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
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