Wireless power transfer

Abstract

The power receiver (105) comprises an input circuit (107, 503) having a receiver coil (107) that extracts power from a power transfer signal generated by the power transmitter (101). A variable load (511) applies a modulation load to an input circuit (107, 503), and a data transmitter (509) transmits data symbols to the power transmitter (101) by load-modulating the power transmission signal during a communication time interval interspersed by a non-communication time interval during which the data symbols are transmitted to the power transmitter (101). The data transmitter (509) does not transmit the data symbols. Data symbols are represented by a modulation loading pattern, and the data transmitter (509) is arranged to control the variable load (511) to repeatedly change the modulation loading during the non-communication time interval. The method may provide improved communication and power transfer operations, and may particularly reduce transients, such as transients in a supply voltage provided to a load of the power receiver (105).

Description

Technical Field

[0001] The present invention relates to wireless power transfer and particularly, but not exclusively, to communications in wireless transfer systems such as the Qi or Ki wireless power transfer specifications. Background Art

[0002] Most current electronic products require dedicated electrical contacts to be powered from an external power source. However, this is often impractical and requires the user to physically plug in a connector or otherwise establish physical electrical contact. Typically, power requirements are also significantly different, and most current devices have their own dedicated power source, resulting in users typically having a large number of different power sources, each dedicated to a specific device. Although the use of internal batteries can avoid the need for a wired connection to a power source during use, this only provides a partial solution because the battery will need to be recharged (or replaced). The use of batteries can also substantially increase the weight of the device and potential cost and size.

[0003] In order to provide a significantly improved user experience, it has been proposed to use wireless power supply, where power is inductively transferred from a transmitter coil in a power transmitter device to a receiver coil in an individual device.

[0004] Power transfer via magnetic induction is a well-known concept, mainly applied in transformers with tight coupling between the primary transmitter inductor / coil and the secondary receiver coil. By separating the primary transmitter coil and the secondary receiver coil between the two devices, wireless power transfer between these devices becomes possible based on the principle of loosely coupled transformers.

[0005] Such an arrangement allows wireless power transfer to a device without the need to make any wired or physical electrical connections. In practice, it may simply allow a device to be placed near or on top of a transmitter coil for external charging or powering. For example, a power transmitter device may be arranged with a horizontal surface on which a device may simply be placed in order to be powered.

[0006] Furthermore, such wireless power transfer devices can advantageously be designed so that a power transmitter device can be used with a range of power receiver devices. In particular, a wireless power transfer method, known as the Qi specification, has been defined and is currently being further developed. This method allows a power transmitter device that meets the Qi specification to be used with a power receiver device that also meets the Qi specification, without having to be from the same manufacturer or having to be dedicated to each other. The Qi standard also includes some functionality for allowing operation to be adapted to a specific power receiver device (e.g., depending on a specific power consumption).

[0007] The Qi specification was developed by the Wireless Power Consortium and more information can be found, for example, on its website: http: / / www.wirelesspowerconsortium.com / index.html, where in particular the defining specification documents can be found.

[0008] Based on the Qi specification, known approaches such as the Ki specification were developed for high power applications, such as specifically for kitchen appliances.

[0009] In order to support efficient wireless power transfer, wireless power transfer systems such as Qi-based systems utilize extensive communication between the power transmitter and the power receiver. Initially, Qi only supported communication from the power receiver to the power transmitter using load modulation of the power transfer signal. Therefore, initially Qi devices only supported one-way communication from the power receiver to the power transmitter.

[0010] US2013 / 147279A1 and US2013 / 0235632A1 disclose a wireless power transmission system using load modulation-based communication between a power transmitter and a power receiver.

[0011] However, the development of the standard introduced bidirectional communication, and many functions are supported by the communication exchange between the power receiver and the power transmitter. In many systems, the communication from the power transmitter to the power receiver is achieved by modulating the power transfer signal.

[0012] In some systems, it has been proposed to use separate and dedicated communication functionality, such as communication based on Bluetooth or NFC (near field communication). However, while such an approach may tend to provide effective operation in many scenarios, it is also associated with a number of disadvantages, including the need for dedicated and complex communication circuitry and potentially reduced certainty that the power transmitter is actually communicating with the power receiver being powered. In addition, backward compatibility with, for example, Qi-based devices may be problematic for newer devices based on separate communication.

[0013] However, communicating using load modulation of a power transfer signal that transfers power to a power receiver may also tend to have some associated disadvantages. For example, load modulation tends to introduce some electrical noise, including noise to the device's signal as well as radiated electromagnetic noise. Load modulation can increase electromagnetic interference to other devices, and maintaining adequate or optimal electromagnetic compatibility has been found to be challenging.

[0014] It has also been found in practice that load modulation may result in the introduction of undesired spurious oscillations into the drive signal and the power transfer signal. The power transfer path in a wireless power transfer system tends to include significant inductance and tends to have resonant behavior. Such load modulation tends to affect the power transfer path and indeed the communication path. Therefore, load modulation also results in noise and interference (self-interference) to the communication itself. This is fundamentally different from other communication systems, where random noise or interference from other transmissions is the main cause of bit errors.

[0015] Another disadvantage is that the load modulation of the power transmission signal may cause acoustic noise. This noise may arise from the influence of the mechanical elements on the changes of the electromagnetic field caused by the load modulation, and in particular, it may cause the mechanical elements to move and vibrate, thereby generating potential acoustic noise.

[0016] In some cases, such as the load modulation communications used in the initial version of the Qi specification may not have perfect reliability and some bit errors may occur in some cases. For example, high levels of noise or self-interference may cause bit errors and / or an increased modulation depth may be required, which may result in increased electrical or acoustic noise caused by the load modulation.

[0017] Load modulation also potentially has an impact on the operation of the power transfer, and in particular may affect the operating point of the power transfer. This may result in undesirable changes in the power transfer operation and performance.

[0018] While it is desirable to change to a different communication method in some way, maintaining backward compatibility or reducing the amount of changes required to existing designs and methods are major challenges that often make it unattractive.

[0019] Hence, improved methods would be advantageous and in particular, improved methods for load modulation would be advantageous which allow increased flexibility, reduced cost, reduced complexity, improved power transfer operation, increased reliability, reduced communication errors, improved backward compatibility, improved electromagnetic compatibility, reduced electrical and / or acoustic noise, improved communications, more stable power transfer, reduced power transfer variation, increased stability and / or improved performance. Summary of the invention

[0020] Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0021] According to one aspect of the present invention, there is provided a power receiver for wirelessly receiving power from a power transmitter via an electromagnetic power transfer signal, the power receiver comprising: an input circuit comprising a receiver coil, the receiver coil being arranged to extract power from the power transfer signal; a variable load coupled to the input circuit and arranged to apply a modulated loading to the input circuit; a data transmitter arranged to transmit data symbols to the power transmitter by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter does not transmit data symbols; the data transmitter is further arranged to vary the variable load to vary the power symbol in response to a communication time interval. Each data symbol transmitted during the communication time interval applies a modulation loading pattern, and each possible data symbol value is represented by a different modulation loading pattern for the modulation loading; and the data transmitter is arranged to control the variable load to repeatedly change the modulation loading during the non-communication time interval; wherein the data transmitter is arranged to control the variable load to apply a repeated loading change pattern during the non-communication time interval, and the maximum absolute difference between the cross-correlation of the repeated loading change pattern and the modulation sequence data sequence and a reference correlation is not greater than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and a reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0022] In many embodiments, the invention may allow improved performance and in many embodiments may in particular allow improved communication between a power receiver and a power transmitter.In many embodiments, the scheme may allow, facilitate or enable improved power transfer.

[0023] In many cases, the scheme can allow for reduced impact of load modulation on power transfer performance and operation. In many embodiments, reduced variation in properties and operation of input circuits when extracting power from a power transfer signal can be achieved. In many embodiments, more stable operation can be achieved. In many scenarios, reduced voltage variation of a load provided by a power receiver can be achieved.

[0024] During the non-communication time interval, there is no communication of information data from the power receiver to the power transmitter. In some embodiments, the data transmitter may be arranged to control the variable load during the non-communication time interval so that the resulting modulation loading does not match any modulation loading pattern representing possible data symbol values.

[0025] During the communication time interval, the data transmitter 509 may be arranged to vary the variable load such that the modulation loading pattern represents a data symbol value for the data symbol. Each possible data symbol value may be represented by / linked with one modulation loading pattern, wherein the modulation loading pattern is different for different data symbol values. The data transmitter may be arranged to transmit a first symbol value by controlling the variable load to apply a modulation loading pattern linked with the first symbol value.

[0026] The modulation loading is determined by the load value of the variable load. The variable load may be a modulation load with a load modulation applied to the power transfer signal by a variation of the variable load. The modulation loading may be a (partial) loading of the power transfer signal that varies in response to a data symbol being transmitted.

[0027] Each communication time interval may correspond to a time interval during which a data packet is transmitted from the power receiver to the power transmitter. Each non-communication time interval may correspond to a time interval between communication time intervals. Each non-communication time interval may correspond to a time interval during which no data packet is transmitted from the power receiver to the power transmitter.

