Communication modulation for wireless power transfer

Abstract

A wireless power receiver may include: a wireless power transfer coil; a rectifier receiving an AC voltage induced in the wireless power transfer coil by the wireless power transmitter, and thereby generating a DC output voltage; a load modulation circuit; and a control circuit operating the rectifier to supply power to a load coupled to the rectifier, and operating the load modulation circuit to communicate with the wireless power transmitter by selectively changing power drawn from the wireless power transfer coil according to an amplitude shift keying modulation scheme having a plurality of modulation depths.

Description

Cross-references to related applications

[0001] This patent application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 586,454, filed September 29, 2023, entitled "Communication Modulations for Wireless Power Transfer," and co-pending U.S. Patent Application No. 18 / 746,744, filed June 18, 2024, entitled "Communication Modulations for Wireless Power Transfer," which are incorporated herein by reference. Background Technology

[0002] Load modulation can be used for in-band communication from a wireless power receiver (PRx) to a wireless power transmitter (PTx) using amplitude shift keying (ASK). The load modulator circuitry uses some of the power from the PRx to implement ASK communication. This use increases at relatively high power levels. Summary of the Invention

[0003] Therefore, it may be desirable to provide improved load modulation circuitry systems and methods to improve the communication reliability and operational efficiency of wireless power transmission systems.

[0004] A wireless power receiver may include: a wireless power transmission coil; a rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; a load modulation circuit; and a control circuit that operates the rectifier to supply power to a load coupled to the rectifier and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to an amplitude shift keying modulation scheme employing differential Manchester coding. The modulation scheme employed by the control circuit may further include initially employing a first modulation depth for a first symbol and a second symbol transmitted to the wireless power transmitter; and, in response to a communication failure, increasing the modulation depth associated with the first symbol to a higher modulation depth while maintaining the first modulation depth for the second symbol. Increasing the modulation depth associated with the first symbol to a higher modulation depth while maintaining the first modulation depth for the second symbol reduces power consumption associated with the modulation scheme.

[0005] The modulation scheme employed by the control circuit may further include increasing the modulation depth associated with the second symbol to a higher modulation depth in response to a further communication failure. The first symbol may be a single bit, and the second symbol may be a zero bit. The load modulation circuit may include a controllable current source coupled to the DC side of the rectifier, and the higher modulation depth may correspond to a higher current drawn from the controllable current source. The load modulation circuit may include one or more controllable capacitors connected to the AC side of the rectifier.

[0006] A method for transmitting data from a wireless power receiver to a wireless power transmitter via load modulation can be performed by control circuitry of the wireless power receiver operating the load modulation circuitry of the wireless power receiver by: initially employing a first modulation depth for a first symbol and a second symbol transmitted to the wireless power transmitter; and, in response to a communication failure, increasing the modulation depth associated with the first symbol to a higher modulation depth while maintaining the first modulation depth for the second symbol. The method may further include increasing the modulation depth associated with the second symbol to a higher modulation depth in response to a further communication failure.

[0007] The first and second symbols transmitted to the wireless power transmitter can be encoded using a differential Manchester coding scheme, where the first symbol is one bit and the second symbol is zero bits. Increasing the modulation depth associated with the first symbol to a higher modulation depth while maintaining the first modulation depth for the second symbol reduces the power consumption associated with the modulation scheme. The load modulation circuit includes a controllable current source coupled to the DC side of the rectifier of the wireless power receiver, and the higher modulation depth corresponds to a higher current drawn from the controllable current source. The load modulation circuit may include one or more controllable capacitors connected to the AC side of the rectifier of the wireless power receiver.

[0008] A wireless power receiver may include: a wireless power transmission coil; a rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; a load modulation circuit; and a control circuit that operates the rectifier to supply power to a load coupled to the rectifier and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to a modulation scheme. The modulation scheme employed by the control circuit may further include: initially employing a first modulation depth for a first symbol and a second symbol transmitted to the wireless power transmitter; increasing the modulation depth associated with the first symbol to a higher modulation depth in response to a communication failure, while maintaining the first modulation depth for the second symbol. The modulation scheme employed by the control circuit may further include increasing the modulation depth associated with the second symbol to a higher modulation depth in response to a further communication failure.

[0009] The first symbol and the second symbol transmitted to the wireless power transmitter can be encoded using a differential Manchester coding scheme, wherein the first symbol is one bit and the second symbol is zero bits.

[0010] Increasing the modulation depth associated with the first symbol to a higher modulation depth while maintaining the first modulation depth for the second symbol reduces the power consumption associated with the modulation scheme.

[0011] The load modulation circuit may include a controllable current source coupled to the DC side of the rectifier, and the higher modulation depth may correspond to a higher current drawn by the controllable current source. The load modulation circuit may include one or more controllable capacitors connected to the AC side of the rectifier. The one or more controllable capacitors may include at least one communication capacitor capable of being selectively coupled to ground via a communication switch. The one or more controllable capacitors may include: a capacitor bank including a first communication capacitor and one or more additional communication capacitors, the one or more additional communication capacitors being selectively coupled in parallel with the first communication capacitor via one or more switches corresponding to the one or more additional communication capacitors; and a communication switch selectively coupling the first communication capacitor and any communication capacitors selectively connected in parallel to ground. The one or more controllable capacitors may include at least one communication capacitor capable of being selectively coupled to ground via one or more of a plurality of communication switches capable of selectively operating in parallel.

[0012] A wireless power receiver may include: a wireless power transmission coil; a rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; a load modulation circuit; and a control circuit that operates the rectifier to supply power to a load coupled to the rectifier and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to an amplitude shift keying modulation scheme having multiple modulation depths.

[0013] The amplitude shift keying (ASK) modulation scheme may include initially applying an initial modulation depth to symbols transmitted to the wireless power transmitter; and increasing the modulation depth associated with the symbol in response to a communication failure, thereby improving communication reliability. Increasing the modulation depth associated with the symbol may include incrementally increasing the modulation depth in response to multiple communication failures. The ASK modulation scheme may also include decreasing the modulation depth associated with the symbol in response to the absence of a communication failure, thereby improving operational efficiency. Decreasing the modulation depth associated with the symbol may include incrementally decreasing the modulation depth in response to the absence of multiple communication failures.

[0014] The absence of a communication failure can be determined by referring to at least one of a missed response counter and a modulation timer. A communication failure can be determined by referring to a series of missed responses indicated by the counter. These multiple modulation depths can be selectively applied to symbols more susceptible to channel interference.

