• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 32 subscribers
  • Views 693 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

What is the relative position requirement for OPT8241 and the laser module?

Justin Liu27
Prodigy 170 points
Other Parts Discussed in Thread: OPT8241

Hi TI,

I'm trying to put the laser module and OPT8241 on the same PCB( on the same level) which is different from the evaluation board 2-level design. However, I've run through all the datasheets and I didn't find any specific requirements for the relative position of OPT8241(and its lens module included) and laser module. Can you please help me out?

  • 0
    Prodigy 90 points
    Hello Justin,

    I´am also interested in this topic, we as well plan a module with possibly sensor and illumination in one plane. In my eyes the relevant questions are:
    - straylight from illum. directly into sensor (~>flying pixels)
    - heat spreading (~>sensor performance)
    - finite distance between illum. and sensor (~>distortion for close objects)
    The absolute height difference of illumiation source and sensor should not be relevant, it will occure as a constant phase offset, to be calibrated.

    Do you plan to go with Lasers, or have you looked into alternatives as LEDs or VCSELs?

    regards,
    Marcus
  • 0 in reply to Marcus Schwenk
    Prodigy 170 points

    Hi Marcus,

    I'm going to stick with lasers since I need higher frequencies.

  • 0 in reply to Justin Liu27
    TI__Expert 3800 points

    Justin, Marcus,

    You have raised good points to consider when placing the lasers. There are a couple of other things to take care of.

    1. Ground bounce: The illumination driver injects a lot of high frequency currents into the ground and probably will cause the ground net to vary in voltage with respect to the ground net in other parts of the PCB. If the lasers are very close to the sensor, They may cause the sensor's ground to bounce resulting in crosstalk.

    2. Lens shadowing: If the lasers are very close to the lens, the lens may stop some of the light emitted from the lasers from reaching the scene. This necessitates a minimum distance between the lasers and the lens.

    3. Shadowing in the image: Because the lasers are always together and on one side of the lens at some distance, there will be some part of the scene which will be eclipsed by nearer objects. These shadows are a typical problem in photographs which rely on flash. The practical solution to this problem is to have the lasers elevated to the lens' height and move them very close to the lens. This alleviates most of the typical shadowing concerns. Placing the lasers on both sides of the lens is NOT a good solution as driving lasers/LEDs at high modulation frequencies when they are separated from each other is impractical.

    You have already discussed the thermal concerns.

    The distortion because of the non-zero distance between the lens and the lasers may not be too much if the object distances are not too large compared to the laser to lens separation.

    Hope this helps.

    Regards,
    Subhash