This paper addresses the problem of refining settling-time upper-bound estimates for fixed-time stable systems under a three-term Lyapunov characterization. Without resorting to inequality-based techniques or special functions, a closed-form analytical upper bound for the settling-time function is derived using only elementary functions. Comparative analyses demonstrate that the proposed bound is tighter than existing results. The theoretical findings are further validated through the design of a fixed-time controller for a memristive neural network, with numerical simulations confirming the accuracy of the estimated settling time and the independence of the control scheme from initial conditions.
nonlinear systems, fixed-time stability, settling-time estimation, Lyapunov inequality, generalized homogeneity
93C10, 93D40, 93D05