Anish Aaryan

The Hartley oscillator is an LC electronic oscillator that derives its feedback from a tapped coil in parallel with a capacitor (the tank circuit). Although there is no requirement for there to be mutual coupling between the two coil segments, the circuit is usually implemented as such. A Hartley oscillator is essentially any configuration that uses a pair of series-connected coils and a single capacitor.


Fig:Transistor Hartley oscillator


In the oscillator, the feedback voltage is developed by the inductive voltage divider, L1 & L2. Since the output voltage appears across L1 and the feedback voltage across L2, the feedback fraction is
β = V / Vout = XL2 / XL1 = L2 / L1
As usual, the loading effect of the base is ignored. For oscillations to start, the voltage gain must be greater than 1/ β. The frequency of oscillation is given by
f=1/(2π√(L_eq C))
Similarly, an opamp based Hartley oscillator circuit is shown below:



Fig: Op amp Hartler Oscillator