Overview

Many of the analog and linear integrated circuits that have been developed over the past 20 years are now recognized electronic building blocks. They continue to perform vital functions in circuits, products, and systems despite the significant gains made in digital circuitry. All circuits are either linear or digital, but some people distinguish between linear and analog circuits. Linear circuits are broadly defined as those whose outputs vary in direct proportion to their inputs, but analog circuits are considered to be a subset of linear circuits that represent physical quantities such as velocity, pressure, and temperature by variable values of voltage, current, or resistance. Many analog circuits were originally developed for use in analog computers.

Analog circuits generally include operational amplifiers, comparators, and both analog-to-digital and digital-to-analog converters. They were originally designed as vacuum-tube circuits, but they were subsequently redesigned with transistors. They were then offered commercially as discrete transistor modules, while others were made as proprietary hybrid circuits. The most popular analog circuits were then manufactured as monolithic ICs, which became available as standard catalog or off-the-shelf devices.

But discrete modules and hybrid ICs continued to be made long after the introduction of monolithic ICs because the commodity ICs were unable to achieve the higher speed or higher precision required for some applications. Later commodity ICs were included in modules and hybrid circuits to reduce the discrete device count, but they were still supplemented with off-chip precision resistors and capacitors for performance improvements.

Conventional low-frequency and...