Synthesis of multifeedback active filters based on the simulation of LC filters

Abstract

AbstractThis paper presents a synthesis method for the LC simulation‐type active RC filter. In the proposed method, the second‐order active RC filter, which has been used as the unit section in the traditional cascade structure, is modified into a multifeedback structure. The node equation of the original LC filter is set up and then simulated using the multi‐input circuit for each node voltage, which is a modification of the second‐order active RC circuit. The desired circuit is then obtained. As the original second‐order active RC circuit, Sallen‐Key's network and the SAB circuit of Friend are used in this paper. The design method for the circuit is summarized in a table as the design formula. The low element‐sensitivity property of the resistor‐terminated LC filter is retained in the proposed circuit. In particular, the element sensitivity is low when the relative errors among R‐ and C‐elements are small as in the thin‐film hybrid circuit. Finally, a design example and experimental result are shown for the fifth‐order elliptic filter, verifying that the circuit operates in accordance with the theory.