forwarding for George.. ____________________Reply Separator____________________ Subject: RE: Charge moving from decoupling capacitors Author: [email protected] List-Post: [email protected] Date: 5/23/00 2:19 PM
Barry, The current can flow from the cap, but it will get to the IC at the wrong time. Regards, George [email protected] -----Original Message----- From: Barry Ma [mailto:[email protected]] Sent: Tuesday, May 23, 2000 10:22 AM To: [email protected] Cc: [email protected]; [email protected] Subject: RE: Charge moving from decoupling capacitors George, I am impressed by your attitude to pursue the correctness, and glad to discuss with you further on "How does a decoupling capacitor support an IC?" Here is my two cents worth. The decap supplies necessary charge to the IC during Tr through a transmission line. As you mentioned before: "The current is an impulse function, although the voltage waveform is a step function." This impulse function, actually a bell-like function on Tr, happens every time period T when the IC gate switches from low to high. The corresponding frequency spectrum contains lots of frequencies. There must be some frequencies making the transmission line a 1/4, 3/4, ... wavelength. It is hard for me to be convinced that currents of those frequencies cannot flow from the decap to the IC. ... Pleas correct me if misunderstood. Thanks. Regards, Barry Ma [email protected] -------- On Mon, 22 May 2000, [email protected] wrote: > > Barry, > > I need to make a correction. I was rushing to lunch on Thursday, so I did > not read over what I wrote. Here is the correction for the 2nd comment > below: > > At 1/4 wavelength, the charges are 180 degrees out of phase, so they are > working against the IC current draw. 1/8 wavelength (90 degrees out of > phase) is what I consider to be acceptable. > > Regards, > > George Tang > [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
