Accelerating Deep Neural Networks in Processing-in-Memory Platforms: Analog or Digital Approach?

Nowadays, research topics on AI accelerator designs have attracted great interest, where accelerating Deep Neural Network (DNN) using Processing-in-Memory (PIM) platforms is an actively-explored direction with great potential. PIM platforms, which simultaneously aims to address power- and memory-wall bottlenecks, have shown orders of performance enhancement in comparison to the conventional computing platforms with Von-Neumann architecture. As one direction of accelerating DNN in PIM, resistive memory array (aka. crossbar) has drawn great research interest owing to its analog current-mode weighted summation operation which intrinsically matches the dominant Multiplication-and-Accumulation (MAC) operation in DNN, making it one of the most promising candidates. An alternative direction for PIM-based DNN acceleration is through bulk bit-wise logic operations directly performed on the content in digital memories. Thanks to the high fault-tolerant characteristic of DNN, the latest algorithmic progression successfully quantized DNN parameters to low bit-width representations, while maintaining competitive accuracy levels. Such DNN quantization techniques essentially convert MAC operation to much simpler addition/subtraction or comparison operations, which can be performed by bulk bit-wise logic operations in a highly parallel fashion. In this paper, we build a comprehensive evaluation framework to quantitatively compare and analyze aforementioned PIM based analog and digital approaches for DNN acceleration.