Analog Filter Design Revisited: Circuit Configurations Using Newer Varieties of CCs - Current Conveyors: Variants, Applications and Hardware Implementations - page 399

Fig. 12.32 Symbolic
notation of the DCVC
or CDBA

I x1

V x1

x 1

V 0 =V z

O

DCVC

V x2

x 2

z

I x2

I z

V z

the difference of two currents at its two low input-impedance terminals. Its sym-
bolic notation is shown in Fig. 12.32 . A DCVC is a four terminal analog building
block which is characterized by the following set of equations:

V X1 ¼ V X2 ¼ 0, I Z ¼ ð I X1 I X2 Þ and V 0 ¼ V Z ð 12 : 132 Þ

In view of the departure from the normal variety of CCs, this results in new
possibilities of realizing universal biquads filters. It must be however, recognized
that a DCVC or CDBA is easily realizable from three normal types of CCII s +
elements or AD844s. On the other hand, a number of CMOS-compatible
implementations of the CDBAs have been advanced by a number of researchers.
Although the literature is flooded with a variety of biquads using CDBAs, in the
following, we present some exemplary biquads using these building blocks.

Salama-Elwan-Soliman biquad In 2001, Salama et al. [ 101 ] have proposed a
universal biquad filter configuration employing two DCVCs, two grounded capac-
itors, one floating capacitor and ten MOSFETs (see Fig. 12.33 ). The filter structure
is suitable for higher-order filter realization by cascading second-order sections.
Also most of the parasitic capacitances can be eliminated because both the input
terminals are virtually grounded and parasitic capacitances at Z-terminals can be
absorbed in C 1 and C 2 .
Assuming ideal DCVCs and operation of all MOSFETs in triode region, a
routine circuit analysis of Fig. 12.33 reveals the following VM transfer function:

s 2 C C 2

C 2 R 4

1 1

C 1 C 2 R 3 R 2

þ s þ

V o
V i ¼

C 2 R 5

ð 12 : 133 Þ

1 1

C 1 C 2 R 1 R 2

s 2 þ s þ

where