Adjusting Signal Timing: Part 1
It is becoming a routine requirement for PCB designers to tune traces on boards. Such tuning can be relative (i.e. traces are equal length) or absolute (i.e. traces must be a proscribed length.) This article, Part 1 of a two-part series, addresses why traces need to be tuned at all, how to determine signal propagation speeds and times so that proper trace length can be determined, and how sensitive propagation time (and therefore tuning) is to factors such as Er, trace length, trace pattern, etc. The special case of differential traces is mentioned, and some examples of tuning on a high-speed computer motherboard are illustrated.
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