Hardware Reference
In-Depth Information
a
R
s
X
CCII+
V
0
Z
Y
V
in
R
2
R
1
b
V
0
V
satH
R
1
−
R
s
R
1
+R
2
)
V
satH
(
V
in
R
1
−
R
s
R
1
+R
2
(
)
V
satL
V
satL
Fig. 8.24 (a) Schmitt trigger using CCII+ introduced by Cataldo et al. (b) its transfer character-
istic (Adapted from [
9
]
1995 Wiley)
©
The first ever Schmitt trigger using a single CCII+ along with two resistors was
introduced by Cataldo et al. in [
9
] which is shown in Fig.
8.24a
.
In this circuit, the re-generative feedback required to make a Schmitt trigger is
created by the potential divider made from the two resistors. The operation of this
circuit can be explained as follows. A decrease in the output voltage leads to a
decrease in v
y
; since v
x
¼
V
x
)/R
s
,
this implies that as a consequence i
x
will be increased. In turn i
z
also increases by
the same amount as i
x
which results in the increase in the voltage v
z.
. However, the
maximum voltage V
0
is limited by the two power supply voltages hence, the circuit
output will exhibit only two stable states, V
satH
and V
satL
, corresponding to which
the two output saturation currents are found to be [
9
]:
v
y
therefore, v
x
also deceases. Since i
x
¼
(V
in
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