Analysis and Design of a Robust, Low-Power, Inductively Coupled LSK Data Link

A low-power half-duplex data link transmits data at up to 4 Mb/s over coupled inductors across distances of up to 5 cm. The inductors are part of two resonators which tune a free-running oscillator to one of their natural modes. This gives robustness to changes in coil distance and relative orientation. With load-shift keying (LSK) employed in the remote transponder, the link is modeled analytically to reveal some unexpected properties. A complete design guide aids selection of coil size for range, carrier frequency for data rate, and $Q$ -switching to extend range. Owing to low power circuit design, the remote transponder consumes 0.075 pJ/b in transmit, 5 pJ/b in receive mode.