[0028] According to an optional feature of the invention, the data transmitter is arranged to control a variable load to repeatedly change the modulation loading during a non-communication time interval so that the difference between the average modulation loading during the non-communication time interval and the average modulation loading during the non-communication time interval is less than 10% of the maximum modulation loading change during the communication time interval.

[0029] In many embodiments, this can provide improved performance. In many scenarios, it can ensure low voltage variations in the sensing signal and supply voltage to the load. The scheme can reduce, mitigate, or in some cases substantially eliminate the effects of transients in properties or operating points that occur at the beginning of a communication time interval.

[0030] In some embodiments, the load variation during the non-communication time interval may be such that the average modulation loading during the non-communication time interval is the same as the average modulation loading during the communication time interval. In some embodiments, the difference between the averages may vary by no more than 2%, 5%, 20% of the maximum modulation loading during the communication time interval.

[0031] According to an optional feature of the invention, the data transmitter is arranged to control a variable load to repeatedly change the modulation loading during a non-communication time interval so that the average time between modulation loading changes during the non-communication time interval is not less than 50% of the average time between modulation loading changes during the non-communication time interval.

[0032] In many embodiments, this may provide improved performance.In many scenarios, a reduced voltage variation of the sense signal may be provided and a voltage provided to the load.

[0033] In some embodiments, the average time interval between load changes during the non-communication time interval is the same as the average time interval between load changes during the communication time interval.

[0034] In some embodiments, the minimum time interval between load changes during the non-communication time interval is the same as the minimum time interval between load changes during the communication time interval.

[0035] According to an optional feature of the invention, the modulation loading pattern for each possible data symbol value comprises at least two different loading values.

[0036] In many embodiments, this may allow improved performance.

[0037] According to an optional feature of the invention, the modulation loading pattern for each possible data symbol value comprises a load modulation chip sequence of at least five load modulation chips.

[0038] In many embodiments, this may allow improved performance.

[0039] According to an optional feature of the invention, the data transmitter is arranged to repeatedly vary the modulation loading during the non-communication time intervals so as not to include a modulation loading pattern corresponding to any load modulation chip sequence.

[0040] In many embodiments, this may allow improved performance.

[0041] The features may allow improved communication and, in many embodiments, may allow improved tradeoffs between different parameters and operating characteristics. The scheme may, for example, allow highly reliable communication but allow the use of reduced modulation depth. The scheme may reduce electrical noise (such as modulation switching noise) and / or electromagnetic interference and allow improved electromagnetic compatibility. In many cases, the scheme may reduce or prevent acoustic noise. In many embodiments, voltage variations for a load supply voltage may be reduced during communication time intervals and / or non-communication time intervals.

[0042] The chip sequence may be a sequence / pattern of chip values. Each chip value may be represented by such a load modulation level or pattern. The chip sequences for different data symbols have different chip value sequences / patterns.

[0043] In many embodiments, the length of the chip sequence is no less than 5 and no more than 1024 chips.

[0044] According to an optional feature of the invention, each chip of the load modulation chip sequence is represented by a modulation loading transition.

[0045] In many embodiments, this may allow improved performance.

[0046] According to an optional feature of the invention, the number of modulation loading changes during the load modulation chip sequence duration in the non-communication time interval is not less than a maximum number of modulation loading changes in the load modulation chip sequence.

[0047] In many embodiments, this may allow improved performance.

[0048] The data transmitter is arranged to control the variable load to apply a repetitive loading variation pattern during non-communication time intervals.

[0049] In many embodiments, this may allow improved performance.

[0050] According to an optional feature of the invention, the repetitive loading variation pattern is a periodic alternation between two modulation loadings.

[0051] In many embodiments, this may allow improved performance.

[0052] The maximum absolute difference between the cross-correlation of the repetitive loading variation pattern and the modulation sequence data sequence and the reference correlation is no more than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and the random sequence.

[0053] In many embodiments, this may allow improved performance.

[0054] According to an optional feature of the invention, the data transmitter is arranged to control the variable load to exclude any modulation loading pattern representing data symbols during non-communication time intervals.

[0055] In many embodiments, this may allow improved performance.

[0056] According to an optional feature of the invention, the data transmitter is arranged to switch the variable load between two modulation loading values.

[0057] In many embodiments, this may allow improved performance.

[0058] According to an optional feature of the invention, claim 14 is provided.

[0059] According to one aspect of the present invention, there is provided an operating method for a power receiver to wirelessly receive power from a power transmitter via an electromagnetic power transfer signal, the method comprising: an input circuit including a receiver coil extracting power from the power transfer signal; a variable load coupled to the input circuit applying a modulated load to the input circuit; a data transmitter transmitting data symbols to the power transmitter by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter does not transmit data symbols; the method further comprising: varying the variable load to adjust the power symbol during the communication time intervals; A modulation loading pattern is applied to each data symbol transmitted during a communication time interval, and each possible data symbol value is represented by a different modulation loading pattern for the modulation loading; and the variable load is controlled to repeatedly change the modulation loading during a non-communication time interval; wherein the data transmitter controls the variable load to apply a repeated loading variation pattern during the non-communication time interval, and the maximum absolute difference between the cross-correlation of the repeated loading variation pattern and the modulation sequence data sequence and a reference correlation is no greater than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0060] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] By way of example only, embodiments of the present invention are described with reference to the accompanying drawings, in which:

[0062] Figure 1 illustrates examples of elements of a power delivery system according to some embodiments of the present invention;

[0063] Figure 2 An example of elements of a power transmitter is illustrated;

[0064] Figure 3 An example of a half-bridge inverter for a power transmitter is illustrated;

[0065] Figure 4 An example of a full-bridge inverter for a power transmitter is illustrated;

[0066] Figure 5 illustrates examples of elements of a power receiver according to some embodiments of the present invention;

[0067] Figure 6 The diagram shows the Figure 5 An example of a power path of a power receiver;

[0068] Figure 7 illustrates an example of a supply voltage provided to a load of a wireless power receiver;

[0069] Figure 8 illustrates an example of a supply voltage provided to a load of a wireless power receiver;

[0070] Fig. 9 illustrates an example of a supply voltage provided to a load of a wireless power receiver;

[0071] Fig.10 An example of a chip sequence is illustrated;

[0072] Fig.11 An example of load communication in a wireless power transfer system is illustrated;

[0073] Fig.12 illustrates an example of a supply voltage provided to a load of a wireless power receiver;

[0074] Fig.13 illustrates an example of a supply voltage provided to a load of a wireless power receiver;

[0075] Fig.14 The diagram provides Figure 5 An example of a supply voltage for a load of a wireless power receiver; and

[0076] Fig.15 The diagram provides Figure 5 An example of a supply voltage to a load of a wireless power receiver. DETAILED DESCRIPTION

[0077] The following description focuses on an embodiment of the invention applicable to a high power wireless power transfer system utilizing a power transfer method such as known from the Qi specification or the Ki specification. However, it will be appreciated that the invention is not limited to this application but may also be applied to many other wireless power transfer systems.

[0078] Figure 1 An example of a power transmission system according to some embodiments of the present invention is illustrated. The power transmission system comprises a power transmitter 101, which comprises (or is coupled to) a transmitter coil / inductor 103. The system also comprises a power receiver 105, which comprises (or is coupled to) a receiver coil / inductor 107.

[0079] The system provides an inductive electromagnetic power transfer signal that can inductively transfer power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated by the transmitter coil or inductor 103 as magnetic flux. The power transfer signal can typically have a frequency between about 20kHz and about 500kHz, and in many practical systems can be about 120-150kHz. The transmitter coil 103 and the power receiving coil 107 are loosely coupled, and thus the power receiving coil 107 picks up (at least part of) the power transfer signal from the power transmitter 101. Therefore, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the power receiving coil 107. The term "power transfer signal" is primarily used to refer to the inductive signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the power receiving coil 107, but it should be understood that, by equivalence, it can also be considered and used as a reference to the electrical signal provided to the transmitter coil 103 or picked up by the power receiving coil 107.

[0080] In the example described, the power receiver 105 is specifically a power receiver that receives power via a receiver coil 107. However, in other embodiments, the power receiver 105 may comprise a metallic element, such as a metallic heating element, in which case the power transmission signal directly induces eddy currents resulting in direct heating of the element.

[0081] In the following, the operation of the power transmitter 101 and the power receiver 105 will be described with particular reference to embodiments according to the Qi or Ki specifications (except for the modifications and enhancements described herein (or thereafter). Many wireless power transmission systems utilize resonant power transmission, wherein the transmitter coil 103 is part of a resonant circuit, and typically the receiver coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit may be a series resonant circuit, and thus the transmitter coil 103 and the receiver coil 107 may be coupled in series with corresponding resonant capacitors. The use of a resonant circuit tends to provide more efficient power transmission.

[0082] Typically, wireless power transfer systems employ a power control loop in order to steer the system to an appropriate operating point. This power control loop varies the amount of power transferred from the power transmitter to the power receiver. The received power (or voltage or current) can be measured, and together with the set point power value, an error signal can be generated. The power receiver sends this error signal to the power control function in the power transmitter to reduce the static error, ideally to zero.

[0083] Figure 2 A more detailed illustration Figure 1 Elements of the power transmitter 101.

