Dave Hoover wrote:
>
> Can anyone outline the advantages and disadvantages of using broadside
> coupled
> vs. edge coupled differential traces?

        (agreeing w/all of Groovy's comments)

> Is it easier to route broadside coupled traces in high density applications?
>
        Two things to consider are layer utilization and component
        types.

        As Dave mentioned, broadside diff routing takes two layers
        with no other cross traffic.  If your differential signals
        are contained to only a portion of the board and there is
        no other traffic, this factor can "go away".

        The other frequent issue is connector styles.  If you are
        crossing pluggable connectors with your pairs, and it is a
        high density connector system (2mm staggered comes to mind)
        you may not have the routing room to keep edge-coupled lines
        together.  Using broadside routing helps to limit the dis-
continuity experienced at the connector to that of the con-
        tact itself, rather than including the meandering routing
        through the pin fields on both sides of the connector.

        The same situation presents itself w/fine pitch BGAs, if
        the diff pairs are not pinned out on the outer two rows.

        YMMV!
--

      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800

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