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OPA348-Q1: how to estimate Gain Error for Shunt Amplifier application ?

Paul Kim
Intellectual 1430 points
Part Number: OPA348-Q1

Hi Team

using OPAMP, I would like to make Shunt Amplifier to measure a current.

the output will be affected by DC Offset and Offset Drift over temperature and Gain error.

I can estimate worst case of DC Offset and Offset Drift over temperature with D/S specification,

but how can I estimate Gain Error for unity gain and any x times set gain ?

without that, i cannot set the worst case current measuing error, using OPAMP for Shunt Amplifier.

of course, I wnat to know any best/correct & general way to estimate Gain Error at any Gain setting

, which is applicable for any all other OPAMPs other than OPA348-Q1.

can you help me ?

  • 0
    TI__Mastermind 30600 points
    Hi Paul,

    Here is a good article discussing gain error in some detail that I think will help you out: www.ti.com/.../slyt374.pdf
    Gain error has to do with the relationship between the closed loop gain of the circuit and the finite open loop gain of the op amp itself.

    Let me know if that article leaves any questions unanswered and I'll help clarify.

    Thanks,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Intellectual 1430 points

    Hi Paul

    the artical mentions to calculate the worst close loop gain about Inverting and Non-Inverting OPAMP.

    I would like to know the worst close loop gain for differnetial Amplifier configuration.

    could you teach it to me ?

    further, the artical don't incluse PSRR in calculating the worst close loop gain for Inverting/Non-Inverting.

    can you also teach it to me on how to include PSRR in the worst close loop gain calculation ?

  • 0 in reply to Paul Kim
    TI__Mastermind 30600 points
    Hi Paul,

    Calculating the gain error doesn't depend on the circuit configuration, only the open-loop gain of the amplifier and the closed-loop gain of the circuit. The worst case closed-loop gain error is found simply by converting the DC open-loop gain from dB to V/V and using equation 15 in the document I referenced.

    As far as the impact of PSRR, CMRR, and offset, they're going to impact your system the same way that the offset voltage will and in fact, they will present themselves as additional offset voltage at the input. This blog will teach you how to calculate the real Vos for your system accounting for CMRR and PSRR: e2e.ti.com/.../will-the-real-vos-please-stand-up

    Best,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Intellectual 1430 points

    Hi Paul

    the toal offset caused by PSRR/CMRR/Offset Initial/Offset Drift will be multiplied by Gain on Vout pin ?

    AND

    the toal offset caused by PSRR/CMRR/Offset Initial/Offset Drift can be canceled  by a  periodic calibraion ?

  • 0 in reply to Paul Kim
    TI__Mastermind 30600 points
    The total offset caused by PSRR/CMRR/Offset Initial/Offset Drift will be multiplied by Gain on Vout pin?
    --> Yes.

    The total offset caused by PSRR/CMRR/Offset Initial/Offset Drift can be canceled by a periodic calibration?
    --> Yes. You may need a multi-point calibration to account for temperature or other conditions.

    -Paul