Input referred offset voltage in an operational amplifier is defined as what?

• A. The maximum input differential voltage the amplifier can tolerate before clipping.
• B. The differential input voltage required to drive the output to zero, caused by device mismatch and manufacturing variations.
• C. The voltage drop across the input transistors due to bias current.
• D. The supply voltage difference needed to turn on the input stage.

Answer: (B)

The idea being tested is that input offset voltage is the small difference that must exist between the two inputs of an op-amp in order to drive the output to zero. This offset comes from inevitable mismatches between the input pair transistors and other device variations introduced during manufacturing. Because the transistors aren’t perfectly identical, the amplifier behaves as if there’s a tiny, inherent voltage difference at its inputs. The offset voltage is precisely this differential voltage referred to the input that would cause the output to be zero (or to reach the reference point used for measurement).

So, even with no signal applied, the input pair isn’t perfectly balanced, and a small voltage difference at the inputs is required to cancel that imbalance and produce zero output. This is why the input offset voltage is described as the differential voltage between the inputs that yields zero output.

The other options describe different concepts: a limit on how large the input differential can be before clipping is about dynamic range, not offset; the voltage drop due to input bias currents is related to bias current errors and source resistance, not the intrinsic offset needed to null the output; and the supply difference needed to turn on the input stage is about power rails, not the input-side offset.