Systems and methods for calibration of a wireless power transmitter

Systems and methods for alignment and calibration of a wireless power transmitter and a wireless power receiver are disclosed. According to one aspect, a wireless power transmit coil is first aligned with a wireless power receive coil. An alignment signal is received indicated that the transmit coil and the receive coil are aligned is received by the wireless power transmitter. A signal indicative of a characteristic of an electrical signal received by the wireless power receiver is generated and communicated to the wireless power transmitter. A calibration feedback signal is generated to adjust a driving signal of the wireless power transmitter based on the received signal.

FIELD

The present invention relates generally to wireless power. More specifically, the disclosure is directed to alignment of a wireless power receiver with a wireless power transmitter, and calibration of the wireless power transmitter.

BACKGROUND

An increasing number and variety of electronic devices are powered via rechargeable batteries. Such devices include mobile phones, portable music players, laptop computers, tablet computers, computer peripheral devices, communication devices (e.g., Bluetooth devices), digital cameras, hearing aids, and the like. While battery technology has improved, battery-powered electronic devices increasingly require and consume greater amounts of power. As such, these devices constantly require recharging. Rechargeable devices are often charged via wired connections through cables or other similar connectors that are physically connected to a power supply. Cables and similar connectors may sometimes be inconvenient or cumbersome and have other drawbacks. Wireless charging systems that are capable of transferring power in free space to be used to charge rechargeable electronic devices or provide power to electronic devices may overcome some of the deficiencies of wired charging solutions. As such, wireless power transfer systems and methods that efficiently and safely transfer power to electronic devices are desirable.

SUMMARY OF THE INVENTION

One aspect of the disclosure provides a wireless power receiver including a wireless power receive coil, and a controller configured to receive an alignment signal indicative of an alignment of the receive coil with a transmit coil of a wireless power receiver. The wireless power transmitter generating a wireless field based on a driving signal, and when the alignment signal indicates that the transmit coil is substantially aligned with the receive coil, the controller is further configured to determine a characteristic of an electrical signal received by the wireless power receiver, and generate a feedback signal to adjust the driving signal based on the determined characteristic received by the wireless power receiver.

Another aspect of the disclosure provides a wireless power transmitter including a wireless power transmit coil, and a controller configured to receive an alignment signal indicative of an alignment of the transmit coil with a receive coil of a wireless power receiver. The transmit coil configured to generate a wireless field based on a driving signal, and when the alignment signal indicates that the transmit coil is substantially aligned with the receive coil, the controller is further configured to receive a signal indicative of a characteristic of an electrical signal received by the wireless power receiver, and generate a feedback signal to adjust the driving signal based on the received signal.

Another aspect of the disclosure provides a method of calibrating a wireless field including

receiving power via a wireless field with a receive coil, the wireless field being generated by a transmit coil of a wireless power transmitter based on a driving signal, and receiving an alignment signal indicative of an alignment of the receive coil with the transmit coil. When the alignment signal indicates that the transmit coil is substantially aligned with the receive coil, the method further includes determining a characteristic of an electrical signal received by the wireless power receiver, and generating a feedback signal to adjust the driving signal based on the determined characteristic.

Another aspect of the disclosure provides a method for calibrating a wireless field including generating a wireless field using a transmit coil based on a driving signal to transmit power to a wireless power receive coil of a wireless power receiver, and receiving an alignment signal indicative of an alignment between the transmit coil and the receive coil. When the alignment signal indicates that the transmit coil is substantially aligned with the receive coil, the method further includes receiving a signal indicative of a characteristic of an electrical signal received by the wireless power receiver, and generating a feedback signal to adjust the driving signal based on the received signal.

Another aspect of the disclosure provides an apparatus for calibrating a wireless field including means receiving power via a wireless field, the wireless field being generated by a transmit coil of a wireless power transmitter based on a driving signal, and means for receiving an alignment signal indicative of an alignment of the means for receiving power with the transmit coil. When the alignment signal indicates that the transmit coil is substantially aligned with the means for receiving power, the apparatus further includes means for determining a characteristic of an electrical signal received by the wireless power receiver, and means for generating a feedback signal to adjust the driving signal based on the determined characteristic.

Another aspect of the disclosure provides an apparatus for calibrating a wireless field comprising means for generating a wireless field based on a driving signal to transmit power to a wireless power receive coil of a wireless power receiver, and means for receiving an alignment signal indicative of an alignment between the means for generating the wireless field and the receive coil. When the alignment signal indicates that the means for generating the wireless field is substantially aligned with the receive coil, the apparatus further includes means for receiving a signal indicative of a characteristic of an electrical signal received by the wireless power receiver, and means for generating a feedback signal to adjust the driving signal based on the received signal.

DETAILED DESCRIPTION

Wirelessly transferring power may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field) may be received, captured by, or coupled by a “receiving coil” to achieve power transfer.

FIG. 1is a functional block diagram of an exemplary wireless power transfer system100, in accordance with exemplary embodiments of the invention. Input power102may be provided to a transmitter104from a power source (not shown) for generating a field105for providing energy transfer. A receiver108may couple to the field105and generate output power110for storing or consumption by a device (not shown) coupled to the output power110. Both the transmitter104and the receiver108are separated by a distance112. In one exemplary embodiment, transmitter104and receiver108are configured according to a mutual resonant relationship. When the resonant frequency of receiver108and the resonant frequency of transmitter104are substantially the same or very close, transmission losses between the transmitter104and the receiver108are minimal. As such, wireless power transfer may be provided over larger distance in contrast to purely inductive solutions that may require large coils that require coils to be very close (e.g., mms). Resonant inductive coupling techniques may thus allow for improved efficiency and power transfer over various distances and with a variety of inductive coil configurations.

