Hardware Reference
In-Depth Information
Fig. 7.5 Canonic SRCO
using a CCII + proposed by
Abuelma
'
amatti and
Humood [
10
] and also by
Celma et al. [
16
]
C
1
R
y
CCII+
z
x
R
2
R
1
C
2
three/two op-amps along with two grounded capacitors to realize SRCOs however,
similar circuit with a single op-amp is although in principle possible but the required
design constraints are very complex and so are the resulting tuning laws.
In this section, we show that the current conveyors outperform the op-amps in
this respect. In particular, not only such circuits can be realized using current
conveyors while avoiding complex design equations but also the resulting circuits
employ invariably the least possible number of passive components. We highlight
some exemplary circuits exhibiting these features from amongst many such circuits
advanced by various researchers in the literature, for instance, [
2
,
14
,
18
,
31
,
41
,
43
,
47
,
51
,
54
,
62
].
We first present two minimum-component oscillators which employ only two
CCIIs, only two resistors and both grounded capacitors. Such circuits were pro-
posed by Horng et al. in [
31
] and are shown in Fig.
7.6
. Both the circuits are
characterized by the same characteristic equation and have the same CO and FO
given respectively by:
s
2
C
1
C
2
R
1
R
2
þ
sR
1
C
2
ð
C
1
Þ þ
1
¼
0
ð
7
:
16
Þ
CO
:
C
1
¼
C
2
ð
7
:
17
Þ
r
1
C
1
C
2
R
1
R
2
andFO
:
ω
0
¼
ð
7
:
18
Þ
In both these circuits, the only point of inconvenience is the adjustment of the COwhich
will require in practice a variable capacitor which is not a very convenient option.
Two other circuits, with exactly same number of active and passive components
and also governed by exactly the same equations, are shown in Fig.
7.7a, b
and were
proposed by Horng [
41
] and Fongsamut et al. [
47
] respectively.
From a non-ideal analysis of both the circuits assuming the current gains of the
CCIIs as
α
1
and
α
2
and the voltage gains as
ʲ
1
and
ʲ
2
. The non-ideal expressions for
the FO of the two circuits are given by:
s
ʲ
1
ʱ
1
ʱ
2
C
0
1
C
0
2
R
0
1
R
0
2
FO
:
ω
0
¼
for the Fig
:
7
:
7a
ð
7
:
19
Þ
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