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Cross Talk Time of Flight Product Selection

JGarrettW
Associate II

Hey, I am a researcher and I have an odd requirement for a TOF sensor. I need to create an array of TOF sensors in which cross-talk is purposefully used. In other words, I want one TOF sensor to send a pulse and all the other sensors tell me when the pulse from the first sensor reached them. I would like to avoid making this system from base-emitter and receiver components, though that may be what I have to do. I hesitate since TOF requires accurate timing down to picoseconds.

For those interested, my specific application is in soft robotics. I have a grid of interconnected stretchable fiber optic waveguides. The amount of time and amplitude of the signal that makes it through one of these waveguides is affected by how stretched and bent these waveguides are. I want to send a pulse from one point in the grid and measure how long and how much makes it to the other points on the grid and then repeat that process for each point on the grid. This is very similar to optical time domain reflectometry, but I am hoping to avoid the large and expensive equipment that field uses. Another researcher has done this on a small scale with one of the STMicroelectronics VL53L3CX sensors (Multitouch Pressure Sensing With Soft
Optical Time-of-Flight Sensors: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9674750).

Screenshot 2023-06-28 112638.jpgAny help anyone can give would be appreciated.

1 ACCEPTED SOLUTION

Accepted Solutions
Anne BIGOT
ST Employee

Hello
There are some problems with this approach. The VCSELs generate a lot of EMi. To avoid them, the sensors provide a bit of spread spectrum clock jitter. This keeps the relatively large, fast power on/off from screwing up all the chips around it by having one large EMI spike.

But it seems you want to use the VCSEL output of one chip and the RX of lots of chips.

To do this they all have to run in lock step. And the jitter would prevent this from working.

It might be that you can disable the EMI protection on the chip, but then you still have to find some way to keep them in lock step. 

And interesting idea, but financially untenable. 

Regards

Anne

 


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3 REPLIES 3
Anne BIGOT
ST Employee

Hello
There are some problems with this approach. The VCSELs generate a lot of EMi. To avoid them, the sensors provide a bit of spread spectrum clock jitter. This keeps the relatively large, fast power on/off from screwing up all the chips around it by having one large EMI spike.

But it seems you want to use the VCSEL output of one chip and the RX of lots of chips.

To do this they all have to run in lock step. And the jitter would prevent this from working.

It might be that you can disable the EMI protection on the chip, but then you still have to find some way to keep them in lock step. 

And interesting idea, but financially untenable. 

Regards

Anne

 


In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question.
JGarrettW
Associate II

Thanks @Anne BIGOT, this may be a stupid question, but if I cover the emitters on many VL53L3CX to make them only able to receive and run the chips all in interrupt mode with the interrupts all tied together (and of the appropriate length so that the clearing of the interrupt reaches them all at the same time) would that work? I had not heard of spread spectrum clock jitter, so I looked it up. Are you saying that each chip will not act the same when it comes to clocking? Sorry if I'm not understanding you.

Unfortuantely that is exactly want it means. This approach has advantages (to everyone but you). Our chips don't interfere with each other (very much) because they operate with slightly different timings. And they don't cause problems for all the other chips in the design. 

To do what you are proposing, I think all the chips have to run on the same clock, otherwise slight variations in phase are going to make a mess of the timings.

- john


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