RE: [SI-LIST] : Terminator location with larger BGA's

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From: Chris Cheng (chris.cheng@3pardata.com)
Date: Fri Apr 07 2000 - 15:45:38 PDT


i would love to know what kind of fpga can generate a 170ps edge coming
out of the package.
chris

-----Original Message-----
From: mcgiffb@ttc.com [mailto:mcgiffb@ttc.com]
Sent: Friday, April 07, 2000 1:17 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : Terminator location with larger BGA's

We are using some 484 pin BGA's (FPGA's), which have edge rates of about
170ps.
Using a series termination, it would have to be placed within 1/10 of the
transition length according to Howard Johnson. On FR4, the transition length
would be .98, making the distance from source to termination .098. It is not
possible to get all of the required termination's within that distance.

Aside from slowing down the edges (not desirable), waiting longer for things
to
settle, or going with buried resistance, are there any other solutions for
placement of termination's? How are other people terminating large, high pin
count devices?

Thanks

Bill McGiffin

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