RC phase shift and wein bridge oscillators

Discussion in 'The Projects Forum' started by zechyr, Nov 26, 2011.

  1. zechyr

    Thread Starter New Member

    Nov 8, 2011
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    what is the difference between RC phase shift oscillator and a wein bridge oscillator?

    what are the present day applications for both?
    pls help
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    A phase shift oscillator usually uses an amplifier that has 180° of phase shift. The reactive components bump a specific frequency by a set amount of degrees, the classic phase shift oscillator is 3 RC circuits, each handling around 60° (give or take). The total phase shift for only one frequency is 180°, the rest is more or less due to the reactance. Therefore only one frequency is selected. Another rather unique phase shift design is the "Bubba Oscillator", found in Sine Wave Oscillators, a PDF abstract by TI.

    http://en.wikipedia.org/wiki/Phase_shift_oscillator

    [​IMG]

    A Wien Bridge uses two RC circuits, one as a high pass filter, one as a low pass filter. The end result is a band pass filter made up of RC components.

    http://en.wikipedia.org/wiki/Wein_bridge_oscillator

    [​IMG]
     
  3. Yako

    New Member

    Nov 24, 2011
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    The wein bridge's amplitude is stable across a very broad spectrum of frequencies, because of the NTC light bulb in the feedback path.

    The bulb heats up at higher frequencies, thus its internal impedance increases therefore changing the portion of positive feedback.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Bill Hewlett (of HP) made HP by making the first really stable, really pure sine wave generator, whose design you see a simplification of above. The light bulb used as a automatic gain control was a major breakthrough.
     
  5. Yako

    New Member

    Nov 24, 2011
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    They're very good, I have done a few of them ...

    Very low distortion and suitable for evaluting audio amps.
     
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