Difficulty: Medium
Correct Answer: Stop oscillation
Explanation:
Introduction / Context:Neutralization in RF amplifiers is a stability enhancement technique. It is used to prevent unwanted oscillations caused by internal feedback through interelectrode capacitances of active devices such as vacuum tubes or transistors.
Given Data / Assumptions:
Concept / Approach:The amplifier can inadvertently become an oscillator if uncontrolled positive feedback occurs. Neutralization provides an out-of-phase feedback path that cancels the unwanted coupling, thereby stabilizing the amplifier without affecting desired gain significantly.
Step-by-Step Solution:
Unneutralized amplifier: input-output coupling through C_m.Feedback may satisfy Barkhausen criterion → oscillation.Neutralization introduces counter-signal of equal magnitude, opposite phase.Oscillation is suppressed, amplifier remains stable.Verification / Alternative check:
Classic RF tube circuits used neutralizing capacitors for stability.Why Other Options Are Wrong:
Neutralization does not primarily increase bandwidth or improve selectivity.It focuses on stability, not on reducing noise.Common Pitfalls:
Assuming neutralization improves selectivity—this is handled by tuned circuits, not neutralization.Final Answer:
Stop oscillation
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