Improved LDI digital filters derived from analog LC ladder filters

Abstract

Lossless discrete integrator (LDI) digital filters derived from analog LC ladder filters are known to possess low sensitivities of the passband gain with respect to quantizations of the multiplier coefficients. However, previously reported LDI digital filter structures do not generally retain the desired one-to-one correspondence between the LDI digital ladder filter and the original LC analog ladder filter after quantizations of the multiplier coefficients are taken into account. This leads to increased transfer function sensitivities of the LDI digital filter, relative to that of the original LC analog filter. In this paper, it is shown that classical equivalent transformations of the LC ladder network can be used to obtain new LDI ladder structures that do retain (even after coefficient quantizations) the one-to-one correspondence with the LC ladder filter, leading to LDI digital filters having improved performance under coefficient quantizations. These equivalent network transformations also facilitate the design of different types of LDI ladder filters. The obtained LDI filters are suitable for VLSI implementation on a single chip FPGA using one multiplier.