What is Barkhausen criteria?

Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations. “Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity”.

The condition of unity loop gain -A? = 1 is called the Barkhausen criterion. This condition implies that
A?= 1and that the phase of - A? is zero.