[0015] The load modulation circuit may include a controllable current source coupled to the DC side of the rectifier, and the higher modulation depth may correspond to a higher current drawn from the controllable current source. The load modulation circuit may include one or more controllable capacitors connected to the AC side of the rectifier.

[0016] A method for transmitting data from a wireless power receiver to a wireless power transmitter via load modulation can be performed by a control circuit of the wireless power receiver that operates the load modulation circuit of the wireless power receiver by: initially employing a first modulation depth for the symbol being transmitted to the wireless power transmitter; increasing the modulation depth associated with the symbol in response to a communication failure, thereby improving communication reliability; and decreasing the modulation depth associated with the symbol in response to the absence of a communication failure, thereby improving operational efficiency.

[0017] Increasing the modulation depth associated with a symbol may include incrementally increasing the modulation depth in response to multiple communication failures. Decreasing the modulation depth associated with a symbol may include incrementally decreasing the modulation depth in response to multiple absence of communication failures. The absence of communication failures may be determined by referring to at least one of a missed response counter and a modulation timer. Communication failures may be determined by referring to a series of missed responses indicated by the counter. The increased modulation depth may be selectively applied to symbols more susceptible to channel interference.

[0018] A wireless power receiver may include: a wireless power transmission coil; a rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; a load modulation circuit; and a control circuit that operates the rectifier to supply power to a load coupled to the rectifier and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to a modulation scheme. The modulation scheme employed by the control circuit may further include initially employing a first modulation depth for symbols transmitted to the wireless power transmitter; increasing the modulation depth associated with the symbol in response to a communication failure, thereby improving communication reliability; and decreasing the modulation depth associated with the symbol in response to the absence of a communication failure, thereby improving operational efficiency.

[0019] The modulation scheme employed by the control circuit may further include incrementally increasing the modulation depth in response to multiple communication failures and incrementally decreasing the modulation depth in response to multiple absence of communication failures. The symbol transmitted to the wireless power transmitter can be encoded using a differential Manchester coding scheme. The increased modulation depth can be selectively applied to symbols more susceptible to channel interference.

[0020] The load modulation circuit may include a controllable current source coupled to the DC side of the rectifier, and the higher modulation depth may correspond to a higher current drawn from the controllable current source. The load modulation circuit may include one or more controllable capacitors connected to the AC side of the rectifier. The one or more controllable capacitors may include at least one communication capacitor capable of being selectively coupled to ground via a communication switch. The one or more controllable capacitors may include: a capacitor bank including a first communication capacitor and one or more additional communication capacitors, the one or more additional communication capacitors being selectively coupled in parallel with the first communication capacitor via one or more switches corresponding to the one or more additional communication capacitors; and a communication switch selectively coupling the first communication capacitor and any communication capacitors selectively connected in parallel to ground. The one or more controllable capacitors may include at least one communication capacitor capable of being selectively coupled to ground via one or more of a plurality of communication switches capable of selectively operating in parallel. Attached Figure Description

[0021] Figure 1 A simplified block diagram of a wireless power transmission system is shown.

[0022] Figure 2 A schematic diagram illustrates a wireless power receiver that uses AC-side capacitor modulation for PRx to PTx communication.

[0023] Figure 3 A schematic diagram illustrates a wireless power receiver that uses DC-side load modulation for PRx to PTx communication.

[0024] Figure 4 An exemplary bit sequence of the differential Manchester coding scheme for in-band communication in a wireless power transmission system is illustrated.

[0025] Figure 5 Examples of using different modulation bit depths to improve the communication reliability of in-band communication in wireless power transmission systems are presented.

[0026] Figure 6 Examples illustrate the use of different modulation bit depths to improve the reliability and efficiency of in-band communication in wireless power transmission systems.

[0027] Figure 7 A flowchart illustrating the selection of different modulation bit depths to improve the communication reliability and efficiency of in-band communication in a wireless power transmission system is presented.

[0028] Figures 8A to 8B An alternative configuration of the capacitor modulation circuitry in capacitor modulation for PRx to PTx communication is illustrated.

[0029] Figure 9 An example of a control technique for controlling the modulation depth in a wireless power transmission system is illustrated. Detailed Implementation

[0030] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a full understanding of the disclosed concepts. As part of this description, for simplicity, some of the accompanying drawings of this disclosure are shown as block diagrams of structures and devices. For clarity, not all features of actual specific embodiments are described in this disclosure. Furthermore, the language used in this disclosure has been chosen for readability and guidance purposes and has not been selected to depict or limit the subject matter disclosed. Rather, the appended claims are intended for this purpose.

[0031] Various embodiments of the disclosed concepts are illustrated by way of example and are not limited to the individual figures, in which the same reference numerals indicate similar elements. For simplicity and clarity, reference numerals are repeated in different figures where appropriate to indicate corresponding or similar elements. Furthermore, numerous specific details are set forth to provide a full understanding of the specific embodiments described herein. In other instances, methods, procedures, and components are not described in detail so as not to obscure the related functions described. References to “an,” “a,” or “another” embodiments in this disclosure do not necessarily refer to the same or different embodiments, and imply at least one. The given figures may be used to illustrate more than one embodiment or more types of features of this disclosure, and not all elements in the figures may be necessary for a given embodiment or type. When provided in a given set of figures, reference numerals refer to the same elements throughout the figures, but may not be repeated in every figure. Unless otherwise specified, the figures are not drawn to scale, and the scale of certain parts may be enlarged to better illustrate the details and features of this disclosure.

[0032] Figure 1 A simplified block diagram of a wireless power transfer system 100 is illustrated. The wireless power transfer system includes a power transmitter (PTx) 110 that wirelessly transmits power to a power receiver (PRx) 120, such as via inductive coupling 103. The power transmitter 110 can receive input power, which is converted by an inverter 114 into an AC voltage with specific voltage and frequency characteristics. The inverter 114 can be controlled by a controller / communication module 116, which operates as further described below. In various embodiments, the inverter controller and communication module can be implemented in a common system, such as a microprocessor-based, microcontroller-based system. In other embodiments, the inverter controller can be implemented by a separate controller module and communication module having communication means therebetween. The inverter 114 can be constructed using any suitable circuit topology (e.g., full-bridge, half-bridge, etc.) and can be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., made using silicon, silicon carbide, or gallium nitride devices).

