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OPA657

OPA657

This question is answered
Khaled M. Dadesh
Posted by Khaled M. Dadesh
on Feb 27 2012 18:04 PM
Prodigy65 points

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

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  • Luke Lapointe
    Posted by Luke Lapointe
    on Feb 28 2012 11:08 AM
    Expert4200 points

    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

    Regards,
    Luke Lapointe
    High Speed Amplifiers

    TIA
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  • Khaled M. Dadesh
    Posted by Khaled M. Dadesh
    on Feb 28 2012 18:39 PM
    Prodigy65 points

    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.  

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  • Luke Lapointe
    Posted by Luke Lapointe
    on Mar 02 2012 13:54 PM
    Expert4200 points

    Khaled,

    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?

    Regards,
    Luke

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  • Georgy
    Posted by Georgy
    on Mar 13 2012 05:39 AM
    Prodigy100 points

    Hi, Khaled

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

    Regards!

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  • Khaled M. Dadesh
    Posted by Khaled M. Dadesh
    on Mar 13 2012 08:05 AM
    Verified Answer
    Verified by Khaled M. Dadesh
    Prodigy65 points

    Hi Georgy,

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

    Regards

    Khaled 

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