PATENT DOCUMENT

Publication Number: US-11196298-B2
Application Number: US-201816005382-A
Country: US
Kind Code: B2

Title: Wireless charging device with sinusoidal pulse-width modulation

Abstract:
A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may include an inverter configured to drive a resonant circuit and may further include a sinusoidal pulse-width modulation (PWM) signal generator configured to generate a corresponding sinusoidal PWM control signal. The inverter may have an input that receives the sinusoidal PWM control signal. The sinusoidal PWM control signal may exhibit a plurality of different pulse widths summing to the target duty cycle of the sinusoidal PWM control signal. Operated in this way, the wireless power transmitting device exhibits reduced harmonic distortions, which mitigates undesired radiated spurious emissions.

Claims:
What is claimed is: 
     
       1. A wireless power transmitting device configured to transmit wireless power signals to a wireless power receiving device, the wireless power transmitting device comprising:
 a wireless power transmitting coil; 
 an inverting circuit configured to drive the wireless power transmitting coil at a selected duty cycle; and 
 a pulse-width modulation signal generator configured to output a periodic control signal having a plurality of different pulse widths, wherein a sum of the plurality of different pulse widths in a period of the control signal is equal to the selected duty cycle, and wherein the inverting circuit is configured to receive the control signal from the pulse-width modulation input generator to reduce harmonic distortion at the wireless power transmitting device. 
 
     
     
       2. The wireless power transmitting device of  claim 1 , wherein the pulse-width modulation signal generator comprises a comparator having an output terminal at which the control signal is generated. 
     
     
       3. The wireless power transmitting device of  claim 2 , wherein the comparator further comprises:
 a first input configured to receive a first periodic signal; and 
 a second input configured to receive a second periodic signal. 
 
     
     
       4. The wireless power transmitting device of  claim 3 , wherein the first periodic signal has a first frequency, and wherein the second periodic signal has a second frequency that is different than the first frequency. 
     
     
       5. The wireless power transmitting device of  claim 4 , wherein the second frequency is at least ten times the first frequency. 
     
     
       6. The wireless power transmitting device of  claim 5 , wherein the first periodic signal is a sine wave. 
     
     
       7. The wireless power transmitting device of  claim 5 , wherein the second periodic signal is a triangle wave. 
     
     
       8. The wireless power transmitting device of  claim 5 , wherein the second periodic signal is a sawtooth wave. 
     
     
       9. The wireless power transmitting device of  claim 5 , wherein the inverting circuit comprises:
 a first switch; 
 a second switch coupled in series with the first switch; and 
 a capacitor coupled in parallel with the first switch, wherein the capacitor is configured to filter out high-frequency components associated with the second periodic signal. 
 
     
     
       10. The wireless power transmitting device of  claim 1 , further comprising:
 a driver circuit interposed between the pulse-width modulation signal generator and the inverting circuit. 
 
     
     
       11. A method of operating a wireless power transmitting device configured to transmit wireless power signals to a wireless power receiving device, the method comprising:
 with an inverting circuit, driving a wireless power transmitting coil at a given duty cycle; 
 with a pulse-width modulation signal generator, generating a periodic control signal having a plurality of different pulse widths, wherein a sum of the plurality of different pulse widths in a period of the control signal is substantially equal to the given duty cycle; and 
 receiving the control signal at an input of the inverting circuit to reduce harmonic distortion at the wireless power transmitting device. 
 
     
     
       12. The method of  claim 11 , further comprising:
 with the inverting circuit, driving a resonant circuit. 
 
     
     
       13. The method of  claim 11 , wherein the pulse-width modulation signal generator includes a comparator, the method further comprising:
 receiving a first periodic waveform at a first input of the comparator; and 
 receiving a second periodic waveform at a second input of the comparator. 
 
     
     
       14. The method of  claim 13 , wherein the first periodic waveform has a first frequency, and wherein the second periodic waveform has a second frequency that is at least 10 times the first frequency. 
     
     
       15. The method of  claim 14 , wherein the first periodic waveform is a sine wave, and wherein the second periodic waveform is a selected one of: a triangle wave and a sawtooth wave. 
     
     
       16. A wireless power transmitting device, comprising:
 a resonant circuit; 
 an inverter configured to drive the resonant circuit, wherein the inverter is configured to receive a pulse-width modulation control signal; and 
 a pulse-width modulation signal generator configured to output the pulse-width modulation control signal, wherein the pulse-width modulation control signal has a given frequency and includes a plurality of different pulse widths in a period of the given frequency. 
 
     
     
       17. The wireless power transmitting device of  claim 16 , wherein the resonant circuit comprises:
 a wireless power transmitting coil; and 
 a capacitor coupled in series with the wireless power transmitting coil. 
 
