At 08:41 AM 7/9/2004 -0700, al smith wrote:

>Typically on our boards...ranging from 2 to 16 layers, we simply drop a via
>to the plane from the cap.  IF you can place the cap where it can tie
>directly to the pins, its better of course.

I make a fine distinction between the current on the bottom of the cap dumping into a plane, and returning it to the chip pin, and from there, to the plane.
When it goes by discrete track, (or no track) you control where it goes.
When you dump it into a plane, it does NOT take the shortest path. It takes ALL paths, according to their relative impedance.

If you draw the circuit, then in place of all the tracks, draw inductors, with their value proportional to the length and width of the track, then it becomes clear.

While the total amount of inductance is the same, you can control how it is distributed in the circuit, which if done right, acts as a "tee" filter.

Those parasitic inductances have to be there anyway, you might as well get them to work FOR you..

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