Low active-sensitivity allpole active-RC filters using impedance tapering

Abstract

To reduce the low-power allpole active-RC filter's output magnitude sensitivity to passive components, the "impedance tapering" design method was used. This design procedure has been applied to the design of 2 nd -and 3 rd -order low-pass (LP) (class 4) Sallen-and-Key filters and has already been published [1]. In this paper the active sensitivity analysis using MATHEMATICA was performed on the same "impedance tapered" filter sections as in [1]. The analysis was performed by calculation of the real filter's transfer-function magnitude which was denormalized to various cut-off frequencies from low to high, using a single-pole model of a real operational amplifier. The amount of active and passive sensitivity reduction was compared using the same degree of impedance tapering. It was demonstrated that both sensitivities, i.e. active and passive, were correspondingly reduced for the same filter. Thus, a judicious selection of component values accounts for a considerable decrease in both passive and active sensitivities.