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LMH3401: OPA847, LMH3401

Joana Melo
Prodigy 80 points
Part Number: LMH3401
Other Parts Discussed in Thread: LMH5401, , OPA847, OPA657, OPA656, OPA846, LMH6629, OPA857, THS4304

Hello everyone

I need some technical support with the following issue:
My team and me are developing a amplifier module for a SiPM current output and we’re thinking to use the OPA847, LMH3401 or LMH5401 amplifier. The module has two op amps: one to convert current in voltage and other to amplify the signal. So, I’d like to know your opinion about what is better for this application and to check my schematic and board designs for each high amplifier.

  • 0
    TI__Genius 12631 points
    Hello Joana,
    It is difficult to suggest the correct amplifier without knowing more about your required specs. for a transimpedance application, it is important to know:
    1. The capacitance of the photodiode/PM
    2. The required transimpedance gain.
    3.(OR) Required bandwidth

    See the 2 part blog post below on how to deisgn a TIA.

    e2e.ti.com/.../what-you-need-to-know-about-transimpedance-amplifiers-part-1

    Usually for a TIA application we can use an amplifier like the LMH6629, OPA847, OPA846, OPA657, OPA656 or OPA857 to convert the current into voltage. The next stage can be a wide bandwidth low noise, voltage amplifier like the OPA847 or LMH6629. If you are driving an ADC and need a fully differential output signal then the LMH3401/LMH5401 is a god choice to get a lot of gain and bandwidth at low noise levels.
    -Samir
  • 0 in reply to Samir Cherian
    Prodigy 80 points
    Hello Samir,
    Thank you for your fast reply and attention.
    The capacitance of the SiPM is 35 pF and the total gain of the two amplifiers should be around 40x.
    For now my team and me are evaluating the performance of the amplifiers, so we did the stages with the same amplifiers. Bad choose?
    Also we don't have much practice designing boards.. Could you take a look for our designs?
  • 0 in reply to Joana Melo
    Prodigy 80 points
    Gain 400x. Sorry.
  • 0 in reply to Joana Melo
    TI__Genius 12631 points

    Joana,

      We may be able to get a gain of 400x in a single stage and not require a 2-stage design. What bandwidth are you looking to achieve? Finally are you driving an ADC after this stage?

    Thanks,

    Samir

  • 0 in reply to Samir Cherian
    Prodigy 80 points
    We are using two stages because the output signal of the first stage (TIA) is negative so we use the second stage to invert the signal and amplifier it.

    Our bandwidth is > 100 MHz and the amplified signal will drive to an ADC and a Counter.

    Thanks,
    Joana
  • 0 in reply to Joana Melo
    TI__Genius 12631 points

    Joana,

     Does the ADC have a single-ended or differential input interface?

    Also, using the calculators that are referenced in the blogs I sent you and assuming:

    Closed-loop TIA Bandwidth (f-3dB) 150.000 MHz

    Feedback Resistance (RF) 0.400 kOhm

    Input Capacitance (CIN) 40.000 pF (I have to include the photodiode capacitance, amplifier input capacitance and any PCB parasitics)

    The above specs require an amplifier with an Opamp Gain Bandwidth Product (GBP) 2261.9467 MHz

    I think the LMH6629 or the THS4304 will both work for you. I would lean towards the LMH6629 with its lower noise.

    Based on the above inputs, I don't see the need for the LMH3401/LMH5401 in your design. Depending on whether your ADC needs a single-ended or differential interface will help me point out the appropriate 2nd stage amplifier to use in your design. I would not use the OPA847 in your design because it has a limitation on minimum stable gain which is not appropriate for your system. (This is a slightly more advanced topic on using decompensated amplifiers for TIAs and how their minimum stable gain requirements affect appropriate amplifier choice).

    -Samir

  • 0 in reply to Samir Cherian
    Prodigy 80 points
    We don't define the ADC yet, but we're thinking to use a differential input.
    We'll try LMH6629 then.

    Thanks you for all your help,
    Joana