And just for completeness, the proposed alternative.
(*) Intermediate nodes can't be treated the same way, so default to the base case regardless. (Note this means the proposal is inclusive, it's a superset of the base case; only the end nodes can be terminated in this way, and it is optional whether one or both do.)
V_N shown to suggest noise; note that in the terminal cases, the split terminators with CMCs are highly effective against interference (large CM attenuation ratio), but the intermediate nodes see no such benefit while in recessive mode.
Also consider the case with terminator inside the CMC (notice the CMC is itself a stub length!!) versus outside, or if the distance between say nodes 1 and 2 is small enough and they share GND so that they can be behind the same CMC, which then realizes the grouped-nodes case I mentioned.
To be perfectly precise, note I'm not saying one way is strictly better than the other; I would need to know all possible use-cases, sources of interference, loads, etc., and that's just not possible, I don't have nearly enough experience in this (and, I would suspect no one else yet in this thread does, either). But I can claim (with some justification) that the tapped-terminator case is generally better (lower emissions, higher immunity) -- when the optional is available to do so -- and that this will be true
for more cases than the default connection is.
Not even sure what circumstances I could craft that would make it strictly worse;
maybe in a double-isolated case, where the bus itself is floating, and now the fact that it's ~statically anchored to one ground more than others see a different impedance, and, maybe it's still fine for the given node, but the others are worse or something? I'm kind of grasping at straws here, honestly.
It's great when you can do it is the point, you can just do it at only two points.
Perhaps it's bad for bulk current injection; automotive heads might offer some insight here. BCI is a weird test; they don't care how the current gets in, they just crank up the test level until it's met. Scary, probably wildly unrealistic when impedances are extreme, but if one wants to play against such tests, a lower impedance is desired. Mind, that's the whole point, the split terminator
does better with BCI
in and of itself, but the real question is the CMC, does it saturate, does it catch fire, when that much (10s mA? at RF) current is applied?
Tim
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