Folks,
This is close to voodoo but repeatable. Unfortunately I can't disclose the schematic since it is for a client. Just wondering , anyone had this before?
At the far end of a TX line I used to have a diode connected across because a previous version of a chip would have such a substrat path. Nice waveforms, fast sims. Everything as expected and peachy. Now the new iteration of the chip design won't have this diode path so I chopped off its cathode connection. Sims fine. So I deleted the diode ->
ka-crunch ... sim slows down and the ouput is junk.
If I put the diode back in and connect only its anode -> fine. If I leave the anode open and only connect the cathode it still sims but the results are different.