Hardware Reference
In-Depth Information
a
b
I
B1
I
B1
Y
I
out
Y
CCCII+
CCCII+
X
Z
Z
V
0
I
in
V
in
X
X
X
CCCII+
Z
Z
Y
CCCII+
Y
I
B2
I
B2
Fig. 9.13 Voltage and current amplifiers with adjustable gains [
2
](a) current-controlled voltage
amplifier (b) current-controlled current amplifier [
11
]
9.4 Current Controlled VM/CM Amplifiers
The minimum number of resistors needed to make a VCVS is two. It is apparent
that with R
x
of CCCII accounted for; only two CCCIIs should suffice for this
purpose. One such circuit is shown in Fig.
9.13a
which is characterized by:
V
out
V
in
¼
R
x
2
R
x
1
¼
I
B
1
I
B
2
ð
9
:
8
Þ
Thus, the voltage gain is electronically-controllable by I
B1
and/or I
B2
and is
temperature-insensitive since the parameter V
T
is cancelled out!
A current amplifier with current gain equal to the ratio of the two external bias
currents can also be realized by appropriate connections of only two CCCIIs as
shown in Fig.
9.13b
. In this case, the current gain can be expressed as:
I
out
I
in
¼
R
x
1
R
x
2
¼
I
B
1
I
B
2
ð
9
:
9
Þ
It may be noted that this circuit also offers the desirable properties of low input
impedance, high output impedance and temperature-insensitive gain.
9.5 Active-Only Summing/Difference Amplifiers
CCCIIs make it possible to realize sum and difference circuits using only active
devices without requiring even a single resistor [
12
]. One such circuit is shown in
Fig.
9.14
. The output voltage of this circuit is given by:
Search WWH ::
Custom Search