     
     
       18. The wireless power transmitting device of  claim 16 , wherein the inverter comprises:
 a first transistor; 
 a second transistor coupled in series with the first transistor; and 
 a capacitor coupled in parallel with the first transistor. 
 
     
     
       19. The wireless power transmitting device of  claim 16 , wherein the pulse-width modulation signal generator comprises:
 a comparison circuit configured to receive a first periodic signal of a first frequency and a second periodic signal of a second frequency that is greater than the first frequency. 
 
     
     
       20. The wireless power transmitting device of  claim 19 , wherein the first periodic signal is a sinusoidal signal, and wherein the second periodic signal is a triangular signal.

Description:
This application claims the benefit of provisional patent application No. 62/649,486, filed Mar. 28, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to power systems, and, more particularly, to wireless power systems for charging electronic devices. 
     BACKGROUND 
     In a wireless charging system, a wireless charging mat wirelessly transmits power to a portable electronic device that is placed on the mat. The portable electronic device has a coil and rectifier circuitry. The coil in the portable electronic device receives alternating-current wireless power signals from a coil in the wireless charging mat that is overlapped by the coil in the portable electronic device. The rectifier circuitry converts the received signals into direct-current power. 
     SUMMARY 
     A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power receiving device has a receive coil that receives wireless power signals from the wireless power transmitting device and has a rectifier that produces direct-current power from the received wireless power signals. 
     The wireless power transmitting device has wireless power transmitting circuitry that includes a resonant circuit, an inverter for driving the resonant circuit, and pulse-width modulation (PWM) signal generator that outputs a periodic control signal to the inverter at a selected duty cycle. The resonant circuit may include a wireless power transmitting coil and a capacitor coupled to the wireless power transmitting coil. The inverter may include a first switch, a second switch coupled in series with the first switch, and a capacitor that is coupled in parallel with the first switch and that is configured to filter out undesired high-frequency components. 
     The PWM signal generator may include a comparator having a first (negative) input that receives a first periodic signal, a second (positive) input that receives a second periodic signal, and an output at which the control signal is provided. The first periodic signal may have a first frequency, whereas the second periodic signal may have a second frequency that is greater than the first frequency (e.g., the second frequency may be at least 10 times the first frequency). The first periodic signal may be a sinusoidal waveform. The second periodic signal may be a periodic ramp signal such as a triangular waveform or a sawtooth waveform. 
     Configured in this way, the PWM signal generator may output a sinusoidal PWM control signal oscillating at a given power frequency, where the control signal has a plurality of different pulse widths in a period of the power frequency summing to the selected duty cycle of the control signal. The use of a sinusoidal PWM control signal with different pulse widths reduces harmonic distortion at the input of the inverter, which dramatically decreases radiated spurious emissions at the wireless power transmitting circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative wireless charging system that includes a wireless power transmitting device and a wireless power receiving device in accordance with an embodiment. 
         FIG. 2  is a top view of an illustrative wireless power transmitting device in accordance with an embodiment. 
         FIG. 3  is a circuit diagram of illustrative wireless power transmitting circuitry and illustrative wireless power receiving circuitry in accordance with an embodiment. 
         FIG. 4  is a diagram showing harmonic distortion levels at the wireless power transmitting circuitry as a function of duty cycle. 
         FIG. 5  is a circuit diagram of illustrative wireless power transmitting circuitry that includes a sinusoidal pulse-width modulation input generator, an inverting circuit, and a wireless power transmitting coil in accordance with an embodiment. 
         FIG. 6A  is a diagram illustrating a sinusoidal pulse-width modulation (SPWM) control signal that can be used to control the wireless power transmitting circuitry in accordance with an embodiment. 
         FIG. 6B  is a diagram illustrating SPWM output waveforms generated by the wireless power transmitting circuitry in accordance with an embodiment. 
         FIG. 6C  is a diagram showing how the high frequency component in the SPWM current output waveform can be suppressed in accordance with an embodiment. 
         FIG. 7A  is a diagram of a rectangular wave having fixed 25% duty cycle. 
         FIG. 7B  is a diagram showing harmonic distortion levels at wireless power transmitting circuitry controlled using the rectangular wave of  FIG. 7A . 
         FIG. 8A  is a diagram of a rectangular wave having fixed 45% duty cycle. 
         FIG. 8B  is a diagram showing harmonic distortion levels at wireless power transmitting circuitry controlled using the rectangular wave of  FIG. 8A . 
         FIG. 9A  is a diagram showing input signals for the comparator of  FIG. 5  in accordance with an embodiment. 
