Hardware Reference
In-Depth Information
a
b
I f
f
X
I x+
x+
f
X
g m
CCII+
CFTA±
Z
+
x−
Y
X
I x-
Z
I z
z
V z
Fig. 11.14 CFTA realization (a) block diagram implementation (b) Implementation of the CFTA
using CCII and OTA [ 87 ]
a
b
I A
I B1
I B2
+I x
I p
I B1
I B2
V x+
I A
x+
p
V p
z
p
MO-CCCTTA
n
I n
−I x
MO-CCCTTA
I in2
I in1
V n
x
−x
z
x−
V x−
I out
n
I z
V z
Fig. 11.15 The CTTA and its application (a) Block diagram (b) Current-mode multiplier/divider
[ 107 ]
V T
2 I A ;
I B 1
2 V T , g m 2 ¼
I B 2
2 V T
where R i ¼
g m 1 ¼
ð
11
11
Þ
:
An interesting application of this block was proposed by Pisutthipong and
Siripruchyanun [ 107 ] in realizing a current mode multiplier/divider as shown in
Fig. 11.15b . A novel feature is this circuit is that does not require even a single
external passive component and both the function are realized in the same circuit.
By a straight forward analysis of this circuit, taking cognizance of its character-
izing equations, the current output of the circuit in terms of the two input currents is
found to be
I in 1 I in 2
8 I A
I out ¼
ð
11
12
Þ
:
:
From the above equation, it is clear the circuit functions as a four-quadrant multiplier
because both the input currents can be either positive or negative. A novel feature of
this circuit is that its performance is temperature-insensitive . Furthermore, if either
I in1 or I in2 and I A are the input currents, the proposed circuit can also function as a
current-mode divider although in this case, since I a cannot have negative value, the
realized analog divider would be only a two-quadrant divider.
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