Simple design procedure for active lowpass filters using exponential RC lines

Abstract

Design equations are given for realising a pair of complex poles by an active distributed structure, utilising exponential RC lines. It is shown that the response of the structure closely approximates that of a 2nd-order low-pass filter. The loci of the complex poles may be considered, to a high degree of accuracy, to lie on parabolas, resulting in a simple design procedure. It is shown that the sensitivity of the structure with respect to the active element decreases with increasing taper, and that it may be made considerably lower than that of Kerwin's structure, which uses uniform RC lines.