Tutorial: EMC & Signal Integrity using SPICE, page 44 - IEEE EMC ...

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Book Review
Thomas A. Jerse, Guest Reviewer, The Citadel
Title: Electromagnetic Compatibility Engineering
Author: Henry Ott
Publisher: John Wiley, 2009
ISBN: 9780470189306
Henry Ott is one of the true pioneers of EMC education at the
professional level, and his widely read book Noise Reduction
Techniques in Electronic Systems (1976, 2nd edition 1988) has
served as an entry point for many engineers in our field. Mr.
Ott began his latest offering by contemplating a third edition
to this venerable text, but the changes and additional material
became so extensive that it grew into a new one. The author has
taught professional EMC courses for many decades, gaining a
vast experience that adds considerable depth and clarity to the
text because in explaining the material, he also answers the
many “what about?” and “what if?” questions
that his students have posed over the years. He
also explicitly dispels many of the myths of EMC
that he has heard along the way.
Mr. Ott retains the philosophy found in his
earlier works that although precise solutions to
real-world EMC problems are seldom reached
by mathematical calculation, an understanding
of functional dependence of the various parameters
involved is highly valuable for the practicing
engineer. Equations are given for simple cases
where a closed form solution exists, and they subsequently
are graphed to give the reader a feel for
the parametric variation. Further, electromagnetic
phenomena are modeled by lumped element
circuits where possible to give insight more easily
to engineers who are generally more familiar with circuit concepts.
This approach leads to a text that is highly practical in
nature. The book offers an abundance of specific EMC design
practices, but the reader is provided sufficient background and
insight to understand why they work and how they can be applied
to actual situations.
The author divided the material in the text into two parts:
the first ten chapters dedicated to the theory of EMC, and the
last eight presenting the application of the principles to EMC
design. The first chapter gives basic principles, motivating
examples of EMI problems, and a fairly detailed exposition of
commercial regulations and military standards. The second
chapter discusses coupling to cables, primarily for electrically
short cables. Chapter 3 covers grounding techniques in ac power
distribution, in signal transmission, and in systems. It also
discusses ground loops and some mitigation methods. Chapter
4 describes the use of balanced signal transmission which is becoming
increasingly popular and filtering. In the fifth chapter,
the electrical behavior of various passive components including
ferrites and their non-idealities are examined. It is here
that transmission line theory is given, although it is used in
the fourth chapter to explain decoupling filters. Basic shielding
theory is presented in the sixth chapter. Schelkunoff’s approach
is used to show that, except for very low frequency magnetic
fields, direct penetration of electromagnetic waves through a
shield wall is not an issue. Some basic equations for the shielding
effectiveness of apertures are given along with a description
of the properties of seams formed between mating parts. A vital
feature is the emphasis on the importance of providing adequate
contact pressure between the two pieces that form the seam.
Throughout the second half of the chapter, the concept – crucial
to the design of effective shields, that the shield must provide a
low-impedance with a minimum of discontinuities for the surface
current induced by an impinging field – is emphasized.
Chapter 7 discusses contact protection and the switching of inductive
loads. The eighth and ninth chapters characterize various
sources of random noise found in passive and
active devices along with the classic technique for
calculating the overall noise in a system formed
by cascading blocks. The first half of the text ends
with chapter 10 where the grounding of digital
circuits is examined with an eye to minimizing
the noise voltage induced in the ground system.
Chapter 11 begins the EMC applications half
of the book with a detailed examination of digital
circuit power distribution. The relatively wideband
spectrum of the transition pulses drawn
through the power supply leads of digital logic
devices are discussed, and a particularly valuable
section points out the potentially deleterious
parallel resonances that occur when capacitors of
different sizes are placed in parallel. The twelfth
chapter covers radiated emissions from digital circuits, decomposing
them into the two mechanisms, differential mode
and common mode. The characterizations used are for radiating
structures that are somewhat smaller than a wavelength,
but the design principles gained by examining parametric dependence
are effective even at higher frequencies. Conducted
emissions are discussed in Chapter 13 with an emphasis on
switch-mode power supplies. Power line filters are also covered
with a wealth of practical information on their application and
mounting. Chapter 14 is devoted to product immunity from
RF radiation and transients. Audio rectification of RF is explained,
but unlike some of the author’s previous work, the role
of resonances in exacerbating it is absent. The chapter continues
with a thorough survey of the devices and their application
for protecting power and signal lines from transients. Attention
is paid to devices for high-speed digital lines where the
quiescent shunt impedance of the device must be very high.
Electrostatic discharge (ESD) is covered in Chapter 15 with
mitigation techniques for both grounded and ungrounded
products. Some of the most crucial elements in product design
for EMC are the printed-circuit boards which are the focus of