Using speed-power product for logic choice: Does the speed-power product provide a useful basis to compare logic families when both propagation delay and power dissipation matter?

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
When selecting a logic family, engineers often juggle speed and power. A single metric that multiplies typical propagation delay by power dissipation helps compare options on an equal footing. This question checks whether you recognize the speed-power product as that comparative figure of merit.



Given Data / Assumptions:

  • Propagation delay reflects switching speed per gate.
  • Power dissipation includes static and dynamic components under specified conditions.
  • We seek a simple, comparative metric, not an exhaustive characterization.


Concept / Approach:
The speed-power product (sometimes called the energy per transition proxy) is defined as power dissipation * propagation delay. Lower values indicate greater efficiency at delivering speed per watt. While it abstracts away many details (load, supply, temperature), it remains a useful first-pass metric for family selection and system-level budgeting.



Step-by-Step Solution:

Compute SPP = P_diss * t_pd for each candidate family.Compare results: lower SPP suggests better speed-per-power trade-off.Select the family that meets timing within power limits.


Verification / Alternative check:
Datasheets and textbooks frequently introduce SPP as a way to summarize logic-family efficiency; it complements, not replaces, detailed timing and power analyses.



Why Other Options Are Wrong:

Incorrect: Disagrees with established practice.CMOS-only or 5 V-only: The concept applies broadly; numeric results vary with supply and process but the metric remains meaningful.


Common Pitfalls:
Relying solely on SPP without checking drive strength, fanout, and dynamic loading; SPP is a starting point, not the whole story.



Final Answer:
Correct

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