controlling the frequency of oscialtor

Discussion in 'General Electronics Chat' started by legolas11, May 3, 2013.

  1. legolas11

    Thread Starter Member

    Feb 26, 2013
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    Hi, is there a oscilator type, the frequency of which can be controlled using one component(capacitor). I mean unlike wien bridge oscilator where RC network determines the condition of oscilation and frequency of oscilaion, i want a oscilator of which frequency can be controlled by a capacitor indepoendent of conditions for oscilations.

    Please help!!!

    Thnx
     
  2. Ramussons

    Active Member

    May 3, 2013
    557
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    All Oscillators relate to a factor "Time Constant", either in terms of RC or LC.
    In a LC oscillator, frequency can be changed by varying a Single Capacitor.
    In a Phase Shift / Wien Bridge Oscillator, the frequency can be changed by varying all the Caps or all the Resistors of the "Tank".
    All the above are Sine wave Oscillators; the capacitors can be Voltage Controlled (Varicaps), Mechanical (Spindle); the Resistors Variable Ganged.

    In the case of Non Sine Wave Oscillators (normally Square Wave), frequencies are normally varied by the Resistors in the tank.

    To answer your question; Yes, in an LC oscillator, the Frequency can be changed by One Component, the Capacitor.

    Ramesh
     
  3. legolas11

    Thread Starter Member

    Feb 26, 2013
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    Thanks Ramesh for your reply. So that means no RC oscilator serve this purpose. I was looking for over the internet but i could not and so i wanted to be confirm that its not possible through a RC based oscilators.
     
  4. Ramussons

    Active Member

    May 3, 2013
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    Can you please be a little more specific? What's "this purpose"?

    Ramesh
     
  5. legolas11

    Thread Starter Member

    Feb 26, 2013
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    Well,my purpose is rather complicated. But all i need in this part is to vary the frequency of the oscilator based on need rather than keeping it fixed. In case of RC based oscilator i have to vary two capacitor but i am looking for if that is possible by only chnaging one capacitor. All i need is to vary frequency and that is through capacitence.
    Could you please look at the schematic i attached. I have designed it based on a paper where the author explained the ic model, compnent value every thing and claimed the oscilation can be controlled through C2 only (from 10p to 1n) and oscilation condition depend on C1/C4= R2/R4. But somehow i cant make it work.
    Please have a look if i am missing something.
    Thanks
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    Try a 555 timer.
     
  7. Ramussons

    Active Member

    May 3, 2013
    557
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    Your idea is adapted from on a paper " Single-Capacitor-Controlled Oscillators using a Single CFOA" by Dharmesh Kumar Srivastava and V. K. Singh.

    However, the diagrams shown there is in variation with what you have.

    If this is of academic interest, you may have to do a little more study.

    If you are looking for a single element controlled VCO, and a Non Sinosoidal is acceptable, there are plenty. For eg, a 555 oscillator can be made where the frequency can be controlled by a Single Resistor or by a Voltage.

    Ramesh
     
  8. legolas11

    Thread Starter Member

    Feb 26, 2013
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    ahh...sorry for the mistake. i have interchanged the inputs. But now its same as the author's design , still not oscilating.
    Thanks, I will study on VCO.
     
  9. Ramussons

    Active Member

    May 3, 2013
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  10. legolas11

    Thread Starter Member

    Feb 26, 2013
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  11. Ramussons

    Active Member

    May 3, 2013
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    Sorry legolas11, I have not tried out this. Maybe there's some other point that is being missed. Maybe you can ask the authors for some clarification.

    Ramesh
     
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