Found the Z80-based annecdote interesting! And probably relevent to problems that we occasionally experience here WRT part-substitution :-<. ---------- Forwarded message ---------- From: Hackaday <[email protected]> Date: Sat, Jun 21, 2014 at 7:01 PM Subject: [New post] Delving Deep into High Speed Digital Design Will Sweatman posted: " In high speed digital circuits, fast doesn't necessarily mean "high clock rate". [Jack Ganssle] does an excellent job at explaining how the transition time of signals in high speed digital circuits is just as important as the speed of the signal itse" Respond to this post by replying above this line New post on *Hackaday* <http://hackaday.com/author/willsweatman/> Delving Deep into High Speed Digital Design <http://hackaday.com/2014/06/21/delving-deep-into-high-speed-digital-design/> by Will Sweatman <http://hackaday.com/author/willsweatman/>
[image: scope capture showing ringing affect in a high speed digital signal] In high speed digital circuits, fast doesn't necessarily mean "high clock rate". [Jack Ganssle] does an excellent job at explaining <http://www.ganssle.com/video/episode1.html#.U4zBcF4y3lE> how the transition time of signals in high speed digital circuits is just as important as the speed of the signal itself. When the transition time is large, around 20 nanoseconds, everything is fine. But when you cut it down to just a few nanoseconds, things change. Often you will get a ringing effect caused by impedance mismatch. As the signal travels down the trace from the driver and hits the receiver, some of the signal will get reflected back toward the driver if the impedance, which is just resistance with a frequency component, does not exactly match. The reflected signal then heads back to the driver where the impedance mismatch will cause another reflection. It goes back and forth, creating the 'ringing' you see on the scope. [Jack Ganssle] goes on to explain how a simple resistor network can help to match the impedance and how these should be used in circuits with fast transition times, especially where you will be taking readings with a scope. As the scope probe itself can introduce impedance and cause the ringing. In case you didn't pick up on it, [Jack Ganssle] also happens to be one of the judges for The Hackaday Prize <http://hackaday.io/prize/judges#Ganssle>. Read more of this post <http://hackaday.com/2014/06/21/delving-deep-into-high-speed-digital-design/#more-125114> *Will Sweatman <http://hackaday.com/author/willsweatman/>* | June 21, 2014 at 4:01 pm | Tags: high speed <http://hackaday.com/?tag=high-speed>, impedance <http://hackaday.com/?tag=impedance>, Signals <http://hackaday.com/?tag=signals> | Categories: misc hacks <http://hackaday.com/?cat=5611793> | URL: http://wp.me/pk3lN-wxY Comment <http://hackaday.com/2014/06/21/delving-deep-into-high-speed-digital-design/#respond> See all comments <http://hackaday.com/2014/06/21/delving-deep-into-high-speed-digital-design/#comments> Thanks for flying with WordPress.com <http://wordpress.com> -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
