• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 49 subscribers
  • Views 921 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Current feedback amplifier for high speed photodiode

Hsing Cheng
Prodigy 10 points
Other Parts Discussed in Thread: OPA695, OPA847, TINA-TI

I plan to use a photodiode in a room (with 120 Hz background light) to pick up very weak laser pulses (pulse width 50 nS). Can I use only one stage current feedback amplifier (e.g. OPA695, single 5V)? Is it easy to filter out noise < 5 kHz? The photodiode: rise time = 6 nS (for Rload <1000 ohm), capacitance = 5 - 6 pF, dark current = 10 nA. Thanks.

  • 0
    TI__Expert 4115 points

    I have not seen a CFB (current feedback) amplifier like the OPA695 used for TIA (transimpedance amplifier) design. The typical compensation scheme where you put a capacitor in the feedback will be a problem for the CFB. The OPA847 is a VFB (voltage feedback) amplifier that works for very fast TIA design. The data sheet has a great section on TIA application starting on page 11. A series output capacitor can be used to filter out noise < 5 kHz; the correct value to use will depend on the load. I attach a TINA Spice file to illustrate the TIA design with output RC filter using the OPA847, the information you gave, and the information in the data sheet. If you do not have TINA, you can download and install the free TINA-TI software; visit www.ti.com/tina-ti and click the Download button.

    Regards,

    Jim Karki

    TI High Speed Op Amps

     

    OPA847 TIA For Hsing Cheng 9-11-09.zip
  • 0
    Prodigy 70 points

    I've started a project dealing with the same issues. We want to pick up scattered laser pulses with a rate of 1MHz or better. I assume you made progress with your front end circuit and would be delighted to learn what you found out.

     

  • 0 in reply to H.W.
    TI__Expert 4625 points

    H.W.,

    If Hsing does not respond with details on his front end set-up, I would be glad to help you with any questions you might have.

     

    Regards,

    Nick - TI High Speed Amps