On the Realization of Universal Current Mode Biquads Using a Single CFOA

The four terminal Current feedback op-amps (CFOA) with an external compensation pin, such as AD844, have received prominent attention during the past decade as alternative building blocks for analog circuit design because of their significant advantages over the traditional voltage-mode op-amp (VOA). A popular application of CFOAs has been in realizing voltage-mode (VM) and current-mode (CM) biquad filters. Previously known universal CM biquads (i.e. those capable of realizing all the five generic filter functions namely, low-pass, band-pass, high-pass, notch and all-pass) realizable with CFOAs require two to nine CFOAs. Although a few dual-function/three-function single-CFOA-based CM circuits have appeared in literature, no single-CFOA-based canonic universal CM biquad with explicit CM output has been reported in the literature up until now. This paper fills this void by presenting a set of eight minimal universal CM biquads all of which are realizable with only a single CFOA. The non-ideal analysis of the proposed circuits has been presented, their comparative features, advantages and limitations have been brought out. The workability of all the proposed circuits has been confirmed by PSPICE simulations and experimental results based upon AD844 type CFOAs.