How to reduce high-frequency bus interference in intelligent controllers (PACs)?

High-frequency buses (such as DDR, PCIe, EtherCAT) of intelligent controllers generate rich harmonic radiation interference during high-speed switching, extending to several GHz. Reducing interference requires a comprehensive approach using filtering, shielding, and termination techniques. A PBZ1005B-501Z0T ferrite bead (500Ω@100MHz) is connected in series at the bus driver output to attenuate high-frequency noise, while an ESDLC5V0D3B electrostatic discharge protection diode is connected in parallel for surge protection. For differential buses, CMZ... The 20212A-900T common-mode inductor (90μH) suppresses common-mode radiation, and the differential pairs are strictly equal in length and tightly coupled, with the spacing controlled within 2W.

The PCB uses a complete ground plane, and a shield is added above the bus area. The shield is grounded to the system ground through multiple points. The clock signal needs to use spread spectrum technology (SSC) to reduce peak radiation. According to actual measurements, this solution can make the radiated emission of the PAC high-frequency bus 8dB below the EN55032 limit in the frequency band below 1GHz, and the bit error rate is less than 10^-9.