Negative feedback and noise: Determine whether the statement “Negative feedback reduces noise originating at the amplifier input” is correct in the context of linear feedback amplifiers.

Introduction / Context:
Negative feedback is used to stabilize gain, extend bandwidth, and reduce distortion in amplifiers. Its effect on noise depends on where the noise originates. This item probes whether feedback specifically suppresses input-source noise.

Given Data / Assumptions:

• Linear voltage-series feedback topology typical of audio and instrumentation amplifiers.
• “Noise originating at the amplifier input” means noise coming from the signal source or input resistor, added in series with the intended signal.

Concept / Approach:

Negative feedback divides the closed-loop gain by approximately (1 + loop gain). Both the desired signal and any input-referred noise from the source are amplified by the same closed-loop gain; thus the output signal-to-noise ratio due to input noise is not inherently improved by feedback. Feedback can reduce the contribution of internal amplifier noise (e.g., output-referred disturbances) by the factor of the loop gain, but it does not preferentially suppress noise that is indistinguishable from the input signal.

Step-by-Step Solution:

Verification / Alternative check:

Closed-loop noise analysis shows source noise remains unchanged in input-referred form; only amplifier-generated noise is suppressed by feedback.

Why Other Options Are Wrong:

• Options asserting “True” ignore that feedback treats input signal and source noise equally.
• Topology-dependent statements do not change this fundamental point.

Common Pitfalls:

• Confusing reduction of internal noise and distortion with reduction of source noise.

Final Answer:

False