Single-CFA first-order allpass filter

Abstract

A simple first order allpass filter (APF) realization scheme with single current feedback amplifier (CFA) is presented; the phase-select component Y (= sC) is grounded. Analysis indicates that effects of imperfect port mismatch ratio of the CFA are quite insignificant. However the device parasitic capacitors introduce certain phase error at relatively higher frequencies. This simple circuit may be extended to second order APF design, if desired with Y as a shunt −LC resonator; L being a lossless inductor simulated by a DVCCTA element. Literature study on recent first order APF indicates that these are based on active elements that are based essentially on assorted conjoined versions of two types of devices.