Wireless Power Transmission

Abstract

The power receiver 105 includes an input circuit 107, 503 having a receiver coil 107 that extracts power from the power transmission signal generated by the power transmitter 101. A variable load 511 applies a modulation load to the 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 communication time intervals that are scattered during non-communication time intervals when data symbols are not being transmitted. The data symbols are represented by a modulation load pattern, and the data transmitter 509 is configured to control the variable load 511 to repeatedly change the modulation load during non-communication time intervals. This approach can provide improved communication and power transmission operations, and in particular, can reduce transients, for example, in the supply voltage supplied to the load of the power receiver 105.

Description

Technical Field

[0001] The present invention relates to wireless power transmission, and in particular, but not limited to, communication in a power transmission system such as the Qi or Ki wireless power transmission standard.

Background Art

[0002] Most current electrical products require dedicated electrical contacts to supply power from an external power source. However, this tends to be impractical and requires the user to physically insert a connector or otherwise establish a physical electrical contact. Typically, the power requirements also vary widely, and currently, most devices are provided with a dedicated power source, and as a result, a typical user will have a number of different power sources, each power source being specific to a particular device. However, the use of a built-in battery can avoid the need for a wired connection to a power source during use, but this only provides a partial solution as it requires battery recharging (or replacement). Also, using a battery can substantially increase the weight and potential cost and size of the device.

[0003] To provide a significantly improved user experience, it has been proposed to use a wireless power source in which power is inductively transmitted from a transmitter coil in a power transmission device to a receiver coil in an individual device.

[0004] Power transmission through magnetic induction is a well-known concept and is mostly applied to transformers having a tight coupling between a primary transmitter inductor / coil and a secondary receiver coil. By separating the primary transmitter coil and the secondary receiver coil between two devices, wireless power transmission between them becomes possible based on the principle of a loosely coupled transformer.

[0005] Such a configuration enables wireless power transmission to the device without the need for a wired or physical electrical connection. In fact, to recharge or supply power from an external source, the device can simply be placed adjacent to or on the transmitter coil. For example, the power transmitter can be configured to have a horizontal plane on which the device can simply be placed to supply power.

[0006] Furthermore, such a wireless power transmission configuration can be advantageously designed to be used with a range of power receivers by the power transmitter. In particular, a wireless power transmission approach known as the Qi standard has been defined and is currently being further developed. This approach allows power transmitter devices that meet the Qi standard to be used with power receiver devices that meet the Qi standard, without the need for them to be from the same manufacturer or to be dedicated to each other. The Qi standard further includes several features to enable operation to be adapted to a particular power receiver (e.g., depending on a particular power drain).

[0007] The Qi standard is developed by the Wireless Power Consortium, and its information can be found, for example, on its website at http: / / www.wirelesspowerconsortium.com / index.html, and in particular, the defined specification can be found.

[0008] Based on the Qi standard, an approach known as the Ki standard has been developed, particularly for high-power applications such as for kitchen appliances.

[0009] To support efficient wireless power transmission, a wireless power transmission system, such as a Qi-based system, utilizes substantial communication between the power transmitter and the power receiver. Initially, Qi supported only communication from the power receiver to the power transmitter using load modulation of the power transmission signal. Thus, initial Qi devices support only one-way communication from the power receiver to the power transmitter.

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

[0011] However, the development of the standard has introduced two-way communication, and many functions are supported by communication exchanges between the power receiver and the power transmitter. In many systems, communication from the power transmitter to the power receiver is achieved by modulating the power transmission signal.

[0012] In some systems, it has been proposed to use separate dedicated communication functions, such as Bluetooth® or NFC (Near Field Communication)-based communication. However, while such an approach tends to provide efficient operation in many scenarios, it is associated with several drawbacks, including the need for dedicated complex communication circuitry and potentially reducing the confidence that the power transmitter is actually communicating with the power receiver being powered. Also, backward compatibility with, for example, Qi-based devices can be a problem for newer devices based on separate communication.

[0013] However, communicating using load modulation of the power transmission signal that transmits power to the power receiver tends to have several associated drawbacks. For example, load modulation tends to introduce some electrical noise, including both noise to the device's signal and radiated electromagnetic noise. Load modulation can sometimes increase electromagnetic interference to other devices, and it has been found to be difficult to maintain sufficient or optimal electromagnetic compatibility.

[0014] It has also been found that, in practice, load modulation can introduce unwanted spurious oscillations into the drive signal and the power transmission signal. The power transmission path in a wireless power transmission system tends to include a significant amount of inductance and tends to exhibit resonant behavior. Therefore, load modulation tends to affect the power transmission path and, in fact, the communication path. Therefore, load modulation also results in noise and interference (self-interference) to the communication itself. This is very different from other communication systems where random noise or interference from other transmissions is the main cause of bit errors.

[0015] Another drawback is that load modulation of the power transmission signal can result in acoustic noise. Such noise can arise from the effect of the variations in the electromagnetic field caused by load modulation on mechanical elements, specifically, it can move and vibrate the mechanical elements, potentially generating acoustic noise.

[0016] In some cases, for example, the load modulation communication used in the initial version of the Qi standard may not have complete reliability and, in some cases, some bit errors may occur. For example, high levels of noise or self-interference may result in bit errors and / or may require an increase in the modulation level that can result in an increase in electrical or acoustic noise arising from load modulation.

[0017] Load modulation can also potentially affect the power transmission operation, particularly the operating point for power transmission. This can result in unwanted variations in the power transmission operation and performance.

[0018] In some ways, it may be desirable to maintain backward compatibility or change to a different communication approach that reduces the amount of change required for existing designs and approaches, but this is often a major issue that is not very attractive. SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

[0019] Therefore, an improved approach, particularly, an increase in flexibility, a reduction in cost, a reduction in complexity, an improvement in power transmission operation, an improvement in reliability, a reduction in communication errors, an improvement in backward compatibility, an improvement in electromagnetic compatibility, a reduction in electrical and / or acoustic noise, an improvement in communication, a more stable improvement in power transmission, a reduction in power transmission fluctuations, an improvement in stability, and / or an improvement in performance would be advantageous.

[0020] Therefore, the present invention preferably attempts to alleviate, reduce or eliminate one or more of the above-mentioned drawbacks, either alone or in any combination.

Means for Solving the Problems

[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 transmission signal. The power receiver includes an input circuit including a receiver coil configured to extract power from the power transmission signal, a variable load coupled to the input circuit and configured to apply a modulation load to the input circuit, and a data transmitter configured to transmit data symbols to the power transmitter by load-modulating the power transmission signal during communication time intervals sandwiched between non-communication time intervals during which no data symbols are transmitted by the data transmitter. The data transmitter is further configured to vary the variable load to apply a modulation load pattern for each data symbol transmitted during the communication time interval, and each possible data symbol value is represented by a different modulation load pattern of the modulation load. The data transmitter is configured to control the variable load to repeatedly change the modulation load during the non-communication time interval. The data transmitter is configured to control the variable load to apply a repetitive load variation pattern during the non-communication time interval, and the maximum absolute difference between the cross-correlation and the reference correlation of the repetitive load variation pattern and the modulation sequence data sequence is 50% or less of the maximum absolute difference between the autocorrelation and the reference correlation of the modulation sequence data sequence. The reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0022] The present invention can enable improved performance in many embodiments, and in particular, can enable improved communication between a power receiver and a power transmitter in many embodiments. This approach facilitates or enables improved power transmission in many embodiments.

[0023] This approach enables the reduction of the impact of load modulation on power transmission performance and operation in many scenarios. In many embodiments, fluctuations in the characteristics and operation of the input circuit when extracting power from the power transmission signal are reduced. In many embodiments, more consistent operation can be achieved. Reduction of voltage fluctuations for the load supplied by the power receiver is achieved in many scenarios.

[0024] During non - communication time intervals, there may be no communication of information data from the power receiver to the power transmitter. In some embodiments, the data transmitter can be configured to control the variable load during non - communication time intervals such that the resulting modulated load does not match the modulated load pattern representing the possible data symbol values.

[0025] During communication time intervals, the data transmitter 509 can be configured to vary the variable load such that the modulated load pattern represents the data symbol value of the data symbol. Each possible data symbol value can be represented / linked by one modulated load pattern, and the modulated load patterns are different for each data symbol value. The data transmitter can be configured to transmit the first symbol value by controlling the variable load to apply the modulated load pattern linked to the first symbol value.

[0026] The modulated load is determined by the load value of the variable load. The variable load may be a modulated load to which load modulation is applied to the power transmission signal by the variation of the variable load. The modulated load may be (part of) the load of the power transmission signal that changes according to the data symbol being transmitted.

