OPT3101: The OPT3101 channel switch has a distance jump

Pengsheng,

  Based on the plot, labeled number of points, this looks like amplitude not distance. If this is distance and if this is the same system from another E2E, then it looks like you are getting better than 5m which is further than expected. The shift can be from the OPT3101 increasing the current due to the overall distance and that produces a larger error. I will need more information to understand what happening if this is not the same project. 

Pengsheng,

This is an effect of using HDR. The current will change as neded to maintain the proper amplitude and phase based on the distance. The step should be minimal or non existant if the calibration is correct. If you see the step then you need to look closer at the calibration for HDR mode especily when doing the phase offset calibration. 

Super HDR Mode calibration

 In HDR mode, the current can switch between 2 current settings on one TX channel, and with super-HDR, TX1 can be used to add 2 more current settings.

 What we think is going on here is that the phase offset measurements are not being done at the proper amplitude for each current setting.

 The documentation recommends doing phase offset calibration at a target distance where the amplitude is between 16000-24000. The preset values in the SDK are arbitrary and definitely don’t follow this rule. The values are set like below in OPT3101Coefficients.cpp.

 void environmentalController::manuallySetReferenceDistances(){

       this->refDistancesInMM[0][0]=50;

       this->refDistancesInMM[0][1]=120;

       this->refDistancesInMM[1][0]=60;

       this->refDistancesInMM[1][1]=150;

       this->refDistancesInMM[2][0]=0;

       this->refDistancesInMM[2][1]=0;

}

 The indexing on refDistancesInMM is [Tx channel] and [current setting, 0 being H and 1 being L]. In order for them to find the proper distances to set for each current and tx setting, you will need to change your configuration to do just one current, flash that, and see at what distance you can get 16000-24000 codes for that particular current. At higher currents, that distance will be pretty far with a white background, so you can use darker backgrounds in order to get lower amplitude settings, but they’ll need to remember what current settings used what color background when you do the calibration.

 Once you know these distances, you can enter that into OPT3101Coefficients.cpp and then use super-HDR configuration and perform the calibration.

Pengsheng,

  1) The max current of the emitter is 100mA. However the OPT3101 is first off a 10Mhz signal so it is not always on or off. It actually has a duty cycle, The duty cycle is based on "Duty Cycle = (NUM_AVG_SUB_FRAMES + 1) / (NUM_SUB_FRAMES + 1)" If the duty cucly is 50% then the OPT3101 at full current of 173mA would be 86mA average, so the current will not exceed the 100mA max of the emitter. 

2) 20uA is correct based on the corner frequency

7.3.3 Ambient Cancellation
The ambient cancellation circuit provides the dc and low-frequency diode current while biasing the diode at 1 V.
Figure 22 shows the frequency response of the ambient cancellation circuit. A diode current with frequency
below fc2 has second-order rejection. The corner frequency fc2 is designed to be at 50 kHz for IAMB_MAX_SEL =
0 (20 μA ambient current support). Below frequency fc1 (approximately at 10 Hz), attenuation becomes first-order.
So for a frequency of 1 kHz, the rejection would be (50 kHz / 1 kHz) × 2 = 2500 = 68 dB.

3) I don't have the exact answer to this, except that it sets a ratio of the 4 currents. Super HDR is an extension of Auto HDR. In Auto HDR there is a setting for Auto HDR Scale. The ratio will impact the scale and the final currents. All of this is based on your entire distance range that you are trying to achieve. Example: If your distance range is 1m - 3m then you reduce the ratio because you don't need the ultra low currents. If you need 100mm to 3m then you will increase the ratio to to get the ultra low and the high currents. You can tweek this ratio to put one of the currents and distance for the calibration near the step that you see. 

4) the H threshold is based on the amplitude level that you want it to switch currents. At each current when the amplitude reaches 26000 the current will increase to the next level. This can switch current earlier to minimize the step as well. Only you can determine this by testing your system.

In the plot you can see that changing the current can create a potential step in distance. This is not always the case. Use the System estimator to look at the currents and expected operations, then use the System Configurator to get the currents. The two compliment each other so use them they will help you maximize the system. Then set the distances based on the currents and the amplitude. Put that into the CCS code and run your calibration. 

Much of what you are asking is in using the tools. Good luck.