         FIG. 9B  is a diagram showing harmonic distortion levels at the wireless power transmitting circuitry controlled using the input signals of  FIG. 9A . 
         FIG. 10A  is a diagram showing input signals for the comparator of  FIG. 5  in accordance with an embodiment. 
         FIG. 10B  is a diagram showing harmonic distortion levels at the wireless power transmitting circuitry controlled using the input signals of  FIG. 10A . 
         FIG. 11  is a diagram illustrating how controlling the wireless power transmitting circuitry using sinusoidal pulse width modulation reduces harmonic distortion in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A wireless power system includes a wireless power transmitting device such as a wireless charging mat. The wireless power transmitting device wirelessly transmits power to a wireless power receiving device such as a wristwatch, cellular telephone, tablet computer, laptop computer, or other electronic equipment. The wireless power receiving device uses power from the wireless power transmitting device for powering the device and for charging an internal battery. 
     An illustrative wireless power system (wireless charging system) is shown in  FIG. 1 . As shown in  FIG. 1 , wireless power system  8  includes a wireless power transmitting device such as wireless power transmitting device  12  and includes a wireless power receiving device such as wireless power receiving device  24 . Wireless power transmitting device  12  includes control circuitry  16 . Wireless power receiving device  24  includes control circuitry  30 . Control circuitry in system  8  such as control circuitry  16  and control circuitry  30  is used in controlling the operation of system  8 . This control circuitry may include processing circuitry associated with microprocessors, power management units, baseband processors, digital signal processors, microcontrollers, and/or application-specific integrated circuits with processing circuits. The processing circuitry implements desired control and communications features in devices  12  and  24 . For example, the processing circuitry may be used in selecting coils, determining power transmission levels, processing sensor data and other data, processing user input, handling negotiations between devices  12  and  24 , sending and receiving in-band and out-of-band data, making measurements, and otherwise controlling the operation of system  8 . 
     Control circuitry in system  8  may be configured to perform operations in system  8  using hardware (e.g., dedicated hardware or circuitry), firmware and/or software. Software code for performing operations in system  8  is stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) in control circuitry  8 . The software code may sometimes be referred to as software, data, program instructions, instructions, or code. The non-transitory computer readable storage media may include non-volatile memory such as non-volatile random-access memory (NVRAM), one or more hard drives (e.g., magnetic drives or solid state drives), one or more removable flash drives or other removable media, or the like. Software stored on the non-transitory computer readable storage media may be executed on the processing circuitry of control circuitry  16  and/or  30 . The processing circuitry may include application-specific integrated circuits with processing circuitry, one or more microprocessors, a central processing unit (CPU) or other processing circuitry. 
     Power transmitting device  12  may be a stand-alone power adapter (e.g., a wireless charging mat that includes power adapter circuitry), may be a wireless charging mat that is coupled to a power adapter or other equipment by a cable, may be a portable device, may be equipment that has been incorporated into furniture, a vehicle, or other system, or may be other wireless power transfer equipment. Illustrative configurations in which wireless power transmitting device  12  is a wireless charging mat are sometimes described herein as an example. 
     Power receiving device  24  may be a portable electronic device such as a wristwatch, a cellular telephone, a laptop computer, a tablet computer, an accessory such as an earbud, or other electronic equipment. Power transmitting device  12  may be coupled to a wall outlet (e.g., an alternating current power source), may have a battery for supplying power, and/or may have another source of power. Power transmitting device  12  may have an alternating-current (AC) to direct-current (DC) power converter such as AC-DC power converter  14  for converting AC power from a wall outlet or other power source into DC power. DC power may be used to power control circuitry  16 . During operation, a controller in control circuitry  16  may use power transmitting circuitry  52  to transmit wireless power to power receiving circuitry  54  of device  24 . Power transmitting circuitry  52  may have switching circuitry (e.g., inverter circuitry  60  formed from transistors) that is turned on and off based on control signals provided by control circuitry  16  to create AC current signals through one or more transmit coils  42 . Coils  42  may be arranged in a planar coil array (e.g., in configurations in which device  12  is a wireless charging mat). 
     As the AC currents pass through one or more coils  42 , alternating-current electromagnetic (e.g., magnetic) fields (signals  44 ) are produced that are received by one or more corresponding receiver coils such as coil  48  in power receiving device  24 . When the alternating-current electromagnetic fields are received by coil  48 , corresponding alternating-current currents are induced in coil  48 . Rectifier circuitry such as rectifier  50 , which contains rectifying components such as synchronous rectification metal-oxide-semiconductor transistors arranged in a bridge network, converts received AC signals (received alternating-current signals associated with electromagnetic signals  44 ) from coil  48  into DC voltage signals for powering device  24 . 
