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OPA188: Amps gain error caculation

Part Number: OPA188
Other Parts Discussed in Thread: TINA-TI, INA592

Hi team,

Do you have document of AN to show caculation of amps gain error, our customer use 4 external resistor and OPA188 to design differential amps, they need to know how to caculate the gain error.

Thanks very much.

Regards, Sunny

  • Hi Sunny,

    the fastest methode is to run a TINA-simulation. Can you show a schematic?

    Kai

  • High Sunny

    Kai is correct, the fastest and most complete methods for determining the circuit's gain error is to use circuit simulation. TINA Industrial (purchased version)includes Worst Case and Monte Carlo Analyses, but the free TINA-TI version doesn't include them. The new TI Pspice tool available for free download includes Monte Carlo, but I am not sure about Worst Case analysis. I am just beginning to learn that tool.

    I've gone though and created the information shown below that provides the manual method for calculating the difference amplifier gain error. You can usually pick the worst case extremes R1 through R4 and come up with the worst case gain error situations fairly readily.

    I hope this helps.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Hi Thomas,

    Many thanks for your comments, this information helps indeed.

    Customer already has best case caculation, but result is not good you know, so customer may need typical error analysis method to do the caculation. we know that this may not easy, we just check with you and amps team to see if we have some application note or documents about this, then we can learn it and do the caculation by ourself.

    Thanks very much.

    Regards, Sunny

  • Hi Sunny,

    The error issues with attempting to apply a precision op amp with four, discrete resistors as a difference amplifier are well understood. The resistors require very precise accuracy to attain low Gain error and achieve high a Common-mode rejection ratio. Hence, the creation of integrated difference amplifiers that combine the precision op amp, with precision thin-film resistor technology. Even if high quality, matched resistors can be obtained for the function, their cost will far exceed, and probably won't be as good as what is achieved, with an integrated difference amplifier.

    If I were embarking on a solution for this kind of application, I would have a look at the INA592 difference amplifier. It features very low gain error, and other very high parametric performances:

    • Low offset voltage: 40 μV (maximum)

    • Low offset voltage drift: ±2 μV/°C (maximum)

    • Low noise: 18 nV/√Hz at 1 kHz

    • Low gain error: ±0.03% (maximum)

    • High common-mode rejection: 88 dB (minimum)

    See if this is an option for the customer:

    https://www.ti.com/lit/ds/symlink/ina592.pdf

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Hi Thomas,

    got it, thanks for comments.

    Regards, Sunny