Barkhausen Criterion and Loop Gain
The Barkhausen criterion is necessary but not sufficient to sustain a constant oscillation. e.g. There must some nonlinear mechanism to regulate the loop gain to be 1 for a sine signal.

When 1-AB goes 0, Vs (the input) also go to 0, meaning no input is necessary to maintain a constant oscillating output.

However, some initial condition and a non-linear mechanism are needed for a sine oscillator to determine the peak amplitude.


for |AB| &lt; 1 it can be underdamped determined by the phase margin relative to 360 deg. (or multiples.)

for |AB| &gt; 1 the oscillations will grow larger until the output limits are reached.

e.g. sine wave is clipped since gain becomes zero (0) if the output is saturated
the amount of clipping is determined by the average time |AB|&gt;1 and |AB|=0 when saturated.