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

Dima Smolyansky (dima@tdasystems.com)
Fri, 27 Aug 1999 12:10:18 -0700

Allen:

Perhaps coupling between the adjacent sections on the trace with many turns
affects the impedance value? How close are these sections together?

-Dima
=================
Dima Smolyansky
Time Domain Analysis Systems, Inc.
7465 SW Elmwood St.
Portland, OR 97223
(503) 977-3629
(503) 804-7171 (mobile)
(503) 245-5684 (fax)
www.tdasystems.com
The Interconnect Modeling Company (TM)

-----Original Message-----
From: Allen Wang <Allen_Wang@asus.com.tw>
To: si-list@silab.eng.sun.com <si-list@silab.eng.sun.com>
Date: Friday, August 27, 1999 11:59 AM
Subject: [SI-LIST] : PCB impedance variation v.s. layout pattern

>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
>
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