INTRODUCTION TO OPERATIONAL AMPLIFIERS
INTRODUCTION – WHAT ARE OPERATIONAL AMPLIFIERS?
An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands of times larger than the voltage difference between its input terminals. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network). Differential signaling is a method of transmitting information electrically with two complementary signals sent on two paired wires, called a differential pair. The op-amp is today thought of as quintessentially a differential amplifier, responding to the difference of the input voltages while (hopefully) ignoring any common-mode component. The history of differential amplifiers goes back to that great man Alan Blumlein, and his 1936 patent  for a pair of valves with their cathodes connected to ground through a common resistor. However, the first valve-based operational amplifiers, i.e. those intended to be capable of performing a mathematical operation, were in fact not differential at all, having only one input. That had to be an inverting input, of course, so you could apply negative feedback. The first op-amp to get real exposure in the UK was the Fairchild uA709, designed by the...
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