An approximate bound for sampling rate selection

A simple bound on the maximum gain crossover frequency of a sample data control system is derived. The bound is shown to depend on the plant as well as the sampling rate and the computational delay. The bound is based on the non minimum phase zeros of the discretized system, zeros which are present in nearly all non trivial discrete control systems, even if the continuous time plant is stable, minimum phase and there is no (computation) delay in the system.