[SI-LIST] : RE: Split Plane

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From: Barry Ma ([email protected])
Date: Wed May 24 2000 - 14:20:39 PDT


There is another way to figure out what is the highest frequency we might need to take care of:

Howard Johnson call it Fknee = 0.5/Tr. Given Tr = 0.4 ns, We have Fknee = 1.25 GHz.

Barry Ma
[email protected]

From: "Doug McKean" <[email protected]>, on 5/24/00 10:49 AM:

Just some ideas I thought I might mention. I'm sure you're probably well aware.

A 100 MHz signal with a 400ps edge *might* not be that slow.

First, don't know what the requirements of the clock are but if the need is a nice crisp signal, something like the 7th harmonic may be needed. That brings you out to 700 MHz before the a half power point.

Second, the board must be have a bandwidth out to something like 750 MHz in order to allow a 400 ps edge to exist. So the 100 MHz digital board might end up like a
700 - 800 MHz analog board.

If by chance this is a critical design and your board vendor is board testing only up to 1 MHz at the fab house (you'd have to check on this), then you *might* want to consider some extra check of the board. Not sure what that would be.

At a former company, we noticed a 3dB difference in signal level from one side of the board to the other during normal runs. That was unacceptable due to FCC req.'s of CATV signals and ended up with a complete respin of the board. First release boards ended up
being very expensive.

Don't mean to complicate things. Just thought an extra 2 cents might be worth while.

Doug McKean
Brad Crowell wrote:
> Short answer...
> Around 0.4ns
> Brad


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