Pulse Width and Range Resolution in a Rangefinder

One nanosecond of round-trip time is about 15 cm of one-way distance. That's the conversion that makes pulse width matter.

Resolution isn't accuracy

Resolution is the smallest distance step the receiver can tell apart. Accuracy is how close the reading is to the truth. A 1 ns pulse can support centimetre-class resolution and still be metres off if the system delay is uncalibrated.

People conflate the two when they compare modules. Ask for both, and ask how accuracy was measured.

What the pulse width does

A shorter pulse gives a sharper leading edge, which helps the timing discriminator. A longer pulse carries the same energy at lower peak power, which is kinder to the coatings. That's the trade the source design makes, and it's why our pulse widths grow with energy: 3.5 ns on the microchip, 5–7 ns in the compact range, 12–13 ns from 2 mJ up.

The rest of the error budget

Detector jitter, threshold walk on the leading edge, time-to-digital quantisation, clock drift, and the calibration of system delay. In a well-built receiver, the pulse width stops being the limit early; the other terms take over.

Walk error is the one that surprises people. A strong return and a weak one cross the threshold at different points of the pulse, which shifts the timestamp. Constant-fraction discrimination exists for that reason.

How to check it

Measure against a known target at several distances, with strong and weak returns, at both ends of the temperature range. If the reading moves with signal strength, the discriminator needs work.

Ask how our modules are characterised

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