What Is Offset Voltage?
Offset voltage, also known as input offset voltage, refers to the difference between the DC voltages applied to the two input terminals in order to obtain a constant zero voltage output at the output terminal in a differential amplifier or a differential input operational amplifier. This parameter characterizes the level of matching of the differential amplifier. When equal input voltages are applied to the two input terminals of a differential amplifier, the differential output voltage is called the output offset voltage. [1]
- If the inputs of the op amp are shorted together and grounded (as shown), there is a certain output
- The output offset voltage is caused by an internal mismatch in the input stage. A simple differential pair (see picture)
- Many single op amps provide additional pins for zeroing the offset voltage. When using this function, a potentiometer is usually connected to the two pins of the op amp, and the sliding end of the potentiometer is connected to the positive power terminal (or negative power terminal) through a resistor, depending on the specific operational amplifier. As shown:
- The method of external offset voltage adjustment is divided into an external adjustment method of an offset voltage of an inverting operational amplifier circuit and an external adjustment method of an offset voltage of a non-inverting operational amplifier circuit. The external adjustment method of the offset voltage of the non-inverting operational amplifier circuit is taken as an example to explain the external adjustment of the offset voltage.
- For the in-phase operational amplifier circuit, you can use the circuit shown in the following figure
- External adjustment method for offset voltage of non-inverting operational amplifier circuit
- Inject a small bias voltage at the inverting input of the op amp. When R 3 R 1 , the offset voltage is small and the circuit works better; otherwise, the signal gain will be affected by the potentiometer used to adjust the offset voltage. However, when R 3 is connected to a fixed low-impedance reference supply ± V REF , the signal gain will stabilize. [3]