Page 36 - Analog Circuit Design Art, Science, and Personalities

Jim Williams

4. Is Analog Circuit Design Dead?
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Rumor has it that analog circuit design is dead. Indeed, it is widely rcported and
accepted that rigor niortis has set in. Precious filters, integrators, and the like seem
to have been buried beneath an avalanche of microprocessors, ROMs, RAMS, and
bits and bytes. As some analog people see it (peering out from behind their barri-
cades), a digital monster has been turned loose, destroying the elegance of contin-
uous functions with a blitzing array of flipping and flopping waveforms. The intro-
duction of a ”computerized” oscil loscope-the most analog of all instruments-
with no knobs would seem to be the coup de gr4ce.
These events have produced some bizarre behavior. It has been kindly suggested,
for instance, that the few remaining analog types be rounded up and protected as an
endangered species. Colleges and universities offer fcw analog design courscs. And
soine localities have defined copies of Korn and Korn publications, the Philbr-ick
Applications Munuul, and the Linear Applicutiorzs Handbook as pornographic
material, to be kept away from engineering students‘ innocent and impressionable
minds. Sadly, a few well-known practitioners of the art are slipping across the
border (James E. Solomon has stated, for example, that *‘all classical analog tech-
niques are dead”), while more principled ones are simply leaving town.
Can all this be happening? Is it really so? Is analog dead‘? Or has the hysteria oi‘
the moment given rise to exaggeralion and distorted judgment?
lo answer these questions with any degree of intelligence and sensitivity, it is
iiccessary to consult history. And to start this process. we must examine the
patient’s body.
Analog circuit design is described using such terms as subtractor, int.egrator,
differentiator: and summing junction. These mathematical operations are performed
by that pillar of analoggery, the operational amplifier. The use of an amplifier as a
computing tool is not entirely ohvious and was first investigated before World War
11. Practical “computing amplifiers” found their first real niche inside electronic
arialog computers (as opposed to mechanical analog computers such as the Norden
bombsight or Bush’s Differential Analyzer). which werc developed in the iate 1940s
and 1950s. These machines were, by current stmdards, monstrous assemblages
made up of large numbers of amplifiers that could be programmed to integrate, sum,
differentiate, and perform a host of mathematical opcrations. Individual amplificrs
performed singular functions, but complex operations werc performed when all the
amplifiers were interconnected in any desired configuration.
Thc analog computer’s forte was its ability to model or simulate cvcnts. Analog
compiltcrs did not (lie out because analog simulations are no longer uscful or do not
approximate rruth; rather, the rise of digital machines made it enticingly easy to usc
digital fakery to sirnulute the sinrulalions.

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