no no, i was not at all suggesting that support for split planes be
removed
only that their contribution to the overall goal of quiet boards
efficiently designed should not be over estimated or utilized as a cure
all when they in fact may be a significant source of loop area antenna
effects
Geoff, I (and I think we all) appreciate your careful and thoughtful
comments on these matters which can be difficult to explain as
explicitly as you do, thanks
Dennis Saputelli
Geoff Harland wrote:
>
> > interesting article in the new 'printed circuit design' mag (june 2001)
> > by Henry W. Ott (EMI consultant)
> > title: 'partitioning and layout of a mixed signal pcb'
> >
> > in it he basically makes the case that split planes are generally a bad
> > thing
> >
> > their best use he says is to correct a badly laid out board after the
> > fact and also in some cases they are needed for safety isolation
> <snip>
> > i won't go into all that he has covered but as the split planes are so
> > pervasive and enough of a nuisance to implement i thought i would throw
> > this out there
> >
> > Dennis Saputelli
> >
> > What about mixed supply voltage boards?
> <snip>
> > On the other hand I do agree that splitting the ground plane in most cases
> > is almost as bad as the stupid design we have where they eliminated the
> > analog plane in one area to route analog input signals.
> <snip>
> > Rob
>
> I think that there is a very good case to be made for saying that when split
> planes are used, then they should be used intelligently. But even though an
> expert has suggested that split planes are generally a bad thing, I consider
> that there can still be times when users legitimately want Power Plane
> layers to be used for more than one net, and as such, Protel should *not*
> contemplate removing support for split planes (and should even *still*
> contemplate acting on a previous suggestion of mine: that the capability be
> provided for split plane polygons to reside *entirely* within other split
> plane polygons).
>
> Even if support for split plane polygons was removed, users could still
> implement split planes on Power Plane layers by the use of primitve items on
> these layers, i.e. arcs, tracks, and fills. However, the provision of the
> split plane polygon feature permits the Protel application *itself* to be
> aware of which net is associated with each (partitioned) region on each
> Power Plane layer, and that aspect would presumably be lost if the split
> plane polygon feature was ever removed.
>
> I appreciate Dennis alerting other users about this article, but I for one
> would be very unhappy if Protel lost its current ability to *fully* support
> more than one net being assigned to each Power Plane layer.
>
> On a slightly different note, I am pretty sure that there was a time when
> users could *both* place polygons on Power Plane layers *and* define split
> planes on these layers, and these were *different* beasts. As such,
> "standard" polygons (also) removed copper from *within* their perimeters
> (remembering that Power Plane layers are *negative* layers), while split
> planes *only* removed copper on their (perimeter) *boundaries*. In some
> instances, e.g. PCBs incorporating modems, the loss of the genuine polygon
> feature is annoying, as users currently have to effectively "pour" their own
> "polygons" in the regions concerned themselves. As such, it would be nice if
> this feature could be restored.
>
> There would be complications (including in all probability some legacy
> considerations) in restoring *both* polygons *and* split planes to Power
> Plane layers, but perhaps split planes could be treated as *special* cases
> of polygon objects (so that on Power Plane layers, some polygons would be of
> the "customary" sort, while others (that have an associated "SplitPlane"
> Boolean variable set True?) would be split planes instead). That way, the
> requirement for Protel to support a new type of Object (either
> PowerPlane_Polygon or PowerPlane_SplitPlane) could be avoided.
>
> The other desirable enhancement for Power Plane layers has been mentioned on
> assorted previous occasions, but for the record, I will repeat it now. It
> would be nice if the Design Rule checking procedure could detect (through
> hole) pads and vias which are disconnected from *other* pads and vias
> connected to the *same* net on each Power Plane layer (or in an extension of
> this concept, whenever the "quality" of each such connection is not
> compliant with a minimum standard defined by the user). But this is easier
> said than done, and I think that it is realistic to say that it would be
> more difficult to implement than supporting split planes being totally
> surrounded by other split planes on each of these layers. (However, the fact
> that it would not be straightforward to implement still does not alter the
> desirability of having it provided.)
>
> Regards,
> Geoff Harland.
> -----------------------------
--
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