Editing Electronic oscillator (section)

===Feedback oscillator===
The most common form of linear oscillator is an [[electronic amplifier]] such as a [[transistor]] or [[operational amplifier]] connected in a [[feedback loop]] with its output fed back into its input through a frequency selective [[electronic filter]] to provide [[positive feedback]].  When the power supply to the amplifier is switched on initially, [[electronic noise]] in the circuit provides a non-zero signal to get oscillations started.{{sfn|Gottlieb|1997|p=113–114}} The noise travels around the loop and is amplified and [[Filter (signal processing)|filtered]] until very quickly it converges on a [[sine wave]] at a single frequency.

Feedback oscillator circuits can be classified according to the type of frequency selective filter they use in the feedback loop:<ref name="Chattopadhyay" /><ref name="Garg" />

*In an ''[[RC oscillator]]'' circuit, the filter is a network of [[resistor]]s and [[capacitor]]s.<ref name="Chattopadhyay" /><ref name="Garg" /> RC oscillators are mostly used to generate lower frequencies, for example in the audio range.  Common types of RC oscillator circuits are the [[phase shift oscillator]] and the [[Wien bridge oscillator]]. LR oscillators, using [[inductor]] and resistor filters also exist, however they are much less common due to the required size of an inductor to achieve a value appropriate for use at lower frequencies.

{{anchor|LC oscillator}}

[[File:Oscillator comparison.svg|thumb|right|400px|Two common LC oscillator circuits, the Hartley and Colpitts oscillators]]

*In an ''[[LC circuit| LC oscillator]]'' circuit, the filter is a [[tuned circuit]] (often called a ''tank circuit'') consisting of an [[inductor]] (L) and [[capacitor]] (C) connected together, which acts as a [[resonator]].<ref name="Chattopadhyay" /><ref name="Garg" />  Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its [[resonant frequency]]. The amplifier adds power to compensate for resistive energy losses in the circuit and supplies the power for the output signal. LC oscillators are often used at [[radio frequency|radio frequencies]],<ref name="Chattopadhyay" /> when a tunable frequency source is necessary, such as in [[signal generator]]s, tunable radio [[transmitter]]s and the [[local oscillator]]s in [[radio receiver]]s.  Typical LC oscillator circuits are the [[Hartley oscillator|Hartley]], [[Colpitts oscillator|Colpitts]]<ref name="Chattopadhyay" /> and [[Clapp oscillator|Clapp]] circuits.
*In a [[Crystal oscillator#Crystal oscillator circuits|''crystal oscillator'' circuit]] the filter is a [[piezoelectric]] crystal (commonly a [[quartz crystal]]).<ref name="Chattopadhyay" /><ref name="Garg" />  The crystal mechanically vibrates as a [[resonator]], and its frequency of vibration determines the oscillation frequency. Since the [[resonant frequency]] of the crystal is determined by its dimensions, crystal oscillators are fixed frequency oscillators, their frequency can only be adjusted over a tiny range of less than one percent.<ref name="Terman" /><ref name="Misra" /><ref name="Scroggie" />{{sfn|Gottlieb|1997|p=39-40}}  Crystals have a very high [[Q-factor]] and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most [[radio transmitter]]s, and to generate the [[clock signal]] in computers and [[quartz clock]]s. Crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the [[tuned circuit]];<ref name="Chattopadhyay" /> the [[Pierce oscillator]] circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30&nbsp;MHz or below.<ref name="Chattopadhyay" />  Other types of resonators, [[dielectric resonator]]s and [[surface acoustic wave]] (SAW) devices, are used to control higher frequency oscillators, up into the [[microwave]] range.  For example, SAW oscillators are used to generate the radio signal in [[cell phone]]s.<ref>{{Cite web|last=APITech|title=SAW Technology|url=https://info.apitech.com/saw-technology-va|access-date=2021-05-12|website=info.apitech.com|language=en}}</ref>
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