Why do designers increasingly specify controlled impedance?
Telecommunications and computing equipment are operating at ever increasing speeds and switching rates. Because of this some of the laws of physics which could be ignored at lower frequencies now have to be given serious consideration. At high speeds PCB traces act as transmission lines and the electrical energy can reflect back and forth similar to a wave on a lake when it meets an obstruction. Controlled impedance traces are designed to minimize electrical reflections and ensure an error free transition between the PCB track and interconnections.
