Hardware Reference
In-Depth Information
Fig. 9.25 Universal
voltage mode biquad filter
proposed by Parveen
et al. [ 22 ]
Y
Z−
Z+
X
Y
I B1
C 1
V 0
Z+
V 1
X
C 2
V 2
I B2
V 3
V 4
The various filter responses can be determined through the following selection of
the inputs:
Type of filter
Condition of realization
HPF
V 4 ¼ V in ,V 1 ¼ V 2 ¼ V 3 ¼ 0
Non-inverting HPF
V 3 ¼ V in ,V 1 ¼ V 2 ¼ V 4 ¼ 0
Inverting BPF
V 2 ¼ V in ,V 1 ¼ V 3 ¼ V 4 ¼ 0
LPF
V 1 ¼ V 2 ¼ V in ,V 3 ¼ V 4 ¼ 0, and R x1 ¼ R x2
Band stop filter (BSF)
V 1 ¼ V 2 ¼ V 4 ¼ V in ,V 3 ¼ 0, and R x1 ¼ R x2
APF
V 1 ¼ V 2 ¼ V 4 , ¼ V in ,V 3 ¼ 0, and R x1 ¼ 2R x2
In case of HPF, and BPF responses, one does not require any matching con-
straints. On the other hand, the constraints in LPF, BSF and APF are simple to
satisfy through design, particularly in monolithic implementations, where matching
of the devices is not difficult to achieve. The pole frequency
ˉ o and the pole-Q 0 of
the filter are given by:
r
R x 1
R x 2
1
R x 1 R x 2 C 1
C 1
C 2
ˉ o ¼
p
, Q 0 ¼
:
ð
9
:
27
Þ
C 2
Universal VM biquad of Fig. 9.25 , although realizes all the five filtering functions,
however, in case of LPF and BSF, it requires a matching condition Rx1
¼
Rx2 and
in case of APF, it requires Rx1
2Rx2.
An alternative circuit which although employs same number of CCCIIs and only
two equal-valued capacitors but does not require such conditions for realizing
various functions was presented by Ranjan and Paul in [ 23 ] and is shown here in
Fig. 9.26 .
¼
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