CMOS logic families: For a CMOS gate, which listed speed–power product (energy per operation) represents the best performance?

Introduction / Context:
The speed–power product is an energy-per-operation metric widely used to compare digital logic families and device technologies. For CMOS gates, a smaller speed–power product indicates faster switching for less energy. This question asks you to pick the best (lowest) value among options.

Given Data / Assumptions:

• Speed–power product is expressed in joules (commonly picojoules for logic).
• Lower energy-per-transition is better for performance per watt and thermal efficiency.
• All options are comparable units (pJ).

Concept / Approach:
Since all numeric values are in the same unit, the optimal speed–power product is simply the smallest number. In energy terms, each logic transition costs less energy, reducing dynamic power at a given activity factor and frequency (Pdynamic ≈ C * V^2 * f). With lower energy per switch, a design can achieve higher speed for the same power or the same speed at lower power.

Step-by-Step Solution:
List values: 1.4, 1.6, 2.4, 3.3 pJ.Select the minimum value.Conclude that 1.4 pJ is best.

Verification / Alternative check:
Compare any two entries: 1.4 pJ < 1.6 pJ, and 1.4 pJ < 2.4 pJ, 3.3 pJ, so 1.4 pJ is indeed the minimum.

Why Other Options Are Wrong:
Larger pJ values correspond to higher energy per operation, which is less desirable.

Common Pitfalls:
Confusing “best” with “largest.” In speed–power product metrics, smaller is better.

Final Answer:
1.4 pJ