     The DC voltages produced by rectifier  50  may be used in powering a battery such as battery  58  and may be used in powering other components in device  24 . For example, device  24  may include input-output devices  56  such as a display, touch sensor, communications circuits, audio components, sensors, and other components and these components may be powered by the DC voltages produced by rectifier  50  (and/or DC voltages produced by battery  58 ). 
     Device  12  and/or device  24  may communicate wirelessly using in-band or out-of-band communications. Device  12  may, for example, have wireless transceiver circuitry  40  that wirelessly transmits out-of-band signals to device  24  using an antenna. Wireless transceiver circuitry  40  may be used to wirelessly receive out-of-band signals from device  24  using the antenna. Device  24  may have wireless transceiver circuitry  46  that transmits out-of-band signals to device  12 . Receiver circuitry in wireless transceiver  46  may use an antenna to receive out-of-band signals from device  12 . 
     Wireless transceiver circuitry  40  may also use one or more coils  42  to transmit in-band signals at a given power frequency (or power transmission frequency) that are received by wireless transceiver circuitry  46  using coil  48 . Similarly, wireless transceiver circuitry  46  may use one or more coils  48  to transmit in-band signals at the given power frequency that are received by wireless transceiver circuitry  40  using coil  42 . Any suitable modulation scheme may be used to support in-band communications between device  12  and device  24 . 
     In some cases, wireless transceiver circuitry  40  in power transmitting device  12  and wireless transceiver circuitry  46  in power receiving device  24  may communicate in-band by modulating the AC drive signals that are used to transfer power. Frequency shift keying (FSK), amplitude shift keying (ASK), or any other desired modulation of the AC drive signals may be used to convey in-band data between device  12  and device  24  while power is conveyed wirelessly from device  12  to device  24 . 
     For example, during wireless power transfer operations, while power transmitting circuitry  52  is driving AC signals into one or more of coils  42  to produce signals  44  at the power transmission frequency, wireless transceiver circuitry  40  uses FSK modulation to modulate the power transmission frequency of the driving AC signals and thereby modulate the frequency of signals  44 . In device  24 , coil  48  is used to receive signals  44 . Power receiving circuitry  54  uses the received signals on coil  48  and rectifier  50  to produce DC power. At the same time, wireless transceiver circuitry  46  uses FSK demodulation to extract the transmitted in-band data from signals  44 . This approach allows FSK data (e.g., FSK data packets) to be transmitted in-band from device  12  to device  24  with coils  42  and  48  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     In-band communications between devices  12  and  24  may also use ASK modulation and demodulation techniques. For example, wireless transceiver circuitry  46  may transmit in-band data to device  12  by using a switch (e.g., one or more transistors in transceiver  46  that are coupled coil  48 ) to modulate the impedance of power receiving circuitry  54  (e.g., coil  48 ). This, in turn, modulates the amplitude of signal  44  and the amplitude of the AC signal passing through coil(s)  42 . Wireless transceiver circuitry  40  monitors the amplitude of the AC signal passing through coil(s)  42  and, using ASK demodulation, extracts the transmitted in-band data from these signals that was transmitted by wireless transceiver circuitry  46 . The use of ASK communications allows ASK data bits (e.g., ASK data packets) to be transmitted in-band from device  24  to device  12  with coils  48  and  42  while power is simultaneously being wirelessly conveyed from device  12  to device  24  using coils  42  and  48 . 
     To increase the rate of data transmission and increase noise immunity of in-band communications, wireless transceiver circuitry  40  and wireless transceiver circuitry  46  may be configured to inject one or more data carrier waves (that have a higher frequency than the AC drive signals) to the AC drive signals used for wireless power transfer. The data carrier waves may be transmitted between devices  12  and  24  using coils  42  and  48 . The data carrier waves may have a higher frequency than the AC drive signals to enable faster data transmission between devices  12  and  24 . Power receiving device  24  can transmit data to power transmitting device  12  by modulating the data carrier waves. 
     Control circuitry  16  has external object measurement circuitry  41  (sometimes referred to as foreign object detection circuitry or external object detection circuitry) that detects external objects on a charging surface associated with device  12 . Circuitry  41  can detect foreign objects such as coils, paper clips, and other metallic objects and can detect the presence of wireless power receiving devices  24 . During object detection and characterization operations, external object measurement circuitry  41  can be used to make measurements on coils  42  to determine whether any devices  24  are present on device  12 . 