[0027] Each communication time interval corresponds to the time interval during which a data packet is transmitted from the power receiver to the power transmitter. Each non - communication time interval corresponds to the time interval between communication time intervals. Each non - communication time interval corresponds to the time interval during which a data packet is not transmitted from the power receiver to the power transmitter.

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

[0029] This can provide improved performance in many embodiments. This can ensure low voltage fluctuations of the induction signal and the supply voltage to the load in many scenarios. This approach can reduce, mitigate or in some cases substantially eliminate the transient effects at the characteristics or operating points that occur at the start of the communication time interval.

[0030] In some embodiments, the load change during the non - communication time interval can be such that the average modulation load during the non - communication time interval is the same as the average modulation load during the communication time interval. In some embodiments, the average difference varies by 2% or less, 5% or less, or 20% or less of the maximum modulation load during the communication time interval.

[0031] According to an optional feature of the present invention, the data transmitter is configured to control the variable load to repeatedly change the modulation load during the non - communication time interval such that the average time between the modulation load changes during the non - communication time interval is 50% or more of the average time between the modulation load changes during the non - communication time interval.

[0032] This can provide improved performance in many embodiments. This reduces the voltage fluctuations of the supply voltage with respect to the induction signal and the load in many scenarios.

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

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

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

[0036] This enables improved performance in many embodiments.

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

[0038] This enables improved performance in many embodiments.

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

[0040] This enables improved performance in many embodiments.

[0041] This feature can enable improved communication and, in many embodiments, can enable an improved trade - off between different parameters and operating characteristics. This approach, for example, enables reliable communication while allowing a reduced modulation depth to be used. This approach reduces electrical noise (such as modulation switching noise) and / or electromagnetic interference and enables improved electromagnetic compatibility. This approach can often reduce or prevent acoustic noise. This can reduce voltage fluctuations in the load supply voltage during communication time intervals and / or non - communication time intervals in many embodiments.

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

[0043] In many embodiments, the length of the chip sequence is 5 chips or more and 1024 chips or less.

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

[0045] This enables improved performance in many embodiments. According to an optional feature of the present invention, the number of modulated load changes during the load modulation chip sequence period in a non-communication time interval is greater than or equal to the maximum number of modulated load changes in the load modulation chip sequence.

[0046] This enables improved performance in many embodiments.

[0047] The data transmitter is configured to control a variable load to apply a repetitive load variation pattern during a non-communication time interval.

[0048] This enables improved performance in many embodiments.

[0049] According to an optional feature of the present invention, the repetitive load variation pattern periodically alternates between two modulated loads.

[0050] This enables improved performance in many embodiments.

[0051] The maximum absolute difference between the cross-correlation and the reference correlation between the repetitive load variation pattern and the modulation sequence data sequence is 50% or less of the maximum absolute difference between the autocorrelation and the reference correlation of the modulation sequence data sequence, where the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0052] This enables improved performance in many embodiments.

[0053] According to an optional feature of the present invention, the data transmitter is configured to control the variable load so as not to include a modulation load pattern representing data symbols during non - communication time intervals.

[0054] This enables improved performance in many embodiments.

[0055] According to an optional feature of the present invention, the data transmitter is configured to switch the variable load between two modulation load values.

[0056] This enables improved performance in many embodiments.

[0057] According to an optional feature of the present invention, claim 14 is provided.

[0058] According to one aspect of the present invention, there is provided a method of operating a power receiver that wirelessly receives power from a power transmitter via an electromagnetic power transmission signal. The method includes: extracting power from the power transmission signal by an input circuit including a receiving coil; applying a modulated load to the input circuit by a variable load coupled to the input circuit; and transmitting a data symbol to the power transmitter by the data transmitter by load-modulating the power transmission signal during a communication time interval sandwiched between non-communication time intervals in which no data symbol is transmitted by the data transmitter. The method further includes changing the variable load to apply a modulation load pattern to each data symbol transmitted during the communication time interval, wherein each data symbol value is represented by a different modulation load pattern for the modulated load; and controlling the variable load to repeatedly change the modulated load during non-communication time intervals. The data transmitter controls the variable load to apply a repetitive load variation pattern during non-communication time intervals, and the maximum absolute difference between the cross-correlation and the reference correlation between the repetitive load variation pattern and the modulation sequence data sequence is 50% or less of the maximum absolute difference between the autocorrelation and the reference correlation of the modulation sequence data sequence. The reference correlation is the average correlation between the modulation sequence data sequence and a random sequence.

[0059] These and other aspects, features, and advantages of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter.

Brief Description of the Drawings

[0060] Embodiments of the present invention are described by way of example only with reference to the drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0061] The following description focuses on embodiments of the present invention applicable to a high-power wireless power transmission system that utilizes a power transmission approach known from the Qi standard document or the Ki standard document. However, it will be understood that the present invention is not limited to this application and may be applied to many other wireless power transmission systems.

[0062] FIG. 1 shows an example of a power transmission system according to some embodiments of the present invention. The power transmission system includes a power transmitter 101 that includes (or is coupled to) a transmitter coil / inductor 103. The system further includes a power receiver 105 that includes (or is coupled to) a receiver coil / inductor 107.

[0063] The system provides an inductive electromagnetic power transmission signal that can inductively transmit power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal, which is propagated as a magnetic flux by the transmitter coil or inductor 103. The power transmission signal can typically have a frequency between about 20 kHz and about 500 kHz, and in many practical systems, it can be about 120 - 150 kHz. The transmitter coil 103 and the receiver coil 107 are loosely coupled, and thus the receiver coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Accordingly, power is transmitted from the power transmitter 101 to the power receiver 105 via a wireless inductive coupling from the transmitter coil 103 to the receiver coil 107. The term power transmission signal is mainly used to refer to the inductive signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the receiver coil 107, but equivalently, it can be considered and used to refer to the electrical signal supplied to the transmitter coil 103 or extracted by the receiver coil 107, as will be understood.

[0064] In an embodiment, the power receiver 105 is a power receiver that receives power specifically via the receiver coil 107. However, in other embodiments, the power receiver 105 may include a metal element such as a metal heating element, in which case the power transmission signal directly induces eddy currents that cause direct heating of the element.

[0065] In the following, the operation of the power transmitter 101 and the power receiver 105 will be described specifically with reference to embodiments that generally comply with the Qi or Ki standard (excluding modifications or extensions described (or necessarily) in this specification). Many wireless power transfer systems utilize resonant power transfer where the transmitter coil 103 is part of a resonant circuit and typically the receiver coil 107 is also part of a resonant circuit. In many embodiments, the resonant circuit can be a series resonant circuit, and thus, the transmitter coil 103 and the receiver coil 107 can be coupled in series with corresponding resonant capacitors. The use of resonant circuits tends to provide more efficient power transfer.

[0066] Typically, a wireless power transfer system uses a power control loop to direct the system to an appropriate operating point. This power control loop varies the amount of power transmitted from the power transmitter to the power receiver. The received power (or voltage or current) can be measured and, based on a set power value, an error signal can be generated. The power receiver sends this error signal to the power control function of the power transmitter, ideally reducing this static error to zero.

[0067] FIG. 2 shows the elements of the power transmitter 101 of FIG. 1 in more detail.

[0068] The power transmitter 101 includes a driver 201 that can generate a drive signal supplied to the transmitter coil 103, which in turn generates an electromagnetic power transfer signal, thereby providing 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 this example, the output resonant circuit is a series resonant circuit, but it will be understood that in other embodiments the output resonant circuit can be a parallel resonant circuit. It will be understood that any suitable resonant circuit can be used, including those that use multiple inductors and / or capacitors.

[0069] Driver 201 generates the current and voltage supplied to the output resonant circuit and thus to the transmitter coil 103. The driver 201 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 201 is usually a switch bridge that generates a drive signal by appropriate switching of the switches of the switch bridge. FIG. 3 shows a half-bridge switch bridge / inverter. Switches S1 and S2 are controlled so as not to close simultaneously. Alternately, S1 is closed while S2 is open, and S2 is closed while S1 is open. The switches are opened and closed at a desired frequency, thereby generating an AC signal at the output. Typically, the output of the inverter is connected to the transmitter inductor via a resonant capacitor. FIG. 4 shows a full-bridge switch bridge / inverter. Switches S1 and S2 are controlled so as not to close simultaneously. Switches S3 and S4 are controlled so as not to close simultaneously. Alternately, S1 and S4 are closed while S2 and S3 are open, and S2 and S3 are closed while S1 and S4 are open, thereby generating a square wave signal at the output. The switches are opened and closed at a desired frequency.

[0070] The power transmitter 101 further includes a power transmitter controller 205 configured to control the operation of the power transmitter 101 according to a desired operating principle. Specifically, the power transmitter 101 can include many functions required to perform power control according to the Qi or Ki standard.

