Guides / Reference

Differential pairs & length tuning

USB, LVDS and similar signals travel as coupled pairs. The app routes a pair as one object and shows how close the result is to the declared impedance target.

The Board Stackup sheet where impedance intent is declared, with layer presets including an 8-layer SDR profile reserving paired RF signal layers
Where pair intent lives: the stackup. Note the 8L SDR preset, it reserves paired RF signal and reference-plane layers, which is pair routing thought about at the cross-section level.
  1. State the intent in the stackup

    Impedance targets (50 Ω single, 90/100 Ω differential) live in the stackup editor, intent declared where the geometry that realises it is decided.

  2. Route the pair

    Pair routing engages for nets under a differential target; the routing-time readout shows achieved vs target as you go.

  3. Match lengths

    Where skew matters, length tuning adds meanders to a trace you have drawn, to bring it inside its length tolerance, and the readout shows the difference so you don’t measure by hand. Guides that steer a net to a target length aren’t built yet (see the limits below).

When to care: below roughly 10 MHz, rarely. At USB 2.0 high speed and faster, always. Marginal boards in between may pass bench testing and still fail intermittently, which is the expensive version of this mistake.