Simultaneous Transmission of Up To 94-mW Self-Regulated Wireless Power and Up To 5-Mb/s Reverse Data Over a Single Pair of Coils

A method to transmit power and to communicate data in the reverse direction over only one pair of inductive coils is described. The system self-regulates the delivered load voltage, with no monitoring of or explicit feedback from the power receiver. Up to 94 mW of power can be transmitted over distances as large as 4.2 cm using coils of 3 cm diameter. The received voltage is unaffected by changes in coil separation up to a certain limit and also by changes of up to 40 \times in load current demand. A constant envelope frequency-shift keying (FSK) modulation is also described to transmit data in the reverse channel that exploits mode-selection properties of a free-running oscillator. This allows smooth, uninterrupted delivery of power while data is being transmitted.