Signal Path
A high-speed communication path transmits serialized digital data over differential copper traces on a printed circuit board. High-performance SerDes channels compress wide parallel data buses into a single high-speed differential signal to minimize the number of traces required on the board. This consolidation reduces routing complexity and saves board real estate while achieving gigabit-per-second transmission rates.
Loss Mechanism
Signal degradation over long traces is driven by dielectric absorption and conductor skin effect loss at multi-gigahertz frequencies. Inside SerDes channels, these losses increase with frequency, leading to closed signal eyes and inter-symbol interference at the receiver. Designers mitigate this by using low-loss laminate materials with low dissipation factors and smooth copper foils.
They also apply transmitter pre-emphasis and receiver equalization to compensate for high-frequency attenuation. These active compensation techniques allow signal recovery even when the trace introduces substantial loss, ensuring data integrity in high-density backplanes and routers.
Geometric Design
Differential routing requires extremely tight impedance control and precise skew matching between the positive and negative traces. Any length mismatch between the two traces converts the differential signal to a common-mode signal, causing electromagnetic interference and signal degradation. Routing SerDes channels requires the avoidance of sharp bends and adjacent high-speed traces that could cause crosstalk.
Consistent trace geometry along the entire length of the channel maintains the characteristic differential impedance.
