Colpitts Oscillator Discussion

Discussion in 'General Electronics Chat' started by athulascc, Mar 7, 2015.

  1. athulascc

    Thread Starter Member

    Aug 15, 2014
    86
    1
    http://www.electronics-tutorials.ws/oscillator/colpitts.html

    here I find nice explain about it.

    but there I do not know how they have calculated phase shift and feedback gain.

    I know that phase shift of feedback should be 180 dgrees and feedback gain should be 1/amp gain.

    so how to calculate feedback gain and phase shift
     
  2. Motanache

    Member

    Mar 2, 2015
    70
    4
    That's too little for the calculation of an oscillator.
    I am familiar with colpitts common base:

    [​IMG]

    http://www.elektropage.com/images/circuits/mini_FM_transmitter1.gif

    There appear into account the parasitic capacitances of transistors and hybrid Parameters.

    Phase shift at feedback A first it is given by capacitor C5 and that seems to be only 90 degrees.
    C5 provide a part of collector signal with phase shift in emitter.
     
    Last edited: Mar 7, 2015
  3. Motanache

    Member

    Mar 2, 2015
    70
    4
    The two conditions (the phase and gain) are for self-sustained oscillation.

    But there must be met and necessary conditions to start oscillation.

    Even more strange mathematical is that I do scheme without R3 and works.
     
    Last edited: Mar 7, 2015
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