Editing Electronic oscillator (section)

===Amplitude-stabilized oscillators===
In applications where a 'pure' very low [[harmonic distortion|distortion]] sine wave is needed, such as precision [[signal generator]]s,  a nonlinear component is often used in the feedback loop that provides a 'slow' gain reduction with amplitude.  This stabilizes the loop gain at an amplitude below the saturation level of the amplifier, so it does not saturate and "clip" the sine wave.  Resistor-diode networks and [[field effect transistor|FETs]] are often used for the nonlinear element.  An older design uses a [[thermistor]] or an ordinary [[incandescent light bulb]]; both provide a resistance that increases with temperature as the current through them increases.

As the amplitude of the signal current through them increases during oscillator startup, the increasing resistance of these devices reduces the loop gain.  The essential characteristic of all these circuits is that the nonlinear gain-control circuit must have a long [[time constant]], much longer than a single [[frequency|period]] of the oscillation.  Therefore, over a single cycle they act as virtually linear elements, and so introduce very little distortion.  The operation of these circuits is somewhat analogous to an [[automatic gain control]] (AGC) circuit in a radio receiver.  The [[Wein bridge oscillator]] is a widely used circuit in which this type of gain stabilization is used.<ref name="Mancini">{{cite book
  | last = Mancini
  | first = Ron 
  | title = Op Amps for Everyone: Design Reference
  | publisher = Newnes
  | date = 2003
  | location = 
  | pages = 247–251
  | language = 
  | url = https://books.google.com/books?id=0zqU01lKPCEC&dq=wein+bridge+oscillator&pg=PA247
  | archive-url= 
  | archive-date=
  | doi = 
  | id = 
  | isbn = 9780750677011
  | mr = 
  | zbl = 
  | jfm =}}</ref>