[0071] The power transmitter controller 205 is particularly configured to control the generation of the drive signal by the driver 201 and, in particular, can control the power level of the drive signal and thus the level of the generated power transmission signal. The power transmitter controller 205 includes a power loop controller that controls the power level of the power transmission signal in response to a power control message received from the power receiver 105 during the power transmission phase.

[0072] The power transmitter 101 further includes a data receiver 207 configured to receive data transmitted from the power receiver 105 to the power transmitter 101. The data is transmitted by load modulation, where the power receiver 105 changes the load of the power transmission signal according to the communicated data symbol. The data receiver 207 is coupled to the output circuits 103, 203 and is configured to detect variations in the load of the power transmission signal. The data receiver 207 is configured to determine the received data symbol based on the measured load value. It will be understood that many different approaches for receiving load modulation are known to those skilled in the art.

[0073] The received data symbol is supplied from the data receiver 207 to a power transmitter controller 205 that can adapt the operation of power transmission according to this data. For example, power error data can be received, and the power transmitter controller 205 can adapt the power level of the drive signal, thereby implementing a power control loop with the power receiver 105.

[0074] FIG. 5 shows some exemplary elements of the power receiver 105. In this example, the receiver coil 107 is coupled to a power receiver controller 501 via a capacitor 503 that forms an input resonant circuit together with the receiver coil 107. Thus, power transmission can be resonant power transmission between resonant circuits. In other embodiments, only one of the power receiver and the power transmitter can utilize a resonant circuit for power transmission, or neither can utilize it.

[0075] 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 supply suitable for the load 505. In some embodiments, the power receiver controller 501 can provide a direct power path that simply connects the input resonant circuit to the switch 507 or the load 505, that is, the power path of the power receiver controller 501 can be implemented simply by two wires. In other embodiments, the power path can include, for example, a rectifier and, optionally, a smoothing capacitor to supply a DC voltage. In still other embodiments, the power path can include more complex functions such as, for example, a voltage control circuit, an impedance matching circuit, a current control circuit, and the like. Similarly, the switch 507 may only be present in some embodiments, and it will be understood that in some embodiments the load 505 can be permanently coupled to the input resonant circuit.

[0076] Furthermore, the power receiver controller 501 can include various power receiver controller functions required to perform power transmission, particularly functions required to perform power transmission in accordance with the Qi or Ki standard.

[0077] The power receiver 105 is configured to transmit data to the power transmitter 101. Such data can include, in particular, power control loop error messages used to implement a feedback power loop for controlling the power level of the power transmission signal during power transmission, as is known to those skilled in the art. The power receiver can, in many embodiments, transmit various different messages for different purposes, as is known to those skilled in the art. For example, various different messages as defined by the Qi standard can be transmitted. The message can include one or more data bits / symbols.

[0078] The power receiver is configured to transmit a message to the power transmitter using load modulation.

[0079] As is well known to those skilled in the art, for load modulation, a change in the load of the power transmission signal can be introduced by the power receiver, where this change follows the data value to be transmitted. And these changes can be detected by the power transmitter to decode the data from the power receiver.

[0080] Load modulation can be used as a method for the power receiver to communicate control messages or other data to the power transmitter, for example, in accordance with the Qi wireless power standard.

[0081] Typically, there are two main ways to perform load modulation, namely, directly changing the resistive load / power extraction of the input circuit and / or detuning the resonance of the input circuit by changing the reactive load of the input circuit (typically inserting / removing a capacitor along the data to be transmitted). A similar approach can be used by the power receiver to load modulate the power transmission signal. Thus, load modulation can use real load changes and / or reactive load changes.

[0082] Correspondingly, in the power transmitter, a detection approach such as those known for Qi standard systems can be used to detect load fluctuations. For example, a direct measurement of the power level or current amplitude of the drive signal can be used as an indicator of the load and thus the load modulation fluctuations introduced by the power receiver.

[0083] The power receiver 105 includes a data transmitter 509 configured to transmit data to the power transmitter 101 by load modulating the power transmission signal.

[0084] In this example, the data transmitter 509 is configured to control a variable load 511 that provides a modulation load for the power transmission 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 (real power and / or reactive power) changes, and thus the load on the power transmission signal by the receiver coil 107 changes. The load on the receiver coil 107 / power transmission signal depends on the value of the variable load. Specifically, a change in the value of the variable load results in a change in the load on the power transmission signal. The data transmitter 509 is configured to load-modulate the power transmission signal by changing the value of the variable load and thereby changing the modulation load of the power transmission signal. The modulation load is the variable load of the power transmission signal that provides load modulation of the power transmission signal. The modulation load can be considered to be / is / corresponds to / represents the load and / or impedance value of the variable load.

[0085] Accordingly, the data transmitter 509 is configured to change the value of the variable load in accordance with the data symbol value being transmitted, thereby providing a changing modulation load for the power transmission signal.

[0086] The data transmitter 509 is coupled to the variable load 511 and is configured to change it in accordance with the data symbol to be transmitted. Accordingly, the data transmitter 509 is configured to change the variable load to provide a modulation load for the power transmission signal. Specifically, the data transmitter 509 can be configured to provide a modulation load pattern for each data symbol, and the modulation load pattern depends on the data symbol value. The modulation load patterns are different for different data symbol values. Accordingly, the power transmitter can determine the data symbol value by estimating the modulation load pattern of the power transmission signal and, based on this detected modulation load pattern, selecting, for example, the data symbol value that is most likely to have resulted in the received load pattern (maximum likelihood demodulation).

[0087] In many embodiments, the variable load may be a binary variable load having two possible load values. Further, in many embodiments, the variable load may be a pure resistive load or a pure reactive load. For example, the variable load may be a resistor or a capacitor that can be switched (e.g., substantially switched on / off) between being disconnected from and coupled to the input circuit. The data transmitter 509 can be configured to control a switch that switches the resistor / capacitor in / out.

[0088] For example, the data transmitter 509 can be configured to switch a communication capacitor (or other impedance) in / out, for example, arranged in parallel with the power receiver controller 501 or the resonant capacitor 503, thereby changing the resonant frequency and the load of the power transmission signal.

[0089] The modulation load pattern can be a very simple pattern in some embodiments and, in fact, can correspond to a single constant value in some embodiments. For example, binary modulation can be achieved by switching the load impedance in or out depending on the data symbol value modulated on the power transmission signal. For example, in the case of the value "1", the modulation capacitor is switched out of the input circuit (not coupled to the input circuit) throughout the symbol duration, and in the case of the value "0", the modulation capacitor can be switched into the input circuit (coupled to the input circuit) throughout the symbol duration. However, in many embodiments, each data symbol is typically represented by a more complex modulation load pattern, and the modulation load pattern includes at least two different modulation load levels in many embodiments.

[0090] The data transmitter 509 can be coupled to the power receiver controller 501 and configured to receive data from the power receiver controller 501 for transmission to the power transmitter 101.

[0091] For example, the data transmitter 509 can receive power error control data from the power receiver controller 501 and transmit the corresponding power error control message to the power transmitter 101 using load modulation. During operation, the system is typically configured to control the drive signal such that the power transmission signal achieves appropriate operating parameters / characteristics and the power transmission operates at an appropriate operating point. To do so, the power transmitter is configured to control the parameters of the drive signal using a power control loop in which the power characteristics of the power transmission signal / drive signal are controlled in response to the power control error message received from the power receiver.

[0092] The power path of the power receiver can specifically have a simplified equivalent circuit corresponding to the circuit shown in FIG. 6. The input circuits 107, 503 are coupled to a rectifier 601, and the output of the rectifier 601 is coupled to a smoothing capacitor 603. The load 505 is coupled to the smoothing capacitor 603.

[0093] Accordingly, the output level, particularly the voltage supplied to the load, directly depends on the level / electromagnetic field strength of the power transmission signal. The power control loop implemented by the power control loop provides continuous and dynamic adaptation of the level of the power transmission signal to provide the desired power to the load. For example, the voltage across the smoothing capacitor can be measured, and if it falls below a low threshold, a power up message can be sent to the power transmitter 101 to increase the level of the power transmission signal. If the capacitor voltage increases beyond a high threshold, a power down message is sent to the power transmitter 101, and as a result, the level of the power transmission signal is reduced.

[0094] However, although load modulation is an effective communication technique for wireless power transmission systems, the inventors have recognized that it also has some drawbacks, particularly that the communication approach may interfere with the power transmission operation. Specifically, load modulation may cause fluctuations in the signal extracted by the input circuit, which may result in fluctuations in the power / voltage supplied to the load.