[0084] The power transmitter 101 includes a driver 201 that can generate a drive signal that is fed to the transmitter coil 103, which in turn generates an electromagnetic power transfer signal to provide power transfer to the power receiver 105. The transmitter coil 103 is part of an output resonant circuit that includes the transmitter coil 103 and a capacitor 203. In the example described, the output resonant circuit is a series resonant circuit, but it should be understood that in other embodiments, the output resonant circuit can be a parallel resonant circuit. It should be understood that any suitable resonant circuit can be used, including resonant circuits using multiple inductors and / or capacitors.

[0085] The driver 201 generates a current and a voltage which is fed to the output resonant circuit and hence to the transmitter coil 103. The driver 201 is typically a drive circuit in the form of an inverter which generates an AC signal from a DC voltage. The output of the driver 201 is typically a switching bridge which generates the drive signal by appropriate switching of the switches of the switching bridge. Figure 3 A half-bridge switching bridge / inverter is shown. Switches S1 and S2 are controlled so that they are never closed at the same time. Alternatingly closing S1 while opening S2, and closing S2 while opening S1. The switches are opened and closed at the desired frequency, generating an AC signal at the output. Typically, the output of the inverter is connected to the transmitter inductor via a resonant capacitor. Figure 4 A full-bridge switching bridge / inverter is shown. Switches S1 and S2 are controlled so that they are never closed at the same time. Switches S3 and S4 are controlled so that they are never closed at the same time. Alternatingly closing switches S1 and S4 while opening S2 and S3, then closing S2 and S3 while opening S1 and S4, creates a square wave signal at the output. The switches open and close at the desired frequency.

[0086] The power transmitter 101 further comprises a power transmitter controller 205 arranged to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 may comprise a number of functions required to perform power control according to the Qi or Ki specifications.

[0087] The power transmitter controller 205 is particularly arranged to control the generation of the drive signal by the driver 201, and it may specifically control the power level of the drive signal, and correspondingly control the level of the generated power transfer signal. The power transmitter controller 205 comprises a power loop controller that controls the power level of the power transfer signal in response to power control messages received from the power receiver 105 during the power transfer phase.

[0088] The power transmitter 101 further comprises a data receiver 207, which is arranged to receive data transmitted to the power transmitter 101 from the power receiver 105. The data is transmitted by load modulation, wherein the power receiver 105 changes the loading of the power transmission signal according to the data symbol being transmitted. The data receiver 207 is coupled to the output circuit 103, 203 and is arranged to detect the change in the load of the power transmission signal. The data receiver 207 is arranged to determine the received data symbol based on the measured load value. It should be understood that a person skilled in the art will know many different methods for receiving load modulation.

[0089] The received data symbols are fed from the data receiver 207 to the power transmitter controller 205, which can adjust the operation of the power transmission in response to this data. For example, power error data can be received and the power transmitter controller 205 can adjust the power level of the drive signal, thereby implementing a power control loop with the power receiver 105.

[0090] Figure 5 Some exemplary elements of the power receiver 105 are illustrated.

[0091] In the example, the receiver coil 107 is coupled to the power receiver controller 501 via the capacitor 503, which together with the receiver coil 107 forms an input resonant circuit. Therefore, the power transfer can be a resonant power transfer between the resonant circuits. In other embodiments, only one or none of the power receiver and the power transmitter can utilize the resonant circuit for power transfer.

[0092] The power receiver controller 501 couples the receiver coil 107 to the load 505 via the switch 507. The power receiver controller 501 includes a power control path that converts the power extracted by the receiver coil 107 into a suitable power supply for the load 505. In some embodiments, the power receiver controller 501 may provide a direct power path that simply connects the input resonant circuit to the switch 507 or the load 505, i.e., the power path of the power receiver controller 501 may be simply implemented by two wires. In other embodiments, the power path may include, for example, a rectifier and possible smoothing capacitors to provide a DC voltage. In other embodiments, the power path may include more complex functions, such as, for example, a voltage control circuit, an impedance matching circuit, a current control circuit, etc. Similarly, it should be understood that the switch 507 may only be present in some embodiments, and in some embodiments, the load 505 may be permanently coupled to the input resonant circuit.

[0093] Additionally, the power receiver controller 501 may include various power receiver controller functions required to perform power transfer, and in particular functions required to perform power transfer according to the Qi or Ki specifications.

[0094] The power receiver 105 is arranged to transmit data to the power transmitter 101. In particular, such data may include a power control loop error message for implementing a feedback power loop for controlling the power level of the power transfer signal during power transfer, as known to those skilled in the art. In many embodiments, the power receiver is capable of transmitting a series of different messages serving different purposes, as known to those skilled in the art. For example, a series of different messages may be transmitted, such as those specified in the Qi specification. A message may include one or more data bits / symbols.

[0095] The power receiver is arranged to transmit a message to the power transmitter using load modulation.

[0096] As known to those skilled in the art, for load modulation, changes in the loading of the power transmission signal can be introduced by the power receiver, wherein the changes depend on the data value to be transmitted. These changes can then be detected by the power transmitter in order to decode the data from the power receiver.

[0097] Load modulation may be used as a method for a power receiver to communicate control messages or other data to a power transmitter according to, for example, the Qi wireless power standard.

[0098] There are generally two main ways of performing load modulation, namely, directly varying the resistive load / power extraction of the input circuit and / or detuning the resonance of the input circuit, for example by varying the reactive loading of the input circuit (typically switching capacitors in / out in line with the data to be transmitted). A power receiver may use a similar approach to load modulate the power transfer signal. Thus, load modulation may use active and / or reactive load variations.

[0099] Accordingly, at the power transmitter, load changes may be detected using detection methods such as those known for Qi specification systems. For example, a direct measurement of the power level or current amplitude of the drive signal may be used as an indication of loading, and therefore of changes in load modulation introduced by the power receiver.

[0100] The power receiver 105 comprises a data transmitter 509 arranged to send data to the power transmitter 101 by load modulating the power transfer signal.

[0101] In the example described, the data transmitter 509 is arranged to control a variable load 511 that provides a modulated loading of the power transfer signal. A change in the value of the variable load 511 results in a changed effective load provided to the receiver coil 107. As a result, the induced power (active and / or reactive power) changes, and thus the loading of the power transfer signal by the receiver coil 107 changes. The loading of the receiving coil 107 / power transfer signal depends on the value of the variable load. In particular, a change in the value of the variable load results in a change in the loading of the power transfer signal. The data transmitter 509 is arranged to load modulate the power transfer signal by changing the value of the variable load, thereby changing the modulated loading of the power transfer signal. The modulated loading is a variable loading of the power transfer signal that provides a load modulation of the power transfer signal. The modulated loading can be considered to / correspond to / represent a load and / or impedance value of the variable load.

[0102] Thus, the data transmitter 509 is arranged to vary the value of the variable load depending on the value of the data symbol being transmitted, thereby providing a varying modulation loading of the power transmission signal.

[0103] The data transmitter 509 is coupled to a variable load 511 and is arranged to modify this data in response to the data symbol to be transmitted. Therefore, the data transmitter 509 is arranged to change the variable load to provide a modulation loading of the power transmission signal. In particular, the data transmitter 509 can be arranged to provide a modulation loading pattern for each data symbol, wherein the modulation loading pattern depends on the data symbol value. The modulation loading pattern is different for different data symbol values. The power transmitter can accordingly estimate the modulation loading pattern for the power transmission signal and determine the data symbol value based on the detected modulation loading pattern, for example by selecting the data symbol value that is most likely to result in the received loading pattern (maximum likelihood demodulation).

[0104] In many embodiments, the variable load may be a binary variable load having two possible load values. Furthermore, in many embodiments, the variable load may be a purely resistive load or a purely reactive load. For example, the variable load may be a resistor or a capacitor that may be switched between being decoupled from the input circuit and being coupled to the input circuit (e.g., effectively switched on / off). The data transmitter 509 may be arranged to control a switch that switches the resistor / capacitor in and out.

[0105] For example, the data transmitter 509 may be arranged to switch in / out a communication capacitor (or other impedance), for example located in parallel with the power receiver controller 501 or the resonant capacitor 503, thereby being able to vary the resonant frequency and loading of the power transfer signal.

[0106] In some embodiments, the modulation load pattern can be a very simple pattern, and in some embodiments, can actually correspond to a single constant value. For example, binary modulation can be achieved by switching the load impedance in or out depending on the data symbol value being modulated onto the power transfer signal. For example, for a "1" value, the modulation capacitor can be switched out of the input circuit (not coupled to the input circuit) for the entire symbol duration, and for a "0" value, the modulation capacitor can be switched into the input circuit (coupled to the input circuit) for the entire symbol duration. However, in many embodiments, each data symbol is typically represented by a more complex modulation load pattern, and in many embodiments, the modulation load pattern can include at least two different modulation load levels.

[0107] The data transmitter 509 may be coupled to the power receiver controller 501 and may be arranged to receive data from the power receiver controller 501 to transmit to the power transmitter 101 .

[0108] For example, the data transmitter 509 may receive power error control data from the power receiver controller 501 and may use load modulation to transmit a corresponding power error control message to the power transmitter 101. In operation, the system is generally arranged to control the drive signal so that the power transfer signal reaches suitable operating parameters / properties and the power transfer operates at a suitable operating point. To achieve this, the power transmitter is arranged to control the parameters of the drive signal using a power control loop, wherein the power properties of the power transfer signal / drive signal are controlled in response to a power control error message received from the power receiver.

