Hardware Reference
In-Depth Information
Fig. 6.33 Universal active
current filter proposed by
Chang [ 27 ]
I HP
x
z
CCI-
y
C 1
y
y
CCII+
z
I in
CCII-
z
x
C 2
x
R 2
I LP
y
I BP
x
z
CCI+
z
CCI+
x
y
R 1
R 3
orthogonal control of
ω 0 and Q 0 through grounded resistors. The filter responses
realized by the circuit are given by:
R 1 C 1
Ds
1
s
1
C 1 C 2 R 2 R 3
Ds
s 2
Ds
I HP
I i ¼
I BP
I i ¼
I LP
I i ¼
ð
6
:
47
Þ
ðÞ ;
;
ðÞ
ðÞ
The notch (NH) and all pass (AP) responses can be obtained by the following
equations:
I NH ¼
(I HP +I LP ) and I AP ¼
(I HP +I BP +I LP ) i.e.,
s 2
1
C 1 C 2 R 2 R 3
Ds
s 2
1
1
C 1 C 2 R 2 R 3
þ
s
C 1 R 1 þ
I NH
I i ¼
and I AP
I i ¼
ð
6
:
48
Þ
ðÞ
Ds
ðÞ
where Ds
1
C 1 C 2 R 2 R 3
The advantages of this configuration are (i) requirement of only five CCs
(ii) realisations of APF without any realization constraints and (iii) orthogonal
tunability of
ðÞ ¼
s 2
þ
s
C 1 R 1 þ
1
ω 0 and Q 0 through grounded resistors.
With CCs realized by OMA based CC formulations based upon LF356 op-amps
and CA3096E mixed transistor arrays, the practical implementations of the circuit
have been reported to yield measured frequency responses of the notch and all pass
functions in good agreement with the theory.
6.2.3.6 Single-Input-Single-Output (SISO)-Type CM Biquad
A number of SISO Cm biquads have been reported by various researchers in
literature, for instance, [ 28 , 61 , 67 , 86 , 88 , 98 , 99 , 103 , 109 , 112 , 114 , 116 , 117 ,
118 , 154 , 158 , 165 ].
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