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What is the difference between those two Colpitts oscillators ?

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Tukan

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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
50_1285056546.png


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
18_1285056546.gif


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

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.
 

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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