Hardware Reference
In-Depth Information
2
3
2
3
2
3
i v
v x
i z
000
100
0
v v
i x
v z
4
5 ¼
4
5
4
5
ð
1
3
Þ
:
10
It was demonstrated in [ 3 , 4 ] that CCII was, indeed, a versatile building block as it
could realize all the four controlled sources, a negative impedance converter, a
negative impedance inverter and can also be used to realize a number of other linear
and non-linear functional circuits with a bare minimum number of external passive
components quite easily and in a much simpler way than the way in which the same
functional circuits were being realized with the traditional op-amps. Thus, the CCII
was shown to be quite promising for realizing many basic functions needed for
analog computation such as current amplifier, current differentiator, current inte-
grator, current summer, weighted current summer and generalized nonlinear func-
tion generator- all employing only a bare minimum number of passive components.
In [ 4 ], they demonstrated that CCIIs were also versatile building blocks for realiz-
ing the family of new non-linear elements namely, mutator, scalor, reflector and
rotator, introduced by Chua in [ 74 , 75 ].
1.4 An Historical Overview of the Evolution of the Other
Varieties of Current Conveyors
Since the introduction of CCII by Sedra and Smith in 1970, the next decade
witnessed a considerable interest by academicians and researchers in evolving a
large number of their applications in realizing various analog signal processing and
signal generation applications. However, on the other hand, very little work was
done on the implementation of CCs themselves. It was only in 1989 that a fully
integrated CC was proposed by Wadsworth which was produced by the Canadian
company Phototronics Ltd. Although the now popular AD844 was already being
manufactured by Analog Devices Inc., since it was disguised as a high slew rate
op-amp. Although the internal circuit architecture of AD844 was based upon a
translinear CCII+ and a unity gain voltage follower the CCII+ inherent in AD844
was not explicitly noticed till about 1990 or so. That AD844 did provide external
access to the Z-terminal (as the compensation pin) makes it possible to use it as a
CCII+ and also enables the realization of CCII
using two such devices.
A chronological listing of the important developments which have taken place
on the realization and applications of CCs, starting from 1968 onwards, is as under:
• 1968: Smith and Sedra introduced the basic concept of Current Conveying and
its implementation as the Current Conveyor (later renamed as the first generation
Current Conveyor).
• 1970: Sedra and Smith introduced the more versatile second generation Current
Conveyor (henceforth referred as CCII+). In another paper during the same year,
Sedra and Smith demonstrated that CCIIs were useful building blocks for
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