need urgent help with crystal oscillator based circuit plzzzzzzzzzz

Discussion in 'Homework Help' started by farairo, Aug 10, 2009.

  1. farairo

    Thread Starter New Member

    Jun 5, 2009
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    I need to build a crystal oscillator(square wave) at 2.4MHz and then using divider circuit divide it by 8 to get 300khz square wave.i dont know much about the crystal oscillator so i dont know which type of crystal oscillator to use and with what values of components ........Actually i need to build a oscillator at 300khz for my switch capacitor filter...i first tried to build a relaxation oscillator but after building it realized that it cant work at 300khz ....then i build a oscillator using 555 timer but its also not stable at this frequency........so i really need some help as i am stuck in this circuit from last 15 days and i dont know much about crystal oscillator circuits.......thanks in advance.............
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Take a look at the attached PDF's.

    Greetings,
    Bertus
     
  3. farairo

    Thread Starter New Member

    Jun 5, 2009
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    thanks buddy for u reply.......but i need to design crystal oscillator using transistor or FET.......i have tried some design in multisim but i am getting sine wave as output instead of square wave.......wt am i doing wrong......
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Fet and bjt oscillators are mostly for sinewaves.
    You can convert the sinewave to a squarewave using a schmitt-trigger.

    Greetings,
    Bertus
     
  5. farairo

    Thread Starter New Member

    Jun 5, 2009
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    thanks i didnt know that......then what changes can i make in circuit to get square wave if i dont want to use schimtt circuit...........i mean with what components i should replace the transistor or FET.....can i get some example of the circuit ......


    actually the easy way i thought was by using the 555 timer but i am not able to make it work at 300khz which is the required frequeny.....its frequency is varying to rapidly with slight change in resistance and capacitance above 200khz.....is their problem with 555 timer stability above 200khz or is something wrong with my circuit..... i am attaching my 555 circuit below......
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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  7. bertus

    Administrator

    Apr 5, 2008
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