Basic properties of the operational transconductance amplifier (OTA) are discussed. Applications of the OTA in voltage-controlled amplifiers, filters, and impedances are presented. A versatile family of voltage-controlled filter sections suitable for systematic design requirements is described. The total number of components used in these circuits is small, and the design equations and voltage-control characteristics are attractive. Limitations as well as practical considerations of OTA-based filters using commercially available bipolar OTAs are discussed. Applications of OTAs in continuous-time monolithic filters are considered.

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Active filter design using operational transconductance amplifiers: A tutorial

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 letter reports two circuits simulating ideal floating inductances and a capacitor floatation scheme using grounded copacitors. Both the inductances and capacitors are tunable through a single resistance and it has been shown that it is possible to simulate these realisations with unmatched passive components.

New inductance and capacitor floatation schemes using current conveyors

A lossless floating inductance has been simulated using two differential voltage current conveyors, two resistors and one grounded capacitor. The proposed floating inductance needs not component matching condition. Base on the proposed floating inductance as building block, a new voltage-mode universal biquadratic filter with one input and five outputs can be obtained. The proposed universal biquad uses two differential voltage current conveyors, three resistors and two grounded capacitors. All standard filter functions; highpass, bandpass, lowpass, notch and allpass can be obtained, simultaneously, without changing the passive elements. The proposed universal biquad has the features of using only grounded capacitors and orthogonal controllable of resonance angular frequency and quality factor.

Lossless inductance simulation and voltage-mode universal biquadratic filter with one input and five outputs using DVCCs

Recent developments in current conveyors and their applications

A floating-ideal-inductor realisation scheme with one d.v.c.c.s., two amplifiers and a grounded capacitor is presented. It is also shown that, from this scheme, a grounded-capacitor/three-amplifier floating-ideal-inductor realisation scheme can be easily derived.

Floating ideal inductor with one d.v.c.c.s.

A circuit consisting of a negative-impedance convertor, suitable for the realisation of an inductor, is presented. For a certain circuit condition the realisation is independent of frequency, and by the variation of a single capacitor the inductance value of the inductor can be varied over a wide range while the resistive part remains constant. Both the inductance and the associated resistive part are shown to be frequency-dependent if this condition is not exactly satisfied.

Inductor realisation with a negative-impedance convertor

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.

Floating inductor with two current conveyors

An earlier suggested ideal floating inductor realisation circuit is extended to a capacitor floatation scheme with the addition of only one operational amplifier. Appropriate comments regarding practical realisability of both floating capacitor and inductor are appended.

D. Patranabis

Papers

Floating ideal inductor with one d.v.c.c.s.

Inductor realisation with a negative-impedance convertor

Generating a family of grounded capacitor ideal integrators and differentiators

Floating inductor with two current conveyors

Novel capacitor floatation scheme