[0033] Inverter 114 delivers the generated AC voltage to transmitter coil 112. In addition to allowing magnetic coupling to the receiver's wireless coil, Figure 1The illustrated transmitter coil block 112 may include tuning circuitry (such as additional inductors and capacitors) that facilitates transmitter operation under various conditions, such as different degrees of magnetic coupling to the receiver, different operating frequencies, etc. The wireless coil itself can be constructed in a variety of different ways. In some embodiments, the wireless coil may be formed as a metal wire winding around a suitable spool. In other embodiments, the wireless coil may be formed as a trace on a printed circuit board. Other arrangements are also possible and can be used in conjunction with the various embodiments described herein. The wireless transmitter coil may also include a magnetically permeable material (e.g., ferrite) core configured to influence the flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of the various transmitter coil arrangements suitable for a given application.

[0034] The PTx controller / communication module 116 can monitor the transmitter coil and use information derived therefrom to control the inverter 114 to suit a given situation. For example, the controller / communication module can be configured to operate the inverter 114 at a given frequency or output voltage depending on the specific application. In some embodiments, the controller / communication module can be configured to receive information from the PRx device and control the inverter 114 accordingly. This information can be received via the power transmission coil (i.e., in-band communication) or via a separate communication channel (not shown, i.e., out-of-band communication). For in-band communication, the controller / communication module 116 can detect and decode signals (such as voltage, frequency, or load changes) applied to the magnetic link by the PRx to receive information, and can command the inverter to modulate the delivered power to transmit information to the PRx by manipulating various parameters of the generated voltage (such as voltage, frequency, etc.). In some embodiments, the controller / communication module can be configured to use frequency shift keying (FSK) communication to transmit data to the PRx, in which the frequency of the inverter signal is modulated. The controller / communication module 116 can be configured to detect amplitude shift keying (ASK) communication or load-modulated communication from the PRx. In either case, the controller / communication module 126 can be configured to change the current drawn on the receiver side to manipulate the waveform seen on the Tx coil, thereby delivering information from the PRx to the PTx. For out-of-band communication, additional modules, such as WiFi, Bluetooth, or other radio links, or any other suitable communication channel, can be provided to allow communication between the PTx and PRx.

[0035] As described above, the controller / communication module 116 can be, for example, a single module disposed on a single integrated circuit, or it can be constructed from multiple modules / devices disposed on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of the controller / communication circuitry.

[0036] The PTx device 110 may optionally include other systems and components, such as a separate communication module 118. In some embodiments, the communication module 118 may communicate with a corresponding module in the PRx via a power delivery coil. In other embodiments, the communication module 118 may communicate with the corresponding module using a separate physical channel 108.

[0037] As mentioned above, the wireless power transmission system also includes a wireless power receiver (PRx) 120. The wireless power receiver may include a receiver coil 122 that is magnetically coupled 103 to the transmitter coil 112. As discussed above, the transmitter coil 112... Figure 1 The illustrated receiver coil block 122 may include tuning circuitry (such as additional inductors and capacitors) that facilitates the operation of the transmitter under various conditions, such as different degrees of magnetic coupling to the receiver, different operating frequencies, etc. The wireless coil itself can be constructed in a variety of different ways. In some embodiments, the wireless coil may be formed as a metal wire winding around a suitable spool. In other embodiments, the wireless coil may be formed as a trace on a printed circuit board. Other arrangements are also possible and can be used in conjunction with the various embodiments described herein. The wireless receiver coil may also include a magnetically permeable material (e.g., ferrite) core configured to influence the flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of the various receiver coil arrangements suitable for a given application.

[0038] Receiver coil 122 outputs an AC voltage induced therein via transmitter coil 112 through magnetic induction. This output AC voltage can be provided to rectifier 124, which provides DC output power to one or more loads associated with the PRx device. Rectifier 124 can be controlled by controller / communication module 126, which operates as further described below. In various embodiments, the rectifier controller and communication module can be implemented in a common system, such as a microprocessor-based, microcontroller-based system. In other embodiments, the rectifier controller can be implemented by a separate controller module and communication module having communication means therebetween. Rectifier 124 can be constructed using any suitable circuit topology (e.g., full-bridge, half-bridge, etc.) and can be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., made using silicon, silicon carbide, or gallium nitride devices).

[0039] The PRx controller / communication module 126 can monitor the receiver coil and use information derived therefrom to control the rectifier 124 to suit a given situation. For example, the controller / communication module can be configured to cause the rectifier 124 to provide a given output voltage depending on the specific application. In some embodiments, the controller / communication module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information can be received via the power transmitting coil (i.e., in-band communication) or transmitted via a separate communication channel (not shown, i.e., out-of-band communication). For in-band communication, the controller / communication module 126 can, for example, modulate the load current or other electrical parameters of the received power to transmit information to the PTx. In some embodiments, the controller / communication module 126 can be configured to detect and decode signals (such as voltage, frequency, or load changes) applied to the magnetic link by the PTx to receive information from the PTx. In some embodiments, the controller / communication module 126 can be configured to receive frequency shift keying (FSK) communication to transmit data to the PRx, in which the frequency of the inverter signal has been modulated. The controller / communication module 126 can be configured to generate amplitude shift keying (ASK) communication or load modulation-based communication from the PRx. In either case, the controller / communication module 126 can be configured to change the current drawn on the receiver side to manipulate the waveform seen on the Tx coil, thereby delivering information from the PRx to the PTx. For out-of-band communication, additional modules, such as WiFi, Bluetooth, or other radio links, or any other suitable communication channel, can be provided to allow communication between the PTx and PRx.

[0040] As mentioned above, the controller / communication module 126 may be a single module disposed on a single integrated circuit, or it may be constructed from multiple modules / devices disposed on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of the controller / communication circuitry. The PRx device 120 may optionally include other systems and components, such as a communication (“communication” module 128. In some embodiments, the communication module 128 may communicate with a corresponding module in the PTx via a power delivery coil. In other embodiments, the communication module 128 may communicate with the corresponding module using a separate physical channel 108.

[0041] Many variations and enhancements to the wireless power transmission system 100 described above are possible, and the following teachings apply to any of such variations and enhancements.

