In an op-amp circuit, what is the effect of negative feedback on performance?

• A. Feedback reduces closed-loop gain and improves linearity, input/output impedance, and bandwidth; negative sign ensures error correction.
• B. It increases closed-loop gain and reduces bandwidth.
• C. It destabilizes unless used with high supply rails.
• D. It only affects input impedance.

Answer: (B)

Negative feedback works by feeding a portion of the output back in opposite phase to the input, so the circuit continually corrects the difference between the input and a sample of the output. This correction forces the closed-loop gain to be set primarily by the feedback network and, because the loop reduces large errors, the overall gain is reduced compared to the open-loop gain. The result is a more linear response: distortions from the amplifier’s own nonlinearities are diminished because any deviation is constantly corrected. At the same time, the feedback broadens the frequency range over which the amplifier behaves predictably, effectively increasing the closed-loop bandwidth while keeping the gain suppressed. Impedance characteristics and robustness to component variations also improve in a way that helps the stage be less sensitive to loading and tolerances. The negative sign is what makes this improvement possible, by ensuring the feedback acts to oppose the error rather than reinforce it.