• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 48 subscribers
  • Views 403 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA855: OPA855

Soumya Pratap Tripathy
Prodigy 10 points
Part Number: OPA855
Other Parts Discussed in Thread: OPA858, OPA838

Tool/software:

Hi,

I am trying to design AC-coupled TIA for two germanium-on-silicon waveguide photodiodes (Cd = 10-50 pF, Rs=1-10 MOhm) in a balanced configuration.

I need a TIA gain of 10E6 to 10E7 V/A at a 3-5 MHz bandwidth. I am looking for a suitable op amp and corresponding circuit design. 

Please let me know if you have a suitable op amp or available evaluation board.

Looking forward to hearing back!

Best,

Soumya

  • 0
    TI__Intellectual 2065 points

    Hi Soumya, 

    We have created a TIA circuit design tool where you can provide all your circuit requirements and the tool will compute all the output parameters like bandwidth, Rf, offset errors, noise analysis, etc.

    Tool link: Analog circuit design studio

    I will also look into your query and get back to you, till then please try our tool and let me know what you think.

    Regards,
    Aditya

  • 0
    TI__Intellectual 2065 points

    Hi Soumya sorry for the delay,

    I would suggest to use OPA858 for the following reasons:

    1. Low input bias current: For such high Rf TIA designs, input bias currents can significantly affect the offset voltages at the TIA output. OPA858 offers ultra low bias current inputs of 10pA.
    2. Lower input capacitance: OPA838 offers low inverting input capacitance (Ccm + Cdm), which helps significantly in achieving high bandwidth.
    3. Very high GBW: OPA838 offers a gain bandwidth product of 5.5GHz.

    Also please try the tool: Analog circuit design studio using which I was able to suggest you the best device for your design.

    Regards
    Aditya

  • 0 in reply to Aditya Gosavi
    Prodigy 10 points

    Thanks, Aditya!

    The Cf is in femtofarad range. Will that be affected by parasitic resistance from the PCB? Also, do you have an analytical tool to simulate AC-coupled TIA?

    Best

    Soumya

  • 0 in reply to Soumya Pratap Tripathy
    TI__Intellectual 2065 points

    Hi,

    Yes parasitic capacitance from the PCB can significantly affect a Cf of femto Farad range. To tackle this I think you can use a higher Cf so that it is not dominated by PCB parasitic cap, but higher Cf will reduce the TIA bandwidth. Also increasing Cf will ensure there will be a larger phase margin, thus your TIA will be more stable. Also currently we don't have any tool to simulate AC coupled TIA, we will let you know if we plan to do so.

    Regards,

    Aditya

  • 0 in reply to Aditya Gosavi
    TI__Intellectual 2065 points

    Hi,

    We would love to hear your feedback on the tool mentioned above: its usability, accuracy and any improvements you'd suggest. Please let us know your thoughts as it will be extremely useful to us.

    Regards,

    Aditya