ADC-Free ReRAM-Based In-Situ Accelerator for Energy-Efficient Binary Neural Networks

With the ever-increasing parameter size of deep learning models, conventional ASIC-based accelerators in mobile environments suffer from low energy budget due to limited memory capacity and frequent data movements. Binary neural networks (BNNs) deployed in ReRAM-based in-situ accelerators provide a promising solution, and various related architectures have been proposed recently. However, their performances are largely compromised by the tremendous cost of domain conversion via analog-to-digital converters (ADCs), essential for mixed-signal processing in ReRAM. This article identifies two root causes of the need for such ADCs and proposes effective solutions to address them. First, we minimize redundant operations in BNNs and reduce the number of ReRAM arrays with ADCs approximately by half. We also propose a partial-sum range adjustment technique based on a layer remapping to deal with the remaining ADCs. Proper handling of the partial-sum distribution allows ReRAM-based in-situ processing without domain conversion, completely bypassing the need for ADCs. Experimental results show that the proposed architecture achieves a 3.44x speedup and 91.5% energy savings, making it an attractive solution for on-device AI at the edge.