Hardware Reference
In-Depth Information
C
1
CCII-
R
1
CCII+
+
y
V
1
1
z
y
x
-
+
z
2
x
V
2
+
C
2
V
0
-
R
2
V
3
R
3
-
Fig. 6.18 Universal active VM filter proposed by Horng et al. 16]
Assuming ideal CCIIs, a straight forward circuit analysis yields the following
relation between the output voltage in terms of the various input voltages:
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
:
30
Þ
s
2
C
1
C
2
R
1
R
2
R
3
þ
sC
2
R
2
R
3
þ
R
1
The various filter functions can be obtained are (i) HPF: if V
2
¼
V
3
¼
0 (grounded)
and V
1
¼
V
in
(ii) BPF:
if V
1
¼
V
3
¼
0 (grounded) and V
2
¼
V
in
(iii) LPF:
V
2
¼
V
1
¼
0(grounded)
and V
3
¼
V
in
(iv) Notch: V
2
¼
0 (grounded)
and
V
1
¼
V
3
¼
V
in
and (v) APF: if V
1
¼
V
2
¼
V
3
¼
V
in
. Note that this circuit also
requires an additional CCII and two resistors for inverting one of the voltage inputs
to enable the realization of the APF.
With CCII+ implemented from one AD844 and CCII
from two AD844s, and
components chosen as R
1
¼
R
2
¼
R
3
¼
1K
ʩ
and C
1
¼
C
2
¼
0.1
ʼ
F, the circuit has
been found to realize all the five filters as predicted by theory.
Chang Universal Biquad Another MISO-type VM biquad was proposed by
Chang [
17
] as shown in Fig.
6.19
.
By straight forward analysis, the output voltage of this circuit as a function of the
various inputs is given by
V
a
þ
s
2
C
1
C
2
R
2
R
3
R
4
R
5
ð
sC
1
R
1
R
3
R
5
Þ
V
b
þ
ð
R
1
R
2
Þ
V
c
V
out
¼
ð
:
Þ
6
31
s
2
C
1
C
2
R
2
R
3
R
4
R
5
þ
sC
1
R
1
R
3
R
5
þ
R
1
R
2
Like the previous cases, it can be easily seen that by appropriate selection of various
input signal(s), all the types of fitter responses can be derived.
The attractive features of this circuit are: realisability of all the five functions,
lack of component-matching requirements, employment of both grounded capaci-
tors as preformed for IC implementation, orthogonal tunability of
ω
0
and Q
0
and the
low-sensitivity performance.
Search WWH ::
Custom Search