Editing Operational amplifier (section)

==Historical timeline==
'''1941: A vacuum tube op amp.''' An op amp, defined as a general-purpose, DC-coupled, high gain, inverting feedback amplifier, is first found in {{US patent|2,401,779}} "Summing Amplifier" filed by [[Karl D. Swartzel Jr.]] of Bell Labs in 1941. This design used three [[vacuum tube]]s to achieve a gain of {{nowrap|90 dB}} and operated on voltage rails of {{nowrap|±350 V}}. It had a single inverting input rather than differential inverting and non-inverting inputs, as are common in today's op amps. Throughout [[World War II]], Swartzel's design proved its value by being liberally used in the M9 [[Director (military)|artillery director]] designed at Bell Labs. This artillery director worked with the [[SCR-584 radar]] system to achieve extraordinary hit rates (near 90%) that would not have been possible otherwise.<ref name="Jung-2004">{{cite book |title=Op Amp Applications Handbook |page=777 |chapter=Chapter 8: Op Amp History |first=Walter G. |last=Jung |publisher=Newnes |year=2004 |isbn=978-0-7506-7844-5 |url=https://books.google.com/books?id=dunqt1rt4sAC |access-date=2008-11-15}}</ref>

[[Image:K2-w Vacuum Tube Op-amp.jpg|right|thumb|120px|GAP/R K2-W: a vacuum-tube op amp (1953)]]

'''1947: An op amp with an explicit non-inverting input.''' In 1947, the operational amplifier was first formally defined and named in a paper by [[John R. Ragazzini]] of Columbia University.<ref>{{cite journal |last1=Ragazzini |first1=John R. |author1-link=John R. Ragazzini |last2=Randall |first2=Robert H. |last3=Russell |first3=Frederick A. |title=Analysis of Problems in Dynamics by Electronic Circuits |journal=Proceedings of the IRE |volume=35 |issue=5 |pages=444–452 |publisher=IEEE |date=May 1947 |issn=0096-8390 |doi=10.1109/JRPROC.1947.232616}}</ref> In this same paper a footnote mentioned an op-amp design by a student that would turn out to be quite significant. This op amp, designed by [[Loebe Julie]], had two major innovations. Its input stage used a long-tailed [[triode]] pair with loads matched to reduce drift in the output and, far more importantly, it was the first op-amp design to have two inputs (one inverting, the other non-inverting). The differential input made a whole range of new functionality possible, but it would not be used for a long time due to the rise of the chopper-stabilized amplifier.<ref name="Jung-2004"/>

'''1949: A chopper-stabilized op amp.''' In 1949, Edwin A. Goldberg designed a [[Chopper (electronics)|chopper]]-stabilized op amp.<ref>{{cite web |url=http://www.analog.com/library/analogDialogue/archives/39-05/Web_ChH_final.pdf |title=Op Amp Applications |publisher=[[Analog Devices]] |access-date=2012-12-27 |url-status=dead |archive-url=https://web.archive.org/web/20121007072916/http://www.analog.com/library/analogDialogue/archives/39-05/Web_ChH_final.pdf |archive-date=2012-10-07 }}</ref> This set-up uses a normal op amp with an additional [[Alternating current|AC]] amplifier that goes alongside the op amp. The chopper gets an AC signal from [[Direct current|DC]] by switching between the DC voltage and ground at a fast rate (60 or 400&nbsp;Hz). This signal is then amplified, rectified, filtered and fed into the op amp's non-inverting input. This vastly improved the gain of the op amp while significantly reducing the output drift and DC offset. Unfortunately, any design that used a chopper couldn't use the non-inverting input for any other purpose. Nevertheless, the much-improved characteristics of the chopper-stabilized op amp made it the dominant way to use op amps. Techniques that used the non-inverting input were not widely practiced until the 1960s when op-amp [[Integrated circuit|IC]]s became available.<!--[[User:Kvng/RTH]]-->

'''1953: A commercially available op amp.''' In 1953, vacuum tube op amps became commercially available with the release of the model K2-W from [[George A. Philbrick]] Researches, Incorporated. The designation on the devices shown, GAP/R, is an acronym for the complete company name. Two nine-pin [[12AX7]] vacuum tubes were mounted in an octal package and had a model K2-P chopper add-on available that would effectively "use up" the non-inverting input. This op amp was based on a descendant of Loebe Julie's 1947 design and, along with its successors, would start the widespread use of op amps in industry.

[[Image:Discrete opamp.png|right|thumb|120px|GAP/R model P45: a solid-state, discrete op amp (1961).]]

'''1961: A discrete IC op amp.''' With the birth of the [[transistor]] in 1947, and the silicon transistor in 1954, the concept of ICs became a reality. The introduction of the [[planar process]] in 1959 made transistors and ICs stable enough to be commercially useful. By 1961, solid-state, discrete op amps were being produced. These op amps were effectively small circuit boards with packages such as [[edge connector]]s. They usually had hand-selected resistors in order to improve things such as voltage offset and drift. The P45 (1961) had a gain of 94&nbsp;dB and ran on ±15&nbsp;V rails. It was intended to deal with signals in the range of {{nowrap|±10 V}}.

