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Op-Amps suggestions for Instrumentation Amplifier

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by pavanbabut, Jul 25, 2017.

  1. pavanbabut

    pavanbabut Member

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    Hi,

    I am trying to build a circuit to implement the schematic attached (taken from here). I have an input signal coming from a photo diode with -3dB Electrical bandwidth of 160MHz that has differential output. Eventually I want to amplify that signal (to 50dB about 500 times) and convert into single ended output.

    Any suggestions are greatly appreciated.

    thanks
     

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  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    You'll get greater accuracy by buying an instrumentation amplifier rather than trying to build one from opamps.
     
  3. pavanbabut

    pavanbabut Member

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    Any examples that would meet the specs that I am looking for? thanks
     
  4. dave

    Dave New Member

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  5. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Your photo-diode may well have a 160MHz bandwidth, but what bandwidth will you actually be using?
     
  6. pavanbabut

    pavanbabut Member

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    320MHz is what I am aiming for.
     
  7. crutschow

    crutschow Well-Known Member Most Helpful Member

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    You definitely don't want to try to built your own at those frequencies. :eek:

    One listed in this search should work for you.
    But it still will require careful layout and decoupling on a circuit board with a ground plane.
    Don't even think about trying a solderless breadboard. ;)
     
  8. pavanbabut

    pavanbabut Member

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    Exactly, hence my search for a good op-amp or equivalent so that I can start by using demo SMT boards and try out different op-amps.
     
  9. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Why do you insist on using op amps when a differential IC amp is much better suited to the job? :confused:
     
  10. pavanbabut

    pavanbabut Member

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    I meant op-amp or equivalent which includes differential amps as well, definitely not tied to using op-amps only :)
     
  11. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Okay.
    Generally common usage of the terms is that an op amp is considered to be distinctly different from a differential amp, even though op amps do have a differential input.
     
  12. pavanbabut

    pavanbabut Member

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    Thanks for clearing up, I never had to use differential amps till now, so not that knowledgeable in them.
     
    Last edited: Jul 26, 2017
  13. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    1) The module you picked has gain inside. I don't think you need a gain of 5oox more.

    2) "Gain band width" Here is a graph of a 1ghz op-amp.
    It works to 1ghz with a gain of 1.
    It works to 100mz with a gain of 10.
    It works to 10mhz with a gain of 100.
    I don't think there is a single amp that will give you a gain of 500x at 300mhz.
    You can use several stages of gain to get to 500x.
    Probably you want "differential" to "single ended" and a gain of 1 or 2 or many be 10 at most.
    10x at 300mhz = 3gh upload_2017-7-26_7-54-17.png z amp minimum.
     
  14. pavanbabut

    pavanbabut Member

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    Thanks for your reply Ron,
    I am pretty sure I have to end up using multiple stages of gain if I want to achieve 50dB. But since I am not that familiar with differential amps, thought I would just put my specs out so that knowledgeable people like you can give your suggestions.
     
  15. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    It would be nice to know what the output level is of your module.
     
  16. pavanbabut

    pavanbabut Member

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    Max output we are seeing in out setup is +/-12mV
     
    Last edited: Jul 27, 2017
  17. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Nice, so a gain of 10 gives you 2V.
    Is that single ended? Using a scope?
    What is the next stage? ADC??
     
  18. pavanbabut

    pavanbabut Member

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    I think I gave you the wrong number as +/-200mV, I did some calculations today for a real-world situation and the max we can get is about +/-12mV output signal from the module.

    Here is what I am planning on doing, using the differential output from the module, convert into SE signal while doing about Gain of 2 to 5 within this stage and then use multiple stages of op-amps to amplify the signal to 1V max. For amplifying SE signal, I am thinking of using two MAX4305 followed by a MAX4105 and MAX4101 (as buffer) all in series.

    Any ideas or suggestions?
     
    Last edited: Jul 27, 2017

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