RE: [SI-LIST] : RE: 100 ohm differential Vs 150 ohm

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From: Ron Miller (rmiller@brocade.com)
Date: Thu Jan 25 2001 - 10:36:39 PST


We have had a lot of previous discussion on this:

100 ohms diff is 50 per side which is standard for
cable and test equipment. 75 ohms(half of 150) was
at one time standard for intermediate frequency(IF) radio
use and also for TV video so you will find some cables,
and test equipment but not very much.

For laying out PCBs, it is much easier to get to 50 ohms
than to 75. 75 means the traces must have more ground
clearance, and therefore traces cannot be as dense. Also,
nearly all RF connectors are 50 rather than 75 ohms.

Ron Miller

-----Original Message-----
From: Doug Hopperstad [mailto:doug.hopperstad@qlogic.com]
Sent: Thursday, January 25, 2001 10:14 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : RE: 100 ohm differential Vs 150 ohm

Can someone give me some feedback on using 100 Vs 150 differentials? Is
there a reason that one would choose the 100 over the 150 in a design.

Doug Hopperstad
Qlogic

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