Second Generation Controlled Current Conveyors (CCCII) and Their Applications - Current Conveyors: Variants, Applications and Hardware Implementations - page 269

Z−

X

X

Z+

Y

V in1

Z−

I B1 V 0

Y

C

I B2

V in2

V in3

C

V in4

Fig. 9.26 A voltage mode universal biquad presented by Ranjan and Paul [ 23 ]

The output voltage (V out ) of this circuit is obtained as:

V in 4

s 2 C 2 R x 1 R x 2 þ

V in 1 þ sCR x 1 V in 2 sCR x 1 V m 3 þ sCR x 1

V out ¼ ð 9 : 28 Þ

s 2 C 2 R x 1 R x 2 þ

sCR x 1 þ 1

An inspection of the equation ( 9.28 ) reveals that a LPF is realizable by choosing
Vin2 ¼ Vin3 ¼ Vin 4 ¼ 0; a HPF is realized by choosing Vin1 ¼ Vm2 ¼ 0 and

Vin3 ¼ Vm4; a BPF is realizable by choosing Vin1 ¼ Vin2 ¼ 0; a band-reject is

realizable with Vin2 ¼ 0 and making Vin1 ¼ Vin3 ¼ Vin4 and finally, an APF is

realizable by choosing Vin1 Vin.

Although it is claimed that this circuit removes most of the short comings of the
other previously known CCCII-based topologies, an apparent difficulty is that in
case of APF, it does require an additional inverting amplifier.
From the available VM universal biquads, it appears that any circuit which can
realize all the five functions completely without any constraints, while using no
more than two or three CCCIIs, has still not appeared in the literature and hence,
constitutes an interesting problem for investigation.

¼ Vin3 ¼ Vin4 ¼ Vin but Vin2 ¼

9.9 Current-Mode Universal Biquad Filters

A large number of universal current-mode biquad filter circuits have been proposed
by various authors using CCCII as active elements. In the following, we present
some exemplary circuits possessing some interesting and useful properties.
The classical Kerwin, Huelsman and Newcomb (KHN) biquad has been a very
popular and versatile biquad filter structure which has been translated into almost
every new technology and using almost every new building block over the past two
decades. Altuntas and Toker

[ 24 ] have presented KHN-equivalent biquads