Comments on "Multifunction biquadratic filters using current conveyors"

Most of the authors accept that a current conveyor-based filter or oscillator will exhibit low output impedance, permitting easy cascadability, and no buffering needed if the output is taken from the x terminal of the CCII, as is also claimed by the above paper [see ibid., vol. 44, p. 956-8,1997]. The aim of this comment is to show that such a direct conclusion is not possible. The generally accepted behavior of the x terminal is that it is a low-impedance voltage source since it copies the voltage at the y terminal. However, it may be shown that there are cases where the x terminal alone acts as a current source with high output impedance. Conversely, a circuit where the output is taken from a node with only y and z terminals connected, the node may exhibit low output impedance. In this comment, both cases are illustrated by simple theory and examples.