Unity-gain amplifier terminology: What is another common name for a unity-gain buffer stage built with an op-amp?

Introduction:
Unity-gain stages are used to buffer signals without changing their amplitude while providing high input impedance and low output impedance. Recognizing the common names for such stages helps in reading schematics and selecting the right building block for impedance matching and isolation.

Given Data / Assumptions:

• Op-amp configured with 100% negative feedback from output to inverting input.
• Input is applied to the noninverting terminal (+).
• Ideal op-amp assumptions for conceptual clarity.

Concept / Approach:
The voltage follower (also called a unity-gain buffer) forces Vout to follow Vin because the feedback drives the differential input toward zero. This provides a gain of approximately 1 while transforming impedance. It is not a comparator (which saturates between rails) and not a difference amplifier (which amplifies V+ − V− with settable gain using a resistor network).

Step-by-Step Solution:

Verification / Alternative check:
Impedance transformation: input impedance is very high (limited by input bias network), output impedance is low (≈ ohms with feedback). Bench measurements show negligible gain error at low frequency when Aol is large.

Why Other Options Are Wrong:

• Difference amplifier: Requires specific resistor ratios; not unity by default.
• Comparator: Operates open-loop, saturating rather than following.
• Single ended: Describes drive type, not a unity-gain buffer topology.

Common Pitfalls:
Confusing buffer with follower-plus-offset circuits; assuming a comparator can be “used as an op-amp” (its output stage and input structures differ).

Final Answer:
Voltage follower.