An exhaustive search algorithm for checking limit cycle behavior of digital filters

In this paper, an algorithm that can be utilized to determine the presence or absence of limit cycles in fixed-point implementation of digital filters is given. It is applicable for filters in state-space formulation (and hence, application to the corresponding direct form follows as a special case), and is independent of the order, type of quantization, and whether the accumulator is single- or double-length. Bounds on the amplitude and period of possible limit cycles are presented. The robustness of the algorithm in terms of limit cycle performance with respect to filter coefficient perturbations is verified. The algorithm is then used to obtain regions in the coefficient space where a filter of given order is limit cycle free. In this process, we have obtained limit cycle free regions that were previously unknown for the two's complement case.