I 1111111111111111 11111 1111111111 1111111111 1111111111 111111111111111 IIII IIII
`US009425864B2
`
`c12) United States Patent
`Staring
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 9,425,864 B2
`Aug. 23, 2016
`
`(54) WIRELESS INDUCTIVE POWER TRANSFER
`
`(71) Applicant: KONINKLIJKE PHILIPS N.V.,
`Eindhoven (NL)
`
`(72)
`
`Inventor: Antonius Adriaan Maria Staring,
`Eindhoven (NL)
`
`(73) Assignee: KONINKLIJKE PHILIPS N.V.,
`Eindhoven (NL)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 122 days.
`
`(21) Appl. No.:
`
`14/347,338
`
`(22) PCT Filed:
`
`Sep.21,2012
`
`(86) PCT No.:
`
`PCT /IB2012/055019
`
`§ 371 (c)(l),
`(2) Date:
`
`Mar. 26, 2014
`
`(87) PCT Pub. No.: WO2013/046104
`PCT Pub. Date: Apr. 4, 2013
`
`(65)
`
`Prior Publication Data
`
`US 2014/0232201 Al
`
`Aug. 21, 2014
`
`(30)
`
`Foreign Application Priority Data
`
`Sep. 30, 2011
`
`(EP) ..................................... 11183389
`
`(51)
`
`Int. Cl.
`H0JF 38/14
`H02J50/05
`
`(2006.01)
`(2016.01)
`(Continued)
`
`(52) U.S. Cl.
`CPC .............. H04B 510037 (2013.01); H0JF 38/14
`(2013.01); H02J 51005 (2013.01); H04B
`510031 (2013.01)
`
`( 58) Field of Classification Search
`CPC .... H04B 5/0037; H04B 5/0031; H0lF 38/14;
`H02J 5/005
`
`USPC .......................................................... 307/104
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`2/2003 Reis
`2003/0024985 Al
`2003/0043027 Al * 3/2003 Carson .
`
`H04B 3/54
`375/259
`
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`
`1/2006
`W02006004990 A2
`10/2006
`W02006109032 Al
`OTHER PUBLICATIONS
`System Description, Wireless Power Transfer, vol. I: Low Power, Part
`1: Interface 25 Definition, Version 1.0 Jul. 2010, published by the
`Wireless Power Consortium www.wirelesspowerconsortium.com/
`downloads/wireless-power-specification-part-1.html.
`(Continued)
`
`Jared Fureman
`Primary Examiner -
`Assistant Examiner - Emmanuel R Dominique
`(74) Attorney, Agent, or Firm - Larry Liberchuk
`ABSTRACT
`(57)
`A power transmitter (101) transfers power to a power receiver
`(105) using a wireless inductive power signal. The power
`transmitter (101) comprises an inductor (103) for providing
`the power signal and a power signal generator (207) for driv(cid:173)
`ing the inductor (103) to provide the power signal. The power
`receiver (105) comprises an inductor (107) for receiving the
`power signal and a transmitter (305) which transmits data
`messages to the power transmitter (101). The data are com(cid:173)
`municated by load modulation of the power signal in repeat(cid:173)
`ing load modulation intervals which are separated by inter(cid:173)
`vening time intervals. The power transmitter (101) transmits
`data to the power receiver (105) by modulating the power
`signal with a message during the intervening time intervals
`and the power receiver demodulates the data in these time
`intervals. The power transmitter (101) transmits single bit of
`the message by modulating it across a plurality of intervening
`time intervals and the power transmitter (101) receives it by
`demodulating over these time intervals.
`18 Claims, 12 Drawing Sheets
`
`PTX
`
`/105
`
`PRX
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`US 9,425,864 B2
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`Int. Cl.
`H04B 5100
`H02J5/00
`
`(51)
`
`(56)
`
`(2006.01)
`(2016.01)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2005/0077356 Al*
`
`4/2005 Takayama.
`
`2009/0284082 Al
`2009/0302800 Al
`2010/0146308 Al
`2011/0006613 Al
`2011/0065398 Al
`
`11/2009 Mohammadian
`12/2009 Shiozaki
`6/2010 Gioscia
`1/2011 Stevens
`3/2011 Liu
`
`2011/0238518 Al*
`
`9/2011 Florek .
