LC Oscillators

• The general form of lc oscillator using amplifier

• The feedback network uses three impedences which are practically pure reactances.
1. i.e. Z1=jX1,Z2=jX2,Z3=jX3
• Amplifier provide the phase shift of 180* while the feedback network provides the additional 180* to compleate 360* phase shift around a loop
• To satisfy Aβ >=1, it is observed thet the X1 and X2 must be of same type while X3 must be opposite.
• Thus if X1 and X2 are inductive the x3 must be capacitive while if X1 and X2 are capacitive then X3 must be inductive. Hence in LC oscillators, the feedback network consists of two inductors and one capacitor or two capacitors and one inductor.