Managing Time Delays

摘要

TO KEEP A good high-speed signal quality from driver to receiver on a PCB is not an easy task for designers. One of the most challenging issues is managing the propagation delay and relative time delay mismatches. To manage the time delays, we need to know how to calculate trace length from time delay value in order to implement the PCB trace routing accordingly. Let me take you through the process. Calculating signal speed. According to physics, electromagnetic signals travel in a vacuum or through the air at the same speed as light, which is: Vc = 3 × 10~8M/sec = 186,000 miles/sec = 11.8 ins A signal travels on a PCB transmission line at a slower speed, affected by the dielectric constant (Er) of the PCB material. The transmission line structure also affects the signal speed.