[0095] Figures 7 and 8 show examples of voltages that can be supplied to load 505 for the power path as shown in FIG. 6. In most wireless power transfer systems, data is transmitted in data packets, and FIG. 7 shows an example in which such data packets are transmitted by switching so that 10 nF modulation capacitors are each disconnected from the output of the input circuit and then coupled thereto. FIG. 7 shows an example of an 18 V, 30 W load, which has a relatively high coupling, and FIG. 8 shows an example of a 7 V, 0.1 W load, which has a relatively low coupling.

[0096] In this example, it can be seen that load modulation data packets cause voltage (and thus power) fluctuations in what is provided to the load. In some applications such voltage fluctuations are acceptable, but in many practical applications they are highly undesirable. Voltage fluctuations can, for example, introduce noise or, in some cases, cause malfunction of the device or apparatus powered by power receiver 105 (i.e., the device or apparatus that is load 505 with respect to power receiver 105).

[0097] The inventors have recognized in particular that voltage fluctuations can be caused by different effects and that different approaches can be applied to reduce various aspects of voltage fluctuations.

[0098] The approaches described in FIGS. 1, 2 and 5 can include functions for improving power transfer and, in many scenarios, can reduce voltage fluctuations, for example, when load modulation is used for communication from the power receiver to the power transmitter.

[0099] In this approach, data communication is performed in communication time intervals that are interspersed during non-communication time intervals when data symbols / information data are not transmitted from the power receiver to the power transmitter.

[0100] In this approach, data symbols are communicated to the power transmitter during communication time intervals using load modulation. Thus, during the communication time intervals, the data transmitter 509 is configured to vary a variable load to apply a modulated load pattern to the input circuit / power transmission signal, and the modulated load pattern depends on the data symbol values being transmitted. Each possible data symbol is linked to a modulated load pattern, and when transmitting a particular data symbol value, the data transmitter 509 reads out the modulated load pattern linked to this data symbol value and supplies this to the data transmitter 509, and the data transmitter 509 can proceed to vary the variable load accordingly. Specifically, in many embodiments, the variable load is binary, and the data transmitter 509 can be configured to switch between two load values, for example, by switching a modulation capacitor, according to the modulated load pattern. The modulated load pattern is different for different data symbol values.

[0101] In some embodiments, the modulated load pattern may be a simple constant load corresponding to a variable load that does not change during the duration of the data symbol. For example, in the case of a binary data symbol, one value can be represented by a modulation capacitor switched into the input resonant circuit, and the other value can be represented by a modulation capacitor switched out of this circuit.

[0102] In other embodiments, the modulated load pattern can include a plurality of different sub-intervals, and the variable load can be switched between different sub-intervals.

[0103] As a specific example, in some embodiments, the modulated load pattern for each possible data symbol value can include at least two different load values. For example, a communication approach can be used that provides binary communication where one binary value is represented by a load transition from a high load to a low load, and the other binary value is represented by a load transition from a low load to a high load.

[0104] During the communication time interval, multiple data symbols, specifically bits, can be transmitted, and often data packets are transmitted. In many embodiments, the communication time interval can have a duration of 1 μsec or more and 1 msec or less. In many embodiments, 24 bits or more, and in some cases 48 bits or less, can be transmitted during each communication time interval.

[0105] Accordingly, during the communication time interval, load modulation is used to communicate data from the power receiver to the power transmitter, and thus multiple, often many, load transitions occur. Typically, these occur relatively quickly / frequently, and in many embodiments, the load transitions are such that the average load / value of the variable load is substantially the same for all communication time intervals, and in some cases even for each modulation load pattern.

[0106] In the approach being described, during non-communication time intervals, data symbols and information are not communicated. However, even though there is no communication of information, the data transmitter 509 is configured to control a variable load to repeatedly change the modulated load during non-communication time intervals. The data transmitter 509 can specifically be configured to apply a load variation pattern that includes multiple load transitions. For example, a repetitive load variation pattern can be applied by the data transmitter 509 during non-communication time intervals.

[0107] In many embodiments, the load variations during non-communication time intervals can be configured to have substantially the same (average) characteristics as the load variations that occur during communication time intervals. For example, a repetitive modulated load pattern can be designed to have characteristics such that the average modulated load is the same as the modulated load pattern of the data symbols, and the average time between load transitions / changes is the same as in the case of communication time intervals.

[0108] Accordingly, in this approach, modulated load variations occur not only during communication time intervals but also continue during non-communication time intervals, and in many cases, at least the average or typical characteristics of the load variations continue during non-communication time intervals.

[0109] The inventors recognized that such an approach can reduce the impact on power transmission caused by load modulation, specifically, it can reduce fluctuations, specifically voltage fluctuations.

[0110] In particular, the inventors recognized that when load modulation is initiated according to the conventional approach, steps or transient phenomena occur due to changes in the modulated load, specifically, by bringing about the average total load of the input circuit. Specifically, when the variable load is a reactive load, the load fluctuations result in a change in the effective resonance frequency of the input circuit. This change in the resonance frequency results in changes in power transmission and the output voltage to the load. Therefore, when load modulation is initiated, the average resonance frequency of the input circuit changes, which results in a step effect as seen, for example, in FIG. 8. The step effect in the average voltage is maintained as long as data packets are being transmitted. However, in an example where the power control operates and is fast enough to affect the voltage between data packets, the average voltage can be returned to the desired level by the power control loop. However, in such a case, adverse transient phenomena may occur at the start and end of each data transmission. This transient effect exists until the system adapts to the modified average operating point. An example of such a transient phenomenon is shown in FIG. 9, where it can be seen that the average voltage is returned to the desired level during and after data transmission.

[0111] However, intuitively, changing the modulated load when no data is being transmitted is considered counterintuitive due to the voltage fluctuations that occur with each load change and due to the increased complexity of operation. However, the inventors recognized that by implementing dummy load modulation fluctuations during non-communication time intervals, the steps and / or transient phenomena at the start of the communication time interval can be reduced and potentially substantially eliminated.

[0112] Furthermore, this can be advantageous in many embodiments even if it results in some voltage fluctuations / noise during communication time intervals that would not otherwise exist. In particular, in many embodiments, this typically occurs during steps or transients, so that peak voltage fluctuations can be reduced (which can potentially be dominant or, for example, as seen in FIG. 9, due to the addition of both the transient and switch fluctuations to provide the peak value). For example, in FIG. 9, in this scenario, it is clear that the amplitude of the initial transient at the start of the communication time interval is significantly higher than the amplitude of the individual switch noise that occurs with each switching of the variable load. Thus, the average change in the resonant frequency has a more substantial effect than the effects and resulting noise of the individual switches. In FIG. 7, the two effects are of the same magnitude. However, since the effects are additive, reducing the transient is still highly advantageous and can reduce the peak voltage deviation / fluctuation. This is advantageous in many embodiments even if switch noise is always present not only during the communication time interval (indeed, if the load is designed to operate with switch noise during the communication time interval, it is likely to operate with this as well during non-communication time intervals).

[0113] Furthermore, various approaches can be implemented to reduce switch noise during non - communication time intervals. As a specific example, switching during non - communication time intervals can be configured to occur faster, potentially significantly faster, than during communication time intervals. In fact, during communication time intervals, variable load / modulated load switching is determined by communication parameters and operations. However, in many embodiments, switching during non - communication time intervals is not limited by such considerations and can be optimized to reduce switch noise. For example, switching can be performed such that the average variable load value / modulated load / resonant frequency is substantially the same in both communication and non - communication time intervals. However, switching during non - communication time intervals can be at a faster rate, for example, 10 times faster. This may not affect the amplitude of the switch noise introduced into the input circuit, but will result in a much higher frequency than during communication time intervals. The filtering provided by smoothing capacitors and associated circuitry is more efficient at this higher frequency, and as a result, the voltage switch noise at the load is reduced.

[0114] Accordingly, in some embodiments, data transmitter 509 can be configured to vary the modulated load during non - communication time intervals at an average frequency higher than the average frequency at which the modulated load changes during communication time intervals. In each embodiment, it is at least 2 times, 5 times, or 10 times higher.

[0115] Load modulation switching during non - communication time intervals improves power transmission operation, reduces and / or mitigates the impact of load modulation on the power transmission operating point, and typically reduces voltage fluctuations of the load.

[0116] The actual modulation variations during non - communication time intervals depend on the requirements and preferences of the individual embodiments, particularly the desired effects. For example, in some embodiments, it may be desirable to have a slow load variation that can only partially reduce the transient phenomena at the start of the communication time interval. In many embodiments, it is desirable to reduce the difference in the characteristics of the typical or average load variations between the communication time interval and the non - communication time interval. Thus, in many (but not all) embodiments, it is desirable to configure the modulation variations during the communication time interval to have characteristics that match those of the communication time interval.

