Editing Electronic oscillator (section)

===Negative-resistance oscillator===
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| image1   = Negative resistance oscillator.svg
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| image2   = Ganna gjenerators M31102-1.jpg
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| footer   = ''(left)'' Typical block diagram of a negative resistance oscillator. In some types the negative resistance device is connected in parallel with the resonant circuit.  ''(right)'' A negative-resistance microwave oscillator consisting of a [[Gunn diode]] in a [[cavity resonator]].  The negative resistance of the diode excites microwave oscillations in the cavity, which radiate out the aperture into a [[waveguide]].
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In addition to the feedback oscillators described above, which use [[two-port network|two-port]] amplifying active elements such as transistors and operational amplifiers, linear oscillators can also be built using [[port (circuit theory)|one-port]] (two terminal) devices with [[negative resistance]],<ref name="Chattopadhyay" /><ref name="Garg" /> such as [[magnetron]] tubes, [[tunnel diode]]s, [[IMPATT diode]]s and [[Gunn diode]]s.<ref name=" Raisanen" /><ref name="Solymar" />{{rp|p.197–198}}{{sfn|Gottlieb|1997|p=103}}  Negative-resistance oscillators are usually used at high frequencies in the [[microwave]] range and above, since at these frequencies feedback oscillators perform poorly due to excessive phase shift in the feedback path.

In negative-resistance oscillators, a resonant circuit, such as an [[LC circuit]], [[crystal oscillator|crystal]], or [[Resonator#Cavity resonators|cavity resonator]], is connected across a device with [[negative differential resistance]], and a DC bias voltage is applied to supply energy.  A resonant circuit by itself is "almost" an oscillator; it can store energy in the form of electronic oscillations if excited, but because it has electrical resistance and other losses the oscillations are [[Harmonic oscillator#Damped harmonic oscillator|damped]] and decay to zero.<ref name="Edson">{{cite book
  | last = Edson
  | first = William A.
  | title = Vacuum Tube Oscillators
  | publisher = John Wiley and Sons
  | date = 1953
  | location = 
  | pages = 7–8
  | language = 
  | url = https://archive.org/details/dli.ernet.504339/page/7/mode/2up
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  | last1  = Solymar
  | first1 = Laszlo
  | last2  = Walsh
  | first2 = Donald
  | title = Electrical Properties of Materials
  | publisher = Oxford University Press
  | date = 2009
  | location = 
  | pages = 181–182
  | language = 
  | url = https://books.google.com/books?id=AiWyp0NQW6UC&q=%22negative+resistance%22
  | archive-url= 
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  | isbn = 9780191574351
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  | jfm =}}</ref>  The negative resistance of the active device cancels the (positive) internal loss resistance in the resonator, in effect creating a resonator circuit with no damping, which generates spontaneous continuous oscillations at its [[resonant frequency]].

The negative-resistance oscillator model is not limited to one-port devices like diodes; feedback oscillator circuits with [[two-port network|two-port]] amplifying devices such as transistors and [[vacuum tube|tubes]] also have negative resistance.{{sfn|Gottlieb|1997|p=104}}<ref name="Kung">{{cite web
 | last = Kung
 | first = Fabian Wai Lee
 | title = Lesson 9: Oscillator Design
 | website = RF/Microwave Circuit Design
 | publisher = Prof. Kung's website, Multimedia University
 | year = 2009
 | url = http://pesona.mmu.edu.my/~wlkung/ADS/rf/lesson9.pdf
 | access-date = October 17, 2012
 | archive-url = https://web.archive.org/web/20150722165131/http://pesona.mmu.edu.my/~wlkung/ADS/rf/lesson9.pdf
 | archive-date = July 22, 2015
 | url-status = dead
 }}, Sec. 3 Negative Resistance Oscillators, pp. 9–10, 14</ref><ref name=" Raisanen" /><ref name="Ellinger">{{cite book
 | last = Ellinger
 | first = Frank
 | title = Radio Frequency Integrated Circuits and Technologies, 2nd Ed
 | publisher = Springer
 | year = 2008
 | location = USA
 | pages = 391–394
 | url = https://books.google.com/books?id=0pl9xYD0QNMC&pg=PA391
 | isbn = 978-3540693246}}</ref>  At high frequencies, three terminal devices such as transistors and FETs are also used in negative resistance oscillators. At high frequencies these devices do not need a feedback loop, but with certain loads applied to one port can become unstable at the other port and show negative resistance due to internal feedback.  The negative resistance port is connected to a tuned circuit or resonant cavity, causing them to oscillate.<ref name="Kung" /><ref name=" Raisanen">{{cite book
 | last =  Räisänen
 | first = Antti V.
 | author2=Arto Lehto
 | title = Radio Engineering for Wireless Communication and Sensor Applications
 | publisher = Artech House
 | year = 2003
 | location = USA
 | pages = 180–182
 | url = https://books.google.com/books?id=m8Dgkvf84xoC&pg=PA181
 | isbn = 978-1580535427}}</ref><ref name="Maas" /> High-frequency oscillators in general are designed using negative-resistance techniques.<ref name="Kung" /><ref name=" Raisanen" /><ref name="Ellinger" />