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Original question:

INA826: Gain Drift and CMRR with different Gain

INA826: Compensating for gain drift

David Shroyer
Prodigy 70 points
Part Number: INA826
Other Parts Discussed in Thread: INA141, INA818, INA828, INA823

Are there any tricks to compensate for the large gain drift in instrumentation amplifiers when the gain is not = 1?

  • 0
    TI__Genius 10850 points

    Hi David,

    Thanks for your post. There isn't really a compensation scheme for this. The best advice I can offer is to use the lowest temperature coefficient Rg (assuming G > 1V/V)

  • 0 in reply to Tamara M Alani
    Prodigy 70 points

    Do you have any suggested circuits that will provide performance similar to the INA141 (for example) but with a gain of 70? I am interfacing to a load cell. I need low noise, low offset drift and low gain drift and input protection. Overall bandwidth needs to be on the order of 10 kHz. I am driving an ADC.

    Thank you.

  • 0 in reply to David Shroyer
    TI__Genius 10850 points

    Hi David,

    The gain error is determined by the internal resistors + Rg of the circuit. INA141 does have a really low gain error. Have you tested this IC? Can you provide feedback? Another option could be a more modern instrumentation amplifier like the INA818.

  • 0
    Prodigy 70 points

    I have not tested the INA141. Unfortunately, it has a fixed gain of 10 or 100. 10 is too low and 100 is too high. The INA818 has high gain drift for gains other than 1.

    I'm sure I am not the only one who needs lower temperature drift at a gain other than 10 or 100. Someone with more experience with amplifiers I am sure has already solved this problem. I hoped you had some designers in-house who could point us to some reference material showing example of circuits for best performance.

    Thank yoiu

  • 0 in reply to David Shroyer
    TI__Genius 10850 points

    David,

    The gain error and drift of the INA141 is set by the ratio of internal SiCr resistors. These are laser trimmed in production and no external additional circuitry will reduce this error. Certainly you can measure and correct for room temperature offset in software. Temperature drift, however, is difficult and expensive to calibrate out and will limit the overall system performance. 

    Due to the topology of a traditional instrumentation amplifier, errors generated by the input stage (such as input offset voltage) are more dominant at higher gains. Note that the gain error and gain drift error are much more significant for gains greater than 1 because of the contribution of the resistor drift of the internal feedback resistors in conjunction with the external gain resistor. 

    We have many high-precision instrumentation amplifiers with adjustable gain, INA823 / INA818 / INA828, to name a few. You may also browse our portfolio and sort the selections by your key-care-abouts. This link shows you our portfolio sorted from least input offset voltage: https://www.ti.com/amplifier-circuit/instrumentation/products.html#sort=p768max;asc