[0117] In many embodiments, the data transmitter 509 is configured to control the variable load so as to repeatedly change the modulation load during the non - communication time interval such that the average value of the variable load / average modulation load is substantially the same in the communication time interval and the non - communication time interval.

[0118] In some embodiments, the data transmitter 509 can be configured to keep only the average load / modulation load substantially the same. This typically allows for a significant reduction in, for example, voltage variations while still enabling relaxed low - complexity operation during non - communication time intervals. In many embodiments, this approach allows, for example, a predetermined fixed load variation pattern to be used during non - communication time intervals.

[0119] In many embodiments, the data transmitter 509 is configured to control the variable load to repeatedly change the modulation load during non - communication time intervals such that the difference between the average modulation load (and the average value of the variable load) during non - communication time intervals and during communication time intervals is less than 10% of the maximum modulation load change / variation that can occur during communication time intervals. The maximum variation / change in modulation load during a communication time interval is the difference between the minimum modulation load and the maximum modulation load for a data symbol. The modulation load can be considered to correspond to the value of the variable load, and thus, in many embodiments, the minimum modulation load and the maximum modulation load are equivalent to the minimum and maximum values of the variable load for a data symbol. The maximum modulation load is the highest modulation load, and the minimum modulation load is the lowest possible modulation load for all possible data symbol values.

[0120] Typically, the variable load, and thus the modulation load, has only a limited number of possible values. In fact, in many cases, binary operation is used with a variable load and a modulation load having only two possible values (each data symbol being represented by various patterns / sequences of such two possible values). In that case, the maximum load value / modulation load corresponds to one of the two possible values, and the minimum load value / modulation load corresponds to the other. Thus, the maximum modulation load change / variation corresponds to the difference between the maximum modulation load and the minimum modulation load and is simply the difference between these values.

[0121] Thus, in many embodiments, the variable load is switched during non - communication time intervals such that the average modulation load / variable load value is less than 10% of such a difference. In some embodiments, it can be maintained at less than 1% or less than 5% of such a value.

[0122] Thus, such an approach contributes to reducing the change in the average modulation load when entering a communication time interval and thus reducing transient phenomena at the power transmission operating point, specifically in voltage.

[0123] In many embodiments, the timing characteristics of the load variation during the communication time interval can be controlled to provide improved advantageous operation. As described above, in many embodiments, the switching operation during the non-communication time interval can be configured to occur during the non-communication time interval at the same frequency as or more frequently than during the communication time interval.

[0124] For example, in many embodiments, the frequency of the average load change of the variable load during the non-communication time interval is controlled by the data transmitter 509 to be at least as high as during the communication time interval. In many cases, it may even be higher. However, in some cases, it may be desirable for the switching during the non-communication time interval to be slow while still allowing it to be fast enough to provide an operating point (including the average resonance frequency of the input circuit) that is not very different from that during the communication time interval. In many embodiments, the average frequency during the non-communication time interval is 50% or more of the average frequency during the communication time interval.

[0125] In some embodiments, the data transmitter 509 is configured to control the variable load to repeatedly change the modulated load during the non-communication time interval such that the average time between changes in the modulated load during the non-communication time interval is 50%, 100%, or 150% or more of the average time between changes in the modulated load during the communication time interval. This allows the load switching to be fast enough to ensure that the operating point is maintained close enough to the average operating point during the communication time interval in many embodiments.

[0126] In some embodiments, data transmitter 509 can be configured to control the variable load to repeatedly change the modulation load during non - communication time intervals such that the maximum average time during changes in the modulation load during non - communication time intervals is 50%, 100%, or 150% or more of the average time change during changes in the modulation load during communication time intervals. This allows, in many embodiments, the load switching to be fast enough to ensure that the operating point is maintained close enough to the average operating point during communication time intervals. In particular, it can prevent the operating point from having a time of stability at a value corresponding to one particular value of the variable load / modulation load (due to being positioned at this value for too long).

[0127] In some embodiments, each data symbol can be represented, as described above, by a single constant modulation load applied throughout the symbol time. For example, in the case of binary communication, data transmitter 509 can simply switch the variable load between an impedance coupled to the input circuit and an impedance not coupled to the input circuit. For each new bit, data transmitter 509 selects the appropriate switch setting for the variable load and maintains that level until the start of the next bit at which a new switch decision is made based on the new bit value.

[0128] However, in many embodiments, a data transmitter 509 having two or more different load values / modulation loads for at least one data symbol value, typically at least two data symbol values, can be used. In many embodiments, the modulation load for one, two, or in some cases more data symbol values is represented by a modulation load pattern that includes at least one load change / transition. In many embodiments, all data symbol values include at least two different load values and are thus represented by a modulation load pattern that includes at least one transition.

[0129] As a specific example, the variable load is a binary load, and the binary communication is implemented by a modulation load pattern by a load transition from a first value of the variable load / modulation load to a second value of the variable load / modulation load for one data symbol value and a modulation load pattern by a load transition from the second value of the variable load / modulation load to the first value of the variable load / modulation load for the other data symbol value.

[0130] The system can use load modulation where each symbol is represented by a load transition that occurs during the symbol duration (typically at the center time), and the direction of the load transition indicates the binary symbol value.

[0131] Such a load transition approach offers significant advantages in many scenarios, which enables load modulation detection to be performed without the need for an absolute reference level to be generated and used to determine the received data symbol. In fact, the data symbol value can be determined by measuring the load values in the first and second halves of the data symbol time and determining the binary value as the sign of the difference between these.

[0132] A further significant advantage of such an approach in the described system is that it guarantees a relatively large number of load transitions during the communication time interval. Frequent load transitions allow the output voltage to remain close to the average value, and thus the switch noise on the output can be reduced. This is specifically the case when the smoothing capacitor is large enough to ensure that no load remains for a length of time sufficient for the power transmission to stabilize. Another significant advantage is that the modulation load during the communication time interval is highly predictable. For example, it is predictable how long a given value will remain before the modulation load changes, the average load is predictable, and it is actually independent of the data.

[0133] As a result, the load variations during the communication time intervals can be effectively and accurately repeated during non-communication time intervals, for example, such that average / typical / intermediate characteristics are repeated. For example, the load variation pattern can be applied during non-communication time intervals having the same average modulated load and transition intervals as during the communication time intervals.

[0134] Accordingly, using modulation load transitions for each data symbol is highly advantageous in the approach described, for example, enabling the transient operation at the start of the communication time interval to be mitigated or reduced, or in some cases actually eliminated.

[0135] In some embodiments, the data transmitter 509 can be configured to transmit data symbols by load modulating a power transmission signal with a sequence of modulation load values corresponding to a chip sequence. The data transmitter 509 can transmit data symbols, for example, using an approach similar to direct sequence spread spectrum (DSSS) modulation that uses a chip sequence to modulate the data symbols. The data symbols / bits are modulated by a bit sequence, also called a spreading sequence (typically pseudo-random). Each spreading sequence bit, known as a chip, has a much shorter duration (larger bandwidth) than the original message bits.

[0136] In some embodiments, each symbol is represented by a chip sequence that includes a plurality of chips, typically with the sequence including from 5 to 1023 chips. Thus, rather than simply varying the load according to each symbol or bit, data transmitter 509 is configured to transmit a given symbol (typically a bit) by a series of load changes and variations, which vary from symbol to symbol. Specifically, the chip sequence can be defined for each symbol, and when transmitting a given symbol, data transmitter 509 can read out the chip sequence for that particular symbol and proceed to load modulate the power transmission signal according to the chip sequence for that symbol. Each chip sequence is directly linked to a modulation load pattern that is specifically the same as the chip sequence.

[0137] Thus, in some embodiments, the modulation load pattern for each possible data symbol value comprises a load modulation chip sequence of at least 5, and in some cases at least 8, 16, or 32 load modulation chips.

[0138] Similarly, as will be described in more detail later, the power transmitter can detect load modulation by considering the entire chip sequence, specifically by attempting to determine the received symbol as the symbol whose measured load variation chip pattern most closely matches the chip sequence pattern of that symbol.

[0139] Thus, in some embodiments, direct sequence spread spectrum load modulation is used, and each data symbol value is represented by a different chip sequence / modulation load pattern.

[0140] Such an approach enables, in particular, a significant reduction in the modulation depth, i.e., the magnitude of the load variation, which can, for example, reduce electromagnetic noise and interference, reduce acoustic noise, and reduce spurious vibrations. It also results, in many embodiments, in an improved signal-to-noise ratio, which can, for example, result in significantly improved, more reliable communication, often with a lower bit error rate. Thus, overall improved power transmission can be achieved.

