Noise Margin Across Logic Families: Which family typically offers the highest noise margin under 5 V operation?

Introduction / Context:
Noise margin quantifies how much unwanted voltage (noise) a logic input can tolerate while still recognizing a valid HIGH or LOW. Larger noise margins make systems more robust against crosstalk, ground bounce, and supply ripple.

Given Data / Assumptions:

• Classic 5 V CMOS has input thresholds near fixed fractions of VCC, creating wide margins.
• Standard TTL and LS-TTL use different VIH/VIL points and generally have smaller noise margins than CMOS for the same 5 V supply.
• HCMOS (high-speed CMOS) can be fast, but its thresholds and margins still reflect CMOS behavior; the “CMOS” option here captures the largest nominal margin.

Concept / Approach:
At 5 V, CMOS logic typically provides a HIGH threshold well above mid-rail and a LOW threshold well below mid-rail, leaving a wide band of guaranteed recognition and therefore higher noise margins than TTL families that use narrower bands.

Step-by-Step Solution:
Compare typical VIH/VIL for CMOS vs. TTL/LS-TTL.Observe that CMOS reserves a larger “safe” region for logic interpretation.Conclude that CMOS has the highest noise margin among the listed choices.

Verification / Alternative check:
Representative data sheets show TTL VIH(min) only modestly above 2.0 V and VIL(max) around 0.8 V, while CMOS thresholds are larger fractions of VCC, yielding larger margins at the same 5 V.

Why Other Options Are Wrong:

• TTL / LS TTL: Smaller margins due to their input threshold definitions.
• HCMOS: Still CMOS based, but the option “CMOS” most directly reflects the highest margins in the general case.

Common Pitfalls:
Assuming “faster” means “more immune”; speed and noise margin are separate trade-offs.

Final Answer:
CMOS