Editing Electronic oscillator (section)

==History==
The first practical oscillators were based on [[electric arc]]s, which were used for lighting in the 19th century. The current through an [[arc lamp|arc light]] is unstable due to its [[negative resistance]], and often breaks into spontaneous oscillations, causing the arc to make hissing, humming or howling sounds{{sfn|Hong|2001|p=161-165}} which had been noticed by [[Humphry Davy]] in 1821, [[Benjamin Silliman]] in 1822,<ref>{{cite book | url=https://archive.org/details/firstprinciples05sillgoog | page=[https://archive.org/details/firstprinciples05sillgoog/page/n653 629] |quote=Davy Silliman Hissing. |title=First Principles of Physics: Or Natural Philosophy, Designed for the Use of Schools and Colleges |publisher=H.C. Peck & T. Bliss |last1=Silliman |first1=Benjamin |year=1859}}</ref> [[Auguste Arthur de la Rive]] in 1846,<ref>{{cite web |url=https://archive.org/details/wirelesstelephon00ruhmrich|title=Wireless telephony, in theory and practice |year=1908 |publisher=N.Y. Van Nostrand}}</ref> and [[David Edward Hughes]] in 1878.<ref>{{cite journal |doi=10.1007/BF00611436 |title= The humming telephone as an acoustic maser |journal=[[Optical and Quantum Electronics]]|volume = 23 |issue=8 |pages=995–1010 |year=1991 |author1-link=Lee Wendel Casperson |last1=Casperson |first1=L. W |bibcode= 1991OQEle..23..995C |s2cid=119956732}}</ref> [[Ernst Lecher]] in 1888 showed that the current through an electric arc could be oscillatory.<ref name="Anders">{{cite book |last1=Anders |first1=André |title=Cathodic Arcs: From Fractal Spots to Energetic Condensation |publisher=Springer Science and Business Media |date=2009 |pages=31–32 |url=https://books.google.com/books?id=rwIUhsbBHQYC&pg=PA31 |isbn=978-0387791081}}</ref><ref name="Cady">{{cite journal |last1=Cady |first1=W. G. |last2=Arnold |first2=H. D. |title=On the electric arc between metallic electrodes |journal=American Journal of Science |volume=24 |issue=143 |pages=406 |date=1907 |url=https://books.google.com/books?id=0KD0BuvSOokC&pg=PA406 |access-date=April 12, 2017}}</ref><ref name="Ayrton">{{cite journal |title=Notes |journal=The Electrical Review |volume=62 |issue=1578 |pages=812 |date=February 21, 1908 |url=https://books.google.com/books?id=it9QAAAAYAAJ&pg=PA312 |access-date=April 12, 2017}}</ref>

An oscillator was built by [[Elihu Thomson]] in 1892{{sfn|Morse|1925|p=23}}<ref>{{cite patent |inventor-first=Elihu |inventor-last=Thomson |title=Method of and Means for Producing Alternating Currents |country-code=US |patent-number=500630 |publication-date=18 July 1892 |issue-date=4 July 1893 |doi=}}</ref> by placing an [[LC circuit|LC tuned circuit]] in parallel with an electric arc and included a magnetic blowout. Independently, in the same year, [[George Francis FitzGerald]] realized that if the damping resistance in a resonant circuit could be made zero or negative, the circuit would produce oscillations, and, unsuccessfully, tried to build a negative resistance oscillator with a dynamo, what would now be called a [[parametric oscillator]].<ref name="Fitzgerald">G. Fitzgerald, ''On the Driving of Electromagnetic Vibrations by Electromagnetic and Electrostatic Engines'', read at the January 22, 1892, meeting of the Physical Society of London, in {{cite book |editor-last=Larmor |editor-first=Joseph |title=The Scientific Writings of the late George Francis Fitzgerald |publisher=Longmans, Green and Co. |date=1902 |location=London |pages=277–281 |url=https://books.google.com/books?id=G0bPAAAAMAAJ&pg=PA277}}</ref>{{sfn|Hong|2001|p=161-165}} The arc oscillator was rediscovered and popularized by [[William Duddell]] in 1900.{{sfn|Morse|1925|pp=80&ndash;81}}<ref>{{cite patent |inventor-first=William du Bois |inventor-last=Duddell |inventorlink=William Duddell |title=Improvements in and connected with Means for the Conversion of Electrical Energy, Derived from a Source of Direct Current, into Varying or Alternating Currents |country-code=GB |patent-number=190021629 |publication-date=29 Nov 1900 |issue-date=23 Nov 1901 |doi=}}</ref> Duddell, a student at London Technical College, was investigating the hissing arc effect.  He attached an [[LC circuit]] (tuned circuit) to the electrodes of an arc lamp, and the negative resistance of the arc excited oscillation in the tuned circuit.