Q. Explain the conditions to be satisfied for sustained oscillations in an oscillator circuit with the help of block diagram.

The essential condition for sustained oscillations are :

· | AB | = 1,i.e. the magnitude of loop must be unity.

· The total phase shift around the closed loop is zero or 360 degrees.

The condition that | AB | = 1 gives a single and precise value of AB which should be set throughout the operation  of the oscillator circuit.But in practice,as transistor characteristics and performance of other circuit components change with time,|AB| will become greater or less than unity.Hence,in all practical circuits |AB| should be set greater than unity so that the amplitude of oscillations will continue to increase without limit but such an increase in amplitude is limited by the onset of the nonlinerarity of operation in the active device associated with the amplifier as shown in the figure above.In this circuit,AB is larger than unity for positive feedback.This onset of nonlinearity is an essential feature of all practical oscillators.