Hardware Reference
In-Depth Information
In this chapter, therefore, we revisit the problem of realizing universal biquad
filters but the main focus is now on configurations using numerous variants of CCs
such as, DVCC [ 1 - 30 ], DDCC [ 31 - 69 ], FDCCII [ 70 - 87 ], ICCII [ 88 - 100 ] DCVC
[ 101 , 102 ], CCIII [ 103 - 110 ], DXCCII [ 111 - 116 ], CFCCII [ 117 - 121 ], OFCC [ 122 ,
123 ], DOCCs/MOCCs [ 125 - 195 ] and the so-called universal current conveyor
(UCC) [ 124 , 196 - 202 ].
12.2 Filter Design Using Different Varieties of CCs
In the various subsections of this chapter, we undertake a discussion of some
prominent configurations evolved during the past several years to realize universal
biquad filters in VM, CM, dual-mode or mixed-mode from among those published
in [ 1 - 212 ].
12.2.1 Filter Design Using DVCCs
Since a DVCC has differential input capability with infinite input impedance
looking into its two y-terminals, it becomes possible to realize a number of
functions with not only the least possible number of external passive components
but also with reduced requirements of the number of active components. Before
enumerating a number of interesting topologies for universal biquad designs, we
present here one such example.
The example is that of an instrumentation amplifier which, when designed with
normal CCs requires two resistors only one of which is grounded but needs as many
as three CCs; by contrast, the same function can be performed with only one DVCC
and with a minimum of only two resistors both of which are grounded as shown in
Fig. 12.1
An ideal DVCC+ is characterized by the following hybrid matrix:
2
4
3
5 ¼
2
4
3
5
2
4
3
5
I Y 1
I Y 2
V X
I Z
0000
0000
1
V Y 1
V Y 2
I X
V Z
ð
12
:
1
Þ
100
0010
Assuming the characterization of equation ( 12.1 ), the expression for the output
voltage in terms of differential input voltage for the circuit of Fig. 12.1a is given by:
R 2
R 1 V id
V out ¼
ð
12
:
2
Þ
It is obvious that the circuit can realize both inverting and non-inverting amplifiers
by grounding V Y1 or V Y2 . Furthermore, the circuit is expected to exhibit constant
3 dB-bandwidth for different values of the gains. That it is indeed so, has been
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