In applications where it's necessary to amplify signals that include DC components, the BUL128A operational amplifier must be properly adjusted. This means compensating for the internal offset of the op amp, primarily from the differential input stage, to ensure that the output is zero when the circuit is closed. Proper adjustment is essential to maintain signal integrity and avoid unwanted drift or errors.
Some op amps come with a dedicated nulling pin, allowing for easy compensation by following the manufacturer’s instructions. For example, the LM318 and LM741 have zero adjustment circuits shown in Figures 5.3.5(a) and (b). When performing this adjustment, care must be taken not to touch the wiper of the potentiometer with ground or power lines, as this can potentially damage the op amp.
For op amps that do not have a nulling pin, you can use an inverting or non-inverting configuration to adjust the offset, referencing the circuits shown in Figures 5.3.5(c) and (d). During the process, the input of the circuit should be grounded, and a multimeter in DC mode or an oscilloscope in DC coupling should be connected to the output. Adjust the potentiometer until the output reads zero. It's worth noting that modern op amps are often designed with excellent symmetry and low offset voltages, making manual zero adjustment unnecessary. With deep negative feedback, these devices can effectively suppress drift, and in many cases, the offset is so small that it goes unnoticed. Additionally, some advanced op amps, such as chopper-stabilized or auto-zero types, are designed to eliminate the need for manual zeroing altogether.
When using an integrated operational amplifier in applications where only AC signals need amplification, it's possible to simplify the power supply by using a single supply—either positive or negative. In such cases, a single-supply op amp like the LM324 can be used directly. Even dual-supply op amps can be configured for single-supply operation. However, it's crucial to ensure that the static potentials at both input terminals are equal. The input and output should also be properly biased so that the center of the op amp’s linear operating range aligns with the midpoint of the power supply voltage. This allows for the maximum dynamic range and prevents signal clipping or distortion.
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