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

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Fri Apr 07 2000 - 18:51:35 PDT


Chris,

The answer to this question based on measured data from the Mentor/ICX
model library is:

Altera 7K series
Altera 8K series
Altera 10K series

Measured data at the pins of these devices show significant numbers of
outputs capable of 170ps edge rates and some as low as 100ps. These
are measurements made at room temperature into 500 ohm loads and will,
of course, show some reduction when driving PCB traces at lower
impedances. Given that these measurements are made with equipment that
has a 3dB rolloff point probably in the area of 2 to 4 GHz, the actual edge
rate of these devices is possibly even faster ... even into a 50 ohm load.

I am sure there are newer devices out there that are just as fast, if not
faster, as the FPGA vendors push process technology like everyone
else.

regards,

scott

Chris Cheng wrote:

> 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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--
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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