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searching for an Op- amp

Flummi Loong
Prodigy 40 points
Other Parts Discussed in Thread: OPA827, OPA140

Hello,

I have a signal from a photodiode. It is an S1226 and S1336 from Hamamatsu. I need an OP-amp to convert this signal into a voltage. It should also amplify this signal. That’s the reason why I want to use the OP-amp as a transimpedance amplifier. The signal will change with less than 5 Mhz. Which OP-amps can I use? I hope you can help me. If not, which information do you need?

  • 0
    TI__Genius 12325 points

    Hi Flummi,

    It would help to know what the expected output current of your photodiode is and what voltage the op amp must produce at this output current, that will allow you to calculate the gain of the transimpedance amplifier and will also assist us in finding an amplifier with a suitable gain bandwidth. Another piece of helpful information is what power supply voltage you will use to power the amplifier. Finally, are there any other constraints in your design such as power consumption, size, noise level, or cost?

  • 0 in reply to John Caldwell
    Prodigy 40 points

    Hi John,

    thank you for your reply. I expect an output current of 500 uA, but that depends on the laser I want to use. I can check this on Monday with some experiments. Then I will have a small range of the output current. The output voltage of the op amp should be more than 20mV. I have no other constraints with the power supply voltage or size or cost. The noise level should be as small as possible.

    Flummi

  • 0 in reply to Flummi Loong
    TI__Genius 12325 points

    Flummi,

    For transimpedance applications the OPA827 offers very good AC performance and extremely low noise for a FET input type amplifier (the preferred type for transimpedance applications). Below I show an example configuration with a 10kOhm feedback resistor which would produce 5V out for a 500uA input:

    The -3dB bandwidth of this configuration is about 1.85MHz with a 10pF feedback capacitor (C2) and about 3.47MHz with a 6pF feedback capacitor. Additional gains in bandwidth could be made by selecting photodiodes with lower junction capacitance as well. If the OPA827 is too expensive for your application the OPA140 offers very similar performance for a lower price.

    Edit: Picture updated to avoid confusion.