The receiver108may receive power when the receiver108is located in an energy field105produced by the transmitter104. The field105corresponds to a region where energy output by the transmitter104may be captured by a receiver105. In some cases, the field105may correspond to the “near-field” of the transmitter104as will be further described below. The transmitter104may include a transmit coil114for outputting an energy transmission. The receiver108further includes a receive coil118for receiving or capturing energy from the energy transmission. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the transmit coil114that minimally radiate power away from the transmit coil114. In some cases the near-field may correspond to a region that is within about one wavelength (or a fraction thereof) of the transmit coil114. The transmit and receive coils114and118are sized according to applications and devices to be associated therewith. As described above, efficient energy transfer may occur by coupling a large portion of the energy in a field105of the transmit coil114to a receive coil118rather than propagating most of the energy in an electromagnetic wave to the far field. When positioned within the field105, a “coupling mode” may be developed between the transmit coil114and the receive coil118. The area around the transmit and receive coils114and118where this coupling may occur is referred to herein as a coupling-mode region.

FIG. 2is a functional block diagram of exemplary components that may be used in the wireless power transfer system100ofFIG. 1, in accordance with various exemplary embodiments of the invention. The transmitter204may include transmit circuitry206that may include an oscillator222, a driver circuit224, and a filter and matching circuit226. The oscillator222may be configured to generate a signal at a desired frequency, such as 468.75 KHz, 6.78 MHz or 13.56 MHz, that may be adjusted in response to a frequency control signal223. The oscillator signal may be provided to a driver circuit224configured to drive the transmit coil214at, for example, a resonant frequency of the transmit coil214. The driver circuit224may be a switching amplifier configured to receive a square wave from the oscillator222and output a sine wave. For example, the driver circuit224may be a class E amplifier. A filter and matching circuit226may be also included to filter out harmonics or other unwanted frequencies and match the impedance of the transmitter204to the transmit coil214.

The receiver208may include receive circuitry210that may include a matching circuit232and a rectifier and switching circuit234to generate a DC power output from an AC power input to charge a battery236as shown inFIG. 2or to power a device (not shown) coupled to the receiver108. The matching circuit232may be included to match the impedance of the receive circuitry210to the receive coil218. The receiver208and transmitter204may additionally communicate on a separate communication channel219(e.g., Bluetooth, zigbee, cellular, etc). The receiver208and transmitter204may alternatively communicate via in-band signaling using characteristics of the wireless field206.

As described more fully below, receiver208, that may initially have an associated load (e.g., battery236) that is selectively capable of being disabled, may be configured to determine whether an amount of power transmitted by transmitter204and receiver by receiver208is appropriate for charging a battery236. Further, receiver208may be configured to enable a load (e.g., battery236) upon determining that the amount of power is appropriate. In some embodiments, a receiver208may be configured to directly utilize power received from a wireless power transfer field without charging of a battery236. For example, a communication device, such as a near-field communication (NFC) or radio-frequency identification device (RFID may be configured to receive power from a wireless power transfer field and communicate by interacting with the wireless power transfer field. Further, the communication device may be configured to utilize the received power to communicate with a transmitter204or other devices.

FIG. 3is a schematic diagram of a portion of transmit circuitry206or receive circuitry210ofFIG. 2including a transmit or receive coil352, in accordance with exemplary embodiments of the invention. As illustrated inFIG. 3, transmit or receive circuitry350used in exemplary embodiments may include a coil352. The coil may also be referred to or be configured as a “loop” antenna352. The coil352may also be referred to herein or be configured as a “magnetic” antenna or an induction coil. The term “coil” is intended to refer to a component that may wirelessly output or receive energy for coupling to another “coil.” The coil may also be referred to as an “antenna” of a type that is configured to wirelessly output or receive power. The coil352may be configured to include an air core or a physical core such as a ferrite core (not shown). Air core loop coils may be more tolerable to extraneous physical devices placed in the vicinity of the core. Furthermore, an air core loop coil352allows the placement of other components within the core area. In addition, an air core loop may more readily enable placement of the receive coil218(FIG. 2) within a plane of the transmit coil214(FIG. 2) where the coupled-mode region of the transmit coil214(FIG. 2) may be more powerful.

As stated, efficient transfer of energy between the transmitter104and receiver108may occur during matched or nearly matched resonance between the transmitter104and the receiver108. However, even when resonance between the transmitter104and receiver108are not matched, energy may be transferred, although the efficiency may be affected. Transfer of energy occurs by coupling energy from the field105of the transmitting coil to the receiving coil residing in the neighborhood where this field105is established rather than propagating the energy from the transmitting coil into free space.

