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High Speed Photodiode Amplifier for ADC Drive

Nicholas Vrahoretis
Prodigy 30 points
Other Parts Discussed in Thread: OPA857

We're designing an analog front end for a 5GHz bandwidth photodiode. We'd like to know more about TI products and strategies we could use to buffer the photodiode current to adequately drive a high speed ADC while maximizing bandwidth.

  • 0
    TI__Mastermind 25975 points

    Hello Nicholas, 

      Thank you for your interest in our products! I have a few questions before I recommend devices/solutions especially due to your very fast bandwidth requirement. 

    1. Are you able to share the end equipment? We have two sets of transimpedance devices we recommend, our voltage/current feedback amplifier portfolio used as a TIA (transimpedance amplifier) or for a more specific GBPS optical communication, we have our ONET products which come as a die and typically used in optical networking solutions. 

    2. Do you need a wide gain range?

    3. Does your ADC require a differential input?

    4. What is your photodiode internal capacitance? 

    5. Any noise, supply configuration requirements?

    Best Regards,

    Sima 

  • 0
    Guru 140200 points

    Hi Nicholas,

    when it comes to stability and bandwidth the detector capacitance is the key factor here.

    Kai

  • 0 in reply to Sima Jalaleddine
    Prodigy 30 points

    We're planning to use the ThorLabs DET08CFC, Cj = 0.3pF in the datasheet. At these high speeds it seems most ADCs recommend if not require differential input, but we're evaluating how that impacts overall bandwidth as well. Right now we're reading up to 1.4V output into a 50 ohm load directly from the detector so I think 50 ohm transimpedance gain will be sufficient.

  • 0 in reply to Nicholas Vrahoretis
    TI__Mastermind 25975 points

    Hello Nicholas,

       Using this TIA calculator, system design requirements for 65 degree phase margin is below:

       Here is a link of filtered transimpedance amplifiers that are above the require GBP: If gain requirement increases; then I would suggest picking amplifiers with on the faster end for headroom. 

       Overall signal chain suggested below for TIA to differential signal conversion:

       We do have a TIA with pseudo-differential output if your design is space constrained which is the OPA857. Otherwise, a filtered FDA list can be found at this link.

    Thank you,
    Sima