Benchmark Non-volatile and Volatile Memory Based Hybrid Precision Synapses for In-situ Deep Neural Network Training

Compute-in-memory (CIM) with emerging non-volatile memories (eNVMs) is time and energy efficient for deep neural network (DNN) inference. However, challenges still remain for in-situ DNN training with eNVMs due to the asymmetric weight update behavior, high programming latency and energy consumption. To overcome these challenges, a hybrid precision synapse combining eNVMs with capacitor has been proposed. It leverages the symmetric and fast weight update in the volatile capacitor, as well as the non-volatility and large dynamic range of the eNVMs. In this paper, in-situ DNN training architecture with hybrid precision synapses is proposed and benchmarked with the modified NeuroSim simulator. First, all the circuit modules required for in-situ training with hybrid precision synapses are designed. Then, the impact of weight transfer interval and limited capacitor retention time on training accuracy is investigated by incorporating hardware properties into Tensorflow simulation. Finally, a system-level benchmark is conducted for hybrid precision synapse compared with baseline design that is solely based on eNVMs.