[0109] Specifically, the power path of the power receiver may have a power path corresponding to Figure 6 Simplified equivalent circuit of the circuit shown. Input circuit 107, 503 is coupled to rectifier 601, the output of rectifier 601 is coupled to smoothing capacitor 603. Load 505 is coupled to smoothing capacitor 603.

[0110] Therefore, the output level and in particular the voltage provided to the load directly depends on the level of the power transfer signal / electromagnetic field strength. The power control loop implemented by the power control loop provides continuous and dynamic adjustment of the level of the power transfer signal to provide the desired power to the load. For example, the voltage at the smoothing capacitor can be measured, and if it drops below a lower threshold, a transmission power increase message can be transmitted to the power transmitter 101, thereby increasing the level of the power transfer signal. If the capacitor voltage increases above an upper threshold, a transmission power decrease message can be transmitted to the power transmitter 101, which thereby results in reducing the level of the power transfer signal.

[0111] However, although load modulation is an effective communication technique for wireless power transfer systems, the inventors have realized that it also has some disadvantages, and in particular, the communication method may interfere with the power transfer operation. Specifically, load modulation may cause changes in the signal extracted by the input circuit, which may cause changes in the power / voltage provided to the load.

[0112] Figure 7 and Figure 8 The diagram shows the Figure 6 The power path shown is an example of the voltage provided to the load 505. In most wireless power transfer systems, data is transmitted in packets, and Figure 7 An example is illustrated in which such a data packet is transmitted by switching a 10 nF modulation capacitor to be disconnected and coupled, respectively, to the output of the input circuit. Figure 7 An example of 18V, 30W load with relatively high coupling is shown, and Figure 8 An example of 7V, 0.1W load and with relatively low coupling is shown.

[0113] In the example, it can be seen that the load modulation data packets cause the voltage (and therefore power) provided to the load to vary. In some applications, such voltage variations may be acceptable, but in many practical applications, they are highly undesirable. For example, the voltage variations may introduce noise, or in some cases may cause a malfunction of the device or devices powered by the power receiver 105 (i.e., the device or devices acting as the load 505 of the power receiver 105).

[0114] The inventors have particularly recognised that voltage variations may be caused by different effects and that different approaches may be applied to reduce various aspects of the voltage variation.

[0115] Figure 1 , Figure 2 and Figure 5 The described methods may include functionality for improving power transfer and, in many scenarios, may reduce voltage variations, for example, when load modulation is used for communication from a power receiver to a power transmitter.

[0116] In the method, data communication is performed in communication time intervals interspersed with non-communication time intervals in which no data symbols / information data are transmitted from the power receiver to the power transmitter.

[0117] In the method, during a communication time interval, data symbols are transmitted to a power transmitter using load modulation. Therefore, during the communication time interval, the data transmitter 509 is arranged to change the variable load to apply a modulation loading pattern to the input circuit / power transmission signal, wherein the modulation loading pattern depends on the data symbol value to be transmitted. Each possible data symbol is linked to a modulation loading pattern, and when a specific data symbol value is transmitted, the data transmitter 509 can retrieve the linked modulation loading pattern for the data symbol value and feed it to the data transmitter 509, which can continue to change the variable load accordingly. Specifically, in many embodiments, the variable load is binary, and the data transmitter 509 can be arranged to switch between two load values ​​according to the modulation loading pattern, for example by switching a modulation capacitor. The modulation loading pattern is different for different data symbol values.

[0118] In some embodiments, the modulation loading pattern may be a simple constant loading corresponding to a variable load that does not change over the duration of a data symbol. For example, for a binary data symbol, one value may be represented by a modulation capacitor switched into the input resonant circuit, and another value may be represented by a modulation capacitor switched out of the circuit.

[0119] In other embodiments, the modulation loading pattern may include a plurality of different sub-intervals, with the variable load potentially switching between the different sub-intervals.

[0120] As a specific example, in some embodiments, the modulation loading pattern for each possible data symbol value may include at least two different loading values. For example, the communication method may be used to provide binary communication, where one binary value is represented by a load transition from a higher loading to a lower loading, and another binary value is represented by a load transition from a lower loading to a higher loading.

[0121] During a communication time interval, a plurality of data symbols, in particular bits, and typically data packets may be transmitted. In many embodiments, the communication time interval may have a duration of no less than 1 microsecond and no greater than 1 millisecond. In many embodiments, no less than 24 bits and in some cases no more than 0.48 bits may be transmitted during each communication time interval.

[0122] Thus, during a communication time interval, load modulation is used to communicate data from the power receiver to the power transmitter, and therefore multiple, and often many, loading transitions occur. Typically, these occur relatively quickly / frequently, and in many embodiments, the load transitions may be such that the average loading / value of the variable load is substantially the same for all communication time intervals, and in some cases even for each modulation load pattern.

[0123] In the described method, data symbols and information are not transmitted during the non-communication time interval. However, despite the lack of information communication, the data transmitter 509 is arranged to control the variable load to repeatedly change the modulation loading during the non-communication time interval. The data transmitter 509 may be specifically arranged to apply a loading change pattern comprising a plurality of loading transitions. For example, a repeated loading change pattern may be applied by the data transmitter 509 during the non-communication time interval.

[0124] In many embodiments, the loading changes during the non-communication time intervals can be arranged to have substantially the same (average) properties as the loading changes that occur during the communication time intervals. For example, the repetitive modulation loading pattern can be designed to have properties such that the average modulation loading is the same as the modulation loading pattern of the data symbols and the average time between loading transitions / changes is the same as the communication time interval.

[0125] Thus, in the described method, modulation loading changes occur not only during communication time intervals, but also persist into non-communication time intervals, and in many cases such that at least average or typical properties of the loading changes persist into non-communication time intervals.

[0126] The inventors have realised that such an approach may reduce the impact, and in particular reduce variations in power delivery caused by load modulation, and in particular may reduce voltage variations.

[0127] In particular, the inventors have realised that when load modulation is started according to conventional methods, a step or transient occurs due to the change of the modulated load and in particular an average total loading of the input circuit thereby results. In particular, when the variable load is a reactive load, the change in load results in a change in the effective resonant frequency of the input circuit. This change in the resonant frequency results in a change in the power transfer and a change in the output voltage to the load. Thus, when load modulation is started, the average resonant frequency of the input circuit changes, which results in, for example, Figure 8 The step effect in the average voltage remains constant as long as the data packet is transmitted. However, in examples where power control is operational and fast enough to affect the voltage during a data packet, the average voltage can be returned to the desired level by the power control loop. However, in this case, undesirable transients may occur at the beginning and end of each data transmission. The transient effect exists until the system adjusts to the modified average operating point. An example of this transient effect is in Fig. 9 , where it can be seen that the average voltage returns to the desired level during and after data transmission.

[0128] However, although it would be intuitively considered counterintuitive to change the modulated load when there is no data to be transmitted due to the voltage changes caused by each load change and due to the increased operational complexity, the inventors have recognized that by implementing virtual load modulation changes during non-communication time intervals, the steps and / or transients at the beginning of the communication time interval can be reduced, and potentially even substantially eliminated.

[0129] Furthermore, this may be advantageous in many embodiments even if it results in some voltage variations / noise during the communication time interval which would otherwise not be present. In particular, in many embodiments this may reduce the peak voltage variations as this typically occurs during steps or transients (either because this may be dominant or because transients and switching variations co-add to provide a peak, as in e.g. Fig. 9 For example, in Fig. 9 It is clear from Figure 1 that in this case the amplitude of the initial transient at the start of the communication time interval is substantially higher than the amplitude of the individual switching noise that occurs for each switching of the variable load. Therefore, the average change in the resonant frequency has a more substantial impact than the individual switching effects and the generated noise. Figure 7 , both effects are of similar order of magnitude. However, since the effects are additive, reducing transients may still be highly advantageous and may reduce peak voltage deviations / variations. This may be advantageous in many embodiments, even if this results in the switching noise being present at all times and not only during communication time intervals (indeed, if the load is designed to operate with switching noise during communication time intervals, it may also be able to operate with it during non-communication time intervals).

[0130] In addition, various methods can be implemented to reduce switching noise during non-communication time intervals. As a specific example, switching during non-communication time intervals can be arranged to occur faster than during communication time intervals, and potentially substantially faster. In fact, during the communication time interval, the variable load / modulation load switching is determined by the communication parameters and operation. However, in many embodiments, the switching during the non-communication time interval may not be limited by such considerations, and can be optimized to reduce switching noise. For example, switching can be performed so that the average variable load value / modulation load / resonant frequency is substantially the same in the communication time interval and the non-communication time interval. However, the switching during the non-communication time interval can be at a faster rate, such as 10 times faster. This may not affect the amplitude of the switching noise introduced at the input circuit, but may cause this to be at a much higher frequency than during the communication time interval. The filtering provided by the smoothing capacitor and the associated circuit is more effective at this higher frequency, thereby causing the voltage switching noise at the load to be reduced.

