Issue link: https://resources.pcb.cadence.com/i/1532920
Differential pairs (High-Speed) Definition: Rules for routing differential pairs, which are pairs of traces that carry equal and opposite signals. Differential pairs showing signal propagation with Static Phase vs. Dynamic phase. This blog on our website explains two important concepts for differential pairs, inter pair skew, and intra pair skew: "Ideally, synchronized signals need to arrive at their destination simultaneously to ensure there is no loss of data arising from timing issues. In reality, however, differences (even minute) in the propagation paths mean no two signals will ever arrive at the same time. For greater ease of use, components are forgiving and allow for some timing mismatch – known as clock skew – within tolerable limits. Timing mismatches are most heavily reliant on the length of the traces, resulting in two variations: f Intra pair skew between two lines of a differential pair, which indicates the timing difference between the positive and negative signal lines. Keeping the mismatch low between the two differential signals allows for more headroom and better noise protection in balanced lines. f Inter pair skew indicates the timing difference between signals used in data formats that do not have an embedded clock signal. Inter-pair skew can cover both single-ended and differential pairs within a data format, making some signals doubly constrained by skew. Example: For this example, we will use Constraint manager to ensure differential pairs are routed together with consistent spacing to maintain signal integrity for dynamic signals and for overall length matching. 1. Open the Constraint Manager 2. Go to the worksheet Electrical > Electrical Constraint Set > Routing > Differential Pair. 3. Create a constraint set (e.g. ECS1). 4. Fill in values for Static Phase Tolerance and Dynamic Phase Tolerance as shown below. 5. You should already have values populated for the other parameters. Now apply the constraint set to any relevant diff pairs by going to the worksheet Electrical > Net > Differential Pair. 14 www.cadence.com OrCAD X Constraint Management Guide