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Ringing on square wave: how to eliminate?

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October 15th 03, 04:05 PM

James Beck

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In article ,
says...
On Wed, 15 Oct 2003 11:47:40 +0100, Don Pearce
wrote:

Layout, layout and layout.

Decouplers close to chips, short ground leads. Also be quite certain
that the ringing is really there. Ditch the ground lead from the scope
probe and make a very short one by wrapping stiff wire round the earth
ring at the end of the probe and leaving a piece as long as the probe
tip sticking out. Get up close to the chip signal and ground pins and
see if the ringing is gone.

Thanks Don. I'll try that suggestion. I've read Mike's reply but I
think he's pretty much saying the same thing as you.
I've ended up with a decoupling cap that straddles diagonally over the
top of the IC. For some reason, on this chip, the supply and gnd pins
are on opposite corners, which is a nuisance, so the cap's leads are
longer than I'd have liked. I suppose this sort of situation doesn't
help?

How about swapping the '04 for a '14, AND make sure it is properly
decoupled?
Maybe the '04 is getting a little funky in the zone between a valid high
and low?

Jim

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