[0141] FIG. 10 shows an example of a portion of two possible chip sequences / modulation load patterns. Each chip sequence consists of a sequence of chips. Typically, the set of chip values is two and corresponds to a binary chip sequence. And the symbol time is divided into a plurality of chip intervals, and the chip sequences of the chips are different for different data symbols. Typically, each sequence includes at least 10 chips and, in many cases, significantly more chips. In many embodiments, each chip sequence can have a length of 2N - 1, where N is typically an integer of 4 or more.

[0142] Each of the stored chip sequences is assigned to one symbol. Thus, each possible data symbol value that needs to be transmitted to the power transmitter can have an associated / linked chip sequence / modulation load pattern. For example, if only two data symbols are considered, i.e., if binary communication is implemented, the set of chip sequences can include only two chip sequences. Each possible data symbol value can be linked / represented by one modulated chip sequence. Thus, for a given data symbol value to be transmitted, the corresponding / linked modulated chip sequence is determined and modulated onto the power transmission signal by load modulation. For example, if only two data symbols are considered, i.e., if binary communication is implemented, the set of chip sequences can include only two chip sequences.

[0143] In many embodiments, one or more chip sequences can be represented by their relationship to another chip sequence. For example, in binary communication, data transmitter 509 can store a single modulated chip sequence corresponding to one of the binary data values. The chip sequence for the other binary data value can be given as the reverse of the stored bit sequence and thus can be represented by the same stored bit sequence. Thus, in many cases, a set of chip sequences utilizes complementary reverse chip sequences for pairs of data symbols, and thus only half of the chip sequences used are typically explicitly stored / determined in data transmitter 509, and the remaining chip sequences are automatically and implicitly stored / determined as their reverses.

[0144] Thus, in some embodiments, a modulated chip sequence can include a reverse chip sequence. Equivalently, the same modulated chip sequence can be considered to represent two data symbol values, specifically two binary data symbol values.

[0145] The modulation chip sequence is for a given data symbol selected from a set of modulation chip sequences and transmitted. In this example, the data transmitter 509 provides a set of modulation chip sequences, and each chip sequence is linked to a data symbol value. Typically, the set of modulation chip sequences includes one modulation chip sequence for each possible data symbol value. For example, if binary communication is used, the first set of chip sequences can include only two chip sequences. The data transmitter 509 can store the chip sequences in any suitable form, and it will be understood that it is not necessary to store the complete sequence for each possible data symbol. For example, a given modulation chip sequence can be multiplied by a binary symbol value represented by the values 1, -1. And at the receiving end, i.e., the power transmitter, the data value can be determined by correlation with a given modulation chip sequence, and the determination of the corresponding binary data value depends on whether this is a positive correlation or a negative correlation.

[0146] Accordingly, in many embodiments, binary communication can be used where only two data symbol values (corresponding to a "0" bit value or a "1" bit value) are possible. In such a case, one bit value can be represented by a given chip sequence, and the other bit value can be associated with the reverse bit sequence, i.e., the bit sequence resulting from changing each chip value to the opposite value. Thus, the two bit sequences are typically complementary, with one resulting from multiplying the other by -1 (the chip values are represented by +1 and -1).

[0147] A particular advantage in such a case is that demodulation is particularly easy because the bit values can be distinguished using a single correlation, which is because the magnitude of the correlation is the same for the chip sequence but the sign of the correlation value is opposite.

[0148] It will be understood that it is equivalent to consider that the data symbol represented by the inverse modulation chip sequence is represented by one chip sequence or two chip sequences. Such a binary approach in which two inverse chip sequences are used is equivalent to considering that two possible binary values are modulated by the same chip sequence, but the data symbol has opposite data values (e.g., +1 and -1).

[0149] When the power receiver attempts to transmit a data symbol, its value is supplied from the power receiver controller 501 to the data transmitter 509, and the data transmitter 509 proceeds to determine the chip sequence linked to the data symbol value to be transmitted.

[0150] The data transmitter 509 is configured to modulate the chip sequence on the power transmission signal. Specifically, the modulation load can be switched in and out (on / off) according to the chips, that is, the load can be changed according to the variable load value of the chip sequence / modulation load pattern.

[0151] The chip sequence is selected from a set of chip sequences. In this example, the data transmitter 509 stores such a set of chip sequences, and 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 can include only two chip sequences. The data transmitter 509 can store the chip sequences in any suitable form, and it will be understood that it is not necessary to store the complete sequence for each possible data symbol. For example, one or more chip sequences can be represented by their relationship to another chip sequence. For example, in the case of binary communication, the data transmitter 509 can store only a single chip sequence corresponding to one of the binary data values. The chip sequence for the other binary data value can be given as the inverse of the stored bit sequence and thus can be represented by the same stored bit sequence. Thus, often the set of chip sequences utilizes complementary inverse chip sequences for pairs of data symbols, and thus only half of the chip sequences used are typically explicitly stored in the data transmitter 509, and the remaining chip sequences are automatically and implicitly stored as their inverses.

[0152] The chip sequences in the set typically have the same length.

[0153] The systems of FIGS. 1, 2, and 5 can utilize an approach that can address one or more of the problems associated with load modulation in many situations. While load modulation is used, each symbol is represented by a chip sequence that includes multiple chips, typically a sequence that includes 5 to 127 chips. Thus, rather than simply varying the load according to each symbol or bit, the data transmitter 509 is configured to transmit a given symbol (typically a bit) by a series of load changes and variations, where the changes and variations are different for each symbol. Specifically, the chip sequence can be defined for each symbol, and when transmitting a given symbol, the data transmitter 509 can read out the chip sequence for that particular symbol and proceed to load modulate the power transmission signal according to the chip sequence for that symbol.

[0154] The power transmitter can detect load modulation by considering the entire sequence. Specifically, the power transmitter can attempt to determine the received symbol as the symbol whose detected load variation pattern most closely matches the chip sequence pattern of that symbol.

[0155] And the data transmitter 509 can be configured to receive data symbols to be transmitted to the power transmitter, typically from the power receiver controller 501, determine the corresponding chip sequence, and proceed to load modulate the power transmission signal by the modulation load pattern representing this chip sequence. Typically, the data symbols are binary, but in some cases higher-order modulation symbols may be used (i.e., having three or more possible values). In some cases, such higher-order data symbols can correspond to a combination of received data bits. For example, 2 bits can be combined into a single quaternary data symbol. Such combinations can be possible both when those data bits are related to each other and when, for example, they are completely independent.

[0156] Longer chip sequences can provide improved noise suppression etc., but for a given chip rate, the symbol time will increase, so the data rate will also decrease. An increase in the chip sequence length also increases complexity and resource requirements, especially in receivers where correlation with longer sequences may require a large number of calculations. A typical suitable value is N = 5, which corresponds to a chip length of 31 chips.

[0157] Figure 11 shows an example of how the power transmission signal is load - modulated by the chips of the chip sequence. In this example, the modulation is synchronized to the power transmission signal at a rate of 1 chip per 2 power signal cycles. The arrows in Figure 11 indicate the times at which the load of the power transmission signal is measured / sampled by the power transmitter to generate load samples correlated with the possible chip sequences. Sampling is synchronized with the power transmission signal, and one sample is generated for each chip.

[0158] To determine the (binary) chip value, the sampled load value is compared with an average level 1101. In a specific example, the load of the power transmission signal is determined as the peak cycle value of the measured signal (which can specifically 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. Further, an average level 1001 of the peak cycle value is first determined, and the chip value is then determined based on whether the measured sample value is above or below the average level 1101.

[0159] The example of Figure 11 requires that a reference level be determined, and typically this can be determined as an average level. However, this can introduce some uncertainties and potentially some bit errors.

[0160] In some embodiments, each chip of the load modulation chip can be represented by a modulation load transition occurring in the chip. Thus, each load modulation chip includes at least two different modulation load values / variable load values. For example, with respect to differential data symbol modulation, individual chips can be modulated by a biphase state transition approach. For example, one chip value can be represented by a transition from a low modulation load to a high modulation load, and the other chip value can be represented by a transition from a high modulation load to a low modulation load. In such an example, each chip sequence can be represented by a modulation load pattern having two modulation load values for each chip.

[0161] Such an approach can provide a great advantage of allowing the receiver to determine the chip value by simply considering the difference between the two measured load values for each chip. However, furthermore, it increases the switch rate, makes it more predictable, thereby allowing for improved correspondence between switch operations in communication time intervals and non - communication time intervals.

[0162] Using an approach of such a direct - sequence spread - spectrum (DSSS) or differential direct - sequence spread - spectrum (D - DSSS) type approach in the described system provides several advantages. This approach in particular allows the modulation depth, i.e., the magnitude of the load variation, to be substantially reduced, which can, for example, reduce electromagnetic noise and interference, reduce acoustic noise, and reduce spurious vibrations. It also, in many embodiments, results in an improved signal - to - noise ratio, which can lead to significantly improved, more reliable communication, often with a lower bit - error rate. Thus, overall improved power transmission can be achieved.

