Communication in a wireless power transfer system

A power receiver comprising:

• an input circuit comprising a receiver coil and a communicator circuit,
• wherein the receiver is arranged to extract power from a power transfer signal,
• wherein the communicator comprises:
• a receiver circuit, wherein the receiver circuit is arranged to receive a first data symbol;
• a determiner circuit, wherein the receiver circuit is arranged to determine a first chip sequence for the first data symbol;
• and
• a load modulator circuit, wherein the load modulator circuit is arranged to load modulate the first chip sequence on the power transfer signal,
• wherein the communicator circuit is arranged to synchronize the load modulation of the first chip sequence to the power transfer signal,
• wherein the communicator circuit is arranged to transmit symbols to a power transmitter by load modulation of the power transfer signal,
• wherein each symbol is represented by a chip sequence,
• wherein the chip sequence is a sequence of modulation load values wherein a sampling rate is equal to a chip frequency of the load modulation.

A method comprising:

• generating a power transfer signal in response to a drive signal applied to an output circuit;
• receiving symbols transmitted from a power receiver using load modulation of the power
• wherein each symbol is represented by a chip sequence,
• wherein each chip sequence is a sequence of modulation load values,
• wherein each symbol is synchronized with the power transfer signal;
• generating the drive signal;
• storing a plurality of reference chip sequences, wherein each reference chip sequence is linked to a data symbol;
• correlating a first chip sequence received from the power receiver with the plurality of reference chip sequences;
• and
• determining a received data symbol as the data symbol linked to a reference chip sequence with a highest correlation with the first chip sequence.

A method comprising:

• extracting power from a power transfer signal;
• transmitting symbols to a power transmitter load modulation of the power transfer signal,
• wherein each symbol is represented by a chip sequence,
• wherein the chip sequence is a sequence of modulation load values;
• receiving a first data symbol;
• determining a first chip sequence assigned for the first data symbol;
• modulating the first chip sequence on the power transfer signal;
• and
• synchronizing the load modulation of the first chip sequence to the power transfer signal.