Low sensitivity digital LDI ladder filters with elliptic magnitude response

A method of designing elliptic LDI [I] type switched-capacitor filters is known [2], [3]. However, this method cannot be extended directly to digital filter design and implementation. Preliminary results involving the design of a fifth-order digital LDI ladder filter have been proposed 141. In this contribution a complete design method for low sensitivity digital LDI ladder filters which have elliptic magnitude response is presented. A relationship between the bilinear and LDI transformed impedances is investigated. A precompensation procedure together with the bilinear transformation are applied to transform an elliptic analog ladder filter into a realizable digital LDI ladder filter. A voltage-current signal flowgraph (
V/I
SFG) simulation method is adopted in this design procedure. The design procedure provides a method of realizing the bilinear transformed transfer function using the LDI as a building block. An example of fifth-order elliptic LDI low-pass filter design is given. The effects of multiplier coefficient quantization on both the digital elliptic LDI ladder filter and an equivalent wave digital ladder are compared.