Page 18 - Analog and Digital Filter Design

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Preface

The subject of Inverse Chebyshev filters are covered in some detail, because
information on this topic has been difficult to find. Natural application of
Inverse Chebyshev design techniques leads to a stopband beginning at w = 1.
This may be academically correct, but I describe how to obtain a more practi-
cal 3dB cutoff point. I also give explicit formulae for finding third-order passive
filters, and show a method of finding component values for higher orders.

Chapter 3 provides the foundation for filter design theory. This leads from trans-
fer function equations to pole and zero locations in the s plane. The s plane and
its underlying Laplace transform theory are described. This should give the
reader a feel for how the filter behaves if it has a certain pole-zero pattern or a
certain transfer function. Pole and zero placing formulae and the tables derived
from them are given for normalized lowpass filter responses.

Pole and zero locations are important in active filter design. With only knowl-
edge of the normalized lowpass pole and zero locations for a certain transfer
function, an active filter can be designed. Pole and zero locations can be scaled
or converted for highpass. bandpass, or bandstop designs.

Chapters 4 to 7 describes how to design active or passive lowpass. highpass.
bandpass, and bandstop filters to meet most desired specifications. Separate
chapters describe each type because the reader is usually interested only in a
particular type, for a given application. and will not want to search the book to
find the information. Formulae are given for the denormalization of the com-
ponent values or pole-zero locations that were given in earlier chapters.

Chapter 8 describes the diplexer and its application and performance. Diplex-
ers are passive filters and are used in RF design to split signals from different
frequency bands in either a highpassAowpass or a bandpasshandstop combi-
nation. One of the most common applications is in terminating mixer ports in
radio frequency system designs.

Chapter 9 describes the use of phase-shift networks, with examples for flatten-
ing the group delay response of Butterworth filters. One application is the
Weaver single sideband modulator, which uses a phase-shift network to cancel
out the unwanted sideband of an AM radio transmission. A description of the
Weaver single sideband modulator are given. both in mathematical terms and
with practical applications, This chapter also provides details of how to go about
the design of passive and active phase-shift networks.

Chapter 10 is very practical in orientation, describing how different materials
and component types can affect the performance of filters. Capacitor dielectric
and component lead lengths can be critical for a good filter performance. Details
on the construction of inductors using ferrite cores are given, and transformer
construction using similar techniques is included. Active filter components