The requirements for the RefSPAD calculation are "no close target" and by that they mean 5cm or so.
If you wanted, in your factory to do the offset calculation at say 14cm (it's what we suggest). It would be fine to set up a target at 14cm, do the RefSpad calc, then do the offset calc.
Once that is done, we have to work on Crosstalk.
You need a target where the normal ranging ends up being 10-20% short. If you use a dark target, that might only be 30cm. Or it could be more depending on the target reflectivity and the quality of your coverglass.
Experiment to find this. Make sure the diameter of the target is at least 1/2 the distance you are ranging.
Once you have this distance. Create a set-up to do your calibration. Create some sort of flap that can fall down and create the 14cm offset target.
Fold the flap down, do the RefSpad and the offset cal. Then lift the flap and do the crosstalk cal.
If you have very consistent glass quality and the air gap between sensor and glass is consistent, consider calibration of the first few off the production line, then just use the worst of these calibration values for your entire line.
(The penalty for over calibration of the cross talk is a short measurement, but under calibration can lead to a ghost image - and you don't want that.
For the best accuracy, go ahead and crosstalk cal them all. But if you don't absolutely need the best accuracy, lots of people crosstalk the design, then just use the numbers.
- john
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