A current conveyor is an abstraction for a three-terminal analogue

electronic device The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

. It is a form of electronic amplifier with unity gain. There are three versions of generations of the idealised device, CCI, CCII and CCIII. When configured with other circuit elements, real current conveyors can perform many analogue

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...

functions, in a similar manner to the way op-amps and the ideal concept of the op-amp are used.

History

When Sedra and

Smith Smith may refer to: People * Metalsmith, or simply smith, a craftsman fashioning tools or works of art out of various metals * Smith (given name) * Smith (surname), a family name originating in England, Scotland and Ireland ** List of people wi ...

first introduced the current conveyor in 1968, it was not clear what the benefits of the concept would be. The idea of the op-amp had been well known since the 1940s, and integrated circuit manufacturers were better able to capitalise on this widespread knowledge within the electronics industry. Monolithic current conveyor implementations were not introduced, and the op-amp became widely implemented. Since the early 2000s, implementations of the current conveyor concept, especially within larger

VLSI Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) ...

projects such as mobile phones, have proved worthwhile.

Advantages

Current conveyors can provide better gain-bandwidth products than comparable op-amps, under both small and large signal conditions. In

instrumentation amplifier An instrumentation amplifier (sometimes shorthanded as in-amp or InAmp) is a type of differential amplifier that has been outfitted with input buffer amplifiers, which eliminate the need for input impedance matching and thus make the amplifie ...

s, their gain does not depend on matching pairs of external components, only on the absolute value of a single circuit element.

First generation (CCI)

The CCI is a three-terminal device with the terminals designated ''X'', ''Y'', and ''Z''. The potential at ''X'' equals whatever voltage is applied to ''Y''. Whatever current flows into ''Y'' also flows into ''X'', and is mirrored at ''Z'' with a high

output impedance The output impedance of an electrical network is the measure of the opposition to current flow (impedance), both static ( resistance) and dynamic ( reactance), into the load network being connected that is ''internal'' to the electrical source. The ...

, as a variable

constant current source A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the dual of a voltage source. The term ''current sink'' is sometimes used for sources f ...

. In sub-type CCI+, current into ''Y'' produces current into ''Z''; in a CCI-, current into ''Y'' results in an equivalent current flowing ''out'' of ''Z''.

Second generation (CCII)

In a more versatile later design, no current flows through terminal ''Y''. The ideal CCII can be seen as an ideal transistor with perfected characteristics. No current flows into the gate or base which is represented by ''Y''. There is no base-emitter or gate-source voltage drop, so the emitter or source voltage (at ''X'') follows the voltage at ''Y''. The gate or base has an infinite input impedance (''Y''), while the emitter or source has a zero input impedance (''X''). Any current out of the emitter or source (''X'') is reflected at the collector or drain (''Z'') as a current in, but with an infinite output impedance. Because of this reversal of sense between ''X'' and ''Z'' currents, this ideal bipolar or field-effect transistor represents a CCII−. If current flowing out of ''X'' resulted in the same high-impedance current flowing ''out'' of ''Z'', it would be a CCII+.

Third generation (CCIII)

The third configuration of the current conveyor is similar to the CCI except that the current in ''X'' is reversed, so in a CCIII whatever current flows into ''Y'' also flows out of ''X''.

References