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Phase Shift Oscillator Question

  1. Jul 29, 2011 #1
    Hello everyone. I understand that a phase shift oscillator works by connecting an amplifier through a feedback network that shifts the input by 180 degrees. Although I remembered building a phase shift oscillator in my circuits class using an omp amp, I would like to build one using a bjt transistor or a mosfet amplifier. Will any transistor amplifier work with a phase shift oscillator, or do you have to use a certain amplifier?
     
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  3. Jul 29, 2011 #2

    vk6kro

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    You can make a phase shift oscillator using one transistor and a few components.

    Basic-Phase-Shift-Oscillator-1KHz.gif

    Ignore the opamp circuit.
     
  4. Jul 29, 2011 #3
    So it does not matter which type of transistor amplifier it is for the phase shift network as long as it has some voltage gain?
     
  5. Jul 29, 2011 #4

    vk6kro

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    No, these are quite tricky to get going. I recall you need a gain of 27 minimum for the circuit to oscillate.

    So, the transistor needs to be a high gain type and you should follow the components described exactly.
     
  6. Jul 30, 2011 #5

    The Electrician

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    The image shows a BJT circuit with a 4 stage phase shift network. The formula shown is for a 3 stage network.

    This page will help you with the design of a BJT phase shift oscillator:

    http://home.earthlink.net/~doncox/wec/Oscillators.html
     
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