Re: [SI-LIST] : RF & Digital

Mitch Morey (mitch.morey@nsicomm.com)
Wed, 11 Aug 1999 07:59:28 -0700

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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