timing jitter - VL53L3CX

v++ · ‎2023-03-06

Hello Community,

Any documentation on timing jitter in relation to this sensor ?

In a single range how does changes in the timing jitter affect the spread of peaks ?
1. For two different histograms generated from two different distance, does slight changes in timing jitter affect the spread of peaks ?

Thanks

John E KVAM · ‎2023-03-09

I don't think I truly understand the question. There is timing jitter in the chip to help with the EMI footprint - but the sensor makes maybe a million flashes in a 30ms integration time. The slight timing jitter works out in the accumulation of the photon counts per clock cycle.

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v++ · ‎2023-03-12

Thank you @John E KVAM

-To clarify more lets assume ranging starts from a target 20cm away. Also we assume target is a perfect flat surface with same reflectance rate across whole surface. Can this perfect flat surface imply a single peak or low spread in peaks ? or is the peak spreak mainly dependent on offset in timing jitter ?

-Also compared to another object at same distance with multiple roughness and depths on surface, given the same timing jitter for both scenarios, what are some key properties of the two histograms to be expected ? For instance will the perfectly flat surface have lower spread peaks (or even a single peak) than the rough surface ?

How does properties of these two target histograms vary with offsets in timing jitter ?

Hopefully I was able to clarify properly

John E KVAM · ‎2023-03-13

If the laser flashed very quickly you would get all the photons in one bin. But then you could not tell if your target were in the front of the bin (20cm) or the back of the bin (39cm). The design was to leave the laser on for at least 2 bin times. So you could use the ratio of bin heights to indicate where in the bin the target resides.

Forget offset jitter. We do a million plus flashes in that 30ms collect. The jitter gets averaged out.

Smooth vs rough (specular vs Lambertain) does not matter. A mirror only returns more photons assuming it's perpendicular.

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v++ · ‎2023-03-13

Thank you.

but if the bin height indicates where the full target height is for instance, then from my tests it’s not quite clear.

if I position an object at distance 60mm, can I expect the tallest bin to be the bin at index 0 ? Because my tallest bin ended up around bin 6? But target was so close by the sensor.

if ranging distance is at 20cm I’d expect both ambient and signal from target.

but if it ranges above 20cm, bin 2 onwards I’d expect only ambient.

but I have consistently received signals from bin 5 to 7 for same object

v++ · ‎2023-03-13

How exactly does the ranging operation happen? Any flow diagrams could possibly help ?