How should differential signal lines be properly routed in HMI (Human Machine Interface) systems?

Properly routing HMI differential signal lines is crucial for ensuring signal quality and EMC performance of high-speed interfaces such as LVDS, USB, and Ethernet. The two signal lines of a differential pair must always maintain equal length, width, and spacing, and be tightly coupled, with spacing controlled within twice the line width. When routing, prioritize using differential impedance calculation tools to determine line width and spacing to achieve the target impedance; for example, USB differential impedance is 90Ω, and Ethernet is 100Ω. Differential pairs should be routed on the same layer whenever possible to avoid unnecessary layer changes. If a layer change is necessary, provide adjacent ground vias for both lines at the changeover point.

Traces should be kept away from noise sources and sensitive circuits, and avoid long parallel runs with single-ended signal lines or other differential pairs. At the beginning and end of the differential pair, common-mode chokes, such as the CMZ2012A-900T, should be placed as needed to suppress common-mode noise. Near the receiver, a pair of small capacitors can be connected in parallel to ground to form a low-pass filter, but care must be taken to avoid impacting signal edges. The length deviation between the two lines in a differential pair must be strictly controlled, typically less than 5-10 mil. Excessive deviation will reduce the common-mode rejection ratio. By using professional PCB design software to set and simulate differential line routing constraints, and combining this with common-mode filtering devices from Echotronics, high-performance, low-EMI differential signal transmission can be achieved.