FreeLists / si-list / [SI-LIST] Re: stripline return paths etc.

[steve weir <weirsp@xxxxxxxxxx>]

JP, it depends on the actual dimensions and how well isolated the islands are.

Steve

At 12:43 PM 12/6/2004 -0600, Bharathan, Jayapratap wrote:
>Hello all,
>I have this general question with me. (I'm a beginner)
>Suppose, if a High Frequency Signal Line is surrounded by a solid GND 
>plane on one side and a SPLIT GND plane on the other side, & supposing 
>that the solid GND plane is closer to the signal Line, the return path 
>will be thru the solid GND plane, since the High Frequency Signal takes 
>the path of least inductance (a smaller loop).
>
>If this is the case, will it still matter if a high frequency signal Line 
>has a split plane next to it?
>
>Thank you,
>
>-JP
>(Bharathan, Jayapratap)
>----- Original Message ----- From: "steve weir" <weirsp@xxxxxxxxxx>
>To: <lalexman@xxxxxx>; <si-list@xxxxxxxxxxxxx>
>Sent: Monday, December 06, 2004 11:16 AM
>Subject: [SI-LIST] Re: stripline return paths etc.
>
>
>>Leonard, what you have with all the plane breaks is much more like a buried
>>microstrip.  The signal layer closer to the solid plane will exhibit higher
>>impedance than a true stripline, and some modulation along the frequency
>>axis.  The signal layer closer to the split planes could look like a mess
>>depending on several factors.  You should avoid placing signals with high
>>edge rates close to those splits.  If you must run signals across the
>>splits then bypass the splits with capacitors.
>>
>>It is all in the inductance.  If you have a high inductance loop, between
>>the two grounds, then you are setting yourself up for a lot of
>>trouble.  You really need to ask yourself, or whoever came up with this
>>scheme what it is they are trying to do, and why those grounds need to be
>>single pointed.  You really ought to consider getting some expert help.
>>
>>Steve
>>At 07:55 AM 12/6/2004 -0800, Leonard Alexman wrote:
>>>Hi All,
>>>I am designing many pcb's with multiple power and ground planes and I was
>>>curious if some has an opinion or could point me to any articles on the
>>>following questions.
>>>
>>>
>>>1.      I know its best to have a sold ground plane (or solid power plane )
>>>on either side of the a stripline trace but is it acceptable to have a solid
>>>ground plane on one side and a power plane on the other side with many
>>>splits in the plane ?  The same question for a dual stripline configuration
>>>?
>>>
>>>2.      I have some high speed differential signals that have a separate
>>>ground (HSGND). HSGND is tied to digital ground thru a zero ohm resistor. I
>>>am routing these signals in a stripline configuration with HSGND planes on
>>>either side. Can I also route digital signals(that use the digital ground )
>>>on this layer ? I am concerned that the return path goes thru the zero ohm
>>>resistor to the digital ground plane. and it will be a very long return
>>>path. Is my assumption correct ?
>>>
>>>
>>>Thanks for any help
>>>
>>>Leonard Alexman / American Electronics Group Inc.
>>>PH: 951-354-6493
>>>Cell: 951-640-5469
>>>Fax: 208-247-33470
>>>
>>>
>>>
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>>>-- Type: application/ms-tnef
>>>-- File: winmail.dat
>>>
>>>
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