[0131] Thus, in some embodiments, the data transmitter 509 may be arranged to change the modulation loading during the non-communication time intervals at an average frequency that is higher than the average frequency of modulation loading changes during the communication time intervals. In different embodiments, it may be at least 2 times, 5 times, or 10 times higher.

[0132] Switching of load modulation during non-communication time intervals may improve power transfer operation and reduce and / or mitigate the impact of load modulation on the power transfer operating point, and generally it may reduce voltage variations at the load.

[0133] The precise modulation change during the non-communication time interval will depend on the requirements and preferences of the individual embodiment, and in particular on the desired effect. For example, in some embodiments, it may be desirable to have a slow loading change, which may, for example, only partially reduce the transient at the beginning of the communication time interval. In many embodiments, it may be desirable to reduce the difference between the properties of the typical or average loading change during the communication time interval and the non-communication time interval. Therefore, in many (but not all) embodiments, it may be desirable to arrange the modulation change during the communication time interval to have properties that match the properties of the communication time interval.

[0134] In many embodiments, the data transmitter 509 is arranged to control the variable load to repeatedly vary the modulation loading during the non-communication time intervals such that the average value of the variable load / average modulation loading is substantially the same during the communication time intervals and the non-communication time intervals.

[0135] In some embodiments, the data transmitter 509 may be arranged to simply keep the average load / modulation loading substantially the same. This may generally allow, for example, a substantial reduction in voltage variations, while still allowing easy and low complexity operation during non-communication time intervals. In many embodiments, the method may, for example, allow the use of a predetermined and fixed load variation pattern during non-communication time intervals.

[0136] In many embodiments, the data transmitter 509 may be arranged to control the variable load to repeatedly change the modulation loading during the non-communication time interval so that the difference between the average modulation load (and the average value of the variable load) during the non-communication time interval and the communication time interval differs by less than 10% of the maximum modulation loading change / variation that may occur during the communication time interval. The maximum change / variation of the modulation loading during the communication time interval is the difference between the minimum modulation loading and the maximum modulation loading for the data symbol. The modulation loading may be considered to correspond to the value of the variable load, and thus in many embodiments, the minimum modulation loading and the maximum modulation loading may be equal to the minimum and maximum values ​​of the variable load for the data symbol. The maximum modulation loading may be the highest modulation loading, and the minimum modulation loading may be the lowest modulation loading possible for all possible data symbol values.

[0137] Typically, the variable load, and thus the modulation loading, has only a finite number of possible values. In practice, typically binary operations are used with the variable load, and the modulation loading has only two possible values ​​(and each data symbol is represented by a different pattern / sequence of these two possible values). In this case, the maximum load value / modulation loading corresponds to one of the two possible values, and the minimum load value / modulation loading corresponds to the other. Thus, the maximum modulation loading change / variation, which corresponds to the difference between the maximum modulation loading and the minimum modulation loading, is simply the difference between these values.

[0138] Therefore, in many embodiments, the switching of the variable load during the non-communication time interval makes the average modulation load / variable load value less than 10% of this difference. In some embodiments, it can even be maintained at less than 1% or 5% of this value.

[0139] Thus, this approach may allow the change in average modulation loading to be relatively low upon entering a communication time interval, and may therefore help reduce transients in the power transfer operating point, and in particular reduce voltage.

[0140] In many embodiments, the timing properties of the loading changes during the communication time interval can be controlled to provide improved advantageous operation.As previously mentioned, in many embodiments, the switching operation during the non-communication time interval can be arranged to occur frequently during the non-communication time interval, or even more frequently than during the communication time interval.

[0141] For example, in many embodiments, the average load change frequency for the variable load is controlled by the data transmitter 509 to be at least as high during the non-communication time interval as during the communication time interval. In many cases, it may even be higher. However, in some cases, it may also be desirable to have slower switching during the non-communication time interval while still allowing it to be fast enough to provide an operating point (including the average resonant frequency of the input circuit) that is not too different from the operating point of the communication time interval (including the average resonant frequency of the input circuit). In many embodiments, the average frequency during the non-communication time interval is not less than 50% of the average frequency during the communication time interval.

[0142] In some embodiments, the data transmitter 509 may be arranged to control the variable load to repeatedly change the modulation loading during the non-communication time intervals so that the average time between modulation loading changes during the non-communication time intervals is no less than 50%, 100%, or 150% of the average time between modulation loading changes during the communication time intervals. In many embodiments, this will allow the load to switch quickly enough to ensure that the operating point remains sufficiently close to the average operating point during the communication time intervals.

[0143] In some embodiments, the data transmitter 509 may be arranged to control the variable load to repeatedly change the modulation loading during the non-communication time intervals so that the maximum average time between modulation loading changes during the non-communication time intervals is no less than 50%, 100% or 150% of the average time between modulation loading changes during the communication time intervals. In many embodiments, this will allow the load switching to be fast enough to ensure that the operating point remains sufficiently close to the average operating point during the communication time intervals. In particular, it may be prevented that the operating point has a time to stabilize at a value corresponding to one particular value of the variable load / modulation loading because it remains at that value for too long.

[0144] In some embodiments, as previously described, each data symbol may be represented by a single constant modulation loading applied during the entire symbol time. For example, for binary communications, the data transmitter 509 may simply switch the variable load between an impedance that is coupled to the input circuit and that is not coupled to the input circuit. For each new bit, the data transmitter 509 may select the appropriate switch setting for the variable load and leave it at that level until the start of the next bit, when a new switching decision is made based on the new bit value.

[0145] However, in many embodiments, a data transmitter 509 may be used that includes two or more different loading values / modulation loadings for at least one data symbol value and typically for at least two data symbol values. In many embodiments, the modulation loading for one, two, or possibly more data symbol values ​​is represented by a modulation loading pattern that includes at least one loading change / transition. In many embodiments, all data symbol values ​​are represented by a modulation loading pattern that includes at least two different loading values ​​(and thus includes at least one transition).

[0146] As a specific example, the variable load can be a binary load, and binary communication can be achieved by one data symbol value and another data symbol value, wherein the one data symbol value is represented by a modulation loading pattern having a load transition from a first value of the variable load / modulation loading to a second value of the variable load / modulation loading, and wherein the other data symbol value is represented by a modulation loading pattern having a load transition from the second value of the variable load / modulation loading to the first value of the variable load / modulation loading.

[0147] The system may use load modulation, where each symbol is represented by a load transition that occurs during the symbol duration (usually at a center time) and the direction of the load transition that indicates the binary symbol value.

[0148] This load transition method can provide substantial advantages in many scenarios. It can allow load modulation detection to be performed without the need to generate an absolute reference level and for determining received data symbols. In practice, the data symbol value can be determined by measuring the load value during the first half and the second half of the data symbol time, and determining a binary value as the sign of the difference between these values.

[0149] Another substantial advantage of this approach in the described system is that it ensures a relatively large number of load transitions during a communication time interval. Frequent load transitions can allow the output voltage to remain closer to the average value, and thus can reduce switching noise on the output. This can be particularly the case if the smoothing capacitor is large enough to ensure that no load remains long enough for the power transfer to stabilize. Another substantial advantage is that the modulation loading during the communication time interval is highly predictable. For example, it can be predicted how long the modulation loading will be at a given value before changing, and it will provide a predictable and virtually data-independent average load.

[0150] Thus, the load variation during the communication time interval can be effectively and accurately repeated during the non-communication time interval, such that, for example, the average / typical / mean properties are repeated. For example, a load variation pattern can be applied during a non-communication time interval having the same average modulation loading and transition interval as during the communication time interval.

[0151] Thus, in the described approach, the use of a modulation loading transition for each data symbol may be highly advantageous and may, for example, allow transient performance at the beginning of a communication time interval to be mitigated or reduced, or indeed in some cases even removed.

[0152] In some embodiments, the data transmitter 509 may be arranged to transmit data symbols by load modulating the power transmission signal by a sequence of modulated load values ​​corresponding to a chip sequence. The data transmitter 509 may transmit data symbols using a method similar to direct sequence spread spectrum (DSSS) modulation that modulates data symbols using a chip sequence. The data symbols / bits are modulated by a (usually pseudo-random) bit sequence also referred to as an extended sequence. Each extended sequence bit, referred to as a chip, has a much shorter duration (larger bandwidth) than the original message bit.

[0153] In some embodiments, each symbol is represented by a chip sequence comprising a plurality of chips, and typically has a sequence comprising 5 to 1023 chips. Thus, rather than simply varying the load per symbol or bit, the data transmitter 509 may be arranged to transmit a given symbol (typically a bit) through a series of load changes and variations, wherein the changes and variations are different for each symbol. Specifically, a chip sequence may be defined for each symbol, and when transmitting a given symbol, the data transmitter 509 may retrieve the chip sequence for that particular symbol and proceed to load the modulated power transmission signal according to the chip sequence for the symbol. Each chip sequence is directly linked to a modulation loading pattern, which may specifically be the same as the chip sequence.

[0154] In some embodiments, the modulation loading pattern for each possible data symbol value may accordingly include a sequence of at least 5 load modulation chips, and in some cases at least 8, 16, or 32 load modulation chips.

[0155] Similarly, as will be described in more detail later, the power transmitter may detect load modulation by considering the entire chip sequence, and specifically may seek to determine the received symbol as the symbol for which the measured load variation chip pattern most closely matches the chip sequence pattern of that symbol.