The resonant frequency of the loop or magnetic coils is based on the inductance and capacitance. Inductance may be simply the inductance created by the coil352, whereas, capacitance may be added to the coil's inductance to create a resonant structure at a desired resonant frequency. As a non-limiting example, capacitor352and capacitor354may be added to the transmit or receive circuitry350to create a resonant circuit that selects a signal356at a resonant frequency. Accordingly, for larger diameter coils, the size of capacitance needed to sustain resonance may decrease as the diameter or inductance of the loop increases. Furthermore, as the diameter of the coil increases, the efficient energy transfer area of the near-field may increase. Other resonant circuits formed using other components are also possible. As another non-limiting example, a capacitor may be placed in parallel between the two terminals of the coil350. For transmit coils, a signal358with a frequency that substantially corresponds to the resonant frequency of the coil352may be an input to the coil352.

In one embodiment, the transmitter104may be configured to output a time varying magnetic field with a frequency corresponding to the resonant frequency of the transmit coil114. When the receiver is within the field105, the time varying magnetic field may induce a current in the receive coil118. As described above, if the receive coil118is configured to be resonant at the frequency of the transmit coil118, energy may be efficiently transferred. The AC signal induced in the receive coil118may be rectified as described above to produce a DC signal that may be provided to charge or to power a load.

FIG. 4is a functional block diagram of a transmitter404that may be used in the wireless power transfer system ofFIG. 1, in accordance with exemplary embodiments of the invention. The transmitter404may include transmit circuitry405and a transmit coil414. The transmit coil414may be the coil352as shown inFIG. 3. Transmit circuitry405may provide RF power to the transmit coil414by providing an oscillating signal resulting in generation of energy (e.g., magnetic flux) about the transmit coil414. Transmitter404may operate at any suitable frequency. By way of example, transmitter404may operate at the 13.56 MHz ISM band.

Transmit circuitry405may include a TX impedance adjustment circuit409for adjusting the impedance of the transmit circuitry405based on the impedance of the transmit coil414to increase efficiency. The transmit circuitry405may also include a low pass filter (LPF)408configured to reduce harmonic emissions to levels to prevent self-jamming of devices coupled to receivers108(FIG. 1). Other exemplary embodiments may include different filter topologies, including but not limited to, notch filters that attenuate specific frequencies while passing others and may include an adaptive impedance match, that may be varied based on measurable transmit metrics, such as output power to the coil414or DC current drawn by the driver circuit424. Transmit circuitry405further includes a driver circuit424configured to drive an RF signal as determined by an oscillator423. The oscillator423, driver424, low pass filter408and impedance adjustment circuit409may be commonly referred to as transmitter driving circuit470. The transmit circuitry405may be comprised of discrete devices or circuits, or alternately, may be comprised of an integrated assembly. An exemplary RF power output from transmit coil414may be on the order of 2.5 Watts.

Transmit circuitry405may further include a controller415for selectively enabling the oscillator423during transmit phases (or duty cycles) for specific receivers, for adjusting the frequency or phase of the oscillator423, and for adjusting the output power level for implementing a communication protocol for interacting with neighboring devices through their attached receivers. It is noted that the controller415may also be referred to herein as processor415. Adjustment of oscillator phase and related circuitry in the transmission path may allow for reduction of out of band emissions, especially when transitioning from one frequency to another.

The transmit circuitry405may further include a load sensing circuit416for detecting the presence or absence of active receivers in the vicinity of the near-field generated by transmit coil414. By way of example, a load sensing circuit416monitors the current flowing to the driver circuit424, that may be affected by the presence or absence of active receivers in the vicinity of the field generated by transmit coil414as will be further described below. Detection of changes to the loading on the driver circuit424are monitored by controller415for use in determining whether to enable the oscillator423for transmitting energy and to communicate with an active receiver. As described more fully below, a current measured at the driver circuit424may be used to determine whether an invalid device is positioned within a wireless power transfer region of the transmitter404.

The transmit coil414may be implemented with a Litz wire or as an antenna strip with the thickness, width and metal type selected to keep resistive losses low. In a one implementation, the transmit coil414may generally be configured for association with a larger structure such as a table, mat, lamp or other less portable configuration. Accordingly, the transmit coil414generally may not need “turns” in order to be of a practical dimension. An exemplary implementation of a transmit coil414may be “electrically small” (i.e., fraction of the wavelength) and tuned to resonate at lower usable frequencies by using capacitors to define the resonant frequency.

The transmitter404may gather and track information about the whereabouts and status of receiver devices that may be associated with the transmitter404. Thus, the transmit circuitry405may include a presence detector480, an enclosed detector460, or a combination thereof, connected to the controller415(also referred to as a processor herein). The controller415may adjust an amount of power delivered by the driver circuit424in response to presence signals from the presence detector480and the enclosed detector460. The transmitter404may receive power through a number of power sources, such as, for example, an AC-DC converter (not shown) to convert conventional AC power present in a building, a DC-DC converter (not shown) to convert a conventional DC power source to a voltage suitable for the transmitter404, or directly from a conventional DC power source (not shown).

As a non-limiting example, the presence detector480may be a motion detector utilized to sense the initial presence of a device to be charged that is inserted into the coverage area of the transmitter404. After detection, the transmitter404may be turned on and the RF power received by the device may be used to toggle a switch on the Rx device in a pre-determined manner, which in turn results in changes to the driving point impedance of the transmitter404.

