Tag
signal integrity
4 articles.
- Reflections you can see: when a trace becomes a transmission line
The rule is not length, it is rise time. TI's criterion is four times the one-way delay — below it a trace is a wire, above it every unterminated end is a mirror. With a lattice diagram for the ringing you are looking at.
- RS-485 termination: when 120 Ω helps and when it just costs you
Where the 120 Ω comes from, the loop-time test that decides whether you need it at all, why AC termination is a data-rate trade, and how failsafe bias resistors quietly eat a third of your node budget.
- The via is the decoupling: 40 dB from layout alone
Würth built one board with the same ferrite and the same two 100 nF capacitors in every channel, and changed only the layout. The worst channel is more than 40 dB down on the next best. The capacitor was never the variable.
- Why 100 nF, and the frequency where it stops being a capacitor
The value is inherited, not derived. What actually decides whether a decoupling capacitor works is its inductance — and above a few tens of megahertz your 100 nF is an inductor.