Feedback basics in amplifier design: When negative feedback is applied around an amplifier stage, what is the nature of the feedback signal with respect to the input signal at the summing node?

Introduction:
Negative feedback underpins accurate, stable, and linear amplifier behavior. Recognizing how the returned signal combines with the input clarifies why gain becomes predictable and distortion is reduced.

Given Data / Assumptions:

• Classical negative feedback loop with a portion of the output sampled and returned.
• Summing junction compares input to the feedback signal.
• Standard linear small-signal operation.

Concept / Approach:
In negative feedback, the feedback signal is subtracted from the input at the summing node. If the output momentarily increases, the feedback increases in a way that reduces the effective error signal, pushing the output back toward the desired value. This opposition stabilizes gain and reduces sensitivity to parameter drift.

Step-by-Step Solution:
1) Define error: Verr = Vin − βVout, where β is the feedback factor.2) If Vout rises, βVout rises, decreasing Verr.3) The amplifier drives its output to force Verr toward zero, creating a self-correcting loop.4) Net effect: the feedback signal always opposes the input change at the summing node.

Verification / Alternative check:
Block-diagram algebra shows closed-loop gain Acl = A / (1 + Aβ). The positive denominator term (1 + Aβ) indicates a negative feedback sign convention leading to opposition at the summing node.

Why Other Options Are Wrong:
Aids the input signal: describes positive feedback, not negative.Proportional to output current: feedback may sample voltage or current; the key attribute here is opposition, not proportionality to current.Proportional to differential voltage gain: gain is a parameter, not the signal itself.

Common Pitfalls:
Confusing feedback polarity or assuming feedback always samples voltage; regardless of sample type, negative feedback opposes the input at the summing node.

Final Answer:
opposes the input signal