Circuit implementation of on-chip trainable spiking neural network using CMOS based memristive STDP synapses and LIF neurons

Computation on a large volume of data at high speed and low power requires energy-efficient architectures for edge computing applications. As a result, scientists focus on memristive circuits and systems for area and energy efficiency. Spiking neural network (SNN) with bio-inspired spike-timing-dependent plasticity learning (STDP) is a promising solution for energy-efficient neuromorphic systems than conventional artificial neural network (ANN). Previous works on SNN with STDP learning primarily use memristor macro models, which are software-based and cannot give complete insight into circuit implementation challenges. Some reported works on SNN use memristive devices, which require additional fabrication steps. This article presents a full circuit-level implementation of the SNN system featuring on-chip training and classification using memristive STDP synapse in standard CMOS technology. A new learning rule using the modified STDP is implemented to simplify the weight modification process. It does not involve FPGAs, CPUs, or GPUs to train the neural network. The approach used in this paper to modify the weights does not require any additional combinational or digital circuits attached to the memristive synapse resulting in less consumption of area, energy and time. We demonstrated the complete circuit-level design, implementation and simulation of SNN with on-chip training and pattern classification using 180 nm CMOS technology. A comprehensive comparison of the proposed SNN circuit with the previous related work is also presented. To demonstrate the versatility of the CMOS synapse circuit for application scenarios requiring rate-based learning, we have tuned the pair-based STDP circuit to obtain Bienenstock-Cooper-Munro (BCM) characteristics and applied it to heart rate classification.