Timesteps meet Bits: Low-Latency, Accurate, & Energy-Efficient Spiking Neural Networks with ANN-to-SNN Conversion
Keywords: ANN-to-SNN conversion, IF neuron model, batch normalization, regularizer, surrogate gradients
TL;DR: In this paper, we propose a novel ANN-to-SNN conversion framework for ultra low-latency and energy efficiency, that shifts the bias term of each Batch Normalizaton layer and introduces a new integrate-and-fire (IF) neuron model.
Abstract: Spiking Neural Networks (SNN) are now demonstrating comparable accuracy to intricate convolutional neural networks (CNN), all while delivering remarkable energy and latency efficiency when deployed on neuromorphic hardware. In particular, ANN-to-SNN conversion has recently gained significant traction in developing deep SNNs with close to state-of-the-art (SOTA) test accuracy on complex image recognition tasks. However, advanced ANN-to-SNN conversion approaches demonstrate that for lossless conversion, the number of SNN time steps must equal the number of quantization steps in the ANN activation function. Reducing the number of time steps significantly increases the conversion error, incurring a significant drop in test accuracy. Moreover, the spiking activity of the SNN, which dominates the compute energy in neuromorphic chips, does not reduce proportionally with the number of time steps. To mitigate the accuracy concern, we propose a novel ANN-to-SNN conversion framework, that incurs an exponentially lower number of time steps compared to that required in the SOTA conversion approaches. Our framework modifies the SNN integrate-and-fire (IF) neuron model with identical complexity and shifts the bias term of each batch normalization (BN) layer in the trained ANN. To mitigate the spiking activity concern, we propose training the source ANN with a fine-grained $\ell_1$ regularizer with surrogate gradients that encourages high spike sparsity in the converted SNN. Our proposed framework thus yields lossless SNNs with ultra-low latency, ultra-low compute energy, thanks to the ultra-low timesteps and high spike sparsity, and ultra-high test accuracy, for example, $73.30%$ test accuracy with only $4$ time steps on the ImageNet dataset.
Primary Area: general machine learning (i.e., none of the above)
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Submission Number: 452
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