8T-SRAM Based Process-In-Memory (PIM) System With Current Mirror for Accurate MAC Operation

Abstract

Process-in-memory (PIM) is an emerging computing paradigm to overcome the energy bottleneck inherent in conventional computing platform. While PIM utilizes several types of memory elements, SRAM based PIM has been researched extensively for its high scalability and feasibility by using CMOS process technology. In this work, we proposed 8T SRAM based process-in-memory system with current mirror for accurate MAC operation. To resolve the nonlinearity issue inherent in current-based SRAM MAC macro, we utilized cascaded current mirror. Furthermore, to enable more precise MAC operation, we allocated RWL timing pulses which drive 8T SRAM bitcells in the middle of timing duration. Our PIM architecture realize 4 bit input, 4 bit weight and 4 bit output precisions. Prototype chip has been fabricated using TSMC 65nm GP process technology. Measurement result has proved the MAC operation linearity of designed 8T SRAM based PIM system, and its throughput and energy efficiency with 0.29 GOPs and 1.05 TOPs/W. Software level analysis proved that our design can achieve upto 98.02 percent accuracy for MNIST dataset classification and 94.93 percent accuracy for CIFAR-10 dataset classification.

Keywords

• Processing-in-memory (PIM)
• current-mode accumulation
• current mirror
• multiply-and-accumulate (MAC)
• multi-bit computing
• static random access memory (SRAM)