Wave digital ladder filters with low sensitivity and roundoff noise

Design techniques for symmetric wave digital ladder filters with extremely low sensitivity and roundoff noise are introduced. The main idea behind this approach is to use nonreciprocal sections to make the overall filter symmetric. The fact that both the attenuation zeros and transmission zeros remain on the unit circuit after coefficient quantization, and that transmission zeros are realized by reflection, makes the proposed structure extremely insensitive to coefficient quantization and low roundoff noise. Symmetric ladder filters can be realized either with special transfer functions or by the introduction of inductive dependence sources in the reference filter. A fifth-order elliptic lowpass filter is used as an illustrative example. However, the method can be extended to more general filter classes.<>