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Starting electronics
Offset nulling
Earlier on it was mentioned that there are two connections
to the 741 which are called offset null connections. In most
op-amp applications these would not be used, but in certain
instances, where the level of the output voltage is of critical
importance they are.
When the op-amp has no input voltage applied to it — or,
more correctly speaking, the input voltage is 0 V — the
output voltage should be the same i.e., 0 V. Under ideal
conditions of manufacture this would be so, but as the 741
is a mass-produced device there are inevitable differences
in circuit operation and so the output is rarely exactly 0 V.
Temperature differences can also create changes in this output
voltage level. The difference in the output from 0 V is known
as the offset voltage and is usually in the order of just a few
millivolts.
Hint:
In the majority of applications this level of offset voltage is no problem
and so no action is taken to eliminate it. But the offset null terminals
of the 741 may be used to control the level of offset voltage to reduce
it to zero.
Figure 9.11 shows a circuit which you can build to see the
effects of the process of offset nulling, where a potentiometer
has been connected between the two offset null terminals
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