ToF sensor

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Hello,

 

out of curiosity i am trying to understand how can ToF sensors measure variations in time in light speed reflection. I know how it works in theory, but how can they measure time so fast, that they can measure delay that occurs between sending out light beam and it returning to sensor?  

After doing some simple math, if object is 5cm away and sensor and emitter are 1cm apart  and you need 1cm resolution in distance reading, you would have to read "input" with 330 THz to measure time difference it takes for beam to return. So do they use some sort of light slowing media or some chemical delay or what?

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Last Edited: Fri. Dec 13, 2019 - 09:26 AM
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The usual method to get sub nanosecond resolution is  by using a linear ramp and a counter. The counter counts, say 20ns periods wherea the linear ramp rises in 20ns, then fall in 20ns. A sample and hold is used to capture the analog value at the end. The measurement consists of the 20ns counts and the portion of the 20ns measured by the analog voltage of the ramp. If you use a 10 bit adc, then you get 20ns/1024 ns resolution. How ST achieve it internal to their sensors is a bit of a mystery, but it is probably something similar.

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thanks for shedding some light on subject :D