Page 16 - Analog and Digital Filter Design

PREFACE

This book is about analog and digital filter design. The analog sections include
both passive and active filter designs, a subject that has fascinated me for several
years. Included in the analog section are filter designs specifically aimed at radio
frequency engineers, such as impedance matching networks and quadrature
phase all-pass networks. The digital sections include infinite impulse response
(IIR) and finite impulse response (FIR) filter design, which are now quite com-
monly used with digital signal processors. Infinite impulse response filters are
based on analog filter designs.

Detailed circuit theory and mathematical derivations are not included, because
this book is intended to be an aid in practical filter design by engineers. The
circuit theory and mathematical material that is included is of an introductory
nature only. Those who are more academically minded will find much of the
information useful as an introduction. A more in-depth study of filter theory
can be found in academic books referred to in the bibliography. Equations and
supplementary material are included in the Appendix.

Designing filters requires the use of mathematics. Fortunately, it is possible to
successfully design filters with very little theoretical and mathematical knowl-
edge. In fact, for passive analog filter design the mathematics can be limited to
simple multiplication and division by the use of look-up tables. The design of
active analog filters is slightly more ditlicult, requiring both arithmetic and
algebra combined with look-up tables. The equations behind many of the look-
up tables are included in the Appendix.

Digital FIR filters perform their function by first passing a digitized signal
through a series of discrete delay elements and then multiplying the output of
each delay element by a number (or coefficient). The values produced from all
the multiplication functions at each clock period are then added together to give
an output. Hence digital filter designs do not produce component values.
Instead, they produce a series of numbers (coefficients) that are used by the mul-
tiplication functions. There are no design tables; the series of coefficients is pro-
duced by an algebraic equation, so the designer must be familiar with arithmetic
and algebra in order to produce these coefficients.