     In an illustrative arrangement, measurement circuitry  41  of control circuitry  16  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). During measurement operations, switching circuitry in device  12  may be adjusted by control circuitry  16  to switch each of coils  42  into use. As each coil  42  is selectively switched into use, control circuitry  16  uses the signal generator circuitry of signal measurement circuitry  41  to apply a probe signal to that coil while using the signal detection circuitry of signal measurement circuitry  41  to measure a corresponding response. Measurement circuitry  43  in control circuitry  30  and/or in control circuitry  16  may also be used in making current and voltage measurements. 
     The characteristics of each coil  42  depend on whether any foreign objects overlap that coil (e.g., coins, wireless power receiving devices, etc.) and also depend on whether a wireless power receiving device with a coil such as coil  48  of  FIG. 1  is present, which could increase the measured inductance of any overlapped coil  42 . Signal measurement circuitry  41  is configured to apply signals to the coil and measure corresponding signal responses. For example, signal measurement circuitry  41  may apply an alternating-current probe signal while monitoring a resulting signal at a node coupled to the coil. As another example, signal measurement circuitry  41  may apply a pulse to the coil and measure a resulting impulse response (e.g., to measure coil inductance). Using measurements from measurement circuitry  41 , the wireless power transmitting device can determine whether an external object is present on the coils. If, for example, all of coils  42  exhibit their expected nominal response to the applied signals, control circuitry  16  can conclude that no external devices are present. If one of coils  42  exhibits a different response (e.g., a response varying from a normal no-objects-present baseline), control circuitry  16  can conclude that an external object (potentially a compatible wireless power receiving device) is present. 
     Control circuitry  30  has measurement circuitry  43 . In an illustrative arrangement, measurement circuitry  43  of control circuitry  30  contains signal generator circuitry (e.g., oscillator circuitry for generating AC probe signals at one or more probe frequencies, a pulse generator, etc.) and signal detection circuitry (e.g., filters, analog-to-digital converters, impulse response measurement circuits, etc.). During measurement operations, device  24  may use measurement circuitry  43  to make measurements to characterize device  24  and the components of device  24 . For example, device  24  may use measurement circuitry  43  to measure the inductance of coil  48  (e.g., signal measurement circuitry  43  may be configured to measure signals at coil  48  while supplying coil  48  with signals at one or more frequencies to measure coil inductances), signal pulses (e.g., so that impulse response measurement circuitry in the measurement circuitry can be used to make inductance and Q factor measurements), etc. Measurement circuitry  43  may also make measurements of the output voltage of rectifier  50 , the output current of rectifier  50 , etc. 
     A top view of an illustrative configuration for device  12  in which device  12  has an array of coils  42  is shown in  FIG. 2 . In the example of  FIG. 2 , device  12  has an array of coils  36  that lie in the X-Y plane. Coils  36  of device  12  are covered by a planar dielectric structure such as a plastic member or other structure forming charging surface  90 . The lateral dimensions (X and Y dimensions) of the array of coils  36  in device  12  may be 1-1000 cm, 5-50 cm, more than 5 cm, more than 20 cm, less than 200 cm, less than 75 cm, or other suitable size. Coils  36  may overlap or may be arranged in a non-overlapping configuration. Coils  36  can be placed in a rectangular array having rows and columns and/or may be tiled using a hexagonal tile pattern or other pattern. Device  12  may, in general, have any suitable number of coils  42  (e.g., 22 coils, at least 5 coils, at least 10 coils, at least 15 coils, fewer than 30 coils, fewer than 50 coils, etc.). Coils  42  may be arranged in rows and columns and may or may not partially overlap each other in one or more layers of coils. Coils  42  may be circular or may have other suitable shapes (e.g., coils  42  may be square, may have hexagonal shapes, may have other shapes having rotational symmetry, etc.). 
     Illustrative circuitry of the type that may be used for forming power transmitting circuitry  52  and power receiving circuitry  54  of  FIG. 1  is shown in  FIG. 3 . As shown in  FIG. 3 , power transmitting circuitry  52  may include drive circuitry such as inverter  60  that supply drive signals at the wireless power transmission frequency to a wireless power transmitter resonant circuit. The wireless power transmitter resonant circuit may include a wireless power transmitting coil  42  and capacitor  70 . Rectifier  50  in wireless power receiving circuitry  54  receives wireless power signals  44  using a wireless power receiver resonant circuit that includes capacitor  74  and wireless power receiving coil  48 . 
     Inverter  60  may include metal-oxide-semiconductor transistors or other suitable transistors that are modulated by AC control signals from control circuitry  16  ( FIG. 1 ) that are received on control signal input  62 . The attributes of AC control signal  62  (e.g., duty cycle, frequency, etc.) may be adjusted by control circuitry  16  dynamically during power transmission to control the amount of power being transmitted by power transmitting coils  42 . 
