Hardware Reference
In-Depth Information
+V
G5
M
15
M
25
−V
G5
+V
G1
+V
G3
M
16
M
12
+V
G2
−V
G6
M
11
M
13
V
BP
x
1
V
HP
x
1
x
2
x
1
DCVC
o
DCVC
V
LP
DCVC
o
o
V
in
x
2
z
z
z
x
2
M
23
M
21
M
22
C
1
C
2
M
26
−V
G3
−V
G1
−V
G2
+V
G6
+V
G4
M
14
M
24
−V
G4
Fig. 12.34 KHN-equivalent employing DCVCs and MOS-C [
102
]
1
KV
a
1
1
KV
a
2
1
KV
a
3
R
1
¼
,
R
2
¼
,
R
3
¼
,
ð
V
b
1
Þ
ð
V
b
2
Þ
ð
V
b
3
Þ
ð
12
:
134
Þ
1
KV
a
4
1
KV
a
5
¼ ʼ
n
C
ox
W
L
R
4
¼
,
R
5
¼
and
K
ð
V
b
4
Þ
ð
V
b
5
Þ
The filter parameters
ˉ
0
and Q
0
can be derived as:
r
1
C
1
C
2
R
1
R
2
r
C
2
C
1
R
1
R
2
ω
0
¼
,Q
0
¼
R
5
ð
12
:
135
Þ
Thus, Q
0
can be tuned independently by varying R
5
without disturbing
ˉ
0.
From equation (
12.133
), the various filter responses can be obtained as follows:
HPF: R
3
¼
R
4
¼1
(i.e., V
a3
¼
V
b3
and V
a4
¼
V
b4
); BPF: R
3
¼1
(i.e., V
a3
¼
V
b3
and C
3
¼
0); LPF: R
4
¼1
(i.e., V
a3
¼
V
b3
and C
3
¼
0); Notch: R
3
¼
R
1
,R
4
¼1
and C
3
¼
C
2
).
A sample result of the SPICE simulation of the circuit is shown in Fig.
12.33b
which shows the magnitude and phase response of the notch filter designed from the
circuit.
C
2
) and APF: R
3
¼
R
1
,R
4
¼
R
5
and C
3
¼
Soliman-Madian MOS-C biquad Another application of DCVC in the realiza-
tion of equivalent form of KHN- biquad is shown in Fig.
12.34
.
Starting from the conventional op-amp-based biquad the derivation of this
MOS-C version using DCVC and using dual MOSFET resistors is straight forward.
The circuit realizes a LPF, BPF and HPF functions at the three output terminals of
the DCVCs employed with the parameters of the realized filters being
electronically-controllable through the various external gate control voltages.
More detailed information about the circuit can be found in [
102
].
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