[0163] Furthermore, in the approach being described, the use of such chip sequences / modulation load patterns significantly reduces switch noise / voltage fluctuations. The use of such long sequences can reduce the modulation depth and reduce the required changes in the modulation load. For example, lower value switch capacitors can be implemented. This reduction makes the changes in the resonance frequency / operating point smaller and the noise / fluctuations smaller. Further, this approach allows for much higher modulation load switching and actually requires that the same symbol rate be maintained. Faster switching can further reduce noise / voltage fluctuations as it spreads over a larger frequency range including higher frequencies. As a result, the smoothing capacitor and its low-pass filtering effect become more efficient, thereby reducing the noise level.

[0164] Furthermore, this approach can not only reduce the noise and voltage fluctuations during the communication time interval, but can also further enable the reduction of the noise during the non-communication time interval when modulation load fluctuations are also performed. In particular, the fluctuations during the non-communication time interval can be set to have switching characteristics that match (typically statistically or on average) those of the communication time interval. In particular, high-frequency switching with low modulation load changes is used, thereby significantly reducing the switching noise.

[0165] Figures 12 and 13 show the same approach as in Figures 7 and 8, but use load modulation with chip sequence-based load modulation having the same data rate. As can be seen, the switch noise during the communication time interval is significantly reduced. Figures 14 and 15 show the corresponding results, where the load fluctuations are performed during the non-communication time interval and these have the same statistical / average characteristics as during the communication time interval. As shown, the voltage fluctuations including both the transient fluctuations at the start and end of the communication time interval and the switch noise between them can be significantly reduced and in some cases almost completely removed. Thus, significantly improved performance is achieved.

[0166] Thus, when using a DSSS or DDSSS type, the switching during non - communication time intervals can be configured to have characteristics that reflect the modulation switching during communication time intervals. In particular, it can typically switch at least as frequently as during the communication time interval and, on average, switch the variable load to have a certain percentage of time at each possible load value that matches that of the communication time interval. Typically, the data symbol and chip sequences are such that each possible load value is selected with the same probability / or the same percentage of time on average. Binary load modulation is typically modulation such that, on average, the modulated load is one modulated load for 50% of the time and the other modulated load for 50% of the time of the communication time interval. The switching during non - communication time intervals is also switching such that each of the modulated load values is applied for 50% of the time.

[0167] The number of load changes introduced by data transmitter 509 during the load modulation chip sequence duration in non - communication time intervals is, in many embodiments, at least the same number as the load changes that occur in the load modulation chip sequence. Thus, typically during a given duration of a chip sequence corresponding to a symbol time, the number of load transitions in non - communication time intervals is at least the same number as would (on average) occur during the transmission of data symbols in communication time intervals. Thus, the switching during non - communication time intervals is at least as frequent as the switching during DSSS transmission of data symbols in communication time intervals. This typically provides improved performance with reduced voltage fluctuations.

[0168] The data transmitter 509 can be configured to control switching during non - communication time intervals so as not to include a modulation load pattern that matches, or specifically is the same as, any load - modulation chip sequence / modulation load pattern for any possible data symbol value. The data transmitter 509 can specifically be configured to avoid any repetition of any data symbol chip sequence. This can reduce the risk of spurious detection for the data receiver and facilitate synchronization and / or detection when the next communication time interval / data packet is received.

[0169] In many embodiments, the data transmitter 509 can be configured to control a variable load to apply a repeating load - variation pattern during non - communication time intervals. In some embodiments, the repeating load 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.

[0170] The repeating load - variation pattern corresponds to a sequence of variable load / modulation load values that are repeated during a communication time interval. The repeating load - variation pattern may be, for example, a chip sequence, specifically one having the same timing characteristics as the data symbol chip sequence. For example, it may have the same length and have load transitions / changes at corresponding times (e.g., the load changes only at the start of the communication time interval, or if differential / modulation of each chip is used, changes at the center of the chip duration). Such an approach allows for low complexity, for example, because in effect the same functionality can be used during both communication and non - communication time intervals.

[0171] In many embodiments, the repetitive load variation pattern is selected to have a low cross-correlation with the modulation chip sequence used to modulate data symbols on the power transmission signal during the communication time interval. Thus, the repetitive load variation pattern can be selected to provide a distinct differentiation from the modulation chip sequence and reduce the probability of being confused by the data receiver. Such an approach improves communication and, for example, facilitates the detection of when a new data packet is transmitted. Continuous modulation / load variation of the power transmission signal during non-communication time intervals using timing parameters that match the modulation during the communication time interval also enables improved synchronization.

[0172] In many embodiments, the repetitive load variation pattern can be selected to be close to what is typically obtained on average when correlating the cross-correlation between the modulation chip sequence and a random sequence. The reference correlation value can be determined as the average correlation between the modulation sequence data sequence and the random sequence. Such a correlation is typically zero when inverted data symbol values such as (-1, 1) are used, and for example 0.5 when data symbol values such as (1, 0) are used. In this case, the maximum absolute difference between the cross-correlation and the reference correlation between the repetitive load variation pattern and the modulation sequence data sequence is 50% or less, 20% or less, 10% or less, and even 5% or less of the maximum absolute difference between the auto-correlation and the reference correlation of the modulation sequence data sequence, so that the repetitive load variation pattern can be determined / selected. The repetitive load variation pattern and the chip sequence can be, for example, binary and can be represented by binary values such as (1, 0) or (-1, +1).

[0173] In some embodiments, the repetitive load variation pattern is a pattern that periodically alternates between two modulated loads. The variable load may be a binary switchable load, and the data transmitter 509 can be configured to periodically alternate between two values. The switching can have a periodicity equal to, for example, the symbol time (e.g., in the case of non-DSSS communication), or the chip time (e.g., in the case of DSSS), or in some embodiments, (e.g., in the case of differential load modulation) a periodicity half of these durations.

[0174] Such an approach typically enables a low-complexity implementation. Furthermore, it can enable fast and symmetric switching that can reduce voltage fluctuations. Additionally, it can typically result in a sequence that has a very low correlation with a modulated load pattern, such as a chip sequence typically used for DSSS.

[0175] In many embodiments, the repetitive load variation pattern can correspond to, for example, an alternating modulation of 1010101010... chips or bits, and / or, if differential communication is used, a continuous modulation of chips or bits of a constant value.

[0176] In some embodiments, the modulated load of the power transmission signal during non-communication time intervals can be randomly generated. For example, for each new chip or bit, a random value (e.g., with a 50% probability) can be determined and modulated on the power transmission signal.

[0177] This approach can provide an improved load modulation operation, particularly improved power transmission. Advantageous effects such as reduction of voltage fluctuations of the voltage supplied to the load can be achieved in many scenarios. Further, this approach can also provide advantages on the power transmitter side. It enables improved synchronization as it can be executed continuously and / or, for example, facilitates detection when a new data packet / communication time interval starts. Also, in many embodiments, more continuous load fluctuations enable improved demodulation and thus can provide improved detection. For example, if an average reference level is used for demodulation, the continuous presence of load fluctuations can provide an improved determination of such a reference level and thus improved data detection.

[0178] The modulated load can be the load component of the power transmission signal / driving signal that is caused by / depends on / varies with the load modulation.

[0179] It will be understood from the above description for clarity that embodiments of the present invention have been described 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 can be used without departing from the present invention. For example, functions shown to be executed by separate processors or controllers may be executed by the same processor or controller. Thus, references to specific functional units or circuits should be regarded only as references to suitable means for providing the described functions and not as indicating a strict logical or physical structure or organization.

[0180] The present invention can be implemented in any suitable form including hardware, software, firmware, or any combination thereof. Optionally, the present invention can be at least partially implemented as computer software executed on one or more data processors and / or digital signal processors. Elements and components of embodiments of the present invention can be physically, functionally, and logically implemented in any suitable manner. In fact, the functions may be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the present invention may be implemented in a single unit or may be physically and functionally distributed among different units, circuits, and processors.

[0181] Although the present invention has been described in connection with several embodiments, it is not intended to be limited to the specific forms set forth herein. Rather, the scope of the present invention is defined only by the appended claims. Further, although a certain feature may appear to be described in connection with a particular embodiment, one of ordinary skill in the art will recognize that various features described in the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0182] Furthermore, although listed individually, a plurality of means, elements, circuits or method steps can be implemented, for example, by a single circuit, unit or processor. Further, although individual features may be included in different claims, these may in some cases be advantageously combined, and inclusion in different claims does not mean that a combination of features is not feasible and / or not advantageous. Also, including a certain feature in one category of claims does not mean a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories as required. Including a certain feature in a dependent claim of an independent claim does not mean a limitation to this independent claim, but rather indicates that the feature is equally applicable to other independent claims if appropriate. Furthermore, the order of features in the claims does not mean a specific order in which the features must operate, and in particular, the order of individual steps in method claims does not mean that the steps must be performed in this order. Rather, the steps can be performed in any suitable order. Further, a reference to the singular does not exclude the plural. Thus, references such as "a", "an", "first", "second", etc. also do not exclude the plural. The reference signs in the claims are provided merely as illustrative examples and should not be construed as limiting the scope of the claims in any way.