     When transmitting wireless power, control circuitry  16  ( FIG. 1 ) selects one or more appropriate coils  42  to use in transmitting signals  44  to coil  48  (e.g., control circuitry  16  supplies control signals to input  62  of inverter  60  that is to drive the selected coils  42  to produce signals  44 ). When device  24  is placed on the surface of device  12 , the selected coils  42  in device  12  that are driven to produce signals  44  tend to be coils  42  that at least partially overlap with coil  48  in device  24  (when viewing the charging surface of device  12  from above) and are sometimes referred to as “active” wireless transmitting coils. Coils  42  in device  12  that are non-overlapping with coil  48  in device  24  (when viewing the charging surface of device  12  from above) may be unselected and undriven by inverter  60  and are sometimes referred to as “inactive” or temporarily idle coils. Coil  48  and capacitor  74  form a resonant circuit in circuitry  54  that receives signals  44 . Receiver  50  rectifies the received signals and provides direct-current output power at output  68 . 
     In a multicoil configuration such as one shown in the example of  FIG. 2 , the magnetic cross-coupling and leakage between active and inactive coils  42  across the charging surface of power transmitting device  12  can be unacceptably high. Moreover, the magnetic cross-coupling and leakage between coil  48  of device  24  and inactive coils  42  of device  12  can further exacerbate the issue. This results in generation of high harmonic distortion, which causes increased levels of spurious radiated emissions and makes it challenging for power transmitting device  12  to meet worldwide regulatory requirements. 
     Conventionally, the inverter in the power transmitting circuitry is controlled by a rectangular clock signal. While proper grounding can help reduce the magnetic flux coupling between adjacent coils  42  in power transmitting device  12 , the harmonic distortion exists due to the use of the rectangular clock signal controlling the inverter. The rectangular clock signal may have a duty cycle.  FIG. 4  is a diagram showing harmonic distortion levels at the wireless power transmitting circuitry as a function of the duty cycle of the rectangular clock signal. 
     As shown in  FIG. 4 , the second harmonic distortion HD 2  exhibits a trough at about 50% duty cycle; the third harmonic distortion HD 3  exhibits a trough at about 34% duty cycle; the fourth harmonic distortion HD 4  exhibits a trough at about 25% duty cycle; and so on. In other words, the harmonic distortion profile can vary significantly with duty cycle, which results in radiated spurious emissions (RSEs) across different receivers. According to  FIG. 4 , since the eighth harmonic distortion HD 8  has a trough at around 13% duty cycle, it would be optimal to fix the duty cycle of the rectangular clock signal to 13% in order to minimize HD 8 . While fixing the duty cycle of the rectangular clock signal to 13% would help minimize HD 8 , emissions are other harmonic frequencies (e.g., HD 2 -HD 7 , HD 9 , HD 10 , etc.) would still be significant. 
     In accordance with an embodiment, wireless power transmitting circuitry  52  may be controlled using a signal having different pulse widths to help reduce the harmonic content from that signal.  FIG. 5  is a circuit diagram of illustrative wireless power transmitting circuitry  52  that is controlled by a periodic signal exhibit a plurality of different pulse widths. As shown in  FIG. 5 , power transmitting circuitry  52  includes an inverter  60  configured to drive a corresponding wireless power transmitter resonant circuit that includes coil  42  and capacitor  70 . 
     Inverter  60  may include a first switch (e.g., a first transistor T 1 ) and a second switch (e.g., a second transistor T 2 ) coupled in series between a first power supply line (e.g., a positive power supply terminal  504 ) and a second power supply line (e.g., a ground power supply terminal  506 ). Inverter  60  may be modulated to create an AC output waveform signal suitable for driving drive coil  42  for wireless power transfer. In some examples, this signal has a frequency in the kilo-Hertz range, such as between 100 to 400 kHz, including frequencies particularly in the 125 to 130 kHz range. In some examples, this signal is in the mega-Hertz range, such as about 6.78 MHz or more generally between 1 to 100 MHz. In some examples, this signal is in the giga-Hertz range, such as about 60 GHz and more generally between 1 to 100 GHz. As this AC signal passes through coil  42 , a corresponding wireless power signal (electromagnetic signal  48 ) is created and conveyed to coil  48  of circuitry  54 . This AC frequency at which power transmitting circuitry  52  is modulated is sometimes referred to as the power frequency (“fp”). 
     Transistors T 1  and T 2  have gate terminals connected to each other and serve as the input of inverter  60 . To generate the AC output waveform at the desired power frequency, inverter  60  may receive at its input a periodic control signal from an input source generator such as sinusoidal pulse-width modulation (PWM) signal generator  500 . Signal generator  500  may sometimes be considered as part of control circuitry  16  (see  FIG. 1 ). A buffer circuit such as driver circuit  502  may optionally be interposed between sinusoidal PWM signal generator  500  and the input of inverter  60  to help drive the input of inverter  60  to the desired voltage level. 
     Sinusoidal PWM signal generator may be configured to generate a periodic control signal having multiple different pulse widths, where a sum of the different pulse widths in a period of the periodic control signal is equal to a selected duty cycle. In other words, the different pulse widths within a period of the control signal, in sum, substantially equal the selected duty cycle. A control signal of this type can be generated using a sinusoidal input source and is thus sometimes referred to as a sinusoidal PWM control signal Vspwm. 
