 434 (i.e., a receive
antenna).
[0063] A driver 410 generates an oscillating signal at a desired
resonance frequency, such as, for example, about 13.56 MHz. As one
example, this driver 41 may be configured as a class E driver as
illustrated in FIG. 6. A low pass matching circuit 420 filters and
impedance matches the signal from the driver 410 to the transmit
antenna 432 of the coupled coil transformer model 430.
[0064] Energy is transferred through near field radiation to the
receive antenna 434 of the coupled coil transformer model 430. The
oscillating signal coupled to the receive antenna 434 is coupled to
an impedance match and rectifier circuit 440 to provide an AC
impedance match for the receive antenna 434 and rectify the
oscillating signal to a substantially DC signal. A DC-to-DC
converter 450 converts the DC signal from the rectifier 440 to a DC
output useable by circuitry on a receiver device (not shown). The
DC-to-DC converter 450 is also configured to adjust the DC
impedance seen by the rectifier 440, which in turn adjusts the
overall AC impedance of the input to the rectifier 440. As a
result, changes in the DC impedance at the input of the DC-to-DC
converter 450 can create a better match to the impedance of the
receive antenna 434 and better mutual coupling between the receive
antenna 434 and the transmit antenna 432.
[0065] The self inductances (Ltx and Lrx), mutual inductance (m),
and loss resistances of the transformer model 430 may be derived
from the measured or simulated coupling characteristics of the
antenna pair.
[0066] It can be shown that given the mutual inductance (m), and
the resistive losses, R1 and R2 of the transmit and receive
antennas, respectively, there is an optimum load for the receive
antenna that will maximize power transfer efficiency. This optimal
load may be defined as:
R.sub.eff=R1*[1+(omega*m).sup.2/(R1*R2)].sup.5.
[0067] Typically, R.sub.eff may be in a range from 1 to 20 ohms.
Through the use of DC load control, the RF load seen by the receive
coil 434 can be set to its most efficient value, as the mutual
inductance (m) varies due to the reasons described above.
[0068] Another use for controlling the RF load is that a variation
in load can be used to control the power delivered to the receiver
device. This may be at the expense of some efficiency, but enables
the maximum use of available power when serving a mix of wireless
devices in various charge states.
[0069] Yet another use for controlling the RF load is that a
variation in load can be used to widen the bandwidth of the
transfer function, a result which depends on the matching network
420 between a very low impedance, or reactive impedance, transmit
power amplifier 410, typical for wireless changing amplifiers, and
the transmitting antenna 432. This bandwidth adjustment may work
best over a large variation in the mutual inductance (m) and load
if the input matching circuit includes a third tuned inductance
(not shown), mutually coupled to the TX antenna 432. In this case,
the bandwidth will increase linearly with increasing RF load
resistance if the power amplifier has a very low source
impedance.
[0070] Existing wireless charging systems appear unconcerned about
bandwidth, since the FCC allowed signal bandwidth is quite small.
As stated before, changing the load to widen the bandwidth may
reduce the efficiency somewhat from its maximum value, but this may
be useful to maintain a functional charging system when an
increased bandwidth may be needed. Although not a substantially
desirable option in wireless charging where high efficiency is
required, this bandwidth expansion effect can be applied in a short
range communication system where efficiency is far less
important.
[0071] The use of a low inductance mutually coupled to the transmit
antenna 432 provides significant system advantages over a more
common passive match. This input series tuned DC-to-DC converter
450 results in a second impedance inversion, the first being
between the transmit and receive antennas (432 and 434). As a
result, when the load impedance increases the input impedance
increases. This allows the load to "cloak" the receiver from the
transmitter simply by raising the load impedance of the receiver.
This effect may be restated as having the input conductance be a
linear function of the load conductance.
[0072] Without this cloaking feature, the load from the receiver
would have to present a short in order to cloak, using a mechanism
such as element 312 discussed above with reference to FIG. 5. As a
result, a charging pad with no receiver device present would appear
as a highly tuned short circuit rather than an open circuit.
Furthermore, when multiple uncloaked loads are present the total
input conductance for the transmit antenna 432 will be the sum of
the individual conductances of the receive antennas 434 and power
will be distributed according to their relative value.
[0073] Yet another advantage of the tuned input transformer match
is that the resulting in/out admittance is real at the center
(resonant) frequency and is "flat" topped with respect to
frequency. Thus, first order variations in the circuit parameters
have little affect on the power transfer process.
[0074] FIGS. 7A-7B show Smith charts illustrating change in input
impedance of a coupled coil pair (no inductive match added)
responsive to a change in DC impedance at the receiver device. In
FIGS. 7A and 7B, the darkened circles 510 and 520, respectively,
indicate constant resistance circles.