As another non-limiting example, the presence detector480may be a detector capable of detecting a human, for example, by infrared detection, motion detection, or other suitable means. In some exemplary embodiments, there may be regulations limiting the amount of power that a transmit coil414may transmit at a specific frequency. In some cases, these regulations are meant to protect humans from electromagnetic radiation. However, there may be environments where a transmit coil414is placed in areas not occupied by humans, or occupied infrequently by humans, such as, for example, garages, factory floors, shops, and the like. If these environments are free from humans, it may be permissible to increase the power output of the transmit coil414above the normal power restrictions regulations. In other words, the controller415may adjust the power output of the transmit coil414to a regulatory level or lower in response to human presence and adjust the power output of the transmit coil414to a level above the regulatory level when a human is outside a regulatory distance from the electromagnetic field of the transmit coil414.

As a non-limiting example, the enclosed detector460(may also be referred to herein as an enclosed compartment detector or an enclosed space detector) may be a device such as a sense switch for determining when an enclosure is in a closed or open state. When a transmitter is in an enclosure that is in an enclosed state, a power level of the transmitter may be increased.

In exemplary embodiments, a method by which the transmitter404does not remain on indefinitely may be used. In this case, the transmitter404may be programmed to shut off after a user-determined amount of time. This feature prevents the transmitter404, notably the driver circuit424, from running long after the wireless devices in its perimeter are fully charged. This event may be due to the failure of the circuit to detect the signal sent from either the repeater or the receive coil that a device is fully charged. To prevent the transmitter404from automatically shutting down if another device is placed in its perimeter, the transmitter404automatic shut off feature may be activated only after a set period of lack of motion detected in its perimeter. The user may be able to determine the inactivity time interval, and change it as desired. As a non-limiting example, the time interval may be longer than that needed to fully charge a specific type of wireless device under the assumption of the device being initially fully discharged.

FIG. 5is a functional block diagram of a receiver508that may be used in the wireless power transfer system ofFIG. 1, in accordance with exemplary embodiments of the invention. The receiver508includes receive circuitry510that may include a receive coil518. Receiver508further couples to device550for providing received power thereto. It should be noted that receiver508is illustrated as being external to device550but may be integrated into device550. Energy may be propagated wirelessly to receive coil518and then coupled through the rest of the receive circuitry510to device550. By way of example, the charging device may include devices such as mobile phones, portable music players, laptop computers, tablet computers, computer peripheral devices, communication devices (e.g., Bluetooth devices), digital cameras, hearing aids (an other medical devices), and the like.

Receive coil518may be tuned to resonate at the same frequency, or within a specified range of frequencies, as transmit coil414(FIG. 4). Receive coil518may be similarly dimensioned with transmit coil414or may be differently sized based upon the dimensions of the associated device550. By way of example, device550may be a portable electronic device having diametric or length dimension smaller that the diameter of length of transmit coil414. In such an example, receive coil518may be implemented as a multi-turn coil in order to reduce the capacitance value of a tuning capacitor (not shown) and increase the receive coil's impedance. By way of example, receive coil518may be placed around the substantial circumference of device550in order to maximize the coil diameter and reduce the number of loop turns (i.e., windings) of the receive coil518and the inter-winding capacitance.

Receive circuitry510may provide an impedance match to the receive coil518. Receive circuitry510includes power conversion circuitry506for converting a received RF energy source into charging power for use by the device550. Power conversion circuitry506includes an RF-to-DC converter520and may also in include a DC-to-DC converter522. RF-to-DC converter520rectifies the RF energy signal received at receive coil518into a non-alternating power with an output voltage represented by Vrect. The DC-to-DC converter522(or other power regulator) converts the rectified RF energy signal into an energy potential (e.g., voltage) that is compatible with device550with an output voltage and output current represented by Voutand Lout. Various RF-to-DC converters are contemplated, including partial and full rectifiers, regulators, bridges, doublers, as well as linear and switching converters.

Receive circuitry510may further include Rx impedance adjustment and switching circuitry512. The Rx impedance adjustment and switching circuit may be configured to adjust an impedance of the receive circuitry510based on an impedance of the receive coil518to improve efficiency during power transfer. Further, the Rx impedance adjustment and switching circuitry may be configured to connect receive coil518to the power conversion circuitry506or alternatively disconnect the power conversion circuitry506. Disconnecting receive coil518from power conversion circuitry506not only suspends charging of device550, but also changes the “load” as “seen” by the transmitter404(FIG. 2).

As disclosed above, transmitter404includes load sensing circuit416that may detect fluctuations in the bias current provided to transmitter driver circuit424. Accordingly, transmitter404has a mechanism for determining when receivers are present in the transmitter's near-field.

When multiple receivers508are present in a transmitter's near-field, it may be desirable to time-multiplex the loading and unloading of one or more receivers to enable other receivers to more efficiently couple to the transmitter. A receiver508may also be cloaked in order to eliminate coupling to other nearby receivers or to reduce loading on nearby transmitters. This “unloading” of a receiver is also known herein as a “cloaking.” Furthermore, this switching between unloading and loading controlled by receiver508and detected by transmitter404may provide a communication mechanism from receiver508to transmitter404as is explained more fully below. Additionally, a protocol may be associated with the switching that enables the sending of a message from receiver508to transmitter404. By way of example, a switching speed may be on the order of 100 μsec.

