Scalable Time-Domain Compute-in-Memory BNN Engine with 2.06 POPS/W Energy Efficiency for Edge-AI Devices

Time-domain (TD) computing has attracted attention for its high computing efficiency and suitability for applications on energy-constrained edge devices. In this paper, we present a time-domain compute-in-memory (TDCIM) macro for binary neural networks (BNNs) realized by standard as well as custom delay cells. Multiply- and-accumulate (MAC) operations, batch normalization (BN) and binarization (Bin) are all processed in the time-domain, avoiding costly digital domain post-processing. In addition, it supports flexible mapping for different kernel sizes, achieving 100% utilization. Starting from a standard cell-based implementation, we propose two custom cells that provide interesting trade-offs between energy efficiency, area and accuracy. The two proposed custom designs can achieve 1.5 and 2.06 POPS/W energy efficiencies at 0.5V and 0.6V with less cell area while maintaining model test accuracy.