     One suitable arrangement for generating control signal Vspwm is shown in  FIG. 5 . In the example of  FIG. 5 , generator  500  may include a comparison circuit such as comparator  510  having a first input (i.e., the negative input) configured to receive a first periodic input signal, a second input (i.e., the positive input) configured to receive a second periodic input signal, and an output at which control signal Vspwm is provided. The first periodic input source may be a sinusoidal waveform Vsine oscillating at power frequency fp. The second periodic input source may be a reference signal Vref oscillating at a much higher frequency N*fp, where N may at least 10, at least 20, at least 50, at least 100, between 2-10, or some other suitable integer. In certain embodiments, signal Vref may be a triangle wave, a sawtooth wave, a sine wave, or other suitable waveform. 
       FIG. 6A  is a diagram illustrating a sinusoidal pulse-width modulation (SPWM) control signal Vspwm that is provided at the output of comparator  510  and that can be used to control wireless power transmitting circuitry  52 . As shown in  FIG. 6A , signal Vspwm exhibits a plurality of different pulse widths. The sum of the different pulse widths in signal Vspwm may equal to a selected duty cycle. For example, in the scenario in which the selected duty cycle is 30%, the duration of time when signal Vspwm is high (i.e., the sum of all the high pulses) will be approximately 30% of a period of signal Vsine. As another example, in the scenario in which the selected duty cycle is 50%, the sum of all the different pulse widths in Vspwm will be equal to substantially half of the period of signal Vsine. 
       FIG. 6B  is a diagram illustrating waveforms that can be generated by wireless power transmitting circuitry  52  (e.g., by feeding in signals Vsine and Vref to the input of comparator  510 ). Sinusoidal signal Vsine has a frequency fp, and  FIG. 6B  shows one period of frequency fp. In the example of  FIG. 6B , signal Vref is a triangle waveform having a frequency of about 30*fp. These signals are fed into comparator  510  ( FIG. 5 ) to generate corresponding signal Vspwm as shown in  FIG. 6A . Signal Vspwm, which can be optionally amplified or level-shifted using driver  502 , is received at the input of inverter  60 . In response to receiving the SPWM control signal, inverter  60  may generate at its output voltage waveform Vout and current waveform Iout. Still referring to  FIG. 6B , waveform Vout exhibits a similar shape as Vspwm (e.g., Vout also has a plurality of different pulse widths summing to the target duty cycle). 
     Radiated spurious emissions is generally dominated by output current Iout. In the example of  FIG. 6B , the different pulses in Vout can cause corresponding high-frequency spikes in the Iout waveform.  FIG. 6C  shows a more zoomed-out version of Iout (see, e.g., waveform  650 ). In accordance with certain embodiments, the high-frequency components in the output current can be filtered out using a capacitor such as capacitor C 1  coupled in parallel with transistor T 1  (see, e.g.,  FIG. 5 ). Configured in this way, capacitor C 1  will filter out any undesired high-frequency components associated with Vref (such as undesired high-frequency components at N*fp, 2N*fp, 3N*fp, 4N*fp, 5N*fp, etc.), thereby achieve low radiated spurious emissions. A resulting output current Iout′ with high-frequency components filtered out is shown as waveform  652  in  FIG. 6C , which does not include the unwanted spikes. 
     The exemplary configuration of  FIG. 5  in which sinusoidal PWM signal generator  500  is implemented using a comparator that receives two different periodic input signals to generate a sinusoidal PWM control signal is merely illustrative and is not intended to limit the scope of the present embodiments. If desired, PWM signal generator  500  may be implemented in other suitable ways to generate a control signal with a plurality of different pulse widths summing to the desired duty cycle. 
     The improvement provided by use of a sinusoidal PWM control signal is illustrated in  FIGS. 7-10 .  FIG. 7A  is a diagram of a rectangular wave Vsq having a fixed 25% duty cycle. If this signal Vsq were fed to the input of inverter  60  via driver  502 , the corresponding frequency response at the output of inverter  60  is shown in  FIG. 7B . The power level at power frequency fp is labeled as fundamental frequency component F 0 ; the second harmonic distortion component is labeled as HD 2 ; the third harmonic distortion component is labeled as HD 3 ; the fourth harmonic distortion component is labeled as HD 4 ; and so on. In the example of  FIG. 7B , the harmonic distortion components are undesirably high relative to F 0 . The fourth harmonic distortion HD 4  and the eight harmonic distortion are comparatively low when the duty cycle is at 25%, which is consistent with the diagram of  FIG. 4  where HD 4  and HD 8  both exhibit a local trough at 25% duty cycle. 
       FIG. 8A  is a diagram of a rectangular wave Vsq having a fixed 45% duty cycle. If this signal Vsq were fed to the input of inverter  60  via driver  502 , the corresponding frequency response at the output of inverter  60  is shown in  FIG. 8B . In the example of  FIG. 8B , the harmonic distortion components are also undesirably high relative to F 0 . The ninth harmonic distortion HD 9  is comparatively low when the duty cycle is at 45%, which is consistent with the diagram of  FIG. 4  where HD 9  exhibits a local trough at around 45% duty cycle. 
