• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 46 subscribers
  • Views 7536 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.

Photodiode transimpedance amplifer

Ali Tekin
Prodigy 50 points
Other Parts Discussed in Thread: OPA314

Hello,

  I need to receive a raw infrared data streams by photodiode. The infrared emiter has different baudrates(300 to 115200 bps) and different light intensity. I used OPA314 op-amp as a transimpedance amplifer. In my tests, output signal looks good at low light intensities but the output signal has a distortion at higher light intensities. How can i solve it? Maybe this problem will be sloved when i use an automatic gain control method, but then i think i will miss some of data at the begining of the stream until AGC controls the gain.

  • 0
    TI__Genius 12325 points

    Ali,

    What gain is your transimpedance amplifier configured for? Also, if you have any oscilloscope screenshots of the distortion you are seeing at higher light intensities it would really help us to determine what the cause of the problem is.

  • 0 in reply to John Caldwell
    Prodigy 50 points

    Hi John,

    Here is the schematic

    This the waweform, it is about 20cm between IR emiter and photodiode

    Here is the problem, it is about 1cm between IR emiter and photodiode

    Thank you,

  • 0 in reply to Ali Tekin
    Guru 21975 points

    Ali,

    It appears that you have sufficient current from the photodiode to drive the output of the op amp to the negative rail. With strong overdrive, the voltage on the anode of the photodiode will change (go more positive) and this will slow the recovery time of the circuit. You could use a lower value feedback resistor--one that does not allow the output of the op amp to approach 0V with the maximum expected signal.

    It appears that linear response to light is not required in your application. Another possible solution is to add a silicon signal diode (a low capacitance type) in parallel with the feedback resistor, cathode side on the output of the op amp. This will limit the negative-going signal to approximately 1.8V or so with a large photodiode current. This provides, in effect, a primitive logarithmic response for large photodiode current.

    Regards, Bruce.

     

  • 0 in reply to Bruce Trump
    Prodigy 50 points

    Hi Bruce,

       Logarihmic amplifier is solved the problem and it works also under high light intensities now. Thanks for the solution.

    Best Regards.