Noise margin formulas in logic families Which of the following equations correctly expresses the high-level noise margin of a logic family?

Introduction / Context:
Noise margins quantify how much unwanted voltage can be superimposed on a logic level without causing an error. There are two margins: high-level (NMH or VNH) and low-level (NML or VNL). Correct formulas are essential for robust interface design and mixed-family connections.

Given Data / Assumptions:

• VOH(min): minimum guaranteed output HIGH voltage of a driver.
• VIH(min): minimum input voltage that will be recognized as HIGH by a receiver.
• VIL(max): maximum input voltage that will be recognized as LOW.
• VOL(max): maximum output LOW voltage of a driver.

Concept / Approach:

High-level noise margin is the “headroom” between what the driver guarantees at HIGH (VOH(min)) and what the receiver needs to see to accept a HIGH (VIH(min)). Thus, VNH = VOH(min) – VIH(min). Low-level noise margin is VNL = VIL(max) – VOL(max).

Step-by-Step Solution:

Verification / Alternative check:

Check any logic family datasheet; noise margins are commonly listed using these definitions, ensuring interoperability between drivers and receivers.

Why Other Options Are Wrong:

• VNL = VIL(max) + VOL(max): incorrect operation and sign.
• VNH = VOH(min) + VIH(min): adding values makes no physical sense for margin.
• VNL = VOH(min) – VIH(min): that expression is the high-level margin, not low-level.

Common Pitfalls:

• Swapping high and low symbols; remember “H” pairs with VOH/VIH, “L” with VOL/VIL.

Final Answer:

VNH = VOH(min) – VIH(min)