I'm working with a mid-infrared (~4um) photodiode model Lms43PD-03-CG (Datasheet) and a matching LED (Datasheet). (I can't switch from this photodiode/LED pair) I'm trying to make a functioning photodiode amplifier but have not been able to get the photodiode to respond.

I've tried a basic photodiode amplifier but no feedback resistor value would work. I tried adding a capacitor to stabilize the trans-impedance amplifier but no values appeared to work. I tried biasing the positive input of the op amp to not ride the rails, and still nothing.

I've recently started experimenting with using photoconductive mode (to increase the power source of the photodiode), but don't know/can't find much information about designing a photoconductive photodiode amplifier. I even tried using Analog's design tool but photodiode's specifications our outside of their photodiode parameters.

This is the design that I'm looking to design around with the photodiode being reverse biased. I am connecting the photodiode amplifier to a lock-in amplifier once I get the photodiode responding to light and creating a voltage response. I am checking the output signals with an oscilloscope.

Some other important information:

The op-amp I am using is the MCP6002. The desired frequency is at most 10kHz.

Photodiode Amplifier

Here are my questions:

  1. In the photodiode datasheet, there is a reverse voltage of 0.1V. Is this the same as the breakdown voltage, the max voltage that photodiodes may safely receive?

  2. Would this circuit require a capacitor? If so, what equations should I use to determine this capacitor value? I've tried several such as TI's photodiode design guide to no avail.

  3. What should I be cautious about designing this photodiode amplifier? I'll make sure to bias the positive input to avoid the rails.

  4. What else could be causing this circuit to not respond? No matter how much I shine a MIR LED to the photodiode from a short distance, it doesn't respond.

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    \$\begingroup\$ What supply voltages have you tried? \$\endgroup\$ – Andy aka Jun 19 '18 at 16:02
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    \$\begingroup\$ You say you can't change devices, but at the same time your photodiode has a big hole in its response spectrum right at the peak of your LEDs output spectrum. You might just have a bad set of requirements here. \$\endgroup\$ – The Photon Jun 19 '18 at 16:09
  • \$\begingroup\$ What is your purpose in this circuit? To get Logic output? If you want to get logic, than i would ask you what is the resistor value do you use or did you try other values suitable for your design? Transimpedence amplifiers usually require big feedback resistance values. \$\endgroup\$ – pacman Jun 19 '18 at 16:18
  • \$\begingroup\$ I've tried positive and negative voltages of 5V, 3.3V, 1V, and nothing else. Also the purpose of the circuit is a CO2 sensor. I'll probably use an Arduino to pick up the signal and process it. So @ThePhoton, if CO2 is absorbed at 2.7, 4.3, and 15um, 2.7um would be better sensitivity for the photodiode? I didn't realize that the hole in the spectral response was literally what my LED was outputting. Would this overlap in peaks really not allow me to see any signal change? For the resistor values I used (Vsupply - Vled)/Imaxcurrent and got ~30ohms \$\endgroup\$ – Amaury Jun 19 '18 at 16:23
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    \$\begingroup\$ @JohnD, maximum power supply for this op-amp is 6 V, 7 V is absolute maximum. OP, if you tried +/- 5 V supplies, you may have killed your op-amp. \$\endgroup\$ – The Photon Jun 19 '18 at 16:47

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