In an exemplary embodiment, communication between the transmitter404and the receiver508refers to a device sensing and charging control mechanism, rather than conventional two-way communication (i.e., in band signaling using the coupling field). In other words, the transmitter404may use on/off keying of the transmitted signal to adjust whether energy is available in the near-field. The receiver may interpret these changes in energy as a message from the transmitter404. From the receiver side, the receiver508may use tuning and de-tuning of the receive coil518to adjust how much power is being accepted from the field. In some cases, the tuning and de-tuning may be accomplished via the Rx impedance adjustment and switching circuitry512. The transmitter404may detect this difference in power used from the field and interpret these changes as a message from the receiver508. It is noted that other forms of modulation of the transmit power and the load behavior may be utilized.

Receive circuitry510may further include signaling detector and beacon circuitry514used to identify received energy fluctuations, that may correspond to informational signaling from the transmitter to the receiver. Furthermore, signaling and beacon circuitry514may also be used to detect the transmission of a reduced RF signal energy (i.e., a beacon signal) and to rectify the reduced RF signal energy into a nominal power for awakening either un-powered or power-depleted circuits within receive circuitry510in order to configure receive circuitry510for wireless charging.

Receive circuitry510further includes processor516for coordinating the processes of receiver508described herein including the control of the Rx impedance adjustment and switching circuitry512described herein. Cloaking of receiver508may also occur upon the occurrence of other events including detection of an external wired charging source (e.g., wall/USB power) providing charging power to device550. Processor516, in addition to controlling the cloaking of the receiver, may also monitor beacon circuitry514to determine a beacon state and extract messages sent from the transmitter404. Processor516may also adjust the DC-to-DC converter522for improved performance.

FIGS. 6A-6Billustrate example configurations of a wireless power receiver and a wireless power transmitter according to some embodiments. As shown inFIG. 6A, a wireless power receiver608may be configured to receive power via a wireless power receive coil618from a wireless power transmitter604including a wireless power transmit coil614.FIG. 6Billustrates another example of a configuration of a wireless power receiver608configured to receive power from a wireless power transmitter604. While not shown, the wireless power transmitter604may be integrated into a furnishing, for example, such as the underside of a desk or countertop. The thicknesses of various surfaces which may include an integrated wireless power transmitters604may vary. For example, as shown inFIG. 6A, a distance between a charging surface of the wireless power receiver608and a charging surface of a wireless power transmitter604may be equal to a distance X. InFIG. 6B, the distance between a charging surface of the wireless power receiver608and a charging surface of a wireless power transmitter604may be equal to a distance Y, where Y>X. The difference in distances Y and X may be due to the thickness of a surface separating an integrated wireless power transmitter604including the wireless power receive coil614and the wireless power receiver608including the wireless power receive coil618.

For example, a wireless power transmitter604may be integrated into a surface of a desk or countertop, which are available in a wide variety of thickness ranging from about 10 mm to about 50 mm. Further, different types of wireless power receivers608may include an integrated wireless power receive coil618at different distances from a charging surface of the wireless power receiver608. According to some embodiments, systems and methods are described for calibration of a wireless power transmitter604to meet charge port requirements of a device to be charged when a wireless power receiver608is placed at different distances from the charging surface of the wireless power transmitter604.

For a given wireless power transmitter604design, as the separation from a transmitter604increases, a voltage and power received by a wireless power receiver608is reduced. Further, for a given design, as separation between the wireless power transmitter604and wireless power receiver608decreases, the voltage received by the wireless power receiver608increases and the device to be powered or charged may be subjected to greater electromagnetic field intensity. The higher voltages and elevated field intensities may damage the wireless power receiver608and a corresponding device to be powered or charged by the wireless power receiver.

Further, the voltage and power received by a wireless power receiver604is a function of the alignment of the wireless power receive coil618with the wireless power transmit coil614. As discussed above, coupling between the wireless power receive coil618and the wireless power transmit coil614impacts the efficiency of power transferred from the wireless power transmitter604and the wireless power receiver608via the wireless field. A wireless power transmit coil614in proper alignment with a wireless power receive coil618exhibits greater coupling, and thereby more efficient power transfer, than a corresponding misaligned system. For example, as shown inFIG. 6A, the orientation and position of a wireless power receiver coil618relative to the orientation and position of the wireless power transmit coil614is different than the orientation and position of the wireless power receive coil618and the wireless power transmit coil614inFIG. 6B. As a result, coupling between the wireless power receive coil618and the wireless power618is different between the systems shown inFIGS. 6A and 6B.

According to some embodiments, a wireless power transmitter604may be calibrated based on the position of the wireless power transmitter604in relation to a wireless power receiver608. The calibration of the wireless power transmitter604includes an alignment detection and adjustment mechanism. The calibration is performed following detection of alignment between the wireless power receive coil618and wireless power transmit coil614. The components of the wireless power receiver608and the wireless power transmitter604for alignment and calibration of the wireless power system will be described in greater detail with reference toFIGS. 7-8below.

