Second Generation Controlled Current Conveyors (CCCII) and Their Applications - Current Conveyors: Variants, Applications and Hardware Implementations - page 278

An important deficiency of this circuit is that it does not provide an all pass filter
response either in voltage mode or current mode.
In fact, from the inspection of available mixed-mode biquad circuits using
CCCIIs it appears that a completely universal circuit capable of realizing all the
five basic filtering functions in both VM and CM without any constraints with
electronic controllability of the filter parameters while employing a reasonably
small number of CCCIIs has still not been discovered so far. This, therefore,
constitutes an interesting problem which is open to investigation.

9.11 Tunable Ladder Filters Using Multiple-output
CCCIIs

Whereas a majority of publications dealing with CCCII-based filters have dealt
with universal VM filters or CM filters, comparatively less attention appears to have
been given on the design of higher order filters using CCCIIs and only earlier works
[ 31 - 36 ] can be cited in this context.
In this section, we elaborate only two specific methodologies of designing
CCCIIs based higher order filters; namely the FDNR based approach of Ozoguz
and Toker [ 31 ] and the signal flow graph based method of Jiraseree-amornkun and
Surakampontorn [ 32 ].
The method of Ozoguz and Toker [ 31 ] is based upon a new two CCCII-based
realization of a series FDNR-R equivalent circuit and a known realization of current
controlled floating resistance of Fig. 9.12a . The method is explained here for the
design of a ladder type electric filter for which the LC prototype shown in
Fig. 9.34a .
Applying Bruton

s transformation, the LC ladder filter is transformed into RCD
ladder of Fig. 9.34b , the conversion of this circuit requires three floating resistances
to be simulated by CCCIIs and simulation of two shunt RD branches by CCCIIs
based circuit. Ozoguz and Toker [ 31 ] in their paper have shown that a floating
resistance can be simulated by only a single CCCII as can be seen in the circuit of
Fig. 9.34c whereas two CCCIIs and two grounded capacitor are required for the
FDNR-R branch as per their preposition. The resulting circuit is shown in
Fig. 9.34c . It maybe seen that it appears to be quite economical design in the
sense that the total number of active building blocks namely CCCIIs is exactly
equal to the number of reactive elements in the original LC prototype. Furthermore,
another advantageous feature of this circuit is that it employs all grounded capac-
itors as preferred for integrated circuit implementation. Lastly, because of the
electronic controllability of R x of the various CCCIIs, the circuit has excellent
tuning capability.
Jiraseree-amornkun and Surakampontorn [ 32 ] presented a signal flow graph
based methodology to realize continuous time current mode tunable ladder filters
of any order using multi output CCCIIs (MCCCIIs) and grounded capacitors.

'