Active RC filters employing a single operational amplifier to obtain biquadratic responses

Abstract

In this paper, networks are presented in tabular form to simplify the design of RC active filters having magnitude responses characterised by pass-band attenuation ripples and stop-band transmission zeros. The responses of these networks may be described by biquadratic rational functions. In all, the form and element values for 11 different networks are tabulated.The basic network discussed in the paper is an operational amplifier with multiloop feedback in cascade with a passive RC circuit and having a second-order response. Higher-order responses than the second may be obtained by cascading second-order stages of the tabulated networks, with suitable isolating stages when necessary.Two different forms of passive circuit are given, together with their design formulas. Both low-pass and high-pass filters are considered; these can be cascaded to give band-pass or band-stop characteristics.The operational amplifier is assumed to have infinite input and zero output impedance; the effects of departure from these ideal conditions on the filter response is considered.