Op-amp input connection styles: Textbooks describe several basic ways to drive the two op-amp inputs. Which of the following is NOT considered a standard mode of intended operation?

Introduction:
Op-amps can be excited in different ways depending on whether one or both inputs carry signal. Understanding intended modes helps in analyzing gain and common-mode rejection properly.

Given Data / Assumptions:

• Standard linear applications of op-amps.
• Idealized behavior with negative feedback.
• Typical textbook terminology.

Concept / Approach:
Common intended modes: inverting (signal into − input, + at reference), noninverting (signal into + input), and differential/double-ended (signals applied to both inputs with opposite polarity). Common-mode refers to the same signal simultaneously applied to both inputs; it is generally an undesired stimulus used to quantify rejection (CMRR), not a purposeful operating mode for gain.

Step-by-Step Solution:
1) List intended modes: inverting, noninverting, and differential (double-ended).2) Define common-mode: identical signal on both inputs; ideally produces zero output.3) Since common-mode is measured to characterize rejection, it is not a standard gain mode.4) Therefore, the exception is common-mode.

Verification / Alternative check:
CMRR metric explicitly quantifies how little output should result from common-mode input, reinforcing that common-mode is not an intended amplification configuration.

Why Other Options Are Wrong:
Inverting mode: fundamental textbook topology.Double-ended: another way to say differential input, a standard mode.Single-ended: describes inverting or noninverting cases with one driven input and the other at reference.

Common Pitfalls:
Confusing differential mode (desired) with common-mode (undesired) due to similar wording; the sign and symmetry differ.

Final Answer:
common-mode