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V
0
C
2
R
1
+
V
1
-
CCII-
y
CCII+
z
y
R
2
x
x
+
V
3
z
-
+
V
2
C
1
-
Fig. 6.17 VM universal biquadratic Filter proposed by Horng et al. [
15
]
implementation. In addition, these circuits provide orthogonal control of
ω
0
and Q
0
by grounded resistors, are easily convertible into a voltage-controlled filter and
have low total-component- count.
The practical feasibility of all the three circuits has been verified using AD844 to
realize CCIIs.
Horng, Lee, Cheng and Chang Universal Biquad Another low-component-
count MISO-type two CCII-based VM universal biquadratic filter was introduced
by Horng et al. [
15
] and is shown in Fig.
6.17
.
By straight forward circuit analysis, the transfer functions realizable by this
circuit can be expressed by the following expression:
V
1
þ
s
2
C
1
C
2
R
1
R
2
ð
sC
1
R
2
Þ
V
2
þ
V
3
V
0
¼
ð
6
:
29
Þ
s
2
C
1
C
2
R
1
R
2
þ
sC
1
R
2
ð
Þþ
1
From the above equation, one can see that all the five generic filter functions can be
realized as follows: (i) LPF: if V
1
¼
V
2
¼
0 (grounded) and V
3
¼
V
in
(ii) BPF: if
V
1
¼
V
3
¼
0 (grounded) and V
2
¼
V
in
(iii) HPF: V
2
¼
V
3
¼
0 (grounded) and
V
1
¼
V
in
(iv) Notch: V
2
¼
0 (grounded) and V
3
¼
V
in
¼
V
1
and (v) APF:
if
V
1
¼
V
in
. Thus, the penalty to be paid for realizing an APF is that
one more CCII, along with two resistors will be needed to realize an inverting
amplifier to negate the sign of the input V
2
.
The circuit has been found to work as predicted by theory when CCIIs are
realized with AD844. The Q-factors of the order of 10 and f
0
of the order of
40 KHz were found to be easily realizable.
V
2
¼
V
3
¼
Horng, Tsai and Lee Universal Biquad A two CCII-based MISO-type VM filter
using three resistors and two capacitors was proposed by Horng et al. in [
16
]
(Fig.
6.18
).
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