Re: [SI-LIST] : RF & Digital

Ron_F_Parson@notes.seagate.com
Wed, 11 Aug 1999 16:35:23 -0500

Depends on what you are looking for, but the most likely effect is the
possibility of noise coupling directly between the two power planes. With
the stackup as shown here, 5V couples tightly to L6 and more loosely to L2,
giving enhanced plane-to-plane capacitance. If 2.5V needs to be the less
noisy, then switch L9 and L5 layers.

Ron

Shayle Hirschman <shayle@mho.net> on 08/11/99 07:19:24 AM

Please respond to si-list@silab.eng.sun.com

To: si-list@silab.eng.sun.com
cc: (bcc: Ron F Parson)

Subject: Re: [SI-LIST] : RF & Digital

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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