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The first signal conditioning op amps were constructed with vacuum tubes prior to the
introduction of transistors, so they were large and bulky. During the ’50s, miniature vacu-
um tubes that worked from lower voltage power supplies enabled the manufacture of op
amps that shrunk to the size of a brick used in house construction, so the op amp modules
were nicknamed bricks. Vacuum tube size and component size decreased until an op
amp was shrunk to the size of a single octal vacuum tube. Transistors were commercially
developed in the ’60s, and they further reduced op amp size to several cubic inches, but
the nickname brick still held on. Now the nickname brick is attached to any electronic mod-
ule that uses potting compound or non-integrated circuit (IC) packaging methods. Most
of these early op amps were made for specific applications, so they were not necessarily
general purpose. The early op amps served a specific purpose, but each manufacturer
had different specifications and packages; hence, there was little second sourcing among
the early op amps.
ICs were developed during the late 1950s and early 1960s, but it wasn’t till the middle
1960s that Fairchild released the µA709. This was the first commercially successful IC
op amp, and Robert J. Widler designed it. The µA709 had its share of problems, but any
competent analog engineer could use it, and it served in many different analog applica-
tions. The major drawback of the µA709 was stability; it required external compensation
and a competent analog engineer to apply it. Also, the µA709 was quite sensitive because
it had a habit of self destructing under any adverse condition. The self-destruction habit
was so prevalent that one major military equipment manufacturer published a paper titled
something like, The 12 Pearl Harbor Conditions of the µA709. The µA741 followed the
µA709, and it is an internally compensated op amp that does not require external com-
pensation if operated under data sheet conditions. Also, it is much more forgiving than
the µA709. There has been a never-ending series of new op amps released each year
since then, and their performance and reliability has improved to the point where present
day op amps can be used for analog applications by anybody.
The IC op amp is here to stay; the latest generation op amps cover the frequency spec-
trum from 5-kHz GBW to beyond 1-GHz GBW. The supply voltage ranges from guaran-
teed operation at 0.9 V to absolute maximum voltage ratings of 1000 V. The input current
and input offset voltage has fallen so low that customers have problems verifying the
specifications during incoming inspection. The op amp has truly become the universal
analog IC because it performs all analog tasks. It can function as a line driver, comparator
(one bit A/D), amplifier, level shifter, oscillator, filter, signal conditioner, actuator driver, cur-
rent source, voltage source, and many other applications. The designer’s problem is how
to rapidly select the correct circuit/op amp combination and then, how to calculate the pas-
sive component values that yield the desired transfer function in the circuit.
This book deals with op amp circuits — not with the innards of op amps. It treats the cal-
culations from the circuit level, and it doesn’t get bogged down in a myriad of detailed cal-
culations. Rather, the reader can start at the level appropriate for them, and quickly move
on to the advanced topics. If you are looking for material about the innards of op amps
