A Resilience Framework for Synapse Weight Errors and Firing Threshold Perturbations in RRAM Spiking Neural Networks

Spiking Neural Networks (SNNs) can be implemented with power-efficient digital as well as analog circuitry. However, in Resistive RAM (RRAM) based SNN accelerators, synapse weights programmed into the crossbar can differ from their ideal values due to defects and programming errors, degrading inference accuracy. In addition, circuit nonidealities within analog spiking neurons that alter the neuron spiking rate (modeled by variations in neuron firing threshold) can degrade SNN inference accuracy when the value of inference time steps (ITSteps) of SNN is set to a critical minimum that maximizes network throughput. We first develop a recursive linearized check to detect synapse weight errors with high sensitivity. This triggers a correction methodology which sets out-of-range synapse values to zero. For correcting the effects of firing threshold variations, we develop a test methodology that calibrates the extent of such variations. This is then used to proportionally increase inference time steps during inference for chips with higher variation. Experiments on a variety of SNNs prove the viability of the proposed resilience methods.