FIG. 7illustrates a partial block diagram of wireless power transmit circuitry included in a wireless power transmitter according to some embodiments. The wireless power transmit circuitry705may include a TX wireless field generating unit762, including TX driving circuitry770and TX power transmit circuit714. The TX driving circuitry770may be configured to generate a driving signal for driving the TX power transmit circuit714to generate the wireless field. For example, the TX driving circuitry770may correspond to the TX driving circuitry470as described above with reference toFIG. 4. The TX power transmit circuit714may include a resonant circuit (e.g., a coil coupled to a capacitor) configured to generate a wireless field based on the received driving signal. The wireless power transmit circuitry705also includes a TX alignment and calibration unit782. The TX alignment and calibration unit782may include a TX alignment circuit784coupled to a rectification circuit786. For example, the TX alignment circuit784include one or more sensing coils configured to receive an alignment signal transmitted from a wireless power receiver. The output of the TX alignment circuit784be rectified by the rectification circuit786to generate an alignment signal. A controller715may be configured to receive and process the alignment signal to determine if a wireless power transmit coil614is in alignment with the wireless power receive coil618. Additionally, or alternatively, the controller715may be coupled to a communication interface (e.g., a communication antenna, not shown) and may be configured to receive a signal from the wireless power receiver608indicative of the alignment of the wireless power receiver coil618with a wireless power transmit coil614.

Further, the controller715is configured to receive a signal from the wireless power receiver608indicative of a characteristic of an electrical signal received the wireless power receiver608as will be described in greater detail below with reference toFIG. 8. For example, the controller715may receive a signal indicating one or more of a voltage level and a current level received by the wireless power receiver608. The controller715may be configured to generate a feedback signal to adjust the driving signal generated by the TX driving circuitry770based on received signal from the wireless power receiver608when the wireless power transmit coil614is determined to be in alignment with the wireless power receiver coil618.

As discussed above, the TX driving circuit770may be configured to generate an AC voltage when a wireless power receiver608is placed within range of the wireless power transmitter604to generate the wireless filed. The controller715, through feedback, may be configured to adjust an input voltage of a power supply coupled to the TX driving circuit770. According to some embodiments, the controller715may also be used to adjust other parameters of a driving signal used to drive a coil of the wireless power transmitter604. For example, the feedback signal may be configured to adjust one or more of the voltage level of a power supply, the current through the TX power transmit circuit714(e.g., current through a transmit coil), and the frequency of the driving signal. According to some embodiments, the adjustment of the field generated by the wireless power transmitter604may be performed by varying one or more of a capacitance and inductance of the wireless power transmitter604through the use of, for example, a variable impedance adjustment circuit similar to the TX impedance adjustment circuit409discussed above with reference toFIG. 4. According to some embodiments, the signal communicated from the controller715to other components of the wireless power transmit circuitry705is communicated via a wireless communication link. In some embodiments, calibration may be performed by signaling or displaying information to a user to perform a manual adjustment of the wireless power transmitter604driving signal based on one or more audio and visual cues that are generated by the controller715.

FIG. 8illustrates a partial block diagram of wireless power receive circuitry included in a wireless power receiver according to some embodiments. As shown inFIG. 8, the wireless power receive circuitry810may includes an Rx alignment unit890which includes an Rx alignment circuit892and a rectifier circuit894. The Rx alignment circuit892may include, for example, one or more sensors configured to receive a signal from the wireless power transmitter604. An example of Rx alignment circuit892will be described in greater detail with reference toFIG. 9below. The rectification circuit894is configured to rectify the received signal and transmit an alignment signal to the processing and/or signaling controller816. The processing and/or signaling controller816may perform similar functions to those performed by processing and/or signaling controller516as discussed above with reference toFIG. 5. As shown inFIG. 8, the processing and/or signaling controller816is coupled to a communication circuit819which is configured to communicate the alignment signal to the wireless power transmitter604.

Further, the wireless power receive circuitry810also includes an Rx power receiver circuit818(e.g., a resonant circuit including a coil and a capacitor) and a power conversion circuit806. The Rx power receive circuit818is configured to receive power from the wireless field generated by the wireless power transmitter604, and the power conversion circuit806is configured to convert the received power to power for charging or operating a device. For example, the power conversion circuit806may include a rectification circuit configured to generate a DC current and/or DC voltage for powering a portable device based on an AC current induced in the Rx power receive circuit. The processing and/or signaling controller816is configured to receive a signal indicative of a characteristic of the electrical signal received by the Rx power receive circuit (e.g. a signal indicating at least one of a current level and voltage level received by the power conversion circuit806) and communicate the information to the wireless power transmitter604through the communication circuit819.

In some embodiments, the processing and/or signaling controller816may be configured to read one of the voltage level and current level generated by the power conversion circuit806and compare the voltage level or current level with a reference voltage level or current level respectively. The processing and/or signaling controller816may generate a feedback signal to adjust the driving signal of the TX driving circuit770as described above with reference toFIG. 7. Alternatively, the information may be transmitted to the controller715of the wireless power transmitter604, and the controller715may be configured to generate the feedback signal. Further, the processing and/or signaling controller816may be configured to transmit identification information regarding the wireless power receiver608. The wireless power transmitter604may include a memory (not shown) for storing the identification information regarding the wireless power receiver608along with values corresponding to the calibrated driving signal. The stored information may then be retrieved by the controller715to adjust the driving signal in the presence of a similar wireless power receiver608. Additionally, or alternatively, the stored information may be used as a baseline for further calibration in the presence of a similar or different wireless power receiver608.