[0156] Therefore, in some embodiments, direct sequence spread spectrum load modulation may be used, where each data symbol value is represented by a different chip sequence / modulation loading pattern.

[0157] Such an approach may specifically allow modulation depth, i.e., substantially reducing the size of load changes, which may, for example, reduce electromagnetic noise and interference, may reduce acoustic noise, and may reduce stray oscillations. In many embodiments, it may also result in an improved signal-to-noise ratio, and may result in substantially improved and generally more reliable communications, typically with, for example, lower bit error rates. Thus, an overall improved power transfer may be achieved.

[0158] Fig.10 An example of a portion of two possible chip sequences / modulation loading patterns is illustrated. Each chip sequence includes a sequence of chips. Typically, the set of chip values ​​is 2, corresponding to a binary chip sequence. Thus, the symbol time is divided into a plurality of chip intervals, where the chip sequence of chips is different for different data symbols. Typically, each sequence includes at least ten chips, and often substantially more. In many embodiments, each chip sequence may have 2 N -1, where N is an integer usually not less than 4.

[0159] Each stored chip sequence is assigned to a symbol. Therefore, each possible data symbol value that may need to be transmitted to the power transmitter may have a linked / associated chip sequence / modulation loading mode. For example, in the case where only two data symbols are possible, that is, in the case of implementing binary communication, the group of chip sequences may include only two chip sequences. Each possible data symbol value may be linked / represented by a modulation chip sequence. Therefore, for a given data symbol value to be transmitted, the corresponding / linked modulation chip sequence is determined by load modulation and modulated to the power transmission signal. For example, in the case where only two data symbols are possible, that is, in the case of implementing binary communication, the group of chip sequences may include only two chip sequences.

[0160] In many embodiments, one or more chip sequences may be represented by a relationship to another chip sequence. For example, for binary communications, the data transmitter 509 may store a single modulation chip sequence corresponding to one of the binary data values. The chip sequence for the other binary data value may be represented by the same stored bit sequence that may be given as the inverse of the stored bit sequence. Thus, typically the set of chip sequences utilizes complementary inverse chip sequences for data symbol pairs, and thus only half of the chip sequences used are explicitly stored / determined in the data transmitter 509, with the remaining chip sequences automatically and implicitly stored / determined as the inverses of these.

[0161] Thus, in some embodiments, the modulation chip sequence may comprise an inverse chip sequence.Equivalently, the same modulation chip sequence may be considered to represent two data symbol values, and specifically two binary data symbol values.

[0162] The modulation chip sequence is used to transmit a given data symbol selected from a set of modulation chip sequences, and in this example, the data transmitter 509 provides a set of modulation chip sequences, wherein each chip sequence is linked to a data symbol value. Typically, the set of modulation chip sequences includes a chip sequence for each possible data symbol value. For example, if binary communication is used, the first set of chip sequences may include only two chip sequences. It should be understood that the data transmitter 509 can store chip sequences in any suitable form, and does not need to store a complete sequence for each possible data symbol. For example, a given modulation chip sequence can be multiplied by a binary symbol value represented by a value of 1, -1. At the receiving end, i.e., at the power transmitter, the data value can then be determined by correlation with a given modulation chip sequence and determination of a corresponding binary data value depending on whether this is a positive correlation or a negative correlation.

[0163] In many embodiments, binary communication may be used accordingly, where only two data symbol values ​​are possible (corresponding to a "0" bit value or a "1" bit value). In this case, one bit value may be represented by a given chip sequence, while the other bit value may be associated with an inverse bit sequence, i.e., a bit sequence produced by changing each chip value to an opposite value. Thus, the two bit sequences are typically complementary, with one producing the other by multiplying by -1 (where chip values ​​are represented by +1 and -1).

[0164] A particular advantage in this case is that demodulation is particularly easy since a single correlation can be used to distinguish between the bit values ​​since the magnitude of the correlation is the same for the chip sequence, but the signs of the correlation values ​​are opposite.

[0165] It should be understood that it is equivalent to considering the data symbols represented by the inverse modulated chip sequence represented by one chip sequence or two chip sequences. It should be understood that the binary method using two inverse chip sequences being used is equivalent to considering two possible binary values ​​modulated by the same chip sequence, but the data symbols have opposite data values ​​(e.g., +1 and 1).

[0166] When the power receiver is to transmit a data symbol, the value is fed to the data transmitter 509 from the power receiver controller 501 which proceeds to determine the chip sequence linked to the data symbol value to be transmitted.

[0167] The data transmitter 509 is arranged to modulate the chip sequence onto the power transmission signal. Specifically, the modulation load may be switched in and out (on / off) in line with the chips, ie the load may be varied according to the variable load value of the chip sequence / modulation loading pattern.

[0168] The chip sequence is selected from a set of chip sequences, and in the example, the data transmitter 509 stores such a set of chip sequences, wherein each chip sequence is linked to a data symbol value. Typically, the set of chip sequences includes a chip sequence for each possible data symbol value. For example, if binary communication is used, the first set of chip sequences may include only two chip sequences. It should be understood that the data transmitter 509 can store chip sequences in any suitable form, and does not need to store a complete sequence for each possible data symbol. For example, one or more chip sequences may be represented by a relationship with another chip sequence. For example, for binary communication, the data transmitter 509 may store only a single chip sequence corresponding to one of the binary data values. The chip sequence for another binary data value may be represented by the same stored bit sequence given as the inverse of the stored bit sequence. Therefore, typically the set of chip sequences utilizes a complementary inverse chip sequence for a data symbol pair, and therefore only half of the chip sequences used are typically explicitly stored in the data transmitter 509, wherein the remaining chip sequences are automatically and implicitly stored as the inverse of these.

[0169] The chip sequences in a set usually have the same length.

[0170] Figure 1 , Figure 2 and Figure 5 The system may utilize an approach that may, in many cases, address one or more issues associated with load modulation. Load modulation is employed, but each symbol is represented by a chip sequence comprising a plurality of chips, and typically has a sequence comprising 5 to 127 chips. Thus, rather than simply varying the load per symbol or bit, the data transmitter 509 is arranged to transmit a given symbol (typically a bit) through a series of load changes and variations, wherein the changes and variations are different for each symbol. Specifically, a chip sequence may be defined for each symbol, and when transmitting a given symbol, the data transmitter 509 may retrieve the chip sequence for that particular symbol and continue to load modulate the power transmission signal in accordance with the chip sequence for the symbol.

[0171] The power transmitter may detect the load modulation by considering the entire sequence, and specifically, the power transmitter may seek to determine the received symbol as the symbol for which the detected load variation pattern most closely matches the chip sequence pattern for that symbol.

[0172] Thus, the data transmitter 509 may be arranged to receive data symbols to be transmitted to the power transmitter, typically from the power receiver controller 501, which may proceed to determine the corresponding chip sequence and load modulate the power transmission signal by a modulation loading pattern representing this chip sequence. Typically, the data symbols are binary, but in some cases, higher order modulation symbols (i.e., having more than two possible values) may be used. In some cases, such higher order data symbols may correspond to a combination of received data bits. For example, two bits may be combined into a single four-bit data symbol. This combination is possible when the data bits are related and when they are, for example, completely independent.

[0173] Longer chip sequences can provide improved noise suppression, etc., but can also reduce the data rate while increasing the symbol time for a given chip rate. Increased chip sequence length also increases complexity and resource requirements, especially at the receiver, where correlation with longer sequences can substantially require the required computations. A typical suitable value is N=5, and a chip length of 31 chips.

[0174] Fig.11 An example of how a power transfer signal may be load modulated by chips of a chip sequence is illustrated. In the example, the modulation is synchronized to the power transfer signal at a rate of one chip every two power signal periods. Fig.11 The arrows in indicate the time at which the load of the power transfer signal is then measured / sampled by the power transmitter to generate load samples that are then associated with a possible chip sequence. The sampling is synchronized with the power transfer signal and one sample is generated for each chip.

[0175] To determine the (binary) chip value, the sampled load value is compared to an average level 1101. In a specific example, the load of the power transmission signal is determined as a peak period value of the measured signal (specifically, it can be the current, voltage, phase or power of the power transmission signal), and the sampling is synchronized with the peak of the power transmission signal. In addition, the average level 1001 of the peak period value is first determined, and then the chip value is determined based on whether the measured sample value is above or below the average level 1101.

[0176] Fig.11 The example requires determining a reference level, and typically this can be determined as an average level. However, this may introduce some uncertainty and may result in some bit errors.

[0177] In some embodiments, each chip of the load modulation chip may be represented by a modulation loading transition that occurs during the chip. Thus, each load modulation chip includes at least two different modulation load values / values ​​of the variable load. For example, for differential data symbol modulation, individual chips may be modulated by a two-state transition method. For example, an on-chip value may be represented by a transition from a lower modulation loading to a higher modulation loading, while another chip value may be represented by a transition from a higher modulation loading to a lower modulation loading. In such an example, each chip sequence may be represented by a modulation loading pattern having two modulation loading values ​​for each chip.

