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History
The invention of the vacuum tube in the early 1900s led to the development of amplifiers for radio, audio and other purposes. In the 1940s, scientists at Bell Laboratories developed a general theory of amplification with feedback, opening the door for general-purpose op amps based on vacuum tubes. In the 1950s and '60s, more compact and energy-efficient transistorized circuits began to replace vacuum tubes in op designs. In the 1960s and 70s, op amps took the form of integrated circuits, or ICs, combining many transistors onto a single device. Since then, most op designs have been ICs.
Description
The op integrated circuit is a single device having a plastic or ceramic body about a centimeter in size. The op has eight-wire pins bonded to the body, carrying electrical power and signals into, and out of, the circuit. Depending on the device, an 8-pin package may contain one or two separate op amps. Packages with four op amps are also common, though they are slightly larger and have more pins.
Use
Many electronic circuits used in television, radio and audio have active designs; that is, they use amplifiers to increase the gain of signals. Passive components, such as capacitors and resistors, also affect signals, but they cannot amplify. With amplification, circuits can perform complex and useful tasks, such as signal generation and conditioning. Rather than add hundreds of transistors, resistors and capacitors to an already-complex circuit, an electronics designer can use a few op amps to conveniently produce gain where it is needed. In addition to simple amplification of signals, op amps form the core of circuits like oscillators and filters. op amps also perform addition, subtraction and other mathematical operations on voltages, giving the designer sophisticated control over signals.
Electronic Characteristics
An op follows a few simple rules. Signals applied to its non-inverting input appear with the same polarity at the output; those going to the inverting input have their polarity reversed. The op shifts its output until the voltages at its two inputs match. The inputs draw no appreciable amounts of current, meaning that an op can process signals that have very low power. Some op amps, such as the 741, require a bipolar power supply with positive, negative and ground connections. Others, such as the 358, can run on a positive voltage and ground.