At 01:07 PM 1/17/99 -0800, William Chops Westfield wrote:
>    >you can buy sockets for your chips that have decoupling caps built in.
>
>    Those are not nearly as nice as they look at first glance. Look at
>    the long leads on the cap!
>
>I think you'll have to explain how to connect pin 8 to pin 16 of a typical
>DIP using "leads" that are any shorter than that!
>
>(this *is* why the newer generations of fast chips have moved the power pins
> to the center of the package.)
>
>BillW


No problem. I route a solid ground to the ground pin. I mount the bypass
cap at this point. Then I run a track from here to the package's VCC pin.
The same idea is seen in the Murata and Panasonic three-lead EMI
supressors. The EMI is forced to travel to the cap, before it can get to
anything else. Distribuiting the L and C differently in the circuit forms a
Tee filter, rather than a high pass filter (well, actually a notch, but at
the wrong frequency)

The total lead length isn't any less, but look at the circuit it makes. The
noise from the IC has only one place to go, which is to the + side of the
cap.  With the capped sockets, the cap is in the middle, with lead
inductance on both sides, and nothing at all to prevent the noise from
going out to the system.

It really does make a large difference, but it's kind of like a tuneup in a
car, $100 racing plugs don't help you if your timing is off.  You have to
get a solid ground to everyone that makes any noise, and you have to
provide low Z paths between devices that exchance high speed signals.