First, Second and Higher Order Filter Design Using Current Conveyors - Current Conveyors: Variants, Applications and Hardware Implementations - page 179

(continued)

It may be noted that all the circuits presented in this chapter can be
practically realized using commercially available IC AD844 (with CCII+
realized by one IC and CCII

realized with two ICs) or using
CC-implementations based upon op-amps and current mirrors in
operational-mirrored amplifier formulations or using PA630 IC CCs although
the AD844 appears to have been the preferred choice of most of the
researchers whose propositions we have included in this chapter.
It must also be pointed out that in this chapter we have limited ourselves to
only those configurations which use the basic CCI and CCII as per their
original definitions; the discussion of a variety of other filter configurations
realizable from numerous other variants of CCs is the subject matter of a
subsequent chapter of this monograph (see Chap. 12 ).
Lastly, from a critical study of various configurations described here, as
well as those omitted from inclusion, it can be readily inferred that there is
still enough scope for deriving new circuits having properties superior to
those included herein. For example, any circuit providing ideally zero input
impedance, very high output impedance and capable of realizing all the five
filtering functions without any realization constraints and with independent
tunability of all the three parameters H0, ω 0 and Q 0 having all passive

grounded elements and yet not requiring more than three CCs, has still not
been discovered! This, therefore, appears to be an interesting problem which
is open to investigation.

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