Download Op-amps Brandon King

Running head: OPERATIONAL AMPLIFIERS
Operational Amplifiers
Brandon King
Columbus High School
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OPERATIONAL AMPLIFIERS
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Abstract
The objective of this paper is to briefly discuss the purpose, history, and applications of
operational amplifiers. The general purpose of operational amplifiers, or op-amps, is to amplify
or increase voltage in a circuit. An op-amp is a unique integrated circuit generally used to
increase voltage. Op-amps have two inputs of opposite polarity, and a single output, typically
with a very high gain in signal from the input signal. Op-amps were first used in the early 1940s
in analog computers, and have become a widely-used electrical component in all types of
complex integrated circuits ever since.
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The operational amplifier, or “op-amp,” was first invented in 1941 by Karl D. Swartzel
Jr. of Bell Labs. Their first major use was in artillery directors, to precisely calculate where to
fire artillery strikes to hit a moving target. These tools were originally used in World War II, and
have been improved since then, but still take advantage of op-amps’ technology. Later, in 1947,
the first op-amp with 2 opposite-polarity inputs was created, one inverting, and the other noninverting. This method, created by Loebe Julie, was far superior to the previous design. Two
years later, Edwin A. Goldberg designed the new “chopper-stabilized” op-amp. The
improvements he added made it so that the op-amp worked alongside an AC amplifier, and made
it so that the chopper could change a DC signal into AC by very quickly switching between
ground and the DC input signal. This design helped simplify many complex integrated circuits.
Operational amplifiers finally became commercially available in 1953. In 1961, due to the
creation of the transistor, a discrete IC op-amp was created. Throughout the 1960s, many
different variations of op-amps were made for different purposes. In 1970, the first low-input,
high-speed design was made using FETs (field effect transistors). In 1972, companies began
producing single sided supply op-amps. The Signetics μa741 op-amp later became one of the
most successful op-amps. Nowadays, you can find operational amplifiers in just about any
electronic device.
Operational amplifiers are now used for consumer, industrial, and scientific devices of all
kinds. Op-amps have, in fact, become one of the most commonly used electrical component in
today’s technological era. Without op-amps, very few electronic devices would be as advanced
as they currently are with the use of op-amps. They are used for converting a small voltage into a
larger current, sometimes hundreds of thousands of times greater than the input voltage. This
allows electrical engineers to save a lot of power and resources by simplifying circuitry and
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improving efficiency. Open loop operational amplifiers are most commonly used for converting
Voltages into much higher output voltages, as stated before. Closed loop op-amps are more
popular for working with smaller, more predictable output voltages. Typically, an ideal,
somewhat perfect operational amplifier has an infinite open-loop gain, infinite input
independence, no input offset voltage, infinite voltage output possibilities, infinite bandwidth, no
phase shift, no noise, and infinite power rejection ratio. Basically, all these properties are
summarized by saying the output voltage can be manipulated to anything the user wants, and the
inputs don’t draw any excess current. However, in real applications, it’s practically impossible
for all of these model characteristics of an op-amp to be met, as they would require infinite
precision and completely, impossibly perfect conditions. Most real op-amps even change slightly
based on temperature, input conditions, and many other uncontrollable variables.
Operational amplifiers typically contain three main gain stages, including a differential
amplifier, a voltage amplifier, a n output amplifier, and often other components including a
current mirror. The key of operational amplifiers is that they can turn a very small voltage into a
much larger one as easily as possible. To do this, the device takes advantage of a few major
physics laws, particularly Ohm’s Law. Ohm’s law states that V=IR, or that the potential
difference is proportional to the current through a conductor, multiplied by its resistance.
,
where 𝑖 = 𝑐𝑢𝑟𝑟𝑒𝑛𝑡, 𝑉 = 𝑣𝑜𝑙𝑡𝑎𝑔𝑒, 𝑎𝑛𝑑 𝑅 = 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒. These equations show the basic way
that the op-amps amplify the input voltage from a power source into much greater output
voltages, by varying the resistance and current. This method of voltage amplification is one of
the most revolutionary findings of nineteenth century electrical engineering, and is currently
used in millions of different electronic devices.
,
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Vacuum-tube Op-amp (1953)
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Signetics μa741Op-amp
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