[0042] As described above, load modulation can be used to facilitate in-band communication in wireless power transfer systems. For example, receiver-side load modulation can be used to enable amplitude shift keying (ASK) communication from a PRx device to a PTx device. This paper describes an improved modulation scheme based on two or more separate modulation depths for 0 bits (zero bits) and 1 bits (one bit) to allow for improved communication performance while also allowing for reduced energy usage in the load modulator, thereby improving operational efficiency while maintaining or improving communication reliability. The approach described herein can be robust, highly integrable (requiring no additional passive components), and low-cost. Reduced energy consumption can improve the user experience, for example, by improving charging efficiency in the form of faster charging times. Furthermore, in some implementations, the improved modulation technique can be implemented entirely on the power receiver side (PRx), allowing this technology to be combined with Qi and / or proprietary wireless power transmitters (PTx) without modification on the PTx side. Qi is a family of wireless power transfer standards issued by the Wireless Power Consortium.

[0043] In wireless power transmission, in-band communication (i.e., modulating power waveforms to transmit information) can be used to allow in-band communication, that is, communication that uses the wireless power transmission itself as a communication channel. Amplitude Shift Keying (ASK) can be used to send information from the PRx to the PTx. An industry standard for wireless power transmission (the Qi standard cited above) describes two circuit structures for implementing ASK: AC-side modulation and DC-side modulation. AC-side modulation can be implemented in different ways, for example, by changing the AC impedance of the PRx circuit, or by carefully manipulating the rectifier signal. See below for reference. Figure 2 An exemplary implementation of AC-side modulation using additional capacitors and switches is described. DC-side modulation can employ a modulator that generates data-dependent load current variations on the DC side of the PRx rectifier. A common implementation uses a controlled current source as the modulator connected to the rectifier's DC line. This adds a transient additional load to the PRx rectifier output. See below for reference. Figure 3 An exemplary implementation scheme is described.

[0044] Figure 2A schematic diagram illustrating a wireless power receiver (PRx) 220 for PRx-PTx communication using AC-side capacitor modulation is shown. The wireless power receiver 220 includes a receiver coil 122 as described above. The receiver coil 122 can be coupled to a rectifier circuit via a resonant capacitor 223. The illustrated exemplary rectifier circuit is depicted as a full-bridge rectifier composed of switching devices 224a-224b (depicted as MOSFETs); however, other rectifier topologies and / or other rectifier switching device types may be appropriately used for a given application. The rectifier output is a DC voltage Vrect, which may appear across the output capacitor Crect and may be supplied to a load (not shown), such as a battery for an electronic device or other power system.

[0045] The wireless power receiver 220 may also include capacitor modulator circuitry 227. In the illustrated exemplary embodiment, this includes communication capacitors 223a and 223b connected to each AC branch of the receiver winding resonant circuit, which can be selectively coupled to ground (e.g., the negative power supply rail of the rectifier output) via switching devices 235a and 235b. These switching devices are depicted as MOSFETs, similar to rectifier switches; however, other types of switching devices may be appropriately used for a given application. In any case, selectively coupling or decoupling these capacitors from the circuitry allows modulation of the AC impedance seen by the wireless power transmitter, thereby enabling communication from the wireless power receiver 220 to the wireless power transmitter.

[0046] The switching devices of the wireless power transmitter 220 may (but need not) be integrated into a single integrated circuit 231, which may also include the controller and communication circuitry 126 as described above. The communication capacitor may be separate from the integrated circuit 231 (e.g., Figure 2 (As depicted), this allows their values ​​to be changed according to the requirements of a specific system. Alternatively, communication capacitors can also be part of an integrated circuit. AC-side capacitance modulation provides advantages such as increased bandwidth, and message propagation from PRx to PTx can occur rapidly.

[0047] Figure 3A schematic diagram illustrating a wireless power receiver (PRx) 320 for PRx-PTx communication using DC-side load modulation is shown. The wireless power receiver 320 includes a receiver coil 122 as described above. The receiver coil 122 can be coupled to a rectifier circuit via a resonant capacitor 223. The illustrated exemplary rectifier circuit is depicted as a full-bridge rectifier composed of switching devices 224a-224b (depicted as MOSFETs); however, other rectifier topologies and / or other rectifier switching device types may be appropriately used for a given application. The rectifier output is a DC voltage Vrect, which may appear across the output capacitor Crect and may be supplied to a load (not shown), such as a battery for an electronic device or other power system.

[0048] The wireless power receiver 220 may also include load modulator circuitry 327. In the illustrated exemplary embodiment, this is depicted as a controllable current source that adds a momentary additional load to the PRx rectifier output. Although described herein as a current “source,” the circuitry may also be considered a current “sink” as it increases the current drawn from the rectifier and thus ultimately increases the current drawn from the wireless power receiver coil and the PTx device. Although the term “current source” is used herein, it should be understood to include a current sink. Other embodiments of such circuitry are known to those skilled in the art; therefore, details of such circuitry are omitted herein for brevity. The switching devices of the wireless power transmitter 320, along with the load modulator circuitry 327, may (but need not) be integrated into a single integrated circuit 331, which may also include the controller and communication circuitry 126 as described above. The advantages of DC-side modulation may include a reduction in passive components, such as AC-side communication capacitors. When load modulation is employed, various modulation and coding schemes can be used. It may be desirable to have a load modulation scheme that reduces power dissipation in ASK communication, thus allowing its application in higher power designs, while simultaneously achieving higher modulation current and Vrect values. It may also be desirable to prevent Vrect from decreasing, thereby maintaining the power delivery capability of the PTx-PRx system. Furthermore, it may be desirable to implement such schemes with a reduced number of passive components.

[0049] As mentioned above, at least one industry standard employs amplitude shift keying (ASK), where the amplitude of a signal is modulated to provide data communication. Different techniques can be used to encode amplitude-based modulated data about a load signal, such as differential Manchester coding. Figure 4An exemplary form of differential Manchester encoding is depicted. Differential Manchester encoding uses the variation in the amplitude of the modulation current in each bit period to represent 1 or zero. Therefore, each bit period will have at least one modulation current (or voltage) transition during each bit period. A “guaranteed” transition may occur, for example, at the beginning of the bit period. In some encoding schemes, this can be used to encode zero bits. Therefore, for a single bit, there will be a second transition during the bit period, as further described below.

