Condition for Oscillation in Feedback Oscillator Circuit

Introduction:
Feedback oscillator circuit is a type of electronic oscillator circuit that generates a periodic signal without any input signal. The oscillation frequency is determined by the feedback network components. The condition for oscillation is that the loop gain should be greater than unity and the total phase shift around the loop should be zero or 360 degrees.

Loop Gain:
The loop gain of an oscillator circuit is the product of the gains of all the components in the feedback loop. If the loop gain is greater than unity, the output signal will be amplified and fed back to the input, resulting in sustained oscillations.

Phase Shift:
The phase shift of a signal is the difference in phase between the input and output signals. In an oscillator circuit, the total phase shift around the feedback loop should be zero or 360 degrees for sustained oscillations to occur.

Condition for Oscillation:
The condition for oscillation in a feedback oscillator circuit is that at the frequency of oscillation, the loop gain is greater than unity while the total phase shift around the loop in degree is zero or 360 degrees. This ensures that the output signal is amplified and fed back to the input in phase, resulting in sustained oscillations.

Option Analysis:
Option A states that the total phase shift around the loop is zero degrees. This is the correct option since a total phase shift of zero degrees ensures that the output signal is in phase with the input signal, resulting in sustained oscillations.

Option B states that the total phase shift around the loop is 90 degrees. This is not the correct option since a total phase shift of 90 degrees results in a negative feedback, which reduces the loop gain and prevents sustained oscillations.

Option C states that the total phase shift around the loop is 180 degrees. This is not the correct option since a total phase shift of 180 degrees results in a positive feedback, which increases the loop gain and may cause unstable oscillations or distortion.

Option D states that the total phase shift around the loop is 270 degrees. This is not the correct option since a total phase shift of 270 degrees results in a negative feedback, which reduces the loop gain and prevents sustained oscillations.

Therefore, the correct answer is option A, which states that the total phase shift around the loop is zero degrees.