Measuring digital pulse width: At what relative amplitude should pulse-width measurements be taken to obtain consistent and comparable results?

Introduction / Context:
Pulse width is the time between two amplitude thresholds on a pulse waveform. Standards are necessary so different instruments and engineers obtain matching measurements, independent of overshoot or ringing.

Given Data / Assumptions:

• Digital pulse with finite rise/fall times and possible overshoot.
• Oscilloscope with cursor measurements or automated timing.
• Industry-standard thresholding is desired.

Concept / Approach:
The conventional method measures between the 50% amplitude points of the leading and trailing edges (mid-levels). This choice reduces sensitivity to edge asymmetry and overshoot/undershoot. Rise/fall time measurements commonly use 10–90% or 20–80%, but pulse width uses the 50% criterion for consistency.

Step-by-Step Solution:
Determine baseline LOW and HIGH amplitudes (e.g., 0 V and VHIGH).Compute the 50% level: (LOW + HIGH) / 2.Place time cursors at the instants the waveform crosses 50% on the leading and trailing edges.Pulse width = Δt between these two crossings.

Verification / Alternative check:
Compare automated pulse-width readout to manual cursor measurement at 50%; they should agree within instrument tolerance.

Why Other Options Are Wrong:
Overshoot/undershoot points are nonstandard and vary with loading.

10–90% applies to rise/fall time, not width.

Damping/ringing envelopes are irrelevant to width metrics.

Peak overshoot is transient and unsuitable for width timing.

Common Pitfalls:
Failure to average noisy signals or trigger stably can cause jitter in crossings; use proper triggering and bandwidth limits if needed.

Final Answer:
50% of the leading and 50% of the trailing amplitude