Wireless power back channel communication
In accordance with embodiments of the present invention, data is modulated for transmission phase modulation. A method of transmitting data in a wireless power transmitter, includes transmitting a wireless power signal; encoding data to be transmitted into symbols; determining a phase shift to represent the symbols; and phase modulating the wireless power signal with the phase shift. A method of receiving data in a wireless power receiver includes receiving a wireless power signal that includes a phase modulated data signal; determining a period of each cycle of the wireless power signal; providing a running average over N−1 cycles of the wireless power signal, where N represents the number of cycles of the wireless power signal in which each phase modulation is provided; and decoding the data from the running average.
1. A wireless power transmitter, comprising:
a transmit coil that provides a wireless power signal;
a driver coupled to provide an AC current to the transmit coil to produce the wireless power signal; and
a modulator coupled to the driver to provide phase change modulation to the wireless power signal to transmit data, wherein the modulator provides a phase change to the wireless power signal every N cycles of a switching frequency of the driver, and wherein the modulator comprises
a data register receiving the data,
a data encoder coupled to encode the data into symbols,
a cycle counter providing a cycle count from the switching frequency of the drier, and
a phase shifter receiving the symbols and the cycle counter and providing the phase change to the driver.
2. The transmitter of claim 1 , wherein the driver includes switching transistors driven by a controller, the modulator providing control signals to the controller resulting in modification of gate control signals to the switching transistors.
3. The transmitter of claim 1 , wherein the symbols include two symbols to include one bit of the data.
4. The transmitter of claim 1 , wherein the symbols four symbols to include two bits of the data.
5. The transmitter of claim 1 , wherein N is four.
6. The transmitter of claim 1 , wherein N is greater than 2.
7. A wireless power receiver, comprising:
a receive coil;
a switching rectifier coupled to receive a wireless power signal from the receive coil; and
a demodulator coupled to the switching rectifier to receive the wireless power signal and to recover data provided in the wireless power signal by phase modulation, wherein the demodulator detects a phase change in the wireless power signal every N cycles of a switching frequency of the switching rectifier, and wherein the demodulator comprises
a counter coupled to receive the wireless power signal and determine the time between cycles of the wireless power signal,
a running average circuit that takes a running average of the time between cycles over N−1 cycles of the switching frequency, and
a data decoder coupled to receive the running average and recover data sent on the wireless power signal.
8. The receiver of claim 7 , wherein the switching rectifier includes switching transistors driven by a controller, the demodulator receiving the wireless power signal.
9. The receiver of claim 7 , wherein the counter receives a high speed clock signal and counts the clock signal cycles between zero crossings of the wireless power signal.
10. The receiver of claim 7 , wherein the data decoder determines a phase shift from the running average, determines a data symbol from the phase shift, and determines the data sent on the wireless power signal from the data symbol.
11. The receiver of claim 10 , wherein the data symbol is one of a set of two symbols to represent one bit of the data.
12. The receiver of claim 10 , wherein the data symbol is one of a set of four symbols that represents two bits of the data.
13. The transmitter of claim 7 , wherein N is four.
14. The transmitter of claim 7 , wherein N is greater than 2.
15. A method of transmitting data in a wireless power transmitter, comprising:
transmitting a wireless power signal;
encoding data to be transmitted into symbols;
determining a phase shift to represent the symbols; and
phase modulating the wireless power signal with the phase shift, wherein the phase modulating provides a phase change to the wireless power signal every N cycles of a switching frequency of the driver, and wherein the phase modulating comprises
receiving the data into a data register,
encoding the data into symbols with a data encoder,
providing a cycle count from the switching frequency of the drier with a cycle counter, and
receiving the symbols and the cycle counter and providing the phase change to the drive with a phase shifter.
16. The method of claim 15 , wherein phase modulating the wireless power signal includes providing a phase shift in every N cycles of the wireless power signal.
17. A method of receiving data in a wireless power receiver, comprising:
receiving a wireless power signal that includes a phase modulated data signal;
determining a period of each cycle of the wireless power signal;
providing a running average over N−1 cycles of the wireless power signal, where N represents the number of cycles of the wireless power signal in which each phase modulation is provided; and
decoding the data from the running average.
18. The method of claim 17 , wherein the data is encoded in the phase modulated data signal in symbols.