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INA116 for electrometer application

Hello

 

I'm a radiometric engineer and would like to design a simple, current input, 0-10V output, precision amplifier module using the INA116 IC.

As it can be read from the INA116 datasheet, it is an instrumetation amplifier, but can it be used as a transimpedance amplifier?

I mean: the current input could be connected to the inverting input (with designing all the guarding stuff as well) the feedback resistor would be connected to the inverting input and the output, the non-inverting input and the "REF" pin is grounded, and the gain setting pins (RGs) shorted for the maximum gain.

Do you think this idea can work?

And my other question: could this circuit work with tee feedback to increase the feedback resistor's effectice resistance?

Thank you for your answer in advance.

3 Replies

  • I would not recommend wasting time trying to make an instrumentation amplifier into a transimpedance amplifier. Use a good low input bias current op amp instead.

    You did not mention either the sensitivity or the bandwidth that you require.........?

  • In reply to Neil Albaugh:

    I agree with Neil, my esteemed former colleague. It would be better to use a low bias current op amp. Consider the OPA128 or OPA129.

    Using the INA116 as you describe seems plausible but the resulting open-loop transfer function is not the well-behaved integrator response that describes nearly all op amps. It is a complex multi-pole function that combines the response of the two input amplifiers with the closed-loop output amplifier. Closing a loop around this combined amplifier would yield serious stability problems.

    You may also want to consider a switched integrator approach. See the IVC102.

    Regards, Bruce

  • In reply to Bruce Trump:

    Dear Bruce and Neil!

     

    Thank you for your advice!

    I'll consider using OPA129 instead.

    By the way, to answer your question: it would measure the current of an ionisation chamber in the range of 5 nA - 100 pA. The bandwidth is not critical, since it should be a "classical", first order low pass filter transimpedance amplifier (the mesuring resistor is in Gohm range in parallel with ~10pF cap).

     

    Thank you for your answer!

    Laszlo Boromisza