Which of the following criteria should be satisfied in order to use an amplifier as an oscillator?

Option 3 : Aβ = 1, Loop phase shift = 360°

Concept:

Barkhausen's crierion:

It states that if

A  →  gain of the amplifying element in the circuit 

 β →  transfer function of the feedback path

βA  →  loop gain around the feedback loop of the circuit,

∠ β A  → The phase shift around the loop 

then the circuit will sustain steady-state oscillation only at the frequency for which 

|βA| = 1  and

∠ β A = 2πn , n = 0,1,2… 

Barkhuasen criterion is a necessary condition for oscillation but not a sufficient condition.

Analysis:

To use an amplifier as an oscillator it must satisfy Barkhuasen criterion 

Therefore

|βA| = 1  and

∠ β A = 2πn , n = 0,1,2…