Electronic Devices - Oscillator Circuits - Discussion

For oscillations to occur, the phase shift between input and feedback signal from the tank circuit should be 0 or 360 deg. In the normal tank circuit with one inductor and capacitor, no phase shift is provided. So, two inductors are connected in series and this combination is connected in parallel to the capacitor. The node between the 2 inductors should be grounded, so it provides 180 deg phase shift. One of these inductor voltage is given to the amplifier as feedback signal which provides another 180 deg phase shift