Recent Advances and Future Directions of Research - Current Conveyors: Variants, Applications and Hardware Implementations - page 520

the free end of the norator represents terminal-Z. On the other hand, it was found
that a CCII + could not be represented by only nullators and norators and did require
two nullors along with two equal-valued resistors for its nullor representation.
In [ 1 ] Awad and Soliman introduced two new pathological elements which they
called a current mirror (CM) and a voltage mirror (VM) and argued that with the
introduction of these two new elements, the set of the pathological elements has
been completed. This development made it possible to represent a CCII +with a
nullator and a CM thereby not requiring any resistor. Subsequently, it has been
shown in a number of publications that by a judicious combination of nullators,
norators, CMs and VMs, almost all the building blocks can be represented without
requiring any redundant resistor. Of late, even the floating versions of CM and VM
have been proposed in the literature [ 2 ].
In reference [ 3 ], Haigh and his co-workers formulated a systematic method of
synthesizing a class of linear active-RC networks such as synthetic impedances
using nullator- norator formalism as a basis. The introduction of a number of new
pathological elements by a number of researchers has, thus, further enriched the
literature. These pathological elements are currently being used in evolving sys-
tematic derivation procedures for a larger class of functional circuits that include
mutators, biquad filters, single resistance controlled oscillators etc.
This field of systematic active network synthesis using pathological elements,
thereby ultimately leading to practicable designs of the considered circuits in terms
of their realizations using various types of current conveyors, is currently a very
popular area of research. Needless to say, many important new results might be
waiting to be discovered through this methodology of synthesis. The interested
readers are referred to [ 4 , 5 - 17 ] for the details of the various significant works done
in this direction.
16.3 Recent Advances in the Hardware Implementation
of Current Conveyors
In this section, we present some recent innovations made in the hardware imple-
mentation of current conveyors which have a bearing on the numerous variants of
CCs discussed in this monograph.
16.3.1 New CCII Implementation Based Upon Modified
Bipolar Translinear Cell
There has been a large number of CC implementations based upon the four
transistor mixed-translinear-cell. Recently Merz et al. [ 18 ] proposed a new mixed
translinear cell composed of eight bipolar transistors as shown in Fig. 16.1 .