Neuromorphic Functional Modules of a Spiking Neural Network

Abstract—In the current era, the design and development of artificial neural networks exploiting the architecture of the human brain have evolved rapidly. Artificial neural networks (ANN) effectively solve a wide range of common artificial-intelligence tasks involving data classification and recognition, prediction, forecasting and adaptive control of the behavior of an object. The biologically inspired underlying principles of ANN operation have certain advantages over the conventional von Neumann architecture including unsupervised learning, architectural flexibility and adaptability to environmental change and high performance under significantly reduced power consumption due to large parallel and asynchronous data processing. In this paper, we present a circuit design of main functional blocks (neurons and synapses) intended for the hardware implementation of a perceptron-based feedforward spiking neural network. As the third generation of artificial neural networks, spiking neural networks perform data processing utilizing spikes, which are discrete events (or functions) that take place at points in time. Neurons in spiking neural networks initiate precisely timed spikes and communicate with each other via spikes transmitted through synaptic connections or synapses with adaptable scalable weight. One of the prospective approaches to emulating synaptic behavior in hardware implemented spiking neural networks is to use nonvolatile-memory devices with analog conduction modulation (or memristive structures). Here we propose a circuit design for functional analogues of memristive structures to mimic synaptic plasticity, pre- and postsynaptic neurons which could be used for developing a circuit design of spiking-neural-network architectures with different training algorithms including the spike-timing-dependent-plasticity learning rule. Two different circuits of an electrical synapse are developed. The first one is an analog synapse with a photoresistor optocoupler used to ensure the tunable conductivity for synaptic-plasticity emulation. While the second one is a digital synapse, in which the synaptic weight is stored in a digital code with its direct conversion into conductivity (without a digital-to-analog converter and photoresistor optocoupler). The results of prototyping the developed circuits for electronic analogs of synapses, pre- and postsynaptic neurons and the study of transient processes are presented. The developed approach could provide a basis for the ASIC (application-specific integrated circuit) design of spiking neural networks based on CMOS (complementary metal—oxide–semiconductor) design technology.