Heterogeneous Neurons and Plastic Synapses in a Reconfigurable Cortical Neural Network IC

Abstract — This paper presents an analogue VLSI circuit intended to be used in a neural network architecture that closely resembles the small-scale laminar micro-circuits of the neocortex. The Cortical Neural Layer (CNL) chip comprises of 120 reconfigurable cortical neurons and 7,560 synapses. The neurons can be configured to produce regular spiking, fast spiking, chattering, intrinsically bursting, and other complex activity patterns. The synaptic circuits include inhibitory / excitatory, facilitating/depressing and spike-time dependent plasticity (STDP) dynamics. The connectivity of the neural network can be configured using off-chip spike-routing and on-chip axonal arbor connections. A pre-synaptic spike can be sent to a group of crossbar synapses simultaneously, reducing latency in the pre-synaptic spike routing, enabling a high degree of connectivity of the neural network. The device is fabricated in a 0.35 µm CMOS technology and on-chip neural dynamics are experimentally verified. I