Questions about colpitts oscillator design


Posted on Feb 6, 2014

amplifier input and output impedance, load and source resistance are strongly mutually dependent in the CC circuit. That`s a reason, why `impedance matching` doesn`t achieve results representative for the circuit operation. Analyzing the circuit as CB with virtual ground, as suggested by LvW, gives a better decoupling of both amplifier ports. Impe


Questions about colpitts oscillator design
Click here to download the full size of the above Circuit.

dance matching isn`t a bad design idea, when the amplifier power gain is small and must be well utilized to get the oscillator working at all. But it must consider the actual frequency dependent transistor parameters. - amplifier input and output impedance, load and source resistance are strongly mutually dependent in the CC circuit. That`s a reason, why "impedance matching" doesn`t achieve results representative for the circuit operation. Analyzing the circuit as CB with virtual ground, as suggested by LvW, gives a better decoupling of both amplifier ports. Impedance matching isn`t a bad design idea, when the amplifier power gain is small and must be well utilized to get the oscillator working at all. But it must consider the actual frequency dependent transistor parameters. For an aid to understanding the operation of these LC tank oscillators, I suggest you watch my Youtube videos which show an animation of Colpitts and Clapp oscillators. It`s a pity that samy uses symbols without sufficient explanation, but I think he didn`t make any error as far as RE is concerned (but I am surprised about his comment "yes, you are right"). According to his calculation I suppose the symbol "RB" stands for the resulting DYNAMIC input resistance of the whole amplifier stage and the symbol "RE(total)=RE+re" is just an intermediate step for the sum of two resistances. It`s true, that the original circuit also covers the clapp oscillator...




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

CLASSIC MINIMALIST AMPLIFIER
Solid State Tesla Coil/High Voltage Generator Circuit
ITU-R 468 noise weighting
A E1T Decade Scaler Tube raised from the dead
UHF Indicator - Wavemeter
Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor
Adding sync pulses to the video signal
Updated Circuit Details for Clara Rockmores Theremin
Factory secondary low-voltage distribution electrical panel wiring diagram



Top