• Resolved


I am trying to operate the OPA657 as a trans-impedance amplifier, but I am not able to get it to work. any help

  • Khaled,

    What specifically is not working? If you upload your schematic we can take a better look at the problem.

    There are also a couple app notes that might help you get started:

    • Transimpedance Considerations for High-Speed Operational Amplifiers - sboa122
    • Compensate Transimpedance Amplifiers Intuitively - sboa055

    Luke Lapointe
    High Speed Amplifiers

  • In reply to Luke LaPointe:

    Please refer to page 11 figure 3 in the datasheet of the OPA380. I am using the same schematic. I couldn't get it to work properly. I replace many of it,  but every one gives different random and strange  results. one of them gave 5V DC output modulated by my square wave light signal.  

  • In reply to Khaled M. Dadesh:


    Did you mean figure 3 of the OPA657 datasheet?

    If so, the compensation capacitance could be an issue here. The feedback capacitor was chosen based on the input diode having a 50pF of capacitance. If this value changes, you will have to recalculate the value of the feedback capacitor again.

    What is the capacitance value of your input diode?


  • In reply to Khaled M. Dadesh:

    Hi, Khaled

    Try cleaning PSB with alcogol (CH2 H5 OH). On PSB may suffisient stray resistanse with dirt.


  • In reply to Georgy:

    Hi Georgy,

    Thank you for your advice. I was able to get it to work now, and it looks that there was soldering  issues.