       FIG. 9A  is a diagram showing input signals for comparator  510  of  FIG. 5 . Signal Vsine oscillates at frequency fp, whereas Vref toggles at a much higher frequency N*fp (where N is approximately equal to 40 in the example of  FIG. 9A ). When these signals are fed into the inputs of comparator  510 , a corresponding control signal Vspwm with a plurality of different pulse widths summing to an effective duty cycle of 25% can be produced (see, e.g.,  FIG. 6A ). Inverter  60  receiving such control signal Vspwm may exhibit a corresponding frequency response of  FIG. 9B  at the output of inverter (see, e.g., Vout in  FIG. 6B ). The power level at power frequency fp is labeled as fundamental frequency component F 0 ; the second harmonic distortion component is labeled as HD 2 ; the third harmonic distortion component is labeled as HD 3 ; the fourth harmonic distortion component is labeled as HD 4 ; and so on. 
     In the example of  FIG. 9B , the harmonic distortion components (i.e., HD 2 , HD 3 , HD 4 , HD 5 , etc.) are all much lower than that of  FIG. 7B , both yielding a 25% duty cycle. For example, HD 2  in  FIG. 7B  is around 16 dB, whereas HD 2  in  FIG. 9B  is around −7 dB. In other words, using a sinusoidal PWM control signal instead of a conventional rectangular clock signal can yield around a 23 dB improvement in HD 2 . The reduction of harmonic distortion at the various higher order frequencies is due to the different pulse widths in Vspwm, each of which helps to contribute a destructive trough for each of the harmonic frequencies. The use of a sinusoidal PWM control signal therefore mitigates harmonic content from the source (i.e., at the input of inverter  60 ). As a result, any re-radiation among the coils  42  will have little impact on far-field radiated spurious emissions and can help power transmitting device  12  better meet worldwide regulatory requirements. 
     As described above, the input signals of  FIG. 9A  are used to provide an effective duty cycle of 25%. To change the effective duty cycle in the sinusoidal PWM scheme, the amplitude of input source Vsine can be adjusted.  FIG. 10A  is a diagram showing input signals for comparator  510  of  FIG. 5  that produces an effective duty cycle of 45% (e.g., by increasing the amplitude of Vsine). Signal Vsine oscillates at frequency fp, whereas Vref toggles at a much higher frequency N*fp (where N is approximately equal to 40 in the example of  FIG. 10A ). When these signals are fed into the inputs of comparator  510 , a corresponding control signal Vspwm with a plurality of different pulse widths summing to an effective duty cycle of 45% can be produced. Inverter  60  receiving such control signal Vspwm may exhibit a corresponding frequency response of  FIG. 10B  at the output of inverter. 
     In the example of  FIG. 10B , the harmonic distortion components (i.e., HD 2 , HD 3 , HD 4 , HD 5 , etc.) are all much lower than that of  FIG. 8B , both at 45% duty cycle. For example, HD 2  in  FIG. 8B  is around 5.5 dB, whereas HD 2  in  FIG. 10B  is around −4.5 dB. In other words, using a sinusoidal PWM control signal instead of a conventional rectangular clock signal can yield around a 10 dB improvement in HD 2 . The reduction of harmonic distortion at the various higher order frequencies is due to the different pulse widths in Vspwm, each of which helps to contribute a destructive trough for each of the harmonic frequencies. The use of a sinusoidal PWM control signal therefore mitigates harmonic content from the source (i.e., at the input of inverter  60 ). As a result, any re-radiation among the coils  42  will have little impact on far-field radiated spurious emissions and can help power transmitting device  12  better meet worldwide regulatory requirements. 
       FIG. 11  is a diagram illustrating how controlling the wireless power transmitting circuitry using sinusoidal pulse width modulation reduces harmonic distortion. Line  1100  represents the power levels at fundamental frequency F 0  and harmonic frequencies HD 2 -HD 6  when inverter  60  is controlled by a rectangular clock signal with only one fixed pulse width. Line  1102  represents the power levels at fundamental frequency F 0  and harmonic frequencies HD 2 -HD 6  when inverter  60  is controlled by a sinusoidal PWM control signal with a many different pulse widths. As shown in the example of  FIG. 11 , the harmonic distortion levels are substantially reduced for line  1102  relative to line  1100 , where HD 2  is reduced by more than 20 dB, HD 3  is reduced by more than 20 dB, HD 4  is reduced by more than 5 dB, HD 5  is reduced by more than 10 dB, HD 6  is reduced by more than 20 dB, etc. Reducing harmonic content in this way can dramatically decrease radiated spurious emissions at the wireless power transmitting device. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180611
Publication Date: 20211207
Grant Date: 20211207
Priority Date: 20180328
Inventors: MANTHA, SOUMYA
WALIA, MANJIT S.
SABNANI, RAHUL A.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/00712", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33571", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33571", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33571", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/5395", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00712", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y02B70/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/5395", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M1/0058", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M1/0064", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M7/5395", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 68054040