"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

Low-Pass Filter Design
16-12
1st order
2nd order
3rd order
4th order
5th order
6th order
1st order
a=1
2nd order
a 1 , b 1
1st order
a 1
2nd order
a 1 , b 1
1st order
a 1
2nd order
a 1 , b 1
2nd order
a 2 , b 2
2nd order
a 2 , b 2
2nd order
a 2 , b 2
2nd order
a 2 , b 2
2nd order
a 3 , b 3
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
Figure 16–12. First-Order Noninverting Low-Pass Filter
R 1
C 1
R 3
R 2
V OUT