Hardware Reference
In-Depth Information
R
11
R
2
R
1
R
10
+
3
−
R
3
−
+
a
d
Z
5
R
9
R
4
R
5
R
8
R
7
Y
r
+
1
−
R
6
+
−
c
b
2
−
+
4
X
R
12
Fig. 2.3 CCII implementation proposed by Bakhtiar and Aronhime [
2
]
in negative feedback path ensures I
y
¼
V
y
. Among the remaining four
amplifiers the two op-amps along with resistors R
6
to R
12
ensure that the output
voltage of the third op-amp is V
A
-V
C
when connections A-D and C-B are made.
The fifth op-amp is configured as voltage to current converter. With (
R
6
/
R
10
)
0 and V
x
¼
¼
(
R
7
/
R
8
),
R
7
¼
R
8
,
R
6
¼
R
9
¼
10
R
7
,
R
11
¼
R
12
¼
R
7
k
R
6
and
R
2
R
5
¼
R
1
(
R
3
+
R
4
),
and
rR
2
¼
i
x
, depending on the connections among terminals a, b, c
and d. A major limitation of this circuit is the (employment of large number of
op-amps along with a large number of resistors). In addition, the bandwidth of the
current conveyor achieved is about 29 KHz only when the op-amp used (CA3130)
has the gain bandwidth product A
0
ˉ
p
¼
R
1
R
3
,i
z
equals
10
7
.
5.1
2.2.3 Senani
s Op-Amp-OTA Based Implementation
'
A novel three port active- R circuit capable of implementing all the four forms of
current conveyors namely CCI+, CCI
using an op-amp, an
OTA and only one/two resistors was proposed by Senani in [
3
]. The circuit to
realize CCII requires only one external resistor as shown in Fig.
2.4
. A straight
forward analysis of this circuit shows that i
y
¼
, CCII+ and CCII
0, V
x
¼
V
y
and i
z
¼
g
m
R
01
i
x
, thus
i
z
¼
i
x
is obtained if R
01
is chosen as 1/g
m
. Alternatively, since the g
m
of the OTA is
electronically controllable through an external bias current I
B
, the circuit realizes an
electronically controllable current conveyor CCII+. If the polarities of the input
terminals of the OTA are reversed, the same circuit realizes a CCII
.
To realize a CCI, one more resistor needs to be connected between the
non-inverting input terminal and the output of the op-amp as shown in Fig.
2.5
,if
R
01
¼
R
02
¼
1/g the circuit realizes a CCI+. If the polarities of the input terminals of
the OTA are reversed, the same circuit realizes a CCI
.
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