Kenny, My answer applies to the case you cite as well. > [Original Message] > From: Kenny Frohlich <kenny_frohlich@xxxxxxxxx> > To: <leeritchey@xxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > Date: 7/22/2006 12:55:57 PM > Subject: [SI-LIST] Re: Current Return Vias > > Lee, > I'm not talking about jumping from one layer to the next adjacent layer which shares the same referrence plane. In this case, I do not need a ground via. But I'm asking about jumping from one layer to another layer that has a differrent reference ground plane. For example, on an 8 layer PCB stackup where the two ground planes are layers 2 and 7, the signal jumps from the top layer (layer 1) to the bottom layer (layer 8). > > Thank you > Kenny > Lee Ritchey <leeritchey@xxxxxxxxxxxxx> wrote: > Kenny, > > It is not true that you need a "return current" via next to each layer > changing signal via. I continue to be amazed that engineers who are > looked upon as SI experts say such things. > > Imagine you have a 4 layer PCB, such as the mother board in a PC, where > there are only two planes, one Vdd and one ground, where would such vias > connect? There have been billions of these made to date that work just > fine and have very fast signals on them. The return currents you are > concerned about find their way from plane to plane through the collection > of decoupling capacitors and interplane capacitance that you had to > engineer into the power delivery system in order to make it stable. Focus > on this and the return currents take care of themselves. EMI is minimized > he same way.. > > > > > > [Original Message] > > From: Kenny Frohlich > > To: > > Date: 7/22/2006 6:45:56 AM > > Subject: [SI-LIST] Current Return Vias > > > > Dear Experts, > > I understand that I need to provide ground vias next to via explictly > for the purpose of letting return currents jump between layers. I know > it's a requirement for high speed signals, especially differrential > signals. Is this also required for low speed single-ended signals (133Mhz > or slower)? > > If this is a requirement, what would be a good signal via to ground via > ratio? For example, there are five signal vias within a 1 inch area, how > many ground vias do I need? > > > > Thank you > > Kenny > > > > __________________________________________________ > > Do You Yahoo!? > > Tired of spam? Yahoo! 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