Design of digital allpass functions with specified phase tolerances

In this paper, a new method is introduced for designing IIR digital allpass functions with specified phase tolerances. Since the phase error characteristics subject to the desired phase response have been specified in the interest bands, the phase design of digital allpass functions in the form of a linear programming problem can be formulated by using the Remez exchange algorithm. Then the linear equations are solved to obtain a set of filter coefficients and the optimal coefficients in the Chebyshev sense can easily be obtained through a few iterations. By appropriately selecting the initial extremal frequencies, the proposed design algorithm always converges, and the phase error characteristics can be arbitrarily specified. Finally, some design examples are presented to demonstrate the effectiveness of the proposed method.