`
`2013/0058263 Al*
`
`3/2013 Ishizaki
`
`2014/0062588 Al*
`
`3/2014 Gopalan
`
`G06K 19/07732
`705/26.1
`H04W 4/008
`370/278
`H03D 3/00
`329/304
`
`OTHER PUBLICATIONS
`
`G06K 7/10237
`235/451
`
`Puers R. et al., "Wireless Inductive Transfer of Power and Data
`Modulation", Analog Circuit Design, 2006 Springer, pp. 395-414.
`Coup R. et al., "An Inductively Coupled Universal Battery Charger",
`Department of Electrical and Electronic Engineering, Part IV Project
`Report 2003.
`
`* cited by examiner
`
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`U.S. Patent
`
`Aug. 23, 2016
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`US 9,425,864 B2
`
`1
`WIRELESS INDUCTIVE POWER TRANSFER
`
`FIELD OF THE INVENTION
`
`The invention relates to inductive power transfer and in
`particular, but not exclusively, to an inductive power transfer
`system in accordance with the Qi wireless power transfer
`standard.
`
`BACKGROUND OF THE INVENTION
`
`2
`The Qi standard is developed by the Wireless Power Con(cid:173)
`sortium and more information can e.g. be found on their
`website:
`http ://www.wirelesspowerconsortium.com/index.html,
`5 where in particular the defined Standards documents can be
`found.
`The Qi wireless power standard describes that a power
`transmitter must be able to provide a guaranteed power to the
`power receiver. The specific power level needed depends on
`10 the design of the power receiver. In order to specify the
`guaranteed power, a set of test power receivers and load
`conditions are defined which describe the guaranteed power
`level for each of the conditions.
`Qi originally defined a wireless power transfer for low
`power devices considered to be devices having a power drain
`of less than 5 W. Systems that fall within the scope of this
`standard use inductive coupling between two planar coils to
`transfer power from the power transmitter to the power
`receiver. The distance between the two coils is typically 5
`mm. It is possible to extend that range to at least 40 mm.
`However, work is ongoing to increase the available power,
`and in particular the standard is being extended to mid-power
`devices being devices having a power drain of more than 5 W.
`The Qi standard defines a variety of technical require(cid:173)
`ments, parameters and operating procedures that a compat(cid:173)
`ible device must meet.
`Communication
`The Qi standard supports communication from the power
`receiver to the power transmitter thereby enabling the power
`receiver to provide information that may allow the power
`transmitter to adapt to the specific power receiver. In the
`current standard, a unidirectional communication link from
`the power receiver to the power transmitter has been defined
`and the approach is based on a philosophy of the power
`35 receiver being the controlling element. To prepare and control
`the power transfer between the power transmitter and the
`power receiver, the power receiver specifically communicates
`information to the power transmitter.
`The unidirectional communication is achieved by the
`40 power receiver performing load modulation wherein a load(cid:173)
`ing applied to the secondary receiver coil by the power
`receiver is varied to provide a modulation of the power signal.
`The resulting changes in the electrical characteristics ( e.g.
`variations in the current draw) can be detected and decoded
`( demodulated) by the power transmitter.
`Thus, at the physical layer, the communication channel
`from power receiver to the power transmitter uses the power
`signal as a data carrier. The power receiver modulates a load
`which is detected by a change in the amplitude and/or phase
`50 of the transmitter coil current or voltage. The data is formatted
`in bytes and packets.
`More information can be found in chapter 6 of part 1 the Qi
`wireless power specification (version 1.0).
`Although Qi uses a unidirectional communication link, it
`55 has been proposed to introduce communication from the
`power transmitter to the power receiver. However, such a
`bidirectional link is not trivial to include and is subject to a
`large number of difficulties and challenges. For example, the
`resulting system still needs to be backwards compatible and
`60 e.g. power transmitters and receivers that are not capable of
`bidirectional communication still need to be supported. Fur(cid:173)
`thermore, the technical restrictions in terms of e.g. modula(cid:173)
`tion options, power variations, transmission options etc. are
`very restrictive as they need to fit in with the existing param(cid:173)
`eters. It is also important that cost and complexity is kept low,
`and e.g. it is desirable that the requirement for additional
`hardware is minimized, that detection is easy and reliable, etc.
