Hardware Reference
In-Depth Information
I
in
y
z−
x
z-
I
BP
y
z+
z+
z-
I
HP
y
z−
x
I
LP
x
z+
2C
1
2C
2
R
2
R
1
/
I
HP
2C
2
2C
1
z+
x
y
z−
I
i
/
z+
x
/
/
I
BP
I
LP
z+
y
x
z−
z−
y
z−
Fig. 12.56 Fully-differential CM filter proposed by Kumar [
137
]
Fully-differential biquad Fully differential filters offer the advantages of immu-
nity from common mode noise signals, lower harmonic distortion and enhanced
dynamic range etc. An exemplary fully-differential CM biquad [
137
] is shown in
Fig.
12.56
.
Assuming a multiple output CCII (MOCCII) is to be characterized by i
y
¼
0,
v
x
¼
v
y
,i
z
+
¼
i
z
¼
i
x
, a straight forward circuit analysis of the circuit shown in
Fig.
12.56
yields:
H
0
ω
Q
0
s
Ds
I
BP
I
in
¼
I
LP
I
in
¼
H
0
ω
0
2
Ds
I
HP
I
in
¼
s
2
Ds
H
0
ð
12
:
197
Þ
ðÞ
;
ðÞ
;
ðÞ
R
1
C
1
s
2
1
1
ω
0
2
1
where
Ds
ðÞ¼
þ
s
þ
R
1
R
2
C
1
C
2
;H
0
¼
1,
¼
R
1
R
2
C
1
C
2
, and
ω
0
Q
0
¼
1
R
1
C
1
ð
12
:
198
Þ
From the above equations, it is clear that a notch filter is realizable by adding I
HP
and I
LP
and by combining I
HP
,I
BP
and I
LP
an APF can be obtained without any
component matching condition(s) except equal valued capacitors (which is inherent
in all the earlier fully differential configurations as well). The filter parameters
bandwidth and angular frequency are orthogonally controllable through R
1
and R
2
while the gain is unity in all the responses.
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