A multiple output active filter based on current followers

Abstract

In this paper a multiple output current follower (CF)-based active filter (MOCFF) is presented. The construction of basic filtering oriented biquadratic transfer functions (low-pass, high-pass, band-pass, band-notch and all-pass) is realized by means of two independent stages of identical topology. Each of them incorporates three CFs appropriately interconnected with R,C branches; a CF-based adder (CFA) in conjunction with a versatile CF-incorporating mutual feedback symmetric circuit (MFSC) implement three different frequency responses. The pair of CFs composing the MFSC should be visualized as a voltage transfer function generator. The MOCFFs salient feature is the current-based signal processing while voltage remains the input and output variable. Taking into consideration the innate CF current tracking error, transfer function modifications owing to CF non-ideality are provided. Our theoretical analysis is confirmed by HSPICE simulation results with the CF block function implemented by a properly modified pure CMOS CCII. The proposed topologies, being able to realize high quality factor frequency responses obtainable by three CFs, constitute a good choice for trading off between the desired multiple character, the number of necessary active elements and a satisfactory performance.