[0050] Figure 4 An exemplary bit sequence of the differential Manchester coding scheme for in-band communication in a wireless power transmission system is illustrated. Figure 4 The upper portion depicts eight possible bit-pair codes 441-448 for each possible two-bit sequence. Each bit-pair code exemplifies two bit periods, one bit period per bit. Which of the two possible codes used for each bit pair depends on the value of the preceding bit. Bit-pair code 441 depicts one possible code for a zero bit followed by a zero bit (i.e., 00). Thus, there is a single high-to-low transition between the two bit periods. Bit-pair code 442 depicts an alternative possible code for a zero bit followed by a zero bit (i.e., 00). Thus, there is a single low-to-high transition between the two bit periods. Similarly, bit-pair codes 443 and 444 depict a zero bit followed by a bit (i.e., 01). These codes include a single transition during the first bit period for zero (at the beginning of the first bit period), a second transition at the beginning of the second bit period, and a third transition in the middle of the second bit period corresponding to a bit. Likewise, bit-pair codes 445 and 446 depict a bit followed by a zero bit (i.e., 10). These codes include a first transition at the beginning of the first bit cycle corresponding to 1, wherein a second transition also occurs during the first bit cycle, and a third transition at the beginning of the second bit cycle corresponding to the zero bit. Finally, bit pair codes 447 and 448 depict a bit followed by another bit (i.e., 11). These codes include a first transition at the beginning of the first bit cycle corresponding to 1, wherein a second transition also occurs during the first bit cycle, and a third transition at the beginning of the second bit cycle corresponding to 1, wherein a second transition also occurs during the second bit cycle. These eight possible bit pair codes 441-448 are combined into a bit stream 449 indicating possible transitions.

[0051] As understood from the preceding text, a differentially encoded Manchester-coded ASK signal associated with one or more bits can have a higher frequency content than one or more zero bits. In other words, a zero bit may have only a single transition of the modulation current per bit cycle, while a single bit has two transitions per bit cycle. When a wireless power transfer circuit is used as a communication channel, this circuit can exhibit different electrical behaviors at different frequencies associated with a single bit and a zero bit. For example, an inductive power transfer system can act as a low-pass filter, attenuating a portion of the signal associated with a single bit. This can become more pronounced as the communication data rate and therefore the effective frequency of the differentially encoded Manchester-coded ASK signal increases.

[0052] In the event of unsuccessful ASK communication, one mitigation method could be to increase the amplitude of the modulation current, such as... Figure 5 As shown, this illustrates the use of different modulation bit depths to improve the communication reliability of in-band communication in wireless power transmission systems. This single modulation current level can be referred to as the modulation depth, and Figure 5 The scheme described herein can be referred to as a one-layer modulation depth method because it uses only a single modulation current level. Therefore, a first lower modulation current level 537 can be used to modulate bit stream 549a (which corresponds to the one mentioned above in the reference). Figure 4 The bitstream discussed is 449). In cases of unsuccessful communication, such as when PTx fails to successfully detect and / or decode the load modulation for any of a variety of reasons, the modulation bit depth can be increased, as... Figure 5 The lower part is depicted. More specifically, bit stream 459b (also corresponding to bit stream 449 discussed above) can be modulated with an increased modulation depth 539 higher than the initial modulation depth 537. In other words, a higher current value is used, which imposes a larger load variation that is presumably easier to detect and decode by the receiving device (e.g., a PTx device). In some implementations, the modulation current may have multiple bit depths corresponding to different modulation currents. As an example, the modulation depth may be between 30mA and 140mA in 20mA steps, although other minimum, maximum, and step values ​​may also be used.

[0053] exist Figure 5 As can be seen, for all zero bits with a non-zero modulation current, the duration of current flow is twice that for a single bit. This means that the energy dissipation associated with a zero bit (with a non-zero modulation current) can be approximately twice that associated with a single bit. To reduce the energy consumption of in-band communication while mitigating the potential impact on the robustness of ASK modulation and differential Manchester coding schemes, improved techniques are likely desirable. In at least some applications, such solutions can provide similar energy dissipation for both zero and single bits for the desired communication. V The rect value can provide an energy dissipation ratio closer to one for zero bits (with non-zero modulation current) than for one bit.

[0054] The inventors' research has revealed that at operating points with unfavorable conditions, ASK packet failures often occur first in a single bit, although ASK communication failures may be caused by the failure to correctly receive one or more single bits or one or more zero bits. This is believed to stem from the lower amplitude of a single bit relative to a zero bit due to the higher frequency content of the single bit and the low-pass nature of the channel. Therefore, a single bit is considered to be more affected by the nature of the wireless power path.

[0055] Figure 6 Examples illustrate the improved use of different modulation bit depths (e.g., two-layer modulation) to enhance the communication reliability and efficiency of in-band communication in wireless power transmission systems. More specifically, Figure 6 The arrangement illustrated here enhances a bit that is more prone to failure without unnecessarily increasing the energy consumption associated with the zero bit. Such a solution can be provided by using two separate modulation depths, one for the zero bit and the other for the first bit, instead of a single-level (one-layer) modulation depth that increases uniformly for both the first and zero bits (as referenced above). Figure 5 (As described above). In an example of a wireless power receiver (PRx) communicating with a wireless power transmitter (PTx), the PRx can initially apply a minimum modulation depth value to both the zero bit and the one bit to establish ASK communication with minimal power consumption, such as... Figure 6 The top drawing in the diagram shows this. Therefore, bitstream 649a can be modulated using a first modulation depth of 637. In the event of unsuccessful communication, the initial response may include increasing the modulation depth for a single bit, but not for a zero bit, as shown in the diagram above. Figure 6 The intermediate plot is shown in the diagram. In other words, the zero bit of bit stream 649b can continue to be modulated using the initial modulation depth 637, while a single bit can be modulated using a second modulation depth 639 that is higher than the first modulation depth 637 (e.g., corresponding to a higher current). This reduces the energy used by the zero bit. If a persistent communication failure exists, the modulation depth can also be increased for the zero bit, such as... Figure 6 The lower part of the drawing shows that bit stream 649c has both zero bits and one bit modulated by a second modulation depth 639 greater than the first modulation depth 637.

[0056] Figure 7 Examples of descriptions are shown in the reference. Figure 6 The flowchart 700 describes the selection of different modulation bit depths to improve the communication reliability and efficiency of in-band communication in a wireless power transmission system. Such a method can be formed by the controller of a communication transmitting device, which can be a wireless power receiver as described above. Therefore, Figure 7 The method described herein can be performed, for example, by the controller and communication circuitry 126 described above. Other implementations are also possible, wherein the method can be performed by other suitable processing or control circuitry in various types of devices. Starting from block 751, the controller can use an initial modulation depth, for example, Figure 6 Modulation depth 637 is depicted and described above. Then, in block 753, the controller can determine whether communication was successful. This can be determined in various ways, including receiving a communication failure indication from a communication receiving device (e.g., a wireless power transmitter / PTx device). Such a communication failure indication can be an explicit message received from the corresponding device, or an inference derived from the behavior of the corresponding device, such as the absence of an expected acknowledgment.

