OPT3101: OPT3101 amplitude information

Markus Stadler1

Part Number: OPT3101

Hi,

I use the OPT3101 on a custom board.

If I initialize the sensor and read ot the amplitude value (reg 9h[15:0] I get values from around 700 to up to the saturation value of 65535, depending on where I point to. That makes perfectly sense to me.

After calibration of external crosstalk, however, the amplitude readout minimum is 40 but saturates at 1023. Pointing to a high reflective surface the amplitude value can also take on 65535. It seems to me that the value in reg 9[15:0] is scaled or processsed in some way, depending on settings after calibration. Could you explain this amplitude value is calculated internally in OPT3101?

Many Thanks!

Markus

over 5 years ago

0 Alex Bhandari-Young over 5 years ago

TI__Mastermind 25855 points

Hi Markus,

Amplitude is directly proportional to received signal if the calibrations are correctly applied. If your amplitude is not going above a certain level then you may not be outputting enough optical power from the LED to saturate the RX even when the target is close and very reflective. This could be sensitive to angle so it is possible at some angles you saturate (64k) but most angles have a low setting if this is the case.

Best,

Alex

0 Markus Stadler1 over 5 years ago in reply to Alex Bhandari-Young

Prodigy 135 points

Hi Alex,

no, it has noting to do with the optical power. The fact that the value is pinned at either 1023 or 64k is suggesting a systematic thing.

Reason seems to be related to auto scaling: DIS_AUTO_SCALE must be set to 1 (disabled), as it seems, both during calibration and operation. Is that correct?

0 Alex Bhandari-Young over 5 years ago in reply to Markus Stadler1

TI__Mastermind 25855 points

Hi Markus,

Didn't mean to mark your post resolved, clicked the wrong button and looks like I cannot undo.

Have you followed the steps on the calibration docs listed here? https://e2e.ti.com/support/sensors/f/1023/t/815766

This one discusses scaling for crosstalk https://www.ti.com/lit/ug/sbau310/sbau310.pdf

What is the level of the crosstalk you are correcting for? Can you follow step 4 here to measure crosstalk level before and after running your calibration? This will give me more info to work with https://e2e.ti.com/support/sensors/f/1023/t/727462?-FAQ-OPT3101EVM-Troubleshooting

Best,

Alex

0 Alex Bhandari-Young over 5 years ago in reply to Alex Bhandari-Young

TI__Mastermind 25855 points

Hi Markus,

Going to mark resolved for now since some time has passed, but please let me know on the above questions if you still need help here.

Best,

Alex

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OPT3101: OPT3101 amplitude information