# RE: [SI-LIST] : Charge moving from decoupling capacitors

From: Kai, Francis ([email protected])
Date: Fri May 12 2000 - 09:02:53 PDT

Dear Electrical Engineers,

Based on Mr. Ma's questions, I would like to know if you guys are
really interested in the electron movements in metal.
The transport of electrons in a solid is dominated by Boltzmann's Equation.
How do you solve this equation for an electron to
move from the decoupling capacitor to a chip (package and...) it serves in a
metal plane? This might be something that the
tools vendors are interested in for the next generation high-speed tools.

Kind Regards,

Francis Kai
Intel Corporation

-----Original Message-----
From: Barry Ma [mailto:[email protected]]
Sent: Thursday, May 11, 2000 3:50 PM
To: EMC-PSTC; [email protected]
Subject: [SI-LIST] : Charge moving from decoupling capacitors

Hi,

As the speed of digital signals gets faster and faster, people begin being
concerned with the distance for electric charge to move on power and ground
planes of multilayer PCB during the signal rise time from a decoupling
capacitor (cap) to a chip it serves. I would like to raise two questions.

(1) The charge is moving in a metalic plane, not inside the dielectric
between pwr and gnd planes. Please let me know why you have to use the
propagation velocity in the dielectric, instead of that in the metal.

(2) The second question is regarding distance between the cap and the chip.
Do we really have to limit the distance letting the charge have enough time
to move from the cap to the chip during the rise time interval? I doubt it.

Take the running water system for example. When we open, then close the
water faucet within one second, does the water we've got in basin come from
water tower (or water station, or reservoir)? No, it is the water that
resides in the pipe. As a matter of fact, we have a very large pipe -
pwr/gnd planes. Well, of cause you know, I did not mean we don't need water
tower - the cap. ......

Regards,
Barry Ma
[email protected]
Morgan Hill, CA 95037
Tel. 408-778-2000

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