Closed-loop gain dependence — in a linear op-amp circuit, does changing the input voltage alter the circuit’s closed-loop voltage gain, or is the gain set by the feedback network (until nonlinearity or saturation occurs)?

Introduction / Context:For op-amps operated with negative feedback in their linear region, the closed-loop voltage gain is determined by the feedback network, not by the instantaneous input level. This distinction prevents a common misconception that “turning up the input” changes gain; it changes output amplitude until a limit is reached, but the ratio Vout/Vin remains set by the feedback.

Given Data / Assumptions:

• Standard inverting or non-inverting closed-loop configuration.
• Operation within linear limits (no output saturation or slew-rate limiting).
• Bandwidth and phase margin are adequate for the intended frequency range.

Concept / Approach:In a non-inverting amplifier, Av = 1 + (Rf/Rg). In an inverting amplifier, Av = −Rf/Rin. These gains do not depend on Vin; they are functions of resistor ratios. If Vin increases, Vout increases proportionally as long as the op-amp can supply the required voltage and current. When limits are exceeded (clipping, current limit, slew rate), the effective “gain” appears to change only because the amplifier is no longer linear.

Step-by-Step Solution:

Verification / Alternative check:Measure Vout/Vin for several input amplitudes within the linear region; the ratio remains essentially constant. Distortion and clipping occur only near output or input headroom limits.

Why Other Options Are Wrong:

Common Pitfalls:Attributing clipped or slewed waveforms to “gain change”; forgetting that saturation and slew limits are nonlinear behaviors outside closed-loop linear assumptions.

Final Answer:Incorrect — closed-loop gain is set by the feedback network, not by input amplitude (within linear range).