[SI-LIST] Re: decoupling
- From: Ed Priest <Ed_Priest@xxxxxxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 12 Jul 2001 10:09:06 -0700
You can pass out a +ghz signal single endedly and if you think you can't get >
100Mhz noise out of a package you are using some really &^%$* packages or are
using die that don't have >100Mhz switching activity. In a package with coupled
planes - the power planes look like transmission lines with distributed poles
and zeros. Good flip chip packages have very low impedance between PCB and the
die. I guarantee you can get high frequency noise down to the PCB - I've help
troubleshoot a lot of boards for people who thought they couldn't. If you have
a bunch of chips on a board with 400Mhz switching, spending time lowering the
impedance of your power distribution at 400Mhz is time well spent.
Ed
-----Original Message-----
From: Chris Cheng [mailto:chris.cheng@xxxxxxxxxxxx]
Sent: Wednesday, July 11, 2001 6:13 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: decoupling
ghz+ signals come out as differential signals. and 400mhz+ signals
come out as transmission lines. most packages, coupled with on
die capacitance resonant around 100mhz or below.
>For you comment that 400Mhz can not propagate through the package ( good
packages can propagate higher frequencies >>than that) - how to you think
the Ghz + signals get out. The noise that comes out is a voltage divider
between the >reactance on the die/package and the power distribution
impedance on the board - another way to see why you want the >impedance on
the board to be small.
>
>Ed
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