In pulse and timing measurements, the rise time of a digital pulse is normally measured between which reference levels?
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A0 and 100% level
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B10% and 90% level
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C30% and 70% level
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D50% level on the leading edge to the 50% level on the trailing edge
Answer
Correct Answer: 10% and 90% level
Explanation
Introduction:Rise time characterizes how quickly a signal transitions from LOW to HIGH. Consistent reference levels avoid distortion from overshoot, noise, and edge rounding across technologies.
Given Data / Assumptions:
- We need the conventional measurement points for rise time on a single transition.
- Assume a monotonic leading edge with possible overshoot or rounding.
Concept / Approach:Industry convention defines rise time as the interval between when the waveform first crosses 10% of its final value and when it first crosses 90% of its final value. This avoids sensitivity to baseline noise near 0% and to final settling near 100%.
Step-by-Step Solution:
Identify standard reference points: 10% and 90% of final amplitude.Measure time of first crossing at 10%.Measure time of first crossing at 90%.Rise time = t(90%) - t(10%).Verification / Alternative check:Some instruments allow 20–80% as an alternative, but 10–90% is the canonical definition used for datasheets and comparisons.
Why Other Options Are Wrong:
- 0 and 100%: Too sensitive to noise and settling behavior.
- 30% and 70%: Non-standard; sometimes used in specific contexts but not the primary convention.
- 50% to 50% (leading to trailing): That is pulse width, not rise time.
Common Pitfalls:Confusing rise time with propagation delay or pulse width; always check which metric and thresholds are specified.
Final Answer:10% and 90% level