Why do op amps need to be zeroed?

In applications where signals containing DC components need to be amplified, the BUL128A integrated operational amplifier must be withered, that is, the offset of the operational amplifier itself (mainly the differential input stage) must be compensated to ensure After the op amp operates in a closed loop, when the input is O, the output is also O.

Some op amps already have a compensation terminal, and you only need to connect it to the zero-adjustment circuit according to the provisions of the device manual. For example, the zero-adjustment circuits of LM318 and LM741 are shown in Figure 5.3.5(a), ( b) shown. You must be careful when adjusting zero. Never let the sliding end of the potentiometer touch the ground wire or power wire, otherwise the op amp will be damaged.

For op amps without a zero-adjustment terminal, the inverting and amplifier zero-adjustment circuits can be zeroed by referring to the zero-adjustment circuits shown in Figure 5.3.5(c) and Figure 5.3.5(d) respectively.

When adjusting the zero, connect the input end of the circuit to the ground, connect the DC current block of the multimeter or the DC coupling block of the oscilloscope to the output end of the circuit, and adjust the potentiometer so that the output is 0.

What should be pointed out here is that the newly designed op amp has good symmetry, small offset, and no zero adjustment terminal. When deep negative feedback is added, the drift of the zero point can be suppressed by deep negative feedback, and the offset is almost invisible. If it doesn’t come out, you don’t need to adjust it to zero when the requirements are not too high. There are also some op amps (such as chopper auto-zero op amps) that do not require zeroing.

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