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  1. #1
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    LC oscilator type

    Hello, I have queastion about type of the osclator I found on wikipedia here:
    File:NPN Colpitts oscillator collector coil.png - Wikipedia, the free encyclopedia


    This oscillator is described as "Colpitts", bud I compared it to another schematics of Colpitts oscilators and I see big difference here.
    For example this circuit


    Is on wikipedia real Colpitts oscilator, or can somebody give me the type of it please?

    •   Alt21st September 2010, 09:12

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  2. #2
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    Re: LC oscilator type

    I think both are Colpitts oscillator. One major difference is in how transistor is biased. One is fixed biased and other one is biased with voltage divider and an emitter resistor for stability over temerature. I think second figure is more standard. In that figure inductor is connected across the nonconnected ends of capacitor C1 and C2. But can see that in first figure it is same in ac analysis. In ac analysis, DC power supply will be shorted in sense. I think capacitor C3 is used to isolate the DC conditions in base of the transistor from the feedback network.



    •   Alt21st September 2010, 12:48

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  3. #3
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    Re: LC oscilator type

    Both are Colpitts oscillators. First is common base, and second is common emitter. In both cases C1 and C2 are feedback capacitors.
    Second oscillator using the given values is oscillating around 36 kHz.



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