Synthesis of LDI digital filters based on symmetrical lattice network simulation

It is important to realize a low-sensitivity digital filter, from the view point of economy such as hardware complexity, for which numerous studies have been made. From those studies it is known that the digital filter simulating the analog network, such as leapfrog and wave digital filters, exhibit low coefficient-sensitivity characteristics. This paper is based on the symmetrical lattice reactance network. It is shown that the required transfer function is given as the output difference between the doubly resistively terminated IX ladder networks constructed with two kinds of one-port LC reactance elements as the series elements. A method to construct a digital filter is proposed by the leapfrog structure using LDI. the digital filter constructed by the proposed method requires a fewer number of elements. the operating transfer function and the return- loss function are realized simultaneously. It is shown by examples that compared with the traditional method based on the simulation of the analog network, almost comparable passband characteristics can be realized.