How to prevent AI filtering in I/O modules from reducing accuracy?

When designing the filtering circuit for the analog input channels of I/O modules, careful selection of components and topology is crucial to maintain signal accuracy. First, choose high-precision, low-temperature-drift resistors and capacitors, such as thin-film resistors with 0.1% accuracy and 25ppm/°C temperature drift, and C0G/NP0 ceramic capacitors. The introduction of the filtering network should not alter the DC offset of the signal; therefore, avoid using series DC blocking capacitors. Active filters can be used, leveraging the high input impedance and low output impedance characteristics of operational amplifiers to provide filtering while achieving impedance matching and signal buffering.

In multi-stage filtering, the first stage should use an anti-aliasing filter with a cutoff frequency slightly higher than the signal bandwidth to suppress high-frequency noise from aliasing to low frequencies after sampling. On the PCB layout, the filtering circuit should be kept away from digital circuits and power supplies, and a separate analog ground plane should be used. All analog traces should be as short as possible and avoid crossing digital areas. The reference voltage of the signal conditioning chip must be highly stable; a dedicated reference voltage source can be used in conjunction with the filtering. Finally, testing is required to verify that the system's gain error, offset error, and nonlinearity accuracy indicators still meet the requirements after adding filtering.