Ocelli: Efficient Processing-in-Pixel Array Enabling Edge Inference of Ternary Neural Networks

Abstract

Convolutional Neural Networks (CNNs), due to their recent successes, have gained lots of attention in various vision-based applications. They have proven to produce incredible results, especially on big data, that require high processing demands. However, CNN processing demands have limited their usage in embedded edge devices with constrained energy budgets and hardware. This paper proposes an efficient new architecture, namely Ocelli includes a ternary compute pixel (TCP) consisting of a CMOS-based pixel and a compute add-on. The proposed Ocelli architecture offers several features; (I) Because of the compute add-on, TCPs can produce ternary values (i.e., −1, 0, +1) regarding the light intensity as pixels’ inputs; (II) Ocelli realizes analog convolutions enabling low-precision ternary weight neural networks. Since the first layer’s convolution operations are the performance bottleneck of accelerators, Ocelli mitigates the overhead of analog buffers and analog-to-digital converters. Moreover, our design supports a zero-skipping scheme to further power reduction; (III) Ocelli exploits non-volatile magnetic RAMs to store CNN’s weights, which remarkably reduces the static power consumption; and finally, (IV) Ocelli has two modes, including sensing and processing. Once the object is detected, the architecture switches to the typical sensing mode to capture the image. Compared to the conventional pixels, it achieves an average 10% efficiency on its lane detection power consumption compared with existing edge detection algorithms. Moreover, considering different CNN workloads, our design shows more than 23% power efficiency over conventional designs, while it can achieve better accuracy.