An Implantable Neuromorphic Sensing System Featuring Near-Sensor Computation and Send-on-Delta Transmission for Wireless Neural Sensing of Peripheral Nerves

This article presents a bioinspired, event-driven neuromorphic sensing system (NSS) capable of performing on-chip feature extraction and “send-on-delta” pulse-based transmission, targeting peripheral nerve neural recording applications. The proposed NSS employs event-based sampling which, by leveraging the sparse nature of electroneurogram (ENG) signals, achieves a data compression ratio of $> 125\times $ , while maintaining a low normalized rms error (NRMSE) of 4% after reconstruction. The proposed NSS consists of three sub-circuits. A clockless level-crossing (LC) analog-to-digital converter (ADC) with background offset calibration has been employed to reduce the data rate, while maintaining a high signal to quantization noise ratio (SQNR). A fully synthesized spiking neural network (SNN) extracts temporal features of compound action potential (CAP) signals and consumes only 13 $\mu \text{W}$ . An event-driven, pulse-based body channel communication (Pulse-BCC) with serialized address-event representation (AER) encoding schemes minimizes transmission energy and form factor. The prototype is fabricated in 40-nm CMOS occupying a 0.32-mm ² active area and consumes in total 28.2 and 50 $\mu \text{W}$ power in feature extraction and full diagnosis mode, respectively. The presented NSS also extracts temporal features of CAP signals with 10- $\mu \text{s}$ precision.