[0075] Referring to FIGS. 7A and 6, a DC impedance R.sub.dc of
about 10.2 ohms at the input to the DC-to-DC converter 450 results
in a complex input impedance at the transmit antenna 432 of about
50 ohms and very little reactance. Referring to FIGS. 7B and 6, a
DC impedance R.sub.dc of about 80 ohms at the input to the DC-to-DC
converter 450 results in a complex input impedance at the transmit
antenna 432 of much less than 50 ohms, with very little
reactance.
[0076] FIGS. 8A and 8B show amplitude plots (530 and 540,
respectively) showing improved coupling between a coupled coil pair
responsive to a change in DC impedance at the receiver device. In
FIG. 8A the amplitude at the center frequency of 13.56 MHz is about
-4.886 dB. After adjusting the input impedance to the DC-to-DC
converter 450 (FIG. 6), the amplitude at the center frequency of
13.56 MHz is improved to about -3.225 dB resulting in better
coupling between the receive antenna and the transmit antenna,
which results in more power transferred to the receive antenna.
[0077] FIGS. 9A-9B show simplified schematics of receiver devices
illustrating exemplary embodiments for adjusting DC impedance at
the receiver device. In both FIGS. 9A and 9B, the receive antenna
304 feeds an exemplary impedance matching circuit 320 including
capacitors C1 and C2. An output from the impedance matching circuit
320 feeds a simple rectifier 330 (as one example) including diodes
D1 and D2 and capacitor C3 for converting the RF frequency to a DC
voltage. Of course, many other impedance matching circuits 320 and
rectifiers 330 are contemplated as within the scope of embodiments
of the present invention. A DC-to-DC converter 350 converts the DC
input signal 340 from the rectifier to a DC output signal 370
suitable for use by a receiver device (not show).
[0078] FIG. 9A illustrates a simple apparatus for maintaining an
optimal power point impedance in a wireless power transmission
system. A comparator, 348 compares the DC input signal 340 to a
voltage reference 345, which is selected such that for a given
expected power, the impedance as seen by the transmitter will
result in the maximum amount of power coupled to the DC output
signal 370. The output 361 of the comparator 348 feeds the DC-to-DC
converter 350 with a signal to indicate whether the DC-to-DC
converter 350 should increase or decrease its input DC impedance.
In embodiments that use a switching DC-to-DC converter 350, this
output of the comparator 361 may be converted to a
pulse-width-modulation (PWM) signal, which adjusts the input DC
impedance, as is explained below. This input voltage feedback
circuit regulates input DC impedance by increasing the PWM pulse
width as the voltage increases, thus decreasing impedance and
voltage.
[0079] FIG. 9B illustrates a slightly more complex apparatus for
maintaining an optimal power point impedance in a wireless power
transmission system. In FIG. 9B, a current sensor 344 may be
included and a multiplexer 346 may be used to switch whether
voltage or current at the DC input signal 340 is sampled by a
processor 360 at any given time. In this system, voltage (Vr) and
current (Ir) of the DC input signal 340 is measured, and a PWM
signal 362 to the DC-to-DC converter 350 may be varied over a
pre-allowed range. The processor 360 can determine which pulse
width for the PWM signal 362 produces the maximum power (i.e.,
current times voltage), which is an indication of the best DC input
impedance. This determined pulse width may be used for operation to
transfer an optimal amount of power to the DC output signal 370.
This sample and adjust process can be repeated as often as desired
to track changing coupling ratios, transmit powers or transmit
impedances.
[0080] As stated earlier, in order to obtain maximum external power
from a source with a finite output resistance or impedance, the
resistance or impedance of the receiver should be the same as that
of the source. In many cases, it is desirable to operate wireless
power systems in order to maximize power received, in order to make
best use of a limited RF power source.
[0081] This maximized power transfer is not always the same as
maximum efficiency. In many cases, it may be advantageous to
operate the load at a higher than equal impedance or resistance in
order to increase the efficiency of the system. In either case,
though, maintenance of a specific impedance at the receiver may be
useful for regulating the amount of power transferred between a
transmitter and a receiver.
[0082] In simple wireless power systems, there may be no control of
input impedance; the output load (often a battery or wireless
device) may be the only driver of the impedance of the system. This
leads to a suboptimal transmitter/receiver impedance match, with
consequent losses of power transfer, efficiency, or a combination
thereof.
