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Low-Pass Filter Design
1st order
1st order
a=1
2nd order
2nd order
a 1
, b 1
3rd order
1st order
a 1
2nd order
a 2
, b 2
4th order
2nd order
a 1
, b 1
2nd order
a 2
, b 2
5th order
1st order
a 1
2nd order
a 2
, b 2
2nd order
a 3
, b 3
6th order
2nd order
a 1
, b 1
2nd order
a 2
, b 2
2nd order
a 3
, b 3
Figure 16–11.
Cascading Filter Stages for Higher-Order Filters
Figure 16–10 demonstrated that the higher the corner frequency of a partial filter, the higher
its Q. Therefore, to avoid the saturation of the individual stages, the filters need to be
placed in the order of rising Q values. The Q values for each filter order are listed (in rising
order) in Section 16–9, Tables 16–4 through 16–10.
16.3.1 First-Order Low-Pass Filter
Figures 16–12 and 16–13 show a first-order low-pass filter in the inverting and in the noninverting
configuration.
V IN
R 1
C 1
R 2
V OUT
R 3
Figure 16–12.
First-Order Noninverting Low-Pass Filter
16-12