[0057] If the controller determines in box 753 that communication has been successful, it may continue to use the initial modulation depth (box 751). Alternatively, if the controller determines in box 753 that communication has not been successful, it may use an increased modulation depth for one bit (box 755), as described above. It should be noted that in other modulation schemes, the increased modulation depth may be used for other bits. As an example, if one bit is encoded using a single transition per bit period and a zero bit is encoded using two transitions per bit period, the increased modulation depth may be more appropriately used with the zero bit. Therefore, a more general statement of this solution could be to use the increased modulation depth for symbols more susceptible to disruptions in the communication channel conditions, while maintaining the initial modulation depth for symbols less susceptible to such disruptions.

[0058] In any case, in box 757, the controller can determine whether communication using the first modulation layer is successful, where the increased modulation depth is used only for certain symbols (e.g., one bit). If communication at the first layer is successful, the controller can continue using that modulation configuration (box 755). Alternatively, if the controller determines in box 757 that communication is unsuccessful, the controller can use the increased modulation depth for all bits (box 759), as described above. Thus, a more general statement of the solution could be to use the increased modulation depth for symbols more susceptible to disruptions in the communication channel conditions, while maintaining the initial modulation depth for symbols less susceptible to such disruptions.

[0059] The modulation scheme can be further extended based on what has been described herein. For example, additional modulation bit depth can be provided, which can further increase the detectability and decodeability of the ASK signal. As in the example described above, the increase in these still relatively high modulation depths can be done gradually, initially applied to symbols more susceptible to channel degradation, and only subsequently applied to all symbols if the initial adjustment does not guarantee successful communication. Alternatively, the gradual increase in modulation depth can be applied to all symbols simultaneously.

[0060] The multilayer modulation scheme described above, which selectively employs increased modulation depth for one or more transmitted symbols, is already being used in applications such as those described above. Figure 3 The description is within the context of wireless power transmitters with DC-side load modulation. More specifically, such schemes have been described in the context of increased load current drawn by a current source associated with such schemes to increase modulation depth. However, the modulation schemes described herein are not limited to increasing the current on the DC side to increase modulation depth. Various techniques can be employed on both the DC and AC sides to provide transmit power modulation that can be detected and decoded by the wireless power transmitting device (communication receiving device). This modulation can be voltage, current, complex impedance phase angle, active power level, reactive power level, etc. As an example, the modulation technique can be extended to capacitor modulation circuits employed on the AC side, as described above relative to... Figure 2 As described above, such systems can selectively change the parameters of reactive power circuits with different modulation depths to achieve similar effects. Figures 8A to 8B An alternative configuration of the capacitor modulation circuit for such implementation is illustrated.

[0061] Figure 8A An exemplary capacitor modulation circuit 800a is illustrated, an example of which can be used on each branch of the PRx AC side, as described above relative to... Figure 2 The switch 835a can be a communication switch, and the communication capacitance can be changed to alter the modulation depth. Therefore, a single communication capacitor 833a can be used in some cases. One or more additional communication capacitors 833b-833d can be selectively coupled in parallel with the communication capacitor 833a via corresponding switches 836b-836d. This allows for different modulation depths as described above.

[0062] Figure 8B An alternative exemplary capacitor modulation circuit 800b is illustrated, examples of which can be used on each branch of the PRx AC side, as described above relative to... Figure 2 The switch 835a-1 can be a communication switch, and the capacitor 833a can be a communication capacitor. Additional switches 835a-2-835a-4 can be connected in parallel with the communication switch 835a-1 and can be selectively operated before and after it to present different resistances in the circuit. These different resistances, associated with the parallel connection of the Rdson resistors of the respective switches, can be used to change the characteristics of the capacitor modulation circuit and thus provide different modulation depths as described herein.

[0063] Figure 9A flowchart 900 illustrates a control technique for controlling multi-layer modulation depth in a wireless power transmission system. This control technique can be applied to a multi-layer modulation depth system as described above. This can include, but is not limited to, modulation schemes in which different modulation depths are applied to some symbols (e.g., symbols more susceptible to channel interference) and other symbols (e.g., symbols less susceptible to channel interference). This can include, but is not limited to, the Manchester coding scheme as described above. Furthermore, [the following can be used...] Figure 9 The control technology is applied to multi-layer modulation schemes, where the same modulation depth is applied to all symbols.

[0064] Further reference Figure 9 The control technology 900 can be performed by the wireless power receiver, for example, by the control / communication circuitry of the wireless power receiver as described above. Starting at block 960, the wireless power receiver can send communications, such as ASK communications, to the wireless power transmitter. The wireless power transmitter is expected to respond, for example, with an FSK message. In some embodiments, this can be a CE (Control Error) or XCE (Extended Control Error) grouping according to a version of the Qi standard issued by the Wireless Power Consortium, potentially including extensions to such standards, which may include public and / or proprietary extensions. In other cases, other types of communications from the wireless power transmitter in response to ASK communications from the wireless power receiver can be used. In any case, in block 961, the wireless power receiver can determine whether a response to the ASK communications in block 960 has been received. If not received, in block 962, the wireless power receiver can set a modulation timer. Such a modulation timer is discussed in more detail below with reference to blocks 967 and 969.

[0065] Subsequently, the wireless power receiver can determine whether the missed response count (discussed further below) is greater than 2, i.e., whether two or fewer expected communications from the wireless power transmitter have been missed. If it is not greater than 2, i.e., two or fewer expected responses from the wireless power transmitter have been missed, the wireless power receiver can increment the missed response counter (box 964) and send another ASK communication (box 960), at which point the process can be repeated. Otherwise, if the missed response count is greater than 2 in box 963, meaning more than two expected responses from the wireless power transmitter have been missed, the wireless power receiver can increase the modulation depth (box 965). As mentioned above, this can include increasing the modulation depth only for certain symbols that are more susceptible to channel interference, or it can include increasing the modulation depth for all symbols. Alternatively, increasing the modulation depth can be done by increasing the modulation depth by one step across multiple available modulation depths. In any case, the receiver can then send another ASK communication message using the increased modulation depth (box 960), where the process is repeated.

