On the realization of current transfer function using voltage amplifiers

Current transfer function is a feature of current-mode filters. Current-mode filters have so far been realized principally using current amplifiers and current conveyors. Some current-mode filter architecture using operational amplifiers have also been reported. In this article it is shown that by using the principles of transposed network and nullor model for the active device, a current transfer function can be realized in a very simple way using a voltage amplifier, i.e. operational amplifier (OA). The key concept is the knowledge that each ideal (i.e. infinite gain) controlled source is exactly equivalent to a nullor. Thus, a voltage-mode filter implemented using an ideal three terminal (output, input and ground) OA can be very easily converted to a current-mode filter using the same OA. The principle has been illustrated by considering single-OA- and multi-OA-based second-order voltage-mode filters. SPICE simulation results are provided to validate the theoretical concept. Copyright (C) 2006 John Wiley & Sons, Ltd.