A 90.7-nW Vibration-Based Condition Monitoring Chip Featuring a Digital Compute-in-Memory- Based DNN Accelerator Using an Ultra-Low-Power 13T-SRAM Cell

This article presents an energy-harvester-powered ultra-low power (ULP) vibration-based condition monitoring (VbCM) chip with a digital compute-in-memory (CIM)-based deep neural network (DNN) accelerator. The VbCM chip achieves end-to-end signal processing, including a piezoelectric (PZ)-based accelerometer sensor and its readout circuit (RoC), a digital CIM-based DNN accelerator and a ULP radio system. To perform the targeted rotating bearing anomaly detection task with best-in-class accelerator power consumption and energy efficiency, the chip integrates several technologies from the algorithm level to the hardware level, including: 1) Compressing deep neural network (C-DNN) to reduce the network size through a feature compressor module (FCM); 2) Signal chain characteristic adaptation from direct training of the time-domain feature extractor (TD-FEx); 3) ULP 13T SRAM CIM bitcell to perform high energy efficiency in-cell multiplication; and 4) ripple counter (RCNT)-based accumulation scheme to improve the overall energy efficiency of the accelerator under a 0.35 V supply voltage. The VbCM chip achieves 90.7 nW total power with an inference FR of 20 frames/s, and the DNN accelerator’s energy efficiency achieves 18.8 fJ/MAC. With all the weight parameters statically stored in the CIM macros, the accelerator can operate with an inference accuracy of 91.3% while consuming 24.7 nW.