ABSTRACT
The concept of the operational amplifier (usually referred to as an op amp) originated at the beginning
of the Second World War with the use of vacuum tubes in dc amplifier designs developed by the
George A. Philbrick Co. (some of the early history of operational amplifiers is found in Williams, 1991).
The op amp was the basic building block for early electronic servomechanisms, for synthesizers, and in
particular for analog computers used to solve differential equations. With the advent of the first
monolithic integrated-circuit (IC) op amp in 1965 (the mA709, designed by the late Bob Widlar, then with
Fairchild Semiconductor), the availability of op amps was no longer a factor, while within a few years the
cost of these devices (which had been as high as $200 each) rapidly plummeted to close to that of
individual discrete transistors.
