O'Reilly logo

Circuit Design: Know It All by Bob Zeidman, Tim Williams, Robert Pease, Walt Kester, Ian Hickman, Bonnie Baker, Darren Ashby

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Chapter 17

Dealing with High-Speed Logic

Walt Kester

Much has been written about terminating printed circuit board traces in their characteristic impedance to avoid reflections. A good rule of thumb to determine when this is necessary is: Terminate the line in its characteristic impedance when the one-way propagation delay of the PCB track is equal to or greater than one-half the applied signal rise/fall time (whichever edge is faster). A conservative approach is to use a 2-inch (PCB track length)/nanosecond (rise/fall time) criterion. For example, PCB tracks for high speed logic with rise/fall time of 1 ns should be terminated in their characteristic impedance if the track length is equal to or greater than 2 inches (including any meanders).

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required