A Sub-10-pJ/bit 5-Mb/s Magnetic Human Body Communication Transceiver

Abstract

This article presents a transceiver designed to exploit the low path loss offered by magnetic human body communication (mHBC) toward ultra-efficient body area networking. A single-stage power oscillator is used to efficiently generate on–off-keying (OOK) modulated magnetic fields via body-worn coils that act as both resonant and magnetic-field-generating elements. To de-couple improved path loss yet reduced data-rate tradeoffs with increasing $Q$ of coils, a synchronous injection-locked kick-start circuit is proposed, enabling 5-Mb/s data at a carrier frequency of 40 MHz with $Q$ of ~50 and also providing dynamic frequency tuning to compensate normal inductor variation during motion. The receiver (RX) exploits the low path loss toward the design of a low-power sub-threshold-biased dynamic-threshold amplifier and envelope detector and successfully performs non-coherent demodulation of received OOK data. The transmitter and RX consume 18.56 and 6.3 $\mu \text{W}$ , which when including a 17.2- $\mu \text{W}$ crystal oscillator for the reference clock, results in an efficiency of 7.15 and 4.7 pJ/bit, respectively, when closing a link across the body.