Re: [SI-LIST] : RF & Digital

Jeff Seeger (jseeger@appliedcad.com)
Thu, 12 Aug 1999 00:42:23 -0400

Ron_F_Parson@notes.seagate.com wrote:
>
> snip <
>
> giving enhanced plane-to-plane capacitance.
>
> snip <
>
Forgive my barging in here, but it seems to me the original
stackup provides "enhanced plane-to-plane capacitance" for
both supplies, very desirable from the EMC perspective:

> >> >L1 : signal
> >> >L2 : GND
> >> >L3 : +5V
> >> >L4 : signal
> >> >L5 : signal
> >> >L6 : signal
> >> >L7 : signal
> >> >L8 : +2.5V
> >> >L9 : GND
> >> >L10 : signal

If the stripline layers are different directions ( | / \ - )
and the center two can have slightly larger line widths for
impedance then basic needs would seem reasonably met.

In the above I would place the majority supply at layer 8
and the minority supply at layer 2, with plenty of vias to
tie the grounds together and plenty of bypass caps for both
supplies, even in unloaded areas.

If the RF portion can be physically seperated then routing
it in microstrip on whichever side is the familial voltage
should be a reasonable approach, using a barrier "picket
fence" of ground vias and some spacing (rather than a cut)
to aid isolation.

Just my $0.02!

-- 
 
      Jeff Seeger                         Applied CAD Knowledge Inc
      Chief Technical Officer                  Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                978 649 9800
       "There goes that wacky guy with the diagonal routing again"

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