January 19, 2011 -- Length-match your traces to within 100 mils. Or is it 10 mils? Or should you go down to 1 mil? Should you include the lengths of the vias? How about the lengths of resistors? Understanding the origin of length-matching requirements, coupled with some rudimentary signal integrity analysis, can help answer these questions.
Determining length requirements requires an understanding of flight time, electrical length vs. physical length, loading and signal quality. Those elements are vital in determining what the length really needs to be, as well as in determining the allowable trade-offs to meet system timing goals.
By Patrick Carrier. (Carrier is a technical marketing engineer for high-speed PCB analysis tools at Mentor Graphics Corp.)
This brief introduction has been excerpted from the original copyrighted article.