Noise is only one source of error and should be considered in the context of other error sources. Input offset voltage (voltage mismatch at the input of the operational amplifier) can be considered as DC noise. Although its impact can be significantly suppressed by implementing one-time system calibration, the offset voltage will change with temperature fluctuations and time due to changes in mechanical stress. In addition, it also varies with the input level (CMRR) and power supply (PSRR). Real time system calibration aimed at eliminating drift caused by these variables quickly became both expensive and impractical. For harsh environmental applications with significant temperature fluctuations, measurement uncertainty caused by offset voltage and drift can have a stronger dominant effect than noise. For example, simply due to temperature drift, a model with 5 μ The operational amplifier with V/° C temperature drift performance indicators will experience a 625 ° C temperature range from -40 ° C to 85 ° C μ The input reference offset of V. In contrast, noise of several hundred nanovolts (nV) is irrelevant. LT6018 has 0.5 μ Excellent drift performance at V/° C and an 80 μ The maximum misalignment specification of V (from -40 ° C to 85 ° C). For better performance, you can pay attention to the recently launched LTC2057 automatic zero amplifier, which has a temperature range of less than 7 ° C from -40 ° C to 125 ° C μ The maximum offset voltage of V. Its broadband noise is 11nV/√ Hz, while its DC to 10Hz noise is 200nVP-P. Although this noise is higher than LT6018, LTC2057 is sometimes a better choice for low-frequency applications due to its excellent input offset drift performance throughout the entire temperature range. It is also worth noting that due to its low bias current, the current noise of LTC2057 is much lower than that of LT6018. Another advantage of LTC2057‘s low input bias current is that it has a very low clock feedthrough compared to many other zero drift amplifiers. When the source impedance is high, some of these other zero drift amplifiers will generate large voltage noise spurious signals.

    In such high-precision circuits, caution must also be exercised to minimize the thermocouple effect, which can occur in any situation where dissimilar metal nodes exist. Even the nodes of two copper wires provided by different manufacturers can generate a thermoelectric potential of 200nV/° C, which is more than 13 times higher than the worst drift of LTC2057. In these low drift circuits, it is important to adopt the correct PCB layout method to match or minimize the number of nodes in the amplifier input path, make the input and matching nodes close together, and avoid generating thermal gradients.

conclusion
    Noise is a fundamental physical limitation. In order to minimize the adverse effects generated during the processing of sensor signals, caution must be exercised in selecting appropriate operational amplifiers, minimizing and matching input resistances, and implementing the physical layout of the design.