I. Introduction
Since hopfield's inspirational work on stability of the Hopfield neural network (HNN) using energy function [1], numerous studies on the stability of various neural networks have been reported. The stability properties primarily concerned are uniqueness, global asymptotic stability, and global exponential stability of equilibria. In recent years, the stability analysis of recurrent neural networks (RNNs) with time delays received increasing attention, e.g., [2]–[21].