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looking for the photodiode preamplifier (the input current of typically 5-50 nA)

Alex Baikov
Prodigy 210 points
Other Parts Discussed in Thread: OPA320, OPA342, OPA376

I'm looking for the photodiode preamplifier for a useful frequency range of at least 0-100 kHz  with  incident light powers  of 10 nW. The  chosen  diode  for  this  application   is  model  FDS100  from Thorlabs.  It  has a sensitivity  of  roughly  0.50 A/W at 800 nm, an operating  bias voltage  of  15 V,  a diode capacitance  of  40 pF,  and  a frequency  response up  to 35 MHz. So we ask to help us to choose correct Low Noise Precision Op Amp in the TI product line. Typical light signal levels  can  range  from   1 to 50  nW. With chosen photodiode (0.50 A/W at 800 nm) it can deliver the current of  typically 5 nA (for a 10 nW input light signal) to the Op Amp. We searched TI site and found different chips: OPA129, OPA320, OPA342 and so on.  Please help to chose right one.

  • 0
    Guru 21975 points

    Alex,

    You may want to consider the OPA376.

    With relatively small signals, you will want a feedback transimpedance resistor as large as possible, in the 1M to 2M-ohm range. The bandwidth you are seeking and the high photodiode capacitance will make low capacitance across the feedback resistor crucial. Two resistors in series may help reduce stray capacitance.

    You would find that circuit simulation with TINA or other circuit simulator would help to get the "feel" on how to optimize the circuit.

    Regards, Bruce.