JFET Colpitts oscillator realized with N-channel JFET is given in figure bellow.
Simulate JFET Colpitts oscillator.
JFET Colpitts oscillator is similar with JFET Hartley Oscillator, but for Colpitts oscillator, excitation for active amplifier comes originally from capacitor voltage divider. In modified scheme given above, L-C resonant circuit is made of one inductor and two capacitors. JFET has good feature for application in Colpitts oscillator since it has high input impedance that not burdening L-C resonant circuit and have good high frequency characteristic. In the drain branch of JFET there is dimmer inductance LP that obtains small damping of L-C circuit i.e. increases quality factor Q as well as output impedance. Oscillation frequency of JFET Colpitts oscillator is:
Coupling capacitors CS1 and CS2 has to have much higher capacitance then C1 and C2.