Direct design of bandstop wave digital lattice filters

This contribution introduces a direct design method for bandstop wave digital lattice filters. The application of this method provides several advantages which can not be obtained by applying frequency transformation techniques. According to this method, the approximation problem is reduced to generating a single polynomial having even degree n, which is the degree of the filter. This polynomial approximates the difference phase function of the two branch polynomials. It is composed of a Hurwitz and anti-Hurwitz parts differing in degree by two. By factorizing this polynomial, the Hurwitz and anti-Hurwitz parts are separated and the two branch allpass functions can be constructed. Consequently, the filter structure can be synthesized in the reference domain and digital domain.