3.2 Calibration flow
Crosstalk (Xtalk) is defined as the amount of signal received on the SPAD array, which is due to VCSEL light
reflection inside the protective window (cover glass) added on top of the module. The VL53L8CX module is
self-calibrated, and can be used without any additional calibration.
Xtalk calibration may be required if the module is protected by a cover glass. The VL53L8CX is immune to
Xtalk beyond 60 cm thanks to a histogram algorithm. However, at short distances below 60 cm, Xtalk can be
larger than the actual returned signal. This gives a false target reading or makes targets appear closer than they
really are. All Xtalk calibration functions are included in a Xtalk plugin (optional). The user needs to use the file
‘vl53l8cx_plugin_xtalk’.
The Xtalk can be calibrated once, and data can be saved so it can be re-used later. A target at fixed distance, with
a known reflectance is required. The minimum distance required is 600 mm, and the target must cover the whole
FoV. Depending on the setup, the user can modify settings in order to adapt the Xtalk calibration, as proposed in
the following table.
Table 1. Available settings for calibration
Setting Min
Proposed by
STMicroelectronics
Max
Distance [mm] 600 600 3000
Number of samples 1 4 16
Reflectance [%] 1 3 99
Note: Increasing the number of samples increases the accuracy, but it also increases the time for calibration. The time
relative to the number of samples is linear, and values follow the approximate timeout:
• 1 sample ≈ 1 second
• 4 samples ≈ 2.5 seconds
• 16 samples ≈ 8.5 seconds
The calibration is performed using the function vl53l8cx_calibrate_xtalk(). This function can be used at any time.
However, the sensor must be initialized first. The following figure represents the Xtalk calibration flow.
Figure 7. Xtalk calibration flow
UM3109
Calibration flow
UM3109 - Rev 1
page 7/20
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