`
`45
`
`The number and variety of portable and mobile devices in
`use have exploded in the last decade. For example, the use of
`mobile phones, tablets, media players etc. has become ubiq(cid:173)
`uitous. Such devices are generally powered by internal bat- 15
`teries and the typical use scenario often requires recharging of
`batteries or direct wired powering of the device from an
`external power supply.
`Most present day systems require a wiring and/or explicit
`electrical contacts to be powered from an external power 20
`supply. However, this tends to be impractical and requires the
`user to physically insert connectors or otherwise establish a
`physical electrical contact. It also tends to be inconvenient to
`the user by introducing lengths of wire. Typically, power
`requirements also differ significantly, and currently most 25
`devices are provided with their own dedicated power supply
`resulting in a typical user having a large number of different
`power supplies with each being dedicated to a specific device.
`Although, the use of internal batteries may avoid the need for
`a wired connection to a power supply during use, this only 30
`provides a partial solution as the batteries will need recharg(cid:173)
`ing (or replacing which is expensive). The use of batteries
`may also add substantially to the weight and potentially cost
`and size of the devices.
`In order to provide a significantly improved user experi(cid:173)
`ence, it has been proposed to use a wireless power supply
`wherein power is inductively transferred from a transmitter
`coil in a power transmitter device to a receiver coil in the
`individual devices.
`Power transmission via magnetic induction is a well(cid:173)
`known concept, mostly applied in transformers, having a tight
`coupling between primary transmitter coil and a secondary
`receiver coil. By separating the primary transmitter coil and
`the secondary receiver coil between two devices, wireless
`power transfer between these becomes possible based on the
`principle of a loosely coupled transformer.
`Such an arrangement allows a wireless power transfer to
`the device without requiring any wires or physical electrical
`connections to be made. Indeed, it may simply allow a device
`to be placed adjacent to or on top of the transmitter coil in
`order to be recharged or powered externally. For example,
`power transmitter devices may be arranged with a horizontal
`surface on which a device can simply be placed in order to be
`powered.
`Furthermore, such wireless power transfer arrangements
`may advantageously be designed such that the power trans(cid:173)
`mitter device can be used with a range of power receiver
`devices. In particular, a wireless power transfer standard
`known as the Qi standard has been defined and is currently
`being developed further. This standard allows power trans(cid:173)
`mitter devices that meet the Qi standard to be used with power
`receiver devices that also meet the Qi standard without these
`having to be from the same manufacturer or having to be
`dedicated to each other. The Qi standard further includes
`some functionality for allowing the operation to be adapted to 65
`the specific power receiver device ( e.g. dependent on the
`specific power drain).
`
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`US 9,425,864 B2
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`3
`It is also important that the communication from the power
`transmitter to the power receiver does not impact, degrade or
`interfere with the communication from the power receiver to
`the power transmitter. Furthermore, an all-important require(cid:173)
`ment is that the communication link does not unacceptably 5
`degrade the power transfer ability of the system.
`Accordingly, many challenges and difficulties are associ(cid:173)
`ated with enhancing a power transfer system such as Qi to
`include bidirectional communication.
`System Control
`In order to control the wireless power transfer system, the
`Qi standard specifies a number of phases or modes that the
`system may be in at different times of the operation. More
`details can be found in chapter 5 of part 1 the Qi wireless 15
`power specification (version 1.0).
`The system may be in the following phases:
`Selection Phase
`This phase is the typical phase when the system is not used,
`i.e. when there is no coupling between a power transmitter
`and a power receiver (i.e. no power receiver is positioned
`close to the power transmitter).
`In the selection phase, the power transmitter may be in a
`stand-by mode but will sense in order to detect a possible
`presence of an object. Similarly, the receiver will wait for the
`presence of a power signal.
`Ping Phase:
`If the transmitter detects the possible presence of an object,
`e.g. due to a capacitance change, the system proceeds to the
`ping phase in which the power transmitter (at least intermit(cid:173)
`tently) provides a power signal. This power signal is detected
`by the power receiver which proceeds to send an initial pack(cid:173)
`age to the power transmitter. Specifically, if a power receiver
`is present on the interface of the power transmitter, the power
`receiver communicates an initial signal strength packet to the
`power transmitter. The signal strength packet provides an
`indication of the degree of coupling between the power trans(cid:173)
`mitter coil and the power receiver coil. The signal strength
`packet is detected by the power transmitter.
