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opt9221: Method for increasing max range?

Bob Rook
Prodigy 40 points
Part Number: OPT9221
Other Parts Discussed in Thread: OPT8241,

Hello - 

I am evaluating the OPT8241 and OPT9221 for a long-range sensing application. This is only theoretical analysis at this time, so many of the operating paramaters may change.

It is my understanding that the max range is limited due to the "wraparound" effect occuring in the integration phase. That is, the sensor is designed to read the signal within the pulse width timing of the illumination pulse.

Our application is to perform in the range of 300m to 1000m. Theoretical design includes an illumination lens design giving a FOV of <1 degree. At these distances, the roud trip timing combined with the sensor design drives an operating frequency of 100kHz, well below the lower limit of the device. This is daylight operation, but the illumination module is yet to be designed, so assume that the power will be sufficient to meet the design needs.

My question: can the illumination start-of-cycle and sensor start-of-cycle can be decoupled in the Integration phase? That is, can I design the illumination module such that it operates in the 20-40MHz range, but delay the sensor activation a suitable time to allow round-trip transit (of course, assuming its timing cycle is locked in with the illumination timing)?

What is the function of the illum_en_early and illum_mod_early settings in the OPT9221 (that is, is it merely to allow an early signal for an external illuminator so there is time for it to awaken, or does it offer a means to achieve longer range through starting the pulses early)?

Thank you,

Bob

  • 0
    TI__Expert 3495 points

    300 m is quite a long range.  To see the kind of power you need please use our System Estimator Tool that can be downloaded for free.

    The maximum range is limited by wrap-around (aliasing) and practicality of required illumination power.  The wrap-around problem can be overcome by turning on our dealiasing feature, explained in this video at the 3:32 mark.  This video describes various operating parameters impacting accuracy and therefore range, including illumination power.

    As you correctly pointed out, narrowing FOV will help extending the effective range, basically operating the TOF device like a LiDAR.  However, high illumination power in narrow FOV also brings about eye safety that must be accounted for.  Daylight operation must avoid pixel saturation by reducing the integration time.

    I don't quite understand your intent behind delaying integration (exposure).  Is it to void saturation?  

    ILLUM_EN_EARLY and ILLUM_MOD_EARLY enables light emission a little bit sooner to accommodate for any propagation/turn-on delay/settling time of the illumination circuit.

  • 0 in reply to Larry Li
    Prodigy 40 points

    Larry,

    Thank you for your response. Sorry for delays, but I have been on another project for a couple of weeks and am now returning to this one.

    The video was very helpful in getting a better understanding of dealiasing, as well as general design and operation of the sensor. The rationale for delaying integration was to allow propagation delay. If I am understanding the design correctly, the dealiasing should accommodate the propagation delay for this range, provided the laser and lensing issues could be resolved. Is this correct?

    There may still be a need to delay the integration time to avoid saturation, but assuming this setting is accessible in the test kit, I could easily try various settings - unless the system estimator tool or other engineering estimations can provide an answer.

    Thank you,

    Bob

  • 0 in reply to Bob Rook
    TI__Expert 3495 points
    Bob,

    Any propagation delay in modulation frequency, either electrical or optical, if constant, will manifest itself as a constant phase offset, which can be calibrated out. This is what we called "Common Phase Offset". Saturation is avoided not by delaying, but by reducing the integration time. Illumination is turned on ONLY during integration time. Our TOF chipsets give you all the knobs to tune.

    -Larry
  • 0 in reply to Larry Li
    Prodigy 40 points
    Larry,

    Thank you for your prompt reply. To clarify, does the Evaluation Module allow access to all settings?

    - Bob
  • 0 in reply to Bob Rook
    TI__Expert 3495 points
    For our EVM, all except a few that could "break" Class-1 laser eye safety guideline for which we "close" them to prohibit change, only on the valuation kit. If you make you own boards all data sheet features are accessible.
  • 0 in reply to Larry Li
    Prodigy 40 points

    Thank you for all of your help, Larry!