A $24\,\mu \text{W}$, Batteryless, Crystal-free, Multinode Synchronized SoC “Bionode” for Wireless Prosthesis Control

Abstract

We present a batteryless, crystal-free, time division multiple access (TDMA) synchronized multinode wireless body sensor node (WBSN) system-on-chip (SoC), referred to as a Bionode, for continuous and real-time telemetry of electromyograms (EMGs), enabling intuitive upper limb prosthesis control by an amputee. The SoC utilizes state of the art in supercapacitive RF energy harvesting, biosensing analog-front-end, switching-optimized SAR ADC, ultra-low-power RF transceiver, and clock circuits. The sensor node SoCs are time synchronized with a base station, mounted on the prosthetic arm, by using the ultra-low-power TDMA controller and receiver, and the digital core circuits. A 915 MHz broadcast RF signal is utilized to synthesize the carrier frequency of the transmitter. This along with the process and voltage compensated on-chip clock obviates the need for a bulky crystal oscillator, thus providing a low-cost and highly integrated solution to the WBSNs. The SoC is verified by capturing the EMG data from a healthy human body and consumes only $24\;{\upmu}\text{W}$ , while operating exclusively from the harvested RF energy. Implemented in a $0.18\;{\upmu}\text{m}$ CMOS process, the SoC occupies $2.025\;{\text {mm}}^{2}$ silicon area. The sensor node has an extremely low weight and physical dimensions, thanks to the flexible carbon nanotube (CNT) supercapacitor, electrically small antenna (ESA), and crystal-free operation of the SoC.