[SI-LIST] : Charge moving from decoupling capacitors

About this list Date view Thread view Subject view Author view

From: Barry Ma ([email protected])
Date: Thu May 11 2000 - 15:49:59 PDT


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. ......

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


Why pay when you don't have to? Get AltaVista Free Internet Access now!


**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected] In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu

About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Wed Nov 22 2000 - 10:50:18 PST