Q. Draw and explain Colpitts oscillator?

Colpitt's oscillator is a superb circuit which is used widely in commercial signal generations of  frequency of 100 Mhz . It consists of  a single state inverting amplifiers and an (phase shift network). The two series capacitors C₁ and C₂ form the potential divider for providing the feedback voltage ie. Voltage developed across the capacitor C₂ provides the regenerating feedback.If you consider positive feedback is applied to compensate for the losses in the tuned circuit, the amplifier and feedback circuit create a negative resistor. When Z₁ and Z₂ are capacitive, the impedance across the capacitors can be estimated from a formula I won't lay on you here because it includes beta, hie, as well as XC₁ and XC₂. Suffice to say it can be shown that the input impedance is a negative resistor in series with C₁ and C₂.  And the frequency is in accordance with: