Introduction
Why write applications?
This is seemingly an odd and unlikely way to begin an
applications publication, but it is a valid question. As such,
the components of the decision to produce this book are
worth reviewing.
Producing analog application material requires an inten-
sive, extended effort. Development costs for worthwhile
material are extraordinarily high, absorbing substantial
amounts of engineering time and money. Further, these
same resources could be directed towards product devel-
opment, the contribution of which is much more easily
measured at the corporate coffers.
A commitment to a concerted applications effort must
be made despite these concerns. Specifically, the nature of
analog circuit design is so diverse, the devices so sophisti-
cated, and user requirements so demanding that designers
require (or at least welcome) assistance. Ultimately, the
use of analog ICs is tied to the user’s ability to solve
the problems confronting them. Anything that enhances
this ability, in both specific and general cases, obviously
benefits all concerned.
This is a very simple but powerful argument, and is the
basis of any commitment to applications. Additional ben-
efits include occasional new product concepts and a way to
test products under ‘‘ real world’’ conditions, but the basic
justification is as described.
Traditionally, application work has involved reviewing
considerations for successful use of a specific product.
Additionally, basic circuit suggestions or concepts are
sometimes offered. Although this approach is useful and
necessary, some expansion is possible. The applications
selected for inclusion in this book are centered on detailed,
systems-oriented circuits, (hopefully) similar to users’
actual designs. There is broad tutorial content, reflected
in the form of frequent text digressions and liberal use of
graphics. Discussions of trade-offs, options and techniques
are emphasized, as opposed to brief descriptions of circuit
operation. Many of the application notes include appended
sections which examine related or pertinent topics in
detail. Ideally, this treatment provides enough background
to allow readers to modify the circuits presented into solu-
tions to their specific problems.
Some comment about the circuit examples is appropri-
ate. They range from relatively simple to quite complex
and sophisticated. Emphasis is on high performance, in
keeping with the capabilities of contemporary products
and users’ needs. The circuit’s primary function is to serve
as a catalystonce the reader has started thinking, the
material has accomplished its mission.
Substantial effort has been expended in working out and
documenting these circuits, but they are not necessarily
finessed to the highest possible degree. All of the circuits
have been breadboarded and bench-tested at the prototype
level. Specifications and performance levels quoted in the
text represent measured and extrapolated data derived
from the breadboard prototype. The volume of material
generated prohibits formal worst-case review or tolerance
analysis for production.
The content in this volume, while substantial, repre-
sents only a portion of the available material. The resultant
winnowing process was attended by tears and tantrums.
The topics presented are survivors of a selection process
involving a number of disparate considerations. These include
reader interest, suitability for publication, time and space
constraints and lasting tutorial value. Additionally, a
minimum 10 year useful lifetime for application notes is
desired. This generally precludes narrowly focused efforts.
Topics are broad, with a tutorial and design emphasis that
(ideally) reflects the reader’s long term interest. While the
circuits presented utilize existing products, they must be
conceptually applicable to succeeding generations of
devices. In this regard, it is significant that some of the
material presented is still in high demand years after initial
publication.
The material should represent a relatively complete and
interdisciplinary approach to solving the problem at hand.
Solving a problem is usually the reader’s overwhelming
motivation. The selection and integration of tools and
methods towards this end is the priority. For this reason
the examples and accompanying text are as complete and
practical as possible. This may necessitate effort in areas
wherewehavenodirectstake,e.g.,thesoftwarepresentedin
Chapter 22 or the magnetics developed for Chapters 6 and 7.
Quality, in particular good quality, is obviously desirable
in any publication. A high quality application note requires
attentive circuit design, thorough laboratory technique,
and completeness in its description. Text and figures should
be thoughtfully organized and presented, visually pleasing,
and easy to read. The artwork and printing should maintain
this care in the form of clean text appearance and easily
readable graphics.
