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How to read datasheets

A non-inverting amplifier with a gain of 100 is built using an op-amp with an input offset voltage of max 2 mV. With the input at 0 V, which is the guide for the maximum error voltage that can appear at the output?

  1. A2 mV
  2. B200 mV
  3. C20 mV
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Answer: B. 200 mV

Input offset voltage behaves like a small voltage source in series with the input and appears at the output multiplied by the non-inverting amplifier's gain (1 + Rf/Ri). 2 mV × 100 = 200 mV, which is a 4% error against a 5 V full scale, for example. Estimate with the max value rather than the typ value, and also add the change due to temperature drift (µV/°C). For precision measurement, choose a zero-drift (chopper) type with an offset of a few µV, or calibrate in software. 2 mV is the value obtained by forgetting to multiply by the gain.

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