[0083] DC impedance is defined by (voltage/current). Therefore, at
any given current and desired impedance, there exists a desired
voltage=(current*desired impedance). With a PWM converter, this
desired voltage (and as a result desired impedance) can be achieved
by providing a feedback term that compares the input voltage to the
(current*desired impedance) term, and adjusts the pulse width up or
down to maintain that term.
[0084] FIGS. 10A-10D show simplified schematics of receiver devices
illustrating exemplary embodiments for adjusting DC impedance at
the receiver device using a pulse-width modulation converter. In
FIGS. 10A-10D, common elements include the receive antenna 304
feeding an impedance matching circuit 320. An output from the
impedance matching circuit 320 feeds a simple rectifier, which is
shown simply as diode D3. Of course, many other impedance matching
circuits 320 and rectifiers are contemplated as within the scope of
embodiments of the present invention. A DC-to-DC converter 350
converts the DC input signal 340 from the rectifier to a DC output
signal 370 suitable for use by a receiver device (not show). A
processor 360 samples parameters of the DC input signal 340, the DC
output signal 270, or a combination thereof and generates a PWM
signal 362 for the DC-to-DC converter 350. The DC-to-DC converter
350 is a switch-mode converter wherein the PWM signal 362 controls
a switch S1 to periodically charge a filtering circuit including
diode D4, inductor L1, and capacitor C4. Those of ordinary skill in
the art will recognize the DC-to-DC converter 350 as a buck
converter, which converts a voltage on the DC input signal 340 to a
lower voltage on the DC output signal 370. While not shown, those
of ordinary skill in the art will also recognize that the
switch-mode DC-to-DC converter 350 may also be implemented as a
boost converter to generate a DC output signal 370 with a voltage
that is higher the voltage on the DC input signal 340.
[0085] In most cases, a requirement to regulate the output voltage
of the wireless power receiver will be most important. For battery
charging, for example, it is often critical to not exceed a maximum
output current or a maximum output voltage. This means that often
the output voltage control term will dominate the control rules for
the pulse width of the PWM signal 362.
[0086] However, in many cases, the battery will be accepting power
at less than its maximum rate. As an example, during the charging
of a lithium ion battery at rates less than its rated capacity, the
voltage will be below the maximum battery voltage and the current
may be limited by the maximum power available from the wireless
power system. During these cases, the secondary impedance-control
term will become dominant in adjusting the pulse width of the PWM
signal in order to control DC impedance.
[0087] Exemplary embodiments of the disclosure provide for DC
impedance control by using a feedback term in the switch-mode
DC-to-DC converter 350 to effectively simulate a steady-state DC
resistance in the receiver. In other words, the DC impedance is
controlled by adjusting the frequency or duty cycle of the PWM
signal 362 to the switch-mode DC-to-DC converter 350 to simulate a
given DC impedance.
[0088] Feedback for the system is created by sampling one or more
characteristics of the DC input signal 340, the DC output signal
370, or a combination thereof by a processor 360. The processor 360
then uses this sampled information, possibly along with other
information such as expected power transfer and efficiency of the
DC-to-DC converter 350 to adjust the PWM signal 362, which adjust
the DC input signal and the DC output signal to close the feedback
loop.
[0089] Individual differences of what is sampled and how the
parameters of the PWM signal are generated are discussed with
reference to four different exemplary embodiments illustrated as
FIGS. 10A-10D.
[0090] In FIG. 10A, the processor 360 samples a voltage of the DC
input signal 340, a current of the DC input signal 340, a voltage
of the DC output signal 370, and a current of the DC output signal
370.
[0091] In some embodiments, a voltage sensor 342 may be used
between the DC input signal 340 and the processor 360. Similarly, a
voltage sensor 372 may be used between the DC output signal 370 and
the processor 360. In other embodiments the voltage sensors 342 and
372 may not be needed and the processor 460 may directly sample
voltages on the DC input signal 340 and the DC output signal
370.
[0092] In some embodiments, a current sensor 344 may be used
between the DC input signal 340 and the processor 360. Similarly, a
current sensor 374 may be used between the DC output signal 370 and
the processor 360. In other embodiments the current sensors 344 and
374 may not be needed and the processor 360 may directly sample
current on the DC input signal 340 and the DC output signal
370.
[0093] With current and voltage measurements of both the DC input
signal 340 and the DC output signal 370, the processor 360 can
determine all the parameters needed for the power conversion
system. Power-in on the DC input signal 340 can be determined as
voltage-in times current-in. Power-out on the DC output signal 370
can be determined as voltage-out times current-out. Efficiency of
the DC-to-DC converter 350 can be determined as a difference
between power-out and power-in. The DC impedance of the DC input
signal 340 can be determined as voltage-in divided by
current-in.
