Hardware Reference
In-Depth Information
+V
Q
9
Q
7
Q
10
Q
8
I
B
I
B
I
B
−V
Vx
b
i
y
X
Z
a
i
x
Y
i
z
Q
1
V
y
Q
2
(I
B
+ i
x
)
(I
B
+ i
x
)
(I
B
+ i
x
)
2
Q
4
Q
5
Q
6
Q
3
−V
Fig. 3.8 A possible CCII implementation based upon Filanovsky
s method of converting a
'
current source into current conveyor [
9
]
This circuit generates a current which directly relates to the absolute temperature
as well as is linearly variable. In this circuit, the transistor Q
1
along with
Wilson current mirror realizes a reference current source which generates a current
I
A
of the form
I
A
¼
ð
V
T
ln
α
Þ=
R
ð
3
:
5
Þ
where
α
is the emitter ratio of the transistor Q
2
to Q
1
which in the present case is
α¼
2I
A
flows in the diode connected
transistors Q
8
and Q
9
. The transistors Q
4
to Q
11
function as the Gilbert translinear
cell which provides an output current I
0
given by
4. Now the current I
1
which is equal to I
1
¼
I
0
¼
I
1
I
B
=
I
2
¼
2
V
T
ln
α
ð
Þ
I
B
=
I
2
R
ð
3
:
6
Þ
where I
B
is the external bias current and I
2
is a fixed constant current.
The temperature-compensated CC architecture, using this idea, is shown In
Fig.
3.10
.
In this circuit, using the above equations, it has been found that
R
x
¼
V
T
=
2
I
0
¼
V
T
=
f
4
V
T
ln
ð
α
Þ
I
B
=
I
2
R
g ¼
I
2
R
=
4ln
α
I
B
ð
3
:
7
Þ
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