Inductorless elliptic filters with reduced number of capacitors using signal-flow graphs

Abstract

In this paper a method of realizing elliptic filters using signal-flow graphs is presented. Elliptic filters having a minimum number of capacitors are compared with those having a higher number of capacitors. This number is particularly significant when comparing filters realized in balanced-to-ground and unbalanced form. The version with a canonic number of capacitors provides area savings in IC form, whereas both (filters with a minimum [i.e. canonic] number of capacitors and those having a higher number of capacitors) have a low sensitivity to component tolerances. The sfg derivations necessary to realize higher-order elliptic filters with a reduced number of capacitors is presented. Transfer function magnitudes are simulated using the PSpice program. Monte Carlo runs confirm the low sensitivity to component tolerances of both circuit types.