Analog Signals and Systems - Digital Signal Processing: An Introduction with MATLAB and Applications - page 58

which yields n = 3, f o = 1,400 Hz. The filter can now be designed using: [A
B] = butter(n,wo,'s') ;
2. Following similar steps:
1.5.9 Active Filters
Inductors require more space in circuits than capacitors and resistors and are
generally less accurate. Active filters enable filters to be constructed without
inductors, simply by incorporating active components such as op-amps. As well as
eliminating the need for inductors, active filters have the advantage that they
can produce a gain, while passive filters cannot. Active filters are considered
briefly in what follows.
1.5.9.1 Overview of Active Amplifiers
This section very briefly reviews the key results from the theory of op amps. For a
detailed explanation of op-amps, the reader should consult standard Op-Amp
references such as [ 4 ]. The conventional inverting and non-inverting active
amplifier configurations are shown in Fig. 1.38 .