FIG. 9illustrates a wireless power receiver including an alignment circuit according to some embodiments. In some embodiments, the wireless power receiver908may be configured as a calibration receiver to adjust the driving signal of a wireless power transmitter when separation between a wireless power receiver and a wireless power transmitter are unknown. The wireless power receiver908may also be configured to power or charge a load as described above with reference to wireless power receivers108,208,408and608above. The calibration system may adjust the driving signal used by the wireless power transmitter604in consideration of a correlation between a characteristic of an electrical signal (e.g., current level, voltage level, etc.) received by the wireless power receiver908, and the ability of the wireless power receiver608to meet charge port requirements for powering or charging an associated load. As discussed above with reference toFIGS. 6A-6B, the correlation may be performed when a wireless power receive coil is properly aligned with a wireless power transmit coil Therefore, to avoid aliasing and ensure proper calibration, the wireless power receive coil918is aligned with a wireless power transmit coil before the calibration process can occur.

As illustrated inFIG. 9, the wireless power receiver908includes three sensing coils971,973, and975which are spaced 120 degrees apart in polar coordinates and equidistant from a center point of the wireless power receive coil918. Each of the sensing coil971,973, and975may be coupled to first, second and third sensing circuits972,974, and976respectively. A controller916may be configured to receive first, second, and third sensing signals from the sensing circuits972,974, and976.

The alignment system may take into account the relationship between the position of a sensing coil (e.g., sensing coils971,974, and977) included in a wireless power receiver908and induced current and/or voltage. For example, for a uniform circular wireless power transmit coil and a constant vertical separation between a wireless power transmitter and the wireless power receiver908, the induced voltage on a sensing coil is a function of distance from the center of the wireless power transmit coil to the sensing coil. Therefore, multiple sensing coils, such as substantially identical coils, in the same plane and placed equidistant from a wireless power transmit coil will exhibit the substantially same induced current and/or voltage.

Since the same current and/or voltage will be induced on the sensing coils971,973, and975when they are equidistant from the center of a uniform, circular transmit coil, monitoring of the sensing signals generated by the sensing circuits972,974, and976can ensure alignment between the center of a wireless power transmit coil and the center of the wireless power receive coil918. In some embodiments, the wireless power receiver908may be determined to be aligned with a wireless power transmitter when a voltage or current received on each of the sensing coils971,973, and975is above a threshold value, and the voltage or current on each971,973, and975is substantially equal. An example method of determining alignment of the wireless power receiver908will be described in greater detail with reference toFIG. 12below.

FIG. 10is a flowchart of a method for alignment and calibration of a wireless power transmitter according to some embodiments. As illustrated inFIG. 10, the method1000includes receiving power via a wireless field with a receive coil, the wireless field being generated by transmit coil of wireless power transmitter based on a driving signal as shown in block1002. For example, the transmit coil may be included as part of a TX power transmit circuit714as described above with reference toFIG. 7, and the receive coil may be included in an Rx power receiver circuit818as described above with reference toFIG. 8. The method further includes receiving alignment signal indicative of an alignment of the receive coil with transmit coil as shown by block1004. The receive signal may be generated by a sensor included in one of the TX alignment circuit784and/or Rx alignment circuit892as discussed above with reference toFIGS. 7-8. At decision block1006, the method may determine whether the TX and Rx coils are aligned based on the received signal. If it is determined that the TX and Rx coils are not aligned the method continues to monitor an alignment signal as shown by block1004. In some embodiments, the method may include generating or displaying an indicator of the alignment between the TX and Rx coils such that the alignment can be automatically adjusted or adjusted by a user. If it is determined that the TX and Rx coils are aligned, the method proceeds to block1008where a characteristic of an electrical signal received by the wireless power receiver is determined. For example, the characteristic may include one of a voltage and current received by and Rx power receiver circuit818and power conversion circuit806as discussed above with reference toFIG. 8. The method then proceeds to block1010, where a feedback signal is generated to adjust the driving signal based on the determined characteristic. For example, as discussed above, the feedback signal may be configured to adjust one of the voltage level of the driving signal, the frequency of the driving signal, and/or adjust the driving signal to adjust the current through wireless power transmit coil.

FIG. 11is a flowchart of a method for alignment and calibration of a wireless power transmitter according to some embodiments. As illustrated inFIG. 11, the method1100includes generating a wireless field with a transmit coil based on a driving signal to transmit power to a wireless power receive coil of a wireless power receiver as shown in block1102. For example, the transmit coil may be included as part of a TX power transmit circuit714as described above with reference toFIG. 7, and the receive coil may be included in an Rx power receiver circuit818as described above with reference toFIG. 8. The method further includes receiving an alignment signal indicative of an alignment of the receive coil with transmit coil as shown by block1104. The received signal may be generated by a sensor included in one of the TX alignment circuit784and/or Rx alignment circuit892as discussed above with reference toFIGS. 7-8. At decision block1106, the method may determine whether the TX and Rx coils are aligned based on the received signal. If it is determined that the TX and Rx coils are not aligned the method continues to monitor an alignment signal as shown by block1104. In some embodiments, the method may include generating or displaying an indicator of the alignment between the TX and Rx coils such that the alignment can be automatically adjusted or adjusted by a user. If it is determined that the TX and Rx coils are aligned, the method proceeds to block1108where a signal indicative of a characteristic of an electrical signal received by the wireless power receiver is received. For example, the characteristic may include one of a voltage and current received by and RX power receiver circuit818and power conversion circuit806and communicated to the wireless power transmitter604as discussed above with reference toFIG. 8. The method then proceeds to block1110, where a feedback signal is generated to adjust the driving signal based on the determined characteristic. For example, as discussed above, the feedback signal may be configured to adjust one of the voltage level of the driving signal, the frequency of the driving signal, and/or adjust the driving signal to adjust the current through the wireless power transmit coil.

