How to resist EMI in high-speed pulse signals of motion controllers (MC)

Improving the EMI immunity of high-speed pulse signals in motion controllers (MCs) requires a comprehensive approach to signal integrity design and port protection. Pulse signals, such as PWM or step direction signals, should be designed for differential transmission, for example, using LVDS or RS-422 standards, which offer strong common-mode rejection. On the PCB, differential pairs must be strictly equal in length and spacing, and reference a complete ground plane. A small resistor should be connected in series at the drive output to control rise time and reduce high-frequency harmonic radiation. A small capacitor can be connected in parallel to ground at the receiver to form a low-pass filter.

Transient protection must be integrated at the port, such as using an ESDLC series low-capacitance TVS array, which has a fast response and minimal impact on signal edges. Shielded twisted-pair cables should be used for transmission, with the shielding layer terminated 360 degrees to the chassis at the controller end. High-speed clock signals generated internally should be grounded and kept away from analog circuits. Signal quality should be verified through simulation and measured eye diagrams to ensure that the pulse waveform remains clearly discernible even in noisy environments. At the system level, pulse signal lines should be laid separately from power lines, with a minimum spacing of 30cm.