This paper is concerned with the stability analysis of second-order direct-form digital filters with two magnitude truncation quantizers. Zero-input stability is proved for the parameter regions where no conclusion can be drawn using the methods previously suggested in the literature. The areas of the parameter plane in which only limit cycles of period 1 or 2 exist, are determined and related to the cycle amplitudes. Finally, a transition graph is suggested to study the convergence patterns of the filter output.