[0183] Generally, examples of power receivers and methods are shown by the following embodiments: [Embodiment] 1. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transmission signal, the power receiver (105) comprising: An input circuit (107, 503) comprising a receiver coil (107) configured to extract power from the power transmission signal, A variable load (511) coupled to the input circuit and configured to apply a modulated load to the input circuit; During communication time intervals that are interspersed between non-communication time intervals when data symbols are not transmitted by the data transmitter (509), a data transmitter (509) configured to transmit data symbols to the power transmitter (101) by load modulating a power transmission signal; having, and the data transmitter (509) is further configured to change a variable load (511) to apply a modulation load pattern to each data symbol transmitted during a communication time interval, with each possible data symbol value being represented by a different modulation load pattern for the modulation load, and the data transmitter (509) is configured to control the variable load (511) to repeatedly change the modulation load during non-communication time intervals, a power receiver. 2. The power receiver according to claim 1, wherein the data transmitter (509) is configured to control the variable load (511) to repeatedly change the modulation load during the non-communication time intervals such that the difference between the average modulation load during the non-communication time intervals and the average modulation load during the non-communication time intervals is different by less than 10% of the maximum modulation load change during the communication time intervals. 3. The power receiver according to claim 1 or 2, wherein the data transmitter (509) is configured to control the variable load (511) to repeatedly change the modulation load during the non-communication time intervals such that the average time between changes in the modulation load during the non-communication time intervals is 50% or more of the average time between changes in the modulation load during the non-communication time intervals. 4. The power receiver according to any of the preceding claims, wherein the modulation load pattern for each possible data symbol value includes at least two different load values. 5. The power receiver according to any one of claims 1 to 3, wherein the modulation load pattern for each possible data symbol value includes 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 configured to repeatedly change the modulation load during non-communication time intervals such that it does not include a modulation load pattern corresponding to any load modulation chip sequence. 7. Each chip of the load modulation chip sequence is the power receiver according to claim 5 or 6, represented by a modulation load transition. 8. The number of modulation load changes during the load modulation chip sequence duration in the non - communication time interval is greater than or equal to the maximum number of modulation load changes in the load modulation chip sequence, according to any one of claims 5 to 7. 9. The data transmitter (509) is configured to control the variable load (511) to apply a repetitive load fluctuation pattern during the non - communication time interval, according to any of the preceding claims. 10. The repetitive load fluctuation pattern is periodically alternating between two modulation loads, according to claim 9. 11. The maximum absolute difference between the cross - correlation and the reference correlation between the repetitive load fluctuation pattern and the modulation sequence data sequence is less than or equal to 50% of the maximum absolute difference between the modulation sequence data sequence and the reference correlation, where the reference correlation is the average correlation between the modulation sequence data sequence and a random sequence, according to claim 9 or 10, dependent on any of claims 5 to 8. 12. The data transmitter (509) is configured to control the variable load (511) so as not to include a modulation load pattern representing a data symbol during the non - communication time interval, according to any of the preceding claims. 13. The data transmitter (509) is configured to switch the variable load (511) between two modulation load values, according to any of the preceding claims. 14. A wireless power transmission system comprising a power transmitter (101) and a power receiver (105) according to any of the preceding claims. 15. An operating method for a power receiver (105) that wirelessly receives power from a power transmitter (101) via an electromagnetic power transmission signal, the method comprising: an input circuit (107, 503) comprising a receiving coil (107) that extracts power from the power transmission signal; a variable load (511) coupled to the input circuit and applying a modulated load to the input circuit (107, 503); and a data transmitter (509) that transmits data symbols to the power transmitter (101) by load-modulating the power transmission signal during communication time intervals that are interspersed during non-communication time intervals when data symbols are not transmitted by the data transmitter (509); the method further comprising changing the variable load to apply a modulated load pattern for each data symbol transmitted during a communication time interval, each possible data symbol value being represented by a different modulated load pattern for the modulated load, controlling the variable load (511) to repeatedly change the modulated load during non-communication time intervals.

Claims

1. A power receiver that wirelessly receives power from a power transmitter via an electromagnetic power transmission signal, An input circuit including a receiver coil configured to extract power from the aforementioned power transmission signal, A variable load coupled to the input circuit and configured to apply a modulated load to the input circuit, A data transmitter is configured to transmit data symbols to a power transmitter by load modulating the power transmission signal during communication time intervals interspersed between non-communication time intervals in which data symbols are not transmitted by the data transmitter, The data transmitter is further configured to vary the variable load to apply a modulation load pattern for each data symbol transmitted during the communication time interval, wherein each possible data symbol value is represented by a different modulation load pattern for the modulation load, and the modulation load pattern for each possible data symbol has a load modulation chip sequence. The data transmitter is configured to control the variable load so as to repeatedly change the modulation load during non-communication time intervals. A power receiver wherein the data transmitter is configured to control the variable load to apply a repetitive load variation pattern during the non-communication time interval, the maximum absolute difference between the cross-correlation of the repetitive load variation pattern and the load modulation chip sequence and a reference correlation is 50% or less of the maximum absolute difference between the autocorrelation of the load modulation chip sequence and the reference correlation, and the reference correlation is the mean correlation between the load modulation chip sequence and a random sequence.

2. The power receiver according to claim 1, wherein the data transmitter is configured to control the variable load so as to repeatedly change the modulation load during the non-communication time interval such that the difference between the average modulation load during the non-communication time interval and the average modulation load during the non-communication time interval differs by less than 10% of the maximum modulation load change during the communication time interval.

3. The power receiver according to claim 1, wherein the data transmitter is configured to control the variable load so as to repeatedly change the modulation load during the non-communication time interval such that the average time between modulation load changes during the non-communication time interval is 50% or more of the average time between modulation load changes during the non-communication time interval.

4. The power receiver according to claim 1, wherein the modulation load pattern for each possible data symbol value includes at least two different load values.

5. The power receiver according to claim 1, wherein the modulation load pattern for each possible data symbol value includes a load modulation chip sequence of at least five load modulation chips.

6. The power receiver according to claim 5, wherein the data transmitter is configured to repeatedly change the modulated load during non-communication time intervals so as not to include a modulated load pattern corresponding to a load modulation chip sequence.

7. The power receiver according to claim 5, wherein each chip in the load modulation chip sequence is represented by a modulated load transition.

8. The power receiver according to claim 5, wherein the number of modulated load changes during the duration of the load modulation chip sequence during a non-communication time interval is equal to or greater than the maximum number of modulated load changes in the load modulation chip sequence.

9. The power receiver according to claim 1, wherein the repetitive load fluctuation pattern is a pattern in which two modulated loads periodically alternate.

10. The power receiver according to claim 1, wherein the data transmitter is configured to control the variable load such that it does not include a modulated load pattern representing data symbols during non-communication time intervals.

11. The power receiver according to claim 1, wherein the data transmitter is configured to switch the variable load between two modulated load values.

12. A wireless power transmission system comprising a power transmitter and a power receiver according to any one of claims 1 to 11.

13. A method for operating a power receiver that wirelessly receives power from a power transmitter via an electromagnetic power transmission signal, The aforementioned power receiver is An input circuit including a receiver coil configured to extract power from the aforementioned power transmission signal, A variable load coupled to the input circuit and configured to apply a modulated load to the input circuit, A data transmitter is configured to transmit data symbols to a power transmitter by load modulating the power transmission signal during communication time intervals interspersed between non-communication time intervals in which data symbols are not transmitted by the data transmitter, The aforementioned operation method is, A step of changing the variable load to apply a load modulation pattern for each data symbol transmitted during the communication time interval, wherein each possible data symbol value is represented by a different modulation load pattern for the modulation load, and the modulation load pattern for each possible data symbol value has a load modulation chip sequence, The step of controlling the variable load so as to repeatedly change the modulation load during a non-communication time interval, A method wherein the data transmitter controls the variable load to apply a repetitive load variation pattern during the non-communication time interval, the maximum absolute difference between the cross-correlation of the repetitive load variation pattern and the load modulation chip sequence and a reference correlation is 50% or less of the maximum absolute difference between the autocorrelation of the load modulation chip sequence and the reference correlation, and the reference correlation is the mean correlation between the load modulation chip sequence and a random sequence.

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