How to ensure impedance matching of the motion controller MC interface

Ensuring impedance matching across all interfaces of the motion controller (MC) is crucial for maintaining signal integrity. First, the characteristic impedance required by the interface standard must be clearly defined; for example, USB is 90Ω, LVDS is 100Ω, and RS-485 twisted pair is approximately 120Ω. During the PCB design phase, the target impedance is achieved by controlling the trace width, trace-to-reference plane spacing, and dielectric constant, typically calculated using simulation software. At connectors, ensure that the pin and pad design does not introduce large impedance discontinuities.

For transmission lines, use matching resistors at the source or load end, with a value equal to the characteristic impedance minus the source resistance, or directly connected in parallel. Measure the actual impedance using an impedance test fixture or time-domain reflectometer. For differential pairs, both differential and common-mode impedances must be controlled simultaneously. Impedance matching effectively reduces reflections, prevents signal overshoot, ringing, and eye diagram closure, thereby improving the EMC performance and reliability of the interface.