• State
  • Replies 1 reply
  • Subscribers 48 subscribers
  • Views 54 views
  • Users 0 members are here
Support feedback
Options
Options
Related

OPA657: TIA Design for the Detector (100 MHz Bandwidth Requirement)

Chou Chu
Prodigy 10 points
Part Number: OPA657
Other Parts Discussed in Thread: LMH6629

Tool/software:

I am currently designing a TIA circuit for a  detector, and my requirements are as follows:

  1. The signal current is approximately 80–300 pA, detector capacitance CD is about 100 pF (with 24 V bias), and the dark current is around 15 nA.
  2. I need a bandwidth f-3dB at 100 MHz (based on other papers that implemented a similar design using the ADA4851 op amp).
  3. I would like the maximum output voltage to fall within 1 V to 1.5 V.

At the moment, I am considering using either the OPA657 or LMH6629 (but I’m also open to other recommendations). My questions are:

  1. How should I design the first-stage TIA circuit ?  Given the influence of dark current, should I use AC coupling between the detector and the TIA?
  2. Considering my bandwidth requirement, do I need to use a smaller feedback resistance in the TIA and then add subsequent amplification stages to gradually achieve the desired output level? If so, what would be an appropriate value for the feedback resistance?
  • 0
    TI__Expert 3035 points

    Hi ,

    1. Is the signal current 80-300pA or nA? The dark current of 15nA and signal current 80-300pA will need an ultra-low noise TIA to detect such currents. Also, the given maximum output voltage would require very high gain which LMH6629 would also fall short. You may have to use 2 stages to achieve the same.
    2. what is the max input frequency?
    3. Given the Bandwidth requirement similar to ADA4851, LMH6629 or OPA657 would be overkill.

    We have Photodiode Circuit Design Tool where you can get the TIA suggestion and choose the right one for the application.
    We also have LMH34400 which comes with ambient light/dark current cancellation.

    Thanks

    Vikas J