The work proposes a new technique to examine and reduce the unusual memory effects in digital filters with saturation nonlinearity when external interference is present via strict passivity approach. Novel criterion is given to show the performance of Hankel norm in interfered digital filters by using strict passivity approach. The unusual behaviour of digital filters about previous excitations can be checked by using this proposed criterion. Given criterion ensures the asymptotic stability nature when there is no external input. The dominance of the proposed method is represented by a mathematical example.