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I have the following circuit, the INA122 instrumental amplifier. when RG pins are not connected, the default gain is 5. I am sure that the bridge is balanced, however, for the simulations, why there is a high offset at the output around 0.3V? I am new to the software, and would like to know why this happens, and how could i bring the output voltage to zero, as the diff is supposed to be 0.0mV. I tried to put the circuit into a breadboard, and it provides better results (Although, still not zero).

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Are there any properties, such as offset voltage or voltage drift that I misread?

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I think your problem is that you don't have an appropriate power supply for your amplifier. The INA122 has a minimum output of, worst case, (V⁻+0.15) V, so with V⁻ grounded, you can never get an output voltage less than 0.15 V (source: page 2 of the datasheet). If you need the output to include ground, you need to have a negative power supply for the INA122.

The simulation model is outputting about twice that, but that could be down to an inaccurate model, or worse characteristics when powered from 10 V (the datasheet spec is given at 30 V); I couldn't say.

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  • \$\begingroup\$ Thank You, i have made another circuit in which the V- is connected to -10V. I got significantly lower voltages, around 77uV, still an offset, but I think it's negligible. \$\endgroup\$ Aug 13 at 14:51
  • \$\begingroup\$ @Lactobacillus Always check the output ratings! Even if it claims to be a rail-to-rail output amplifier, that could mean a few millivolts more above the rail than you can tolerate for your application. You can get tiny charge pump ICs to provide a volt or so negative bias to the amplifier if you don't want to add the complexity of a bipolar power supply. \$\endgroup\$
    – Hearth
    Aug 13 at 14:57

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