Reliable Memristive Neural Network Accelerators Based on Early Denoising and Sparsity Induction

Implementing deep neural networks (DNNs) in hardware is challenging due to the requirements of huge memory and computation associated with DNNs' primary operation—matrix-vector multiplications (MVMs). Memristive crossbar shows great potential to accelerate MVMs by leveraging its capability of in-memory computation. However, one critical obstacle to such a technique is potentially significant inference accuracy degradation caused by two primary sources of errors—the variations during computation and stuck-at-faults (SAFs). To overcome this obstacle, we propose a set of dedicated schemes to significantly enhance its tolerance against these errors. First, a minimum mean square error (MMSE) based denoising scheme is proposed to diminish the impact of variations during computation in the intermediate layers. To the best of our knowledge, this is the first work considering denoising in the intermediate layers without extra crossbar resources. Furthermore, MMSE early denoising not only stabilizes the crossbar computation results but also mitigates errors caused by low resolution analog-to-digital converters. Second, we propose a weights-to-crossbar mapping scheme by inverting bits to mitigate the impact of SAFs. The effectiveness of the proposed bit inversion scheme is analyzed theoretically and demonstrated experimentally. Finally, we propose to use L1 regularization to increase the network sparsity, as a greater sparsity not only further enhances the effectiveness of the proposed bit inversion scheme, but also facilitates other early denoising mechanisms. Experimental results show that our schemes can achieve 40%-78% accuracy improvement, for the MNIST and CIFAR10 classification tasks under different networks.