phase shift oscillator

Discussion in 'General Electronics Chat' started by anjanakg, Nov 23, 2012.

  1. anjanakg

    Thread Starter New Member

    Nov 23, 2012
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    Is there any provision to design the phase shift of a phase shift oscillator?
     
  2. ScottWang

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    Aug 23, 2012
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    RC BJT phase shift oscillator?
    RC Transistor phase shift oscillator?
    LC BJT phase shift oscillator?
    LC Transistor phase shift oscillator?
    RC Op Amp phase shift oscillator?
    LC Op Amp phase shift oscillator?
    Using the above keywords to search on this forum or google.
     
  3. ramancini8

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    Jul 18, 2012
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    The stage gain including the feedback attenuation must be greater than one. The feedback must be in phase. The common circuit shown in the literature is wrong because it does not account for interstage loading.
     
  4. The Electrician

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    Oct 9, 2007
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    Could you give a link to such a circuit where the interstage loading is not accounted for?
     
  5. Audioguru

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    Dec 20, 2007
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    See pages 14, 15 and 16.
     
  6. ramancini8

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    Jul 18, 2012
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    See, I told you so. P.S. I wrote this app note with a helper.
     
  7. Audioguru

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    Hi Ron, SIR!
    Thanks for the excellent app note.
     
  8. The Electrician

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    You said in post #3 of this forum thread, "The common circuit shown in the literature is wrong because it does not account for interstage loading."

    On page 15 of your app note, you said "The usual assumption is that the phase shift sections are independent of each other, allowing equation 14 to be written."

    I don't agree that it is the usual assumption. The discussions about 3 stage phase shift oscillators without buffers between the stages that I find with a search of the web say that the required amplifier gain is 29, not 8. They also say that the frequency of oscillation is sqrt(6)/(2 Pi R C), not sqrt(3)/(2 Pi R C).

    I only found one page (http://www.play-hookey.com/oscillators/audio/phase_shift_oscillator.html) that starts with the (seemingly uncommon, based on my search results) assumption that the unbuffered stages of the phase shifting network don't experience loading effects.

    In your app note you said, "...however, the biggest factor is the incorrect assumption that the RC sections do not load each other". You stated the assumption and then showed that it leads to incorrect results (wrong oscillation frequency, wrong required gain for oscillation).

    That sure sounds to like you're accounting for interstage loading.to me. To use your own app note as an example of a discussion in the literature that doesn't account for loading would seem to not be quite on target.

    Your app note and the other web page I cited examine the non-loading assumption and show that it leads to incorrect (experimental) results. I haven't found any discussion that actually asserts that it is true that there is no loading effect in an unbuffered network.
     
    Last edited: Dec 11, 2012
  9. anjanakg

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    Nov 23, 2012
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    can any one show figure of a phase shift oscillator using opamp which has already implemented
     
  10. t06afre

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    What is wrong with the paper in answer 5 :confused:
     
  11. ramancini8

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    Jul 18, 2012
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    The Electrician; you make an incorrect assumption because I did not reference the app note. Why did you neglect to give references for your web search?
     
  12. The Electrician

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    It's true that you didn't reference any app note specifically in post #3, but when I asked for an example of a circuit that "...does not account for interstage loading.", you didn't respond. Audioguru did however in post #5, and he linked to your app note.

    Then in post #6 you said:

    It seemed to me that by saying "See, I told you so.", you were telling me that the app note Audioguru linked was an answer to my question asking for a link to "...a circuit where the interstage loading is not accounted for?" Did I misinterpret "See, I told you so."?

    You did reference an app note in post #6. My post was dealing with both post #3 and #6.

    When you said "I wrote this app note..." were you not referring to the app note Audioguru linked in the immediately preceding post? It seemed a reasonable assumption to me. If that wasn't the app note you were referring to, I would be pleased to have a link to the one you were referring to.

    I did give a reference; I said in post #8: "I only found one page (http://www.play-hookey.com/oscillato...scillator.html) that starts with the (seemingly uncommon, based on my search results) assumption that the unbuffered stages of the phase shifting network don't experience loading effects."

    Just now checking that link, I see that it has changed. The new link is:
    http://www.play-hookey.com/oscillators/audio/phase_shift_oscillator.html

    I'm going to edit post #8 to reflect the change.
     
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