Hardware Reference
In-Depth Information
a
b
+V
Q
8
Q
9
Q
10
Q
16
I
B
Q
11
Q
12
+V
Q
13
Q
1
Q
2
y
w
x
y
Q
3
Q
4
Q
14
z
−V
Q
17
w
I
B
Q
5
1
CCII+
Q
6
Q
7
Q
15
Q
8
i
z
x
−V
z
Fig. 3.22 Current feedback operational amplifier (a) Block diagram of the internal circuit (b)
Bipolar implementation of AD844 type CFOA [
20
]
The AD844 is quite versatile as it can be used as a CCII+, can be used to realize
CCII
(needing two AD844s), can be used as a direct replacement for the conven-
tional op-amp (with its Z-terminal, the compensation pin, open) due to its
pin-compatibility with the popular IC op-amps such as
A 741 or LF 356 and
lastly, can be used as a four-port building block in its own right.
ʼ
3.3.4 Using OPA-2662 as Current Conveyors
The operational transconductance amplifier OPA2662 [
21
] can be directly used as a
CCII+ as it is (Fig.
3.23a
). Its simplified circuit is shown in Fig.
3.23b
. A CCII
can
be implemented with the help of two such devices. The validity of such a realization
has been demonstrated by Tomawski et al. [
22
] by using such CCII-s to realize a
frequency dependent negative conductance.
3.3.5 CC from OPA 660/OPA 860
Although not mentioned anywhere in the producer
s catalog of OPA660, the
internal circuit architecture of the OPA 660 architecture (Fig.
3.24
) is essentially
a CCII+ made from transistors Q
1
to Q
10
with terminals B, E and C respectively
representing terminals Y, X and Z of the current conveyor CCII+. On the other
hand, the part of the circuit composed of transistors Q
11
to Q
14
constitutes the
translinear voltage follower (VF). In the entire circuit, the transistors Q
5
and Q
6
in
the CCII+ part and transistor Q
15
to Q
20
in the VF part constitute the DC bias
circuitry from which the bias current can be adjusted by an external resistor R
0
'
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