[0094] The processor 360 can periodically sample all of the inputs
(e.g., about once every second, or other suitable period) to
determine power output at that time. In response, the processor 360
can change the duty cycle of the PWM signal 362, which will change
the DC impedance of the DC input signal 340. For example, a narrow
pulse width on the PWM signal 362 allows the input voltage to stay
relatively high and the input current to stay relatively low, which
leads to a higher DC impedance for the DC input signal 340.
Conversely, a wider pulse width on the PWM signal 362 allows more
current to be drawn from the DC input signal 340, resulting in a
lower input voltage and a lower DC impedance for the DC input
signal 340.
[0095] The periodic sampling and adjusting creates the feedback
loop that can find an optimal DC impedance for the DC input signal
340, and as a result, an optimal power for the DC output signal
370. Details of finding these values are discussed below with
reference to FIG. 11.
[0096] In FIG. 10B, the processor 360 samples a voltage of the DC
input signal 340, a voltage of the DC output signal 370, and a
current of the DC output signal 370. As explained above with
reference to FIG. 10A, the voltage sensor 342, the voltage sensor
372, and the current sensor 374 may be included between their
respective signals and the processor 360 depending on the
embodiment.
[0097] As with FIG. 10A, in FIG. 10B, power-out on the DC output
signal 370 can be determined as voltage-out times current-out. In
many cases, the efficiency of the DC-to-DC converter 350 will be
known and relatively constant over the desired operating range.
Thus, the processor 360 can estimate power-in on the DC input
signal 340 based on power-out and an estimation of efficiency at
the current operation point for the DC-to-DC converter 350. With
power-in estimated, and voltage-in measured, the DC impedance of
the DC input signal 340 can be determined. Once again, the periodic
sampling and adjusting creates the feedback loop that can find an
optimal DC impedance for the DC input signal 340, and as a result,
an optimal power for the DC output signal 370.
[0098] In FIG. 10C, the processor 360 samples a voltage of the DC
input signal 340 and a current of the DC input signal 340. As
explained above with reference to FIG. 10A, the voltage sensor 342
and the current sensor 344 may be included between the DC input
signal 340 and the processor 360 depending on the embodiment.
[0099] In FIG. 10C, power-in on the DC input signal 340 can be
determined as voltage-in times current-in and the DC impedance of
the DC input signal 340 can be determined as voltage-in divided by
current-in. As with FIG. 10B, in FIG. 10C the efficiency of the
DC-to-DC converter 350 will be known and relatively constant over
the desired operating range. Thus, the processor 360 can estimate
power-out on the DC output signal 370 based on power-in and an
estimation of efficiency at the current operation point for the
DC-to-DC converter 350. Once again, the periodic sampling and
adjusting creates the feedback loop that can find an optimal DC
impedance for the DC input signal 340, and as a result, an optimal
power for the DC output signal 370.
[0100] In FIG. 10D, the processor 360 samples only voltage of the
DC input signal 340. As explained above with reference to FIG. 10A,
the voltage sensor 342 may be included between the DC input signal
340 and the processor 360 depending on the embodiment.
[0101] In FIG. 10D, a pre-determined estimate can be made as to how
much power is expected to be received through the receive antenna
and rectifier and delivered on the DC input signal. Using this
pre-determined estimate DC impedance of the DC input signal 340 can
be determined relative to the voltage-in. As with FIG. 10B, in FIG.
10C the efficiency of the DC-to-DC converter 350 will be known and
relatively constant over the desired operating range. Thus, the
processor 360 can estimate power-out on the DC output signal 370
based on the pre-determined power-in estimate and an estimation of
efficiency at the current operation point for the DC-to-DC
converter 350. Once again, the periodic sampling and adjusting
creates the feedback loop that can find an optimal DC impedance for
the DC input signal 340, and as a result, an optimal power for the
DC output signal 370.
[0102] The pre-determined power estimate may be a fixed value
programmed in to the receiver device or may be communicated to the
receiver device from the transmitter device, which may have means
for determining how much of the power transmitted will be coupled
to that particular receiver device.
[0103] FIG. 11 illustrates various input and output parameters that
may be used when adjusting DC impedance at the receiver device.
This graph represents a system that has a specific source
impedance, but where a load resistor is allowed to vary over a wide
range. This load resistor is represented as the variable resistor
of the DC-to-DC converter 450 of FIG. 6. Alternatively, the load
resistor may be represented by the DC impedance of the DC input
signal 340 to the DC-to-DC converter 350 shown in FIGS. 9A-10D.