FIG. 12is a flowchart of a method for aligning a wireless power transmitter and a wireless power receiver according to some embodiments. The method1200includes measuring voltage on first through third coils of a wireless power receiver as shown in block1202. For example, method may include measuring voltage induced on first, second, and third sensing coils971,973, and975as discussed above with reference toFIG. 9. At decision block1204, each of the measured voltages Vcoil1, Vcoil2, and Vcoil3are compared to a threshold value (Vmin). If the voltages are less than the threshold value, the method returns to block1202where the voltage of each of the sensing coils is continued to be monitored. If the voltages are greater than the threshold value, the method proceeds to calculate a difference of each pair of voltages as shown in block1206. As shown, DIF1=Vcoil1−Vcoil2, DIF2=Vcoil1−Vcoil3, and DIF3=Vcoil2−Vcoil3. The method then proceeds to decision block1208where an absolute value of each of the difference values (|DIF1|, |DIF2|, and |DIF3|) are compared to a threshold value. If each of the difference values is greater in magnitude than the threshold value, and the receiver is determined to be misaligned and the receiver is repositioned, either manually or automatically, as shown in block1212. If each of the difference values is less in magnitude than the threshold value, then the receiver is determined to be aligned as shown in block1210.

FIG. 13is a flowchart of a method for calibrating a wireless power transmitter according to some embodiments. The method1300may be performed following the termination that the wireless power receiver is in alignment with the wireless power transmitter. The method1300includes measuring a voltage received by wireless power receiver as shown in block1302. At decision block1304, method compares the measured voltage with a threshold voltage. If the measured voltage is greater than the threshold voltage, the method proceeds to decrement the transmission module supply voltage as shown in block1306. For example, as discussed above with reference toFIGS. 7 and 8, a feedback signal may be generated to adjust a driving signal produced by a TX driving circuit770. As shown at decision block1308if the measured voltage is equal to the threshold voltage, the method proceeds to maintain the driving signal. If the measured voltage is both less than been not equal to the threshold voltage, the method proceeds to block1312to increment the transmission voltage level.

The example methods described above with reference toFIGS. 12 and 13are based on voltage measurement calculations. However, the embodiments described herein are not limited thereto. For example, as discussed above, a current level induced in one or more sensing coils may be used to determine the alignment of a wireless power receiver and wireless power transmitter according to a similar method to that described inFIG. 12. Further, the current level received by the wireless power receiver may be compared to a threshold value in order to generate feedback signal for adjusting driving signal similar to the method described with reference toFIG. 13.

FIG. 14is a functional block diagram of an apparatus of a wireless power receiver according to some embodiments. As shown inFIG. 14, the apparatus includes means for receiving power via a wireless field wireless field being generated by transmit coil of a wireless power transmitter based on driving signal as shown in block1402. For example, the means for receiving power1402may correspond to the Rx power receiver circuit818and the power conversion circuit806. The Rx power receive circuit818may include a resonant circuit having a receive coil coupled to a capacitor. The apparatus further includes means for receiving an alignment signal indicative of an alignment of the means for receiving power with the transmit coil as shown in block1404. The apparatus further includes a means for determining a characteristic of electrical signal received by the means for receiving power as shown by block1406, and a means for generating feedback signal to adjust the driving signal based on the determined characteristic as shown at block1408. For example, the means for receiving alignment signal1404, the means for determining a characteristic of an electrical signal1406, and the means for generating a feedback signal1408may correspond to a processing and/or signaling controller816as described with reference toFIG. 8above. Each of the components of the apparatus shown inFIG. 14may be configured to communicate through a communication bus1410.

FIG. 15is a functional block diagram of an apparatus of a wireless power transmitter according to some embodiments. As shown inFIG. 15, the apparatus includes means for generating a wireless field based on a driving signal to transmit power to a wireless power receive coil of a wireless power receiver as shown by block1502. For example, the means for generating a wireless field1502may correspond to the TX wireless field generating unit762as described above with reference toFIG. 7. The apparatus further includes means for receiving an alignment signal indicative of an alignment of the means for generating a wireless field with the transmit coil as shown in block1504. The apparatus further includes a means for receiving a signal indicative of a characteristic of an electrical signal received by the wireless power receiver as shown by block1506, and a means for generating feedback signal to adjust the driving signal based on the determined characteristic as shown at block1508. For example, the means for receiving the alignment signal1504, the means for receiving a signal indicative of a characteristic of an electrical signal1506, and the means for generating a feedback signal1508may correspond to a controller715as described with reference toFIG. 7above. Each of the components of the apparatus shown inFIG. 15may be configured to communicate through a communication bus1510.

The steps of a method or algorithm and functions described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a tangible, non-transitory computer-readable medium. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD ROM, or any other form of storage medium known in the art. A storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer readable media. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

Various modifications of the above described embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.