{{sfn|Hong|2001|p=161-165}} Some of the energy was radiated as sound waves by the arc, producing a musical tone. Duddell demonstrated his oscillator before the London [[Institute of Electrical Engineers]] by sequentially connecting different tuned circuits across the arc to play the national anthem "[[God Save the King|God Save the Queen]]".{{sfn|Hong|2001|p=161-165}} Duddell's "singing arc" did not generate frequencies above the audio range.<!-- no mag blowout --> In 1902 Danish physicists [[Valdemar Poulsen]] and P. O. Pederson were able to increase the frequency produced into the radio range by operating the arc in a hydrogen atmosphere with a magnetic field, inventing the [[Poulsen arc]] [[radio transmitter]], the first continuous wave radio transmitter, which was used through the 1920s.{{sfn|Morse|1925|p=31}}<ref>{{cite patent |inventor-first=Valdemar |inventor-last=Poulsen |inventor-link=Valdemar Poulsen |title=Improvements relating to the Production of Alternating Electric Currents |country-code=GB |patent-number=190315599 |publication-date= |issue-date=14 July 1904 |doi=}}</ref><ref>{{cite patent |inventor-first=Valdemar |inventor-last=Poulsen |inventor-link=Valdemar Poulsen |title=Method of Producing Alternating Currents with a High Number of Vibrations |country-code=US |patent-number=789449 |publication-date= |issue-date=9 May 1905 |doi=}}</ref>

[[File:Parallel rod push-pull 120MHz oscillator.jpg|thumbnail|A 120&nbsp;MHz oscillator from 1938 using a parallel rod [[transmission line]] resonator ([[Lecher line]]). Transmission lines are widely used for UHF oscillators.]]
The vacuum-tube feedback oscillator was invented around 1912, when it was discovered that feedback ("regeneration") in the recently invented [[audion|audion (triode)]] [[vacuum tube]] could produce oscillations.  At least six researchers independently made this discovery, although not all of them can be said to have a role in the invention of the oscillator.<ref name=" Hempstead">{{cite book |last=Hempstead |first=Colin |author2=William E. Worthington |title=Encyclopedia of 20th-Century Technology |volume=2 |publisher=Taylor & Francis |year=2005 |page=648 |url=https://books.google.com/books?id=0wkIlnNjDWcC&pg=PA648 |isbn=978-1579584641}}</ref>{{sfn|Hong|2001|p=156}}  In the summer of 1912, [[Edwin Armstrong]] observed oscillations in audion [[radio receiver]] circuits<ref name="Fleming">{{cite book |last=Fleming |first=John Ambrose |title=The Thermionic Valve and its Developments in Radiotelegraphy and Telephony |publisher=The Wireless Press |year=1919 |location=London |pages=148&ndash;155 |url=https://books.google.com/books?id=ZBtDAAAAIAAJ&pg=PA148}}</ref> and went on to use positive feedback in his invention of the [[regenerative receiver]].{{sfn|Hong|2003|p=9-10}}<ref name="Armstrong">{{cite journal |last=Armstrong |first=Edwin H. |title=Some recent developments in the Audion receiver |journal=Proc. IRE |volume=3 |issue=9 |pages=215&ndash;247 |date=September 1915 |url=http://www.ieee.org/documents/00573757.pdf |archive-url=https://web.archive.org/web/20130728164117/http://www.ieee.org/documents/00573757.pdf |url-status=dead |archive-date=July 28, 2013 |access-date=August 29, 2012 |doi= 10.1109/jrproc.1915.216677|s2cid=2116636}}</ref>  Austrian [[Alexander Meissner]] independently discovered positive feedback and invented oscillators in March 1913.<ref name="Fleming" />{{sfn|Hong|2003|p=13}} [[Irving Langmuir]] at General Electric observed feedback in 1913.{{sfn|Hong|2003|p=13}}  Fritz Lowenstein may have preceded the others with a crude oscillator in late 1911.{{sfn|Hong|2003|p=5}}  In Britain, H. J. Round patented amplifying and oscillating circuits in 1913.<ref name="Fleming" />  In August 1912, [[Lee De Forest]], the inventor of the audion, had also observed oscillations in his amplifiers, but he didn't understand the significance and tried to eliminate it{{sfn|Hong|2003|pp=6&ndash;7}}<ref name="Hijiya">{{cite book |last=Hijiya |first=James A. |title=Lee De Forest and the Fatherhood of Radio |publisher=Lehigh University Press |year=1992 |pages=89&ndash;90 |url=https://books.google.com/books?id=JYylHhmoNZ4C&pg=PA89 |isbn=978-0934223232}}</ref> until he read Armstrong's patents in 1914,{{sfn|Hong|2003|p=14}} which he promptly challenged.<ref name="Nahin">{{cite book
 | last = Nahin
 | first = Paul J.
