In a typical digital logic family, if Logic 0 spans 0 to 0.8 V, what voltage range is recognized as a valid Logic 1 level?
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A2–5V
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B2.5–5V
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C3.0–5.5V
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D3.5–5.5V
Answer
Correct Answer: 2–5V
Explanation
Introduction:Digital logic families define voltage thresholds for interpreting signals as Logic 0 (LOW) or Logic 1 (HIGH). Knowing these ranges ensures reliable interfacing and noise immunity.
Given Data / Assumptions:
- Logic 0 (LOW) range: 0 to 0.8 V.
- We need the corresponding Logic 1 (HIGH) range in a typical 5 V logic system.
- Assume standard TTL-like thresholds where VIH(min) is near 2.0 V.
Concept / Approach:Classic TTL specifies VIL(max) around 0.8 V and VIH(min) around 2.0 V, with VCC near 5 V. Thus, valid HIGH levels are typically any voltage from roughly 2.0 V up to VCC (about 5 V).
Step-by-Step Solution:
Identify VIL(max) = 0.8 V (given).Typical VIH(min) for TTL ≈ 2.0 V.Acceptable HIGH range ≈ 2.0 V to 5.0 V.Match with provided options: 2–5V.Verification / Alternative check:CMOS families at 5 V often use fractions of VCC, but TTL-compatibility commonly accepts ≥ 2.0 V as HIGH in mixed systems; 2–5V remains the broadly correct range here.
Why Other Options Are Wrong:
- 2.5–5V: Too restrictive; 2.1 V or 2.2 V should still be HIGH in TTL-compatible inputs.
- 3.0–5.5V and 3.5–5.5V: Unrealistically high VIH(min); excludes valid HIGHs between 2 and 3 V.
Common Pitfalls:Assuming all families use identical thresholds; always consult the specific datasheet. However, the 2–5 V convention remains a widely taught baseline for TTL levels.
Final Answer:2–5V