'''1961: A varactor bridge op amp.''' There have been many different directions taken in op-amp design. [[Varactor]] bridge op amps started to be produced in the early 1960s.<ref>{{cite web |url=http://www.philbrickarchive.org/ |title=The Philbrick Archive |website=www.philbrickarchive.org |access-date=28 April 2018 |url-status=live |archive-url=https://archive.today/20120907192216/http://www.philbrickarchive.org/ |archive-date=7 September 2012 }}</ref><ref>June 1961 advertisement for Philbrick P2, {{cite web |url=http://www.philbrickarchive.org/p2%20and%206033%20ad%20rsi%20vol32%20no6%20june1961.pdf |title=The all-new, all solid-state Philbrick P2 amplifier |access-date=2011-05-11 |url-status=live |archive-url=https://web.archive.org/web/20111008160503/http://www.philbrickarchive.org/p2%20and%206033%20ad%20rsi%20vol32%20no6%20june1961.pdf |archive-date=2011-10-08 }}</ref> They were designed to have extremely small input current and are still amongst the best op amps available in terms of common-mode rejection with the ability to correctly deal with hundreds of volts at their inputs.

[[Image:Modular opamp.png|right|thumb|120px|GAP/R model PP65: a solid-state op amp in a potted module (1962)]]

'''1962: An op amp in a potted module.''' By 1962, several companies were producing modular potted packages that could be plugged into [[printed circuit board]]s.{{Citation needed|date=January 2009}} These packages were crucially important as they made the operational amplifier into a single [[black box]] which could be easily treated as a component in a larger circuit.

'''1963: A monolithic IC op amp.''' In 1963, the first monolithic IC op amp, the μA702 designed by [[Bob Widlar]] at Fairchild Semiconductor, was released. Monolithic [[Integrated circuit|IC]]s consist of a single chip as opposed to a chip and discrete parts (a discrete IC) or multiple chips bonded and connected on a circuit board (a hybrid IC). Almost all modern op amps are monolithic ICs; however, this first IC did not meet with much success. Issues such as an uneven supply voltage, low gain and a small dynamic range held off the dominance of monolithic op amps until 1965 when the μA709<ref>{{cite book |first=A. P. |last=Malvino |title=Electronic Principles |edition=2nd |date=1979 |isbn=0-07-039867-4 |page=[https://archive.org/details/electronicprinci00malv/page/476 476] |publisher=McGraw-Hill |url=https://archive.org/details/electronicprinci00malv/page/476 }}</ref> (also designed by Bob Widlar) was released.

'''1968: Release of the μA741.''' The popularity of monolithic op amps was further improved upon the release of the LM101 in 1967, which solved a variety of issues, and the subsequent release of the μA741 in 1968. The μA741 was extremely similar to the LM101 except that Fairchild's facilities allowed them to include a 30&nbsp;pF compensation capacitor inside the chip instead of requiring external compensation. This simple difference has made the 741 ''the'' canonical op amp and many modern amps base their pinout on the 741s. The μA741 is still in production, and has become ubiquitous in electronics—many manufacturers produce a version of this classic chip, recognizable by part numbers containing ''741''. The same part is manufactured by several companies.

'''1970: First high-speed, low-input current FET design.'''
In the 1970s high speed, low-input current designs started to be made by using [[FET]]s. These would be largely replaced by op amps made with [[MOSFET]]s in the 1980s. 
[[Image:LH033CG.jpg|right|thumb|120px|LH0033CG: a  high speed hybrid IC  op amp]]

'''1972: Single sided supply op amps being produced.''' A single sided supply op amp is one where the input and output voltages can be as low as the negative power supply voltage instead of needing to be at least two volts above it. The result is that it can operate in many applications with the negative supply pin on the op amp being connected to the signal ground, thus eliminating the need for a separate negative power supply.

The LM324 (released in 1972) was one such op amp that came in a quad package (four separate op amps in one package) and became an industry standard. In addition to packaging multiple op amps in a single package, the 1970s also saw the birth of op amps in hybrid packages. These op amps were generally improved versions of existing monolithic op amps. As the properties of monolithic op amps improved, the more complex hybrid ICs were quickly relegated to systems that are required to have extremely long service lives or other specialty systems.

[[Image:LM741CN.jpg|right|thumb|120px|An op amp in a mini DIP package]]

'''Recent trends.''' Recently{{when?|date=February 2023}} supply voltages in analog circuits have decreased (as they have in digital logic) and low-voltage op amps have been introduced reflecting this. Supplies of 5&nbsp;V and increasingly 3.3&nbsp;V (sometimes as low as 1.8&nbsp;V) are common. To maximize the signal range modern op amps commonly have rail-to-rail output (the output signal can range from the lowest supply voltage to the highest) and sometimes rail-to-rail inputs.<ref name="rail-to-rail" />