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Part Number: OPA858DSGEVM
Other Parts Discussed in Thread: OPA858,

Hi there,

I acknowledge that this may seem like an obvious question but I was wondering if I could get assistance with testing out the OPA858 amplifier as a Transimpedance amplifier. I was wondering if I could get assistance with the correct configuration for using the evaluation board as a TIA amplifier. I am working on verifying a PCB board with multiple circuits, one of which is based off of the OPA858DSGEVM evaluation board, which I am also testing at the moment.

I have been testing it with the default configuration and I am getting serious attenuation on any input frequency signal of 100 MHz or higher (ideally want to run it at 3-5GHz).

Thank you

  • Hello Tayeb,

      Good question! It actually isn't too obvious. You can either use your photodiode, or emulate your photodiode parasitic at the input of the amplifier.

    For the first option, you would need to remove the sma connecter at the inverting input of the amplifier. This might be a bit tricky, but you would then solder the photodiode input + ground to the pads of the sma. Remove R3, short R4, and change R2 to the your desired transimpedance gain. For the compensation capacitor, you would solder this component right on top of R2. 

    For the second option, please follow this thread. It goes over how to use a voltage input but with the addition of the capacitance found internal to the photodiode. This is the most crucial element to test. Let me know if you have any questions on this.

    Depending on the photodiode capacitance and gain requirements, 3-5GHz might be difficult to achieve. I can check this for you; if you can provide these specs. 

    Thank you,