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Sensitive photodiode circuit help

Discussion in 'General Electronics Discussion' started by Rossco, Aug 7, 2014.

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  1. Rossco

    Rossco

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    Aug 7, 2014
    Hello folks,

    I've a detection board made with a Hamamatsu S2386 photodiode, going through a transimpedance amp (an AD8015ARZ chip) and 1MΩ gain. However, the sensitivity is really low with only about 0.4V dynamic range between ambient light and covering the PD completely. It's being powered by 5V DC. First, is there anything simple I've missed? And secondly, any advice would be much appreciated!
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Hello and welcome to Electronics Point :)

    You could start by posting the schematic diagram of your circuit.
     
  3. Rossco

    Rossco

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    Aug 7, 2014
    Thanks!

    It's from a hand-drawn diagram unfortunately...
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Then you could either scan it, or take a photo of it.
     
  5. Laplace

    Laplace

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    Apr 4, 2010
    If you put a current meter in series with the photodiode and measure the difference between the dark current and the ambient light current, is it less than 1 μA?

    In the Hamamatsu Handbook, Chapter 2 for Si Photodiodes, page 29,
    [Figure 1-17] Basic connection example of Si photodiode, the feedback resistor is shown as 10 MΩ. Perhaps that is a clue.
     

    Attached Files:

  6. TedA

    TedA

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    Sep 26, 2011
    Rossco,



    +1 on the need for a schematic!



    And it would help if you shared some basic information, such as required response speed, light levels to be detected or measured, etc.



    I suspect you have a mismatch between what you are trying to do and the IC you are using.



    The AD8015 is all about speed; sensitivity and DC accuracy are secondary concerns.



    I'm not sure how you might have "1M" gain with an AD8015. The part seems to have an internal 10k feedback resistor. So "10k" gain is what you get.



    I think that the photo diode you are using is not intended for fast response, and that the photo current is too small for the AD8015. You may want to look into a low input current op-amp, and use that 10M or larger feedback resistor.



    Ted
     
  7. Rossco

    Rossco

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    Aug 7, 2014
    Thanks for the responses everyone. Attached is the "schematic", which I doubt is much use!

    I'm using it to detect changes in luminescence intensity for an optical sensor. The speed isn't important - sensitivity to changes in light level is paramount. From the advice above it does seem to be the wrong IC - I will look for a low input current IC.

    Laplace, the difference between dark current and ambient light current is around 4μA.

    upload_2014-8-8_14-45-12.jpeg
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Have you looked at the sample circuits shown in the AD8015 datasheet?

    They don't have that feedback loop, and they typically use the complementary outputs.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Added to that, I would google "photodiode amplifier". You'll find plenty or results using similar circuits and normal op-amps.
     
  10. Rossco

    Rossco

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    Aug 7, 2014
    Cheers everyone, I'll try with a sample circuit from the Hamamatsu data sheet and a low-power IC and see how I get on.
     
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