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OPT3101: Calibration setup problem

Part Number: OPT3101

hi,

1)、Use the SDK to calibrate opt3101. When initializing the settings, put "monoshot_mode=3". Read when performing crosstalk calibration,the crosstalk value is all "0". Is this a normal phenomenon? If it is normal, it means that "monoshot_mode=0" is required before performing the crosstalk calibration operation, right?

2)、Some of the descriptions in Section 4.2.3 (Scale Value for Crosstalk Measurement) are in the “OPT3101 Distance Sensor System Calibration” manual. such as:

1. "A system with crosstalk greater than 32768 × 1.64676 / 2⁶ = 843" How did "32768" and "1.64676" come from?
2. "Typically expected crosstalk is < 200 codes with highest LED current" means mask photodiode and measure the amplitude: AMP_OUT register<200?
3.mask photodiode and measure the Amplitude: The AMP_OUT register value is approximately 15000. Will the crosstalk calibration be invalid? How can I confirm that the crosstalk calibration is successful?

Best,

dongming.cui

  • Hi Dongming,

    1) I will need to check this. Also which version of the SDK are you using? (0.8 or 0.9.1)

    2) 1) These are internal device values. 32768 is an internal size indicating max crosstalk that can be corrected. 1.64676 is a constant factor needed when converting this xtalk value to the device AMP_OUT amplitude value. Thus if over this value then values must be scaled.

    2) 2) correct

    2) 3) we would need to explore why the crosstalk is so high. This is quite high for correcting and will make the device much more sensitive to environmental changes than it should be. The usual reasons are board design: not following requirements in the system design doc and datasheet for layout and passives, shielding on the LED and PD for electrical crosstalk if using through-hole optics, and optical isolation between LED and PD. If you would like to share you design specifically schematic, layout, BOM, and shielding/isolation used I can review to check if everything was followed correctly. Datasheet has general requirements and then the system design doc gives all the details.

    You can check crosstalk is corrected by measuring residue xtalk. This is the same amplitude with photodiode masked but after correcting for crosstalk so you can see how much is left after correction. This should be <10 in most cases. You can also see over time, temperature, and moving objects near the OPT how the xtalk changes. We do have temp calibration on device as well to compensate for temp effects, but I would advise getting xtalk low as possible through board design and shielding.

    If you are using old SDK I also want to point out that 0.9.1 online has a calibration mode on MSP430 launchpad to speed calibration process if this is helpful, but I'd suggest we first try to get the xtalk down to <200 or at least <800.

    Best,

    Alex

  • Hi Alex,

    Thank you very much Alex for replying!

    1) SDK version is 0.8.

    2)3)Calibrated by the old version of the SDK, AMP_OUT = (12 ~ 33) after calibration. But there is a strange phenomenon. When the actual distance between the OPT3101 and the measured object does not change, only the optical power received by the OPT3101PD is changed. It is found that the distance measured by the OPT3101 is greatly affected by the change of the optical power of the PD receiving end, which is obvious. Guess, this phenomenon and Section 8.1 of the Introduction to Time-of-Flight Long Range Proximity and Distance Sensor System Design, Figure 26. Vector diagram with residue crosstalk Related to the described situation, observing the measured phase vector diagram in Figure 26, it can be concluded that when the vector direction and size of the residual crosstalk are fixed, the measured optical distance will change when the optical power received by the opt3101 PD changes. I don't know if this guess is reasonable. Is there any other reason for this phenomenon? Please ask Alex?

    Best,

    Dongming.cui

  • Hi Alex,

    Since the crosstalk is 15000, FORCE_SCALE_VAL is set to "5" when doing the above test.

    Best,

    Dongming.cui

  • Hi Dongming,

    Yes I think this is due to crosstalk being so high.  We will need to resolve this first. Can I review your board design/layout and shielding used?

    Best,

    Alex

  • HI Alex,

    Thank you very much!Our hardware engineer told me that the current hardware design is not completely in accordance with the reference design. I will take your advice, the hardware is new design, first reduce the crosstalk, and then do further testing.

    Best,

    Dongming.cui