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How does LC phase shift oscillator work?

  1. Nov 24, 2011 #1
    Heya Everyone :blushing:

    Im slightly confused as to how LC phase shift oscillator work ?

    Its a circuit consisting of 1 op-amp ( used as oscillator), 1 LC loop, few resistors. The op-amp has a reference voltage applied to the non-inverting end (+ve).

    The inverting end has a feedback resistor and the Vout from the LC loop connected. It looks something like this, except replace the 3RC with 1 LC - http://www.play-hookey.com/oscillators/phase_shift_oscillator.html [Broken]

    Ok so whatever Ive read on the internet- 1LC circuit has 2 poles ( not sure what that means ) ,thus it contributes up to 180 degree phase shift per pole pair. RC circuit has a 60 degree phase shift and hence we require 3 of them !

    Now, oscillation occur at the frequency were the total phase shift through 1 LC or 3 RC is 180 degree ( WHY????)

    Could someone please explain to me how this works? As im totally LOST !:confused:

    Thanks :smile:
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 28, 2011 #2
    The CR combination is a PHASE SHIFT oscillator, each section is designed to give 60 phase shift and therefore a total of 180 for oscillation.
    An LC oscillator is a RESONANCE oscillator. At a frequency determined by Xc =Xl resonsnce occurs and it is this frequency that is amplified to be the oscillator frequency
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