In an operational amplifier, the input offset voltage is the difference in the voltage between the + and - input pins when negative feedback is applied. In a comparator, the input offset voltage is the comparison voltage (threshold voltage) error.
Although ideally 0, in an operational amplifier, there is a difference between VBE of the + and - input transistors in the input-stage differential amplifier, which becomes the input offset voltage.
In actual use; for example when using an operational amplifier with an input offset voltage of VlO ≤ ±5mV, if ×100 amplification is created, there will be an error of up to ±5×100= ±500mV at the output. Therefore, when using a circuit that handles very small input signals, you must either select a product with a small input offset voltage, or adjust the offset externally.
Measurement method: Assuming VIN = 0 in the above circuit, the input offset voltage can be measured by dividing the output by 100. The measurement circuit in this case would be as follows.
Remark Because the input offset voltage is the potential difference between two pins, the maximum value is a ± value. However, the ± symbol may be omitted in some general reference materials.