I am watching some videos explaining how reflection can affect a signal and how you should treat these signals as transmission lines to remove reflection. I wanted to understand a more practical example of when terminated a signal is to avoid reflection is important. I have used termination for video signals on a PCB before but what are some other good examples. When should I really be making the effort to have controlled trace impedances (besides video signals) and when is it less important?

  • \$\begingroup\$ This paper does a good job of explaining when that matters. \$\endgroup\$ – Avid Pro Tool Jan 14 at 4:37

This is the quick answer.

1) If the signal is backterminated and/or the amplitude you need requires that you have termination (PECL, video, CML), you have to terminate it.

2) If the rise/fall time of your signal is comparable with the time it takes your signal to transit the path, you have to terminate it.

3) If you have AC coupling, somebody has to provide a DC path to ground on the other side of the coupling capacitor. Such as, the termination. If it's not inside the part, you have to provide it.

4) If it's slow (compared to the path length), DC coupled, and the right amplitude at low frequency, you might be able to get away without anything special.

  • \$\begingroup\$ I'm thinking the termination may reduce deterministic jitter. \$\endgroup\$ – analogsystemsrf Jan 13 at 5:33

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