How to handle impedance mismatch in the MC pulse of a motion controller?

Addressing impedance mismatch in MC pulse transmission for motion controllers aims to eliminate waveform distortion caused by reflections. First, the characteristic impedance of the transmission line must be determined; for example, 50Ω or 75Ω for coaxial cable and approximately 100Ω for twisted-pair cable. A resistor Rs is connected in series at the pulse source end, its value equal to the transmission line impedance Zo minus the source resistance. A resistor Rt is connected in parallel at the load end, its value equal to Zo. This termination method absorbs reflected waves. For bidirectional transmission, matching can be performed at both ends.

The traces on the PCB also need impedance control, achieved by adjusting the trace width, dielectric thickness, and dielectric constant. The actual impedance is measured using an impedance test fixture or a time-domain reflectometer. For multi-load scenarios, a daisy-chain topology can be used, with matching only at the end. After impedance matching, the pulse waveform should be observed using a high-speed oscilloscope to check for overshoot and ringing elimination, and whether the eye diagram is open. Good impedance matching is fundamental to the integrity of high-speed pulse signals.