common based Colpitts oscillator >>>><<<<<

Discussion in 'General Electronics Chat' started by uka, Dec 22, 2014.

  1. uka

    Thread Starter New Member

    Dec 22, 2014
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    Is there any difference between these two circuits (attached) ? please give me some detailed explanation
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The first looks like it came from here.....

    http://makezine.com/projects/super-simple-fm-transmitter/

    So it's a very basic FM transmitter.

    The second is simply an RF oscillator.

    One could "reduce" both circuits to an equivalent Colpitts topology. In the second case, the transistor's internal inter-electrode capacitances would need to be included in the reduction so as to establish the equivalence of each circuit as a [grounded base] Colpitts RF oscillator. The modulation components in the first case could be ignored if one is solely interested in the oscillator function.

    I'm sure both these cases were discussed recently in another thread. Perhaps another member can remind us of precisely where.

    The FM transmitter was at least mentioned here ....

    http://forum.allaboutcircuits.com/t...nsmitter-need-explanation.104468/#post-792309
     
    Last edited: Dec 22, 2014
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  3. uka

    Thread Starter New Member

    Dec 22, 2014
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    thanks , actually I interested in fm transmitter. I'm not EE guy . in order to analyze the fm transmitter , I have digged and found colpitts oscillator. so can i analyse the fm transmitter like a common base colpitts oscillator ? like Fr=1/(2pi(LC)^1/2)
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Yes - with the proviso that depending upon the working frequency, the frequency determining elements could include a significant contribution from the inter-electrode capacitances.
     
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