Question

Which of the following logics possesses highest noise immunity?

• A. DTL
• B. HTL
• C. ECL
• D. TTL

Hint:

HTL logic is ideal for noisy environments due to its high voltage threshold levels. Remember: high threshold = high noise immunity.

Answer 1

The Correct Option is B

Noise immunity is a measure of a logic family’s ability to tolerate noise without misinterpreting logic levels.
Let’s briefly compare the given logic families:
- DTL (Diode-Transistor Logic): Has relatively low noise margin.
- HTL (High Threshold Logic): Specifically designed to operate in industrial environments with high noise. It uses zener diodes to set high logic thresholds, which gives it the highest noise immunity.
- ECL (Emitter-Coupled Logic): Fastest logic but has poor noise margin due to low voltage swing.
- TTL (Transistor-Transistor Logic): Better than DTL but still lower noise immunity than HTL.
Hence, among the choices, HTL has the highest noise immunity.