How to suppress differential mode interference in I/O modules?

Suppressing differential-mode interference in I/O modules primarily targets noise voltage between signal lines or power lines. At the power input, a π-type or LC filter circuit should be used. Power inductors such as PWR6045R6R8M0T can be selected, and X7R or X5R MLCCs should be used as capacitors. For signal lines, a small resistor in series and a capacitor to ground in parallel at the receiving end form a low-pass filter. The cutoff frequency should be higher than the signal frequency but lower than the noise frequency. In cases of severe differential-mode interference, a varistor or TVS diode pair, such as SMBJ5.0CA, can be connected in parallel between signal lines to clamp excessively high differential-mode voltage. For DC power lines, adding a large electrolytic capacitor at the load end can absorb low-frequency differential-mode ripple, while a small MLCC in parallel can filter out high-frequency noise. During PCB routing, differential signal lines should be strictly equal in length, spacing, and parallel to maintain their common-mode interference immunity characteristics and avoid proximity to noise sources. Using balanced transmission methods, such as 4-20mA current loop or RS-485 differential signal, inherently provides good suppression of differential mode interference.