How to perform interference suppression wiring for differential signals in frequency converters

Anti-interference routing for differential signals in frequency converters is crucial for ensuring reliable transmission of critical communication and sampling data. Differential signals include CAN bus, RS485, encoder signals, and differential current sampling outputs. Routing principles include: the two signal lines of a differential pair must always maintain equal length, width, and spacing, and be tightly coupled. The spacing between lines is typically controlled within twice the line width to enhance common-mode rejection of external interference. Before routing, the target differential impedance must be calculated according to the interface standard, for example, 120Ω for CAN, and the line width and spacing must be strictly controlled to achieve impedance matching.

Differential pairs should be routed on the same layer as much as possible to avoid unnecessary layer changes; if a layer change is necessary, adjacent grounding vias should be provided for both lines at the layer change point. Traces should be kept away from power lines, high-frequency clocks, and other noise sources, and long parallel routing with other signal lines is strictly prohibited. Common-mode chokes, such as the CMZ3225A-510T, can be placed at the beginning or end of the differential pair to further suppress common-mode noise. A pair of small capacitors can be connected in parallel to ground near the receiver for low-pass filtering, but signal integrity must be ensured. Differential line routing constraints and simulation functions in professional PCB software can ensure routing quality. Common-mode chokes from Audiotech are commonly used devices to enhance the immunity of differential signals.