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Do ADPD103 and ADPD105 output different signals?

Equated
on Oct 1, 2018

Hi there,

For my project, I’m trying to optimize an optical sensor system which function is to recognize, wether there is a tube in the detection slit. The sensor is based on an emitting LED and a position sensitive device with 2 electrodes on the opposing side, so when refraction of the light changes, so does the state. The system displays different states such as no tube, tube with air or tube with fluid. Because of the ambient light, the plan is to integrate an ADPD IC into the circuit for filtering unnecessary light.

I have tested the ADPD103 Evalboard with an optical sensor system beforehand and it worked wonderfully. I connected the electrodes to PD1 and PD2 and read the signal. Now I’m trying to get the ADPD105 Evaluation board working for my project. But as it seems, the photodiode outputs show entirely different values for the graphs although the function of these ADPD boards should be similar. Am I missing something?

For both boards I used the following setting in the ADPD Openmarket WaveTool:

With a certain formula you can calculate the position out of the values of right and left electrode. There is a correlation between the states and the position, more specifically the difference values.

I have no problem with the ADPD103 but that’s not the case for ADPD105. I have to make it work on the latter module.

Any help is appreciated. Thanks.

  • +1
    •  Analog Employees 
    on Oct 5, 2018 1:25 PM

    Hello,

    The first thing that jumps out is that your timing for slot B will not work, if you're in normal mode with the TIA, BPF, integrator enabled in the signal path. Timing for both channels, assuming you are in the same operating mode, should be approximately the same. The exact optimal timing point may shift by ~200ns for different TIA gains, but if you find the optimal timing point for one timeslot then the same timing should be used for the other timelsot, again assuming you're operating both channels in the same mode.

    The other thing is that for the exact same settings between 103 and 105 you will see ~1/2 the output level. This is because the ADPD105 has twice the dynamic range for a pulsed signal vs the ADPD103. 

    I would also suggest that if this is for a new design then you should be looking at the ADPD1080 which is our latest AFE in that family and gives the best SNR at the lowest power for the entire family of devices.

    Regards.

    Kevin