[0178] This approach can provide significant advantages by allowing the receiver to determine the chip value simply by considering the difference between the two measured load values ​​for each chip. However, further, it can increase the switching rate and make this more predictable, thereby allowing an improved correspondence between switching operations in communication time intervals and non-communication time intervals.

[0179] The method of using such a direct sequence spread spectrum (DSSS) or differential direct sequence spread spectrum (D-DSSS) type method in the described system can provide many advantages. In particular, the method can allow for a substantial reduction in modulation depth (i.e., the magnitude of load changes), which can, for example, reduce electromagnetic noise and interference, can reduce acoustic noise, and can reduce spurious oscillations. In many embodiments, it can also produce an improved signal-to-noise ratio, and can produce substantially improved and generally more reliable communications (with, for example, generally lower bit error rates). Thus, an overall improved power transfer can be achieved.

[0180] In addition, in the described method, the use of such a chip sequence / modulation loading pattern can substantially reduce the switching noise / voltage variation. The use of such a longer sequence can reduce the modulation depth and can reduce the changes required for modulation loading. For example, a lower value of the switching capacitor can be achieved. This reduction can result in a smaller change in the resonant frequency / operating point, resulting in lower noise / variation. In addition, the method allows much higher modulation loading switching and actually requires it to maintain the same symbol rate. When the noise / voltage variation is extended over a larger frequency range including higher frequencies, faster switching can further reduce the noise / voltage variation. This causes the smoothing capacitor and its low-pass filtering effect to be more effective, thereby providing a reduced noise level.

[0181] Furthermore, the method may not only reduce noise and voltage variations during communication time intervals, but may also allow noise to be reduced during non-communication time intervals where modulation loading variations are also performed. In particular, the variations during non-communication time intervals may be arranged to have switching properties that match the switching properties of the communication time intervals (typically statistically or on average). In particular, higher frequency switching with lower modulation loading variations may be used, thereby substantially reducing switching noise.

[0182] Fig.12 and 13 The diagram shows Figure 7 and 8 The same method as in , but in which the load modulation uses chip sequence based load modulation with the same data rate. It can be seen that the switching noise during the communication time interval is greatly reduced. Fig.14 and 15 The corresponding results are shown for a load change performed during a non-communication time interval and having the same statistical / average properties as during a communication time interval. As shown, voltage changes including transient changes at the beginning and end of the communication time interval and switching noise during these time intervals can be substantially reduced, and even almost completely eliminated in some cases. Thus, substantially improved performance is achieved.

[0183] When using DSSS or DDSSS types, the switching during the non-communication time interval can therefore be arranged to have properties that reflect the modulation switching during the communication time interval. In particular, it can typically switch at least as frequently as during the communication time interval, and the variable load can be switched on average to have a time proportion that matches the communication time interval at each possible load value. Typically, the data symbol and code chip sequence is such that on average each possible load value is selected to have the same probability and / or the same time proportion. Binary load modulation typically causes the average modulation loading to be one modulation load for 50% of the time of the communication time interval and another modulation load for 50% of the time of the communication time interval. Switching during the non-communication time interval can also cause each of the modulation loading values ​​to be applied for 50% of the time.

[0184] In many embodiments, the number of load changes introduced by the data transmitter 509 during the load modulation chip sequence duration when in the non-communication time interval can be at least as many as the load changes that occur in the load modulation chip sequence. Thus, for a given duration of the chip sequence, typically corresponding to a symbol time, the number of loading transitions in the non-communication time interval is at least as many as would occur (on average) during a transmit data symbol in a communication time interval. Thus, switching during the non-communication time interval can be at least as frequent as switching during a DSSS transmit data symbol during a communication time interval. This can generally provide improved performance with reduced voltage variations.

[0185] The data transmitter 509 may be arranged to control switching during the non-communication time interval so that it does not include a modulation loading pattern that matches or is specifically the same as any load modulation chip sequence / modulation loading pattern for any possible data symbol value. The data transmitter 509 may specifically be arranged to avoid repeating any of the data symbol chip sequences. For the data receiver, this may reduce the risk of accidental detection and facilitate synchronization with the next communication time interval / data packet and / or detection of when the next communication time interval / data packet is received.

[0186] In many embodiments, the data transmitter 509 may be arranged to control the variable load to apply a repetitive loading variation pattern during the non-communication time interval. In some embodiments, the repetitive loading pattern may be a pattern having the same length as the data symbol chip sequence, but in other embodiments, they may be longer or shorter.

[0187] The repetitive loading variation pattern corresponds to a sequence of values ​​of a variable load / modulation loading that is repeated during a communication time interval. For example, the repetitive loading variation pattern may be a chip sequence, and in particular may be a sequence having the same timing properties as a data symbol chip sequence. For example, it may have the same length and have load transitions / changes at corresponding times (e.g., the load may only change at the beginning of a communication time interval, or in the middle of a chip duration in the case of using differential / modulation of each chip). For example, such an approach may allow for low complexity, since practically the same functionality may be used during a communication time interval and a non-communication time interval.

[0188] In many embodiments, the repetitive loading variation pattern is selected to have a low cross-correlation with the modulation chip sequence used to modulate the data symbols onto the power transfer signal during the communication time interval. Thus, the repetitive loading variation pattern can be selected to provide a clear distinction of the modulation chip sequence and reduce the probability that a data receiver may be confused. This approach can improve communications and facilitate, for example, detecting when a new data packet is transmitted. Continuous modulation / loading variation of the power transfer signal during the non-communication time interval using timing parameters that match the modulation during the communication time interval can also allow for improved synchronization.

[0189] In many embodiments, the repetitive loading variation pattern can be selected so that the cross-correlation is close to the average result when correlating the modulation code chip sequence and the random sequence. The reference correlation value can be determined as the average correlation between the modulation sequence data sequence and the random sequence. If the opposite data symbol value such as (1,1) is used, this correlation can generally be zero, or if the data symbol value such as (1,0) is used, it can be, for example, 0.5. In this case, the repetitive loading variation pattern can be determined / selected so that the maximum absolute difference between the cross-correlation of the repetitive loading variation pattern and the modulation sequence data sequence and the reference correlation is not greater than 50%, 20%, 10% or even 5% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation. For example, the repetitive loading variation pattern and the code chip sequence can be binary and represented by a binary value such as (1,0) or (-1,+1).

[0190] In some embodiments, the repeating load variation pattern is a pattern that periodically alternates between two modulation loads. The variable load may be a binary switchable load, and the data transmitter 509 may be arranged to periodically alternate between two values. For example, the switching may have a periodicity equal to the symbol time (e.g., for non-DSSS communications) or the chip time (e.g., for DSSS), or in some embodiments, a periodicity of half these durations (e.g., for differential load modulation).

[0191] This approach can generally allow a low complexity implementation. In addition, it can allow fast and symmetrical switching, which can reduce voltage variations. In addition, it can generally result in a sequence with very low correlation with the modulated load pattern (e.g., specifically with the chip sequence for DSSS).

[0192] In many embodiments, for example, the repetitive loading variation pattern may correspond to an alternating modulation of 1010101010... chips or bits and / or a continuous modulation of constant value chips or bits if differential communication is used.

[0193] In some embodiments, the modulation loading of the power transfer signal during the non-communication time interval may be randomly generated. For example, for each new chip or bit, a random value may be determined (eg, with a probability of 50%) and the power transfer signal modulated.

[0194] The method may provide improved load modulation operation, and in particular improve power transmission. In many scenarios, advantageous effects may be achieved, such as reduced voltage variations for the voltage provided to the load. In addition, the method may also provide advantages on the power transmitter side. It may allow improved synchronization, as this may be performed continuously and / or may, for example, facilitate detection of when a new data packet / communication time interval begins. In many embodiments, improved detection may also be provided, as more continuous load variations allow improved demodulation. For example, if an average reference level is used for demodulation, the continuous presence of load variations may provide an improved determination of such a reference level, and therefore provide improved data detection.

[0195] The modulated load may be a loaded load component of the power transmission signal / driving signal caused by / depending on / varying with load modulation.

[0196] It should be understood that, for the sake of clarity, the above description has described embodiments of the present invention with reference to different functional circuits, units and processors. However, it will be apparent that any suitable distribution of functions between different functional circuits, units or processors may be used without departing from the present invention. For example, functions shown as being performed by separate processors or controllers may be performed by the same processor or controller. Therefore, references to specific functional units or circuits are only considered references to suitable devices for providing the described functions, rather than indicating a strict logical or physical structure or organization.

[0197] The present invention can be implemented in any suitable form, including hardware, software, firmware or any combination of these. The present invention can be optionally implemented at least in part as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the present invention can be implemented physically, functionally and logically in any suitable manner. In fact, the function can be implemented in a single unit, in multiple units or as a part of other functional units. Like this, the present invention can be implemented in a single unit, or can be physically and functionally distributed between different units, circuits and processors.

[0198] Although the present invention has been described in conjunction with some embodiments, it is not intended to be limited to the specific forms set forth herein. On the contrary, the scope of the present invention is limited only by the appended claims. In addition, although features may appear to be described in conjunction with specific embodiments, those skilled in the art will recognize that the various features of the described embodiments may be combined according to the present invention. In the claims, the term includes does not exclude the presence of other elements or steps.

