A Fully Integrated Analog ReRAM Based 78.4TOPS/W Compute-In-Memory Chip with Fully Parallel MAC Computing

Abstract

Non-volatile memory (NVM) based computing-in-memory (CIM) shows significant advantages in handling deep learning tasks for artificial intelligence (AI) applications. To overcome the decreasing cost effectiveness of transistor scaling and the intrinsic inefficiency of data-shuttling in the von-Neumann architecture, CIM is proposed to realize high-speed and low-power system with parallel multiplication accumulation (MAC) computing [1] [2]. However, current demonstrations are mainly based on single macro and present limited computing parallelism. Realizing a fully-integrated CIM chip with a complete neural network model is still missing. The major challenges lie in: (1) The IR drop and transient errors when carrying out MAC operations in non-volatile memory arrays decrease the computing accuracy and further limit the parallelism; (2) The inefficiency of the interface blocks between different arrays due to the power overhead of the A/D and D/A converters (shown in Fig. 33.2.1). To address these challenges, this work proposes: (1) A sign-weighted 2T2R (SW-2T2R) array to reduce IR drop by decreasing the accumulative SL current (ISL), and eventually boost the computing parallelism; (2) a low-power interface design with resolution-adjustable LPAR-ADC to realize flexible tradeoff between system accuracy and power consumption. In this manner, this work implements a fully-integrated 784-100-10 MLP model on an integrated CIM chip with158.8kb analog ReRAMs. This chip realizes high recognition accuracy (94.4%) on MNIST database, high inference speed (77 μs/lmage), and 78.4 TOPS/W peak energy efficiency. The CMOS circuits are fabricated in a 130nm process.