Quote from: rdl on Today at 12:55:08 amOne more thing, and this is something that I've previously seen evidence of potentially being a real problem. This image is where the crosstalk is looked at on the long 425mm path. The blue trace is the actual signal on the "positive" rail (red jumpers), and the yellow is the induced signal on the "negative" (black jumpers) rail.
>![](https://www.eevblog.com/forum/beginners/voltage-drop-at-breadboard/?action=dlattach;attach=681953;image)
Here the same signal is running through one of the five hole vertical strips (blue trace) with the crosstalk that appears on the adjacent five hole socket strip (yellow trace). Doesn't look that bad actually.
![](https://www.eevblog.com/forum/beginners/voltage-drop-at-breadboard/?action=dlattach;attach=681959;image)
I'd like to point out to anyone reading this thread that running a 10MHz signal through 425mm of conductor, including multiple wire to board insertion connections, is somewhere beyond "worst case scenario". I'm sure decent quality breadboards have a limit to their usefulness, but I don't know where it is and I'm not inclined to go looking today.
I'm not entirely sure what you are showing there, since the detailed wiring matters.
However, NEXT and FEXT on signals can be serious problems. (NEXT= near end crosstalk, FEXT= far end crosstalk). But I doubt the traces show those.
More important is ground bounce, which
does cause serious problems even on well-laid out multilayer PCBs. It is
one of the reasons that modern busses tend to be serial rather than the old-time parallel busses.
Do the calculation using, say, a 3V signal swing with a 10pF load capacitance and a 2ns transition time, and a 6inch/150nH wire:
- current ic required to charge a capacitor C through a voltage dV in time dt is ic= C dV/dt, so ic = 15mA
- voltage Vi induced across a capacitor by a changing current dI in time dt is Vi = L dI/dt, so Vi = 1.125V
- and you can multiply that by however many outputs are changing simultaneously!
Obviously you can play around with the precise numbers until the cows come home, but having a +-1V signal "suddenly" appear on the ground/Vcc line isn't going to lead to operation within the IC's specification.