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from my previous question (this link) i advised to using operational amplifiers to converting current changes to voltage changes then i followed the standard circuit for a transimpedance operation of amplifier with a piece of TLC272CP which you can see how i wired it :
enter image description here

my aim is measuring IR, so i connected a photodiode to the op-amp, i tried single supply because i cant make bipolar supplies +/-, then i create a virtual ground by simply dividing resistors to get a mid rail voltage between VDD(5v) and GND. then connect output (also divided) to an ADC.

unfortunately resaults from ADC are some random noises and IR does not affect them even a bit!!! they are near to 2.5 volt without output division.

also i disconnected +input of opamp (PIN3) from VGND and connected it to the physical GND but still sense less to IR, just get lower noises.

i think my circuit is just follow standards, so what could be wrong with it.

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  • \$\begingroup\$ TLC272C is a dual op-amp. What did you do with the amplifier not being used for your TIA? \$\endgroup\$
    – The Photon
    Jul 22, 2018 at 21:54
  • \$\begingroup\$ @ThePhoton, most opamp's are dual or quad! google is full of tutorials for TIA, they never pointed any thing about problem of dual amps \$\endgroup\$
    – payam_sbr
    Jul 23, 2018 at 6:22
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    \$\begingroup\$ You have to apply a (usually reverse) bias voltage to the photodiode in order to get the photocurrent out. Connect the anode to real ground (not VGnd), and see if it makes a difference. \$\endgroup\$
    – Sven B
    Jul 23, 2018 at 7:11
  • \$\begingroup\$ @SvenB i connected photodiode anode to real groubd and then just get 80% of vcc sense less to IR \$\endgroup\$
    – payam_sbr
    Jul 23, 2018 at 7:51
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    \$\begingroup\$ @payam_sbr, an unused op-amp can cause problems. See here, here, or here. \$\endgroup\$
    – The Photon
    Jul 23, 2018 at 16:24

1 Answer 1

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A photodiode is meant to be used with a bias voltage. This is typically achieved by using the "virtual short-circuit" of the input pins of the opamp in the TIA.

Like so:

schematic

simulate this circuit – Schematic created using CircuitLab

The best way to improve the output signal strength is to get more light on the photodiode.
You can also try increasing the feedback resistance at the expense of stability. If stability is an issue, you can add a feedback capacitance to make it stable again, unfortunately at the expense of bandwidth.

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    \$\begingroup\$ It's entirely possible to operate this circuit with 0 bias on the photodiode. This is called photovoltaic mode, and generally results in lower noise but also lower bandwidth. There is also an effect on responsivity but it is not a large effect. \$\endgroup\$
    – The Photon
    Jul 23, 2018 at 16:20

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