Analog Filter Design Revisited: Circuit Configurations Using Newer Varieties of CCs - Current Conveyors: Variants, Applications and Hardware Implementations - page 402

Fig. 12.35 CM 3rd-order
LP all-pole LC ladder filter

L 2

I 0

C 3

C 1

I i R

R

I in

CCCIII CCII CCCIII

I 0

y z + y z + y

z +

C c3

C c1 C b

z -

z -

x

x x

R a

R a

R a

Fig. 12.36 Active realization of all-pole filter derived by Hwang et al. (Adapted from [ 109 ] ©
2007 Springer)

12.2.6 Filter Design Using CCIII

The third generation CC (CCIII I x

was introduced by Fabre [ 103 ] as a particularly useful element for active current
probes and for sensing current in floating elements and making it available from a
high input impedance node. However, subsequently, the CCIII found numerous
other applications including those of realizing universal biquads. In this section, we
outline some of the prominent biquad structures using CCIIIs as active elements.

) which provides I y ¼ I x ,V x ¼ V y and I z ¼

Hwang-Chen-Li method [ 102 ] of higher order filter design Figure 12.35 shows
a passive CM 3rd-order LP all-pole LC ladder filter and its active realization is
given in Fig. 12.36 .
Assuming ideal CCs, a routine circuit analysis yields the following CM transfer
function:

I 0
I i ¼

1

þ

s 3 R a C c 1 CbC c 3 s 2 R a C b C c 1 þ

ð C c 3 Þ þ sR a C c 1 þ ð C b þ C c 3 Þ þ 2

ð 12 : 136 Þ

The corresponding active realization is shown in Fig. 12.36 which employs three
CCs (one DO-CCII, one DO-CCIII and one CCIII), three grounded capacitors and
three grounded resistors.
As another example, the circuit of Fig. 12.37 shows a passive realization of CM
3rd-order LP elliptic LC ladder filter and its active realization is shown in
Fig. 12.38 . Again assuming ideal CCs, through a straight forward circuit analysis,
the CM transfer function of Fig. 12.38 can be obtained as: