ryu wrote:
>
> I saw the term in the IPC-610.  I think it has something to do with the
> design of a product for cross talk elimination.  But can someone tell me
> if there is a minimal or maximum requirement for the distance, is there
> any number a designer needs to follow? if the answer is no, then how the
> designer comes up with the number ?  Thanks.

        Well I've been trying all day to get to look it up for context
        "but it's not happenin' today!".

        The electrically dependent clearances have to do with either
        noise (often crosstalk) or safety.  What matters is the amount
        and type (i.e. switching or static) of energy and the distances
        (and insulators) around that energy.

        Crosstalk is a complex issue, and Groovy's correct in that
        it involves gory detail on the signals involved as in their
        emmissive (is this a word?) characteristics and their suscept-
        ability (where's my spellchecker - I'll risk flames to get
        the comment out today).  There is not a simple calculation
        to get specifics (a spice/field solver problem) and it is
        complicated (or eased, actually) by the timing of events i.e.
        if the receptor is not listening at that time the aggressor
        can do whatever it needs to.

        Electrical safety depends heavily on the environment and
        is just as deep a calculation to arrive at "knowns" - or
        deeper since you nomally have non-uniform insulators (pwb,
        s/m, air, moisture, contaminants, etc).

        Both issues, however, rely on a simple fundamental principle.
        Like any energy, electric and magnetic fields dissapate
        with the rule of inverse squares.  That is, the effect of
        one conductor on another decreases with the square of the
        change in distance.  One unit change in distance provides
        one unit change in interference but 2 units distance make
        a 4 unit effect.  So while exactitude requires too much
        math, the principle relies on very little.

        This reply is quite hurried (entire books exist on but one
        aspect of the many raised here) but I hope I've helped.

        Regards,
--

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

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