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WJLO
Associate II
May 30, 2024
Solved

VL53L8CX &VL53L5CX Why can VHV be used to compensate for ranging offset?

  • May 30, 2024
  • 1 reply
  • 2028 views

Hi there, 

  I read this document and it mentioned that the function "vl53l8cx_set_VHV_repeat_count" can be used to compensate for the ranging error caused by temperature. I would like to know the principle of VHV calibration compensation. Is it related to the signal power of VCSEL? 
  Does VHV calibration also apply to the compensation mechanism at low voltage (2.5~3V)? Or are there other functions that can compensate for voltage drift?

 

WJLO_0-1717052722890.png

 

Best answer by John E KVAM

Anne is exactly correct, but perhaps a bit more explanation would help.

We invented these sensors for the cell-phone market, and users are not very good at keeping the battery topped up, so one of the design criteria was to work with a wide range of power.

The VHV circuit has to do recharging the Single Photon Avalanche Diode (SPAD) array. We have to reset the diode element to a point where a single photon strike will cause the diode to avalanche, and we can count it. It's kind of tricky and it's temperature sensitive. 

That is what the VHV calibration is trying to do. 

As we base the distance measure on when the photons arrive not how many, slight variations in VCSEL (laser) strength are not important. (We do count how many arrive and useful information can be gleaned from this, but as long as we get enough photons, we get an answer.)

- john

1 reply

R
RogerM
ST Employee
May 30, 2024

VHV is an internally generate voltage used within the SPAD array.  So it is not affecting VCSEL power and should not be affected by external supply voltage variations.
VHV calibration makes small changes to this voltage to stabilise the SPAD sensitivity as device temperature varies.

W
WJLOAuthor
Associate II
May 31, 2024

Hi there, 

  Will the distance measurement be affected when the device is low on battery? Is there any calibration method?

Anne BIGOT
Anne BIGOT
Technical Moderator
May 31, 2024

There is no impact on the measurement. If there is not enough power, the device won't start and will return an error.

Regarding the calibration, you can find information in the UM3109.

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