TOWARDS A PERFECT CMOS CCII

DC offset and inaccurate voltage follower action between terminals Y a nd X, the relatively high impedance seen at terminal X and inaccurate current follower action between terminals X and Z plague simple circui t realizations of the CCII. This paper summarizes the methods employed and compares the improvement of the CCII characteristics achieved by a variety of published circuits, with emphasis laid on CMOS realizatio ns. In these comparisons, the conventionally employed but inaccurate c urrent mirror output stages were replaced by a circuit employing curre nt isolation and thereby providing accurate current follower action be tween terminals X and Z. Furthermore, two novel realizations of a diff erential CCII- based transconductance amplifier are described, which c an also be employed as input stage of an instrumentation voltage ampli fier exhibiting an exceptionally high CMRR and excellent frequency res ponse. Finally, a current fan out circuit for cascode CCII-'s will be introduced, whose transfer function value is electronically adjustable .