• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 48 subscribers
  • Views 1496 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.

OPA365: Can this transimpedance amp circuit work normally with OPA365?Or some others better？

user4501805
Prodigy 20 points
Part Number: OPA365
Other Parts Discussed in Thread: LMV793

  • 0
    TI__Genius 15975 points

    Hi,

    You could use the OPA365 for trans-impedance applications. On a single +5V supply, I would recommend making the OPA365 non-inverting (+) input as 2.5V, even though the device supports rail-to-rail inputs. This is required so that the photo diode connected on the inverting (-) input is reverse-biased to around 2.5V.

    For suggesting a suitable part for trans-impedance application, I will need the below parameters from you:

    1. What photodiode are you using or the photo-diode capacitance? Part number of the photo-diode would be helpful.

    2. What is the trans-impedance gain (feedback resistor - Rf) you are trying to achieve and the targeted BW?

    3. What is the worst-case input current you are trying to detect?

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Prodigy 20 points

    Rohit,

    Thank you very much for your reply!

    I want to implement this circuit in a spectroscopy system. The reason I grounded the anode of the PD and the amp non-inverting input is to offer a voltage  ranged between 0~2.5V to an ADC.And use less parts.

    And I wonder how should I get the bias 2.5V you mentioned? Using a reference or just a Schottky diode?

    The PD is a InGaSn PD,with its capacity of 80pF and shunt impedance of 30MΩ. More specific parameters are attached below.

    The frequence I am interested in is between 10-100 kHz.. DC accuracy is not care about. We usaully use a Rf between 10kΩ-1MΩ, accroding to the intensity of light. So the minimum pohotcurrent may be several hundreds of nA.

  • 0 in reply to user4501805
    TI__Genius 15975 points
    Hi,

    You could use a voltage reference for the 2.5V bias on the non-inverting (+) input, or use a resistive voltage divider from 5V to level shift down to 2.5V. Based on the photo diode (PD) requiring a reverse bias of 5V to achieve 80pF cap, you would need to bias its anode to -2.5V as well. I think rest of the circuit should be okay. The LMV793 is also an option which should provide better noise performance than the OPA365.

    Best Regards,
    Rohit