`Identification & Configuration Phase:
`The power transmitter and power receiver then proceeds to
`the identification and configuration phase wherein the power
`receiver communicates at least an identifier and a required
`power. The information is communicated in multiple data
`packets by load modulation. The power transmitter maintains 45
`a constant power signal during the identification and configu(cid:173)
`ration phase in order to allow the load modulation to be
`detected. Specifically, the power transmitter provides a power
`signal with constant amplitude, frequency and phase for this
`purpose (except from the change caused by load-modula- 50
`tion).
`In preparation of the actual power transfer, the power
`receiver can apply the received signal to power up its elec(cid:173)
`tronics but it keeps its output load disconnected. The power
`receiver communicates packets to the power transmitter. 55
`These packets include mandatory messages, such as the iden(cid:173)
`tification and configuration packet, or may include some
`defined optional messages, such as an extended identification
`packet or power hold-off packet.
`The power transmitter proceeds to configure the power 60
`signal in accordance with the information received from the
`power receiver.
`Power Transfer Phase:
`The system then proceeds to the power transfer phase in
`which the power transmitter provides the required power 65
`signal and the power receiver connects the output load to
`supply it with the received power.
`
`4
`During this phase, the power receiver monitors the output
`load conditions, and specifically it measures the control error
`between the actual value and the desired value of a certain
`operating point. It communicates these control errors in con(cid:173)
`trol error messages to the power transmitter with a minimum
`rate of e.g. every 250 msec. This provides an indication of the
`continued presence of the power receiver to the power trans(cid:173)
`mitter. In addition the control error messages are used to
`implement a closed loop power control where the power
`10 transmitter adapts the power signal to minimize the reported
`error. Specifically, if the actual value of the operating point
`equals the desired value, the power receiver communicates a
`control error with a value of zero resulting in no change in the
`power signal. In case the power receiver communicates a
`control error different from zero, the power transmitter will
`adjust the power signal accordingly.
`The system allows for an efficient setup and operation of
`the power transfer. However, the approach is restrictive and
`may not allow the full desired flexibility and support for
`20 functions as required. For example if a power receiver tries to
`get more than 5 W power from a power transmitter the power
`transmitter may terminate power transfer resulting in a bad
`user experience. Therefore, it is desirably to further develop
`the Qi standard to provide enhanced functionality, flexibility
`25 and performance.
`In particular the unidirectional communication may be
`restrictive. Indeed, this requires that the power transmitter
`must be able to comply with any request by the power receiver
`and thus further requires the power receiver to be limited to
`30 only request parameters that it knows can be met by all power
`transmitters. Such an approach complicates or prevents fur(cid:173)
`ther development of functionality as it will result in a lack of
`backwards compatibility.
`As previously mentioned, the introduction of bidirectional
`35 communication in power transfer systems, such as Qi sys(cid:173)
`tems, is complicated and subject to many restrictions and
`requirements in order to ensure both efficient power transfer,
`efficient operation and not least backwards compatibility.
`Hence, an improved power transfer system would be
`40 advantageous and in particular a system allowing increased
`flexibility, improved backwards compatibility, facilitated
`implementation and/or improved performance would be
`advantageous.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, the Invention seeks to preferably mitigate,
`alleviate or eliminate one or more of the above mentioned
`disadvantages singly or in any combination.
`According to an aspect of the invention there is provided a
`power transmitter for transferring power to a power receiver
`using a wireless inductive power signal, the power transmitter
`comprising: an inductor for providing the power signal; a
`power signal generator for driving the inductor to provide the
`power signal; a receiver for receiving data messages from the
`power receiver, the data messages being communicated by
`load modulation of the power signal in repeating load modu(cid:173)
`lation intervals, the repeating load modulation intervals being
`separated by intervening time intervals; a transmitter for
`transmitting data to the power receiver by modulating the
`power signal with a message during the intervening time
`intervals; wherein the transmitter is arranged to modulate a
`single bit of the message across a plurality of the intervening
`time intervals.
`The invention may provide an improved power transfer
`system. It may in many embodiments allow for further exten(cid:173)
`sion and development of a power transfer system by intro-
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`5
`ducing bidirectional communication. This may in many sce(cid:173)
`narios be
`achieved while maintaining backwards
`compatibility. The invention may allow a practical approach
`and may facilitate introduction into existing systems.
