Current conveyors and related current-mode circuits have begun to emerge as an important class of circuits with properties that enable them to rival their voltage-mode counterparts in a wide range of applications. The use of current rather than voltage as the active parameter can result in higher usable gain, accuracy and bandwidth due to reduced voltage excursion at sensitive nodes. A current-mode approach is not just restricted to current processing, but also offers certain important advantages when interfaced to voltage-mode circuits. The author sets out to survey developments in conveyors and current-mode circuits from both an historical and technical viewpoint and to act as a useful source of reference material.

Recent developments in current conveyors and current-mode circuits

Recent developments in current conveyors and their applications

Ideal integrators and differentiators with second generation current conveyors (CC's) as active devices have been proposed. Single-CC realization schemes are derived from a generalized approach and are shown to have marginal improvement over the conventional types, whereas, the two-CC realizations are canonical with respect to the passive components, amenable for producing independently controllable large time constants and practically insensitive to active prarmeter variation.

Integrators and differentiators with current conveyors

A simple circuit for realizing active-only lossless floating inductor is presented. The circuit uses only two active elements ; a dual output operational transconductance amplifier and an internally compensated operational amplifier. The circuit is suitable for monolithic implementation in either bipolar or MOS technologies. Simulation results of a high-order lowpass filter using two simulated lossless floating inductors are included.

Simulation of Active-only Floating Inductance

A simple method of efficiently extending or lowering the time constants of a single operational amplifier (OA) RC ideal integrator is presented There exist two schemes in this method both of which require cascading of R -ladders to a basic integrator block It is also shown that a consecutive pair of Fibonacci numbers can be effectively used to evaluate the time constant and the gain parameter through a simple rule considerably simplifying the design procedure Finally, a complementary circuit principle has been used to obtain the differentiators to have similar extention and lowering in time constants

Efficient enhancement/lowering of integrator and differentiator time constants with Fibonacci numbers helping their evaluation

Generating a family of grounded capacitor ideal integrators and differentiators

There have been considerable efforts towards the realization of ideal floating inductors where mostly three active blocks are required. The reduction in the number of active blocks to two was however achieved with considerable increase in the number of resistances and passive parameter constraints. The proposed scheme suggests a method to produce a floating inductor with a series negative resistance using two current conveyors, only three resistors and one capacitor, involving only one restrictive constraint. The realized inductor was also used to design a third order Butterworth filter. Experimental results confirm the applicability of the realized immittance.

A. N. Paul

Papers

Generating a family of grounded capacitor ideal integrators and differentiators

Floating inductor with two current conveyors