Question

In an oscillator, for sustained oscillations, Barkhausen criterion is $A\beta$ equal to (A = voltage gain without feedback, $\beta$ = feedback factor)

• A. zero
• B. $\frac{1}{2}$
• C. 1
• D. 2

Answer 1

Answer: (C)

1

In an oscillator, Barkhausen criterion $A\beta$ is equals to 1, because for this condition only the output voltage is sine wave under steady state condition. Hence, option C is correct.

If $A\beta$ is zero, then the product of $A\beta$ and input voltage($v_{in}$) will also be zero.

If $A\beta <1$, then the product, $A\beta v_{in}$ is less than $v_{in}$, and the output signal will die out.

If $A\beta >1$, then the product, $A\beta v_{in}$ is greater than $v_{in}$, and the output signal will built up gradually (i.e. unsteady).

Hence, options A, B and D are incorrect.