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Transimpedance amplifier

Nisha Joshy
Prodigy 160 points

Other Parts Discussed in Thread: OPA376, OPA380, OPA657

Hi,

I am doing a project using photodiode. I need to design the transimpednce amplifier for the photodiode current signal. The TIA should have a gain greater than 10^7 V/A and bandwidth greater than 12 KHz. Could you please recommend a product suitable for my application

  • 0
    Guru 21975 points

    Nisha,

    A critical factor in the selection of an op amp is the capacitance of the photodiode. Also, do you have any special power supply requirements?

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 160 points

    Hi Bruce,

    Thanks for the reply. The capacitance of photodiode is 75pF. I would prefer a single supply voltage.

    Regards,

    Nisha

  • 0 in reply to Nisha Joshy
    Guru 21975 points

    Nisha,

    Operating from a single 5V supply, I would recommend the OPA376. This is a CMOS op amp with quite low noise. This is important in your situation because of the very large photodiode capacitance. The ratio of photodiode capacitance to feedback capacitance is high, which amplifies the voltage noise of the op amp. Thus a low noise op amp is important. I recommend a feedback capacitor of approximately 1pF in parallel with the 10M feedback resistor. Mount these feedback components in a manner to avoid stray capacitance to ground.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 160 points

    Dear Bruce,

    Thanks for the reply. I checked OPA376 and it looks like I can achieve the gain of 10^7 with this but not a higher bandwidth .I can compromise on gain but not on bandwidth as I need the higher order harmonics of the signal. I also saw some more products like OPA380 & OPA657. OPA657 has much more lower noise but its dual supply . Can I use it in single supply configuration? 

    Thanks in advance,

    Nisha 

  • 0 in reply to Nisha Joshy
    Guru 21975 points

    Nisha,

    In a quick simulation, I think you can get 12kHz, -3dB bandwidth with the OPA376 using about 1.5pF feedback capacitance // 10M-ohm. I have assumed that you would bias the non-inverting input up to some positive mid-supply voltage on a 5V supply. Output would be referenced to this mid-supply voltage.

    The OPA380 could be used in a similar manner and would have plenty of bandwidth. It is also capable of a ground-referenced output using a pull-down resistor to a negative supply voltage. It appears, however, that you want to avoid a negative supply.

    The OPA657 has a very limited common-mode range and appears to really need a +/-5V supply with a ground-referred non-inverting input. Alternatively, it could be used on a 10V supply with the non-inverting input biased to 5V. This product is supported on the  "high speed amplifier" forum--the place to go if you have further questions on this device.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 160 points

    Hi Bruce,

    I am using OPA380 in the single supply configuration, The noninverting input is biased at 2.5 V. But with 1.5pF capacitor , the output is oscillating at a very high frequency. What is the optimal value of capacitor to prevent this? I don't need a ground referenced output. Right now I am using a voltage source of 1V with 10 Mohm series resistor as the current source.

    Thanks,

    Nisha