How to reduce EMI radiation on the clock line of an HMI (Human Machine Delivery System)?

Reducing EMI radiation from HMI clock lines requires measures from multiple aspects, including source suppression, path control, and termination matching. Source suppression: Select a clock driver with a slower rise time, or connect a small resistor (e.g., 22Ω-47Ω) in series at the driver output to reduce high-frequency harmonic components of the signal. Path control: Treat clock lines as transmission lines, implement impedance control (typically 50Ω or 100Ω differential), and reference a complete ground plane. Keep traces as short as possible, avoiding unnecessary vias and corners; use 45-degree angles or rounded corners. Clock lines must not be placed near or parallel to I/O ports, power lines, or other sensitive signal lines. Placing clock lines on inner layers of the PCB and surrounding them with ground planes on both sides is the most effective shielding method.

For long-distance clock transmission, consider using low-voltage differential signals, such as LVDS. Termination matching: Match at the far end or both ends depending on the transmission line type to eliminate reflections; matching resistors should be placed close to the receiving end. For clocks fan-out to multiple loads, use a dedicated clock distribution chip to keep the topology simple. In addition, the power supply pins of the clock generator must be adequately decoupled and filtered, and ferrite beads such as the PBZ1005E121Z0T can be used to isolate digital power supply noise. By applying these rules and optimizing with passive components such as ferrite beads and resistors from Etymotic, electromagnetic radiation generated by the clock line can be significantly reduced, helping HMI products pass radiated emission tests.