[0199] In addition, although listed separately, multiple devices, elements, circuits or method steps may be implemented by, for example, a single circuit, unit or processor. In addition, although individual features may be included in different claims, these features may be advantageously combined, and the inclusion in different claims does not imply that the combination of features is not feasible and / or advantageous. In addition, the inclusion of a feature in a claim category does not imply a limitation on the category, but rather indicates that the feature is equally applicable to other claim categories. The inclusion of a feature in a dependent claim of an independent claim does not imply a limitation on the independent claim, but rather indicates that the feature is equally applicable to other independent claims. In addition, the order of the features in the claims does not imply any particular order in which the features must work, and in particular the order of the individual steps in the method claims does not imply that the steps must be performed in this order. On the contrary, the steps may be performed in any suitable order. In addition, singular references do not exclude multiples. Therefore, references to "one", "one", "first", "second", etc. do not exclude multiples. The figure marks in the claims are provided only as clarification examples and should not be interpreted as limiting the scope of the claims in any way.

[0200] In general, examples of power receivers and methods are thus indicated by the following embodiments:

[0201] Example:

[0202] 1. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transfer signal, the power receiver (105) comprising:

[0203] an input circuit (107, 503) comprising a receiver coil (107) arranged to extract power from the power transfer signal;

[0204] a variable load (511) coupled to the input circuit and arranged to apply a modulated loading to the input circuit;

[0205] a data transmitter (509) arranged to transmit data symbols to the power transmitter (101) by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter (509) does not transmit data symbols;

[0206] The data transmitter (509) is further arranged to vary the variable load (511) to apply a modulation loading pattern for each data symbol transmitted during the communication time interval, each possible data symbol value being represented by a different modulation loading pattern for the modulation loading;

[0207] and

[0208] The data transmitter (509) is arranged to control the variable load (511) to repeatedly vary the modulation loading during the non-communication time interval.

[0209] 2. A power receiver according to claim 1, wherein the data transmitter (509) is arranged to control the variable load (511) to repeatedly change the modulation loading during the non-communication time interval so that the difference between the average modulation loading during the non-communication time interval and the average modulation loading during the non-communication time interval is less than 10% of the maximum modulation loading change during the communication time interval.

[0210] 3. A power receiver according to claim 1 or 2, wherein the data transmitter (509) is arranged to control the variable load (511) to repeatedly change the modulation loading during the non-communication time interval so that the average time between the modulation loading changes during the non-communication time interval is not less than 50% of the average time between the modulation loading changes during the non-communication time interval.

[0211] 4. A power receiver according to any preceding claim, wherein the modulation loading pattern for each possible data symbol value comprises at least two different loading values.

[0212] 5. A power receiver according to any one of the preceding claims 1 to 3, wherein the modulation loading pattern for each possible data symbol value comprises a load modulation chip sequence of at least five load modulation chips.

[0213] 6. A power receiver according to claim 5, wherein the data transmitter (509) is arranged to repeatedly change the modulation loading during non-communication time intervals so as not to include a modulation loading pattern corresponding to any load modulation chip sequence.

[0214] 7. A power receiver according to claim 5 or 6, wherein each chip of the load modulation chip sequence is represented by a modulation loading transition.

[0215] 8. The power receiver according to any one of claims 5 to 7, wherein the number of modulation loading changes during the load modulation chip sequence duration in the non-communication time interval is not less than the maximum number of modulation loading changes in the load modulation chip sequence.

[0216] 9. A power receiver according to any of the preceding claims, wherein the data transmitter (509) is arranged to control the variable load (511) to apply a repetitive loading variation pattern during the non-communication time interval.

[0217] 10. The power receiver of claim 9, wherein the repetitive loading variation pattern is a periodic alternation between two modulated loads.

[0218] 11. A power receiver according to claim 9 or 10 referring to any one of claims 5 to 8, wherein the maximum absolute difference between the cross-correlation of the repetitive loading variation pattern with the modulation sequence data sequence and a reference correlation is no greater than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0219] 12. A power receiver according to any preceding claim, wherein the data transmitter (509) is arranged to control the variable load (511) to exclude any modulation loading pattern representing data symbols during non-communication time intervals.

[0220] 13. A power receiver according to any of the preceding claims, wherein the data transmitter (509) is arranged to switch the variable load (511) between two modulation loading values.

[0221] 14. A wireless power transmission system comprising a power transmitter (101) and a power receiver (105) according to any one of the preceding claims.

[0222] 15. A method of operating a power receiver (105) to wirelessly receive power from a power transmitter (101) via an electromagnetic power transfer signal, the method comprising:

[0223] an input circuit (107, 503) comprising a receiver coil (107) that extracts power from the power transfer signal;

[0224] a variable load (511) coupled to the input circuit, the input circuit applying a modulation loading to the input circuit (107, 503);

[0225] a data transmitter (509) transmitting data symbols to the power transmitter (101) by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter (509) does not transmit data symbols;

[0226] The method further comprises:

[0227] varying the variable loading to apply a modulation loading pattern for each data symbol transmitted during the communication time interval, each possible data symbol value being represented by a different modulation loading pattern for the modulation loading;

[0228] as well as

[0229] The variable load (511) is controlled to repeatedly vary the modulation loading during the non-communication time interval.

Claims

1. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transfer signal, the power receiver (105) comprising: an input circuit (107, 503) comprising a receiver coil (107) arranged to extract power from the power transfer signal; a variable load (511) coupled to the input circuit and arranged to apply a modulated loading to the input circuit; a data transmitter (509) arranged to transmit data symbols to the power transmitter (101) by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter (509) does not transmit data symbols; The data transmitter (509) is further arranged to vary the variable load (511) to apply a modulation loading pattern for each data symbol transmitted during the communication time interval, each possible data symbol value being represented by a different modulation loading pattern for the modulation loading; and The data transmitter (509) is arranged to control the variable load (511) to repeatedly vary the modulation loading during non-communication time intervals; Wherein, the data transmitter is arranged to control the variable load (511) to apply a repeated loading variation pattern during the non-communication time interval, and the maximum absolute difference between the cross-correlation of the repeated loading variation pattern and the reference correlation of the modulation sequence data sequence is not greater than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

2. The power receiver according to claim 1, wherein: The data transmitter (509) is arranged to control the variable load (511) to repeatedly change the modulation loading during the non-communication time interval so that the difference between the average modulation loading during the non-communication time interval and the average modulation loading during the non-communication time interval is less than 10% of the maximum modulation loading change during the communication time interval.

3. The power receiver according to claim 1 or 2, wherein: The data transmitter (509) is arranged to control the variable load (511) to repeatedly change the modulation loading during the non-communication time interval so that the average time between the modulation loading changes during the non-communication time interval is not less than 50% of the average time between the modulation loading changes during the non-communication time interval.

4. A power receiver according to any preceding claim, wherein: The modulation loading pattern for each possible data symbol value comprises at least two different loading values.

5. A power receiver according to any one of the preceding claims 1 to 3, wherein: The modulation loading pattern for each possible data symbol value comprises a load modulation chip sequence of at least five load modulation chips.

6. The power receiver according to claim 5, wherein: The data transmitter (509) is arranged to repeatedly change the modulation loading during non-communication time intervals so as not to include a modulation loading pattern corresponding to any load modulation chip sequence.

7. The power receiver according to claim 5 or 6, wherein: Each chip of the load modulation chip sequence is represented by a modulation loading transition.

8. The power receiver according to any one of claims 5 to 7, wherein: The number of modulation loading changes during the load modulation chip sequence duration in the non-communication time interval is not less than the maximum number of modulation loading changes in the load modulation chip sequence.

9. A power receiver according to any preceding claim, wherein: The repetitive loading variation pattern is a periodic alternation between two modulation loadings.

10. A power receiver according to any preceding claim, wherein: The data transmitter (509) is arranged to control the variable load (511) to exclude any modulation loading pattern representing data symbols during non-communication time intervals.

11. A power receiver according to any preceding claim, wherein: The data transmitter (509) is arranged to switch the variable load (511) between two modulation loading values.

12. A wireless power transfer system comprising a power transmitter (101) and a power receiver (105) according to any one of the preceding claims.

13. A method of operating a power receiver (105) to wirelessly receive power from a power transmitter (101) via an electromagnetic power transfer signal, the method comprising: An input circuit (107, 503) including a receiver coil (107) extracts power from the power transfer signal; A variable load (511) coupled to the input circuit applies a modulated loading to the input circuit (107, 503); a data transmitter (509) transmitting data symbols to the power transmitter (101) by load modulating the power transfer signal during communication time intervals interspersed by non-communication time intervals, during which the data transmitter (509) does not transmit data symbols; The method further comprises: varying the variable loading to apply a modulation loading pattern for each data symbol transmitted during the communication time interval, each possible data symbol value being represented by a different modulation loading pattern for the modulation loading; as well as controlling the variable load (511) to repeatedly vary the modulation loading during non-communication time intervals; Wherein, the data transmitter (509) controls the variable load (511) to apply a repeated loading variation pattern during the non-communication time interval, and the maximum absolute difference between the cross-correlation of the repeated loading variation pattern and the modulation sequence data sequence and the reference correlation is no more than 50% of the maximum absolute difference between the autocorrelation of the modulation sequence data sequence and the reference correlation, and the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

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