[SI-LIST] Re: HIGH DC Current on GND Plane

Istvan,
I think your comments apply to serdes signals routed as stripline traces 
that are referenced to both a power plane and a ground plane.

If the traces are routed referencing only ground planes and these ground 
planes also serve as power return, I think the serdes signals will be 
unaffected.

Do you agree?

Thanks,
Vinu

istvan novak wrote:
> Hi Joe,
>
> There are the following generic guidelines that come to my mind, not 
> knowing the
> details of the system:
> - if the 60A power rail serves also as reference for SerDes lines, it 
> has to be quited sufficiently
> for that purpose, which means that you need to design that rail as a 
> high-speed power rail.
> This is especially true if you also need to carry reference clock or 
> sensitive low-level analog
> signals around the backplane. 
> - if you have switching regulators connected to this rail (most probably 
> you have), either
> feeding this rail with raw power or taking this voltage to generate 
> local sypply voltages,
> you want to check very carefully for high-frequency ringing generated by 
> the converters.
> Today the ringing can be anywhere in the 50-500MHz frequency range; if 
> they spread
> freely on the power rail, it will reduce your SerDes margin.  
> Unfortunately the ringing
> is not limited by converter specifications (in other words there is no 
> spec item for the
> potential high-frequency ringing).
> - as others pointed out, you dont need to worry about saturation of 
> copper, unless you
> have local features increasing the current density too much.  Make sure 
> you use the
> largest area that you can afford and many vias for connecting the 
> high-current inputs
> and outputs.
>
> Regards,
>
> Istvan Novak
> SUN Microsystems
>
> Joe Paul M wrote:
>
>   
>> I have a midplane carrying 60Amps of current and Same GND plane is used 
>> as reference for multiple of 6.6 Ghz serdes lines , PCI-e lines and GE lines
>> Is there anything similar to 'saturation' in Inductors applicable to GND 
>> plane?
>> ( Due to saturation of flux in the flux carrying medium , beyond a 
>> certain amount of DC current inductors saturate and wont act as 
>> inductors for any AC superimposed on the DC. )
>> Will cross talk increase due to the absence of mutual inductance between 
>> signals and gnd plane ?
>> Is there anything else that can go wrong due to this DC , AC current 
>> mixing in planes ??
>>
>>
>>
>>
>>
>>
>>
>>  
>>
>>     
>
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