[0066] After sending the ASK communication in box 960, if the wireless power receiver determines in box 961 that a wireless power response has been received, the wireless power receiver can reset the missed response counter to zero in box 966. The incrementing of the missed response counter was discussed above with reference to box 964. The wireless power receiver can then check in box 967 whether the modulation timer (set in box 962 as discussed above) is greater than zero (i.e., not off). If it is greater, the wireless power receiver can send another ASK communication with the current modulation depth (box 960). Otherwise, if the modulation timer has been off, indicating that the current modulation depth has been used for a sufficient period of time, the wireless power receiver can decrease the modulation depth (box 968) and reset the modulation timer (box 969). The modulation timer can be initially set to a value corresponding to a period of time during which communication can be considered stable and successful if all expected responses are received within that interval. In some embodiments, the timer can be initially set (in box 962) and reset (in box 969) to 1500 ms, although other values ​​may also be used.

[0067] In order to summarize relative to Figure 9 In the operation described above, a wireless power receiver (e.g., using its controller / communication circuitry) can send communication packets, such as ASK communication packets, to another wireless power transmitter. If no expected response (e.g., FSK communication packets) is received from the wireless power transmitter, a timer can be set and a counter incremented. If a consecutive number of expected responses are not received, the modulation depth can be increased. In some embodiments, the consecutive number of missed expected responses can be three (i.e., greater than 2), although other thresholds may also be used. As mentioned above, increasing the modulation depth can be incremental, meaning that multiple incremental increases in modulation depth can be applied in response to multiple repeating sequences of missed expected communications. Additionally or alternatively, the increase in modulation depth can be selectively applied to certain symbols that are more susceptible to channel interference, but not to others, to improve operational efficiency, as described above. In some cases, the continuous incremental increase in modulation depth may include increasing the modulation depth for certain symbols that are more susceptible to channel interference in response to a first sequence of missed expected communications, and subsequently increasing the modulation depth to the same level for all symbols in response to a second sequence of missed expected communications, wherein alternating / selective application continues further in response to persistent communication failures.

[0068] In some cases, the number of missed communications that trigger an increase in modulation depth can be related to the modulation timer. In other words, if a response is expected at intervals such as 250 ms, the count of such packets (e.g., 3) may correspond to half of the modulation timer, such as 750 ms. In other cases, the count may correspond to the modulation timer, a multiple of the modulation timer (e.g., 2x, 3x, etc.), or a fraction of the modulation timer (e.g., x / 2, x / 3, etc.).

[0069] Continue to refer to Figure 9 In summary, the missed response counter can be reset if an expected response (e.g., an FSK communication packet) is received from the wireless power transmitter. If the modulation timer has already expired, this, combined with the number of consecutive received expected responses indicating successful communication conditions, can decrease the modulation depth and reset the modulation timer. Otherwise, if the timer has not expired, this can be an indication that the channel conditions appear sufficient, but more time is needed to verify that a lower modulation depth can be attempted. As described in the preceding paragraphs, the missed response counter value and the timer value can be correlated such that the timer corresponds to a selected number of successfully received packets. Similar to the increase in modulation depth, the decrease in modulation depth can also be gradual, as described above, meaning that multiple incremental reductions in modulation depth can be applied in response to multiple repetitive sequences of received expected communications within a selected time interval. Additionally or alternatively, the reduction in modulation depth can be selectively applied to certain symbols less susceptible to channel interference, while omitting those more susceptible to channel interference, to improve operational efficiency, as described above. In some cases, the incremental reduction of modulation depth may include reducing the modulation depth for certain symbols that are less susceptible to channel interference in response to a first sequence of expected communication, and then reducing the modulation depth to the same level for all symbols in response to a second sequence of expected communication, wherein the alternating / selective application continues further in response to successful continued communication.

[0070] Depending on the implementation details, the improved multilayer modulation scheme for in-band communication in wireless power transfer systems, as described herein, offers several advantages. For example, such systems can reduce energy dissipation in the load modulator by reducing the energy used for zero and one bits. Lower power dissipation allows for smaller integrated circuit silicon area, increased operating efficiency, easier PCB design, and potentially higher reliability. These advantages may be particularly beneficial in certain types of wireless power receiver devices, such as smartphones, smartwatches, and other wearable devices. Additional potential advantages may include a lower reduction in Vrect for zero bits during ASK communication, which increases wireless power transfer capability, thereby allowing for shorter charging times in at least some applications.

[0071] Such multilayer modulation and coding schemes can also be used with higher data rate communications without further modification or adaptation. Similarly, it can be used with any of a variety of higher switching frequencies, which can be associated with improved industry-standard wireless power transfer technologies and / or various proprietary wireless power transfer technologies. In some PRx configurations (e.g., as described above relative to...), Figure 2 and Figure 3 In the case described, no additional passive components are required, nor are any additional terminals needed for the receiver integrated circuit (if such a device is provided in the form of such integrated circuits). This allows for highly integrable designs where the ratings of the power circuit components remain unaffected.

[0072] Furthermore, such multi-layer modulation schemes are not particularly sensitive to component tolerances. Additionally, such modulation techniques can be completely transparent to the PTx side (i.e., the communication receiving device). Therefore, a PRx using this approach can be compatible with any existing wireless power transmitter that is already compatible with it. In at least some cases, the use of such multi-layer modulation schemes extends the range of operable PTx-PRx misalignment because it increases the Vrect voltage, thereby allowing the system to operate further away from any undervoltage drop limitations.

[0073] The foregoing describes various features and embodiments related to modulation bit depth adjustment for in-band communication in wireless power transmission systems. Such arrangements can be used in a variety of applications, but are particularly advantageous when used in conjunction with electronic devices (such as mobile phones, tablets, laptops, or notebooks) and accessories (such as wireless headsets, styluses, etc.). Additionally, although many specific features and various embodiments have been described, it should be understood that, unless otherwise stated to be mutually exclusive, various combinations of features and embodiments can be made in specific implementations. Therefore, the various embodiments described above are provided merely by way of illustration and should not be construed as limiting the scope of this disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of this disclosure and the claims.

