Definition of noise immunity in logic circuits: Noise immunity describes a circuit’s ability to tolerate noise without producing spurious changes at the output. Evaluate the statement that it “tolerates noise by causing spurious charges in the output voltage.”

Introduction / Context:
Noise immunity is a foundational specification in digital logic families (TTL, CMOS, ECL). A correct understanding is crucial for robust designs operating in real environments with crosstalk, supply ripple, and electromagnetic interference.

Given Data / Assumptions:

• Noise immunity refers to the maximum noise the input can withstand without causing an unintended output change.
• Input threshold levels (VIL, VIH) define safe input voltage ranges for logical 0 and 1.
• Output integrity should be preserved despite reasonable noise within specified limits.

Concept / Approach:
The correct definition emphasizes resistance to noise-induced misinterpretation at the input. A logic family with good noise immunity ensures that small disturbances do not flip the interpreted logic level. The statement in question incorrectly describes the effect on the output as “causing spurious charges,” which reverses the idea: immunity prevents spurious changes, it does not cause them.

Step-by-Step Solution:

Verification / Alternative check:
Check standard datasheets and textbooks: noise margin = VIH(min) - VIL(max); higher margin implies better immunity and fewer spurious output transitions.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing noise susceptibility (which could cause spurious changes) with noise immunity (which prevents them); assuming output filtering alone guarantees immunity.

Final Answer:
Incorrect