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Discrete Photodiode Array

Arash KANI
Prodigy 30 points
Other Parts Discussed in Thread: OPA657

I'm looking to implement a discrete photodiode array in a circular patern to measure the angle of incidence of a laser on an object. I've estimated <50 photodiodes in total and was hoping there was some example of this being done in practice so I can gain a better idea of how to implement the transimpedance circuitry. The readings will be processed by a microcontroller that is yet to be decided upon.

I am aware of the TI tidu535 document and had some thoughts toward switching the photodiodes via analog switches. I also know about the sample and hold method and would appreciate some guidance as to the best way of moving forward.

Thanks.

  • 0
    TI__Mastermind 45475 points

    Arash,

    TI's analog signal switches are designed to pass the signal from one path to another with as little distortion as possible.  I'm not very familiar with photodiode array application but I would imagine that you would need to be concerned with the parasitic effects an analog switch will have on your signal.  I believe the on- state resistance (Ron), input capacitance (con), and charge injection would be the parasitic effects that would concern your application.  Theses values can be found in our datasheets and you can sort on these parameters in the signal switches parametric table on TI.com.  

    There is another recent post on this topic from Sangkyu Kim.  You may want to add some of your questions to this thread to see if they can help moving you forward. 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Genius 12631 points
    Arash,
    I am an applications engineer from the high-speed amplifier product team and am currently working on a reference design concept to help customers alleviate such problems. If you follow the link that Adam posted above you will see a quick introduction to the design concept. Let me know if you have further questions and Adam and I can try and help.

    -Samir
  • 0 in reply to Samir Cherian
    Prodigy 30 points

    HI Samir,

    I dont see any references to your reference design concept in Adam's link, but would be very interested to know what you're working on and how you are tackling the problem.

    For now, since the intensity of the light I am using is high, I plan to use a transimpedance amplifier and use analog switches to sequential switch the relevant photodiode being measured. 

    Thank you.

  • 0 in reply to Arash KANI
    TI__Genius 12631 points

    Its should be there now, but here it is again.

    -Samir

    2806.TIDA-01222_OnePager.pptx

  • 0 in reply to Samir Cherian
    Prodigy 30 points

    Fantastic, thank you Samir.  Can you provide some thoughts on placing analog switches in between the photodiode and the inverting input of OPA657 shown there? Specifically I am interested in parasitic effects and other issues that may come about in such a design.