Re: [SI-LIST] : RF & Digital

Mitch Morey (mitch.morey@nsicomm.com)
Wed, 11 Aug 1999 14:07:30 -0700

Hi Shayle,

My first thought was to have +5V (real noisy!) coupling with a "good" GND reference plane. The other thought was, maybe +2.5V was for his analog circuit. If that is the case, I'd have it near the outer side, and try to keep all my
"digital" signals (critical ones) on the layers away from that plane. If that's not the case with 2.5V, I'd still keep a GND plane next to the +5V plane. Just me.

Opinions?

Mitch

Shayle Hirschman wrote:

> An excellent suggestion, Mitch.
>
> Any benefit to switching L6 with L9?
>
> Shayle
>
> At 07:59 AM 8/11/99 -0700, you wrote:
> >Hi Lum,
> >
> >As Shayle states this is a rather odd stackup, and I would certainly not
> recommend it unless I was under duress to comply. This will not get you the
> impedance control you're after unless you take some severe steps to control it
> >layer by layer (i.e. differential pairings). I'd suggest the following
> stackup design:
> >
> >L1 : signal
> >L2 : GND
> >L3: signal
> >L4: signal
> >L5: +5V
> >L6: GND
> >L7: signal
> >L8: signal
> >L9: +2.5V
> >L10 : signal
> >
> >Good luck,
> >
> >Mitch Morey
> >Sr PCB Designer
> >San Diego, CA, USA
> >
> >Shayle Hirschman wrote:
> >
> >> Why a stack-up of 4 signal layers in a row (L4 to L7)?
> >>
> >> This seems a bit unusual.
> >>
> >> Shayle
> >>
> >> At 08:09 AM 8/11/99 +0800, you wrote:
> >> >If I have a design that have digital circuit and a small portion of RF.
> >> >There will be some signals going from digital into the RF and out from
> >> >the RF to the digital portion. If the digital portion has to be
> >> >impedance control at 50ohms, how should I go about doing such design to
> >> >ensure that both RF and Digital requirements are taken care of, without
> >> >causing any interference between these two circuits? What about the
> >> >ground? This design will be a 10-layer with the following stack-up :
> >> >L1 : signal
> >> >L2 : GND
> >> >L3 : +5V
> >> >L4 : signal
> >> >L5 : signal
> >> >L6 : signal
> >> >L7 : signal
> >> >L8 : +2.5V
> >> >L9 : GND
> >> >L10 : signal
> >> >
> >> >I would appreciate any advise from you experts out there.
> >> >Thanks and regards.
> >> >
> >> >
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