Difficulty: Easy
Correct Answer: The amplifier loses negative feedback and the output saturates or clips severely
Explanation:
Introduction / Context:Negative feedback stabilizes gain, linearity, and bandwidth in op-amp amplifiers. A failure in the feedback path removes this control, returning the op-amp to near open-loop behavior with huge gain and rail-to-rail saturation for even tiny input offsets. Recognizing this failure mode accelerates troubleshooting.
Given Data / Assumptions:
Concept / Approach:Open feedback means the op-amp no longer compares its inputs in a controlled loop. With open-loop gain typically 10^5 to 10^6, microvolt-level input differences can drive the output to a rail. The result is severe clipping when a signal is applied, or a DC-saturated output in quiescent conditions. Protection or muting is not intrinsic unless extra circuitry is provided.
Step-by-Step Solution:
Model feedback path open → loop gain ≈ 0.Open-loop gain remains huge → tiny input error produces rail output.Applied signals appear severely distorted or fully clipped.Therefore, expect saturation/clipping, not gentle gain change.Verification / Alternative check:Bench test: lift Rf in an inverting amplifier. The output jumps to a rail. Reconnecting Rf restores linear operation and the designed closed-loop gain.
Why Other Options Are Wrong:
Unity-gain glide: wrong—removing Rf does not create a unity follower.Auto-mute: op-amps do not mute unless externally designed to.Phase margin improvement: irrelevant to the primary failure symptom.Only bias change: effects are far larger than bias-current tweaks.Common Pitfalls:Mistaking a broken feedback trace for a fried op-amp; overlooking solder cracks on Rf; assuming the device is faulty when the loop is actually open.
Final Answer:The amplifier loses negative feedback and the output saturates or clips severely
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