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oscillation of Clapp LC circuit

Discussion in 'Electronic Basics' started by jason, Mar 19, 2005.

  1. jason

    jason Guest

    Hello All

    I am studying about Clapp LC oscillator.
    Given below link is the circuit of interests
    http://www.geocities.com/jason_class/ClappLC.jpg

    May I know how do we calculate by hand if this circuit gonna oscillate
    or not?

    I learnt in lecture that I must find Av multiply by beta(feedback
    factor). Av is always given by gm multiply by R efficient , which is
    gmReff
    Reff is the sum of series and parallel resistances of all emitter
    resistance, ac emitter resistance , load resistance and also reflected
    resistances from the tap of capacitors. Emitter is mentioned here
    because I learnt about bipolar transistor configuration.

    For the circuit in the link given, I do not understand why the same
    approach is use?
    Why we can use gmReff as the Av since it is a common drain
    configuration? Is it because we have already sum all the net
    resistances in Reff , therefore we can use gmReff as the Av?

    So for other type of configuration of mosfet such as common gate and
    common source? We can use the same Av=gmReff ?
    If possible show me the correct way of checking if the circuit can
    oscillate by manual calculation..at least the steps or methodology.
    Really appreciate your help in advance.

    Kindly enlighthen

    rgds and thanks
    Jason
     
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