KWS-CIM: A Charge-Domain eDRAM-Based Compute-in-Memory Macro for Ternary DFSMN Keyword Spotting

This paper presents a 3T2C embedded DRAM (eDRAM)-based charge-domain compute-in-memory (CIM) macro for ternary deep feedforward sequential memory network (DFSMN)-based keyword spotting (KWS) with ternary activations and binary weights. The proposed architecture integrates a charge-domain ternary multiply-and-accumulate (MAC) bitcell, a selectable dual-mode sensing scheme, and an in-array offset calibration technique using fixed calibration rows. The dual-mode sensing scheme supports an energy-prioritized conventional sense amplifier (SA) mode for always-on monitoring and an accuracy-prioritized two-step sense amplifier (TSSA) mode for robust inference under reduced sensing margins. The proposed TSSA mitigates decision-timing-induced kickback disturbance, while the calibration rows suppress systematic column-wise sensing offsets. A sense amplifier-based 1-bit readout is employed to minimize area overhead. Fabricated in a 65-nm CMOS process, the proposed macro operates up to 250 MHz and achieves 930–1335 TOPS/W in the conventional SA mode and 82–336 TOPS/W in the TSSA mode, with an area efficiency of 18.45 TOPS/mm2. For DFSMN-based KWS, the measured accuracies with the calibrated TSSA mode reach 91.66%, 89.87%, and 87.30% for the 12-, 20-, and 35-class KWS settings (CLS12, CLS20, and CLS35), respectively. Additional evaluations achieve 98.02% on MNIST and 87.32% on CIFAR-10 with ResNet18, demonstrating the general applicability of the proposed eDRAM CIM macro.