Source-Synchronous Signaling: How High-Speed Parallel Interfaces Stay in Sync
Overview As parallel interfaces push to higher speeds, keeping all data bits synchronized becomes increasingly difficult. This post explains why global clock distribution hits a wall — and how source-synchronous signaling solves it. Signal Propagation on PCB Before diving into timing, it helps to understand how fast signals actually travel on a PCB: Typical propagation speed on FR4: 15–17 cm/ns A 1 cm trace length difference ≈ 60–70 ps of timing skew At 1 GHz (1 ns period), 70 ps of skew already consumes 7% of your entire timing budget from a single centimeter of mismatch. As data rates climb, this becomes unmanageable. ...