High output impedance current-mode third-order Butterworth filter topologies employing unity gain voltage buffers and equal-valued passive components

Abstract

This paper presents eight new current mode third-order band pass filter topologies employing unity-gain active elements, three resistances and three capacitors. An additional topology is identical to a previously reported one, repeated here for completeness. Using equal passive components, all of the proposed topologies realize third-order BP Butterworth filter function, which can easily be converted to a LP if they are cascaded with an integrator, Therefore, without any component spread the circuits are attractive from the integration point of view. In each of the circuits, except one topology, one of the unity gain cells can be replaced by a second-generation current conveyor to pick up the output current and to obtain a high impedance output. The high output impedance provided by the current conveyor permits easy cascadability for the proposed circuits to construct high-order communication filters. Simulation and experimental results are included to verify theory.