The comeback of the all-pass equalization approach for digital filter with combined amplitude and phase specifications

In modern digital communication systems the need for digital filters with high selectivity and good phase linearity is rapidly increasing. A new all-pass equalization approach is presented that uses a new design strategy based on the interaction between amplitude and phase (or group-delay) requirements and lattice wave digital filter (WDF) cascaded by an all-pass filter for the realization. Furthermore for given amplitude and phase specifications a method for predicting the minimum required degree of the transfer function is presented. The design example demonstrates the properties of the proposed method and the efficiency in comparison to simultaneous amplitude and phase approximation method.