CRAM: Collocated SRAM and DRAM With In-Memory Computing-Based Denoising and Filling for Neuromorphic Vision Sensors in 65 nm CMOS

Abstract

This brief presents an energy-efficient collocated random access memory (CRAM) featuring charge based computing. A $9T$ bit-cell-based collocated DRAM and SRAM together with a 2-dimensional charge diffusion paths topology is used to store the input binary image data and compute locally. The computing network performs both denoising approximating a nearest-neighbor median filter for background noise and region filling for the fragmented objects. Compared to conventional in-memory computing (IMC) implementations, the proposed prototype achieves better energy efficiency and throughput without any computational burden and bandwidth overhead, due to the natural in-memory analog computations. The prototype structure fabricated in a standard 65nm CMOS technology exhibit error-free read and write operations with $VDD$ down to $400mV$ and frequency up to $1GHz$ . The energy efficiency is $233 TOPS/W$ at the normal operating frequency of $200MHz$ and normal supply voltage of $1.2V$ . The natural process of charge diffusion makes the process of IMC consuming $\approx 10000 \times $ lesser energy and $5.8 \times $ lesser area cost than conventional digital implementation in the same process node.