Voltage follower (unity-gain buffer) using an operational amplifier: In a classic voltage-follower configuration, is the op-amp output node connected directly to the inverting (−) input while the non-inverting (+) input serves as the signal input?

Introduction / Context:
A voltage follower, also called a unity-gain buffer, is a fundamental operational-amplifier configuration. It provides a gain of approximately 1 while offering very high input impedance and very low output impedance. The question checks whether you remember the exact feedback connection used to realize this behavior.

Given Data / Assumptions:

• Single op-amp operated in linear (closed-loop) region.
• Idealized op-amp assumptions for concept: very large open-loop gain, high input impedance, low output impedance.
• Feedback is intended to be negative.

Concept / Approach:
In a unity-gain buffer, the output is fed back directly to the inverting (−) input. The signal is applied to the non-inverting (+) input. With very high open-loop gain A, the closed-loop transfer becomes v_out ≈ v_in because negative feedback forces the differential input v(+) − v(−) toward zero. This gives near-unity gain with excellent impedance buffering.

Step-by-Step Solution:

Verification / Alternative check:
Closed-loop gain formula for the non-inverting amplifier with Rf = 0 and Rin → ∞ yields gain = 1. Practical measurements show near-unity gain and strong buffering capability (e.g., driving loads without loading the source).

Why Other Options Are Wrong:
Incorrect: would imply a different connection than the standard follower.
Only correct for ideal op-amps: real op-amps also implement this, with minor non-idealities (offset, bandwidth).
AC-coupled only: DC and AC both work; DC accuracy depends on offset and bias currents.

Common Pitfalls:
Accidentally swapping inputs (causing positive feedback and saturation) or forgetting supply headroom and output swing limits.

Final Answer:
Correct