Page 32 - Analog Circuit Design Art, Science, and Personalities

George A. Philbrick

also evident that optimizing and search operations will be made increasingly auto-
matic, as the deliberative functions of the user are encroached on more and more by
deliberately imposed autonomous controls. But one of the principal lessons from
the past is that substantially all the earlier techniques will continue to be used, and
will grow and improve horizontally. Possibly you have a slide rule in your pocket,
though admittedly you may have turned in your abacus for a desk calculator. All the
older apparatus of the above section on origins are in current usage, and will con-
tinue so. As an example may we consider passive models?
It would be a big surprise if passive electric models do not expand in application
and in technical excellence. More adept peripheral instruments, to drive and to mea-
sure them, are either in the cards or on the table. Passive circuit elements, adjustable
as well as fixed, are gradually but surely improving as to accuracy, bandwidth, and
stability. In this category are included not only resistors and capacitors, and less
insistently inductors and transformers, but also certain nonlinear elements. A com-
bination o€ compensation and regulation can cut the parametric effects of tempera-
ture down to size, especially with the advent of flexible devices for thermoelectric
heat pumping. Relatively little work has been done on passive networks for model
building, even for linear systems, compared to that expended for communications.
‘The challenges introduced in the nonlinear cases are considerable, but with newer
analytical techniques and instrumental tools it would be unwise to put limits on what
might be accomplished. Part of the lure is that many biological structures appear to
have been designed along these lines, though not of course without active adjuncts.
Another trend which is evident, and which will probably gain in momentum, is
that of the unification of assorted instrumental techniques based on analog feedback
operations. When it is considered how fundamental is the function of the operational
amplifier, and how its benefits are continually being rediscovered in new fields of
technology, it seems likely that multipurpose modular structures will perform the
tasks of a number of specialized measuring and manipulative instruments. Beyond
its classical and celebrated mathematical operations, comprising addition, algebraic
and functionill inversion, linear combination, differentiation, integration, etcetera,
are ;he abilities to store and to isolate, among a number of others which are less well
known. Since it is well known, on the other hand, where information of this kind is
available, there is no need or propriety to elaborate here on the application of this
basic tool. However, the philosophy of this sort of amplifier as an electrical null-
seeking or balancing agent carries its own impact once it is understood. When basi-
cally similar methods and equipment are found to be effective in each, such fields as
computing, data processing, testing, regulation, and model building will not be kept
separate, but will diffusc and perhaps ultimately fuse with one another. One key to
the future appears to lie in the quasi-paradox of special-purpose instrumental assem-
blages based on general-purpose analog modules.
Systems engineers are coming along now in greater numbers and of higher aver-
age caliber, and they are not now so brutally divided into disparate camps ofprac-
tical and theoretical people. More mutual respect, at least seems to obtain be.tween
these two sides of the track. Analog models will be increasingly resorted to by both
groups in studying the formidable problems of system engineering they must attack.
It is getting around generally that the modelling approach may best be laken in
stages. Not only should subsystems be separately modelled and carefully confirmed,
but a givcn model nced not represent ali the aspects of a given subsystem or system
at once. Linear approximations usually rcprescnt only a crude beginning. but may
be confirmed by relatively simple analysis. Nonlinear models are harder to build
but much harder to analyze, so that I’requently the approach to nonlinear structures

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