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.

OPA857-DIE: Transimpedance amplifier

Part Number: OPA857-DIE
Other Parts Discussed in Thread: OPA857, , OPA855, LMH32401, OPA858, OPA859, OPA856

Hello,

I was wondering if there are any experimental/test data about this device?

I would expect the input capacitance to be affected by the packaging of the OPA857, therefore I would expect a lower capacity and broader bandwidth for the OPA857-DIE compared to the OPA857.

And also as a consequence, if it's been tested with lower photodiode capacitance than 1.5pF. This is because the photodiodes I intend to use will have a capacitance of 0.3pF.

Kind regards,

Francesco

  • Hi Francesco,

    but you would still need a protection cover over the bond wires, increasing the stray capacitance again. So there's probably no gain when using the OPA857-DIE instead of OPA857.

    Referring the detector capacitance, why not running the

    OPA857 TINA-TI Reference Design (Rev. A)

    Kai

  • Hi Kai,

    Thanks for the suggestion. If that's the case, it won't help my application. The OPA855 in this case is still the better option.

    Kind regards,

    Francesco 

  • Hi Francesco,

    The main benefit of using the die is that it allows for lower inductance between IN- and the input capacitance, which can help with overall stability. There is not public testing data for the die package at this time, but here is a reference document that may be helpful. https://www.ti.com/lit/an/sboa337/sboa337.pdf

    Please consider the LMH32401 as an alternative. It uses a current input with internal feedback to maximize bandwidth for small capacitance photo-diode inputs.

    Best regards,

    Sean

  • Hi Sean,

    Thank you for your reply.

    I had a look at your link as well as at the specs of the LMH32401. In my current application I am indeed using the OPA855, which gives me the best performance: decent noise level as well as a good bandwidth when combined with my high-bandwidth photodiodes. With the OPA855 I easily get a 1.5 GHz 3dB bandwidth, that could be stretched a bit further by playing with the gain etc.

    Are you aware of any solution that could bring me to around 5-8 GHz, with similar noise performance of the OPA855 ( which I guess it can be estimated to be approximately -30dBm of optical sensitivity)? I know it is ambitious, but worth asking.

    Many Thanks,

    Francesco

  • Hi Francesco, I have seen customers use a source follower/common drain to buffer the input to the OPA855, since this decreases the effective input current noise. I cannot confirm whether this gives better overall performance than the OPA858, which has a FET input already.

    For a small input capacitance, you may be able to extract a little more bandwidth by using the unity gain stable versions of each device (OPA856 and OPA859). Otherwise, these are the highest bandwidth devices available.

    Best regards,

    Sean