In feedback amplifier design, a portion of the output is fed back for circuit stabilization. What is this type of feedback called?

Introduction:
Stability and predictable gain are central goals in analog amplifier design. Feeding a fraction of the output back to the input can either stabilize or destabilize the system depending on polarity and magnitude. This question assesses knowledge of how feedback polarity influences stability, bandwidth, and linearity in practical circuits.

Given Data / Assumptions:

• An amplifier stage with large open-loop gain.
• A feedback network that returns a portion of the output to the input.
• Linear operation around a bias point; small-signal assumptions.

Concept / Approach:
Negative feedback subtracts a portion of the output from the input drive, thereby reducing overall gain sensitivity to parameter variations and extending bandwidth. It also lowers distortion and noise referred to the input. Positive feedback reinforces deviations and is used to create oscillation or hysteresis (e.g., Schmitt triggers), not stabilization. Open-loop operation means no feedback is applied, which maximizes gain but sacrifices stability and accuracy.

Step-by-Step Solution:

Verification / Alternative check:
Closed-loop sensitivity S ≈ 1 / (1 + β * Aol) demonstrates desensitization to device parameter drift when negative feedback is applied. Empirically, output distortion and temperature drift diminish with appropriate β and phase margin.

Why Other Options Are Wrong:

• Distortion: A performance defect, not a feedback topology.
• Open-loop: Lacks stabilization; gain and offset vary widely.
• Positive feedback: Encourages oscillation or bistability; used in comparators and oscillators.

Common Pitfalls:
Assuming any feedback stabilizes; ignoring phase shift that can turn negative feedback effectively positive at high frequency; forgetting compensation for adequate phase margin to avert oscillation.

Final Answer:
Negative feedback.