OPT3101-SDK: Variation of distance measurements when powering on and off the board

Hi Olga,

What is the board temp and have you loaded the temp calibration coeffs? It seems you are powering on and off multiple times to check repeatability and seeing some change correct? If temp of the board stable during this time? If powering on and off the LED would be expected to heat up the board somewhat.

Best,

Alex

Hi Alex,

I have calibrated the board in the temperature range from 20ºC to 27 ºC. I have observed that the phase variation over this temperature range in distance are only 17 mm. Considering that the expected variation is linear, I don't think this is the cause of the issue since the variation I observe when powering on and off is 280 mm. The temperature of the board during all these measurements is between 26 and 30 ºC.

In addition, I have repeated the same experiment using two different surfaces as a target. Using a white wall the variation of the distance decreases, while using a dark blue surface increases the effect of powering on and off the board. I attach below the dark blue surface. 

Moreover, I have done a study on the dependency of the internal crosstalk that the sensor measures and corrects at the beginning of each time I run the test step. I attach the results of this measurements. 

As you can see in the picture, the variation on the distance of the 3 transmission channels shows the same behaviour and I observe a dependency of the measurement over different internal crosstalk values. Moreover, does the internal crosstalk measurement depend on the target used at the time of correcting it?

Best regards,

Olga

Hi Alex,

I am using another custom board with only 1 transmission channel and I observe the same bahaviour as explained above. In this case, the internal crosstalk variation is higher than in the 3 channel board and also the measured distance after powering on and off the board several times.

Looking forward to your reply,

Olga

Hi Olga,

I was out of office and looks like this post was missed while I was out. I am looking into this now and will get a response this week.

Best,

Alex

Hi Olga,

Internal xtalk will not vary based on the target. It is only correcting for xtalk internal to the device. 

If this is not caused by environmental factors it may be caused by the illumination crosstalk. With a blue wall the amplitude would be lower than a white wall resulting in greater impact of illumination xtalk. You can measure the residual xtalk by following the method described here in step 4.
https://e2e.ti.com/support/sensors/f/1023/t/727462?-FAQ-OPT3101EVM-Troubleshooting
This is the amplitude reported by the device after the illumination xtalk is loaded with photodiode masked. If the amplitude of the measurement in your test is within the same order as the residual xtalk then there could be some effect.

Best,

Alex

Hi Alex,

The amplitude codes at 1000 mm from the target using a white surface are 600, and 250 with the blue surface. The residual crosstalk is around 30 amplitude codes (measured following the procedure that you proposed), which is not the same order as the amplitude reported by the device when measuring at 1000 mm. The amplitude codes do not have anything to do with the distance measurement variation observed when powering on and off several times. Is there a way to avoid this behaviour?

Thanks, 

Olga

Hi Olga,

I have not seen this behavior so it is tough to say what is going on. It may be helpful to check if you are able to replicate the same on the EVM board. Also whether this is board specific, design specific, etc may be helpful to try to trace the cause. Do you have multiple boards are see this happening on all of them?

Best,

Alex