Op-amp feedback fault — effect of an open feedback resistor: In a standard inverting or noninverting op-amp amplifier, what typically happens if the feedback resistor path opens during operation?

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:

• Voltage-feedback op-amp with resistive feedback network.
• Supply rails are finite (e.g., ±15 V or single-supply).
• Small input offsets/noise always exist.

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:

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:

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