How to design onboard filtering for I/O modules?

Onboard filtering design for I/O modules requires differentiated processing for different signal types. Digital input channels can use a 22-100 ohm resistor in series at the input terminal and a 100pF-1nF capacitor in parallel to ground to form an RC filter, while a TVS diode such as an ESDLC series is connected in parallel for transient protection. Digital output channels can use a ferrite bead such as the PBZ1608 series in series at the output terminal of the driver chip, and a freewheeling diode can be added at the load terminal. Analog input channels require multi-stage filtering; the first stage is an anti-aliasing RC filter, and the second stage can use an active filter for fine conditioning. The grounding terminals of all filters must be directly connected to a clean reference ground plane to avoid introducing additional noise through long traces.

Onboard filtering at the power input should include a common-mode inductor, an X capacitor, and a Y capacitor to form a complete π-type or T-type filter network. High-frequency digital circuits, such as the CPU, should have multiple decoupling capacitors of different capacitance values arranged around them to form full-band decoupling from MHz to GHz. During design, attention should be paid to the parasitic parameters of the filtering components, such as the ESR and ESL of capacitors, and MLCC capacitors with good high-frequency characteristics should be selected. In terms of layout, the filter circuit should be located in the entry area of the signal path, protecting the signal before filtering it.