`The approach may in particular provide for communica(cid:173)
`tion from a power transmitter to a power receiver which
`reduces impact on other functionality. In particular, the
`approach may allow an efficient separation of communication
`from the power transmitter to the power receiver and from the
`power receiver to the power transmitter, and may reduce the
`impact of the modulation on the power signal. As such, the
`impact of introducing bidirectional communication may be
`reduced for both the power transfer operation and the power
`receiver to power transmitter communication. This may in
`particular facilitate operation and implementation, as well as 15
`improve backwards compatibility. In particular, introduction
`of bidirectional communication to existing power transfer
`systems previously supporting only unidirectional communi(cid:173)
`cation may be facilitated. The approach may in many embodi(cid:173)
`ments allow reuse of existing hardware for power transmitters 20
`and power receivers, and may require only a small change in
`the firmware, and a marginal change in the complexity.
`A particular advantage of the approach is that it may in
`many embodiments reduce the impact of modulation on the
`power signal. The power signal may be less affected by the 25
`additional modulation and thus may interfere less with the
`power transfer operation. This may in particular be significant
`for backwards compatibility as legacy equipment may not be
`affected by the introduction of modulation that the equipment
`has not been designed for. In many embodiments, the devia- 30
`tions of the power signal due to the introduced modulation
`may be maintained to a sufficiently low level for it not to
`impact the power transfer characteristics for the system.
`Indeed, in many scenarios, the effects of the modulation may
`be kept to a level where they are imperceptible or negligible 35
`for the power transfer phase functionality (e.g. of legacy
`equipment). Thus, in many embodiments, the power transfer
`operation may be unaffected by the presence of modulation
`deviations on the power signal.
`In particular, the modulation deviation may be made 40
`smaller and/or slower thereby reducing the impact. Further(cid:173)
`more, in many embodiments a more reliable communication
`can be achieved as the extended modulation time for the
`single bit allows increased symbol energy and accordingly a
`reduced error rate.
`Furthermore, the approach may fit well with the design
`principles and philosophies of many existing power transfer
`systems. For example, the approach follows the design prin(cid:173)
`ciples and philosophies of the Qi power transfer system.
`The repeating load modulation intervals include at least
`three load modulation intervals corresponding to at least two
`intervening time intervals. The message may consist in the
`single bit or the single bit may be one out of a plurality of bits
`of the message.
`The bit may be an information bit which is converted into
`a plurality of charmel bits. Each channel bit may then be
`modulated on to the power signal. The modulation of one or
`more of the channel bits may be within a single intervening
`time interval. However, at least two charmel bits will be in
`different intervening time intervals corresponding to the
`modulation of the information bit extending over at least
`these intervening time intervals.
`The information bit may have a value that can be set inde(cid:173)
`pendently of other information bits (not part of the same data
`symbol). A charmel bit is dependent on the corresponding 65
`information bit, and typically a plurality of channel bits are
`dependent on the same information bit.
`
`6
`The single (information) bit may be a bit of a data symbol
`comprising more than the single bit. In some embodiments,
`each data symbol may correspond to a non-integer number of
`bits. For example, the bit may be comprised in a data symbol
`5 with three possible values corresponding to the data symbol
`representing logi3)=1.58 bits.
`In accordance with an optional feature of the invention, the
`transmitter is arranged to modulate the single bit in accor(cid:173)
`dance with a predetermined modulation pattern, the modula-
`10 tion pattern defining modulation deviations to apply to the
`power signal in each of the plurality of intervening time
`intervals.
`This may provide an improved communication in many
`embodiments. In many scenarios it may provide a low com(cid:173)
`plexity and reliable approach for enabling communication
`from the power transmitter to the power receiver with a low
`impact on the power signal from the modulation. The
`approach may furthermore facilitate the demodulation, and
`indeed the power receiver need only know the predetermined
`modulation pattern in order to demodulate the power signal to
`provide the single bit.
`The modulation deviation may specifically be an ampli(cid:173)
`tude deviation, a frequency deviation or a phase deviation.
`The deviation represents a deviation relative to the power
`signal without any modulation being applied.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern comprises one modulation
`value for each of the plurality of intervening time intervals,
`each modulation value defining a modulation offset for the
`power signal for a value of the single bit.
