Simple sufficient test for stability of two-dimensional recursive digital filters

The design of recursive digital filters is relatively simple, but such filters introduce a major problem of stability. This problem has been the subject of intensive research during recent decades and the trend is towards finding sufficient conditions, because necessary and sufficient conditions are difficult to find or to test. In this correspondence, a different proof of the sufficient stability condition, recently established by A.J. Kanellakis and N.J. Theodorou (see ibid., vol.134, no.5, p.246-7, 1987) for the two-dimensional case is proposed