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TINA/Spice/OPA354: Transmittance amplifier daylight issue

shakti singh
Prodigy 40 points
Part Number: OPA354
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

hi,

I amusing the circuit suggest for photo diode amplifier. Everything goes well until it don't face towards SUN. it get high pulses or continuous oscillation even if the photo diode have wavelength range for 750 to 1100nm. Please suggest what i can modify or any solution for such problem

shakti singh

  • 0
    TI__Expert 7970 points
    Hi,

    It may be that the circuit is actually unstable due to the diode capacitance. Do you know how much capacitance the diode is adding to the circuit? Also is the large DC input current due to the "dark current" of the diode or just from background light? If it is from background light, you could try adding an optical filter over the diode to reduce the total DC current.

    Regards,
  • 0 in reply to Jacob Freet
    Prodigy 40 points

    Hi Jacob,

    Thanks for reply

    1.  I have checked the dark current, Inside the room with LED light  i am getting 0.3V at output of U2.  In outside direct facing to sun i  am getting 1.02. 

    2. I have replaced the R3 with 1K to allow more DC current through diode

    3. Diode capacitance is 12pf maximum  as per datasheet

    4. Also please let me know if i can increase the lower cutoff to >20Khz without affecting the performance that will reduced the noise from sun

  • 0 in reply to shakti singh
    Prodigy 40 points

    hi,

    I think sunlight has low frequency noise and can be up to 1Khz. So i wan to set the lower threshold for it. I tried to decrease the value of Integrater RC value but getting oscillation. Please suggest

  • 0 in reply to shakti singh
    TI__Expert 7970 points
    Hi,

    You can certainly reduce the low frequency cutoff, that will not hurt the performance. It sounds like your diode is still sensitive to the visible light range. You can get narrow-band optical filters that can be placed over the diode and should significantly reduce the interference.

    Regards,