A 31.1 pJ/b Human Body Communication Transmitter with Standard-basis CDMA for Multi-Node IoB Systems

Voltage-mode Human-Body Communication (HBC) can enable highly energy-efficient medical wearables and implants due to the ability to transmit wideband signals through the body channel with low power consumption. However, with multiple devices envisioned in the emerging Internet of Bodies (IoB) network, the energy-efficiency of conventional 2-device HBC systems degrade due to the need of multiple-access support. In this paper, we introduce the first on-chip synchronous standard-basis (SB)-CDMA implementation for low-power HBC, supporting up to 16 nodes without power-hungry accumulators or ADCs, providing an efficient solution to multiple channel access with HBC. Additionally, for a network of devices, higher drive voltages improve the overall bit error rates (BER), at the cost of higher power consumption. However, realizing that voltage-mode capacitive HBC involves a capacitive load (unlike 50 Ohm radiative communication), we drive it in an adiabatic manner to significantly improve energy-efficiency. For this purpose, we include a symmetric 4-level capacitor-less adiabatic driver in 65 nm, achieving greater than 50% lower power w.r.t. CMOS drivers and 18 times lower area than SoA switched capacitor-based adiabatic designs.