Electronic Engineering 15

Integrated circuits were made possible by experimental discoveries which showed that semiconductor devices could perform the functions of vacuum tubes and by mid-20th-century technology advancements in semiconductor device fabrication. The integration of large numbers of tiny transistors into a small chip was an enormous improvement over the manual assembly of circuits using electronic components. The integrated circuit's mass production capability, reliability, and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of designs using discrete transistors.

Integrated circuits can be classified into analog, digital

and mixed signal (analog and digital on the same chip). Digital integrated circuits can contain anything from

one to millions of logic gates, flip-flops, multiplexers, and other circuits in a few square millimeters. Digital ICs, typically microprocessors, DSPs, and micro controllers work using binary mathematics to process "one" and "zero" signals.

Analog ICs, such as sensors, power management circuits, and operational amplifiers, work by processing continuous signals. They perform functions like amplification, active filtering, demodulation, mixing, etc.

ICs can also combine analog and digital circuits on a single chip to create functions such as A/D converters and D/A converters. Such circuits offer smaller size and lower cost, but must carefully account for signal interference.

The first integrated circuits contained only a few transistors. Called "Small-Scale Integration" (SSI), digital circuits containing transistors numbering in the tens provided a few logic gates for example, while early linear ICs such as the Plessey SL201 or the Philips TAA320 had as few as two transistors.

SSI circuits were crucial to early aerospace projects, and vice-versa. Both the Minuteman missile and Apollo program needed lightweight digital computers for their inertial guidance systems.

The next step in the development of integrated circuits (1960s) introduced devices which contained hundreds of transistors on each chip, called "Medium-Scale Integration" (MSI). They were attractive economically because they allowed more complex systems to be produced using smaller circuit boards, less assembly work and had a number of other advantages.

Further development led to "Large-Scale Integration" (LSI) (1970s) with tens of thousands of transistors per chip.