Lattice wave digital filters with simultaneous conditions on amplitude and phase

Simultaneous amplitude and phase approximation for low-pass lattice wave digital filters has been developed based on the hidden relationship between the amplitude and phase characteristics of a nonminimum-phase transfer function. The iterative approximation process is based on the factorization of the nonminimum-phase transfer function into a minimum-phase and an all-pass part. Separate algorithms are used to design the minimum-phase and the all-pass part, and these algorithms are carried out alternately. The approximation method results in filters with equiripple amplitude both in the passband and the stopband while the phase characteristic is equiripple with respect to a linear phase. A design example shows the properties of these filters and illustrates the efficiency of the proposed method