Reference STATE OF THE ART Stan Augarten

ISBN 0-89919-195-9

Photo of
The First Linear IC
The µA702 Operational Amplifier


One of the great divides in the IC's Lilliputian realm lies between digital and linear circuits. Digital chips can process only binary impulses, the on and off language of computers and most electronic machines, whereas linear ICs react only to analog, or continuous, input. To understand the difference, think of digital watches and ordinary timepieces: one tells the time by means of flashing numbers that grow by increments of one, and only one; the other does the job with continuously rotating hands.

  The chip on the right is a highly versatile piece of microelectronics known as an operational amplifier, or op amp. It has hundreds of uses, although it's probably most frequently employed as a difference amplifier, a circuit that compares incoming signals and reports on their disparity. An op amp like the µA702 (the µ stands for micro, the A for amplifier) might be used, for instance, in a temperature-sensing device called a thermocouple, which consists of a closed circuit made up of two different metals, and which is found in most ovens. When the temperature changes, the voltage passing through the circuit climbs or falls, and the op amp senses and registers the shift.

  An op amp can not only add or subtract incoming signals but can also average, integrate, and otherwise manipulate them. As a result, it's widely employed in control, measurement, and computational systems. It's even useful in certain digital equipment, as an intermediary of sorts between analog and digital machines. As the first op amp on a chip, the µA702, which was designed by Robert Widlar, was a significant milestone in IC history, and a commercial success for Fairchild.

The µA702 can amplify incoming signals up to seven thousand times. It has twelve bipolar transistors and five resistors. The transistors are the small greenish rectangular features on either side of the chip's central spine (the thick white bar with the square pad at the base); two transistors, lying on opposite sides of the upside-down T-shaped feature in the center, are unconnected. The resistors are the light brown loops and line; the aluminum connectors are the thick white bars. The boxlike dark brown moats are the extruding portions of isolation channels. Actual size: 0.60 inches. Photo of


©Copyright Stan Augarten
This book is provided for general reference. The National Museum of American History and the Smithsonian Institution make no claims as to the accuracy or completeness of this work.

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