Re: [SI-LIST] : PCB impedance variation v.s. layout pattern

Scott McMorrow (scott@vasthorizons.com)
Fri, 27 Aug 1999 12:10:43 -0700

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Allen,

Trace meanders will couple from edge to edge across the
meander. This will cause an effective reduction of the
characteristic impedance of the trace, unless the meanders
are spaced quite wide. If you are not currently using them
you should be using meander spacing that is 2X or 3X of the
trace width for Rambus tracks. This should be equivalent to
about a 20 to 30 mil edge to edge seperation of the meander
tracks.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Allen Wang wrote:

> Dear all: > > We are designing a Rambus related product which requires the PCB to > maintain > 28 Ohm +/- 10% trace impedance. > However, what we have found that a straight line trace will get a higher > impedance (through TDR, 1 Ohm or more) than > a trace with many turns on it. We know a turn on the trace will change > the > impedance. However, is it the root cause > that make our trace impedance not consistent? > > Two traces are on the same layer, with the same trace width. > > > +--------------------------------------------------------------------------- > ------------------------------------+ > Straight line > > +-----------+ +------+ +---- \\\\ -----+ > +------------------------+ > | | | | | | > | | | | | | > +-----+ +----+ +---+ > line with turns > > Allen > > **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

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