 | title = The Science of Radio: With Matlab and Electronics Workbench Demonstration, 2nd Ed
 | publisher = Springer
 | year = 2001
 | pages = 280
 | url = https://books.google.com/books?id=V1GBW6UD4CcC&pg=PA82
 | isbn = 978-0387951508}}</ref>  Armstrong and De Forest fought a protracted legal battle over the rights to the "regenerative" oscillator circuit<ref name="Nahin" />{{sfn|Hong|2001|pp=181&ndash;189}} which has been called "the most complicated patent litigation in the history of radio".{{sfn|Hong|2003|p=2}} De Forest ultimately won before the Supreme Court in 1934 on technical grounds, but most sources regard Armstrong's claim as the stronger one.<ref name="Hijiya" /><ref name="Nahin" />

The first and most widely used relaxation oscillator circuit, the [[astable multivibrator]], was invented in 1917 by French engineers Henri Abraham and Eugene Bloch.<ref name="Abraham">{{cite journal
 | last = Abraham
 | first = H.
 | author2=E. Bloch
 | title = Measurement of period of high frequency oscillations
 | journal = Comptes Rendus
 | volume = 168
 | pages = 1105
 | year = 1919
 }}</ref><ref name="Glazebrook">{{cite book
 | last = Glazebrook
 | first = Richard
 | title = A Dictionary of Applied Physics, Vol. 2: Electricity
 | publisher = Macmillan and Co. Ltd.
 | year = 1922
 | location = London
 | pages = 633–634
 | url = https://books.google.com/books?id=bavQAAAAMAAJ&pg=PA633
 }}</ref><ref name="Calvert">{{cite web
 | last = Calvert
 | first = James B.
 | title = The Eccles-Jordan Circuit and Multivibrators
 | publisher =  Dr. J. B. Calvert website, Univ. of Denver
 | year = 2002
 | url = http://mysite.du.edu/~etuttle/electron/elect36.htm
 | access-date = May 15, 2013}}</ref>  They called their cross-coupled, dual-vacuum-tube circuit a ''multivibrateur'', because the square-wave signal it produced was rich in [[harmonic]]s,<ref name="Glazebrook" /><ref name="Calvert" /> compared to the sinusoidal signal of other vacuum-tube oscillators.

Vacuum-tube feedback oscillators became the basis of radio transmission by 1920.  However, the [[triode]] vacuum tube oscillator performed poorly above 300&nbsp;MHz because of interelectrode capacitance.<ref>{{Cite web |last=Peto |first=David Charles |title=The vacuum tube triode at ultra high frequencies |url=https://core.ac.uk/download/pdf/36724402.pdf |access-date=July 8, 2024}}</ref>  To reach higher frequencies, new "transit time" (velocity modulation) vacuum tubes were developed, in which electrons traveled in "bunches" through the tube.  The first of these was the [[Barkhausen–Kurz tube|Barkhausen–Kurz oscillator]] (1920), the first tube to produce power in the [[Ultra high frequency|UHF]] range.  The most important and widely used were the [[klystron]] (R. and S. Varian, 1937) and the cavity [[magnetron]] (J. Randall and H. Boot, 1940).

