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

The current feedback operational amplifiers (CFOAs) are receiving increasing attention as basic building blocks in analog circuit design. This paper gives an overview of the applications of the CFOAs, in particular several new circuits employing the CFOA as the active element are given. These circuits include differential voltage amplifiers, differential integrators, nonideal and ideal inductors, frequency dependent negative resistors and filters. The advantages of using the CFOAs in realizing low sensitivity universal filters with grounded elements will be demonstrated by several new circuits suitable for VLSI implementation. PSPICE simulations using the AD844-CFOA which indicate the frequency limitations of some of the proposed circuits are included.

Applications of the current feedback operational amplifiers

In this paper, using a minimum number of passive components, i.e., new grounded and floating inductance simulators, grounded capacitance multipliers, and frequency-dependent negative resistors (FDNRs) based on one/two modified current-feedback operational amplifiers (MCFOAs), are proposed. The type of the simulators depends on the passive element selection used in the structure of the circuit without requiring critical active and passive component-matching conditions and/or cancellation constraints. In order to show the flexibility of the proposed MCFOA, a single-input three-output (SITO) voltage-mode (VM) filter, two three-input single-output (TISO) VM filters, and an SITO current-mode (CM) filter employing a single MCFOA are reported. The layout of the proposed MCFOA is also given. A number of simulations using the SPICE program and some experimental tests are performed to exhibit the performance of the introduced structures.

A Modified CFOA and Its Applications to Simulated Inductors, Capacitance Multipliers, and Analog Filters

In this paper, a new simulated inductor employing two resistors, one capacitor, and only a single gain-variable third-generation current conveyor (GVCCIII) is proposed. To exhibit the performance of the proposed simulated inductor, it is used in a parallel R-L-C current-mode filter. The frequency-dependent nonideal voltage gain effects of the GVCCIII on the proposed inductor are given. The low- and high-frequency limitations of the simulated inductor are investigated in detail. The simulations performed with the SPICE program agree with the theoretical analysis. Also, the proposed circuit is tested experimentally using commercially available active devices (AD844 ICs of Analog Devices) to confirm the theory

Limitations of the Simulated Inductors Based on a Single Current Conveyor

A novel floating inductance simulator, based on second generation current conveyors, is presented The circuit shows the capability of regulation and, in theory, cancellation of the undesired inductance series resistance, with consequent increase in the low frequency operating range Simulation results are included to prove the effectiveness of this solution

CCII-based floating inductance simulator with compensated series resistance

A new canonic active RC circuit for realizing an ideal grounded inductor using a single second generation current conveyor as the active building block is described. The circuit may be considered as a novel active-gyrator circuit realized using only a single current conveyor.

A.M. Soliman

Papers

New active-gyrator circuit using a single current conveyer