Colpitts Oscillator design questions

Discussion in 'General Electronics Chat' started by cork_ie, Aug 2, 2012.

  1. cork_ie

    Thread Starter Active Member

    Oct 8, 2011
    I posed the following questions on another thread relating to another users Colpitts design problem.Unfortunately the questions appear to have got lost in the overall discussion.His design problem now appears to have been solved and while the thread is still open there are unlikely to be many more replies.

    So can any of the experts on here give me an answer to the following questions.

    As far as I am aware the resonant frequency for a Colpitts Oscillator is 1/2π√(L.C1.C2)/(C1+C2)

    1) Are there any rules of thumb for the values of L , C1 , C2 for a given frequency? (how many times greater or smaller) can C1 be with respect to C2.

    2) What is the ideal capacitance to inductance ratio. ie μF:μH ?

    3) What are the advantages & disadvantages of using either a Colpitts or Hartley oscillator for generating an AM carrier wave of approx 1MHz.

    Many Thanks -
  2. jayaram

    New Member

    Aug 3, 2012
    Go to, and you can rig up the circuit given, with bias resistance values - R1 = 30.1 kΩ, R2 = 10 kΩ, Rc = 2 kΩ, Re = 511 Ω. and use a capacitance and inductor of your choice. You can verify the output for various C and L values :)
    cork_ie and PackratKing like this.
  3. Mahathi

    New Member

    Sep 24, 2012
    Hello.. Can anybody help me in designing a Colpitts Oscillator using a FET?
    I am facing problems in designing the biasing resistors and capacitors in the amplifier stage.. please show me some way.. i have to submit the project by saturday:-(
  4. vk6zgo

    Active Member

    Jul 21, 2012
    As far as (3) is concerned,the main advantage of a Colpitts Osc over a Hartley,is that you don't need a tapped inductor with a Colpitts.
    I would use a Pierce crystal oscillator in the application you refer to.

    Can I get back to you on (1) & (2)?