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a
I
0
z
CCII+
y
x
R
A
y
z
y
CCII+
x
z
CCII+
R
1
C
1
x
C
2
R
2
b
y
R
A
z
CCII+
x
x
y
z
CCII+
C
1
y
z
CCII+
C
2
x
R
1
R
2
Fig. 7.20 Variable frequency sinusoidal oscillators employing CCII + s proposed by Martinez
et al. [
35
]
Such oscillators can neither be made from a single CC nor with two CCs and
therefore, call for the use of a minimum number of three CCs.
One such circuit was proposed by Martinez et al. in [
35
] and is shown here in
Fig.
7.21
.
The circuit is characterized by the following equations:
r
1
C
1
C
2
R
2
R
3
CO
R
1
¼
R
A
;
FO
:
ω
0
¼
ð
7
:
43
Þ
:
Abuelma
atti in [
40
] derived a number of three CCII+ based circuits each
employing exactly the same number of active and passive components namely
four resistors and two capacitors all of which are grounded. Two exemplary circuits
from [
40
] are shown in Fig.
7.22
.
Both the circuits are characterized by same CO and FO which are given by:
'
r
1
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