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My TIA (figure 1) needs due to its op amp at least a negative voltage supply. There is needed a 3V difference (datasheet op amp). But how can I create this negative supply, I have a 12V dc power supply and STM32L432KC, see figure 2? Or should I buy another op amp?

TIA STM

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I think you should justify first why you believe you need to reverse bias the photodiode. I mean this: the LF347 has a unity gain bandwidth of 3 MHz so, it might only have a decent usable BW of 300 kHz yet, you are reverse biasing the PD as if you were expecting performance up to a few tens of MHz.

What I'm trying to get you to think about is the bigger picture because, the addition of a negative rail potentially allows the output to produce negative voltages that might damage your STM32.

So, if you don't need to use a negative bias on your photodiode (because you don't need the speed) then you can use a single rail TIA design that produces a positive output voltage with increased light intensity. Zero light intensity means 0 volts on the output (with the right op-amp) like this from here: -

enter image description here

On the other hand, if you do need the speed boost that negative photodiode bias brings then you need to use a much faster op-amp compared to the LF347 (or LM324).

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  • \$\begingroup\$ Hey Andy, I am using a bpw34 photodiode, which will give with the LF357 (20MHz gain bandwidth) a 300kHz bandwidth, but with reverse bias of about 6-9V a 700kHz bandwidth. I need at least 600kHz speed since my signal of interest will be around there. Using no reverse bias could be an option, but I don't know which opamp is capable of this. So or I need a op amp with the speed of no reverse bias or I need op amp with a difference smaller as 2V with the negative rail or I need an idea to add the negative supply to the op amp. \$\endgroup\$
    – Visje999
    Commented May 6 at 13:32
  • \$\begingroup\$ @Visje999 firstly, if you look at figure 49 in the LF347 data sheet you'll see that to obtain unity gain from the LF347 you need to add components that reduce the GBW to less than 5 MHz. This is to avoid it becoming unstable. A TIA is a unity gain inverting situation so, you cannot use the full 20 MHz you have assumed. Secondly, the BPW34 looks like it will deliver 600 kHz without reverse bias. This bit is tricky to fathom but, I think the 150 pF in your model is a little high. Thirdly, plenty of op-amps can deliver in single supply config. \$\endgroup\$
    – Andy aka
    Commented May 6 at 14:14
  • \$\begingroup\$ In effect, you might as well be using an LF356 and keeping the circuit simpler rather than trying to use an LF347 (that will possibly be unstable) when used as a regular TIA. \$\endgroup\$
    – Andy aka
    Commented May 6 at 14:19
  • \$\begingroup\$ @Visje999 If we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Commented May 17 at 14:57

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