DESIGN AND ANALYSIS OF ANALOG FILTERS A Signal ...

as well as implementation, and the present book is no exception. Most books on
analog filter design briefly present the signal processing / systems concepts, and then
concentrate on a variety of filter implementation methods. The present book reverses
the emphasis, stressing signal processing concepts. The present book does not ignore
implementation, as it does present filter implementation topics in Part II: passive
filters, and operational amplifier active filters. However, greater emphasis on signal
processing / systems concepts are included in Part I of the book than is typical. As
suggested above, this emphasis makes the book more appropriate as part of a signal
processing curriculum, but should also be of interest to those in analog circuit design
as well.
The intended audience for this book includes anyone with a standard electrical
engineering background, with a B.S. degree or beyond, or at the senior level. The
most important background subjects are Laplace and Fourier transform theory, and
concepts in basic systems and signals, and, of course, basic circuits as well. A
background in communications systems would be helpful in fully appreciating the
application examples given in Chapter 1, but these examples are given to illustrate
analog filter applications, and a communications background is not a prerequisite for
understanding the developments in the book. While MATLAB 2 and SPICE 3 are
software packages used, and familiarity with them would be an asset, it is assumed
that the adept student can learn these software tools on his own, or with minimal
guidance, if they are not already known. A brief introduction to MATLAB is given
in Appendix A.
Analog electrical signals are so named because they are analogous to some
other signal from which they are derived: acoustic, electromagnetic, mechanical
motion, etc. Analog filters process analog signals. However, they are also analogous
in another respect. The physically-constructed filter, i.e. the realized filter, responds
in the time-domain and frequency-domain in a manner that is analogous to the
theoretical filter, as defined by, say, as is often done, the magnitude-squared
frequency response. This suggests an important concept. A particular filter response,
as perhaps defined by the magnitude-squared frequency response, such as a
Butterworth response, is mathematically defined. The realization is, at best, an
approximation. Therefore, the “filter” is defined mathematically and abstractly. All
realizations are approximations. A “circle” often refers to a geometrical drawing
representing a circle, as a “filter” often refers to a physical realization of a filter.
Hence, in this textbook, theory is stressed and presented first; implementation (a
schematic drawing) follows, and, in practice, a realization (physical circuit) would
often follow that. It is a fascinating confirmation of the value of theory, that trial and
error, and experimentation, would never come up with a Butterworth filter design, but
theory elegantly and clearly develops it, and states the result in a very simple form.
2
MATLAB is a registered trademark of The Math Works, Inc., and is a high-level language for technical
computing.
3
SPICE is an abbreviation for Simulation Program with Integrated Circuit Emphasis, and is a powerful
circuit simulation computing program. Many commercially available circuit simulation programs are based
on SPICE.
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