`This may provide improved performance and/or facilitate
`operation. In many embodiments, it may provide reduced
`complexity.
`The modulation values may define a value that should be
`applied to the power signal to represent a given value of the
`single bit. In many embodiments, the modulation offset
`applied to the power signal is determined in response to a data
`value independent modulation offset represented by the
`modulation value and the value of the single bit. In many
`embodiments, the single bit may be multiplied by the modu(cid:173)
`lation value
`The modulation offset represents an offset relative to the
`power signal without any modulation, i.e. an unmodulated
`power signal. The offset may for example be an amplitude
`45 offset for amplitude modulation, a frequency offset for fre(cid:173)
`quency modulation, or a phase offset for phase modulation ( or
`a combination thereof).
`In accordance with an optional feature of the invention,
`each modulation offset is a constant offset for the correspond-
`50 ing intervening time interval.
`This may provide improved and/or facilitated communica(cid:173)
`tion from a power transmitter to a power receiver.
`In accordance with an optional feature of the invention,
`each modulation offset is a non-constant predetermined pat-
`55 tern for the corresponding intervening time interval.
`This may provide improved and/or facilitated communica(cid:173)
`tion from a power transmitter to a power receiver.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern corresponds to an average
`60 deviation of the power signal due to modulation of the single
`bit of no more than a maximum deviation between two of the
`plurality of intervening time intervals.
`The approach may provide a modulation pattern for which
`the average modulation deviation is kept low while allowing
`modulation offsets of sufficient size to allow demodulation.
`In particular, in some embodiments, the average deviation
`may be substantially zero. This may allow a modulated power
`
`Ex.1012
`APPLE INC. / Page 17 of 30
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`US 9,425,864 B2
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`5
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`30
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`7
`signal which more closely corresponds to an unmodulated
`power signal and as such may reduce the implications of the
`modulation of the power signal.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern corresponds to a maxi(cid:173)
`mum deviation of the power signal due to the modulation of
`the single bit of no more than 5%.
`The approach may provide a modulation pattern with a low
`peak value, and consequently a reduced deviation from an
`unmodulated power signal. This may allow a modulated
`power signal which more closely corresponds to an unmodu(cid:173)
`lated power signal and as such may reduce the implications of
`the modulation of the power signal.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern corresponds to a series of
`step changes between constant deviations in each intervening
`time interval, the predetermined pattern comprising step
`changes of opposite signs.
`This may reduce complexity in many embodiments and
`may typically allow an efficient implementation and reliable
`performance. The feature may in many embodiments allow a
`reduced deviation from an unmodulated power signal. This
`may allow a modulated power signal which more closely
`corresponds to an unmodulated power signal and as such may 25
`reduce the implications of the modulation of the power signal.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern corresponds to a deviation
`of the power signal due to modulation of the single bit ofless
`than a tolerance value for the power signal.
`This may provide improved operation in many embodi(cid:173)
`ments and may in particular ensure that modulation is suffi(cid:173)
`ciently transparent for e.g. legacy equipment or functionality.
`In particular, it may ensure that the modulated power signal 35
`still meets the requirements for a power receiver.
`In accordance with an optional feature of the invention, the
`modulation pattern corresponds to applying an offset to the
`power signal formed by a series of smaller changes to the
`power signal, each change corresponding to one intervening 40
`time interval.
`This may provide improved operation and/or facilitated
`implementation in many embodiments.
`In accordance with an optional feature of the invention, the
`transmitter is arranged to generate a modulation offset for a 45
`first intervening time interval by determining a sign value of
`the modulation offset in response to the single bit and an
`amplitude of the modulation offset in response to the prede(cid:173)
`termined modulation pattern corresponding to the first inter(cid:173)
`vening time interval, and to apply the modulation offset to the 50
`power signal in the first intervening time interval.
`This may provide efficient, low complexity, reliable and/or
`high performance operation and/or implementation.
`In accordance with an optional feature of the invention, the
`predetermined modulation pattern represents an amplitude 55
`offset pattern for the power signal.
`This may provide efficient, low complexity, reliable and/or
`high performance operation and/or implementation. The
`amplitude may typically be a voltage or current amplitude.
`In accordance with an optional feature of