| ??? 03/02/05 14:07 Read: times |
#88869 - Freely? Responding to: ???'s previous message |
Hi Kai,
A coupling factor of 0.6 means that about 40% of the signal return current will not run directly under the signal copper trace but will run freely over the PCB! I would take exception to describing the current density distribution as "running freely over the PCB." In fact, the current density may well be limited in the plane that is directly beneath the trace, especially if you are using very narrow traces, but the return current will not simply take off in a random direction. It will follow the path of least resistance. This means it will be at its peak density directly beneath the trace, and it will fall off, asymptotically approaching zero, as you get further away from the trace. This, of course, assumes that you haven't inadvertently created some lower impedance route at a given threshold. As for your example, if you really need meaningful 1-bit resolution on a 16-bit scale, then I suspect (and I could be wrong about this) that engineering a couple of well isolated ground planes will be one of the least challenging things you do. Good Luck! ;-) Joe |
