Edge-triggered flip-flops — necessary internal mechanism Which design requirement must an edge-triggered flip-flop include to ensure it responds only at the clock transition and not during the entire clock level?

Introduction / Context:
Edge-triggered flip-flops are engineered to change state only at a specific instant: the transition (edge) of the clock. This protects synchronous systems from hazards that occur when inputs vary during the clock level. The key to this behavior lies in how the flip-flop detects and gates that tiny moment in time.

Given Data / Assumptions:

• We are comparing architectural requirements, not external pin polarities.
• The device is intended to respond to clock edges only.
• Standard synchronous timing (setup/hold) is assumed.

Concept / Approach:
An internal pulse transition detector creates a narrow sampling pulse from the clock edge (rising or falling). That pulse briefly enables the internal storage path, causing the flip-flop to sample inputs only during that short interval. Outside the pulse, the data path is blocked, preventing level-sensitive tracking associated with latches.

Step-by-Step Solution:

Verification / Alternative check:
Examine typical master–slave vs. edge-triggered schematics; the latter commonly synthesize a brief pulse internally (via differentiating networks or logic) to emulate instantaneous sampling.

Why Other Options Are Wrong:

• Very fast response: helpful but not sufficient to enforce edge-only sensitivity.
• At least two inputs for rising/falling: not required; many devices trigger on one edge only.
• Active-LOW inputs/complemented outputs: mere signal conventions, unrelated to edge detection.

Common Pitfalls:
Confusing latches with edge-triggered flip-flops or assuming polarity conventions determine edge sensitivity.

Final Answer:
a pulse transition detector.