Hardware Reference
In-Depth Information
Fig. 6.19 VM universal
active filter with three
inputs and single output
proposed by Chang [
17
]
R
3
CCII-
V
c
x
CCII+
1
z
y
y
C
1
2
z
x
R
5
R
2
V
b
CCII-
V
0
x
CCII+
3
z
y
y
4
C
2
z
x
R
4
R
1
V
a
Ozoguz and Gunes Universal Biquad The universal filter with three inputs and
single output using plus type CCIIs was presented by Ozoguz and Gunes [
18
]as
shown in Fig.
6.20
.
The configuration is capable of realizing all type of second-order filter responses
with proper choice(s) of input signal(s). Assuming ideal CCIIs, routine circuit
analysis yields the following expression of the output voltage in terms of the
various input voltages:
V
in
3
s
2
C
1
C
2
R
1
R
2
R
3
þ
sC
1
R
1
R
3
V
in
2
sC
1
R
1
R
2
þ
V
in
1
R
2
V
out
¼
ð
6
:
32
Þ
s
2
C
1
C
2
R
1
R
2
R
3
þ
sC
1
R
1
R
3
þ
R
2
The practical workability of this circuit had been demonstrated by realizing various
filters with Q
0
¼
1.59 KHz which are typical of those needed when a
second order all pass filter is used to linearize the phase of an nth order low pass
filter.
1 and
f
0
¼
Chang and Lee Universal Biquads The filter circuits proposed by Chang and Lee
[
19
] employ three CCIIs and one voltage follower and realizes a VM biquad having
three inputs and one output (Fig.
6.21
)
Assuming ideal CCIIs, circuit analysis yields the following expression of the
output voltage:
V
1
þ
s
2
C
1
C
2
R
1
R
2
R
3
ð
sC
2
R
2
R
3
Þ
V
2
þ
RðÞ
V
3
V
out
¼
ð
6
:
33
Þ
s
2
C
1
C
2
R
1
R
2
R
3
þ
sC
2
R
2
R
3
þ
R
1
From the inspection of the Eq. (
6.33
), it is clear that all the five filtering functions can
be realized by appropriate choice(s) of input(s) which are: V
1
¼
0, V
2
¼
0, V
3
¼
V
in
,
for LPF; V
1
¼
0, V
3
¼
0, V
2
¼
V
in
for BPF; V
2
¼
0, V
3
¼
0 for HPF; V
2
¼
0,
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