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OPA855: OPA855: When the OPA855 is designed for TIA, what is the maximum closed-loop bandwidth it can achieve?

Xinyi Liu
Prodigy 30 points
Part Number: OPA855

Tool/software:

Hello, everyone.

I am currently going to build a TIA circuit using OPA855, I want to make the TIA bandwidth up to 1.7GHz, and I am designing it based on the values from the TIA calculator. But the bandwidth of the simulation is not able to reach 1.7GHz.
I want to know is there something wrong with my circuit? Or the closed loop gain of OPA855 can't reach 1.7GHz?

  • 0
    Guru 48195 points

    The achievable bandwidth and gain are tightly coupled given a source C and GBP, here I iterated a little and got 2GHz with an 866ohm feedback, you would need to add about a gain of 5 2nd stage amp to get a full 4kohm and the OPA855 can do that also, 

    That 0.2pF feedback Cf is about the parasitic on a surface mount R. 

    OPA855 TIA 2GHz.TSC

  • 0 in reply to Michael Steffes
    Prodigy 30 points

    Hello, .
    Thank you for your reply and help. If I want to achieve a gain of roughly 1000, then do I need to connect an amplifier circuit in series after the TIA circuit? Also, I would like to keep the noise low, so how should I do that? Can you give me some suggestions?

  • 0 in reply to Xinyi Liu
    TI__Genius 14041 points

    Hello Xinyi,

    You can certainly use additional stages after your TIA stage.  You can use an additional OPA855, or select another amplifier.  What noise level are you targeting from the second stage?  Keep in mind the first amplifier contributes more noise than the second in a signal chain, so you may have more tolerance for noise on the second stage than you think.

    Best,

    Alec