FreeLists / si-list / [SI-LIST] Re: Trace Width @ 3Gb/s

["Mustansir Fanaswalla" <mustansi@xxxxxxxx>]

Hi,

There is significant attenuation of the signal, consequently leading to bit
errors.
Your comments indicate that the narrow traces very well could be the cause.

Thanks
Mustansir

-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-
Mustansir Fanaswalla
LSI Logic Corporation
-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Hassan O. Ali
Sent: Monday, June 10, 2002 9:01 AM
To: Rudy Sterner; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Trace Width @ 3Gb/s



Rudy,

Could you be specific on the kind of issues you have with the SerDes link?
That way you
can receive suggestions that are more specific to your situation.

Yes, 4-mil tracks can be a problem. With those tracks, in a microstrip
format you need
less than 3-mil height to achieve close to 50-ohm single-ended line
impedance (which
might be your goal). With that small height and at that data rate, component
pads
(especially AC-coupling cap pads, if you have any) start to dominate heavily
causing
tremendous impedance discontinuities.

In addition, narrow tracks give rise to higher loss - both line-loss and
reflection loss
due to pronounced discontinuities at various locations (the connector
launch-point is
one of the most important ones).

Regards.

Hassan.





On Jun 10, "Rudy Sterner" <rsterner@xxxxxxxx> wrote:
>
> Hello,
>
>    We have some issues with a SerDes which we think
> may be related to the trace width on the serial line.  The
> serial  port is a differential pair passing data at 3 Gb/s.
> The trace width is 4 mils.  Length is approximately 5 inches.
> The differential impedance is 100 Ohms.  Other information
> which may be of use is the board material is FR-4 with an
> Er of 3.9.  It is specified at this data rate.
>
>   My question is:  Are the traces too narrow?  Should I
> expect better performance with 8-mil traces?
>
> Thank You
>
> Rudy Sterner
> LSI Logic
>

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