[0104] In FIG. 11, a 50 ohm source impedance is driven by a signal
with a 1:1 source-to-load coupling. Line 620 shows the current
through the load resistor. Notice as the load impedance increases,
the current decreases due to Ohm's Law. Line 610 shows the voltage
across the load resistor. Notice that as the load impedance
increases, the voltage increases as well per the resistor divider
equation.
[0105] These two data sets for current and voltage of the load
resistor give the power across the load resistor, as shown by line
640. Note that the power peaks at a certain load impedance. In this
case (1:1 load coupling) this maximum power point occurs when the
load impedance equals, or is near, the source impedance. If the
coupling is different, the peak power point may be shifted as
well.
[0106] Line 650 represents a PWM setting (out of 100) that has an
inverse relationship to output impedance. This is the function
exhibited by most buck converters. As can be seen, there is one
ideal PWM setting that maximizes power received by the load
resistor. Wireless power impedance control schemes used with
reference to exemplary embodiments discussed herein attempt to
discover and maintain this ideal PWM setting.
[0107] Of course, as stated earlier, optimal power transfer is not
always necessary. Using embodiments of the invention discussed
above in FIGS. 6 and 9A-10D, the DC impedance of the DC input
signal 340, and as a result the AC impedance of the receive antenna
can be effectively de-tuned from optimal power transfer to limit
the amount of power delivered on the DC output signal 370. This
limiting of power may be useful where the receiver device can not
accept the maximum power deliverable from the DC-to-DC converter
350. Some non-limiting examples of this reduced power need may be
when a battery in the receiver device is nearing full charge or the
DC-to-DC converter 350 can deliver more power than a rated capacity
for the battery.
[0108] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0109] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the exemplary embodiments disclosed
herein may be implemented as electronic hardware, computer
software, or combinations of both. To clearly illustrate this
interchangeability of hardware and software, various illustrative
components, blocks, modules, circuits, and steps have been
described above generally in terms of their functionality. Whether
such functionality is implemented as hardware or software depends
upon the particular application and design constraints imposed on
the overall system. Skilled artisans may implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the exemplary embodiments of the
invention.
[0110] The various illustrative logical blocks, modules, and
circuits described in connection with the exemplary embodiments
disclosed herein may be implemented or performed with a general
purpose processor, a Digital Signal Processor (DSP), an Application
Specific Integrated Circuit (ASIC), a Field Programmable Gate Array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0111] The steps of a method or algorithm described in connection
with the exemplary embodiments disclosed herein may be embodied
directly in hardware, in a software module executed by a processor,
or in a combination of the two. A software module may reside in
Random Access Memory (RAM), flash memory, Read Only Memory (ROM),
Electrically Programmable ROM (EPROM), Electrically Erasable
Programmable ROM (EEPROM), registers, hard disk, a removable disk,
a CD-ROM, or any other form of storage medium known in the art. An
exemplary storage medium is coupled to the processor such that the
processor can read information from, and write information to, the
storage medium. In the alternative, the storage medium may be
integral to the processor. The processor and the storage medium may
reside in an ASIC. The ASIC may reside in a user terminal. In the
alternative, the processor and the storage medium may reside as
discrete components in a user terminal.
[0112] In one or more exemplary embodiments, the functions
described may be implemented in hardware, software, firmware, or
any combination thereof. If implemented in software, the functions
may be stored on or transmitted over as one or more instructions or
code on a computer-readable medium. Computer-readable media
includes both computer storage media and communication media
including any medium that facilitates transfer of a computer
program from one place to another. A storage media may be any
available media that can be accessed by a computer. By way of
example, and not limitation, such computer-readable media can
comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,
magnetic disk storage or other magnetic storage devices, or any
other medium that can be used to carry or store desired program
code in the form of instructions or data structures and that can be
accessed by a computer. Also, any connection is properly termed a
computer-readable medium. For example, if the software is
transmitted from a website, server, or other remote source using a
coaxial cable, fiber optic cable, twisted pair, digital subscriber
line (DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of medium. Disk and disc,
as used herein, includes compact disc (CD), laser disc, optical
disc, digital versatile disc (DVD), floppy disk and blu-ray disc
where disks usually reproduce data magnetically, while discs
reproduce data optically with lasers. Combinations of the above
should also be included within the scope of computer-readable
media.
[0113] The previous description of the disclosed exemplary
embodiments is provided to enable any person skilled in the art to
make or use the present invention. Various modifications to these
exemplary embodiments will be readily apparent to those skilled in
the art, and the generic principles defined herein may be applied
to other embodiments without departing from the spirit or scope of
the invention. Thus, the present invention is not intended to be
limited to the embodiments shown herein but is to be accorded the
widest scope consistent with the principles and novel features
disclosed herein.
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