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TINA/Spice/INA114: Noise level of Instrumentation Amplifiers INAxxx. Tina simulation versus datasheet.

EricT
Prodigy 120 points
Part Number: INA114
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi,

The input referred noise below 10kHz quoted for the INA114 IA is around 15nV/sqrt(Hz) for a gain of 80 according to the datasheet (p. 4 www.ti.com/lit/ds/symlink/ina114.pdf

But the simulation below shows over 29nV/sqrt(Hz), any idea why?

Thanks in advace

  • 0
    TI__Expert 5830 points
    Hello Henry,

    The INA114 is almost a 20 year old part and the macromodel associated with this device is a transistor level model. We have used for some time a different modeling method for macromodels to overcome the transistor model limitations. For this model I have tested the noise at a gain of 1, 10, 100, and 1000. It seems that the broadband noise at a gain of 1 is correct, however, the noise at the other gains seem to be higher than specified in the datasheet. This is due to the limitations of transistor modeling where the IC is represented in a simplified model for pspice to handle and represents parameters for limited cases.

    Best regards,

    Errol Leon
    Texas Instruments
    Precision Op Amp Applications
  • 0 in reply to Errol Leon6
    Prodigy 120 points

    Thanks Errol for your answer and for taking time to test the model.

    It's unfortunate that the noise level given by the INA model does not match the datasheet because studying and minimizing the noise level is one of the key reasons for us to simulate the circuit (in addition to checking gain, bandwidth, etc.).

    Rather than giving up on Tina for this purpose there might be alternatives. I suppose the noise part of the INA IC model could be turned off and simply add a voltage noise source at one of the inputs of the INA. But it should have the right spectral power density to match the datasheet. Editing the macromodels for the IC to remove noise sources in the transistors and creating a voltage noise source seems possible.

    I wonder if you could suggest shortcuts to get this implemented.

    Kin regards

    Henry