[SI-LIST] Re: Serpentine patterns for length matching

Jim, are you looking for minimum radius, maximum parallelism type 
information or more basic information on how to determine the amount of 
serpentine?  Many layout tools calculate the amount of serpentine, but 
fail to account for the impacts of coupling.  A first cut RoT ( All RoTs 
should be treated with caution. ) is to require serpentine diameter 2X 
line to line spacing.  In rough numbers that reduces the cross talk from 
serpentine segments to 1/4th normal line to line coupling.  If that 
spacing is tight enough that you were to have enough serpentine coupling 
to throw your timing, then you would also be a position where your 
timing would potentially be thrown by aggressor coupling pull-in or 
push-out.

Steve.

otter30@xxxxxxxxxxxxx wrote:
> Hello,
> Does anyone know of general guidelines for the serpentine patterns used to 
> match net lengths?
>
> We have a board with lots of diff pairs, and our board designer made the 
> serpentines very
> tight. The separation between the adjacent bends of a pair is the same as the 
> spacing of the 
> traces in the pairs themselves. This seems to imply imedance variations if 
> the trace widths 
> don't change in the bends.
>
> Any insights would be greatly appreciated,
> Jim  
>
>
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