A 24 μW, 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 μW, while operating exclusively from the harvested RF energy. Implemented in a 0.18 μm CMOS process, the SoC occupies 2.025 mm2 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.