[SI-LIST] Re: Impedance confusion

Your confusion may be because:
Offset stripline implies a single-ended impedance, while
edge-coupled offset stripline implies a differential impedance.
If the stackup is
sig --- plane --- sig --- sig --- plane --- sig
The inner layers are asymetric stripline from a single-ended 
standpoint, and if there is parallel coupling between the two inner 
signal layers that coupling is broadside differential coupling 
(unless, of course, it is simple crosstalk coupling.)
Hope that helps.






At 12:18 PM 11/21/2008, you wrote:
>Hi Team,
>
>Between these two stackup,
>a) SIGTOP-PP(5 mils)-SIGINNER1-PP(22 mils)-SIGBOT
>b) SIGTOP-PP(22 mils)-SIGINNER2-PP(5 mils)-SIGBOT
>
>While computing the impedance of the SIGINNER* layer,
>it is offset stripline or edge coupled offset stripline.
>
>Would the impedance be different between these two cases?
>I ask this because, when board (a) is rotated it becomes
>board (b) and hence I do not expect impedance to vary between
>these two stackups.
>
>Can anyone please confirm/clarify on this.
>
>Thanks,
>-LN
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