Page 78 - Analog Circuit Design Art, Science, and Personalities

8. True Analog Circuit Design
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There is no analog vs. digital circuit design. All circuits are designed paying atten-
tion to their speed, power. accuracy, size, reliability, cost, and so forth. It is only the
relative importance of these individual circuit parameters (and, of course, the mode
of their application) that is different from case to case. However, there is something
that can (with a slight twist of tongue) truly be called “analog circuit design,” i.e.,
circuit design by using analogs. This is what this chapter is all about. But first. the
story of how it all started.
In Chdpter IO, you can read how the eight-year-old Jim Williams got hooked
forever on electronics by being close to a hobbyist who owned an oscilloscope. I
would like to share a quite different experience, which nevertheless, had a long-
lasting influence too. It took place much earlier, around the year 10 BT (Before
Transistors).
A long time before taking physics in high school, a good friend of mine and I
tried desperately to understand what volts and amps really meant. No one in our
families or among our family friends was technically inclined enough to help. One
day we noticed rhal on one floor of the apartment house where 1 lived, the label on a
kilowatt-hour-meter listed IS A, while on the tloor above it said S A. We deduced
that the amps were something like water pressure, decreasing with elevation above
ground. This theory survived only until we climbed up one more floor and found
again a 1 5-A label there. Many weeks later it began to dawn on us that volts are like
pressure and amps like strength of flow. Meanwhile, our apartment house got a new
janitor in whom we naively saw a technical expert. We asked him to confirm our
analogy. Hc said: “Yes, you are close, but you have the volts and amps mixed up.”
This was a setback which took weeks to overcome.
Our first hands-on experiments took place in my friend’s home and dealt with
electric arcs. The ability to generate intense light and heat was fascinating. We used
a 1 kW smoothing iron as a series resistor and largc iron nails as electrodes. When
first joining the two nails and then pulling then1 apart, we were able to pull arcs of
up to 1 cm in length. The heal of the arc was so intense that the nail tips melted into
iron droplets. We loved it.
Our experiments were always interrupted during the summer when my friend and
I were taken out of town to separate places for vacations. That year, when school
started again and we. happily rejoined, wanted to pull arcs again, it simply did not
work anymore. We were mystified: the same wall outlet, the same smoothing iron.
the same nails, but no arc. We found out after some time that, during that summer,
the local power company had converted my friend’s home from DC to AC. A new
chapter in our “education” began.
Our getting acquainted with AC started by learning that electrical power was
delivercd to my friend’s home by four wires, three “hot” and one “safe.” We were

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