Mathematical conditions for feedback oscillations, now called the [[Barkhausen stability criterion|Barkhausen criterion]], were derived by [[Heinrich Georg Barkhausen]] in 1921. He also showed that all linear oscillators must have negative resistance.<ref name="Duncan">The requirements for negative resistance in oscillators were first set forth by [[Heinrich Barkhausen]] in 1907 in [https://archive.org/details/dasproblemdersc01barkgoog ''Das Problem Der Schwingungserzeugung''] according to {{cite journal
  | last = Duncan
  | first = R. D.
  | title = Stability conditions in vacuum tube circuits
  | journal = Physical Review
  | volume = 17
  | issue = 3
  | page = 304
  | date = March 1921
  | url = https://books.google.com/books?id=rCgKAAAAIAAJ&q=%22negative+resistance&pg=PA304
  | doi = 10.1103/physrev.17.302
  | access-date = July 17, 2013 | bibcode = 1921PhRv...17..302D }}:  "''For alternating current power to be available in a circuit which has externally applied only continuous voltages, the average power consumption during a cycle must be negative...which demands the introduction of negative resistance ''[which]'' requires that the phase difference between voltage and current lie between 90° and 270°...''[and for nonreactive circuits]'' the value 180° must hold... The volt-ampere characteristic of such a resistance will therefore be linear, with a negative slope...''"</ref>  The first analysis of a nonlinear electronic oscillator model, the [[Van der Pol oscillator]], was done by [[Balthasar van der Pol]] in 1927.<ref name="Van der Pol">{{cite journal
 | last = Van der Pol
 | first = Balthazar
 | title = On relaxation-oscillations
 | journal = The London, Edinburgh and Dublin Philosophical Magazine
 | volume = 2
 | issue = 7
 | pages = 978–992
 | year = 1927
 | url = http://audiophile.tam.cornell.edu/randdocs/classics/vanderpol.pdf
 | doi = 10.1080/14786442608564127
 }}</ref>  He originated the term "relaxation oscillation" and was first to distinguish between linear and relaxation oscillators.  He showed that the stability of the oscillations ([[limit cycle]]s) in actual oscillators was due to the [[linear circuit|nonlinearity]] of the amplifying device.   Further advances in mathematical analysis of oscillation were made by [[Hendrik Wade Bode]] and [[Harry Nyquist]]<ref name="Nyquist">{{cite journal
 | last = Nyquist
 | first = H.
 | title = Regeneration Theory
 | journal = Bell System Tech. J.
 | volume = 11
 | issue = 1
 | pages = 126–147
 | date = January 1932
 | url = http://www3.alcatel-lucent.com/bstj/vol11-1932/articles/bstj11-1-126.pdf
 | doi = 10.1002/j.1538-7305.1932.tb02344.x
 | s2cid = 115002788
 | access-date = December 5, 2012}} on [http://www.alcatel-lucent.com   Alcatel-Lucent website]</ref> in the 1930s.  In 1969 Kaneyuki Kurokawa derived necessary and sufficient conditions for oscillation in negative-resistance circuits,<ref name="Kurokawa">{{cite journal
 | last = Kurokawa
 | first = Kaneyuki
 | title = Some Basic Characteristics of Broadband Negative Resistance Oscillator Circuits
 | journal = Bell System Tech. J.
 | volume = 48
 | issue = 6
 | pages = 1937–1955
 | date = July 1969
 | url = http://www3.alcatel-lucent.com/bstj/vol48-1969/articles/bstj48-6-1937.pdf
 | doi = 10.1002/j.1538-7305.1969.tb01158.x
 | access-date = December 8, 2012}}  Eq. 10 is a necessary condition for oscillation; eq. 12 is a sufficient condition,</ref> which form the basis of modern microwave oscillator design.<ref name="Maas">{{cite book
 | last = Maas
 | first = Stephen A.
 | title = Nonlinear Microwave and RF Circuits, 2nd Ed
 | publisher = Artech House
 | year = 2003
 | pages = 542–544
 | url = https://books.google.com/books?id=SSw6gWLG-d4C&pg=PA542
 | isbn = 978-1580534840}}</ref>