Some op amps are provided with two additional terminals to which a specified circuit
can be connected to trim to zero the output dc voltage due to VOS . Figure 2.30 shows such
an arrangement that is typically used with general-purpose op amps. A potentiometer is
connected between the offset-nulling terminals with the wiper of the potentiometer connected
to the op-amp negative supply. Moving the potentiometer wiper introduces an
imbalance that counteracts the asymmetry present in the internal op-amp circuitry and that
gives rise to VOS. We shall return to this point in the context of our study of the internal circuitry
of op amps in Chapter 12. It should be noted, however, that even though the dc output
offset can be trimmed to zero, the problem remains of the variation (or drift) of VOS
with temperature.