[0074] The foregoing describes an exemplary implementation of a wireless power transmission system capable of sending certain information between PTx and PRx within the system. This disclosure envisions this information transmission improving the ability of devices to efficiently provide wireless power signals to each other to facilitate battery charging, such as by sharing the power handling capabilities of the devices. Entities implementing this technology should take care to ensure compliance with established privacy policies and / or privacy practices to the extent that any sensitive information is used in a particular specific implementation. Specifically, such entities will be expected to implement and consistently apply privacy practices generally recognized as meeting or exceeding industry or governmental requirements for maintaining user privacy. Implementers should inform users where personally identifiable information is expected to be sent in the wireless power transmission system and allow users to "optionally join" or "optionally leave" participation. For example, if the power transmitter is configured to poll for sensitive information from the power receiver, such information may be presented to the user when the user places a device on the power transmitter.

[0075] Once data is no longer needed, risks can be minimized by limiting data collection and deleting data. Furthermore, and where applicable, data de-identification can be used to protect user privacy. For example, device identifiers can be partially masked to convey the power characteristics of a device rather than uniquely identifying it. De-identification can be facilitated, where appropriate, by removing identifiers, controlling the amount or specificity of stored data (e.g., collecting location data at the city level rather than the address level), controlling how data is stored (e.g., aggregating data among users), and / or other methods (such as differentiated privacy). Robust encryption can also be used to reduce the likelihood of communication between inductively coupled devices being spoofed.

Claims

1. A wireless power receiver, the wireless power receiver comprising: Wireless power transfer coil; A rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; Load modulation circuit; and A control circuit operates the rectifier to supply power to a load coupled to the rectifier, and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to an amplitude shift keying modulation scheme having multiple modulation depths.

2. The wireless power receiver according to claim 1, wherein the amplitude shift keying modulation scheme comprises: An initial modulation depth is initially applied to the symbols transmitted to the wireless power transmitter; as well as In response to a communication failure, the modulation depth associated with the symbol is increased, thereby improving communication reliability.

3. The wireless power receiver of claim 2, wherein increasing the modulation depth associated with the symbol comprises incrementally increasing the modulation depth in response to multiple communication failures.

4. The wireless power receiver according to claim 3, wherein the amplitude shift keying modulation scheme further includes: In response to the absence of communication failure, the modulation depth associated with the symbol is reduced, thereby improving operational efficiency.

5. The wireless power receiver of claim 4, wherein reducing the modulation depth associated with the symbol comprises incrementally reducing the modulation depth in response to multiple absence of communication failures.

6. The wireless power receiver of claim 4, wherein the absence of communication failure is determined by reference to at least one of a missed response counter and a modulation timer.

7. The wireless power receiver of claim 2, wherein the communication failure is determined with reference to a series of missed responses indicated by a counter.

8. The wireless power receiver of claim 1, wherein the plurality of modulation depths are selectively applied to symbols more susceptible to channel interference.

9. The wireless power receiver of claim 1, wherein the load modulation circuitry includes a controllable current source coupled to the DC side of the rectifier, and a higher modulation depth corresponds to a higher current drawn from the controllable current source.

10. The wireless power receiver of claim 1, wherein the load modulation circuit includes one or more controllable capacitors connected to the AC side of the rectifier.

11. A method for transmitting data from a wireless power receiver to a wireless power transmitter via load modulation, the method being performed by a control circuit of the wireless power receiver that operates the load modulation circuit of the wireless power receiver by: A first modulation depth is initially applied to the symbols transmitted to the wireless power transmitter; In response to a communication failure, the modulation depth associated with the symbol is increased, thereby improving communication reliability; and In response to the absence of communication failure, the modulation depth associated with the symbol is reduced, thereby improving operational efficiency.

12. The method of claim 11, wherein increasing the modulation depth associated with the symbol comprises incrementally increasing the modulation depth in response to multiple communication failures.

13. The method of claim 11, wherein reducing the modulation depth associated with the symbol comprises incrementally reducing the modulation depth in response to multiple absence of communication failures.

14. The method of claim 11, wherein the absence of communication failure is determined by reference to at least one of a missed response counter and a modulation timer.

15. The method of claim 11, wherein the communication failure is determined with reference to a series of missed responses indicated by a counter.

16. The method of claim 11, wherein the increased modulation depth is selectively applied to symbols more susceptible to channel interference.

17. A wireless power receiver, the wireless power receiver comprising: Wireless power transfer coil; A rectifier that receives an AC voltage induced in the wireless power transmission coil by a wireless power transmitter and thereby generates a DC output voltage; Load modulation circuit; and A control circuit operates the rectifier to supply power to a load coupled to the rectifier, and operates the load modulation circuit to communicate with the wireless power transmitter by selectively changing the power drawn from the wireless power transmission coil according to a modulation scheme, wherein the modulation scheme employed by the control circuit further includes: A first modulation depth is initially applied to the symbols transmitted to the wireless power transmitter; In response to a communication failure, the modulation depth associated with the symbol is increased, thereby improving communication reliability; and In response to the absence of communication failure, the modulation depth associated with the symbol is reduced, thereby improving operational efficiency.

18. The wireless power receiver of claim 17, wherein the modulation scheme employed by the control circuit further comprises: The modulation depth is incrementally increased in response to multiple communication failures; as well as The modulation depth is incrementally reduced in response to multiple non-existent communication failures.

19. The wireless power receiver of claim 17, wherein the symbols transmitted to the wireless power transmitter are encoded using a differential Manchester coding scheme.

20. The wireless power receiver of claim 19, wherein the increased modulation depth is selectively applied to symbols more susceptible to channel interference.

21. The wireless power receiver of claim 17, wherein the load modulation circuitry includes a controllable current source coupled to the DC side of the rectifier, and a higher modulation depth corresponds to a higher current drawn from the controllable current source.

22. The wireless power receiver of claim 17, wherein the load modulation circuitry includes one or more controllable capacitors connected to the AC side of the rectifier.

23. The wireless power receiver of claim 22, wherein the one or more controllable capacitors include at least one communication capacitor capable of being selectively coupled to ground via a communication switch.

24. The wireless power receiver of claim 23, wherein the one or more controllable capacitors comprise: A capacitor bank, the capacitor bank including a first communication capacitor and one or more additional communication capacitors, the one or more additional communication capacitors being selectively coupled in parallel with the first communication capacitor via one or more switches corresponding to the one or more additional communication capacitors; and A communication switch that selectively couples the first communication capacitor and any communication capacitors selectively connected in parallel to ground.

25. The wireless power receiver of claim 23, wherein the one or more controllable capacitors include at least one communication capacitor capable of being selectively coupled to ground via one or more of a plurality of communication switches capable of selectively operating in parallel.

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